[219] Langley's wartime mission was essentially not much different from its earlier peacetime mission: to find practical ways for American aircraft to achieve improved performance, i.e., higher speeds and altitudes, longer range, more maneuverability, and better handling characteristics. The pace of its quest had to be much more frenetic, of course. Though all aircraft used by the United States in combat were designed to the same basic formula (internally braced, all metal monoplane, equipped with retractable landing gear, wing flaps, controllable pitch propeller, and enclosed compartment for the crew), they differed widely and significantly in terms of their aerodynamic details. It was thus essential to refine aircraft on a case-by-case basis as problems arose.
Rarely did the army, the navy, or a manufacturer already know the design problem that needed fixing when it sent an aircraft to the NACA laboratory; in most cases, a prototype would be sent to the lab with instructions for the NACA to determine the aircraft's characteristics and to fix problems if the staff found any. In this way Langley researchers solved various problems in specific configurations. For instance, they recommended a modified tail arrangement and antispin device on the Vought F4U-l and a new elevator for the Curtiss SOC-1.1 Tests in the Full-Scale and 8-Foot High-Speed tunnels and in different tunnels at Ames lab in California led to the development of a simple but effective wing flap which, when deflected, increased lift just enough to make recovery from a high-speed dive possible (see next chapter).2 Tests in the LMAL towing tanks and impact basin led to the development of a "hydroflap" to aid in ditching.3 These are just a few examples of specific refinements to aircraft recommended by NACA Langley. In all, Langley tested 137 different airplane types between 1941 and 1945, representing more than half of all the types contracted for by....
....the army and navy during the war and including virtually all types that actually saw combat service.4
But the design of advanced-performance bombers and fighters involved more than mere aerodynamic refinement based on existing knowledge-among other things, it also required new understanding of high-speed phenomena. By 1939 flying speeds had increased to the point where the fastest aircraft were encountering a unique set of potentially dangerous aerodynamic phenomena known as compressibility effects. Previously, designers had created aircraft on the assumption that the air flowing over the wings and other surfaces was essentially incompressible, like water; though compressibility was always present in air, it was negligible until speeds approached sonic. Thus as aircraft evolved and their speeds increased, engine cowlings, canopies, fuselages, and especially wings and propellers were subject at high speed to a sharp rise in drag and loss of lift, with resulting changes in pitching moments. These compressibility effects limited the speed of aircraft and caused buffeting, control surface flutter, shifts in trim, and other dangerous changes in stability and control characteristics. In some cases, aircraft flying into the compressible regime became completely uncontrollable, could not recover, and crashed.5
To achieve safe high-speed flight, the NACA began to consider some new technologies such, as lighter-weight materials, stronger structures, and radically different types of engines for application in airplane design. Not all of these considerations led to immediate-or even to successful application. (Langley's successful overall response to the "compressibility crisis" is analyzed in the next chapter.) In 1938, for example, Langley engineers Eastman Jacobs and Eugene Wasielewski (a power plants expert formerly employed by Allis-Chalmers) explored the potential of a technology unproven in aeronautics-that they thought might help to solve some of the high-speed problems: they designed an axial-flow compressor, an unconventional piece of machinery that compressed an engine's intake air by sending it through a series of rotating and stationary (stator) blades which were concentric with the axis of rotation. The practical purpose of the axial-flow compressor was to be part of a piston-engine supercharger application (that is, part of a device for sending pressurized air into the engine cylinders to increase thrusting power). That the design posed some ultimate, mind-boggling problems for an airfoil researcher was Jacobs's personal reason for undertaking such a project. To work effectively, each one of the compressor's dozens of rotary and stationary blades had to be designed perfectly, according to airfoil theory, and put into a cascaded series that fed the flow output of one stage of blades into the input of the next stage.6
[222] Though the initial round of tests demonstrated the high performance potential of the new compressor, Jacobs was left with "serious doubts about the axial design when the blades of the test machine were destroyed during a run in which the compressor stalled." Believing incorrectly that this accident was caused by some inherent structural weakness which would prevent success, Jacobs abandoned the project. Wasielewski and other members of the LMAL engine research staff continued to refine the design, however. Though the application to a piston-engine supercharger proved a failure, showing no real advantage over the contemporary General Electric Moss supercharger, Langley's preliminary reports on the overall efficiency of its compressor seem later to have persuaded American manufacturers selecting compressors for jet engines to favor axial designs (wherein the direction of the airflow into and out of the compressor is parallel to the longitudinal axis of the engine) over centrifugal designs (wherein the direction of the airflow out of the compressor is perpendicular to the longitudinal axis).7
A much more notable failure to develop a radically new technology for high-speed aviation at Langley during the war was an attempt between 1941 and 1943 to create a hybrid system of jet propulsion. (Jet propulsion is a means of moving an aircraft forward by sending rearward at high velocity a stream of flowing gases, like sending a balloon across the room by letting go of its neck.) This system, like that developed by Italian engineer Secondo Campini in the 1930s and applied in the early 1940s to a Caproni airplane, was based on the principle of the ducted fan.8
Langley's version of the Campini ducted-fan propulsion system was supposed to complement conventional propulsion in the following way: Air was admitted through a frontal inlet into a duct, where the air slowed to practically stagnation pressure. A fan inside the duct, driven by the aircraft's conventional radial piston engine, then boosted the pressure and passed the air into a combustion chamber (located at the region of highest boosted pressure) where the exhaust gases (i.e., heat) from the piston engine vaporized gasoline for a primary fire. In turn this primary fire vaporized gasoline that was flowing over the main boiler section, igniting a secondary fire. Heated gases from this fire then escaped, accelerating through the constriction of a high-speed nozzle, where the thermodynamic energy accumulated during the various phases of compression and heating added to the driving thrust. This thrust, Langley engineers thought, could be harnessed for assisted takeoffs and emergency high-speed dashes by combat aircraft. (Today, such a system is called an afterburner.) If the jet was shut down, the aircraft could then revert to the conventional power plant, making it capable of long cruising flight.9 Langley's ultimate goal [223] was to apply the Campini system to either a military aircraft or to a small experimental aircraft designed specifically for the purpose of high-speed research. Although this goal was not achieved, the lab did prove the system feasible.
