North American Aviation P-51 Mustang

SERI ES EDITO R: T ON Y H O LME S

PRODUCTION LINE TO FRONTLINE·

1

NORTH AMERICAN AVIATION

P-SI

MUSTANG Michael O'Leary

tmmm AVIATION

FRONT COVER With a mi ni m um

of celeb ration. a worker applies a rather crude number 10.000 to ident ify the 10.OOOth Mustang as it rolls off t he pro duction line BACK COV ER W ith cow lings

neatly stored aboard the Wabash Cannon Ba/l, a facto ry-fresh P-S ID has its Packard Y- 16S0 fired up fo r th e first time afte r its attachment to the airframe

First publi shed in Great Britain in l Y~8 by Osprey Pub lishing Elms Co urt . Chapel Way, Batley, Ox ford OX2 9LP Un ited Kingdom 0 1998 Osprey Publishing Limit ed

All right s reserved . Apart fro m any fair dea ling for the pu rpose o f privat e study, research , criticism o r review, as per m itted unde r t he Co pyrig h t, Design and Pate n ts Act , 198H, no par t o f thi s pu blication ma y he reproduced, stor ed in a retri eval system , o r t ran smitted in any form or by any m eans, electronic . e lec t rical, c he m ical. m ech an ical. optica l. photocopying , recor ding o r oth e rwise, witho ut prior writt en perm issio n . All e nqui ries sho uld be add ressed to th e publi sh er. ISBN I 8553 2 7£H 1 Edited by Tony Holmes I'agc design by Gwyn Lewis Scale Drawings by Arth ur Bentley and Mark Sty ling Prin ted in Hong Kong

ED ITO R's NOTE

To m ake th is new series as au t horitat ive as poss ible, th e ed itor would be ext remel y interested in hea ring from any ind ivid ua l who m ay have relevan t pho tog rap hs, docume ntat ion or first-ha nd ex perie nces rela ting 10 th e elite pilots, a nd their a ircraft, of the va rious th ea tres of war. Any material used w ill he fu lly cred ited to its origin al sou rce. Please writ e to To ny Hol m es at 10 Prospect Road, Scvcnoa ks, Ke nt , TN I3 :~ U A , Un ited Kingd om . FOR A fREE CA T.-\LOG UF. OF ALL fIOO"-~ l'U IILlSHF.O BY O SPREY PLf...\SF. WRITI TO:

The Mark eting Manager, Os prey Puhlishing Limit ed, P.O. Box 140 Wl'Ilingb orough , Northa n ts NN8 4ZA

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CONTENTS

INTRODUCTION 6

THE PROTOTYPE 8

C H A PTE R 2

BUNDLES FOR BRITAIN

C H A PT En 3

PONY SOLDIERS 30

C HA PT ER 4

ON TO BERLIN 47

C H A PT ER 5

BUBBLE TOP 75

C H A PT ER 6

FRONTLINE

105

C H,\ PTER 7

MUSTANG MEN

APPENDICES

126

136

17

INTRODUCTION

W ELCOM E TO T HE FIRST VOLUME in an exc iting new se ries from Osprey. From Production Li ne to Frontli ne was con-

ceived in late 1996 when th e aut hor and ed itor Tony Ho lmes we re go ing through an ex te ns ive co llec tion o f North American Aviatio n P-SI Mustan g p ho tog raphy. Arguabl y one of th e m ore attractive aircraft to come out of World War

2, we were taken by the way t he fighter was created to a British specificatio n in a fairly sho rt space of time, and then we nt on to becom e a mass-produced co mbat classic. There have been n umerous books written o n th e Mustang ov er th e yea rs, but we wan ted to a pproac h th e aircraft from a rather unique perspect ive - its pro d uct ion life. America's direct involvem ent in World War 2 was und er fo ur years, yet in that very shor t tim e period a lifestyle was create d th at would effect fut ure gene rations . The nati on made a massive shift from a mainl y agricultural econ om y to an indust rial giant dur ing th ose few years, and the ra pid ly emerging aviation com pan ies took full advant age of th e lessons of Henry Ford to ap ply mass-p rodu ction techniques to th e building o f aircraft. Los Angeles became on e of the world's major centres for th e p rodu ction o f combat aircraft, origina lly sta rting with desperate orders from the French and British, and th en mov ing in to m assive co ntracts from the US Army Air Force and Navy. With excellent weat her, chea p land prices and an increasing pool o f available workers, aviation co mpan ies bega n huge expansio n programmes, wh ile hi ring tens o f thousands o f new workers. For the first tim e women became a major influence in the wor k place as th ou sands of 'Rosie th e Riveters' were hired to take the place of men go ing into th e mi litary. Barely recovering from the Grea t Depression, families were suddenly taking in more mo ney than they had ever seen. Life styles and con cepts were cha nging, and America wo uld never be th e same agai n. 6

P-S I MUSTAN G

In t his volume we follow the saga of t he 1'-5 1 productio n through a fairly uniqu e series of photographs. In orde r to place the product in its inten ded env ironme nt, we also presen t ph ot ographs of th e Mustang in co mbat. We have used the Wor ld War 2 period as a cut-off date fo r this first volume o n the P-51 , since we wanted to show the aircraft in the global situatio n for which it was design ed - a seco nd volume, featu ring th e experi men tal lightweigh t Musta ngs, 1'-5 1F/H, 1'-82 Twin Musta ng and po stwar F-5 1Ds is plan ned for 1999. I would like to take the o pportunity to thank some indi vidua ls wh o helped make this boo k possible; Gen e Boswell of North Ameri can Rockwell, who realised the im portan ce of preserving some o f the images seen on the se pages; Pete Regi na, Lowell Ford, Simo n Brown , Bruce Lockwood, Alan Preston , David Price and Carl Scho ll, who all provided valuable in form ati on; a nd Scott Bloom for the pro vision of th e vintage Mustang advertisemen ts. We look forward to receiving your com ment s on this

book, and since there are numerous other vo lumes plann ed for this series, we wo uld appreciate yo ur inpu t with memories, documents and photograp hs. Queries to th e aut hor sho uld be add ressed to Michael O'Leary, 1'0 Box 6490 , Wood land Hills, Californ ia, 91365, USA.

Michael O'Leary Los AI/geles May 1998

tNTRODUCTION

7

CHAPTER

rn THE PROTOTYPE

BY M ID-O CTOBER 19 40 , Nort h American Aviation (NAA) had become firml y establi shed at Mines Field in so ut he rn Ca lifo rn ia - th e airfield that is n ow Los Ange les Intern at io na l Airport. Building their rugged NA- 16 series of t ra in ing air craft , NAA h ad decided to move from Ma ryland to join th e many ot her avi at io n co m pa n ies th at h ad establis hed facilit ies in southe rn Californ ia, and Mines Field was picked because i t offered a n estahlished airfield t hat was not only clo se to su pply sou rces bu t was also ch ea p (NAA's 20-acre site was leased to th e co m pa n y fo r th e pr in cely su m of 5600 per yea rl). Th e new NAA factory was opened in 1936 a n d co ve red 159,000 square feet, wh ile I SO em ployees became en gaged in prod uctio n of th e NA-16 train er and the por tly 0 -47 observa tio n a ircraft. Th e ma ny p rob lems t ha t plague a new com pa n y we re co nquered by NAA p resident Ja m es H 'Dutch' Kindelberger an d h is sma li hard-wo rkin g staff. Britain had beco m e in terest ed in th e NA-16, which had turned into t he AT-6 Texan, a nd in 1938 began ordering the stu rdy adva nce d tra in er fo r the Roya l Air Force (RAF) and o t her Com mo nwe alth air forces as th e Harva rd . Because of the rapidly esca lating te n sio n s with Hit le r's Ge rm a ny, the Eu rop ea n na tions we re rearmi n g at a n un precedented pace a nd at tem ptin g to bu y as mu ch m ilitary eq u ipme n t as pos sible. Brit ain h ad orde red th e Cu rt iss P-40 Tomahawk a nd , becau se o f t he large orders, was inte rested in perhaps h avin g NAA build th e type under lice n se. The small, hut creative, NAA ma na gem e nt team decid ed that it wou ld be much mo re ben eficia l to t he co m pany to create th e ir ow n fighte r for t he RAE What t hey wa nte d to do was ta ke the Aliiso n V- 17 1O (at the ti me t he most powe rful V-12 in product io n in the USA) a nd wrap it arou nd a new airfra me th at wou ld out str ip t h e P-40 in pe rfo rma nce. In 1936, NAA h ired a new employee - Germa n-born Austrian Edgar Sch mu ed . For a b it o f co nf using co m pa ny h istor y, we mus t go back to the la te 1920 s when Ge neral Moto rs (GM) created a h o lding com pany wit h th e na me No rt h America n Aviatio n. Th is co m pa ny exis ted so lely to acquire stock in o t her 8

P-5 1 MU STANG

aviatio n co ncerns - giving GM a possible sho t at con trolling t he rap idly emerging aviatio n market. In 1929, NAA took over the Jok kcr Aircraft Co rpora tio n and Sch mu ed, who wo rked for GM as a field service man ager in Brazil, moved to the USA to wor k with aircraft - so meth ing he had always wanted to do , with his training as a mech anical engi nee r. Fokker soo n becam e Gen eral Aviatio n, hu t th e Airmail Act of 1934 forced airm ail car riers to rid th emselves of ho ld ings that controlled aircraf t construction . Th is mea nt tha t GM ha d to get rid of NAA which, in turn, too k over General Aircraft. Kindelbe rger had co me from Douglas Aircraft a year ea rlier, and was now presiden t of th e 'new' NAA. 'Dutch' moved t he co rnpan y west and asked Schmued to join him, bu t Sch rnued 's wife did not wan t to move to Californ ia so the designe r join ed th e firm of Bellanca - a de cision he soon regretted. However, ' Dutch' had kept t he job offe r open, and Sch mued and his famil y finalJy moved west. However, just 100 miles fro m Los Angeles, th e family was in volved in a serious car accident which killed Sch mue d 's wife and left the designer scriously injured - it took him un til February 1936 to recover. Once British in teres t in t he ne w fighter de sign had beco me more so lid ified, t he p roblem of crea ting a new airframe aroun d th e V-17 10 was th e type o f challenge en joye d by Schmued . Th e inline V-12 req uired a large rad iator for coo ling, and its placement cou ld great ly affect performance - to the positive or negative. At the tim e, Lee Atwood was 'Dutch's' right -ha nd man and chief engineer fo r the co mpa ny. Atwood, a co mpo ne n t designer an d mat hematical ana lyst at Douglas, was hi red away by ' Dutch' and was responsible for t he NA-16. In t he 19905, Atwood would clai m he came up with t he idea of placing the radiato r o n the new figh ter design behind th e pilot. However, Atwood 's claim was rebu ffed by several othe r su rviving NAA employees fro m th e time period , w ho stated th at t he location was the obv iou s cho ice.

This view of th e prototype N A~7 3 X shows both the moveable fro nt sco o p and the rear duct in the full dow n position . thus incre asing air flow. O t he r points of inter est include the fact that NAA, for so me obscure reas o n, rat he r cru dely airbrushed the original negative to eliminat e the civil regist ration on the rudd er. Also. a black anti-glare pane l has been added ahead of the wind scr een

T H E PROTOTY PE

9

By placing the rad iat or to the rear, a modest increase in thrust could be achieved hy taki ng in co ld air wh ich wou ld rapi dly expa nd and reduce in ve locity before travelling th roug h the rad iato r. This led to an efficie nt heat excha nge whic h created energy t h at move d through a n arr ow duct, exi ting th rough a movea ble duct. Th us, it was esti ma ted th at aroun d 90 per cen t of the coo ling syste m dra g would be elimi nated by t he efficie nt thru st of t he exi t ing air. In h is new position at NAA, Schmued worke d o n va rious pro jects includi ng t he B-25 bomber and NA-3S p rim ary tra iner, but he also kept wor king on h is own perso na l concept of an ' idea l' fighter. As in t erest fro m the Briti sh Pur chasi n g Com missio n in creased in h avin g NAA lice nse-b uild P-40s, a proposal was presen ted to the 'Brits' on the new figh ter. To give an in di cation of how even ts progressed durin g th is t ryin g ti m e pe riod, the Brit ish liked wha t th ey saw in t heir April 1940 meeting with Atwood a nd issued an orde r for 320 exam ples of t he n ew figh te r (see ch apter two for co n tr actua l de ta ils) 'Dutch' placed Schmucd in cha rge of the pro ject, but th e British also pu t in a req u irement that NAA purchase wind tu nne l da ta from Curtiss on thei r XP-46 (an 'im p roved' versio n of

10

This detail view of t he N A ~ 7 3 X shows t he beautifully streaml ined cow ling which covere d t he Allison v, r 7 10 - t he for me r was handbuilt by NAA's meta l sho p and neat ly hou sed t he e ngine installatio n designed by Art C heste r

P-S l MUSTAN G -,

t he p_.JO design , a nd o ne of th e ugliest aircraft eve r bu ilt ), Curtiss made a quick $50,000 profit from th e sa le an d Atw oo d wen t to Bu ffa lo, New York, to co llect t he pap er s a nd dat a. In correspo nde nce wit h Sir He n ry Self, Atwood wou ld writ e o n 1 May 1940, ' \ Ve have reac hed a n ext re me ly sat isfactory ag reement wit h the Cu rtiss Aeropl a ne Co m pa ny o f Buffa lo whereby th ey are fu rn ishi ng to us dat a cove ring a co m p rehe ns ive series of wind tunn el, cooling a nd performance tests of a sim ilar a irplane, wh ich dat a will assist us in the d esign a nd manufacture of th ese airp lanes'. Ch ief aerodynam icist Ed Horkey ex a m ine d th e dat a and fou nd it Virtua lly useless. Sch m ued wo u ld later claim he neve r eve n saw th e Cu rt iss dat a. On 10 April 1940, t he Brit ish signed t he go-a he ad lett er for the NA-73X pro ject (' 73' for th e NAA model nu mber, ' X' for experimen tal), whil e th e forma l co nt ract was signe d on 23 May. The sma ll NAA eng ineering depar t men t issued d rawings to the fabricatio n sh o ps in a never-endin g st rea m th at in cluded 16hour wor k days, seve n days a wee k. 'D ut ch ' a nd hi s te am we re aiming for a delivery date of a co m ple te airf ram e in Janua ry 1941. Howeve r, th e NA-73X was rolled o ut of the h angar in 117 da ys - alt houg h in complet e in so me det ails an d sitti ng on t yres and wheels grabbed fro m th e Ha rvard production line (NAA would record that they had ex pen de d 78,000 man h our s en gineering the proto type). Also, the eng ine h ad n ot bee n de live red from Allison a nd it wo u ld be another 20 days before th e V- 12 arrived to be mat ed to t he air fram e. Th e firewall fo rwa rd powerplant desig n ins ta llatio n for th e aircra ft h ad bee n en t rusted to Art Chester, a we ll-known race pilot and buddy of 'D utch 's' (and who wou ld go on to figure in other aspe cts of the typ e's prod uct io n h isto ry), who d id a n ex ceptio na l job in stallin g th e powerplan t in a neat pac kage wit h a closely-fitted co wling. Allison eng ineers had rated the V-I710 at 1100 ho rsepower, but had fixed th e criti cal alt it ude at 11/ )00 ft, and here

