Jet - The story of jet propulsion E-Book

Wolfgang Brix

• Herausgeber: Books on Demand
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch
• Veröffentlichungsjahr: 2023

Seitenzahl: 290

Beschreibung

Flying is today part of our life. We can sit in comfortable seats and reach nearly every destination around the world. Few passengers know that the engines one can see through the cabin window have been invented and built and tested just 85 years ago. At the beginning there were inventors, small engines and small aircraft, which have grown in the course of decades into big aircraft, powerful engines and mighty companies.The story of this development is highly fascinating and entertaining. Who wants to know more finds in this book a lot of informations and technical details. Never before a book with this range of inventors, jet engines, jet aircraft and jet companies has been published.

Leseprobe

Table of contents

1 Introduction

2 The Inventors

2.1 The Jet Engine

2.2 The first gas turbine of Aegidius Elling

2.3 The first jet engine ideas

2.4 The first jet flight by Henri Coanda

2.5 The patent of Maxime Guillaume

2.6 The Stern Report

2.7 The turbine bible of Aurel Stodola

2.8 Alan Arnold Griffith

2.9 Frank Whittle

2.10 Alf Lysholm from Milo

2.11 Herbert Wagner and Max Adolf Müller

2.12 Hans Joachim Pabst von Ohain

2.13 Helmut Schelp and Hans Mauch

2.14 On the way to series production

2.15 BMW in München

2.16 Bramo and BMW

2.17 Junkers in Dessau

2.18 Daimler-Benz in Stuttgart

2.19 Heinkel He S 011

3 The civil jet aircraft

3.1 The first generation

3.2 The second generation

3.3 The three big jets

4 The engine companies

4.1 Rolls-Royce

4.2 General Electric

4.3 Pratt&Whitney

4.4 CFM International

4.5 International Aero Engines

4.6 BMW Rolls-Royce

4.7 Engine Alliance

5 Image Sources, Thanks

1 Introduction

This book tells the story of the development of jet propulsion, from the first ideas over the first flight of a turbojet engine on 27 August 1939 up to the present time, from the Heinkel He 178 aircraft with the Heinkel He S 3 B engine up to the Airbus A380 with the Trent 900 turbofan.

I have pursued this subject over decades. After my studies of aircraft and engine technology at the Technical University TUB in Berlin 1963-1969 I started to work in the propulsion department of VFW in Bremen, later named MBB, DA and finally Airbus Bremen. For 36 years I have studied, calculated and evaluated turbojet engines. I have participated as engine expert in nearly all projects and programs of my company, I have worked for the VFW 614, all Airbus models including the A380, the MPC75 hundred-seater, the European Supersonic Commercial Transport ESCT and the military A400M.

My archive of reports, informations and photos had reached over the years a respectable size and looking at it I had the idea to write a book.

But that turned out to be more difficult and time consuming than I initially thought. As first chapter I chose the inventors, because I had been lucky to attend the symposium “50 Jahre Turbostrahlflug” (50 years of turbojet flight) in München on 26/27 August 1989. On this occasion I got to see among other celebrities the German inventors Hans von Ohain and Anselm Franz. The English inventor Frank Whittle unfortunately could not come. When I started then in 2007 with the deeper study of these gentlemen, they had already passed away and I had to turn with questions, that inevitably arose, to other sources. A great help was Dr.Volker Koos from Rostock, who had already written some books about Ernst Heinkel, his aircraft and engines. With his help I got contact to the family of Hans von Ohain, his son-in-law and to his former best friend. And then it was a great stroke of luck, that in 2008 the son of Frank Whittle gave a lecture in Hamburg about his father and Hans von Ohain.The exchange of informations with all the mentioned persons resulted in an extensive collection of data about the story of the inventors and their inventions.

