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  < Back to Table Of Contents  < Back to Topic: Create & Innovate Plus Home Made Gifts & Games

article number 413
article date 01-15-2015
copyright 2015 by Author else SaltOfAmerica
We Develop Jet Propulsion, 1902-1942
by Robert McLarren
   

From the February, 1945 issue of Model Airplane News.

Introduction

The introduction of successful jet propulsion of an airplane has excited and thrilled aviation enthusiasts, layman and professional alike, throughout the world and has captured the imagination of untold millions.

For forty years we have known the airplane as a combination of a wing and a propeller, the two as inseparably linked as wheels and the automobile. Because there has been nothing different, we could not think of its being different.

Now comes jet propulsion with its complete elimination of the propeller, and to think of an airplane flying without a propeller is an extremely difficult mental problem to most of us.

For the curious, there has been seemingly endless sources of information, and those in search of explanations have found available a complete repertoire of arguments running the gamut from the “simple as ABC” treatment to highly abstruse scientific documents.

In the belief that MODEL AIRPLANE NEWS readers want more than the prevalent “it goes in here and comes out there” type of explanation, and yet do not have the time or accessibility to the more complex analyses, nor the interests in higher mathematics frequently required, we are presenting below the summation of all these documents in a readable yet suitably scientific form.

There can be no doubt that the principles of jet propulsion are complex indeed and that the elements of its system require reference to practically every physical science.

To produce a successful jet propulsion plane, engineers have had to master aerodynamics, thermodynamics, chemistry, physics, statics, kinematics, kinetics, material mechanics, hydrodynamics, metallurgy and additional subdivisions of these main branches of research.

That a successful jet propulsion plane is now flying is a manifestation of man’s intellectual power and a genuine tribute to his five thousand years of progress.

Theory of Jet Propulsion

The more thoughtful students of jet propulsion have made recourse to the three fundamental laws of motion as first stated by Sir Isaac Newton with the realization that any system must be in accord with these three principles.

Newton’s Third Law states, in essence, that for every action there is an equal and opposite reaction. (Careless students too quickly interpreted this law as proof that it is the jet “pushing against the air” that explains jet propulsion.)

It is important to carefully analyze this law and to bear in mind that a force is a mass times an acceleration. A small mass with a large acceleration will furnish an equal reaction to a large mass with a comparatively small acceleration. This basic law may be set down as follows: m1 a1 = m2 a2 and this is the fundamental force equation for any system.

   
Known since ancient times: heat air to increase its pressure and temperature, and eject it through a nozzle at extremely high speed.

Theoretically, then, a small mass (burnt gasses) given a high acceleration (jet) can be made to exert an equal force on a large mass (the airplane) with a small acceleration (airplane speed). This, then, is what makes possible the jet propulsion plane.

Jet Propulsion System

GENERAL—The object of a jet propulsion system is to convert the energy of a gas at high temperature and pressure to the kinetic energy of a jet at atmospheric temperature and pressure. This is accomplished by utilizing air as the working medium, adding heat to increase its pressure and temperature, and ejecting it through a nozzle at extremely high speed.

The only essential elements are a venturi tube (a convergent-divergent tube), a flame and a fuel supply. The German robot bomb is about the simplest example of such a system containing only these elements. It consists of a tube with a series of automatic shutters at the front (convergent) end.

Ram pressure forces these shutters open and introduces air into the convergent end of the tube. Fuel is injected steadily into this chamber and ignited.

The combustion explosion closes the shutters and the gases move rearward, attaining a high velocity at the divergent nozzle.

As the pressure of combustion lessens, ram pressure again opens the shutters and the cycle is repeated. It will be noted, however, that this is not a steady flow process, the mechanism operating by a series of explosions. However, for general considerations, this is the fundamental jet propulsion system and illustrates its simplicity.

It will be borne in mind that, obviously, the gas turbine, air compressor, combustion chambers, etc., are merely more complex accoutrements of a jet propulsion system but are not necessary items for its successful operation.

Why, then, are these various elements used in the Whittle-General Electric Bell system? They are used simply to raise the efficiency of the process, which reduces fuel consumption by increasing the amount of work delivered from a given quantity.

This system consists of:
- an air intake in which a divergent chamber converts the air velocity into pressure,
- an air compressor which increases the air pressure,
- a combustion chamber which adds fuel and burns the mixture,
- a gas turbine which drives the air compressor,
- and the exhaust nozzle which provides the thrust required to propel the airplane.