Magnificently co nst r ucted from different type s of wood, a mod el o f the NA-73 X is seen in the wi nd tu nnel at the California Inst itu te of Technol ogy in Pasadena

THE PROTO TYPE

II

lay th e in here nt weakness of th e eng ine. Th is crit ical altitude figure meant th at th e perform an ce of th e fight er would sta rt to fall off at any altitude over 11,000 ft, th us giving a critical advantage to ene my figh ters wit h a higher altitud e rating o n thei r powerp lants. NAA h ired freela nce test pilot Van ce Breese - a co lo urfu l and often o utspo ken perso na lity - to do th e first tes t flight. At t he time, several freelance pilot s vied fo r test wo rk, and the pay was o ften very lucrative. Th e mo rn ing of 26 October 1940 fou nd t he NA-73X parked on th e ramp wit h Breese in the coc kpit , go ing ove r a mental check list. Hitt ing th e starter, t he Cur tiss-huilt propeller jerked a few times an d t he Alliso n burst int o full staccato life, with just a hint of smo ke d issipat ing from the exhaust stacks. The powerplan t had been run up by mechanics ear lier in the mornin g. S-turning, Breese began to taxy th e pro to type - the lo ng nose obscu red forward visio n, whic h mad e Sct ur ni ng mandator y. Po in ting th e nose int o th e wind and stand ing o n th e brakes, Breese gave t he Allison a th orough run -up . On ce sati sfied, the pilot took th e acti ve and moved t he th rott le sma rtly forward. After ro llin g a h un d red feet, he brou gh t t he engine up to full power and pointed the nose do wn the cen t re line o f th e run way, shovi ng in right rudder to cou nteract the torq ue. The NA-73X was quic kly airborne but the first fligh t was a rather sedate affair, Breese keep ing wit hin glidi ng d istance of Min es fi eld. Afte r flying for abo ut 20 mi n ut es, he found t he gleam ing that t he ai rcraft excee ded initia l perfor man ce estimates . Throttlin g back, he b rought th e NA-73X in for a smoot h landing - three more test fligh ts were made by Breese before he went o n to other project s. NAA was fortun at e in hav ing access to an excellent wind tu n nel facilit y at t he California Institu te of Technology in nearby Pasadena . Conc eived in th e 1920s by Th eod ore vo n Karm an (co nsidered by many to be the fat he r of ae rona ut ics), t he tu nnel was used by NAA to prove man y o f its design advances. So imp ort an t was the tu n ne l to th e later war effort t ha t armed gua rds were positioned aro u nd th e buildi ng in wh ich th e tunnel was housed . Cal Tech scien tists and eng ineers worked aro und -the-clock shifts. Ju st befo re t he wa r began, th e tunn el was o fficially inspected by Cha rles A I.ind bergh , who was o n special assign me n t for th e govern me nt to inspect th e nation's ae rona utica l research capabilities . Th e wind tunn el was bu ilt with a gran t from th e Dan iel Guggen he im Fund, which also made possible th e fou nd ing o f th e Guggen heim Aero na utical Labora tory (GALell') and an en tire acad emi c bu ild ing in whi ch to hou se th e facility. NAA used t his facilit y t hro ugho ut t he war. Paul Balfou r (comme rcial pilot ce rti ficate n umber 12596) was hired by NAA and assigne d th e post o f chief test pilot fo r th e NA-73X. Befor e his death in th e early 19 70s, Breese made th e com men t th at he had het mo ney with NAA officials th at Balfou r would cra sh the aircraft on his first fligh t. Breese wo n. 12

The st ricken NA-73 X is seen in a bea n fie ld just 150 yards west of Mines Field sho rt ly afte r its cras h landing o n 20 November 1940. Test pilot Paul Balfour managed t o scramble to safety via the canopy's side window.This view show s th e aircraft's gen erou s flap ar ea to advantage, along with th e o pening for t he air scoop. It is also interesting t o no te th at t he C urt iss propeller is not in sight, having been ripped away from th e engine and tak ing t he nose gear case alo ng in the process. Note that t he both wing t ips have been ben t o ut of shape du ring t he accident - de cade s late r. t hese same o ute r wing panels wo uld be rem oved (since the y were not ess ent ial st ructu res ) for a new ge nerat ion of Mustan g pylo n racers

P-SI MUSTANG .,

One t he mo rn ing of 20 Novem ber 194 I, t he gro un dcrew prepared the NA-73X for Balfo ur 's first night . Wit h t he Allison already ru n n ing, Balfour climbed in to the cockpit an d took off at approx ima te ly 071 O. The pu rpose of the fligh t was to undertake several speed ru ns over tim ing positi ons set up o n t he field. Mechan ic Olaf T Anderson later stated th at t he eng ine ha d run fine on th e grou nd an d, 'at abou t 0540, 1 warme d the engine u p as is the usual proce du re befo re the flight. Oil an d Prestone temperat ures were no rmal (oil 65°C, Prestone 95°C). Oil pressu re and fuel p ressu re were norma l at I ROO to 2000 rp m. Oil pressure was 80 Ib an d fuel 13 lb. The eng ine was ru n fo r five minutes and th en sh ut down. When I sta rte d t he eng ine for Mr Balfou r before take-off, it was a littl e hard to start (t he Alliso n represen ta tive said t hei r eng ines have a ten dency to do such)' . As Balfou r pulled up (after abou t 12 mi n ut es flying time), th e eng ine stop ped completel y. Checking t he inst ru men ts, nothi ng seemed amis s. However, exec uti ng a wide swee ping tu rn ca used t he NA· 73X to lose altitud e and Balfour q uickly realised t hat he was not go ing to make t he ru nway. Du ring t he last portion of th e tu rn , he dumped lan ding gear an d flaps as he directed th e st ricken prototype to ward a ploughed field just west of Lincol n Boulevard. Th e now-glider whistl ed down in a correct lan d ing atti tude, bu t as soon as t he tyres touche d t he soft soil (at approx imately 0 72 :~ ) , the NA-73X vio lent ly flipped over. The built-u p st ruct ure behi nd th e pilot saved Balfou r from being cru sh ed , and th e pilot scramb led for safety from the moveable side window. At the time o f the accid en t t he prototy pe had accu mulated just three hours and twen ty min utes o f flying time (Balfour had logged 2298.40 hours of solo time at th is point). The Civil Aeronautics Autho rity Air Safety Board listed d ama ge to the aircraft as 'e ngi ne hous ing broken, bot h wing tips dam aged, ta il su rfaces da maged , to p of fuselage dam aged, and ot he r miscellaneous damage' .

THE PROT OT YPE

13

The NA-73X is lifted from th e bean fie ld by crane. No te the smashed cowling and vertical fin. and how th e cock pit area escaped damage. co urte sy of the extremely robu st ro ll-ove r stru cture be hind t he pilot

Investigatio n of the cras h revealed that th e Alliso n had ru n d ry whe n th e selected tan k had been allowed to be ru n out of fuel. Nort h American and th e British bot h agreed t ha t, in sp ite o f the crash, th ey had a win ning aircraft and th e accide nt was no way the fault of th e design. Some aviati on h isto rian s have reco rded th at the proto type was scrap ped after the accide n t bu t this was not the case. Actu ally, the p rototype was ca refully lifted out of th e bean field by cran e and tr anspo rted back to th e NAA factor y, wher e it was st rip ped apa rt and rebu ilt in a very short time. R C ' Bob' Ch ilto n was hired as chief test pilot to replace t he u n fo rtu nat e Balfo ur, and a study of h is log hooks indica tes th at he fiew t he rebuilt NA-73X o n 3 April 1941 for a o ne- ho u r fam iliarisation flight fro m Mines Field. Chilton also reca lled t hat th e NA-73X hact made bet ween five to six fligh ts wit h another pilot at the co ntrols im med iately afte r its rebu ild . Chilto n wen t on to mak e at least a dozen mo re fligh ts wit h t he aircra ft. He later remar ked , 'the NA-73X was a clean flying aircraft with no bad vices. It was q uite pleasant in t he air an d handl ed very similar to th e lat er produ ction art icles '. Ch ilto n had accrued co ns ider able fight er expe rience in th e Army Air Co rps before co m ing to NAA, flyin g th e Roeing P-12 14

P-SI MU STANG

and P-26, Curtiss P-36 and ot he r fighter types. His expertise in th e fighter field ena bled the enginee rs to incorporate changes tha t would be be ne ficial to t he comba t pilot. 'I recall tha t the NA-73X was just pushed to the side after it had been retired from its last flight' , sta te d Ch ilto n. 'It probably end ed up on t he company's jun k pile, but I do not reca ll seeing it there. The NA-73X was a very att ractive machi ne and its alumi num skin glowed with constan t wax ing hy George Mounta in Bear Lane, an Ame rican Indi an whose du ty was to keep the airframe as clean as possible to pick up th ose few vita l miles per hou r.' With t he first aircraft coming off the prod uction line, NAA and the British decided to use these airfra mes for cont in ued testi ng. 'Th e "o ld" NA-73X was no lo nge r represen tative of th e design' , state d Chilton. 'We had orders on o ur han ds for h undreds of new fighte rs and t he NA-73X had served its purpose. It had esta blished t he tre nd for what I believe was the finest propeller-d riven fighter ever built by any cou ntry.' Recen t resea rch indicates that the NA-73X, stripped of useable co mponents, may have bee n donated to a local t rad e schoo l.

Following the arrival of this offici al Brit ish Purchasing Co mmission co mmun ique at NA A o n 12 Decem be r 1940 , t he NA-73 be came known as t he Mustan g

EXPORT OFFIC E BRITISH PURCHASING COMM ISSION DECEMBER 9, 1940 IN REPLY PLEASE QUOTE BACfCIA250 (FSC) NORTH AMERICAN AVIATION, IN C ,I N GLEW O O D, CALIFORN IA CONTRACT A2S0 FOR THE SUPPLY O F NA-73 A IRPLANES AND SPARES LETTER O F AMENDMENT N O 13

GENTLEMEN: WE ARE TO INFORM YOU THAT THE ABOVE MENTIONED AEROPLANES HAVE BEEN GIVEN THE OFFICIAL DESIGNATION 'M USTANG', AND THIS NAME SHALL BE USED IN ALL CORRESPONDENCE.. PLEASE RETURN TO US TH E THREE ATTACHED COPIES OF THIS LETTER DULY SIGNED BY AN AUTHORISED OFFICER OF YOUR COMPANY. VERYTRULYYOURS, HIS MAJESTY'S GOVERNMENT IN THE UNITED KINGDOM BY BRITISH PURCHASING COMMISSION BY (SIGNED) R. F. PAYNE FOR AND ON BEHALF OF THE DIRECTOR GENERAL

ACCEPTED: DATE DEC 12, 1940 SUPPLIER: NO RTH AMERICA N AVIATION,INC BY: (SIGNED) NOBLE SHROPSHIRE TITLE: CONTRACT ADM INISTRATOR

T H E PROTOTYPE

15

LAMINAR FLOW ne of the main factors in making the P-51 a high-pe rfo rmance fighte r was the deve lopment and produ ct ion of a wing inco r po rating a laminar airfoil.The co ncept was o riginally devel-

O

oped by the Natio nalAdvisory Committee fo r Aer on autics ' A C Robi nson. wh o did a paper o n the subject, and later supplied data and re sear ch notes on laminar airfoils.Although the laminar concept had been known for quite so me time, it had rar ely been applie d to an act ual airc raft. Basically. a laminar flow featured a symmet rical air foil tha t ut ilised the same curvature o n lower and upper surfaces.The lead ing edge was kept as thin as po ssible w hile the airfoil's greatest th ickness was placed as far back as po ssible . In prac tice , this wo uld kee p t he bou ndary laye r air flow adhe ring to the wing surface further aft of the leading edge th an any oth er type of airfoil. Em ploying a normal airfoi l wo uld mean th at the bo undar y laye r broke up much earlier on th e wing surface , causing t urbulenc e result ing in dr ag, and a drop performan ce. Unfo rtu nate ly, the few w ings th at had bee n construct ed to take advantage of the laminar principle w here hand-built, and t he surfaces had been highly finished to prom ot e a t rue laminar flow. Such hand-finishing wou ld be impractica l on a production -tine fight er. so NAA engineers came up w ith a method of filli ng and san ding the lea ding edge of the wing to insure laminar flow - 'lam inat ing' layers of air over and unde r th e w ing t o insure a pe rfect an d smooth air flow.

16

P- 5 1 MUSTAN G

With such a radi cal airfo il, and a new method o f production, NAA made sure that th ey had an 'escape ro ut e' should the laminar flow wing not work. de signing a more co nve nt ional flying surface th at coul d quickly be put into pro duc t ion should the former unit prov e to be a failure . Fo rt unat ely, the laminar flow experimen t (t est ed in th e wind tu nnel at th e Ca lifornia Inst itu t e of Techn olog y in Pasade na) pr oved wo rkab le in mass pr o duction, and th e final airfo il had a thi ckness ratio of 15. 1 pe r ce nt at the wing root at 39 per cent of the chord. Tip ratio was I 1.4 pe r cent at th e 50 per cent cho rd line, with th e maximum thickn ess area at 40 pe r ce nt from th e w ing's leading edge .This resulted in a small negative pressure gra dient ove r th e first 50 t o 60 pe r cent of the wing. At the factory. the wings were prim ered an d finished with airfo il smoot her. Th e first 40 per cent of th e wing cho rd was shot w it h o ne co at of zinc chromate prime r.This was then fo llowed by en ough co ats of Acme Gray Surface r No 53N 5 to cover all irregularities. Skin butt joints were then filled w ith Acme Red Vellunite glazing putty No 58485.The ent ire area was then sanded down and sprayed wit h o ne coat o f camo uflage e namel (when camouflage was dele ted, the forward port ion o f t he w ing was sprayed silve r) .This was a simple and quick way to create a ne arly perfect laminar flow surface, but one has to wo nde r just w hat effect all th o se size 12 G I boots (wo rn by bo th air- an d grou ndcrew) in th e field had o n the carefully-applied laminar flow finish!

