Bell X-1 Variants

Aerofax Datagraph 3

BeIIX-1 Variants •

By Ben Guenther and Jay Miller ISBN 0-942548-40-X

X-1 SECOND GENERATION GENERAL ARRANGEMENT ©1988

Aerofax, Inc. P.O. Box 200006 Arlington, Texas 76006 ph. 214 647-1105

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Motorbooks International 729 Prospect Ave. Osceola, Wisconsin 54020 ph. 715 294-2090 European Trade Distribution by:

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1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20.

De-icing Fluid Tank 22. Canopy 23. Oxygen Filler 24. Lox Tank 25. Nitrogen Filler 26. External Power Receptacle 27. Hydrogen Peroxide Filter Hydrogen Peroxide Tank Lox Filler Fuel Tank Fuel Filler Turbine Pump Pick-Axe Antenna XLR11·RM-S Motor ANfAPN-60 Antennas AN/APN-60 Radar Installation Pitol Tube Tube Bundles (Nitrogen) Main Wheel Door Actuator Air Bollie Main Wheel Door Actuator Air Bottle Filler 21. AN/AAC-5 Radio Installation

Stor.k No. 0303

ABBREVIATIONS AND ACRONYMS: AAF AB AF AFB AH ARDC ASD g.

NACA NASA PARD PSI RMI tIc tho

USAF VHF X

Army Air Force Air Base Air Force Air Force Base Amp Hour Air Research and Development Command Aeronautical Systems Division Gravity National Advisory Committee for Aeronautics National Aeronautics and Space Administration Pilotless Aircraft Research Division Pounds per Square Inch Reaction Motors, Inc. Thickness/Chord Ratio Thrust United States Air Force Very High Frequency Experimental

THE BELL X·1 VARIANTS STORY

The second X-I, 46-063, during final assembly inside Bell's Niagara Falls, New York facilily, during late 194~. The wing~ with a thickness/chord ratio of 8%, and its associated center section, later were swapped with the 10% wmg of the flfsl X-I, 46-062, pnor to the latter s hlslonc flfst supersonic flight on October 14, 1947. With the exception of their wings and serial numbers, when compfeted, 46-062 and 46-063 were externally, Virtually Identical.

leading edge and all changes in velocity and pressure take place quite sharply and SUddenly. The airflow ahead is not influenced until the air molecules SUddenly are forced out of the way by the concentrated pressure wave set up by the actual object. Simply stated, compressibility anomalies occur at those speeds which approach or exceed the speed of sound. This velocity, in turn, is defined as the speed at which small pressure disturbances will be propagated through the air-which in turn is solely a function of air temperature. The accompanying table illustrates speed of sound variations in the standard atmosphere:

CREDITS: The authors and Aerofax, Inc. would like to express our thanks to the many individuals who contributed to this detailed description of the Bell X-1 research aircraft family. Three people who were particularly helpful in 3ssisting us under the auspices of Bell Aerospace [extron include Eddie Marek, Stanley Smolen, and Bob 3herwood. Eddie's Willingness to pull and file rare original legatives, and Bob's willingness to let him do it, provided the final contribution assuring the publication of this book. Stan's support and assistance gave Eddie the boost needed to persevere while digging. Because of the efforts of these three individuals, much of the imagery seen on the pages of this book has been released for pUblic consumption for the first time. Others whose efforts on our behalf won't soon be lorgotten include David Anderton, Bill Beavers, 'Joe Cannon, Bob and Gloria Champine (the latter of NASA Langley), Robert Cooper, Richard Forest (special thanks), Elaine Heise (Bell Aerospace Textron), Wes Henry (USAF Museum), Cheryl Hortel (Office of History, Edwards AFB), Alvin "Tex" Johnston; Helen Lapp (special thanks); Dave Menard; Robert Perry (RAND Corp.); Terrill Putnam (NASA Dryden); Michael Rich (RAND Corp.); Mick Roth; Sue Seward, Stanley Smith (special thanks); Tom Vranas (NASA Langley); and Lucille Zaccardi (retired from the Edwards AFB History Office). For another perspective on the X-1 story, Aerofax, Inc. highly recommends Richard Hallion's Supersonic Flight (the MacMillan Co., NY, 1972). And for a detailed description of the rest of the X-series aircraft, the pUblisher also recommends author Jay Miller's The X-Planes, X-I to X-31 (Aerofax, Inc., TX, 1988).