   
Cutaway drawing shows basic components of the Whittle-General Electric Bell turbine engine system.

The essential elements of a jet propulsion system are the same as in the conventional airplane, although used in slightly different forms and for different purposes.

For instance, a comparison of the jet engine with an internal combustion engine shows that in both we have an intake, a compression, a combustion and an exhaust; and even the carburization of the fuel is similar in both engines.

A propeller is simply a device for displacing a large mass of air rearward, which is the same purpose as the jet propulsion system.

So we see that, in principle, we have nothing new with jet propulsion, merely a slight rearrangement of an existing system.

The efficiency of a jet propulsion system increases as the plane goes higher since the temperature at the turbine remains substantially constant while the temperature of the incoming air at higher altitudes falls off progressively, thereby giving a great figure for the air-in/air-out temperature ratio.

The efficiency is also increased by higher speeds. At low speeds the jet propelled airplane is notoriously inefficient and a propeller-driven airplane has a far quicker takeoff time and much shorter run.

As an example: Assume a Bell P-59A and a Republic P-47 Thunderbolt are tied tail-to-tail on a runway. As both engines are operated at their maximum power, the Thunderbolt would drag the Bell down the runway and into the air!

However, the power of the Bell at high speed is almost beyond comparison, although no ratings have been given its jet propulsion power plant. At high speeds, ram pressure furnishes progressively greater pressures in the intake duct and the acceleration of the system as a whole provides increased kinetic energy.

AIR INTAKE—First step in the process is the admission of air into the system, and the air intake must be so designed as to bring the air to rest with a minimum of deflection and shock resulting in a dynamic compression.

As the incoming air slows to rest, its kinetic energy is delivered in the form of compression and heat, the amount depending upon the speed of the plane. High speeds will result in considerable heat generation from the shock and from friction.

This air intake is actually a divergent section thereby increasing the pressure of the incoming air and acting as a diffuser for the air compressor. Thus, in this initial stage, we have the air compressing itself, giving up its kinetic energy in the form of heat and pressure.

AIR COMPRESSOR—Next step is the compression of the air in preparation for combustion. This takes place through the use of a single-stage centrifugal compressor, although multi stages may be used. The pressure produced by a centrifugal compressor depends on the tip speed of the impeller blades (greater diameter and higher speeds giving greater pressures), the density of the fluid (in this case air), and the design of the blades.

Centrifugal compressors are free of vibration, small, light and with a minimum of friction. The compressed air is delivered in a steady stream and is completely free of oil. The air is drawn in at the center of the impeller and is discharged at a high velocity into an annular diffuser, designed as a scroll. This diffuser reduces the velocity of the air and thereby converts its kinetic energy into pressure.

The actual total pressure delivered is something less than the theoretical, due to friction losses in the fluid passing over the blades, shocks and turbulence caused by the abrupt changes in direction and speed of flow, and losses due to leaks in the ducts.

Air compression is a negative part of the jet propulsion system and requires the expenditure of considerable power, which is lost to the-stream in the form of heat.

   
Centrifugal compressor components. From FAA Powerplant Mechanics Handbook.

When multi-stage compression is made necessary by the delivery pressures required, the axial flow type is normally used in which several impellers are mounted on a common shaft, the air progressing longitudinally through the various stages. These compressors are more efficient than the radial flow multi-stage type but the former have a tendency to pulsate under load and for this reason are only useful in fairly steady flows.

   
Axial flow compressor components composted of alternating rotating (rotor) and stationary (stator) vanes. From FAA Powerplant Mechanics Handbook.

COMBUSTION—After leaving the diffuser scroll of the air compressor the heated and compressed air is delivered to the combustion chambers. The purpose of the combustion chambers is two-fold (1) to impart energy to the air, and (2) to provide a mass of by-products.

It has long been known that heat is convertible into mechanical energy and that these two are mutually interchangeable. The British Thermal Unit (Btu) furnishes an index for this conversion, 1 Btu being the equivalent of 778 ft. lbs. of energy.

Some idea of the power of heat may be gained from the fact that if 1pound of gasoline is burned in 1 minute, more than 500 horsepower is generated. And if this weight of fuel could be burned in 1 second, more than 30,000 horsepower would be produced thereby!

A fuel possesses potential or chemical energy by virtue of the arrangement of the molecules of which it is composed. This energy is released when the fuel is burned and transformed into heat which can be put to useful work.