CHAPTER

rn BUNDLES FOR BRITAIN

AS MENTIO NED IN TH E p revio us cha pte r, the British Pu rcha sing Co mm ission was ext remely plea sed with the aircraft created by Nort h American's design team, but th eir in itial o rder received a cod icil from th e US govern ment. In return for letting Britain order th e new figh ter, it wan ted two early p roduction aircraft made available to the Un ited States Arm y Air Co rps at absol utely no cost. The British enjoyed putt in g names to th eir ai rcraft designs (as evide nced by t he Spitfire, Hurri can e and Blenheim ) and, fo r a whil e, th e name 'Apac he' was co nsidere d sin ce i t represen ted t he wildness of the American west. However, 'M ustang' was finally chosen for t he figh ter, call ing to m ind th e sma ll, hardy and swift hor se of t he Ame rican plains that had descen ded from Spa nish stock. It wo uld tu rn out to be a partic ularly appropriate na me . In ligh t o f th e British (and American ) in terest in th e new figh ter, it was just as well th at NAA had esta blished an efficien t pro duc tio n lin e p rio r to un veil ing th e NA-73 - a fact t hat has been main ly ove rloo ked when an alysing the suc cess of t he design . Besides cranki ng out a few 0 -47 ob servat ion aircraft, the com pan y's main manufactur ing thrust had been with t he 8T9(fexan /Harvard series o f t raine rs. Co pying th e same efficient style o f train er prod uct io n, a line was set up in rapidly co nstru cted new buildi ngs at Mines Field whi ch wou ld easily acco mmodate the flow of sub-assemblie s that were eve nt ually tu rn ed into complete fighters . In com par ison, t he Supe rma rine Spit fire was a very co mplex fight er to buil d, an d was not reall y suited for th e style of mass-produ ctio n techn iqu es env isioned by Hen ry Fo rd - the creator of really efficie nt mass-production . Un like t he Spitfi re, th e Mustang 'went to geth er' almost like a large met al mo del aircra ft kit, making it ideall y su ited for cons t ructio n in very large num bers. 'Dutc h' Kinde lbcrge r kep t p ressu ring for an adv anced production lin e, apparently realising th at the com ing war, and t he Army's gro win g interest, wou ld lead to man y mo re o rders. Th e year 1941 was an ext remely bus y o ne for NAA. Position vacan t ads in so ut her n Ca liforn ia newspa per s b rough t in hordes of wo rkers fro m all acro ss the natio n - men looki ng for stead y wor k to escape the effects of th e Great Dep ression . BUND LES FOR BRITAIN

17

NAA was hiring by t he hundred s as th e initial orde r fo r t he Mustang Mk I amounted to 320 aircr aft (rapidly growing to 620 aircraft), and skilled wo rkers were at a premium. Typica l for th e time period, th e price of the aircraft would exclude the engine, armament, radi o s etc. The RAF was gett ing th e basic airframe, and although everyt hing else would he added on at th e NAA factory, th e British gove rn men t was resp on sible for purchasing and supplying th e remain ing items. As a co nt ract stipulatio n, t he basic airframe price was not to exceed S40 ,OOO. The prem ier Mustang Mk I (RA F serial AG34S) made its first fligh t from Mines Field , wit h Lou is Wait at th e co n tro ls, o n 23 Ap ril 1941. The seco nd aircraft - AG346 - was di sassem bled and fitt ed in a sto ut woo de n crate for th e hazard o us ocean voyage, arrivin g safely at Liverpool on 24 Octo be r 1941. The Mustan g was ta ken to Speke Aerodro me for ini tia l flight testing, whic h confi rmed the result s reco rded wit h the NA-73X and AG34S. Many Brit ish pilots were assigned to fly AG346, and t hey fou nd the new fighter satisfacto ry in its designed role. As reco rded in th e previous chapter, part o f t he Mu stang's excellen t performan ce was due to the clever design of the cooling system, although th e ma jor co n tributo r was th e aircr aft 's laminar flow win g. Briefly explained, this is a t ype of airflow over an ai rfoil in which the air passes over the su rface in

18

P-S I MUSTANG

LEFT This wonderful high-angle view of Mustang Mk I AG348 (the fourth prod uction aircraft) illustrates the very simple layout of the fighter,and also shows th e angular wingtips to advantage . Most fighter s pro duced pre vio us to the Mustang had elongated curved wlngtips which we re believed, incorrectly,t o cut do wn on drag.Also, the angular wingtips were much easier in build in mass quantity.The photograph also shows the ea rly short air scoop for the Alliso n's car buretto r;This arrangement caused, at different

air speed s and angles of attack, a non- unifo rm flow of air to t he engine which re sulted in surging. This pro blem was so lved by slightly raising the inlet and extending the lip close r to the pro pe ller.The se early Mustangs were camo uflaged in Ear t h and G reen upper su rfaces and Sky Type S unde rside s. Uppe r wing roundels were red and blue while t hose on the fuselage sides were, from o utside in, yellow, blue , white and re d. Finally, the unde rwing ro undels were blue, whit e and re d

A BOVE 'Dutch' Kinde lberger is seen in t he cockpit (minus the comfort of a sea t) of a Musta ng Mk I whilst showing the aircraft off to a visiting British official.As can be seen, the fuse lage was in a movable jig, and various part s we re affixed t o the airframe (like t he box co ntaining t he Parker engine primer o n th e firewall) along wit h a list of sho rta ges for the particular airframe

BU ND LES FOR BRIT A IN

19

Although it looks a bit crude by today's standards, this airframe is being thoroughly studied as more and more lead weights are added to the aircraft to test its ultimate structural integrity. A tempo rary wooden partition encloses t he aircraft from rest of the factory as such testing cou ld be hazardous since there was always

20

P-S I MU STANG

the chance of a catastrophic structural failure, which could send bits of metal flying about at high velocity. Several other Mustang books have wrongly identified this aircraft as the NA·73X. It was an incomplete airframe (often referred to in testing documents as XX. 73) t hat was tested to dest ruction to provide accu-

rate data on the airframe's strength and then scrapped after the trials had been completed. The testing progressed in a very logical manner, finally culminating with crucial wing strength trials the fly ing surface failed at 105 per cent of its design load.This highly-de tailed photograph was take n on 16 January 194 1

.. ......,. ,.

""

A smiling 'Dutc h' Kinde lberger and a so me what dou r Sir Hugh Do wding at t he NAA plant o n 10 Febru ary 1941. Dowding, o n an inspection to ur, is ho lding a prese nta t ion mo del of t he Musta ng Mk I

Dem and fo r t he Mustang Mk I was so grea t t hat early examples we re rapidly crate d and shippe d to Britain. As t his pho tograp h shows , t he packing cra te itse lf was a bit of a work of art, being designed to ho ld all of t he aircra ft's com po ne nts. W hile o ne workman affixes t he vertical fin to the right side of th e crate wall, ano t he r slides in the horizo ntal sta biliser. No te th e pilot's seat fixed t o t he floor of th e crate. The wings in the backgro und are for a Harvard BUNDLES FO R BRIT AIN

21

Left side of a Musta ng Mk l's cockpit, ill ust rating the tr im co nt rols for the ailerons, rudd er and elevator. The landing gear handle is at the bottom of the side co nso le. while the co mpact throttle and propeller controls are co nveniently placed for the pilot's left hand

22

P-SI MUSTANG

smo ot h layers with a minimum of turbu lence. With most airfoils there is a layer of ai r ad jacen t to th e su rface tha t flows in a rando m fash ion , sometimes eve n reversing its d irection of flow. Thi s is th e boundary layer. The laminar flow airfoil is designed in suc h a way t ha t th e bounda ry layer has a mi nim u m th ickness, and nearl y all t he air flows in smooth layers . Lam inar flow o f th e air decreases th e dr ag produced by th e ai rfoil. The laminar flow wing on th e Mustang was the first time that suc h an airfoil had been employed o n a prod uction m ilitar y aircraft , th e design of th e airfoil itself being based up on Russell Robin so n's rep ort s filed with the Nat iona l Advi sory Committe e for Aeronautics (NACA). Rob in son (an ae rody na miclst with NACA) had cond ucted succe ssful wind t un nel expe rime nts wit h th is new gene ration of low dr ag airfoils, and NAA aerody nam icist Ed Horkey and hi s crew laboured for weeks to adopt th is data to the new fighter design. Since time was a factor to be recko ne d wit h, Kinde lberger issued an order to Edgar Schmued th at his team mu st be read y to design a co nve n tio nal wing wit hi n 30 da ys in case th e lam ina r flow concept d id no t

work out (in fact all th e data for t his 'seco nd' wing was unear th ed in 199 7 during resea rch in t he Caltech files). Ed Horkey tested his pre lim inary wing in th e wind tunn el at t he Califo rn ia Institute of Tech no logy but foun d th at th e u nit had an unpl easant stall char acte ristic th at was not acce ptab le to Horkey and would certainly be frowned u pon by t he Briti sh . When a modi fied wing sectio n only sligh tly im proved t he problem, Hork ey suspected t ha t part nf the pro blem lay in t he tigh t confines o f t he Ca ltec h tu nn el, so he shipped t he woo de n wing section to the so mew ha t larger tu n nel at th e Uni versity of Washingto n via a Un ited Airlines DC-3. Horkey's gamble paid off, and the win g perfo rmed as planned in th e larger tu n nel. Th e Mustan g Mk I, designa te d NA-73, was fitte d wit h fnur .50 cal and four .30 cal mac hine guns. Most Ame rican fight ers were still well behind t heir Europea n coun te rpa rts in th e firepower depart ment, and th is arma men t selection was co nside red quit e pow erful. Power came from t he Alliso n F3R which reached its opti mum power at lower altitud es. Several small modificati ons were made on combat-ready Mustan gs by t he

Right side of th e Mustang Mk I's cockpit, showing th e map and data case , map read ing lamp. ox ygen regulator and panel fo r navigatio n lights. land ing light and pitot heat. The ro und device mou nted o n the can opy structu re is th e Morse co de key.The spade type gr ip favoured by t he British is also shown to advantage. with the firing button t o the left. Cockpit placards warn no t to exceed 505 mph in a dive and no t t o lower flaps at speeds abo ve 170 mph

BUND LES FOR BRITA IN

23

British, including slight changes to th e air duct system and rad iat o r air scoo p. During subse q uent flight t rials, a co mbat-ready Musta ng Mk I was found to be 35 mph faste r below 15,000 ft (3 75 mp h) t han th e sta nda rd Spitfi re Mk V, alth ough at ceilings ahove t his height performanc e rap idly fell away du e to t he design limitations of the Alliso n whic h, lacking an efficien t form of supe rcha rging, was str ictly a low to med ium altitude en gine - unfortu na tely t he air battles over t he Continent were being fough t at higher altitudes, As mor e early model Mustangs arrived in Britain aircraft were assigned to RAF Duxford for air co mbat testing, where th e type co mpared favourabl y wit h t he Spitfire at lowe r alti tudes . Few vices were u near t hed , and British pilots were impressed with t he NAA's creat ion of a logical coc kpit layout wit hi n the con fine d space offered by th e st reamlined fuselag e. Also whi le at Duxford , t he Mu stan g Mk I was tested again st a captured Messerschm itt Bf I09E and, once agai n, had a d istinct edge ove r 24

P-5 1 MUSTAN G

Fine study of Musta ng Mk I AG345 in flight on 19 August '94 1 with test pilot Bob Ch ilton at the cont ro ls.The slimness of the radiator scoo p installation is notewo rthy.Th is aircraft was reta ined for a time at NAA to test vario us improvem ents - as can be seen. the fighte r has been fitted with the raised and extend ed carburettor air scoop. The first gro up of Mk Is (se rialled AG34S th rough AG664) we re built and de livered to Britain between Novembe r 1941 and May I942.AG345 was st ruck off charge on 3 Decem ber 1946

This head -on view of Mustang Mk I AG346 emphasises the aircraft's elegant and slim lines.The position of the arm ament is also displayed to advantage.Two of th e .50 cal weap ons were fitted in th e lower nose cowl and the re maining two .50s on the inboard wing positio n, leaving four .30 cal wea pons to be housed outboard .The lack of visibility for the pilo t in th is three-point positio n sho uld also be noted.This particu lar aircra ft enjoyed a long o perat io nal caree r before being finally being shot down by flak near Gace on 20 August 1944 while serving with No 168 Sqn of the Seco nd Tactical Air Fo rce BELOW

the Luftwaffe figh ter, but it must be no ted t ha t t he Emil was by t hat time no longer in producti on , having been repl aced by newer and more deadl y aircra ft. In view o f th e type's rest ricti on to lower altitudes, th e Briti sh decid ed to co n ti n ue to use th e Spitfire as t he ir stand ard high-perfo rma nce fight er. RAF Fight er Com mand re ject ed th e Mustan g Mk I, and t he aircra ft wa s sen t off to th e new Army Cooperation Co mmand (ACC). The ACC was esta blishe d dur ing 1940 to co-ord in ate air /g round act ivities wit h th e Army - a vita l task t hat was neglected, with disast rou s resu lts, by th e British Expe d itionar y Force in Fran ce. Th e Mustang Mk I was idea l for th e ACe since it was heavily armed, high ly man oeuvrabl e, had a very good ran ge and could really get mo ving at altitudes below 10,000 ft - th e regime which wou ld be most beneficial to the Army. Up until the int rodu ction of the Mustang, the ACC had bee n eq uip ped wit h Westland Lysanders an d Curtiss Tomah awks, neith er of whic h were ideal for fron tline ope ration s over heavil y-defended target s in Occu pied Europ e. It was initially plan ned to eq uip 18 squa dro ns with th e Mustang, but only 16 squad ro ns were eve ntu ally so constit ute d. With 'Dutch 's' co ncept of a high-tech production line ha ving bee n in place fro m the early stages o f th e Mustan g's developm ent, aircraft were rap idly rolling o ut o f th e assem bly hangars to join Texans and new B-25 Mitch ells on th e co mpa ny ramp . Furt her modificat ions were in sto re for t he fight er, however, and 150 Mustan g Mk lAs (NA-91) fitte d wit h four 20 mm can no n in t he win gs were built. Fifty Mk lIs (NA-99) were also supplied to Britain, th ese being USAAC P-5 1As pull ed from th e produ ction lin e. The RAF even tua lly received a total of 69 1 Allison- po wered Mustangs from th eir o riginal co n t racts, th is figure deleting t hose aircra ft lost at sea d uring shipping .