PROGRAM HISTORY: As an object moves through the air mass, velocity and pressure changes occur which create pressure disturbances in the airflow surrounding the object. Traveling at the speed of sound, these pressure disturbances are propagated through the air in all directions, extending indefinitely. If the object is traveling at low speed, the pressure disturbances primarily are propagated ahead of Ihe object and the oncoming airflow thus is influenced by the pressure field being generated. Once an object approaches sonic velocity, this scenario dramatically changes. There now is no warning for oncoming air molecules that the object is about 10 pass through. The oncoming air molecules cannot be influenced by a pressure field because none exists ahead. Thus, as flight speed nears the speed of sound, a compression wave (shock wave) is formed at the

Variation of Temperature and Speed of Sound With Altitude in the Standard Atmosphere Altitude

Ft. Sea level 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 50,000 60,000

Temperature

• F. 59.0 41.2 23.3 5.5 -12.3 -30.2 -48.0 -65.8 -69.7 -69.7 -69.7

·C. 15.0 5.1 - 4.8 -14.7 -24.6 -34.5 -44.4 -54.3 -56.5 -56.5 -65.5

Speed of Sound Knots 661.7 650.3 638.6 626.7 614.6 602.2 589.6 576.6 573.8 573.8 573.8

Thus it is that all compressibility effects depend upon the relationship of airspeed to the speed of sound. It is important to note that Ernst Mach (pronounced "Mahk"), a nineteenth century Austrian physicist and mathematician, became the first to enunciate the mathematical theory dealing with airflow. This theory assigned a numerical value to the ratio between the speed of a solid object through a gas (or space) and the speed of sound through that same medium. This became known as "Mach number"-with Mach 1 being equivalent to the speed of sound and with anything more or less than Mach 1 being given in terms of a percentage (i.e..85 Mach would be 85/100ths the speed of sound; Mach 2 would be twice the speed of sound; etc.). Today, Mach is the generally accepted term used to quantify supersonic speeds. By the beginning of WWII, aerodynamicists, structural engineers, powerplant designers, and numerous pilots had concluded that the science of flight was faced with an insidious aerodynamic hurdle of truly staggering implications. For the first time ever, compressibility phenomenon (also later referred to as the "transonic barrier" or "sound barrier"), a dynamic gaseous event wherein air molecules compress into a seemingly im· penetrable wall in front of an aircraft's wings and fuselage (and, as it were, spinning propeller blade leading edges) when it nears Mach 1, had raised its serpentine head. During the late 1930s and very early 1940s, new high·

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Rarely seen view of all three first-generation Bell X-I s under construction inside the Bell plant during late 1945. The aircraft on the left is 46-062, the one m the middle IS 46-064, and the one on the far nght IS 46-063. The forward fuselage section of 46-062 has been rotated 90° in its support crade.

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One of the first Bell design studies, dated early 1945, illustrating what was to become the Model 44, and later, the X-I. Noteworthy are the dual-wheel-and-tire main landing gear, the side-opening canopy, and the unfaired XLRII combustion chambers.

