The highly technical and richly illustrated reference book “The Horsepower Battle of the Second World War” by author Calum E. Douglas has been causing a stir in aviation circles for some time. It focuses on the largely unknown but decisive race for the most powerful piston engines for fighter planes during the years 1939 to 1945 – a competition that had a decisive influence on the course of the Second World War. Second World War influenced the course of the Second World War.
In secret, German and Allied engineers were working flat out to develop new engines whose performance would decide the outcome of the air battles. The protagonists – many of whom knew each other personally from pre-war trade fairs and specialist lectures – were in constant technical competition, accompanied by intensive intelligence activities on both sides.
Although the first jet engines had already been developed, all strategically relevant air battles in this global conflict were fought with piston-engine aircraft. Whoever had the more powerful, more reliable engines secured air superiority – and thus had a decisive influence on the further course of the war.
The author Calum E. Douglas
This book is the first to tell the previously unknown story of a high-tech race that took place behind the closed doors of engineering offices and secret services – with the aim of developing the most powerful piston engine of the Second World War.
The examination of the extraordinary personalities who shaped this competition not only illustrates the central role of basic engineering research, but also shows how research can – and cannot – be conducted. At the same time, the work provides new, profound insights into the air war over Europe and expands our current understanding of this central aspect of the Second World War.
Based on years of research in international archives and previously unpublished memoirs of aircraft designers, Calum E. Douglas – a trained British welder, foundryman and later Formula 1 engineer – paints a fascinating 496-page portrait of a fierce competition that sometimes gave the Allies, sometimes the Axis side a decisive advantage.
The work is illustrated by numerous technical drawings, diagrams and original photographs that not only document the events, but make them tangible.
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Douglas comments in the foreword: “The main characters in this story have long since passed away. To compensate, however, I was able to interview Karl Kollmann in his home in Stuttgart. As the son of Professor Karl Kollmann senior († 1988), he carefully preserves all the technical documents of his father, who was head of the design department at Daimler-Benz. I was given access to these documents in order to view previously unpublished data on the Daimler-Benz engine programs and compressor development. Particularly useful were his father’s memoirs, in which he systematically recorded all his knowledge of compressor development during the war. No one has looked into it scientifically or in the media since! Without these documents, I would not even have attempted to write this book.”
The author continues: “I am also indebted to the chief engine mechanic of the Messerschmitt Foundation, Mr. Siegfried Knoll. He allowed me to visit his house and not only photograph original supercharger components, but also provided me with an original Daimler-Benz clutch for the supercharger drive for study purposes – in addition to copies of the original Benz engine manuals. Siegfried was also one of the few people to have flown the Messerschmitt Bf 109 G himself. Accordingly, his advice was invaluable. During the work on this book, Mr. Knoll unfortunately passed away.”
Reading samples:
MAP: “Soon we’ll have a cry for Mustangs instead of Spitfire IXs!”
On June 1, 1942, the British had already correctly predicted that the top speed of the P-51 Mustang would increase from 595 to 692 km/h if the Allison V-1710 engine was replaced by the Merlin 61. In fact, the result was even more astonishing: the Mustang with a Merlin 61 was almost 160 km/h faster at an altitude of 7,620 meters than with the Allison V-1710 engine.
If this was already embarrassing for Allison, it was equally so for Supermarine – because up to an altitude of 9,100 meters, the Mustang was consistently 40 km/h faster than the new Mk. IX Spitfire.
The reputation of Rolls-Royce and the Merlin 61 reached an all-time high. The engine had fundamentally changed the performance of two of the Allies’ most important fighter aircraft within a year. A flood of letters and coded messages circulated between the MAP (Ministry of Aircraft Production), the RAE at Farnborough and North American: Was there a mistake? A measurement error? It couldn’t be that the Spitfire IX had been hit all round. But there was no mistake – and for the rest of the war, the P-51 Mustang was the best Allied high-altitude fighter in terms of range and speed.
The Mustang’s design and resulting performance were so outstanding that its story was used by the US military in 2010 as an official case study to illustrate successful procurement strategies for future fighter aircraft.
Germany: “This is a disaster!”
A shortage of high-quality raw materials and metals placed an increasing burden on the excellent German engine manufacturers. Low-nickel valves, for example, caused latent knocking problems and led to a conflict of objectives between increasing performance and simultaneously decreasing service life. Heavy chrome plating – as on the Allied side, for example on the Merlin – would have been the only correct solution. This was also confirmed by the RLM meeting of May 16, 1942, chaired by General Luftzeugmeister Milch: “The DB 605 engine proved to be very unsatisfactory in terms of operational reliability during testing with the series engines. The reduction of the nickel content of the valves from 15 percent to 8 percent caused the pistons to burn out. An immediate return to the old material is currently not possible. Although stronger pistons have been introduced into series production since April 1942, the engine’s power is initially limited to such an extent that the Me 109 G has the power of the Me 109 F-4 up to full pressure. That is a catastrophe!”
This meant nothing less than that the new Me 109 G only had the same performance as its predecessor, the Me 109 F. The impact of this metallurgical setback on operational performance was dramatic in military terms – and dashed the Luftwaffe’s hopes of maintaining technological advantages in air combat.
An example of insights gained from the author’s research:
With the suicide of Hans Jeschonnek, Chief of Staff of the Luftwaffe (after the first heavy British air raid on Peenemünde on the night of August 17-18, 1943) and the dismissal of Wolfram Eisenlohr as General Engineer, there was at least theoretically a chance for a new start in German aircraft engine development and production – but it was actually already too late.
Germany’s best remaining chance would have been to concentrate all efforts on the further development of the Jumo 213. However, the decision to develop a completely new engine with 1,750 hp in the late 1930s while retaining the three-valve layout was problematic in retrospect.
The Daimler-Benz (DB) engines were particularly susceptible to inferior materials, fuels and oils. In contrast, Jumo was the first company in the world to develop systems such as crankshaft nose oil supply, oil centrifuge and pressure cooling ready for series production.
It is true that Jumo and DB engines used the same cooling concept – a long pipe over the entire length of the engine housing, which supplied the individual chambers with coolant via nozzles, supplemented by a secondary stream flowing through the cylinder walls. However, the higher water pressure used by Jumo played a decisive role in preventing the coolant in the cylinder heads from evaporating – a problem that Daimler-Benz could also have avoided.
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