The content of this book is based on three sources:

My expertise after 36 years of work on the subject

The knowledge of experts and witnesses

The study of publications, brochures, books and online material

The book is not complete. Who ever looked into the „Jane‘s Aero Engines“ or into the „World Encyclopedia of Aero Engines“, will know that the number of built turbojet engines reaches some hundred and must be muliplied by 3 or 5 by the number of variants. My choice can therefore only be a selection. I left out the Russians, for various reasons, and have concentrated only on the important engines and companies of the West. As far as I know, never before have all the great engine companies and their engines been mentioned together in one book. One exception are the big books of Bill Gunston, which are pure encyclopedias without historical background.

I have also left out all Airbus models. About these aircraft there exist so many books, that I could not contribute anything new. But the engines of the Airbus models are all covered in the appropriate engine company chapter.

For each mentioned engine I have made a box of characteristics with the important informations and with a photo. As most engines stem from the English speaking world, I chose the thrust in pound (lb). With one exeption. The dimension Kilopond (kp) and Tonne (to) were common in Germany long time ago, but were given up in the modern world. In the story of the German engines before 1945 there was only the (kp) and here I made an exception and have used the English (lb) and the German (kp).

Concerning numerical values one has to be cautious. Who looks through 10 sources might find 5 or more different values for a date, a thrust or another parameter. Here one has to compare, to evaluate, to find the most reliable value. Even in the internet not all values are consistent. In technical developments the time plays a role. The takeoff weight of an aircraft changes in the design phase every month or every half year and is later in the service depending on other factors.

For all aircraft and engines being built or used in the presence I have tried to find the status of 2022. That year was not any more part of my work, which ended 2005, so I had to use informations from the internet, which change permanently. I have tried to avoid big formulas, but I have produced plots, a graphic can say more than many words.

I wish the inclined reader an entertaining reading pleasure. My goal would be achieved if the reader occasionally thinks: where did he get that from, or: I didn't know that before, or: he explained that well. After my lecture on Hans von Ohain on 27 August 2009 in Rostock, a lady approached me and said: Now I understand how an engine works. I was a little happy and a little proud.

About this book I am also a little happy and a little proud.

Wolfgang Brix

January 2023

2 The Inventors

2.1 The Jet engine

The simplest jet engine is the balloon, well known to all children. When it is blown up and let loose, it flies away, driven by a (certainly small) force, which arises from the air leaving the balloon through the nozzle, the hole by which it was blown up. The thrust is calculated :

In the special case of the balloon there is no inlet momentum (as for the rocket engine) and it follows :

Soon it becomes obvious, that this jet engine is not working for long, the balloon is landing after some seconds in the corner of the room. The reason is evident: the amount of air in the balloon decreases continuously, the pressure decreases continuously and when the balloon is empty, the thrust comes down to zero.

At this point the jet engines are split into two main groups, into the rocket engines, which like the balloon carry the medium of thrust production in their interior and consume it until it is empty. In the rocket this is called burnout. The second group gets fresh supply from the air, in which the aircraft flies. The same amount of air that is producing thrust in the nozzle is refilled in the inlet of the engine.

At high flight velocities, above the speed of sound (Mach=1) the incoming air has sufficient high pressure from the ram effect to keep the engine running and producing thrust. These ram jets do not need any mechanical compressors, the ram has taken this task.

At small flight speeds the ram produces a too small pressure, at take off the ram is zero. If one intends to make the engine running for a longer time, one has to refill the air in the balloon or the engine at the same speed and the same pressure. To do that one needs a machine that produces a defined amount of air at a defined pressure, which is called a compressor. And this compressor needs a powerunit, the energy for the compressor must be generated.

So the task is clearly defined: for a jet engine for takeoff and subsonic speeds one needs a compressor and a power unit to drive the compressor and a nozzle that accelerates the compressed air to the nozzle velocity, producing with mass flow and nozzle jet velocity the gross thrust.

2.2 The first gas turbine of Aegidius Elling

For the propulsion of a compressor a machine is needed, that produces mechanic power and delivers it via a shaft to the compressor. Two such machines are available. The first one is the piston engine, the second one is the turbine, which can be run with any medium, water, steam or air. When the compressor is run with air, the turbine is also running with air, then it is a gas turbine

The different jet engine types

The turbojet engine with a turbine as propulsion for the compressor

The motor jet engine uses a piston engine as propulsion for the compressor

The schematic pictures above stem from Helmut Schelp, member of the RLM (Reichsluftfahrt ministerium 1940).