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A I/Bth-scale subsonic wind tunnel model representing the X-I as it eventually would be built. Of particular interest is the extended landing gear configuration and the diminutive, rarely-seen, lift dumping upper-wing-surface spoilers.

performance pursuit (as they then were called) aircraft, such as the U.S. Army Air Force's Lockheed P-38 Lightning and Republic P-47 Thunderbolt, capable of achieving Mach numbers approaching. 75 in a dive, had begun to enter the operational inventories of the world's military flying services. Their speed capabilities were close enough to sonic velocity and its associated compressibility phenomenon to cause serious, and sometimes irreversible buffet, structural overload, control, and stability problems. Already compressibility's associated loss of control and resultant occasional catastrophic structural failures had led to the deaths of several pilots. It had become painfully obvious to the world aviation community that, unless something was done to eliminate or circumvent the problem, more deaths soon would follow. Because research tools during the 1930s and early 1940s were limited in capability and technology, compressibility was not an easily understood phenomenon. Wind tunnel data, so commonplace as a means of predicting aircraft performance and flight characteristics today, almost was non-existent in the speed and dynamics regime encompassed by transonic and supersonic aircraft design, and only bullets then were known to be capable of stabilized "flight" at speeds in excess of sonic velocity. Supersonic phenomena, which occurred beyond the speed of sound, also were little understood. Such things as wave drag, high-speed flutter, "shock stall", centerof-pressure shift, the affect of supersonic speeds on interference drag, and the static and maneuvering load anomalies associated with supersonic flight were mysterious, and at times frightening unknowns. There even was concern over the possibility that something beyond prediction might occur-no human being had flown supersonically and lived, and no one knew for certain what strange and potentially disastrous' surprises awaited the first to explore. Over a period of several years, the phrase "sound barrier" came to describe the invisible gaseous wall generated in front of an object moving at or near the speed of sound. On paper, some aerodynamicists had predicted that at supersonic speeds, because of this "wall", drag and lift would reach infinite proportions and

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thus create a barrier that literally could not be penetrated. The first serious thrust in the direction of conquering compressibility had come during the SeptemberlOctober 1935 Fifth Volta Congress on High Speeds in Aviation, held in Campidoglio, Italy. Attended by a large number of the world's leading aerodynamicists and aviation engineers, it proved a historic milestone due to its emphasis on supersonic flight. Among the American representatives attending was Theodore von Karman, who later would have a decidedly influential effect on the birth of the X-plane program in the U.S. von Karman's reaction to the meeting was immediate and significant; he became convinced that supersonic flight was possible, and he became adamant the U.S. should initiate a research program quickly that would explore this monumental leap forward in aircraft performance. During approximately this same time period, another engineer, Ezra Kotcher, who then was an instructor at the Air Corps Engineering School at Wright Field near Day1on, Ohio, also had become enamored with the proposition of supersonic flight. Having attended a lecture by fellow engineer Lt. Col. H. Zornig on the dynamics of supersonic ballistics, Kotcher had come away convinced that flight at supersonic velocities was within the realm of possibility. Over the following several years, Kotcher reviewed what he had gathered at the Zonig lecture and by mid-1939, was prepared when asked to write a report describing his views on the subject of problems confronting future aeronautical research and development. Completed during August, the paper was circulated through several engineering offices, eventually finding its way onto the desk of Maj. Gen. H. H. "Hap" Arnold, and into the offices of the NACA (National Advisory Committee on Aeronautics). Kotcher's paper was progressive and far-sighted. He placed heavy emphasis on the need for an extensive series of full-scale flight test programs to be complemented by related wind tunnel studies. He also placed heavy emphasis on the development of gas turbine and rocket propulsion systems, already noting that the conventional piston engine and its associated propeller propulsion systems would not be sufficient to explore truly

