Read the first column in the series: "Genesis of the Jet Age"

Jet engine development started in Germany in the mid 30s and enjoyed generous corporate support. As a result, Germany was the first country to fly a jet-propelled aircraft. However, jet engines were a technological novelty and their technology required many refinements in order to make them ready for field deployment. One of the main problems affecting jet engine development was the exposure of large parts of the engine to high temperatures and great rotational speeds. The compressor and turbine of jet engines were particularly complicated and delicate components operating under high physical forces. German developers faced more difficulties then their colleagues abroad, because the Reich’s Air Ministry decided in 1940 to concentrate R&D on a more advance form of engine – the axial-flow engine. On paper its design was quite straightforward, but in practice its developers were sailing largely through uncharted waters.

The Jumo 004 (front) and Japanese version of the BMW 003 engines. Their slender shape is obvious in this view (author’s collection)

Two big firms lead the way in German jet engine development: Jumo and BMW. In the meantime the Reich’s Air Ministry contracted Messerschmitt to develop the Luftwaffe’s next generation jet fighter – the Me 262. BMW made faster progress and on March 25, 1942, a prototype Me 262 took off for the first time powered by two BMW P3302 development engines. The aircraft was also equipped with a single piston engine as a safety measure. It was a wise move because soon after take-off both jets failed. Major flows were found in the failed engines and BMW’s engineers were forced to redesign most of the engine. The next jet powered test flight took place on July 17 of the same year with two Jumo 004 engines. This flight was successful, but it was clear that much development work was still necessary.

There were multiple problems with the new engines. Fuel flow control was difficult and the engines responded haphazardly and slowly to throttle movements. The engine frequently caught fire or flamed out. Fuel pipe seals tended to burst as result of high ambient temperatures and there were many cases of leaks. Leaking fuel caused frequent engine fires. Turbines and compressors throwing blades caused catastrophic failures. The rotating parts also caused excessive vibrations, which had to be dealt with.

A large portion of these difficulties was caused by the fact that some part manufacture required the use of expensive metals, like chrome, nickel, cobalt and molybdenum. These metals were scarce in wartime Germany so simple metals were used instead in series production engines. Especially problematic was the manufacture of turbine blades from simple sheet steel with aluminum coating. Since the heat resistance factor of these alloys was below the requirement, a special cooling mechanism had to be devised. It was not enough and the average life span of production engines was only 25 hours – mainly because of damage hot exhaust gas caused to the turbine blades.

 

By the time jet aircraft appeared on the front, Germany’s situation was already desperate. Former German generals and historians argued after WWII that faulty decision-making and lack of commitment bore the main blame for the late appearance of German jets. These notions overlooked the nature of jet engine as a completely new and very complicated technology. Furthermore, detailed historical studies prove that developers of jet technology enjoyed generous official support at least from late 1939 and by 1941 the Luftwaffe decided that its new generation fighter is going to be a jet fighter. Well publicized are orders Hitler gave in November 1943 and May 1944 to produce the Me 262 solely as a fighter-bomber. These decisions created only insignificant delay, because the design changes they required were not so difficult to implement. Anyway, at that time the engines were still not ready for series production. As aviation historian Alfred Price wrote: “…at this time (May 1944) the poor reliability of the 004 engines precluded the operational use of the Me 262 in any rule.” 

Hitler reversed his decision after the Normandy landings, but even when they entered service, German jets continued to suffer from the temperamental nature of their engines.  

BMW 003 engine installed on this grounded He 162 last resort fighter (Credit: NARA – public domain)

One interesting and often overlooked advantage jet engines offered Germany was simpler fuel logistics. German jets required no special fuel like piston engines, which required high-octane fuels. The Me 262 was even flown experimentally on crude Romanian oil, experiencing no meaningful problems.

Unfortunately for the Germans, by the time jets started entering mass production, Germany suffered from general oil shortage. As a result, most of the jet planes produced in Germany spent most of their short time-span grounded.

To sum things up, German jet engine development suffered from two fundamental flows:

It can be said that in contrast to what many Luftwaffe generals and scholars argued after WWII, from the technological perspective, German jets came too early. Due to the technological immaturity of their engines they were far from being the technological marvels they appear to be.