Until March 1943, when the work was officially canceled, Langley's testing of the Campini engine had the full support of a special NACA committee on jet propulsion and the polite tolerance of the military services. But during all of the time it worked on the Campini engine, the laboratory was unaware that another type of jet engine, the gas-turbine or turbojet,* was rapidly becoming a reality-and one that had greater feasibility and more potential than the ducted fan. The world's first jet aircraft, Germany's Heinkel 178, had flown for the first time on 27 August 1939; the experimental airplane was powered by a turbojet engine, designated the S-3, designed for Heinkel by Hans Von Ohain. The S-3 engine produced about 1100 pounds of thrust-which was just enough power to make the flight of the small airplane successful. But the NACA lab knew nothing about this top secret German development until 1944. Nor did the lab hear anything concrete about concurrent turbojet developments in Britain until the summer of 1943 -even though American military leaders knew a lot about them much earlier. In April 1941 Air Corps chief Hap Arnold found to his astonishment during a tour of England that the British were not simply planning to develop gas turbines, but were actually preparing to flight-test a turbojet-powered aircraft, the Gloster E 28/39, which flew successfully the following month with an engine designed by Frank Whittle. Arnold made arrangements with the British to bring engine blueprints, and eventually a prototype of the Whittle WIX engine itself, to the United States. The [224] British, who had just experienced the shocking forced evacuation of their troops from Dunkirk and felt that invasion of England by the Germans was imminent, shared their discovery with Arnold on the condition that he treat it as a top military secret. Upon his return, Arnold assigned the General Electric laboratory at West Lynn, Massachusetts, the task of imitating the prototype engine. Soon thereafter, in the early summer of 1941, the Army Air Corps placed a top secret order with Bell Aircraft Corporation for construction of an experimental jet aircraft. In September 1941, Maj. Donald Keirn carried, manacled to his wrist, a set of design drawings for the Whittle engine from London to G.E. at West Lynn. Thirteen months later the Bell XP-59A, powered by two Whittle I-A "Superchargers" (called that in disguise) developed by G.E., flew successfully at Muroc Dry Lake in California with full armament. Because of the tight lid of secrecy put by Arnold on all jet propulsion developments, Langley had not even an inkling of these important events until after an NACA representative to Bell's plant on the west coast heard rumors about them in May 1942.10
This lack of information put Langley engineers searching for a practical means of jet propulsion for aircraft at a serious disadvantage. What was clear to Arnold in the spring of 1941-that the potential of turbojet technology clearly outstripped that of the ducted fan-was not clear to them until the summer of 1943, when the military began to bring the NACA more into its confidence about secret jet propulsion programs, and when Eastman Jacobs, leader of the Campini project, returned from England with knowledge of British developments.
This chapter illustrates an episode in Langley history in which the engineers had every reason to think they were in charge of the technological situation, when in fact they were not. Though their combustion tests were successful in the sense of showing the general feasibility of the Campini system, their overall program was a failure. The failure was lack of knowledge-not about ducted fans, but about turbojets.
To trace the sources of Langley's interest in a ducted-fan jet propulsion system, it is first necessary to summarize the NACA's earlier analyses of the potential of jet propulsion for aircraft. In 1923 the Committee published a paper by Edgar Buckingham of the Bureau of Standards which declared that jet propulsion for aircraft was practically impossible. From his analysis of the thrust produced by an exhaust of burning compressed air in a combustion chamber, Buckingham determined that there was "no prospect whatsoever that jet propulsion ... will ever be of practical value, [225] even for military purposes." Even at the highest flying speed anyone then had in view-250 miles per hour-a jet-propelled aircraft could not come close to matching the efficiency of an airplane equipped with a piston engine and propeller. The jet's fuel consumption would be far too excessive, he argued, largely because the weight of the compressor machinery would have to be so great. Buckingham calculated that the fuel consumption of a jet would be four times that of a conventional engine producing equivalent thrust. He assumed that aircraft turbines would have to be huge and heavy, similar to industrial turbines then being used in blast furnaces and boilers, to withstand the high temperatures and attendant high pressures. Buckingham's error was in this and other assumptions, not in his subsequent analysis. 11
Throughout the 1920s and early 1930s Langley researchers accepted Buckingham's conclusions as their own; as a result, they did little to investigate the possibilities of a jet power plant for aircraft. The LMAL had one comparatively small research division devoted to engine research, but the outlook of its members was "slaved so strongly to the piston engine because of its low fuel consumption that serious attention to jet propulsion was ruled Out. 12 What little research the lab did do on the subject was done by aerodynamicists, an interesting historical fact, given that the turbojet revolution happened elsewhere largely as a result of investigations made by aerodynamicists, not propulsion experts.13
In 1926 and 1927 Eastman Jacobs and James Shoemaker experimented with "thrust augmentors" for jet propulsion at Langley. The idea behind the program was to increase the mass of the airflow involved in the propulsion process by equipping a conventional gasoline engine with a special device that admitted additional external air and caused it to mix with a primary jet. Jacobs and Shoemaker thought that the momentum and energy relationships involved in this process would permit some augmentation of aircraft thrust. Although preliminary data from a specially built test apparatus indicated that it was possible to increase the thrust of a jet by using suitably designed high-speed nozzles, results warned that the maximum increase of thrust was too small, considering the dimensional and weight limitations of conventional aircraft, to achieve a worthwhile net benefit.14
During this same period, the NACA received a proposal from one Lt. Sidney P. Vaughn, an obscure supply corps officer stationed at the naval air station at Pearl Harbor, for research on a gas-turbine jet engine for aircraft. The Committee sent a copy of Vaughn's proposal to Langley; Carlton Kemper and William Joachim, two power plants engineers, reviewed it. Both of their evaluations were negative. Kemper concluded that the [226] proposed jet was "impracticable" because "the use of a turbine installation with the present low efficiency, excessive weight and high speed would give an installation having a lower overall efficiency than the present internal combustion engine and propeller." Joachim's remarks were equally conservative. He listed as the chief factors preventing favorable comment:
Eastman Jacobs also read Vaughn's proposal, and though his evaluation was not entirely positive, neither was it closed-minded. He said that "the question of whether or not this system is of practical value cannot be answered without a consideration of the efficiency of the system." Because there were no experimental data available which were strictly applicable to the proposed system under consideration, Jacobs recommended, in March 1928, that "some simple tests" be made to furnish "definite information about the efficiency of such a device."15
Henry Reid agreed not with Jacobs but with the engine experts. Because no form of jet engine at the time seemed to offer any theoretical advantages over the conventional gasoline engine, "with the possible exception of [in an application for] very high-speed military airplanes," the LMAL engineer-in-charge advised NACA headquarters that the laboratory "should not undertake further investigations of jet propulsion at this time." 16 Headquarters concurred. In the early 1930s America's young airlines were trying to achieve reliable flight at 100 to 200 miles per hour. The NACA had more pressing problems than the development of aircraft for 500-MPH flight at 30,000 feet (where these aircraft would be required to fly to obtain this high speed). Headquarters authorized only three jet propulsion investigations in the early 1930s, all at the instigation of the Bureau of Standards, which carried out the work. Results sustained Buckingham's pessimism.17
In January 1939, two years after Frank Whittle first bench-tested a jet engine, Eastman Jacobs wrote up a job order covering an analytical reevaluation of Buckingham's authoritative 1923 report on jet propulsion for aircraft. Albert E. Sherman, a member of Jacobs's airflow research....