high speeds. Though appearing quite reasonable from perspective, Kotcher's ideas proved too radical fa The rumblings of war now were becoming quite ( and the momentum being gathered in the aircraft i was strictly production oriented. Compounding th lem, while at the same time adding to its validity, \ fact that wind tunnel data was extremely limite( critical area of transonic flight. Technically the regime approximately encompa: the speeds between Mach .7 and Mach 1.3, the tr, envelope was important because it was in this range that the most radical changes took place a~ ject translated from subsonic to supersonic vel Without wind tunnel data to verify events in this al only way to explore it was with full-scale hardw The basis for the wind tunnel anomaly was the tion of shock waves off wind tunnel walls and ba the model being tested. From Mach .7 to Mach angles of shock wave reflection were such that it' tually impossible to eliminate the reflection difficult then-state-of-the-art tunnel design. Known as "ch, the problem foiled attempts at accurate data acq and prevented aerodynamicists from acquiring into events in the transonic zone. Because of this dilemma, new impetus was pia the Kotcher proposal calling for a full-scale re vehicle to explore transonic phenomena. Kotch not, of course, the very first to conceive the idea 01 sonic research aircraft. His proposal, in fact, ha preceded by the until-1940 generally unheralded fellow aerodynamicist John Stack who, as early a had begun conceptualizing rudimentary aircraft ( optimized for studying transonic phenomena. By 1941 , aircraft such as the aforementioned Lo P-38 Lightning and Republic P-47 Thunderbo, beginning to enter the Army's inventory for the fir: These were the first U.S. aircraft fully capable a in the "compressibility zone" on a routine basis, at the first to confront the realities of its affects. The exigencies of war overshadowed the n thoroughly explore the undesirable affects of tra speeds on extant aircraft design technique, so th, lem was sidestepped:temporarily by limiting aircr
and empennage, and left wingtip required extensive rebuilding and the aircraft was grounded for almost six months. It was not until October that it again was declared f1ightworthy. On November 1, 1948, with Herbert Hoover again in the cockpit, the second X-1 completed its first check flight following the April accident. Later, a new NACA X-1test pilot, Robert Champine, took over the controls and, on November 23, completed his first familiarization flight. Additional flights followed and during early December, the aircraft was grounded in order to install special instrumentation and recording equipment for the NACAsponsored stability and control program. It was not flown again until some five months later. When it was declared airworthy again, the second X-1, beginning on May 6, embarked on a series of test flights that consumed most of the summer and fall of 1949. Eleven missions were flown successfully, these resulting in the accumulation of rather substantial transonic and supersonic data that would serve the aerospace industry well for many years to come. The second X-1 again was grounded during early December 1949 so that recording instrumentation could be installed. It wasn't until the following May that additional missions were undertaken. On May 26,1950, following two flights on May 12 and May 17, NACA pilot John Griffith piloted the second X-1 to its highest speed ever, Mach 1.20 (792 mph). As it were, this aircraft was somewhat slower than the first X-1 due in part to its 10% Uc ratio wing. The speed it attained during the May 26 flight was considered representative of its maximum performance potential. Unfortunately, the May 26 flight did not end without incident. Following touchdown, the nose gear collapsed and significant damage was incurred. Another grounding now followed, this resulting in no further flight testing until August 1950. Following its return to operational status, the second X·j embarked on a pressure distribution survey flight test program. Some nine flights were conducted before it was discovered the fuel tank had begun to rust and that a major overhaul would be required to correct the problem. Yet another grounding followed, this one consuming no less than six months and leading to the installation of anew fuel tank and new test instrumentation. The aircraft was flown for the first time following refurbishment on April 6, 1951, and again on April 20. Two more flights followed, with a month-long break occurring during June. The latter allowed time for the installation of a new powerplant. An additional nine flights completed the NACA's program with the second X-1. Several different pilots checked out in the aircraft in the interim, and by October, problems with battery acid leaks and weak nitrogen spheres had led to another grounding decision. This was made permanent following further analysis of the spheres and an attempted replacement by using spheres from the first X·1-which proved fruitless. The third X-1 (46-064) unquestionably was the most i11~agued aircraft of the original three. From the beginning, lsuffered numerous setbacks including what at first appeared to be a temporary delay in its delivery date caused by Reaction Motors' failure to complete and deliver to Bell a f1ightworthy sample of its steam-driven XLR11-optimized turbopump. The latter, as explained ea~ier, was for transferring propellants from the fuel and oxidizer tanks to the powerplant. Lighter and less volumetrically invasive than its predecessor nitrogen system, the turbopump was considered a significant technological step forward for the X-1 series. As noted, development of the new turbopump did not