BU N DL ES FO R BRITAIN

25

DOLLARS AND CENTS

'We furt her offer to co nt inue th e manufactu re of the se planes at t he rate of 50 airplanes per mo nt h unt il at least the end of the yea r 1941 , sho uld yo u desire to incorporate and exercise an o pt ion for these additional airplanes prior to 30 April 194 1.

hat did it cost for th e first Musta ngs. what did th e Brit ish and NAA expect from each other and how was th e contract awarded? The following is a lett e r from NM's Lee Atw ood to Sir Hen ry Self of th e Anglo-Fren ch Purchasing Co mm ission.The lett er was dated I May 1940. In today's litigious so ciety, th e lett er appears t o almost be a gentlemen's agreement;

W

'In accordance with o ur understanding. we are proceed ing wit h the design of a single-sea t fighter airp lane, ou r Mo del NA-73, incorporating an Allis on engine and fitted with provi sion s for

equipme nt and arma ment as detail ed mo re completely hereunde r. 'We have reach ed an ext re mely satisfact ory agreement with t he Cu rtiss Aeroplane Company of Buffalo wherein the y are furni shing t o us data covering a comprehens ive series of wind tunn el, cooling, and performance te sts of a similar airplane , which data will ass ist us in the des ign and manufact ure of these airp lanes.We have also rece ived release from th e United States Army for the manufacture and export of the se airplanes and wish to assure you that all ar rangeme nts are entirely satisfactory.

'We are prepared to co nst ruct and deliver to you 320 of the se airplanes before 30 Sept ember 1941, and guarantee t o effect deliveries in accordance wit h the following de livery schedu le:

'We have co nstructed a moc kup and have co mpleted t he initial phase of the detail design and are submitting to you herewith certain data and info rmat io n regard ing th e cha ract eristics of th e airp lane. You will no te tha t we have provided for armor prote ctio n fo r the pilot and a sealing arrangement for the fue l tank s. Pro visions are being made for the installation for four .50 caliber machine guns. two of which are in the fuselage and the o th er two in th e wing. As a no rmal load we are specifying 200 ro unds of ammu nition per .50 caliber gun. but are making additional prov isions for more ammun itio n as a special loa d. Pro vision s are being made for four British Type 303 machine guns with ammunit ion boxes to acco mmo date 500 ro unds of amm unitio n per gun as no rmal load. 'Strictly for com parative purpose s, we are including th e results of a study show ing th e differ en ce in size and performance betwe en t he airp lane offered and o ne which might be offe re d with a minimum armam ent and witho ut protective armor. but is otherw ise the same . It will be no te d that th e high speed in t his condition is 400 mph with a wing area of 190 sq ft. W ith a full co mplement of ar mament and armo r plate prote ct ion front and rea r, t he weight is increased from 6450 Ib to 7765 Ib and th e wing area is incr ease d from

1941 FEB

MA R

APR

MA Y

JUN E

JU LY

AU G

SEP

Airplanes

5

20

40

50

50

53

51

50

Spares

3

5

5

5

5

10

15

15

JAN

(equivalent ale)

26

P· 5 I MU STAN G

OCT

NOV

t 90 sq ft to 230 sq ft in ord er to maintain the same landing spee d.The resulting pe rformance is materially redu ced and high speed is 384 mph under the same condition s.

'The speeds quoted above are based on a power of 1030 hp at 16.000 ft altit ude. using 90 octa ne fuel.Since we do not have precise and final information on the powe r rating of the engines to be furnished for th ese airplanes. this rating is still somew hat of an estimate.We believe the AngloFrench Co mmission has. or will shortly have, accurate information on this matter.When we receive the exact figu res. the perfo rmance guarantees will be arithmetically adjusted accordi ngly.

We have made a careful estimate of th e price . including sufficient st ructural tests to guara ntee the st ruct ural integrity of all parts, wind tunnel testing and flight testing.We have include d a pr ice breakdown. separating and pricing all items of equ ipment to be installed and supposedly furnished by us.We have not co nside red the price of engine. propeller. radio. oxygen. machine guns or ot her ite ms of armame nt or military equipment. and it is assumed that the se items will be furnished to us free of charge for installatio n in the airplanes.The price summary for airplanes, ex clusive of crating o r tran sportation. but cove ring all other charges is as follows:

$ 983.9 5 A) Power-plant. eng ine accessorie s 'The genera l provisions for armament have been discussed B) Inst r ume nt s 1787 .35 with Air Co mmodo re Baker and C ) El ec tri cal Equi pmen t 890.75 MI:Thom as and it is believed D ) Miscellaneous Equipme nt 52 8.40 that the arrangement offered is E) Rad io Equip me nt Cu st o me r fu r nished the most pract ical possible at this time, co nsiste nt with the C us tomer fu rn ishe d F) Ar mam e nt general instructions we have received. It is possible to To ta l equ ipm e nt to be increase the fire power 4190.45 furnished by Contr acto r th rough the installation of 33,400.00 Base airplane additional guns if abso lutely necessary,but the perform ance 37,590.45 Total per Airplane will suffer a proportionate loss. We feel there will be no difficulty 12,028,944.00 Total for 320 Airplanes in making any changes o r Spa re parts (20%) 2,405 ,788.80 modifications which you may feel 2 16,000 .00 Crating per a ir plane $6 75. to tal are essential or desirable, and are prepared to co-o perate wit h 96,2 3 1.35 Crating for spare pa rt s (4%) your technical staff to the fullest exte nt.We do feel. however. that 14.746,964,35 To tal Contract Am ount the design as presented is close to an optimum co ndition. all things con sider ed. Details of equipment and installation are yet to be covered. 'Wi thin 60 days after the contract has been executed we will furnish a complete percentage but our previous experience wit h Harvard aircraft, which incorp orate much British breakd own and a rec omm ended list of spare parts to approxi mate 20% of the co ntrac t price s of th e equipment. leads us to be lieve that we will have airplanes. Spares will be delivered in acco rdance no difficulty whatever in ar riving at satisfactory with the delivery schedule attached hereto, agree ments in all these matte rs.

BUNDLES FOR BRITAIN

27

provided a spare parts list is approved and agreed upo n within 60 days after submissio n of such a pro posed list by us. 'We are prepared t o proceed immediately upo n rec eipt of a letter from you acce pt ing th is pro posal and receipt of down-payme nt. We des ire a down-payment of 10% of th e co nt ract amo unt upon approval of th is pro posal and a subsequent monthly payment of 2.5% of the contract am ount each month until 25% of th e contract has been paid. Details of final payments and acceptance will be as mutually agreed upon and in general accordance with our previous contracts with the British Government.We feel t here will be no difficulty in t he prepa ratio n of th e final co nt ract at your convenience inasmuch as we have rea ched agreemen ts with you r staff concern ing all pr incipal po ints invo lved in a co ntract of th is type . 'The price s quo te d above are inten ded t o include all normal and reasonable mod ifications and

changes which yo u may req uire. prov ide d that such change s are agree d upo n w it hin t hree mo nt hs of th e date of th e agreement and provide d th e re is no co nside rable addit iona l ex pense to us as might be invo lved in th e pur chase of additional mate rial or equ ipment. Cha nges init iated after th is time may invo lve a de lay in delivery or a cost increase. 'May we request that you give this matter your ea rly attention as we are prepared to proceed on rece ipt of a letter of approval from you and re ceipt of down -payment as reque ste d above .We will con sider the date of receip t of this payment as the date of the contract. 'If th e re are any matters no t prope rly covered in this lette r o r th e enclo sed data and it is necessary to withho ld the lette r unti l such matters are clarified . we will grea tly appreciate it if you will noti fy us of th ese matt ers by telegram or tele pho ne at o ur ex pe nse in o rder that there will be no delay.'

Brit ish Purchasing Co mm ission acce pta nce pilots C hris C larkso n (cent re) and Battl e of Britain ace Michae l 'Red Knight ' C ross ley (right) po se with LA Coste llo. th e reside nt t echn ical officer with the Brit ish Air Comm ission OP POS ITE TOP

28

P-5 1 MUSTANG

RIGHT They had good reaso n to cover t he ir ea rs - thes e NAA wo rke rs are subjec te d to th e rigours of a canno n t est o n a Mk IA which was fitte d with fou r 20 mm weapon s in place of the machine guns.The aircra ft has been jacked up into flying att itu de and a batte ry cart pro vides power via a plug on th e right side of t he fuselage. To have t he laminar flow airfo il work most effect ively. the paint and skin co ndit io n of th e wing was supposed to have been mainta ined without scratches o r marring - so meth ing not evident on this airc raft!

BUNDLE S FOR BRITA IN

29

CHAPTER

C[]

PONY SO LD IERS

WHE N AMERICA N GO VERNME NT APPROVAL was given to allow Nort h Am erican and the Brit ish to proceed w it h t h e d evelopmen t of t he NA-73, one o f the co n d itions th e fo rmer in sisted upo n was that the fourth and ten t h produ ction a ircraf t be h and ed over to the Army Air Corps. An Aut h o rity fo r Purchase document (n umber 16526 5) was issued o n 24 j u ly 1940 and ca lled for t he delivery of th e t wo aircraft wit h t he AAC designation of Xlt-S1. On 20 Sep tember of t h at same yea r, an official contract was approved by th e Assista n t Secretary of War. Th e two prot otypes were built in accorda nce with t he British Model Spec ification, a lt ho ug h certa in m odi ficat ion s were also mad e to accommod at e sta n dard Army eq uipmen t. As wit h t he British aircraft , th e wings consisted of two pane ls bol ted together at t h e centre p lane of the fuse lage . The mai n and rea r spars were of flan ged aluminum alloy sheet const ructio n, wit h the flap and aile ron hi nge sup ports m o un ted on t he rear sp ar. Th e rem ain in g str ucture co nsisted of ex t ru de d stringe rs and p ressed ribs, onto wh ich a skin covering o f al umi num coat ed alum in um alloy was rivett ed . Space between t he m ain and rear spa rs o n each side of the centreline was arranged t o h old the fuel cells, a struc tural do or being provid ed in the under su rface of eac h win g sectio n to facilitate t hei r installation an d removal. Th e aileron s we re of th e sealed balance type. Th e fuse lage constr uction at t h e cockpit sectio n co n sisted of two curved side panels, four longeron s (two o n eac h side of the cockpit) formi n g its st ructu re togethe r with th e outer skin , wh ich was reinforced by ver tica l fram es. Aft of the coc kp it, the longeron s extended into a sem i-monocou pe st ruct ure rein fo rced by vertical frames. All skin and fra mes we re aluminum coated alu mi n um alloy. Th e fuselage was d ivided into t hree sectio ns - t he eng ine sect io n , t h e m ain section and th e tail sectio n . All sections were de tachable, an d attac hed with bolts. Th e tail u n it was a full-cant ileve r st ruc tu re wit h a sem im onocoupe fin an d stabiliser, the latter being constru cte d as on e unit wit h deta chabl e t ip s. Th e full-cant ileve r m et al-cov ered st ruc ture consisted of tw o spa rs, alum inu m alloy ribs an d extrude d st rin gers. 30

P-5 1 M U S,~T,:;: A.:;: N~ G~_ _

The elevators was mad e up o f two sections, each int erchangeab le with th e o the r, an d were of fabric-covered aluminum alloy co nst ru ction. Th e st ructure co ns isted of a front spar, a short int ercosta l rear spa r, flan ged ribs and metal leading and t railing edge sections. Roth elevato rs were static balan ced and eq uipped with tr im tabs, which were con tro llab le from the cockpit for longitudi nal tri mm ing o f th e aircraft und er all flight cond itions. The vertica l sta biliser was a full -cantilever semi-monocoque stru cture co nsisting o f a for ward and rear spar, flan ged ribs and ext rude d stringe rs. Th e rud der was sim ilar in st ruc tu re to the elevato r, being fabri c covered and dyna mic ally balanced . It was also eq uipped wit h a trim tab controllab le from t he cockpit for d irect ional tr im min g o f th e aircraft u nder all flight co ndit ion s. The land ing gear co mp rised two main lan d ing gear assemblies an d a steerable ta il wh eel, all of wh ich were exte nde d and retracted by hyd raulic pressure. They were com pletely encl osed by fairing doors whe n retract ed . The tail whee l was capa ble of swivelling 360 an d was steerable wit h in th e ran ge of the rud der pedal travel. The main land ing gear whee ls were fitte d with hydraulic brak es.

De tailed facto ry view of P-S IAs undergoing final co mpletio n o uts ide th e NAA factory. During this time period the company was rapidly ex panding, and so me of th e final work had to be com plet ed o utside. No te how the aircraft are on jacks. and th at the NA-99 de signation has bee n applied to th e rear fuse lage of each aircr aft, alo ng with th e last two digits of the manufacture r's co nstruct ion numb er.Also note the additional windscreen window

0

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Produ ct ion o f th e new figh te r for t he Briti sh rapidl y mo ved forwa rd an d on 20 May 1941 Rob e rt Ch ilto n made t he first XP· 5 1 flight in AAC si n 4 t-03K. Alt ho ug h pro gress wit h the British aircraft was relati vely rap id, th e same co u ld not be said o f the Ame rican Mu stan gs, Th e first XP-S1 arrived at \Vright Field on 24 Augu st wh ile th e seco nd XP-5 1 (sin 4 1-0:19 ) did not get to t ha t loca tio n un til 16 December - the two aircraft had been sch edu led to arr ive in Februar y a nd Ma rch ! Exp a n sion of the America n ai rcraft indust ry to face wha t wo uld a p pa rentl y he a certa in e nt ry in to the war in Europe saw Nort h American issued wit h a co nt ract for ISO ('-S Is o n 7 Ju ly 1941 - well before the two Xl's had been teste d . In a report subm itted on 15 j ul y 1942 regard in g th e XI'-51, Capt \V G I.ogan co m me n ted , 'Except for min or incidental ch a nges , the project progressed at a normal rate . O n 24 Februa ry 1942, an Engineer ing Order was issued to rem ove th e origina l h yd rau lic gun cha rge rs o ut o f bot h airpla nes a nd insta ll in lieu th ereo f fu lly auto ma tic gu n cha rge r equ ipme nt which was bein g devel oped by th e Bendi x Co rpo ratio n in t he seco nd airpla ne . Th is was done so th at th e n ew c ha rging eq u ip me n t could

32

P-51 MU STANG

Lo o king no t unlike the NA-73X (and often identified as such in reference bo o ks). the first XP-5 1 poses for its portrait on the NAA ramp. USAAC sin 41-038 was rolled ou t of the factory in a highly po lished natura l metal finish (after its RAF paint had been stri pped) wit h the classy red . w hite and blue tail stri pes th at wer e soon to be eliminat ed as th e th reat of war increase d. The milita r y requested that NAC A perform flight test s on the aircraft. and it was duly flown to Langley.Virginia.Test ing commenced on I March 1942. and was finally completed on IS May of the same year.The aircraft LEFT

was flown for an accumulated total of 24 hours while fitted with special instrumentation. including accelerometers. turn meters and a time r. A recording yaw vane was also added on a boom that extended four feet fro m the right wing t ip. whilst an airs peed boom was mou nted fro m th e left wing t ip.The XP-S I created histo r y d ur ing these tri als as it was t he first aircraft t o fea tu re a low dr ag airfoil t o be te sted by NACA During te st ing. a maximum lo ad fact or of 8 G was calcu lated . along with a te rminal velocity of 0.82 Mach