....staff, was to rework the old problem in terms of the 500-MPH speed range then being approached by high-performance airplanes. The engineer-in-charge signed the job order immediately. Besides knowing that the navy had asked the NACA in July 1938 to determine how the exhaust system of a radial engine should be designed to obtain the maximum jet reaction from its waste gases, the engineer-in-charge had just heard from George Lewis that "the Army Air Corps [was] particularly interested in the development of some form of jet propulsion apparatus to be used for assisted take-off."18
On 11 April 1940, a conference was held in Henry Reid's office to discuss calculations reported by Sherman in his paper "Jet Propulsion for Aircraft at Subsonic Speeds"; present at the meeting were Reid, Elton Miller, Carlton Kemper, chief of the engine research staff, and Benjamin Pinkel, his assistant chief, plus Jacobs and Sherman. The six men agreed that jet propulsion now seemed to offer "the possibility of high enough power outputs with little machinery" to make a new experimental investigation desirable. They also agreed that, at the high air velocities through the combustion chamber, to burn gasoline satisfactorily constituted one of the most definite problems. The trailing flame, in particular, might be dangerous.19 Since these men were not yet aware of the rapid progress of.....
....the turbojet in England and Germany, they were considering jet propulsion in the absence of the turbine component. 20
Jacobs and Sherman proposed studying a ducted-fan system that used only dynamic pressure (that is, the pressure was not boosted by a fan) for compression and the Meredith cycle for thrust. (In 1936 Frank W. Meredith had pointed out in England that not all of the waste heat of a piston engine had to be lost when transferred to the cooling airflow of a radiator. If the pressure at the exhaust of the radiator tubes was higher than the free static pressure of flight, some of the dissipated heat could produce a small thrust.)21 Because this propulsion concept was a hybrid whose success depended only upon a creative modification, rather than a replacement, of the traditional aircraft power plant, it seemed a logical choice for the NACA to study. The results of Sherman's preliminary investigation indicated that an airplane having a ducted-fan system installed in conjunction with a good reciprocating engine would be capable of "truly high" power-power that could be used for short bursts of speed in combat, and for assisted takeoffs. When not using jet power, the airplane could revert to its piston-engine power plant, making it capable of great cruising range.22
Construction of a jet propulsion test bed called the "Jeep" got under way as soon as George Lewis gave authority. Lewis had been no great believer in the future of jet or rocket propulsion (like JATO, or jet-assisted [229] takeoff, a system developed later that used auxiliary jet-producing units, usually rockets, for additional thrust); however, he had a tremendous faith in the talents and intelligence of his Langley staff. In 1940, for example, Lewis expressed his opinion to the laboratory that jet propulsion for assisted takeoff was inherently "inferior" to the catapult method. Even Benjamin Pinkel, head of the LMAL engine analysis section, tried to convince the director of research that jet propulsion offered "many advantages" over the catapult method. Jet-propelled aircraft could take off "simultaneously and in rapid succession" in contrast to the "inherent limited capacity and slowness" of the catapult, Pinkel advised Lewis; moreover, catapults required special apparatus easily put out, of commission. 23
Lewis chose not to press his point. He* might not always agree with every person at the lab on technical matters, but he was certainly tolerant and imaginative enough to know that bright members of his field staff should not be discouraged from pursuing ideas in which they believed strongly, as long as those pursuits did not take too much attention away from work on the higher-priority items of the NACA, and as long as they did not cost much money. On 22 April 1940 Lewis sent a letter giving Langley his personal approval to start building the combustion test rig.24
There was no formal assignment of construction funds for the Jeep, so the Langley engineers had to build it mostly out of cheap sheet iron-which made it almost impossible to make the ducting system very efficient. To drive the rig's simple one-stage compressor, they scrounged a spare Pratt and Whitney aircraft engine (rating 450 horsepower) from the naval air station in Norfolk. The responsibility for designing the combustor fell to Carlton Kemper, who had been in charge of Langley's Power Plants Division since 1931. Kemper turned key aspects of this design over to Ben Pinkel.