occur as rapidly as originally planned. Additionally, problems with funding and a lack of sustained Air Force interest eventually caused the third X-1to fall no less than three years behind its original flight program schedule. It was delivered eventually to Edwards AFB (as Muroc AFB was renamed on January 25, 1950) during April 1951, and on July 20, with NACA pilot Joseph Cannon (by now, retired from Bell) at the controls, it completed its first glide flight. The next attempted flight of the third X·1 proved to be its last. On November 9, 1951, the aircraft had undertaken a captive flight of approximately one hour. This had been scheduled as a rehearsal for the forthcoming first powered flight as well as a test of the rocket propellant and hydrogen peroxide (the latter, which was carried by the third aircraft only, and utilized to power the turbo· pump, was simulated with distilled water) jettisoning system. Jettisoning of fuel and liquid oxygen had been aborted due to loss of X-1 nitrogen source pressure. At 18,000 ft., X-1 pilot Cannon had inadvertently tripped the hydrogen peroxide and fuel jettison switches while struggling to fasten the X-1's door. Since at that time the peroxide tank was pressurized and contained only nitrogen, this could have been the cause of the loss of jettison source pressure. A crew decision now was made to land with the X-1 still in the B·50's bomb bay and still containing most of its liquid oxygen and fuel complement. The landing was completed without incident and the still-mated aircraft were taxied to the propellant loading area to obtain nitrogen source pressure for the purpose of on-theground jettisoning of the liquid oxygen, and to attempt to locate any possible leaks in the nitrogen pressure system. Source pressure was obtained with no difficulty and the aircraft were towed to the east end of the ramp and swung around SO that they faced into the wind. A standard procedure for jettisoning then was begun; i.e., the area to the rear of the aircraft was cleared, fire trucks and firemen were moved into position, and an operator, in this case, pilot Joseph Cannon, was placed in the X-1 's cockpit. Following a visual check, the "all clear" signal was given and Cannon began the normal liqUid oxygen jettisoning procedure. He pressurized the liquid oxygen tank pressure regulator dome until the indicator reached its red line at 52 psi. He then turned his attention to the liquid oxygen tank pressure guage. This pressure was rising slowly, and when it had reached approximately 42 psi, an explosion occurred. All witnesses later agreed that the first explosion was a dull thud, or contained explosion, quickly followed by a "hiss" and a small cloud of white vapor rising from the X-1 center section. Some witnesses reported small flames; the majority remembered none. Within one to five seconds, a sharp, violent explosion occurred, immediately followed by yellow flame and black smoke. This was followed closely by numerous other explosions, varying in intensity from minor to very violent. Additional fire trucks now arrived at the scene and the fire was extinguished in approximately 8 minutes. Unfor-

EARLY 0-37 STUDY

tunately, the X-1 was demolished totally and the B-50 center section, except for the wing, was burned away. At the outset of the explosions and ensuing fire, everyone was evacuated from the premises and there were no fatalities. Cannon, who still was inside the B-50 at the time of the initial explosion, was rescued, though not before receiving serious injuries. Liquid oxygen had spread everywhere following the explosion, and Cannon, in an attempt to extricate himself from the B-50 bomb bay, had had to crawl on his hands and knees through a pool of the cryogenic liquid in order to escape. Freeze burns eventually cost him parts of several fingers and left scars of significant proportions. He would not have made it without the help of several fellow Bell employees who happened to be on hand at the time of the explosion. A lengthy investigation followed the accident. Various conclusions were reached as to its cause and cure, but it was not until the demise of the X-1A, nearly four years later, that the real problem was discovered. As research later would verify, the problem lay with the aircraft's Ulmer leather gaskets.

The interim design between the Bell X-I and the later Bell X·2 was the Bell 0-37 (Design #37), seen in wind tunnel model form .. Essentlally.a compromise configuration utilizing the basic X-I fuselage with swept wings and swept vertical and honzontal tall surfaces, It proVided Bell With a stepping stone to the totally new X·2.

