The father of centrifugal jet engines and them axial-flow design

[10020070122]

Whittle's first axial design during WWII was the LR1, using a nine-stage axial compressor plus one centrifugal stage. Von Ohain also designed a hybrid, the HeS 011, but that program was pushed by an RLM requirement placed on Heinkel, so it may have interrupted von Ohain's original plans and didn't have the same self-directed momentum as LR1.

So would LR1 have run into the same kind of difficult tuning and debugging problems as HeS 011 did? In early turbofan thinking, Whittle and von Ohain seem to have influenced each other. For example, Whittle moved away from the ducted-chamber turbofan idea in his patents and toward a mixed-flow approach, while von Ohain appears not to have liked twin-spool layouts and kept a gear-driven arrangement in the HeS 10.

Also, since both men started mainly on centrifugal engines, does that mean their axial designs would naturally be less specialist than the axial-focused designers at Junkers and BMW?

 

[PStickney]

Whittle's first axial design during WWII was the LR1, using a nine-stage axial compressor plus one centrifugal stage. Von Ohain also designed a hybrid, the HeS 011, but that program was pushed by an RLM requirement placed on Heinkel, so it may have interrupted von Ohain's original plans and didn't have the same self-directed momentum as LR1.

So would LR1 have run into the same kind of difficult tuning and debugging problems as HeS 011 did? In early turbofan thinking, Whittle and von Ohain seem to have influenced each other. For example, Whittle moved away from the ducted-chamber turbofan idea in his patents and toward a mixed-flow approach, while von Ohain appears not to have liked twin-spool layouts and kept a gear-driven arrangement in the HeS 10.

Also, since both men started mainly on centrifugal engines, does that mean their axial designs would naturally be less specialist than the axial-focused designers at Junkers and BMW?

Not to mention the Axial Jet Designers at Westinghouse, GE, Lockheed, Northrop, MetroVick, Armstrong Siddely... Who all had axial jets running.
Getting good efficiency and flow stability through an Axial Compressor series is not easy.

 

[10020070122]

Thanks for the reply. I understand how difficult multi-stage axial compressor development can be, but in my view a mixed-flow engine like the HeS 011 would have been even harder to develop. Its first compressor stage was so unusual that a lot of prior experience wouldn't really apply. HeS had two major design teams and still needed about three years just to reach the pre-production stage. If it had been a pure axial design, maybe it would have taken only one or two years to get into pre-production, and that could have pushed them earlier into the pressure-ratio-above-5 range.

 

[10020070122]

Not to mention the Axial Jet Designers at Westinghouse, GE, Lockheed, Northrop, MetroVick, Armstrong Siddely... Who all had axial jets running.
Getting good efficiency and flow stability through an Axial Compressor series is not easy.

Thanks for the reply. I understand how difficult multi-stage axial compressor development can be, but in my view a mixed-flow engine like the HeS 011 would have been even harder to develop. Its first compressor stage was so unusual that a lot of prior experience wouldn't really apply. HeS had two major design teams and still needed about three years just to reach the pre-production stage. If it had been a pure axial design, maybe it would have taken only one or two years to get into pre-production, and that could have pushed them earlier into the pressure-ratio-above-5 range.

 

[Shortround6]

If it had been a pure axial design, maybe it would have taken only one or two years to get into pre-production, and that could have pushed them earlier into the pressure-ratio-above-5 range.

It took the British and American designers until the late 40s to get into the above 5 range pressure ratio. GE started work on an axial flow compressor for the TG-100 turbo prop on July 25th 1941. They were trying for pressure ratio ratio between 5 and 6 and using a 14 stage compressor to do it. It took until May 15th 1943 for the first test engine to run. The engine was first flown Dec 21st 1945 in the XP-81 at about 60% power.
GE started applying what they knew to the TG-180 (J35) turbo jet in May 1943, but now they were aiming at 4:1 pressure ratio using an 11 stage compressor. Things did not go as smoothly as hoped. Douglas got two engines for their XB-43 bomber in Nov 1944 but in ground running one engine failed and shed quite a number of compressor blades damaging the aircraft. Unfortunately they had problems with the next 10 engines and the XB-43 did not fly until May 17th 1946.
Jet engines are complete unit and raising the compression ratio also affects temperatures in the combustion chambers and in the turbine section due to higher inlet temperatures in both sections. If you can't make higher temperature combustion chambers and/or higher temperature power turbines you won't much out of a higher-pressure ratio compressor. You might get better fuel economy but you are not going to get much in the way of increased power or better power to weight.
US axial flow and centrifugal turbo jets both had crappy overhaul lives for much of the 1940s. Higher pressure ratio was not going to solve that and in fact that might make things worse. Jet engines often had lubrication problems due to the high rpm and high heat with resulting bearing failures.
Getting the jets to work at all was a major accomplishment. Getting them to last for more than 15-30 hours was the next major goal. Worring about pressure ratio may have bothered the designers but the more practical engineers wanted more reliability.

 

[10020070122]

It took the British and American designers until the late 40s to get into the above 5 range pressure ratio. GE started work on an axial flow compressor for the TG-100 turbo prop on July 25th 1941. They were trying for pressure ratio ratio between 5 and 6 and using a 14 stage compressor to do it. It took until May 15th 1943 for the first test engine to run. The engine was first flown Dec 21st 1945 in the XP-81 at about 60% power.
GE started applying what they knew to the TG-180 (J35) turbo jet in May 1943, but now they were aiming at 4:1 pressure ratio using an 11 stage compressor. Things did not go as smoothly as hoped. Douglas got two engines for their XB-43 bomber in Nov 1944 but in ground running one engine failed and shed quite a number of compressor blades damaging the aircraft. Unfortunately they had problems with the next 10 engines and the XB-43 did not fly until May 17th 1946.
Jet engines are complete unit and raising the compression ratio also affects temperatures in the combustion chambers and in the turbine section due to higher inlet temperatures in both sections. If you can't make higher temperature combustion chambers and/or higher temperature power turbines you won't much out of a higher-pressure ratio compressor. You might get better fuel economy but you are not going to get much in the way of increased power or better power to weight.
US axial flow and centrifugal turbo jets both had crappy overhaul lives for much of the 1940s. Higher pressure ratio was not going to solve that and in fact that might make things worse. Jet engines often had lubrication problems due to the high rpm and high heat with resulting bearing failures.
Getting the jets to work at all was a major accomplishment. Getting them to last for more than 15-30 hours was the next major goal. Worring about pressure ratio may have bothered the designers but the more practical engineers wanted more reliability.

You're right，I was being too optimistic. What I'm really trying to say is that engines in the BMW P.3306 size and thrust class appeared too late, and Germany ended up losing the initiative in the 4000–4500 lb range. Looking at the development timeline, if von Ohain's team had been able to keep pace with Whittle and complete a pure axial design by the end of 1943, then something like the P.3306 might have entered service earlier, which in turn could have avoided the time BMW spent maturing the 003.Or was the apparent success of the BMW P.3306 due in large part to BMW simply having a stronger technical and engineering team than HeS?