With very few people inside the NACA or even at Langley knowing anything about this project, and with nothing yet known about the revolutionary progress of European turbojet development, none of these NACA engineers felt any real sense of urgency to expedite their jet propulsion research. While the necessary large-scale equipment was slowly being built in late 1940 and early 1941, Sherman conducted some small-scale experiments consisting of a series of qualitative observations of fuel burning under various windstream conditions. These preliminary experiments gave useful information only about the best methods to be tried later with the large-scale apparatus, if that apparatus was ever completed.25
In early 1941 something dramatic happened to quicken the tempo and expand the purpose of Langley's work on the jet propulsion burner rig. On 25 February Vannevar Bush, chairman of the NACA, received a letter from General Arnold reporting that the Germans were making "considerable progress" in jet propulsion, "both as a means of assisting take-off and as a primary power plant." (This was two months before Arnold discovered that surprising British progress on the Whittle engine.) "In particular," Arnold's letter stated, "the Heinkel 280 is reputed to have been built and tested with experimental rocket motor installations for assisting take-off. Its predicted climb and ceiling will, if obtained, [make] obsolete existing fighter aircraft." Arnold's letter to Bush continued:
In view of the new urgency for an early solution of the "rocket problem," Arnold advised Bush that "further investigation by a large group of able [231] scientists is immediately needed." The most significant point about this letter according to historian Virginia Dawson (who discovered the letter in the National Archives in 1984) is that Arnold addressed it not to NACA Chairman Bush, but to National Defense Research Committee (NDRC) Chairman Bush (as Bush also then was). In paragraph three Arnold made it clear that the army wanted the NDRC, not the NACA, to take over the research on "the general questions dealing with jet propulsion and rocket motors." While the army "realized that any application of rockets as a means of assisted take-off for aircraft ... is properly a function for investigation by the National Advisory Committee for Aeronautics," Arnold felt that "the general questions dealing with jet propulsion and rocket motors, i.e., fuels, efficiencies, weights, basic materials, etc., could properly be investigated by the National Defense Research Committee." His argument was that "the basic problem of rocket propulsion ... has to do essentially with National Defense"; it was not "exclusively restricted to aircraft in its application." 26
Dawson has also found Bush's response to this urgent request by the Air Corps chief, who on 10 March did not yet know about the Langley project. This document shows that Bush agreed with Arnold "entirely in regard to the importance of this subject and the need for immediate steps to evaluate." It shows that he recommended, however, that, since the problem of aircraft propulsion fell "outside the scope of the NDRC," the "best way to do this [was] by setting up a special committee in the NACA organization." 27
A week later, after taking up the issue with Rear Adm. John H. Towers, chief of the Bureau of Aeronautics and a prominent member of the NACA, Bush expanded the scope of a recently constituted NACA subcommittee on auxiliary jet propulsion. Then on 24 March he established a Special Committee on Jet Propulsion. To head this committee, Bush called from retirement Prof. William F. Durand, a member of the NACA since its beginning and the independent dean of American engineers.28
For Durand, to be 82 years old at the time of his appointment as chairman of the Special Committee on Jet Propulsion was only a matter of counting birthdays. After retiring from teaching at Stanford University in 1924 at the statutory retirement age of 65, Durand had stayed extraordinarily active. Besides continuing as a vigorous member of the NACA, he assumed editorial charge of the Daniel Guggenheim Fund's series of monographs by recognized authorities on aerodynamic theory. He wrote parts of three volumes himself, and translated all of the articles written in French, German, and Italian. This work, which would have done credit to a man less than half his age, kept him fully abreast of current foreign and NACA research.29
Until Bush informed him about it by a letter dated 18 March 1941 (six days before the announcement of the formation of the special committee), Durand knew absolutely nothing, however, about new jet propulsion research at Langley. Sherman's March 1940 report on "Jet Propulsion for Aircraft at Subsonic Speeds"-the only paper yet written dealing with the lab's critical reevaluation of Buckingham's conventional wisdom-had not been published in any form because Eastman Jacobs had believed the report's findings too preliminary.30 And all Durand learned about the Langley Jeep and the project in general before assuming the chairmanship of the new special committee on jet propulsion was that it had "attracted the favorable attention of Dr. Bush." In his 18 March letter to Durand (also found by Dawson), Bush reported that "the group at Langley Field and Jacobs, in particular, have been very active in developing one jet propulsion scheme in which I have acquired a large amount of interest and perhaps even enthusiasm, for it seems to have great possibilities and I cannot find any flaw in their arguments." 31
[233] In order to judge firsthand what role this Langley project might play in America's belated effort to develop a jet-propelled aircraft, Durand visited Langley. He made the visit in late March 1941, even before the inaugural meeting of his special committee. Escorted by engineer-in-charge Reid and director of research Lewis, the professor inspected the unfinished burner rig and talked at length with Jacobs and Sherman. Impressed with the potential of what he saw and heard, Durand asked Reid to have his staff prepare for him a memo with drawings illustrating how the test stand could become more nearly a mock-up of a proposed airplane.
At the first meeting of the special committee in April, Durand used this material to describe the Langley project. He told the panel that he felt a ducted-fan system could be incorporated into a military aircraft in a relatively short time and could give it a performance in some ways superior to that of any existing propeller aircraft. The committee reacted to its chairman's message by recommending, in its first resolution, that the NACA laboratory turn the rig into a nonflying model of a jet propulsion system.32 Thereafter, Langley would conduct its project in strict accordance with instructions given by Durand.