In 1900 the folowing power machines are known:

The piston engine

The steam turbine

The gasturbine is not yet invented at this time. But soon it is not only invented, but it is built.

In 1903 a Norwegian makes the first contribution on the way to the turbojet engine, he contributes the word „turbo“, the turbine. His name is Aegidius Elling, he is is born 1861 in Oslo and works after his studies at the Christina Technicum 1881 mainly on the field of ship steam turbines in Sweden and Norway. Already in 1884 his first gas turbine patent is registered, but it is not functioning, what he frankly confesses. The next 19 years lie in the dark, but then comes his great day: on 27 June 1903 Aegidius Elling writes into his diary:

„I have made the world‘s first gas turbine which has given positive (excess) power“

Aegidius Elling (1861-1949)

On the left photo one can see the gas turbine of Elling, as it is shown in the Norwegian Technik Museum in Oslo. In the middle it shows the radial turbine and on the left and right 6 radial compressors.

This work of Aegidius Elling is unknown outside of Norway. In the 60s Prof. Dag Johnson writes an article (in Norwegian) about Elling and sends it to Frank Whittle (s. chapter 2.9). When an English version is available, Whittle writes back:

„…I have read the account of Aegidius Eling’s work with great interest and am very impressed by the extent by which he anticipated later events. My impression is that if materials and aerodynamic knowledge which became available to me had been available to Elling the gas turbine would have been with us some 20-30 years earlier than it was. Unhappily he had the misfortune to be many years before his time – as so often happens with major innovations.

Yours sincerely Whittle“

The first turbojet engine first ran at the beginning of 1937, 34 years after Elling’s successful gas turbine run.

2.3 The first jet engine ideas

The very first ideas to solve the task to design a jet engine are certainly lying in the dark of history. Short before 1910 the first proposals appear in the form of articles in special papers or in the form of patent applications. Several Frenchmen are beginning.

In 1908 René Lorin applies for a patent that shows a piston engine that produces thrust by leading the exhaust gases into long nozzles. When the suction of air is done again through the long nozzles, then the flow is an oscillating to-and-fro flow and the question is, whether this produces a thrust.

In 1909 M.Georges Marconnet apllies for a patent which shows several solutions.The Fig.1 shows an engine with inlet 2, compressor 1 and burner 4, the heated pressure air is passing a chamber 6 and goes into a nozzle 8 to produce thrust.The Fig.2 shows a similiar design, where the heated pressure air is splitted by a turning wheel into seperate streams which flow through channels 10 and 11 into the nozzle. The propulsion of the compressor and the wheel is not shown in this sketch.

In 1913 the above mentioned René Lorin continues to work on the idea of a jet engine and applies for a patent of new ideas. In Fig.8 and 10 he shows ram jets with differing nozzles, whereas in Fig. 7 and 9 blowers G do the compression of air. Again it is not visible how these blowers are driven. The proposals are again incomplete and rather sketchy.

2.4 The first jet flight by Henri Coanda

In 1910 a name appears, that is well known today in the world of aviation, but was totally unknown at that time. Also the country from which he is coming has nothing to do with aircraft. The man is Henri Coanda and he comes from Rumania. On the Aviation Exposition 1910 in Paris he presents a complete aircraft that amazes the expert world because it has no propeller.

Coandas flight apparatus is a doubledecker with an extreme slender fuselage and a motor without propeller.

The poster of the exhibition underlines this novum: Seuls Aeroplanes sans Hélices means: only airplanes without propeller. A photo from the days of the exhibition shows in the background the aircraft and on a platform a part of the motor. Dimly one can read: Turbine Propulsive 50 hp.