ABOVE This mock-up section of wing was used for testing the 20 mm canno n. Some pilots felt that the increased weight of these weapons decreased the type 's overa ll performance. Note spent cartridges under wing

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be flight tested at an ea rly dat e. Sin ce th e delivery in stallati on, it was decid ed th at provision onl y wou ld be made for insta ltat ion of th is eq uipme nt. ' Prelim ina ry flight tesung was co nd ucted o n th e first air plane a t th e co n t ractor 's plant by th e co n t ractor's per son nel and govern ment pilots in accordance with the terms of the co ntract. Co n side rab le t rouhl e was incurred wit h t he Allison engi ne in sta llat io n in th e ea rly stages of th e airplan e's d evelopment. At o ne part icul ar throttle setting, th e engine was found to be ex t remely ro ugh a nd , in o ne instance, the e ngine complet ely cut out resulting in a forced lan di ng in a plo ug hed field . Th is landing was mad e hy th e co n t racto r's pilot without damage to propert y o r personal injury, a lt ho ug h co ns ide rab le damage was do ne to th e air p lane tuuthcr's note: this triers to till' NA-73X, al/d apparently does 1I0t take i1110 account tlu: fact thu! tile accident repotts il1dicatl'd that th e pilot I",d filii olle tank dry ). 'U nde r the terms of the co nt ract, t he Arm}' was SU P POSl>J to receive t he fou rth a nd te n th prod uct io n ar t icles. Th ese airplanes were schedu led for d elive ry in Februar y a nd Ma rch 19-11. The product ion o f th e NA-7J was dela yed both by th e cra sh landing o f the experime n tal m odel and th e dela y of th e eng ines fo r th e British a irplanes . To facilita te th e delivery of th e XI'-S I mod els it was decided to tak e th e fou rt h and tenth articles from th eir place in the asse m bly lin e a nd in stall th e Arm y eng ines in t hem for delive ry to \ Vrigh t Field . This proced ure was followed a nd th e first air p lane was accepted a t th e plan t of th e co n t ractor and flown to Wright Field o n 24 August 194 1, for th e purpose of co nd uct ing o fficial performance test s. ' Upo n arriva l of th e first airplane at \Vright Field , a safety inspection was co nd ucted. Th e ai rp lane was next we ighe d a nd balan ced and a n actual weight a nd ba lance report prepared . Before flight testing co uld be conducted , it was necessar y to in stall backfire scree ns to prevent d amag e to th e airp lan e d ue to 34

P-S I MU STANG

LEFT Weari ng te mporary American markings for flight testing within the United State s. Mustang Mk IA is prepared for its next sortie.The aircraft was finished in Dark Green and Dark Earth upper surfaces with Sky under surfaces . whilst the spinner was in Dark Earth. AM190 went to the Aero plane and Armament Experimental Establishment (A & AEE) at Boscombe Down for further tes ting. before being assigned to No 5 16 Sqn.The aircraft was struck off charge on 31 Octo ber 1945.The Mk l ied directly to the American Mustangs

BELOW Maste r wing jig for th e P·S IA. which allowed for precise construction of the unit. At this point . the main landing gear leg had not been added. but the forward 40 per cent of the wing had been filled and primer ed. Note that the interior is bare metal and devoid of zinc chromate. The completed wing wou ld ho use two 90 gal fuel cells that wo uld weigh 1080 Ib when full

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engine backfi re. Thi s wor k too k co ns ide rably longer th an was an ticipated d ue to th e break ing off of studs. It was also necessary to insta ll new aileron and flap b racket bo lts to co rrect an un satisfactor y co nditio n found by NAA in other airplanes. Th e replace men t parts were fu rnis he d by t he cont racto r and ins ta lled by Army personnel un de r the supervision of the co ntractor 's represe n ta tive . 'Add itio nal fligh t tests were co nducted on th e two airplanes de liven..-d to th e Army. It was during flight testing of th e first Army airplane th at it was d iscovered th at engine d ifficu lties previousl y encou n te red co uld be ove rco me by increasing th e lengt h of t he ram ming air in take scoop . It was on ly after th e co nt racto r co nsider ed th e airplanes to he sat tsfactory th at they were turned ove r to th e Army. ' Prelim inary performance tests were co nd ucted at t he ro ntra ctor 's plant by personnel on t ~ l' co n tracto r's first articl e du ring xtarch 19-11 , Final o fficial perfor man ce flight tests were co nd ucte d at \Vright Field betw een HOcto ber and 22 December 1941 . The reason for th e long pe riod of flight testi ng was du e to t he hig her prio rity of other airplanes to he tested, bad weather 36

P-S I MUSTANG

ABOVE As production at NAA built up. th e Mustang line was mod ified severa l times to accommod ate increased military orders. In th is view. early Mustangs were be ing built alo ng with Har vards for the RAF Early Musta ng fuselages ro ll down a very cr ude production line. the former being mounted o n rou gh wooden dollys fitted with casto rs for easy movement.The ten gallon oil tank has be en se cured to the firewall through th e use of hefty st raps RI GHT

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ABOVE A P·S IA fuse lage is mated to its wing.The aircra ft carries th e co nst ructor's ide ntificatio n number 132 paint ed o n st rategic areas of th e o uter fuselage and inside pane ls.The clipboa rds affi xed to the fuselage are assigned to the particular aircraft and o utline wo rk th at need s to be don e.The squared off tips of the Mustang's fl ying surfaces not on ly ease d produ ction, but also res ulted in re duced turbulence where t hey mat ed with the laminar airflow wing

38

P- 51 MU STAN G

RIGHT Coc kpit of a P-Sl with th e pilot's seat removed. The large handle near t he floor is t he tail whe el lock. No te t he ST IA gun sight. along wit h th e ring-andbead sight

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Installing the SCR-274 command rad io behind the P-51A pilot's positio n.This rad io was th e main co mmunication between th e pilot, ground bases and ot he r aircraft.The substan tial roll over structure immediate ly forward of the radio com par tment would save many pilots during landing or take -off accidents

40

P-51 MUSTAN G

ABOVE This teaching aid displays the Mustang's relatively simple hydraulic system

Fitted to its dolly,a co mpleted P-SIA tail con e assem bly is ready to be moved to th e final production line

LEFT

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Highly detailed view of the cockpit of P-5 IA-I -NA sin 43-6055. with the rear quarter panels removed for additional clarity. Original contracts called for the cons truction of 1200 P-5 IAs. but th is was drastica lly cut back to 3 10 aircraft when th e Me rlin engine was introduced to the Musta ng airframe BELOW

42

P-S I MUSTANG

RIGHT P-SI A- I-NA sin 43-6008 was retained at the factory for the installation and testing of bazooka-style rocket launchers. The P-SIA was fitted with a three-bladed Curtiss C.S3D-F32/50700 electric propeller with aluminum blades - Musta ng Mk Is had steel blade s

and malfun ct ion ing o f th e coo lant scoo p co n tro l and lan d ing gea r ret racting mech anism du ring th e co ld weat her. Th ese d ifficulties and o the rs o f a m ino r nature were corr ected by Army personne l and the co nt racto r's rep resentat ives. The seco nd airplane was th o roughl y inspected by t he Flying Branch after delivery and was then turned over to th e Armament La bo rato ry for firing tests.' Although it is appa rent th at th e aircraft, as wit h any new type, had some development al p roblem s it is also obvio us th at the milita ry either too k t he ir ti me solving th em , or simply forged ahead on testing o t he r types at hand . However, given the fi nal overall co n trihutio n o f th e Mustan g to the Allied victo ry, Dill' must won der just what th ey were th in king. The few su pporters of th e new aircraft had a lo ng and hard fight ahea d to make sure that de velopmen t would conti nue, a nd t he warplan e would en ter service. During December 194 1, No rth America n was bu ilding 3 1{2 Mustangs per day to fulfil th e British o rd er, but Kindlc bcrger felt that he could raise prod uct ion to a who pping ten fight ers per day with in th ree weeks of a substant ial Army o rder, Co l Homer Sanders, frustrat ed co mma nder of th e 5 Ist Fighte r Gro u p in India, who se pilo ts were find ing it increasi ngly d ifficult to fight superior j apa nese eq uipme n t in P-40s, com men ted o n 26 August 1942 t hat , 'App aren tly t he go-ah ead signal was not given (for ~ Iu stan g produ ction ) o r th ere would certai nly he PONY SO LD IERS

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some available fo r co mbat d uty by this time. It appea red th ere was a tenden cy hy th e Mat erial Division to hinder th e development o f t his airplane, wh ich can o nly he accoun ted for by t he fact th at it was st rictly a No rth America n pro ject and Material Divisio n could claim no cred it for it'. Bark at the facto ry, North American was in a t rem endou s sta te of flux . Bet ween the star t of the war in Europe and th e Jap anese snea k attack on Pearl Harbor (a period tha t spanned just two yea rs and two months), th e co mpa ny had go ne from a ca pability of bu ildin g 70 ai rcraft per month to a mass-production facility t hat could ch u rn out ]25 ai rcraft in th e same tim e period . Thi s had also been a period of frant ic h iring , th e co rnpa ny swelling from 3-l00 em ployees to ove r 15,000, with build ings being rapidl y erected to ha nd le prod uctio n. \Vith th e 150 P-5 1s now und er production , th e Air Co rps dec ided to con vert 57 of t hese airfra mes in to armed photo rcco n natssancc ai rcraft for use in Europe and Nort h Africa, whil e th e remain ing 93 x tustan gs 0 11 th e o rde r were transferred back to the RAF as Mustang Mk. lAs. It is int eresting to note t hat

44

P-51 MU STANG

all these aircra ft were fitted with fo u r 20 111m ca n no n in place of th e ma ch ine guns . Th e can no ns ca rried 125 round s per gu n, and five rounds wit h linkage weig he d th ree pounds. Th is co mpared to o ne pound for t h ree .50 cal rou nd s and lin ks, and 011(.' pou nd for fin' 30 rou nd s and links. Nort h Am eri can 's cost to

A·l6A·I·NA sin 42-8 3934 is raised in a cradle for the test firing of its weapo ns.Th e bomb

racks were set close r to the landinggear to benefit from th e greater strength o f the wing structure.A·36 prod uct ion totalled 500 aircraft (NAA cln 97·15881 to 16380). and con sideration was later given ( 0 putting the type back into production since it had proven so effective. but Merlin producti on had by mat time completely ecl ipsed th e

Allison line

produ ce th ese ai rcraft was S26,741, but whe n p rofit and governmc n t furn ished equipment were added, th e price wen t to S5H,69H. Of th e aircraft pull ed fo r ph ot o-recon co nvers io n, th e :U rd and I0 2n d airframes in th e P-Sl co n trac t were withheld by Nor th American fo r cx pe rime n ta l engine wor k. The prot ot ype camera ins tallation was u nderta ken at NAA (P-S t -I -NA), while th e remai ni ng S4 were dep ot modifi ed as P-S I-Z-NAs, but were later redesignated F-6As_ In an attem pt to given thi s va rian t 50111l' special d istinction, th e nam e Apach e was briefly adopted . The Air Corps' next o rde r was for a P-5l of a dif ferent flavou r. On 16 April lY4Z, co ntrac t AC-Z7]96 called for t he constructio n o f 500 NA-97s - wh at wo uld become known as til l' A] 6A. Th e effect of the Luftwaffe's d ive-bom ber. or Stuk« , fo rces had been horrif yingl y portrayed acro ss th e co u nt ry's newsreel scree ns ea rly in the war, an d to t he public, and perhap s the m ilitar y too , th e dive-bomber was a terrif ying th reat th at seemed un sto ppabl e. Only experience wou ld pro ve t hat th e di vebomber, althou gh highl y effective in its design ed role, was at th e mercy of a stro ng fighter force. The Air Co rps real ised th at it lacked just suc h a weapo n. so No rt h Ame rican, with th e m inimu m n u mber o f mod ificat ions, co nve rted th e P-5 I int o a div ebomber - th e A-] 6. Thi s aircraft featured speed brakes built in to th e top and botto m win g sur faces, alo ng with a bom b rack under each Wing. Fitted wit h six .50 cal machine gu ns and ZCX.> round s pl'r gu n, th e A ':~6A (br iefly nam ed In vad er ] would beco me an important stepping stone in th e developmen t of till' Mustang, since it ad ded a ver y effective gro u nd attac k roll' to the aircraft's profile. \Vith th e a\v ard ing of th e :\ -] 6 co n trac t, and fur t her testing on earlier aircraft un derway, th e mo me n to us d ecision was mad e to o rde r a fight er variant of th e Mustang fo r th e Air Co rps. Fitt ed wit h t he new Allison V-17 1O-HI, IZOO exa m ples of th e 1'• .'i t A were ordered o n Z] Jun e 194 Z under co n tract r\C-]047Y, wit h the factor y dcsign atlon NA-99. As production fo rged ahea d , repor ts were comi ng hack from t he co mbat fron ts calling for modifi cation s or Impr ovem en ts to til l' basic design , and one of t hese was a sand filter ing vystem for the Alliso n car burertor since No rth African sand was redu cing reliahilit y o f th e Allisons. The p-s l A wo uld he fitted with four .50 cal Brown ings (two in each wing pan el ) and associated magazin es to carry IZ60 rou nds of amm unitio n. As with virtu ally any othe r co mba t aircraft , weight began to grow as th e ai rcraft neared series p rodu ctio n - t he co mbat load of the A-model was X600 lbs, and thi s further increased to 9600/1 0,:100 lbs if 75/1 50 gal d rop tank, were fitt ed . PON Y SOLDIERS

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With th e awa rdi ng of the P-S IA cont ract, ext reme ly high levels of ma ss product ion were plann ed at Nort h American, and assembly lin es ca pable of co nst ructing 20 aircra ft per day were set in place. The need fo r new fighters was so great t hat th e or iginal co ntra ct for 1200 P-SI As was sup pleme n ted wit h furth er orders for 1050 aircra ft. However, t he P-SI A was to becom e a fairly limited prod uction fighter as orde rs were soo n slashe d to just 3 10 aircraft. The reason for th e dr astic red uction in n u mbers was t ha t th e Mustang airframe had been ma ted to th e vastly su perior (at med ium to high altit ude ) Roll s-Royce Merlin soon after produ ction of t he P-SI A had co m me nce d. Co mhat histo ry wo uld soo n be mad e . . .