The burning of a fuel is known as combustion and is the chemical merging of fuel and oxygen accompanied by the rapid generation of heat. The faster this union takes place, the more heat is generated and, therefore, the more work is done.

Speed of combustion varies with the concentration of the molecules of a volume of fuel, which means that the greater the density of the fuel vapor, the greater the heat and thus the use of the air compressor in a jet propulsion system.

As it is merely heat that is desired, the quality of the fuel used is of little importance. However, the thermal cycle must be as efficient as possible in order that the expenditure of energy made will produce the greatest effect.

There is no common substance with greater heating energy for its weight than gasoline, but the cost of a fuel also is an item in an airplane, and if a cheaper fuel will do the job then it is used.

The modern internal combustion aircraft engine is the most efficient power producer known but it demands the finest gasoline that can be produced, 130 octane aromatic fuel being required by some engines.

The most volatile portions of crude oil are condensed by a distillation process to form gasoline. The portions which come off next are called kerosene, which has a slightly lower heating energy but a much slower evaporation rate.

Being cheaper, more easily available at present, and with an almost comparable heating energy, kerosene is used in the jet propelled airplane.

Combustion in the jet propulsion chamber is continuous and has only to be started after which the flame is maintained by the steady delivery of fuel and compressed air.

Following combustion, chemical changes produce carbon dioxide, water and nitrogen, the latter comprising about 80% of the air and, being an inert gas, it does not burn in the process.

The presence of these products in the exhaust indicates the liberation of heat energy. Incomplete combustion produces, in addition, carbon monoxide, methane hydrocarbons and oxygen, indicating un-liberated energy.

A high efficiency of about 30% (heat delivered as mechanical work divided by total heat put into the process) can be achieved by an internal combustion engine.

The jet propulsion engine is limited theoretically to an efficiency of about 15%, which indicates twice as much fuel consumption when using the same fuel as the conventional engine and considerably more when using fuels with less heat energy.

   
General Electric engine rear view shows several combustion chambers around the periphery.

In the design of jet propulsion combustion chambers, several small units are more efficient than a single large one because the power output increases as the combustion chamber volume decreases, and combustion time (rate of burning) also becomes less as the combustion chamber size decreases.

Since a faster rate of flow insures faster burning, the combustion chamber is “streamlined.” Turbulence of the entering air is also of advantage in speeding the burning rate and this is assured by the delivery of compressed air direct from the air compressor.

GAS TURBINE—The gas turbine in the jet propulsion system is a secondary unit which has the sole purpose of driving the air compressor. It is not an essential or primary unit in a jet propulsion system.

However, it has been the development and perfection of the gas turbine that has made an efficient jet propulsion system practical. And perhaps the development of the gas turbine may transcend in world importance the jet propulsion airplane in the not too distant future.

Although a great deal has been published on the various ideas of men who have played a role in the development of the gas turbine, it seems rather strange that these reports have ignored the real father of the gas turbine engine, Dr. Sanford A. Moss, consultant for the General Electric Company.

In 1890 the steam turbine and the internal combustion reciprocating engine began a contest that quickly eliminated the reciprocating steam engine from competition. Although still in use on steam locomotives and on certain cargo ships now in war service, it has been replaced in industry by one or the other of the above.

It soon occurred to engineers that the combination of the high efficiency of the gasoline burning Otto cycle engine and the high efficiency of the steam turbine might produce a power plant with higher efficiencies than either of the existing systems.

Thus the “gas turbine” idea was born and Sanford Moss first thought of it in 1895 while a student at the University of California.

His thesis for his Master’s degree, taken in 1900, was written on the gas turbine subject and covered the design of such a unit with an analysis of the problems involved. Some of us have been fortunate enough to examine this historic document and it represents something of a landmark in gas turbine history although it was by no means the first prepared on the subject.

Possibly the first clearly outlined plan for a gas turbine was set forth by John Barber in a British patent (No. 1833) issued on November 30, 1791 which contained drawings and data for the construction of such a unit. A series of British patents followed, beginning about 1856.

Charles G. Curtiss was issued a United States patent on June 24, 1895 for the first complete design in America. On December 5, 1895 Leon LePontois received a U. S. patent for a combustion chamber designed for use with a gas turbine.