At this time, because of the changed and expanded scope of the research, Langley began to reexamine the character of the whole project. Jacobs, in particular, argued that various parts of the test rig had to be rebuilt and new machinery added into the system if results were to be applied to the design of an airplane that really could be flown. After all, the original purpose of the equipment had been only to demonstrate, first, how well the burning of fuel could be controlled in a high-speed propulsive duct and, second, whether the addition of heat to the burning fuel mixture actually produced the large increases in thrust predicted by Sherman. Now, without even having finished the equipment to make these preliminary investigations, his staff was being asked to transform a raw test apparatus into a geometrically accurate mock-up of an actual aircraft system.33
In the summer of 1941 the Durand committee reacted to military intelligence reports of British and German turbojet developments by recommending that the U.S. military services let contracts to Allis-Chalmers and Westinghouse for the development of contrasting turbojets and to General Electric of Schenectady, New York, for a turbo-propeller. The army apparently did not inform the NACA, however, that a Whittle engine had been sent to the G.E. lab in West Lynn, Massachusetts, for development of a prototype; nor did the army tell the NACA when it placed an order with Bell for the XP-59A. The NACA first heard about this aircraft in May 1942- six months after the army let the contract-when one of its representatives reported hearing rumors of a "Buck Rogers" project at Bell.34
[234] Ignorant of the jet propulsion projects, which the Air Corps was just starting up, the Langley staff worked through 1941 to complete the Jeep. In this effort the staff had the support of the Durand committee. By February 1942 the Jeep was operational, if not always successful. The machine was awesome. It consumed three gallons of gasoline per second and exhausted a gigantic blowtorch that "impressed, and often terrified" spectators and NACA employees alike.35 In fact, many of the machine's early test runs failed simply because the man (usually Jacobs himself) handling the introduction of the main flow of gasoline into the combustion chamber, who was understandably nervous about his responsibility, either jerked the fuel valves open or backed them off too suddenly.36
By the end of the spring, however, most of the Langley test crew had overcome their fears about working with such volatile equipment. By vaporizing the fuel before mixing it with the combustion air, Jacobs had tried to restrict the main fire to an "intense, small, and short annular blue flame burning steadily in the intended combustion space." His idea had been that the blue flame indicated, and was thus necessary for, high combustion efficiency. It is uncertain whether this technique ever succeeded totally. By ensuring proper conditions, however, Jacobs did demonstrate that "a blanket of cool air" could be maintained between the hot gases and the walls of the test stand. Besides reassuring the men involved that their lives were not in danger, this knowledge meant that an airplane having the propulsion system would probably not burn to pieces or explode from its own energy.37
Eventually the Jeep did demonstrate efficient combustion as the result of a liquid injection system designed by K. K. "Nick" Nahigyan of the LMAL engine analysis section. By late July 1942, the basic features of the system appeared promising enough in the ground mock-up to merit instructions from the Durand committee for a design study of an actual flight article, a research airplane incorporating the Campini system.38
By the time it received those instructions from Washington, the Jacobs staff had in fact already been investigating the aerodynamic and thermodynamic characteristics necessary for such an airplane for at least three months. In the course of this study, Jacobs and Sherman had parted company in strong personal disagreement over how the ducted fan should be applied. In March 1940, Sherman had argued that "the application of jet propulsion to the cooling ducts of fast military or racing airplanes for auxiliary emergency purposes appears interesting enough to warrant immediate experimental investigation." This argument for what later became known as an afterburner had appeared in the draft of the report, which Sherman now said Jacobs had "suppressed."39
In early 1942 Sherman had still believed that "the actual flight application of jet propulsion to the cooling ducts of some of our existing fighter ships" was desirable, "if only for morale and research purposes." The application "could be done in only a few months," he emphasized, "as is indicated by the information that I have already acquired experimentally." Specifically, Sherman had recommended that a twin-engine, high-speed medium bomber-a Martin B-26 Marauder in Langley's test flight fleet-be modified to include the auxiliary jet propulsion system, which the Langley Jeep had proved to be "attractive in all respects." With the afterburner, he had predicted that the top speed of the B-26 could be raised in an emergency from 350 to 400 miles per hour, "with the fuel consumption increased by the order of only 300 percent." The jet's average temperature would be approximately 1700 degrees Fahrenheit, but since the unburned portions of the air would be directed along the walls for cooling, there was no reason to fear overheating.40
Because he knew that Jacobs had a much different application in mind, Sherman had executed an end run around his boss and sent copies of his proposal directly to engineer-in-charge Reid and chairman Durand. At the same time he had requested a transfer from airflow research to another division where he could spend more time on his own developing a 12-inch portable combustion tunnel for testing his afterburner idea.41
The jet propulsion application Jacobs had in mind showed more boldness and less concern for precedent than even Sherman's idea: an out-and-out NACA research airplane that not only could test the Jeep concept for propulsive capacity but that also could explore the frontier of high-speed, perhaps even transonic, flight. Though it was NACA policy to stay clear of designing aircraft, the idea of a special high-speed experimental plane had been gaining steam at Langley since 1941. At one of the first meetings of the Durand committee on 22 April 1941, Jacobs had said that with the NACA's new family of laminar-flow airfoils it would be possible to attain approximately the speed of sound in flight.42 And only in flight tests could knowledge of high speeds be gained, for wind tunnel tests in those days provided little if any reliable data at Mach numbers between 0.7 and 1.3 (that is, between speeds 30 percent below and 30 percent above the speed of sound). Later in the same year John Stack, who had worked for Jacobs in the VDT section for most of the 1930s and was soon to become head of Langley's new Compressibility Research Division, suggested to George Lewis a concept for a transonic research airplane (see next chapter).
With Sherman going his separate way toward a specific military configuration, Jacobs put together an experimental jet airplane design team consisting of young engineers Macon C. Ellis, Jr., and Clinton E. Brown. This team quickly decided that it was advisable, for experimental purposes, to keep the airplane small. On the other hand, to obtain conclusive results, the team realized that the plane had to be large enough to carry a pilot and instruments, and of sufficient dimensions and power so that these items would not exert a marked adverse effect on its flight test performance. Most importantly, the designers concluded that in view of the problems connected with the development of radically new airplane types, it was unwise "to complicate and retard the fundamental development by numerous considerations of adaptability to military requirements" or to hamper a project intended primarily to develop the possibilities of an experimental system by "unnecessarily making components, such as a gas turbine-prime mover, which themselves must be treated as experimental," part of the NACA program.43
By July 1942, the team of Jacobs, Ellis, and Brown had finished preliminary plans for a specific configuration of the experimental jet-propelled airplane. The design featured a modified Pratt and Whitney R-1535 radial engine, an advanced type of nose inlet and high-speed cowling, a cylindrical fuselage, a high-shoulder wing (derived from an NACA low-drag airfoil section), a v-tail, and a cockpit for one pilot, as well as a version of the made during a recent test of the....
....Jeep. Because of uncertain values of drag caused by compressibility effects at speeds over 550 miles per hour, the designers could not pinpoint a prediction of the maximum speed of their creation. They did believe, however, that because the same engine in ground tests produced three times the thrust thought necessary to reach Mach 0.75, their small airplane could reach 600 miles per hour. This meant that it "could have really barreled into the transonic region." 44
For a late July 1942 meeting of the Durand committee at NACA headquarters in Washington, Jacobs brought with him a short reel of film [238] made during a recent test f the Jeep. This film demonstrated achievement of efficient combustion in t e Jeep through liquid injection of the fuel. After showing the film, he recommended that arrangements be made with the military services, either jointly or separately, for the immediate construction of his research airplane. Jobs called such a step "the quickest and most direct approach" to the application of jet propulsion to military aircraft and asked for permission t test the stability and control characteristics of a scale model in the LMA 7 x 10-Foot Tunnel.