To co nvert t he basic Mustang de sign int o th e A-36A, NAA enginee rs ex pended 40.000 manho ur s o f w o rk - o ne suc h modficat ion follo w ing th e fitm ent of dive br ake s saw th e pitot tube reloc at e d to t he starboard wing, Th e A-36A re taine d the NA·73's no se- mounted .50 cals. however. Mechanics are seen her e running up the Alliso n V- 17 10-87 prior to t he aircra ft's acce ptan ce by the milita ry. N ote t he dual landing lights in th e leading edge of the left w ing

46

P- 51 MU STAN G

CHAPTER

rn ONTO BERLIN

W ITH T HE ALLISON-POW ERED Mustangs. Nor t h Amer ican , the USAAF and th e RAF realised th ey had an excellent airf rame mat ed to a not-ideal engi ne . However, t his was not a criticism of the V- 1710, for th e engine perfor me d very well wit hin t he regime for which it had been d esign ed. Ho wever, as the war rapidly progressed, it became obvious that th e air war was going

to be fought at great altitudes - an arena for which the Allison was not suitable. Sometimes a momentous trend sta rts o ut in a thoroughly mundane manner. Dur ing 1942, Wg Cd r Ian Ca m pbell-O rde , com ma ndi ng o f ficer of t he Air fig h ti ng Devel opm ent Un it (AFDU) at Du xford, called h is frie nd Ro nn ie Ha rker an d told

him that one o f th e new Allison Mustan gs was at th e ba se, and invited hi m to co me an d fly t he figh ter. Har ker, Roll s-Royce's service liaison pilot, qui ckly accepted the invita tio n and headed to Duxford . whe re he flew Musta ng AG4 22 (lat er aba ndo ne d in flight on 2 October 19..l ] when its engine qu it while serving wit h No 4 1 Operationa l Train ing Unit ) o n 30 April 194 2. Harker had previo usly flown th e Alliso n-powered Cu rtiss Tomahawk, and was very war y of American claims to high performan ce. However, he was mo st impressed by t he Mustang, and th e next d ay sent a report to Rolls -Royce whi ch , in pa rt, read , 'This ai rcraft sho uld prove itself a fo rm idable low and mid-altitude fight er. It closely resembled a Bf 109F, probably due to its being designed by o ne of t he Messersch m ttt d esigners, wh o is now wit h th e North America n Aeropla ne Co (t h is, of course , was incorrect , as Schm ued was never em ployed by Mcsscrsch rnirt, hut th is sta rted a trail of m isinfor matio n th at wo uld bother t he designer fo r the rest o f h is life). The po int whic h st rtkcs me is t hat with a powerful and good engine like th e Merlin 6 1, its performa nce sho uld he o ut standi ng, as it is 3S mph faster t han a Spitfire V at roug h ly the same pow er'. Harker's qui ck ca lculations showed th at th e Alliso n Mustan g was 30 mp h faster at 5000 ft and 35 mph faster at 15,000 It th an t he frontli ne Spitfi re :-lk V.

The top per son nel at Rolls-Royce too k hi s suggestio ns very seriously, and moved rapid ly with a secret mem o dated 14 xtay O N TO BERLIN

47

194 2 from E \ '1 (late r Lo rd ) Hives, genera l man ager fo r Ro llsRoyce Derb y, sta ting, 'I feel m yself th at it might pay a very goo d di vid en d (t he co nversio n to Rolls-Royce power), if it ca n be don e qu ickly, to inst all t he Merlin XX in thi s mac hi ne. It wo u ld be a relatively qu ick job , a nd m ight fill a very usefu l inter im nich e u nder existing con d itions. I am en deavo uri ng to ob tai n perfor man ce data abou t the ai rcraft so t hat th e ga in th at mig h t he a n ticipated can be estima ted. I recall th at Air Commo do re R R Ma nsel l a nd E T Jon es, whe n in th e USA, d id suggest t hat th e Packa rd sho uld he fitted into th e Mustan g ai rcraft, hut it d id n ot get a ny fu rthe r'. However, t he Air Mini str y vo iced some concern since a stro ng co m mitme n t ha d been given to the prod uct io n of the Spitfire Mk IX. It felt th at th e mod ification of t he Mustan g wo uld d raw va lua ble resou rces away from gett ing th e Mk IX into th e fro n tli ne to comba t th e Luft waffe's pote n t new t hreat - th e Fw 190. Thi s left Harker part icu la r per plexed , and he late r wrote, 't ha t my proposal was u n rea listic, th at t he Air Min istr y wo u ld n ot app rove an d th at th ere wou ld not be any engi nes avai lab le a ny how as th ey were all requ ired for the Spitfires - a nd why waste time o n a n unt ried Amer ica n-b uilt aeropla ne!' 48

P-S I MUSTANG

LEFT With its landing gear firmly chocked and tail raised to simulate level flight attitud e, a natural metal P-5 IB has its four .50 cal Brown ingAN M2 machine guns tested and bore sighte d at the Inglewood factory. Building Mustangs had become an aroundthe-dock effor t by this stage of the war. and e ngine runs and gun fi ring filled the night-time hours. This view shows the P-5 IB's Hamilton Standard 24050 fourblade propeller to advantage along with the canvas dust cover s installed inside the landing gear wells to kee p the interiors free from dirt and grime. Howe ver, in the fie ld, crew chiefs usually dispensed with the covers since the blocked access for mainte nance. With the addition of the Merlin to the Musta ng airframe , the fourblade wide chord propeller became nece ssary to abso rb the increased power at higher altitudes. Also a new. and heavier, radiator was required for better cooling charact eristic s

W hile Rolls-Royce proceeded with the creation of the Merlin-powered Mustang X, similar activity was taking place at NAA with P-51 USAAF sin 41-37352 becom ing the first American Mustang to fly powered by a Merlin. Finished in stand ard O live Drab and Ne utral Grey camo uflage, the aircr aft re tained its four 20 mm cannon , but featured an entirely new air scoop similar to the eventual production sta ndard item . Packard Motor Cars was licensed to build the Rolls-Royce Merlin 61 as the V- I650-3, and two early examples were shipped to No rth American for installation in the aircraft that would initially be designate d XP-78.The con tra ct for the se conversions (USAAF sIn 41-37421 being the oth e r airframe) was signed on 25 July 1942, with the factory designation NA-I 0 I being assigned to the aircraft. Note the NAA logo on the vertical fin.The conver sions were carried out in a building ABOVE

se parate from on-going Mustang production, and although it appea rs that the co nversio n to carry a Merlin was fairly straight. forward. it was no t, and tens of thousands of e nginee ring hours were exp ended to ensure t hat the mod ificatio n work was a success .A new mo to r moun t and cowling was requ ired, while the forw ard fuse lage had to be strengthe ned. Also, a new air scoop and radiato r, as well as a supe rcharger, nee ded to be incorporated into the P-5 I airframe.The V-17 10 had tipped the scales at 1335 lbs (dry), while the Merlin weighed 1690 lbs. The latter's four- bladed Hamilto n Standard pro peller was also heavier than the Allison 's 'th reeblader'. Both the XP-78s retained the four 20 mm cannon of the P-5 Is from which they had been co nve rte d, but the inte ntion from the start was to equip the production Merlin Mustang wit h four .50 cal Brownings

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The Rolls-Royce conversions were more functional , and rather than being aimed at mass production, they were basically utilised to prove that the mating of the Merlin and Mustang would wo rk. As the first aircraft so converted. Musta ng IAL975/G (the G denoted that the aircraft was involved in a classified, and important, project. and should be kept unde r consta nt guard when on the gro und) underwent several cowl ing changes. Fitted with a Me rlin 65 driving a 10ft 9 in diameter Spitfire prope ller, the aircra ft completed its first flight on I3 October 1942 with Capt R T Shepherd in co mmand . On this flight a speed of just 376 mph was reached befo re the cowling started to come apart following a build up of pressure . Further modifications saw a dramatic rise in performance, and one Ro llsBELOW

50

P-5 1 MU STAN G

Royce official wrote to another, 'The speed realisation is most encouraging. Soon we shall have a scream for Mustangs instead of Spitfire IXs!' In the wake of t he first flight Ro lls-Royce engineers calculated that fitting the Merl in 65 to the Musta ng resulted in the aircraft suffering a 44 per ce nt loss in directional stability - or the equ ivalent fin area of 3.8 sq ft. In order to rectify th is situation, a joint Rolls-Royce/NAA dorsal fin modification was proposed, which added another two square feet of area. However. directional sta bility pro blems remained a feature of the Me rlin Mustang until the introduction of the P-5 IH, with its ta ller vertical fin.As for AL975, the aircraft was operated by Ro lls-Royce until struck off charge on 5 April 1945 and scrapped - certainly an unfitting end for such an historic aircraft

This pho tog raph is of interest since several sources have listed t he aircraft featured as being the first NAA Merlin Musta ng - sin 41 -37352. Ho wever, compare this photo with the identified shot of '7352 on page 49. and note that this aircraft has a complete ly fresh paint scheme and unpainted sta inless steel exhaust sh ro uds. The aircraft also has the early national insignia and the landing gear o leos are exten ded to their maximum length, which may indicate that it lacks an engine or that the oleos we re over-in flated for some other purpose.The most noticeable difference is that the wing is complete ly devoid of 20 mm armament. Note the barrage balloon in the background - Mines Field was ringed with these as a defence against a Japanese surprise attack RIGHT

Despit e o fficial reluct ance fo r th e Merlin Musta ng. E \V Hives used h is polit ical power to have t hree aircraft tran sferred to t he facility at Hucknall fo r co nversio n wit h Merlin powerplants. Rolls-Royce freely let North Ame rican know wha t t hey were doin g. NAA was not u na ware of t he benefits of th e mod ifi cation, and o ne of the cha m pions of th e re-engint ng programme was Maj Tho mas Hitch cock, assistant air attac he at th e US l.mbassy in l.ondo n. Ill' issued t he fo llowing mem o, da ted B October 1942, 'The reaso ns for th e rem arkab ly low d rag of th e Mustan g arc not fully understood o n th is side of th e ocean. The English think it is o nly partly du e to the laminar flow wing. The Rolls peopl e became very much interes ted in t he possibilities of the Mustang airfra me with the Merlin engine. Estimates were made as to the speeds tha t could be obtained with the installation of th e 6 1 and 20 Merlin. The Air Minist ry ins tructed the Rolls people to install five Merlin 61 engines in ~f u s t a n g airplanes . Simultaneously with this development it was arranged to have the North America n Co m pany install a Packard version of the Merl in 6 1 in the xtusrang airframe. Requests were sent to the United States to have the Packard Co mpa n y sta rt manufacturing Merlin 61s as promp tly as possib le. 'The inte resting qua lities of the xtusran g airframe were brought to the attention of Gene ral Arno ld an d Adm iral Towers when th ey were in Lo nd on June last, by th e America n ambas sador 1I0l1 n C \Vinan t), Air Chief Marshal Sir Charles Port al, O N TO BERLIN

51

ABOVE A comple te P-5 1B motor mount in a jig,awaiting installation on an airframe. Totally different from the Allison mou nt, the unit was relatively simple and very rugged. Once in combat, it was found that a thorough inspection of early P-5 1B engine mounting bolts and nuts was required, for the stress of high speed, high G, combat manoeu vring in early 1944 resulted in the Merlins tearing away from the airframes .Technicians soon discovered that the engine mounting bolts and nuts used on early pS IBs were not strong enough to retain the Merlin under these condition. Replacement by bolts of greater strength quickly cured this dead ly problem

52

P-51 MUSTA NG

'Rosie the Rivette r' torques exhaust stack bolts on a Y·1650· 3 as it rolls down the production line. Note the custom tool holde rs that would mount on the bare metal cowl former for easy access as equipment was installed.This view shows the header tank. which was a reservoir for engine coolant, and separated air from hot coolant exiting the engine. The header tank was a complex piece of equipment built by NAA and fitted with four Acme Aircraft castings (exit and filler nozzles). The v. I650-3 was equipped with a two-speed. two-stage. supercharger at the rear of the powerplant.The supercharger could produce a sea-level atmosphere OPPOSITE RIGHT

within the induction system , and this allowed the Me rlin to pro duce more horsepower at 25.000 ft than the Allison could at full take-off powe r - thus creating the power needed for the long escort missions into enemy territory

ABOVE Detailed view of the left side of a partial p·S I B fuselage, showing the relative simplicity of the Mustang's construction.The gear handle, trim console and underwing sto res salvo are all in place, as are th e hydrau lic lines for the retractable tail whe el.The large meta l bar in the middle of

the fuselage was part of th e roll. over structure to protect the pilot, while the circular open ing to the rear was an acce ss panel fo r the fuselage cables.The brown leathe rette aircra ft documentatio n case was immediat ely behind the rear window. Note how th e fo rward portion of the fuselage

was painted in 'NAA Green ', while the rear sectio n was left in bare metal

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5]

ABOVE Simple yet rugged. a

P-S IB rudde r is seen before re cei ving its fabr ic co vering.T he re cognitio n light a nd w ir ing are in

place. but t he large slot awaits installation of the phenolic resin trim tab .Written markings are still on the aluminum skin. and it

is interesting to note that these un its never received a protective spray of zinc chro mate .The rudder utilised a single spar with flan ged alc lad ri bs attache d. a V-

t railing edge piece and a beam for attachment of the trim tab .The leading edge of the rudder was cut o ut fo r the vertical tai l's hinge fitti ngs. the un it be ing hinged to t he ve r t ica l tail w ith thre e seale d

54

P·51 MUSTANG

ball bear ing fittings.The rudder was dynamically balanced with a 16.6-lb lead weight fitted to the top. while an addit ional balance weight at th e botto m of the leading edge helped reduce static unbalance.The trim tab was also hinged by three seale d nee dle bearings REMAINING PHOTOS The windshield. canopy st ruct ure and rea r panel windows for a P-5 1B. Although it may lo ok simple. th e canopy frame work had over 1200 pieces.The main portio n of the cano py had a panel o n each side tha t co uld be manually slid to the rear by the pilot via the knobbed handles seen in the photograp h.The flat forward sect ion of the cano py was a fiveply.laminated 11/2 inche s thick. bullet pro of and slante d 31e back from the vertical when installed on the aircraft. The windshie ld's side and upper panels was 3/ 16 inch thick plexiglass

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,

Interest ing view of a main landing gear leg being installed in t he win g of a P-SIB. Th e landing gear

was made und er co nt ract by Bendix. N ote how the leading porti on o f th e win g has received

its layer of filler and a coat o f primer.At this stage of asse mbly. th e phenolic resin ex t ern al sto res shackle has also been installed . Th is pho tograph was ta ken o n 26 August 1943

56

P-S I MU STAN G

Ch ief of th e Air Sta ff, Air C h ief Ma rsh al Sir Shol to Douglas, Com m and er in Ch ief Fighter Comma nd , a n d Air Mars ha l F J Linn ell, Min ist ry of Aircra ft Prod uct ion Resear ch a n d Developme n t. Rober t Lovett, Assista n t Secreta ry fo r Wa r fo r Air, was a lso advised by letter, dated 5 Ju ne 194 2, of th e Impor tan ce wh ich Eng lish a nd va rio us Ame rican rep resen tatives att ach to th e Mus ta ng air fra me a nd t he dc stra bi ltty o f e ne rget ica lly pursu ing the Merli n de ve lopme n t. ' Mr (Ph il) Legarra, Nort h America n represen ta t ive, reported whe n he ca me back fro m the U.s in t he ea rly pa rt of Septe mber th at the Mustang h ad t he lowest prior ity th at co u ld be gra nte d to a n ai rp lan e. 'The Must ang is o ne of th e best , if n ot t he best, fighter airfram es that h as been developed in t he wa r up to da te ... its develop me nt a nd use in this t hea ter h as suffered for var ious reason s. Sired by th e Eng lish o ut of a n Ame rican mot her , the Mu stan g h as had no paren t in t h e Army Air Co rps o r at Wrigh t Field to app recia te a nd pus h it s good poin t s. ' Im po rta n t peo ple o n bot h sides of the Atlan tic see m more int erested in pointing wit h p ride to t he devel o pme n t o f a 100 per cen t nation a l prod uct tha n t he y a re co ncerned wit h th e ve ry d ifficu lt p robl e m of rap id ly developin g a fighte r plan e that will be su perior to an yt h ing t he Ge rma ns h av e.' Alt h oug h Hitch co ck's feelings we re well-place d , he did not kn ow th at wor k was goi ng on to make th e Merl in Mu stan g a

BEL OW Photographed outside the asse mbly hangar under the camouflage netting, t his view of a P-S IB wing shows the large stress doo rs to advantage. Made of Alclad 24S-T aluminium. the str ess doo rs offered access to the wing fuel tanks. while also forming an essential part of the wing's struc ture.The leading edge of the wing has rece ived its coating cfdum-dum' filler (a material that was applied to help maintain the desired laminar flow). while a quick coa t of primer has been sprayed over the fo rward portion of the wing.The main landing gear is inside the wing, but the gea r doo rs have not bee n attached .