That the gas turbine was the work of many minds is clearly shown by the wide use made of a development in a field separate from the immediate one. Carl Gustaf Patrick DeLaval, eminent Swedish research engineer, had made amazing progress on steam turbine research, an outstanding contribution being his theoretical and practical work on nozzles.

The first DeLaval steam turbine to be shown in America was exhibited at the Chicago World’s Fair in 1893, the principle object of which was to display DeLaval’s nozzle patents. At the close of the Fair the turbine was sent to Cornell University.

Dr. Moss joined the staff at Cornell in 1901 and commenced his first practical gas turbine work. In 1902 Moss borrowed the DeLaval turbine wheel and set up his first gas turbine utilizing a combustion chamber of his own design.

During November and December of 1902 the turbine was placed in operation thus becoming the first turbine wheel operated by the products of combustion in the United States.

   
Dr. Sanford Alexander Moss holding a centrifugal compressor rotor. Dr. Moss developed the first working turbine engine in 1902 although it only had the power to keep itself running.

Dr. Moss prepared engineering drawings of this device and in June 1903 showed them to the General Electric Corp., which hired him as a research engineer. It is significant to note that Dr. Moss has continued this association to the present day, more than 41 years of service!

In 1904, Dr. Moss patented a centrifugal air compressor of his of design used on his gas turbine research. This device showed exceptional promise in other fields and is in use throughout the world today for blast furnace blowing, the only type utilized for the purpose.

General Electric discontinued its gas turbine research in 1907 as experiments had early presented the classic impasse of the gas turbine: the utilization of all the gas turbine power output in operation of the air compressor with no energy remaining for useful work.

(Prime object of early gas turbine research was the use of a drive shaft connected to the turbine wheel for operating a motor or similar mechanism.

(It will be noted that even at this early date, airplane jet propulsion would have been possible through the utilization, as at present, of the exhaust gases after passing through the turbine. In early experiments these were vented off to escape.

(Projected gas turbine prime mover designs today—Allis-Chalmers, etc.—indicate a return to the “turbine-driven-shaft” idea proved impractical at the stage of development extant in 1907. These plans would indicate vastly improved turbine efficiency which is mere conjecture at present—Editor)

Early in World War I, Dr. Moss conceived the idea of adapting his gas turbine principle to the aviation engine which had begun to reveal a serious loss of power at altitude. The obvious solution to this problem was to furnish an air compressor to force additional air into the cylinders.

Several experimenters advanced plans for an air compressor and some were actually installed and placed in use. These were all of the positive displacement type.

Dr. Moss introduced his gas turbine operated centrifugal compressor driven by the engine exhaust. In May 1918 the first turbine driven supercharger was completed and installed on a Liberty motor at McCook Field near Dayton, Ohio, research center of the Army Air Service Engineering Division.

Tests followed atop Pike’s Peak, near Denver, Colorado, and the new device, its name, shortened to “turbo supercharger,” has played a vital and essential role in the story of America’s Air Power in this war, being installed on such famed planes as the Boeing B-17 Flying Fortress, Consolidated B-24 Liberator, Boeing B-29 Super Fortress, Lockheed P-38 Lightning, Republic P-47 Thunderbolt, and others.

In 1925 Dr. Moss applied his centrifugal air compressor to the radial aircraft engine, gear driven from the crankshaft, and this has become standard on all high powered radial engines including the famed Pratt & Whitney Double Wasp, the Wright Cyclone, the Allison, and many others.

Certainly modern aviation owes a tremendous debt of gratitude to Dr. Sanford A. Moss, inventor, scientist and courageous experimenter.

   
Rear cutaway view of General Electric engine shows turbine blades fed by hot air from the combustion chamber (top center) and the long exhaust nozzle.

EXHAUST NOZZLE—The object of the exhaust nozzle is to provide an extremely high velocity to the expanding hot gases delivered from the turbine wheel.

Since the pressure and volume of a gas vary approximately with the temperature, the high temperature of these exhaust gases generate extremely high pressures and large volumes. To accommodate these conditions, an extremely high velocity flow results. Further, since the pressure velocity aspect of a moving fluid remains constant, it is evident that increasing the velocity lowers this pressure even more.

A convergent-divergent nozzle with a constriction, known as the “throat,” provides this high velocity which, added to the velocity mentioned previously, adds up to an astonishingly high speed stream of gases, known as a jet.

Thus the mass of burnt gases and the high velocity of their ejection provides the kinetic energy required to propel the jet propelled airplane forward.