It was the decision of the Durand committee, however, that Langley extend its jet propulsion work along both Jacobs's and Sherman's lines of research in definite accordance with military objectives made necessary by the war:
Durand asked that Langley send him a short progress report about this parallel work each week. Proceeding further with definite plans for procurement would wait until the results of both design application studies were compared.45
In late September 1942 Durand notified George Lewis that "there is nothing in particular that we, as a committee, can do with regard to the [jet propulsion] projects in the hands of the industrial companies," but that the committee could help the project at Langley. In this letter Durand admitted feeling "a little anxious about Jacobs's work, due to the fact that the Committee is directly interested in that particular project in the sense that its success or failure will react directly on the reputation of the Committee-at least in conjunction with this particular work." Durand told Lewis that he would be "very grateful ... if you will feel entirely free to represent me in connection with this work and guide Jacobs and his collaborators as may seem best to you."46
A few weeks later the Durand committee visited Langley for the express purpose of witnessing a demonstration of the Jeep. Stationed safely some 200 yards behind the monstrous burner, the visiting dignitaries watched Jacobs's experienced crew ignite the engine. Stable combustion was still [239] not automatic inside the apparatus, however, and the test run fizzled. The failed test was a great disappointment to everyone, especially to those aware that just two weeks earlier at Muroc, Bell test pilot Robert Stanley had flown the XP-59A with Whittle engine successfully. The Durand committee returned to Washington gravely concerned over the delays caused by the fickle apparatus and over the loss of innumerable gallons of precious gasoline. (According to Jacobs's staff, much gas had been stolen from the Jeep for use in private automobiles as a result of wartime rationing.)47
Though some members of the research team were growing increasingly dubious about the Campini system, Jacobs continued to have his staff work hard on the Jeep into the first months of 1943.48 Full-scale burning tests resumed. Albert Sherman analyzed the potential of an afterburner in a Bell P-39 airplane.49 Systematic tests of the stability and control characteristics of Jacobs's aerodynamic configuration were made in the 7 x 10-Foot Tunnel, followed by a round of drag tests on the fuselage, tail surfaces, and central wing portions of the scale model at higher Reynolds numbers in the Two-Dimensional Low-Turbulence Pressure Tunnel.50 Though formal work on Jacobs's engine by the engine analysis section ended in December 1942-when the entire LMAL Power Plants Division moved to the new Aircraft Engine Research Laboratory (AERL)-NACA correspondence indicates that Nick Nahigyan in Cleveland continued making tests related to the liquid injection system for Jacobs's jet airplane into early 1943.51
Virginia Dawson thinks that Nahigyan's continuation of work on the Jacobs engine might have been kept a secret from everyone at the AERL except Edward R. "Ray" Sharp, the field manager. Not even Ben Pinkel, Nahigyan's boss, seems to have known about it. Pinkel recalled in a 1984 letter to Dawson that his engine analysis section completed all work on the Jacobs combustor before the division's move to Ohio in December 1942. According to him, all of the section heads of the LMAL Power Plants Division had been called into Reid's office just before their transfer. There George Lewis informed them that the "top military echelon" had instructed the NACA "that the war would be fought with five reciprocating engines, namely, the Wright 1820 and 3350, the Pratt and Whitney 1830 and 4460, and the Allison V 1710, and that all work on jet propulsion [could] be stopped in order that all effort [could] be directed toward those reciprocating engines." In Pinkel's mind, then, there was "no useful purpose for further work on Jacobs' engine following our successful demonstration of principle" to the Durand committee in July 1942.52
The proscription of further jet propulsion work may have applied to the AERL but not to Jacobs and his staff at Langley, whose overall airplane design was unknown to those power plant engineers brought in [240] periodically to assist on specific engine components. Records show how strongly committed to the Campini system Jacobs and the NACA as a whole remained even after the transfer of the Power Plants Division to AERL. During a visit to Wright Field in January 1943, Jacobs advised Air Corps officials that the Durand committee still supported the experimental airplane idea, as did NACA chairman Hunsaker and director of research Lewis. Jacobs argued that the best way of obtaining the flight article, the research airplane, would be "to have an airplane company appointed to work on the design of the airplane with [the NACA] and then take over the construction." Upon returning to Langley, Jacobs reported that "Wright Field was convinced that flight tests should be made, but was apparently not certain as to how the work should be prosecuted." He believed that "Wright Field would be inclined to build a complete military version rather than building with the least expenditure of effort and time a purely experimental flight article."53
The Langley jet propulsion project died in March 1943 when the military services turned down the NACA's request to construct Jacobs's research airplane:
Certain features of the NACA Jeep interested the services enough for their representatives to recommend jointly that "further investigations be made in order to explore the possibilities of increasing the ratio of thrust to weight." If the NACA could show this ratio to be comparable to those of other types of jet engines, or if the ducted-fan scheme could be modified to show "compensatory advantages," there would then be "ample justification for reconsidering the proposed design application." And since wind tunnel data in the transonic range were not available, and conventionally powered test aircraft were too slow to perform the needed research in actual flight, the services advised the Durand committee, finally, that "a jet-propelled airplane now under construction" should eventually be made available to the NACA. The airplane being referred to was most likely the XP-80, the first U.S. airplane conceived from the beginning for turbojet propulsion, the design of which had just gotten under way for the Air Corps at Lockheed's plant in Burbank, California.54
[241] Langley received word from NACA headquarters on 23 March 1943 to hold the jet propulsion project in check pending further action. A few weeks later, the lab also learned that neither service was interested in Sherman's speed booster application. In May Sherman resigned "to go into another business." Jacobs's immediate reaction was to write a memo in which he charged bluntly that the army and navy were making a big mistake. In concluding that the NACA's proposed experimental airplane was deficient in thrust relative to its weight, the services were comparing "uncertain development projects with a conservative straightforward engineering design which has been partly tested and could be readily constructed by straightforward means and for which we have every reason to expect large gains in performance." The services should do the developmental work only "after the experimental airplane has served its purpose and while the system is being developed for application to a military airplane." In response to a suggestion by Durand that a lighter burner unit might satisfy the military requirement, Jacobs stated that "any gain here would be relatively small." The power-to-weight ratio could not be increased markedly by decreasing the weight of the structure. That feat could only be accomplished by "going over the entire airplane and ruthlessly sacrificing other things." Jacobs doubted whether such alterations in the end would even appear desirable. At any rate, his experimental airplane already showed "ample thrust for its weight." There was no good reason to make the design "less practical or conservative" in order to gain a better ratio of thrust to weight.55