Early pheno lic resin ext ern al stores pylons are in po sition .The long pipe running do wn the cen tr e of th e wing is th e engine co mpart ment scupper drai n which, when completely assem bled. would dra in out of the left side of the scoop.The scupper was in place to drain anything leaking from the engine compartment. NAA employee Geo rge W ing invented an extra hard rivet for use during the construetion of the laminar flow wing. When utilised in the wing struct ure. it replaced nearly 800 rivets and bolts . giving a 60 per cent weight saving, while also increasing shear st rength by 200 pe r

cent. W ing wou ld go on to found his ow n co mpany, producing aviation components and even an unusual two-seat twin-engine d privat e aircraft called the Wing De rringer

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realit y. Hap Arnold had see n th e pot ential in th e design a nd Brig Ge n O liver Echols, Arno ld's Chid, Mater iel Division , was in stru cted to get th e co nce pt in to rea lity. Fro m 1940 o nwa rd s, Echols had been respo nsible for sett in g up th e license-built Packa rd Me rlin prod uction line, and he quietly made Slue that two n ew V- 16S0-3s were tran sferred to No rth Ame rican for th e XP-7H pro ject (the Mer lin Mustan g had been given t his new de signation, but it was to be short-lived) . In Britain , Mustan g A ~ f12 1 was sent to Hucknall o n 7 Ju ne 194 2 to form th e basis for t he first co nversio n. The aircraft was fo llo wed by A1.96 3, '\1.975, AM203 a nd ,\M 20 X (t he last two were ad ded to t he Rolls-Royce prog ramm e hy till' requ est o f th e USAA F). SOI11l' initial flyin g was do ne with Ai\f12 1 in its stoc k co nd itio n to obta in perfo rm an ce data . At an early stag e in the co nversio n it was decided to use the Merlin 65 in stead of th e Merlin 6 1, and th e first aircraft made read y for fligh t was AL9 75/G, whi ch flew o n 13 October 1942. Back in Inglewood ,

58

P-51 MU STAN G

LEFT A batch of early B-mode ls comes together in the Inglewood plant. It is int eresting to note how Ame rican aircra ft manufacturers picked up o n the mass production techniques created by Henry Fo rd for his automotive empire. Close examination of the photograph show how various components were added in a logical order as the aircraft progressed down lo ng lines befo re making a tight l.I-turn and heading down anot her long st retch. all the time being pulled by an electric hoist-At the ext re me left background. Packard Me rlins were

placed in engine mounts, while partia l fuselages were assembled. On th e next turn , fuselages became more co mplete. while tail cone s and tail surfaces wer e installed as the fuselage passed out of the left side of t he photograph.Taking one more If-turn, the wings and engines were installed. along with many other details including the canopy structure and plexiglass (which still wore its pro tective paper coating fro m the manufacturer) .These aircraft were P-SI B-S-NAs

ABOVE Facto ry lay-out illustrating the flow of parts and components into complete P-SI B Mustangs

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ABOVE Nearly complete P-SI B tail cones and tail surfaces in their jigs awaiting transfer to the assembly line on 10 January 1944

60

P-S I MUSTANG

LEFT Electric overhead hoists were utilised to move the tail sections to the assem bly line. Once the P-SI Bs entered combat. Base Air Dep ot Areas in the United Kingdom we re set up to correct faults found in th e B-model after its initial com bat experiences.These faults were eithe r rect ified in the field o r incorporated in the NAA production lines. One fi x was the reinfo rcement of the horizon tal stabfflser afte r it was disco ve red that at high speeds o r whilst being handled carelessly (o r enthusiastically). Merlin-powered Mustangs exhibite d a pre vio usly

unsee n weakness in the tail. which sho wed up as be nt metal o r. in the worst instance. com plete str uctural failure.A doubler plate was prod uced fo r reinforceme nt of the ho rizo ntal tail spar until a strengthene d co mponent could be inco rporate d int o the production line

ABOVE Another view of the P-Sl B production line. Unde r a large Ame rican flag. the V-16S0-3 powerplants can be seen to the left and the very basic fuse lages star ting th eir journey at Station I imme diate ly alongside .The latt er then mo ved up and do wn the rows whe re . at each station . specific co mpo nents and equipment was added . Piles of parts can be see n at each statio n including seats, sco ops, cowlings. et c.The se supplies we re replenished during the day by cons ta nt delive ries fro m the parts dep ot

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61

ABOVE Bcmod el Mustangs head toward com pletion. The dolly which moved each aircraft thro ugh assem bly is clearly visible. As can be see n, vario us wing access panels were not in place when th e wing recei ved its coa t of primer. One worker is hammering sheet metal around a left wing gun po rt. while three colleagues are finishing cockpit installations.Along th e wall.worke rs' cloth ing is o n hangars th at were lifted high from the shop floor. appar ently as a fire prevention aid.The armour plate aroun d the head er ta nk and canvas f itting over the nose gear case are also installed. Note B-25 Mitchells also nearing com pletion on th e left side of the photo

62

P-SI MU STA NG

RIGHT Up on jacks. an early model P·5 J B undergoes gear swing tests. with power being provided by a hydraulic 'mule' locate d under the propeller.The canop y has bee n rem oved and placed o n the wing.Workers found t hat co nducting such wo rk under the camou flage netting was preferable since it he lped diffuse the hot sun or bad weath er

BELOW A Mustang is re mo ved from its dolly.This particular aircraft has had the cowlings taken off. Gene ra l Tires featu red the diamond tread common to th e tyres o n many W orld Wa r 2 com bat aircra ft - it was felt that this type of tread was better suited to grass fie lds or unpre pared runways. Gene ral. Firesto ne and Goodyea r all supplied tyr es for the Mustang prod uction line

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Firmly cho cked, P-51 B-INA USAAF sin 43-12342 is run up by a mechanic pr ior to a test flight. Dou glas SBD Dauntl esse s can be seen be ing prepared for a sim ilar ta sk in th e backgro und . The aircraft carr ies the shortlived red surround to the nationa l insignia, and alth ough just o ut of th e fact ory, the P-5 1B's flat Oli ve Drab and N eutra l G rey camouflage already show co nside rable wea r just from use around the factory.T he se rial num ber wa s painted o n the vertical tai l in Insignia Yellow. USAAF o rders led to so me confusion on how such a numbe r, or 'radio call sign', sho uld be presented. On 13 BELOW

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P-S 1 MU STAN G

Januar y 1943. Spec. 98-241 OS-Q. Amendment N o 2, Paragra ph E·6A read . 'Each air plane shall have a radio call nu mber painted on its vertical tail surfaces.The radio call numbe r shall co nsist of at least four numerals and shall be de termined in the following manner:Th e firs t nu mbe r and th e hyphen shall be om itted from the serial number of the airp lane , using zero wh e re nece ssary between th e yea r de signated and the serial num ber to make at least four numera ls'.The document co nt inued,' Fo r light coloured backgro und s, the numbe rs shall be black in accordance w ith colo ur chip N o 44 o f Army

Air Force s Bulletin N o 41, an d fo r dark backgrounds , the nu mbe rs shall be ye llow in accordance w it h co lour chip N o 48 of Army Air Fo rce s Bulletin N o 4 1'. Even th o ugh this clarified the situ at ion, m istakes were st ill made at various factories and es pecially in the field wh en th e aircraft was re painte d

test pilot Bob Ch ilto n too k the first NAA Merlin-po wered 1'-51A conve rsion, USAAF si n 41 -3 7352, a loft o n :10 November 1942 , so it was a close thing as to which coun try too k the honour of flying the first Merlin Mustan g, Actually, NAA and Rolls-Royce freely exc hanged data as the co nve rsions went along. I.t Col Cass Hough h ad seen t he potential of the Me rlin Mustan g from the sta rt, a nd as a tec h nica l officers at HQ Vilith

High-angle view of P-51 B-I -N A

Fighter Co m ma nd, he kept in close touch wit h Roll s-Royce liai-

ente red com bat, distinguishing

son officer \ Villiam Lappin . w ho eventually invi ted Hough to Hucknall to fly one o f th e new aircraft. ') just assume d it wou ld

hopefully prevent accidental

be a co nvent ional airplane because nobod y to ld me anything. The on ly informa tion I got from Bill Lappin was that the first flight s that had been m ade up at Huckn all resulted in th e pilo ts being just d eligh ted with the airplane. 'Flying a new airplane, I always pu t the power 0 11 easily at the start to ge t the fee l of th e airpla ne o n th e ground, th en gradually give it po we r, \ Vh en I got airborne, a couple of hundred feet off the gro u nd , I pu lled up the gear and decided then I'd sec

USAAF sin 43- 12408 displays the Mustang's broad and simple wing structure to advantage T he square wing tips bor e some similarity to those of the Luftw affe's Bf 109, and w hen the Mustang wing bands were required to firings on the fight er.Th e easy staining of the camouflage paint is readily visible, as are the tapedover gun po r ts for the four .50 cal Brow nings

how it would climb from scratch. I pour ed the coal to it and th e

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Rows of Mustangs (for both the USAAF and RAF) indicate the rapid build-up of production at NAA In RAF service. the aircraft was designated the Mustang HI, and even tho ugh they were fi nished in full grey/green camouflage. they car ried USAAF insignia on t heir fuselage sides pr ior to delive ry.The closest Musta ng III to the came ra is FX968, which served with the RAF until being struck off charge on 24 July 1944 ABOVE

Detai l view of the rear cockpit area of a P-5 1B7-NA that has had the rear quar ter panel plexigtass removed to display the battery holder and racks for the radio transmitter and receiver (both units of which were removed from the aircraft). The large black rubber 85 gallon fuselage tank is also visible.along with its vent tube .The new tank was introduced on the P-5 1B production line, and numerous earlier examples were retrofitted with the unit. Made of the same self-sealing rubber material as the OPPOSITE TOP

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P-S I MUSTAN G

wing tanks. pilots had to carefully monitor the tank, for when full, it placed the centre of gravity at its aft limit.Accordingly. fuselage tank fuel was utilised from the start of a mission, and manoeuvring was restricted until less than 25 gallons remained. However. the fuselage tank greatly increased the range of t he P-S IB/C. The ADF loop can be seen on the rear fuselage. while t he uppe r recognition beacon is fitted directly above the rear view glazing.The open access panels allowed work to be carried out on the electrical systems .The hand hold for the pilot is also visible in th is view. as is the black 'ground here' circle which was utilised when the aircraft was being fuelled.The gauge for the fuselage fuel tank (on a mounting above the vent tube ) has been taped over to avoid damage while equ ipment was installed or removed

Over a snowcrusted section of the San Gabrie l Mounta ins, test pilot Bob Chilton looks upward at the photographer in the B-25 Mitchell camera aircraft.The high angle view of the Musta ng emphasises how some pilots or anti-a ircraft crews co uld mistake the P-51S/C for the mitt Sf 109.This particular aircra ft is carrying two 65 galIon jettisonab le fuel tanks on the underwing pylons. Fuel gauges were not provided for the external tanks. and the pilot was requi red to rotate the fuel selector valve approximately every 15 minutes in order to keep the aircraft in trim. Prior to dropping the tanks . the pilot had to select an internal tank or the Merlin would falter as the fuel supply rapidly depleted. No boo st pumps were provided for the drop tanks. and fuel was forced out of them by a pressure of five PSI from the exhaust side of the vacuum pump. If this system failed. the engine-driven fuel pump cou ld draw fuel from the tanks up to an altitude of 10.000 ft OPPOSITE BELOW

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Camouflage and bare metal P-S IBs are seen at the NAA plant as new unpainted Mustangs supplemen t the last camouflaged exam ples coming off the production line. USAAF sIn ABOVE

43-7 138 is a P-51B-1O-NA (398

examples of which were built), whilst the aircraft to the right displays a white cross under the individual aircraft data block. Such a marking alerted gro undcrews t hat the Musta ng was fitted with the 85 gallon fuselage tank. which required filling. Regarding the fuselage tank. Louis Wait. NAA administrative tes t pilot. commented,'The first o bjectio nable feat ure was t hat t he weight without external tanks was increased to about 10.000 lbs. which decreased the ultimate pullout fact or from an ori ginal t 2 G dow n to 9.5 G. but th is was not as serious as the fact that when

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P-51 MUS TANG

the additional fuel was added . the airplane 's cen tre of gravity was placed so far aft that the it became longitudinally unstab le. This instability was particularly dangerous in that a pullout at high speed was always accom panied by a stick fo rce reversa l which. unless o pposed by the pilot. would quickly carry the airplane into an accelerated condition where the wings wou ld fail at the inboard end of the gun bay" RIGHT Nearly fully equipped P-5 1B cockpit. Items of note include rear view mirror mounted on the upper por tion of the windshield. a cras h pad atop the instrument panel shroud. and basic flight instruments arranged in the central panel. The devices mou nte d to the low er right and left windshields are movea ble fluoresce nt lights

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aircraft snap rolled! Ro lls-Royce hadn't provided enough vertical fin area, and not eno ugh offset. ' I was eager to get it to altitude and sec how it performed because th at was the critical thi ng . I stu d ied th e fuel cu rves of th e Merl in in several other airframes so I knew what the ran ge of the airplane would be on interna l fuel, hut I did n't no w how t he ai rplane would actually hand le at high-a ltitude because no one had ever got an Allison Mustang abo ve 2-l,(X)() or 25,000 ft. O rdi na rily, the two-st age blowers - t he early o nes - were manually o perated o n th e Spitfires . I had just begun to think it was tim e to cha nge blo wers - I hadn 't even inq uired whe re th e hand le was for changing it - whe n, all of a sudde n, I got thi s big "c h ug" and a thu m p around 16,000 ft an d of co urse it was then in high blower. There was an auto mati c su percharger gear cha nge an d it was a co mplete su rprise. ' I go t up to about :n ,ooo ft with it and it was so man oeu vrable, and I co uld tell with out makin g any speed run s, assuming th e airspeed ind icator was calibrate d reaso nably caref ully, that it was pe rfo rm ing won derfully. I just couldn't believe so me of th e thi ngs J saw afte r do ing a couple of speed runs with it.'