History of Jet Propulsion

The development of aircraft jet propulsion proceeded for many years entirely separate from gas turbine research, and it was actually the combination of these two items that produced the first successful jet propulsion airplane.

The idea of propelling an airplane by a high speed jet originated in France, with Marconnet and Lorin advancing various rough ideas in 1908.

Lorin’s machine was a conventional reciprocating internal combustion engine with long nozzles projecting from the top of each cylinder head. Lying horizontally with the nozzles to the rear, this device featured the “power stroke” of the engine as the escape of the gases through the nozzles rather than the driving of a piston.

These nozzles were tested by N.A.C.A. in 1927 and demonstrated considerable thrust, particularly with a slight redesign by Eastman Jacobs of the N.A.C.A. staff.

World War I produced several good ideas, particularly those of H. S. Harris in England and O. Morize in France.

Little was produced along these lines in the following few years until Secundo Campini, Italian engineer, began theoretical research on an aircraft powered by jet propulsion in 1929. His published report was followed by additional writings in 1930, and in 1932 he was granted a patent clearly outlining a jet propulsion system installed in an airplane specifically designed for the purpose.

In 1933 a patent was issued to Leduc in France for a similar system, and a model of his plane was exhibited at the famous Paris Salon de l’Aviation in 1938.

Campini published additional research data on his ideas in January 1938 and attracted the notice of Gianni Caproni of Milan, president of the famed aircraft firm bearing his name, who hired him as engineer.

Work was commenced on an airplane designed around Campini’s power plant and on August 27, 1940 the Caproni-Campini C.C.-1 made a successful flight of 10 minutes from Forlanini Aerodrome near Milan.

This flight was officially witnessed by General Alberto Briganti, Commanding Officer of No. 1 Air Zone, and was the first successful fight of a jet propelled airplane. This machine was of all-metal construction and weighed 8,800 lbs. It took off with a conventional propeller and switched to the jet propulsion unit while in flight.

   
Caproni-Campini C.C.-2 had a piston engine in front of the jet engine to drive the compressor.

Enthused by this success, the team built a second and larger airplane, the C.C.-2, which weighed about 11,000 lbs. and included an additional seat for a passenger. On November 30, 1941 the C.C.-2 made a successful flight of 168 miles from Milan to Rome including a landing near Pisa. The total time was 2 1/4 hours including the stop, and an average speed of 130 miles per hour was announced.

Col. Mario de Bernardi, well known Italian participant in the Schneider Trophy races, piloted the C.C.-2 with Capt. Pedace as passenser.

Power for the air compressor was delivered by an Issota-Fraschini radial engine mounted within the fuselage. The machine was delivered to the Guidonia Research Center and the war has not permitted further information on its development.

Frank Whittle, in England, joined the Royal Air Force as an apprentice in 1923. He attained the rank of Group Captain in 1930, when he received a patent on a jet propulsion system for aircraft.

In September 1931 he conferred with engineers of the British Thomson-Houston Co., an affiliate of the General Electric Corp., for assistance in preparing a paper for the Royal Aeronautical Society titled: “The Turbo Compressor and Supercharging of Aeroengines.”

In 1933 he was placed on detached service with the Royal Air Force to attend Cambridge University where he furthered his knowledge in mechanical engineering. He was graduated with high honors in 1936 and returned to active duty with the R.A.F.

That same year he again conferred with British Thomson-Houston engineers, laying before them his plan for a jet propelled airplane which he had perfected through the preceding years. This firm engaged in the production of steam turbines and had operated an experimental model at an initial temperature of 1000° F.

Whittle had planned on the use of such high temperatures necessary for any degree of efficiency for his unit, and desired to make use of the firm’s knowledge of metals at high temperatures.

In cooperation, Whittle and the Thomson-Houston Co. began construction of a jet propulsion unit which was placed in operation for the first time in April 1937.

General Electric built the turbine for the Thomson-Houston Co. and took renewed interest in Dr. Moss’ gas turbine research program. Spurred on by their success, the Royal Air Force and the British Air Ministry called in the Gloster Aircraft Company and invited them to join in the program.

Mr. W. G. Carter, Gloster Chief Engineer, designed a single-seat monoplane for the installation of the Whittle unit and a contract was signed for its construction in 1939. The first successful flight of this Gloster-Whittle jet propelled airplane was made in May 1941 with Flight Lieutenant P. G. Sayers at the controls.