Jacobs's reaction, especially the phrase "uncertain development projects," implies that he and his colleagues at Langley were still unaware of how far along G.E. and others had come in achieving a successful gas-turbine form of jet propulsion for aircraft. They apparently did not know that the U.S. military was well on the way to having its first jet fighters, with the Bell XP-59 having flown in 1942 with a full armament system and the Lockheed XP-80 under development. The only explanation for Langley's lack of knowledge about these things in the spring of 1943 is that General Arnold and others had been keeping the NACA in the dark. Historian Alex Roland believes that this was in fact the case:
In June 1943 NACA chairman Jerome Hunsaker complained privately:
Roland explains these facts by suggesting that Arnold had lost faith in the NACA. A less controversial explanation is that Arnold and other military leaders felt that it was more dangerous to confide top secret information to the civilian research agency, and thus increase the number of potential leaks, than it was to keep the NACA research staffs ignorant of military programs to develop jet aircraft. This policy helps to explain the army's polite tolerance of the LMAL Campini project in 1941 and 1942.
Other documents dug out by Dawson suggest that Durand knew about the secret military developments just about as they happened, but could not share his timely information with the NACA staff. On 27 February 1942 the chairman of the Special Committee on Jet Propulsion had asked Maj. Gen. Oliver P. Echols, USAAC, for permission to circulate test results among G.E., Westinghouse, and Allis-Chalmers, the three companies secretly and independently involved in jet engine development. "Of course," Durand had added, "this request has no relation whatever to the particular project sponsored by the Army, now being carried on by the General Electric organization, and of English origin [emphasis added]. It relates solely to [243] the projects which have been developed as a result of meetings of the Jet Propulsion Committee."58
When the Bell XP-59A, powered by two G.E. I-A Whittle turbojet engines, made its first successful flight test at Muroc Dry Lake, California, on 1 October 1942, Durand had been there to see it. He wrote four weeks later to Colonel Keirn, the army officer at Wright Field who had brought the plans of the Whittle engine from England a year earlier:
Jacobs and a few other privileged members of the Langley staff heard about what Durand saw only in the summer of 1943 when the military changed the Whittle project from secret to confidential.
Since the policy of secrecy regarding jet propulsion research and development in America contrasts sharply with the policy of a relatively free flow of information within the British aeronautics community,** the wisdom of Arnold's keeping the NACA ignorant of U.S. military programs can be debated. What seems beyond debate, however, is that researchers at Langley laboratory, fully supported and regularly monitored by the Durand committee but with far too little knowledge of the overall turbojet revolution and its security problems, worked through 1941, 1942, and the first three months of 1943 on a questionable system of propulsion that seemed to cancel out the advantages of both the pure propeller and the pure jet.
This fact raises a provocative but unanswerable set of "what if" questions: What if the research staff at Langley had known more about the most recent developments in turbojet technology? Would they still have worked so hard on a jet propulsion system based on the principle of the ducted fan? Would they have made major changes in the system? Would they have abandoned the concept behind the system altogether? Would they still have proposed the construction of a small experimental airplane, or would they have embraced the idea of a complete military version? If the army had shared its intelligence with the NACA through proper and [244] secure channels, would the NACA have leaked the information or simply have improved it?
There are good reasons to think that Jacobs and most other NACA engineers would have turned away from work on the ducted fan much earlier if they had known more about the progress of turbojets. Jacobs today recalls thinking about the potential of gas turbines in the late 1930s, during the period when he was working with Wasielewski on the axial-flow compressor. He and his colleagues had even thought about using a gas turbine to drive the compressor of the Campini system.*** But they decided against this on the technical judgments (erroneous as they turned out, but not farfetched at the time) that the material and fluid-mechanical problems of the turbine were too intractable and that the extra machinery would simply weigh too much for practical application to an aircraft.
In the summer of 1943 Jacobs journeyed to Great Britain, where he spent two weeks in London, one week at the Royal Aircraft Establishment in Farnborough, and a day at Cambridge. At one of these places, he saw aerial photographs of German aeronautical centers which showed scorch marks on the ground thought to be the tracks of jet exhaust. Jacobs also found out a good deal more than what he already knew about the Whittle engine and its applications.60
With this new insight into the state of foreign turbojet technology came a new argument from Jacobs in protest of the military's decision to kill his experimental airplane idea: in subsequent written and oral reports to the NACA about his visits, Jacobs observed that the British were making the same mistake as that already made by the U.S. military in turning down the NACA research airplane proposal; that is, "the mistake of applying the new power plants to more or less conventional airplanes rather than giving careful consideration to essentially new extreme-performance types" made possible through the use of new power plants. He concluded that both in England and the United States "the development of the jet power units themselves had progressed beyond the development of suitable airplanes to employ them." If a system as new as the turbine engine were incorporated without accompanying changes in the principles of the airplane's aerodynamic design, there would be such an imbalance between power plant and airframe, Jacobs feared, as to make both propulsion and aerodynamics ineffective. What was needed, Jacobs emphasized, was a unified cooperative program among the military services, aircraft [245] manufacturers, and the NACA, "with a view toward producing quickly extreme-performance airplanes of several types to be developed around existing units and suitable to exploit to the full the capabilities of those existing jet-propulsion power plants."61
In using this last phrase, Jacobs was almost certainly thinking of turbojets of the kind he had seen in England. As a result of his growing awareness of the advanced state of the new engine technology, Jacobs now shifted his attention away from the power plant problem, which had preoccupied him on the Campini project, to the problem of fully utilizing the overall potential of jet aircraft. This was the natural thing for an aerodynamicist to do. But not once in 1943 did Jacobs confide in his airflow research staff anything about his knowledge of British turbojets; for an NACA researcher accustomed to the free exchange of information at least among his own staff, this was most unnatural.