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THE BELL X·1 A, X-1 B, X~1 C, AND X·1D (The Second Generation)

The second of the second-generation X-Is to be completed, X-lA, 58-1384, was rolled out from Bell's Niagara Falls, New York plant doors during late 1952. Originally painted bright orange over-all, this scheme was replaced by bare metal, (standard for all second-generation X-Is), prior to the aircraft's delivery to Edwards AFB.

0[1 November 14,1947, exactly one mOr'\th after Chud Yeager achieved sonic velocities in the first X-1, theA Force authorized Bell Aircraft Corporation to formall undertake a study calling for the development of a secon generation X-1 aircraft that would offer significant pa formance improvements over its predecessors. Th resulting design was the Bell Model 58 (assigned theA Force project designator MX-984), which utilized th basic wing, horizontal taii surfaces, and powerplant ofth first generation aircraft, but which had an almost tota~ new fuselage featuring increased capacity fuel tanks, revised and much improved cockpit and associate canopy, a low-pressure turbopump powerplant fuel fee system, and improved airframe and powerplar The) maintenance features. Following contract initiation on December 11, 1947, formal contract, W33-038-ac-20062, for four aircraft, w, consummated on April 2, 1948, and less than a year lale a full-scale mock-up was ready for inspection. Th' passed Air Force scrutiny following numerous minor rm. sions and changes, and by the end of 1950, under tn direction of project engineer Richard Frost, the firslr three second generation X-1s (X-1A, 48-1384; X-II 48-1385; X-1 D, 48-1386) approved for construction, tn X-1D, was nearly complete (a fourth aircraft, the X-II was cancelled; to have been a propulsion system tel bed, it is assumed to at one time have been assigm the 48-1386 Air Force serial number). ._The X-1 D, the first of the second generation aircra "to roll from Bell Aircraft Corporation's Buffalo, New y~ plant doors, made its debut at Edwards AFB suspendl from the bomb bay shackles of EB-50A, 46-006A, durin July 1951 . On the 24th of that month, with Bell compa! test pilot Jean Ziegler at the controls, it was launched 01 Rogers Dry Lake on what was to become the only su cessful flight of its career. The unpowered glide was cor Ma pleted after a nine-minute descent, but upon landing, II to nose gear failed and the aircraft slid somewhat ungrao fully to a stop. Repairs took several weeks to compie and it wasn't until mid-August that a second flight cou be scheduled. This mission, on August 22, with the X-1 D attachedl the EB-50A, at first went routinely. However, as the mall aircraft ascended through 7,000 ft., Lt. Col. Fra' Everest, the X-1 D's Air Force pilot, noted upon enterir the cockpit that the nitrogen source pressure indica! was giving a very low reading. After discussing the prd lem with Bell engineers aboard the bomber, the decisir was made to abort the mission and jettison the X-tD propellants. Shortly after Everest initiated the jettison pi cess, an explosion rocked the aircraft's aft end. ThisWi followed immediately by flames visible from the char aircraft following in close trail underneath the EB-5~ Everest now hurriedly egressed the X-1 D's cockpit a! moments later, an engineer onboard the EB-50A, Jat Ridley, pulled the drop handle which released II shackies holding the X-1 D in place. Less than a minu later, the once highly advanced multi-sonic research a craft lay a twisted pile of wreckage on the desert floc some two miles west of the south end of Rogers Dry Lai The X-1 D was followed to Edwards by the similar X·I S. re, which arrived on January 7, 1953, shackled to the san EB-50A carrier aircraft that had transported the X-10t protn its fateful last mission. Just over four weeks later, II X-1 A, on February 14, with Bell company test pilot Jer Ziegler at the controls, successfully completed its fil glide flight. This was followed by a second glide son six days later, and by a first powered flight, also Yn Ziegler, on February 21. The X-1 A originally haa been scheduled for a serH of stability and control test flights under the auspices Cornell Aeronautical Laboratories following completir of Bell's required contractor (Phase I) test flights. 01 to the untimely demise of the third X-1 and the X·II however, the Cornell program was cancelled and shq ly afterwards, the Air Force confirmed that the aircrafti stead would be delivered directly to the NACA. In the meantime, contractor X-1A flights continul through April, at which time the aircraft temporarily~ grounded and returned to Bell's Buffalo plant I modification. At the same time, an elevator flutter anon Iy was examined and the aircraft's nitrogen-tube-buna Land pressurization system was replaced with one consistil fin of simple spherical containers. The decision to incorporate the latter was the resull

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In bare metal, the X-IA is seen at Bell shortly before being delivered to Edwards AFB. The cockpit transparency remains covered in protective paper to prevent scratching and the wing upper surface has a protective mat in place to permit access to the center section equipment bay. Vertical fin tip has just been painted.