   
Gloster-Whittle jet propelled airplane lifts off May, 1941.

The Bell P-59A Airacomet

Several jet propulsion projects were under way in the United States throughout this period and contracts for their construction had been let by the Army Air Forces. When news of this successful flight was received by General Arnold, he called for progress reports from the American researchers and he also visited England and examined the Gloster-Whittle plane and system.

After a careful study of the reports from American contractors he decided to “go ahead” with the Whittle plan in July 1941, due to the urgency of the military situation (five months before Pearl Harbor).

Following his return from England in the late summer of 1941, Arnold held conferences with Maj. General Oliver P. Echols, now Assistant Chief of Air Staff (Materiel, Maintenance and Distribution).

Various civilian engineers were interviewed, and after a careful study contracts were let to the General Electric Co. for the manufacture of the power unit, and to Bell Aircraft for the design and construction of a suitable airplane.

Brig. Gen. B. W. Chidlaw was appointed Liaison Officer for the project, to coordinate the activities at General Electric, Bell, the AAF in Washington, and Gloster and Thomson-Houston in England. Col. Donald J. Keirn was named Engine Project Officer, and Col. Ralph T. Swofford named Airplane Project Officer.

Col. Keirn was sent to England and returned with a Whittle unit on October 1, 1941. General Electric made certain revisions to the unit and the new engine made its first test run in April 1942.

The Bell XP-59, a new single seat fighter design powered by a conventional engine and propeller was selected for installation of the unit, design modifications promising greater speed than the design from scratch of an entirely new airplane.

The Bell P-59A was completed and the General Electric power plants installed in September 1942. The plane was taken in great secrecy to a remote California dry lake bed and ground taxiing tests were made on September 29, 1942.

   
Bell P59A with and escort of a Bell P-63 Kingcobra.

This original model featured an open cockpit in the nose for an observer during these ground tests. A takeoff to an altitude of 1 ft. was made but trouble developed in one of the units. Rather than delay the tests, the engine was shut down entirely and the tests proceeded with a takeoff to an altitude of 2 ft. on one engine!

On October 1, 1942, just a year to the day since the original Whittle power plant had arrived in this country, Robert M. Stanley, Chief Test Pilot for Bell Aircraft, took the P-59A up to an altitude of 25 ft. and landed—the first real “flight” of a jet propelled airplane in the United States. He later went up to 100 ft. and returned.

On October 2, 1942, Stanley “gave ‘er the gun” and made a flight to 6,000 ft., and another to 10,000 ft., thereby removing all doubts about the experimental nature of the airplane.

Later in the day Col. Lawrence Craigie, Chief of the Aircraft Projects Section at Wright Field, went aloft in the P-59A to become the first Army man to fly the plane (breaking the hearts of Chidlaw in Washington, and Kneirn and Swofford in England, all on official business, who had planned on drawing straws among themselves for the honor! All have since flown the plane).

Interesting sidelights on these experiments have come to light: although the plane was covered with a tarpaulin when not in use, a dummy propeller was tied to the nose to allay any suspicions of unauthorized personnel who might get a surreptitious view of it; as each Army officer landed after flying the P-59A, the propeller blades of the AAF color insignia each wore were removed!

The Bell P-59A is now in production though the quantities on order or being delivered cannot, of course, be published because of security reasons. It has been revealed, however, that these planes will be used for pilot training purposes only and will not see action.

It has been revealed, further, that at least one other manufacturer has a jet propelled fighter now flying with performance superior to the P-59A, but speculations concerning the use of an American jet propelled airplane in action in this war cannot be made because of the restricted status of these projects as well as plans for their use.

The story of the jet propelled airplane, like all worthwhile inventions, is a long, tedious one and has required more than a hundred years of painstaking research in many branches of engineering to bring it to fruition.

The news that a successful jet propelled airplane had been flown burst like a bombshell on the world a year ago, but now more of the story can be told. And it is a story, again, of sacrifice and devotion to a goal carrying through disappointments and failures at an amazingly slow pace to eventual victory.

But this program has already produced the centrifugal air compressor, the gear driven supercharger, the turbo supercharger, the gas turbine and the jet propelled airplane—all worthwhile additions to mans possessions.

The years to come will bring further manifestations of this dream and industry will increase its debt to those pioneers of science to whom it owes its creation and development.

   
Bell YP-59A Airacomet.
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