The poster

The motor

In May 1911 Coanda gets a patent in Switzerland for a propulsion (Propulseur) without propeller. It can be assumed, that this is the motor of his aircraft from 1910. It shows a radial compressor, which ejects the air sucked in from ahead (here from above) over an annular nozzle backward (here downward).

Henri Coanda (1886-1972)

This is the original report of Henri Coanda about his flight on 16 December 1910 :

"It was on 16 December 1910. I had no intention of flying on that day. My plan was to check the operation of the engine on the ground but the heat of the jet blast coming back at me was greater than I expected and I was worried in case I set the aeroplane on fire. For this reason I concentrated on adjusting the jet and did not realize that the aircraft was rapidly gaining speed. Then I looked up and saw the walls of Paris approaching rapidly. There was no time to stop or turn round and I decided to try and fly instead. Unfortunately I had no experience of flying and was not used to the controls of the aeroplane. The aeroplane seemed to make a sudden steep climb and then landed with a bump. First the left wing hit the ground and then the aircraft crumpled up. I was not strapped in and so was fortunately thrown clear of the burning machine".

It is the first jet flight in the aviation history! But not a turbojet flight, this will come on 27 August 1939!

2.5 The Patent of Maxime Guillaume

Maxime Guillaume is born in 1888 in the region Le Berry in France. He studies general engineering at the national school of „Arts et Métiers“ (arts and trade) in Paris. Soon after his studies he writes his famous patent and then dedicates himself to agriculture and goes to Marocco and becomes director and inspector of the plantations in the region of Safi. In 1970 his book is published „The soil makes the climat“ (LE SOL FAIT LE CLIMAT). Twice he is honoured as chevalier. His date of death is not known.

The title of the patent

The only known photo of Maxime Guillaume

The figure in the patent shows clearly a gas turbine, consisting of a compressor, a combustor and a turbine. The components are described in detail :

1) Compressor and turbine are located on a common shaft

2) The stages of the compressor and the turbine are consisting of (turning) rotor blades and (standing) stator blades

3) In the combustor energy is introduced by the burning of kerosen

4) The combustor system consists of a pressurized fuel tank, a valve, a governor and pipes

5) Furthermore there is an electrical device with magnetic igniter

6) The starter consists of a hand driven crank turning the shaft over a gear, a free wheel clutch disconnects the crank at higher speeds

7) The shaft is supported at the ends by ball bearings in a housing

For a complete description of a functioning gas turbine one misses:

1) A description of the gas flow in front of the compressor (called inlet)

2) A description of the gas flow behind the turbine (called nozzle)

Maxime Guillaume takes it very easy to describe his patent: he states that his gas turbine produces a thrust, a propulsion force. He does not mention that this force must be in the direction of the flight velocity, because in the case of bad luck his cycle is so weak, that the jet velocity is below the flight speed and the machine produces a negative thrust, a drag.

Guillaumes description of the force of his invention. He should know the terms thermodynamic cycle, inlet, inlet momentum, gross thrust and net thrust, but he does not know.

to compensate the losses of all natures and obtain the force of the desired propulsion by reaction on air which is composed by the sum of forces by sucking in the air in front of the compressor and the blowing out of the air after the turbine.

Result: This patent of Maxime Guillaume is not yet a tubojet engine. With inlet and nozzle it would be one.

The hand crank of Guillaumes gas turbine shows that the inventor had not the right idea of a turbojet engine. The power of a man could never accelerate such a machine to the needed speeds. Also the same number of compressor stages and turbine stages is rather unrealistic, turbojet engines of today can drive with one turbine stage around 5-10 compressor stages. Only in the case of high bypass engines one fan stage might need 1-3 turbine stages.

2.6 The Stern Report

In 1919 a report is requested by the new founded Air Ministry in England from the director of the South Kensington Laboratory Dr.W.J.Stern. He should evaluate the possibilities of an hypothetic engine with a gas turbine of 1000 hp/PS. The report is ready in September 1920 with the title „ARC Engine Subcommittee Report No 54 „The Internal Combustion Turbine“, Price 2 Shillings“.