Prior to completion, the X-IA was check fitted to confirm compatibility with B-29 carrier aircraft. The second-generation X-Is required significantly different bomb bay fittings, snubbers, and attachment assemblies, and therefore represented a totally new entity. Noteworthy is the X-I A's unpolished aluminum skin.

In order to accommodate powerplant test requirements, the X-I A was loaded aboard a flatbed trailer and moved to Bell's engine test facility several miles from the main Bell plant. The aircraft sill was painted bright orange over-all. Interestingly, littfe was done to secure the aircraft from inquisitive eyes.

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The X-IA originally was rolled out in a bright orange over-all scheme. This was to be short lived as it was concluded erosion and the temperatures involved with cryogenic propellants would create a constant maintenance headache.

Mass balances were added to the elevators of the second-generation X-I s in order to alleviate a flutter concern. Flush exhaust nozzles for the turbopump propellant system later were modified to incorporate protruding extensions.

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The turbopump exhaust nozzle extensions are readily discernible in this view of the X-I A. Also visible are the small open hook bay doors on the top of the dorsal spine. There actually were two sets of doors with one pair for each hook.

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The conventional markings applied to the orange-scheme for the X-I A, including the national insigne and serial number, were completely standard. Besides being a maintenance headache, the orange paint also added weight.

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Small hatch, visible on top of X-IA dorsal spine, just ahead of aircraft center section, covered forward attachment hook and electrical umbilical. Aircraft is seen at Bell after removal of orange paint and probably prior to delivery to Edwards AFB. Lox jettison system fairing is visible on ventral spine, just to the rear of the nose landing gear. Small protrusions visible just aft of ventral spine end are AN/APN-60 antennas. Except for white ventral spine and wing undersurfaces, and black anti-glare panel, aircraft was unpainted.

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landing gear tread and related aircraft stance were essentially the same between the first- and second-generation aircraft. Though narrow, the gear provided excellent stability after touchdown and pilots rarely noted handling difficulties.

During late 1952, the X-lA, 48-1384, is seen being prepared for a practice mating with its B-29 carrier, 45-21800. Winters in Buffalo, New York, though often bitter, rarely hampered X-plane flight test operations.

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The XLRll was a bipropellant liquid rocket engine utillizing an alcohol/water mixture as fuel and liquid oxygen as the oxidizer. The fuel and oxidizer were forced either by pressurized nitrogen or a turbopump to the engine combustion chambers.

The XLRll's four Chambers were closely stacked to provide minimal asymmetric thrust anomalies. Regenerative cooling, wherein the propellants were circulated around the combustion chambers before being combusted, was utilized.

57

The XLRII fit neatly into the X-l's empennage section. Regenerative cooling lines are visible as ribbed tubes running forward into the engine compartment.

XLRII combustion chambers in a first-generation X-I. Visible inside each chamber is the propellant injector unit for mixing the lox and water/alcohol.

The four XLRII combustion chambers fit flush against the aft end of the fuselage. Three dump tubes for lox, water/alcohol, and nitrogen are visible.

The configuration of the lox, water/alcohol, and nitrogen dump tubes varied considerably from aircraff to aircraft, and also from modification to modification.

Plastic extensions are seen as the intermediate tubing to ensure that residual lox, water/alcohol, and nitrogen gas are routed into the dump tubes attached to the carrier aircraft. These dump tubes prevented dangerous propellant accummulations in the carrier aircraft bomb bay during the ascent to launch.

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