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P·51 MUSTA NG

Wi th its window s covered over to prevent reflection. the right side of a P-SI B co ckpit is illust rated showing such detail s as the aircraft o pe rating rest rictions plate. SC R522 and SCRSJ S radio co ntrol boxes

It sho uld be not ed tha t th e supercharger had th e ability to maint ain sea level at mos phe re from th e inductio n syste m to th e cylinde rs, whi ch allowed th e Merlin to produce more horsepower a t 26,000 ft than th e Allison could d ur ing- a fu ll power take-off. Th e Mustang Xs were rather crude looking aircraft with ungainly cowlings and cooling syste ms , but th e XP-78 was a much more elegan t package. However, th ey were also not without trouble. Using th e lessons th ey had learned with th e earlier scoops, NAA engineers created a new coo lant rad iato r and scoo p design that was successfully ma ted to th e aircraft. However, th e first en gin e run s on th e devel opment aircraft came to a quick end when temperatures rocket ed into th e red . Th is was ca used by et hy lene glyco l loo sening residu e in th e cooli ng tube, and clogging the new alu m in u m radi ator, which had been de signe d to be of less weight in o rder to avo id strc ngt henl ng the mounting area. Whe n Ch ilto n took th e first ai rcraft up, he was very pleased th at th e Merlin was exceed ing performan ce spec ificanon s. but afte r ap pro xima te ly -IS mi nu tes th e engine ove rheated and he had to make a qu ick landing with th e Mustang

Left side of a P-SI B cockp it. showing the t hro ttle and mixture control, bom b control and antisalvo guard. landing gear handle and rudder. elevator and aileron trim tab contro ls

ON TO BERLIN

71

AB OVE North Ame rican Aviation opened a new plant in Dallas,Texas, to facilitate increased Mustang pro duction (along with other types of aircraft, including the Texans seen in the background). The first Must angs built at Dallas were des ignated P-5I C-I-NTs and were virtually identica l to the B-models - the Dallas facility would produce a total of 1750 P-S ICs. This particular P-SI C- IO- NT is a 'presentation ' machine - an aircraft which had been 'bo ught' by donations from individuals, compan ies or civic o rganisat ions - in th is case Brandeis Aza No. 533 B'nai B'rit h. Fact o ries usually made quite a deal over these aircraft since they se rved as exce llent morale booste rs.Th is view shows the filled and painted wing to advantage, as we ll as the three co loured ident ification lights mounted under the right o ute r wing panel. Natural metal Mustangs had become th e norm following a major revision of Technical Order (TO) 07- 1-1 issued on 26 December 1943, which stated that t he exterior painting of USAAF aircraft was to be discontin ued (except for aircraft being supp lied

72

P-S I MUSTA N G

to Allies by the USAAF): 'Painting of the exterior metal surface of Army Air Fo rces aircraft is hereby discontinued . This does not, however, eliminate t he req uired identification dat a, insignia, anti -glare coatings and corros ion prevention. Man-ho urs ex pended on mainta ining existing camouflage finishes, now cons idered unnecessary, will be held to a minimum.'

RIGHT PackardV- 16S0-J Mer lin, with rocker covers removed, receives a spraying of preservative material prior to sea shipment to Great Britain. In the background can be seen Thunderbo lt s, Lightn ings, and an A-36 also being prepa red for ocean voyages.The large capped tank to the right of t he photograph is the afte rcoo ler filler tank. During August 1940, dialog was started between the American and Brit ish govern ments in order to forge an agreeme nt for license production of the Rolls-Royce Merlin by the Packard Motor Car

Company.An agreement was reached in short order, and RollsRoyce shipped over 2000 drawings to Packard t he next month. Three buildings were acquired fo r engine production, and a team of over 300 engineers was assigned to set up the Merli n for American production. The Brit ish metric system was reta ined, as it would have been too much work to convert, and t he Whitworth thread pitch was utilised on the basic eng ine while accessories were standard American AN units that could eas ily be obta ined and replaced under combat condit ions. The first American production Rolls-Royce was the Merl in 28, wh ich was similar to the unit in the Avro Lancaste r bomber and emp loyed a single-stage two speed supe rcharger.The engine was given the military designation ofV- 16S0, the V denoting the V- 12 configuration and the 1650 being the cub ic inches (actual cubic inches were 1649 but the figure was rounded up). Each Merlin had over 14,000 parts - more than double the number used in a Packard motor car.The super-

charger was the key to the Merlin Mustang's performance, and the addition of a Wright supercharger drive quill to the supercharger created the V- 16S03, which entered production in September 1943.In factory parlance. this became the 'high alritude' Merlin, compared to the V-16S0- 1 used in the Curtiss

P·40F.

trailing a tell-tale wh ite stream . Once again the radiator was clogged , and flight testin g cam e to a halt until the cause of the problem cou ld be found . It was traced to an electroly tic act ion between the various metals and the cool ant, which caused residue to be loosened . In order to overcom e th e problem , NAA contracted with the Harrison Division of General Motors, and a new radiator was bu ilt th at had a frontal area of 2.7 squa re feet. The scoop section had to be slightly redesigned for the extra weight, bu t the new radiato r had a separate section for supercharger coo ling, while th e o il coo ler was mount ed forward of th e coolant radiator in its own separate scoo p, with its ow n shu tter. Chilton resumed flight testing in December of that year, and was delighted to find the new unit worked perfectly, and th at performance was greatly increased over the Allison aircraft. The NAA co nversions involved two P-S1s - USAAF sins 4137320 /37469 (these aircraft also carried RA F sins FD4S0 an d FDSI 9) - which had been transferred to the Merlin Mustang

ON TO BERLIN

73

conversion pro gramm e. The conversion work o n the first aircraft was actua lly comp leted in just six weeks, and it was decided to d rop the XP-78 designation for the new aircraft and adopt th e designation XP-51B (NA-102) instead. Such was the USAAF's faith in the Merlin Musta ng that an ord er for 400 P-51B-l -NA Musta ngs was placed o n 26 August 1942 - almost three month s before the first flight of the XP-5 1B. A plan by the RAF to have its earlier Allison Mustangs conve rted to Merlin s was dropped in favour of obt aining new produ ction aircraft. North American officials serious ly co nside red th e impli cation s of mass-produ cin g th e ne w B-model alongs ide th e hu ge orde r for 1200 P-51As, and, acco rdin gly, a simp le and efficient produ ction lin e was designed and implemented tha t co uld acco mmo date th e delivery of 20 Mustan gs per day. However, th e superiority of th e Merlin P-SIB saw th e A-mo de l o rde r slashed to just 310 examples, and the assembly lin e was dul y mod ified to acco m moda te th e mass-prod uction requ ireme nts of the Packard Merlin instead.

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P·S I MU STANG

Wh ile P-SI B prod uction reached a crescendo, NAA maintained a very active exp erime ntal shop that rea lised new co ncepts and impr ovements.This view shows bazoo ka-style rocket launchers fitted o utside of the norma l underwing pylons fo r te sting on a P-5 1B - such modifications were quickly and efficiently undertaken and se nt o n to flight test. As can be seen, with its four .50 cal Brow nings, six roc kets and two 500 -lb bombs . the aircraft became a potent ground attack weapon

CHAPTER

rn BUBBLE TOP

WITH PRODUCTION IN FULL SWING on th e P-SIB/C at both bo th th e Inglewo od and Dallas plants, constant improvement s and modification s were introduced on the production line as reports cam e back from the combat front . The BIC Mustangs, as well as th e majority of Allied and Axis fighters of that period , had can opies constructed from metal-framed plex iglass.

While efficient in protecting th e pilot from th e elements, the metal panels decreased visibility - especially at night or in po or weather - and o ne o f the complaints coming from th e frontline

was that th e P-SI B/C pilots suffered from poor cockpit visibility. This problem had, to a limited extent, been soived in the field through th e introduct ion of th e Malcolm hood mod ification. Created by the British , th e ho od was a semi-bubble unit wh ich repia ced the framed cano py on early Mustangs. Rails were added on eithe r side of th e cockpit wall to allow th e canopy to be slid back, but this 'field mod' was only an interim measure. The primary reason for the lack of o ne-piece clear vision canopies in th e early war yea rs was th at th e technol ogy required

to create a large 'blown' plexiglass transparen cy simpiy did not exist. How ever, th e incredible pressure of wartim e development

saw suc h technology and machinery qui ckly developed which en sured th at a bubble can op y could be created that would take the pressure of high speed flight and th e stress of combat. Thu s, NAA engineers began sketching out a drawing of a P-SIB with a bubble canopy, and the pap er result s produced a sleek lookin g aircraft with Vi rtually un precede nt ed Visibility. The ne xt ste p was to create a beaut ifull y crafted wind tun-

nel model so that th e bubble canopy concept could be tested. By this tim e NAA had realised the importan ce of havin g th eir own dedicated tunn el and, accord ingly, allocated a large sum of money and critical wartime materials to con struct it in a fortress-like concrete building at the Inglewood plant. Prior to th e advent of th e NAA tunnel, the company had to de pend entirely up on oth er local sites (espec ially th e one at Cal Tech ), which operated on a schedule giving a certain time to each manufacturer. Weeks, sometimes months, of precious time were often wasted in waiting for a chan ce to use these tunn els. With BUBBLE TO P

75

ABOVE The No rth American assembly hangars resound with the noise of P-SI D production in full swing.This photograph shows D-models rapidly nearing completion as they head toward the exit door - the lead aircraft has had its four-blade Hamilton Standard cuffed hydromati c prope ll er already fitt ed. Note the unco mpleted fuselages on the right that seem to head off into infinity. They wou ld finally make a 180" turn and head back towards the photographer as more and more equipment was added

76

P-SI MUSTA NG

RIGHT Testing out the bubble canopy co ncept in the new North American wind tu nnel. Built of mahogany and metal. and costing $20,000, the quarter-scale mode l was sanded down by hand and given five coats of lacquer so that it shined like a fine violin. Weighing 400 lbs. th e test mod el was fi rmly anchored to its suppo rt pylons, since the t unnel co uld produce air speed s of up to 32S mph.Wh en the model was set up for a test. a 3000-hp motor, driving a seven-blade 19-ft prope ller at a maximum of 700 rpm, could send the air flow back over the mode l at high speed.

The model was adjusted for the first run at a zero angle of attack in orde r to initially get nor mal reactions, its final setting being accurate to within III OOth of a degree .Allow ing for the weight of the model, all scales were set fo r zero

-

BU BBLE TOP

77

ABOVE Few of t he early fighters of World War 2 had cockpits which offered good visibility due to the built up canopies (a st ruc t ure t hat utilised numerous metal frames to hold plexiglass panels) then employed.The frames hindered vision under normal cond itions. and could play havoc if the aircraft was being operated at night or in poor wea ther. Accordingly. on 27 February 1943 two P-SI B-I-I O-NA airframes were bailed back to NAA for t he development of a bubble cano py which wou ld lead to t he production of a new Musta ng variant the P-51D. Bob Chilton is see n

flying P-SIB 43 - 12102 wit h th e

sleek new cano py in place. From th is view. it is very evident how the visibility from the cockpit was drastically improved

78

P-SI MUSTANG

OPPOSITE TOP The fi rewall and oil tan k (note t he heavy duty st raps t hat wou ld keep the oil tan k firmly in place. even during the most severe of com bat manoe uvres) are attached to t he basic P-SI 0 fuse lage. to which the majority of interna l fittings and controls are already in place. Four longerons and formers com posed this simple. yet very rugged, structu re

OPPOSITE BELOW A P-SI D wing near ing comp letion. Note how the forward 40 pe r cen t of the airfoil has bee n primered. fil led and sanded. At this point. the basic landing gear structure has been installed. along with t he aluminium drop tan k/bomb pylons and stubs for the 5-in rockets.Also not the cr ude stencil application of the US national insignia.The large stress doors have not yet been put in place. waiting for the installation of the fuel tanks

BUBB LE TO P

79

the new tunn el, NAA engineers could run tests co ntinuously and quickly, covering a mu ch larger field t han befo re. The tunnel utilised a 3000-h p powerpl ant wh ich drove a seven-blade 19-ft propeller at up to 700 rpms, and this could get th e air mo ving at speed s of up to 325 mph. A 200-h p au xiliar y system supplied power for motors to run propellers in the models and fo r various other operation s. Scientific considerations governed all the details in the construction of the tun nel. The redwood test section was sup ported on steel 'I' beams, anchored at each end to the concrete porti on of t he tunnel. The power and propell er sectio n was dou bly strong, whilst th e walls of the con tro l and compu ting roo m were floatin g and heavily sou nd proofed. About 200 years ago , Venturi discovered that, as a passageway narrowed down, the flow of air through it gained speed - hence the Ventu ri effect and the NAA tunnel was built on that principle. The air stream narrowed down nearly eight times, making high speeds possible through the test section. The problem o f making the air flow smoothly arou nd t he square angles of the tunnel was solved by curved metal vanes or plates set up at the corners. Since a tem perature of 150 cenngrade might develop in the air stream during co ntinuo us op eratio n at hig h speeds, water-cooling o f the vanes was 0

80

P-5 1 MUSTANG

BELOW

Bullet-p roo f fuel tanks

aw ait installation in the wi ng. Wing conveyor lines A and B were phot ographed on 29 July

1944

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LIQUID-COOLED AIRCAA" ENG INES

DI V IS IO N OF

Indianapol is, Indiana

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P·51 MUSTAN G,

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