He never did acknowledge that his ducted-an research airplane concept was unworthy of additional consideration. In a personal letter to George Lewis written in England, Jacobs related that the people at the Royal Aircraft Establishment
Lewis agreed with Jacobs, telling his engineer in July 1943, "I have always felt that if a jet-propulsion device was to be considered at this time for a single-engine airplane, and if range was an important factor [which it was not], your particular scheme offered the best opportunity of answering the requirements." 62
This chapter is meant to enrich historical understanding of the NACA's failure to discover jet propulsion, not to explain it away. Nothing can do that. One of the main points of Edward Constant's book The Origins of the Turbojet Revolution is that the turbojet revolution began with the vague feeling of a few farsighted European aerodynamicists that something anomalous was about to block the further progress of aviation to higher and higher speeds and that only a radically new type of power plant such as the turbojet could resolve the anomaly and ensure progress. Since aerodynamics....
...was the NACA's forte, failure here to presume the anomaly before it became an actual problem appears all the more glaring.
The NACA soon made up for the failure, however, by having its three labs shift focus from the old to the new technology and come with skills and alacrity to the aid of American turbojet development. Subsequent history proves that it was this type of flexibility, not the more radical type that first led certain Europeans to explore turbojets seriously, in which the NACA research staffs excelled.
NACA senior staffers in Ohio, California, Virginia, and Washington, D.C., received their first briefings on the General Electric and Bell turbojet projects in late 1943. At Cleveland, Colonel Keirn swore AERL team leaders to secrecy and then showed them a special test cell designed at West Lynn. The army delivered a G.E. I-A turbojet to the AERL in early 1944 under heavily armed guard. Tests were then made confidentially in the Altitude Wind Tunnel, which was built for the study of liquid-cooled engines [247] under altitude conditions, to check G.E.'s refinements of the Whittle 1-14, 1-16, and 1-40 engines. Members of the AERL staff also collaborated with manufacturers in the design of combustion chambers for proposed new engines.
The postwar turbojet revolution affected the Cleveland laboratory more completely and directly than it affected either of the other two NACA labs.63 When the war ended in August 1945, the AERL underwent a sweeping reorganization known by insiders as "The Big Switch." As John Sloop, who headed the group at this lab working on ignition problems during the war, described it: "Overnight, research emphasis shifted from piston engines to jet engines (turbojet and ramjet) with some work on rockets." In the process, the name of the institution was changed to the Flight Propulsion Laboratory (and in 1948 to the Lewis Flight Propulsion Laboratory), the entire work force was reassigned into four new divisions, and top administrators lost or gave up their posts. The Big Switch caught everyone by surprise, especially the lower-level supervisors. Sloop recalled going home one night "deeply engaged in writing a report on spark plug fouling to find in the morning that [his] desk was in another building and [he] was now officially engaged in rocket engine cooling research."64
Though the AERL was most directly affected, Ames and Langley had also become actively involved in developing the technology of jet aircraft starting in 1944. As one would expect, the contributions of these two laboratories mainly involved aerodynamic analysis of turbine engines, compressors, and complete jet aircraft configurations. In May 1944, for example, Langley put the Bell P-59 through drag cleanup in the FST.65 Swept wings, with new flap systems and other high-lift devices, and narrow streamlined compressor units that could be buried cleanly into the wing or fuselage were some of the NACA aerodynamic developments of the midland late 1940s that proved crucial to the ultimate success of the turbojet revolution. With conventional configuration the speed of aircraft would have jumped from the 350- to 450-MPH to the 450- to 550-MPH range because of jet propulsion, but beyond this plateau jet aircraft could not have gone without the breakthroughs in transonic aerodynamics.
It was to this purpose-solving the transonic problem-that NACA Langley had been directing considerable research energy since the late 1930s.
*
Turbine is derived from the
Latin word turbo, meaning whirlwind. The earliest turbojets achieved
their thrusting power by sucking air into the front of the engine,
compressing it, and feeding it into a chamber (or chambers) where the
compressed air was mixed with fuel and was ignited by spark plugs.
The hot gases which resulted from this combustion were piped to a
vane of airfoils, whose rotation ensured an aerodynamically smooth
flow of gas at all engine speeds, and thence expelled into the
buckets of the turbine wheel, whose whirlwind action increased the
velocity of the already rushing exhaust. The gases were then forced
out of the power plant at high velocity (full throttle, at over 2000
feet per second) through a nozzle or tailpipe. The turbojet was long
considered impractical; engine experts felt that the necessary
compressor and turbine equipment would be too heavy for an airplane
and would generally burn too much fuel to be cost-effective. In the
1940s and 1950s, however, the jet proved to have several major
advantages over the conventional reciprocating engine, including the
elimination of the propeller with all its inherent limitations, the
capability of burning almost any type of available fuel (but usually
kerosene), and the power to drive aircraft to supersonic speeds. For
an introduction to the technical details of the turbojet and other
reaction engines, see C. N. Van Deventer, An Introduction to Genera!
Aeronautics, 3d ed. (American Technical Society, 1974), pp.
200-215.
** In Britain, the Gas Turbine Collaboration Committee made sure that British agencies pooled their resources and avoided unnecessary or duplicated efforts. See H. Roxbee Cox, "British Aircraft Gas Turbines," Ninth Wright Bros. Lecture, Journal of the Aeronautical Sciences 13 (Feb. 1946): 53-83.
*** In principle, the only difference between the ducted fan and the turbojet-aside from the dividing-up of the fluid stream in the former (which is not really essential and would be introduced into later turbojets anyway)-was that one drove the compressor with an internal-combustion engine and the other drove it with a turbine.