Sterns calculations and assumptions are based on the technology of 1920. He takes 500 °C as highest gas temperature, and for the turbine rotor he uses bronze and in the combustor cast iron. For the efficiencies he assumes : „Moreover the compression eficiency of 60 -65 percent can only be obtained for slow speed and and thus very bulky rotors… A compression eficiency of 70 percent…is thus only realisable in the case of large plants with well-designed intercooling between the stages…“

As result of his work Stern writes: „In a submitted design for aircraft the weight of a 1000 hp set comes out to something of the order of 10lb per hp, the fuel consumption being 1.5 lb oil per bhp hour.

That means the 1000 PS gasturbine would weigh 10.000 lb (4536 kg) and would consume 1500 lb fuel per hour (680 kg/h). This result is at that time good news for the producer of conventional piston engines for aircraft. The Internal Combustion Turbine ICT is as competitor so bad that it deserves no nearer study.

The piston engines of that time show a weight of under 1.7 kg/PS and a fuel consumption of 200 g/PS/hr. This results for a 1000 PS motor in a weight of 1700 kg and a fuel consumption of 200 kg/hr. The values of the later flight turbojet engines Heinkel He S 3 B and Whittle W1 show that Sterns weight is by 10 times too high, his fuel consumption is nearly right.

The Stern Report in comparison

This Stern Report is well stored in the Air Ministry, but is never updated. Stern has made no comment about the materials and efficiencies of the future. When Sterns report is taken from the archives in 1929 to judge Frank Whittle it is obsolete by 9 years.

2.7 The turbine bible of Aurel Stodola

Prof. Aurel Boreslav Stodola (1859 - 1942)

Title of one of the first books by Stodola from 1906. From 1905 until 1927 it is published in 6 editions and in 5 languages. The book with over 1000 pages becomes the bible of all steam and gas turbine engineers.

Sir Frank Whittle knows the Stodola book. His son Ian Whittle writes :

„My father certainly had Stodolas relevant books. After he died, amongst much else, I gave his copy of the 1927 Stodola book to the IMechE in London. He (my father) studied the fundamentals of steam turbine technology as a school boy (probably when he was 15 years old)”. That was then in 1922. The Nernst turbine is even shown in Whittles book “Gas Turbine Aero Thermodynamics (left figure).

Dr. Hans von Ohain might have known the Stodola book, because here he might have found the Nernst Turbine which becomes the starting point of his inventions (right figure).

Sir Stanley Hooker, later chief of Rolls-Royce and Bristol Engines, starts his career with the lecture of Stodolas book, because he has no idea of superchargers and radial compressors. He writes :

“ I had never even seen a supercharger, and had no idea how it managed to compress air by centrifugal action. I rushed to the library and borrowed two books, The internal Combustion Engine, by D.R.Pye and Stodola’s great work on Steam Turbines.”

This extremely simple idea of Walther Nernst (Nobel prize winner 1920 for the 3rd Main Sentence of Thermodynamic) becomes the starting point of the inventions of Hans von Ohain, of Frank Whittle and the career of Stanley Hooker.

2.8 Alan Arnold Griffith

Dr. Alan Arnold Griffith (1893-1963)

Alan Arnold Griffith belongs into the inner circle of the jet engine pioneers, although he has built his first complete engine after 1939 at Rolls-Royce. His great credit lies in the development of compressors and turbines, he is the first to propose the gas turbine as aircraft propulsion. The chance of his life is a meeting with Frank Whittle in 1929, who presents his invention and is rejected by Griffith. Whittle has to wait until 1936 to proceed with his idea and Griffith makes a break until 1939.

After the studies of engineering and a promotion at the university of Liverpool Griffith starts his career at the Royal Aircraft Establishment (RAE, a research institute of the Defence Ministry) and works for nearly 10 years on the field of metallurgy, metal fatigue and crack propagation. Then he changes completely the subject of his work and writes in 1926 a paper entitled "An Aerodynamic Theory of Turbine Design". He shows that the low efficiencies of actual compressors and turbines (60 %) can be explained by the fact that they operate in a stalled state. He proposes to design the blades as small airfoils. He predicts efficiencies up to 90 % and that with such efficient compressors and turbines the design of gasturbines could be possible to drive an aircraft with propellers.

Before Griffith the subject of „Gas turbine for aircraft“ has only once be treated: in the Stern Report of 1920, just mentioned before. Sterns paper is always held up like a catechism, when this subject is dicussed, even 10 – 15 years after its publication.

In October 1926 Griffith presents his idea of an aircraft gas turbine to a committee consisting of the Air Ministry and the Aeronautical Research Committee (with representatives of the industry and the universities). At the end of the day it is proposed, first to make some tests with components. A stationary cascade and a model of a compressor+turbine with a diameter of 10 cm (4 inch) are tested in 1929 and achieve an efficiency of 91 %.

His first goal Griffith has achieved, but then he gets stuck. In his calculations and considerations about axial compressors he finds that in the off design opration the efficiency drops dramatically, leading to the conclusion, that such axial compressors are impractical and inefficient. But then Griffith finds a solution: the „Contraflow Engine“. Here each compressor stage has its own shaft and turbine stage. At the end of the compressor the flow is turned in the combustor by 180° and flows now in the opposite (contra) direction through the turbine stages which are located at the tip of the compressor stages. The supposed problem of efficiencies is solved, but with the prize of extreme complexity, which later makes the idea fail.

The Contraflow engine , the propeller shaft is not shown

In 1929 Griffith writes a second report entitled „The present position of the internal combustion turbine as a powerplant for aircraft". He presents the Contraflow engine as gas turbine with propeller and thinks that it is superior to the piston engine in important points.

At the end of 1929 the historical meeting between Griffith and Whittle takes place. Whittle has shown his idea of a jet engine first to a comrade, and then the local commandant gets informed who is also excited and arranges a visit to the Air Ministry. There Whittle meets a technical officer, who takes him to Griffith, of whom he knows he is interested in gas turbines.

The judgment of Griffith is total rejection. Griffith finds a greater error in the calculations of Whittle and is principally against the use of a pure jet. One can assume that Griffith can calculate the thrust of the a nozzle jet, as in his own idea, but he sees problems, when the jet blows onto the grass of the runway. Partly Griffith repeats the arguments of the Stern Report, which are now 9 years obsolete, although these are also against his own idea. Why in the end Griffith rejects Whittles idea, is a mystery until today. Whittle later supposes a mixture of incompetence, professional envy and intellectual dishonesty.

At the beginning of 1930 the Aeronautical Research Committee meets again and evaluates the results of the tests and a new report of Griffith. The final judgment is again luke warm. The superiority over the piston engine is not understood and it is not recommended to spend greater sums of money for the development of this engine. As consolation it is proposed to build a test version of that Contraflow engine and to do combustion tests.

Griffith is so deeply discouraged that he stops all work on the sector of gas turbines for aircraft. The proposed Contraflow compressor is later designed 1938 by the RAE, built by Armstrong Siddeley and tested by the RAE with little success. The blading is not good and the leakage beween the stages is higher than anticipated.

In June 1939 Griffith changes to Rolls-Royce, where he can work with great success, here he finds more expertise, more money and more enthusiasm. In the next years he contributes to the development of the engines Avon, Conway, RB-108 and the programs of civil vertical take off and supersonic flight. In 1960 he retires and dies 3 years later.

2.9 Frank Whittle

Sir Frank Whittle (1907-1996)

Frank Whittle was the English inventor of the turbojet engine. Credit is due to him for writing the first patent of an aero-engine producing the propulsive force through jet reaction rather than the propeller – patent application accepted 16 January 1930. This pilot and RAF officer is ahead of his time by five years. Few understand him and funding is not forthcoming. He has to wait several years and fight much opposition before entrepeneurial support materialises.

His first patent expired at the end of 1933. The first version of his engine was run on 12 April 1937 nearly at the same time as the first engine of the German inventor Hans von Ohain. However, the race for the first flight of a turbojet aircraft is claimed by the Germans when, on 27 August 1939, the Heinkel He 178 takes to the air for a brief six-minute flight. The engine He 3 B had been bench tested 10 hours.The English Gloster/Whittle E.28/39 follows 1.5 years later on 15 May 1941 – propelled by a safe pilot-friendly engine Whittle W1 that had been bench tested for 25 hours prior to a clearance being granted for ten hours of flight-testing.

After three years as an RAF Apprentice, Frank Whittle had been posted to the RAF College at Cranwell in 1926 – training to be an officer and pilot. Subsequently, he was assessed as above the average to exceptional in his flying duties but was warned against over-confidence. During his final terms at the college he demonstrated his written capabilities. His first thesis covered the subject: "Chemistry in the Service of the RAF". His second was entitled: "Future Developments in Aircraft Design". This latter paper, now housed in the Science Museum archives, largely deals with high speed flight at high altitudes. He exceeds the existing state of aeronautical technology. The fastest fighters of the Royal Air Force could only achieve 150 mph (240 km/h). If supercharged, they attained altitudes of up to 27,000 feet (8200m). Whittle is thinking in terms of 500 mph (800 km/h) at much higher altitudes. Like many others who think about faster aircraft, he concludes that the piston engine plus propeller cannot fulfil the requirements. As alternatives, the rocket engine and the gas turbine are considered – the latter being combined with the speed-limiting propeller.

The gas turbine of that time was only established as a high-weight stationary machine. An application for aircraft had been examined by Dr. Stern of the Royal Aircraft Establishment (RAE) in 1920, but assessed as too heavy, too large and too fuel-greedy. However, Dr. Griffith (also of the RAE) submitted a report in 1926 wherein he recommended that research into the aerodynamic characteristics of the axial compressor should be undertaken. Griffith had a vision: That a compact and efficient gas turbine engine could be created for aeronautical application if axial-flow compressor technology were sufficiently improved. His focus was on a form of turbo-prop.

Toward the end of 1929, Whittle is transferred to the Central Flying School at Wittering where he is trained to become a flight instructor. And it is here that he finds time to give further thought to the propulsion of a fast high-altitude aircraft. He goes the same way that others also find, he starts with the well known piston engine, which looses perfomance at altitude, he adds the supercharger, a kind of precompressor, driven by the piston engine and he installs both units in a nacelle, containing an inlet and a nozzle. His calculations show, that the propulsion force of the jet by the thermic energy of the piston engine is not sufficient, but can be enforced by additional burning of fuel in front of the nozzle. The result is a heavy machine with excessive fuel burn. The Italian Campini comes 10 years later to the same result and goes the way to the end and flies that propulsion in a special aircraft.

Frank Whittle is not yet happy with the fruit of his thoughts. And then the penny drops, as he later mentions, he replaces the piston engine by a gas turbine, which drives the compressor and installs the fuel burning in front of the turbine. His calculations show, that this propulsion with a jet is superior to all other concepts. A propeller is not more needed by his jet engine.

The stroke of genius is done, the invention is ready.

The all decisive detail oft his invention is the creation of the propulsion force, of the thrust, with the nozzle jet, to be precise: with the difference between gross thrust and inlet momentum, without the use of a propeller. Only this arrangement deserves the name jet engine. Whittle has found the final end of his thinking cascade, and Ohain and Wagner found it, too, only Griffith sticks to the propeller. Unbelievable that Griffith can calculate his propeller engine and does not find this last step. Or he finds arguments against it. We will never know.

Frank Whittle has spent only weeks (or perhaps only an afternoon) to make his invention. And then for him the old experience starts, that an invention consists of 1% inspiration and 99% transpiration. He reveals his great idea to his comrades, one of them is patent expert, then to a chief, then to the local commandant. All are deeply impressed and offer help. The commandant sends Whittle to the Air Ministry and there he is passed to Dr. A.A. Griffith, who is known as expert, and who has a similar invention in mind. At the end of 1929 Whittle and Griffith meet.