Did von Ohain ever propose a compact pure-axial turbojet design, and why was the HeS 011 so underpowered for a Class II engine?

[10020070122]

From HeS 3 to HeS 8, every engine von Ohain designed used a centrifugal compressor. The HeS 8 also never really reached its intended thrust, because von Ohain tried to make it as compact as an axial engine, which made the layout overly tight. But if he wanted a compact engine, he could have designed an axial one—and after Müller left and von Ohain absorbed his team, that should have been even easier. This contradiction in design thinking confuses me. So did von Ohain personally, or his core team, ever have a pure axial engine design (even just an internal concept)? And why is the HeS 011's thrust so low for a Class II engine—BMW and Jumo designs were aiming at 4000 lbs+ while the HeS 011 ends up close to the Jumo 004D in thrust?

 

[GrauGeist]

The HeS011 was a hybrid design that incorporated both centrifugal and axial function.

In regards to thrust, you need to take "Thrust to Weight Ratio" into consideration rather than final thrust output.

The HeS8 was actually smaller than the Jumo004 at 30" in diameter opposed to the 004's 32" diameter.

The Jumo weighed 1,585 pounds with a Thrust to Weight Ratio of 1.25 where the HeS8 weighed 838 pounds with a Thrust to Weight Ratio of 1.61 which means the HeS8 was producing more power per pound than the 004.

The He280 performed extremely well with it's HeS8 engines and would have been performing at a higher level if it had been allowed to be installed with the intended HeS30 engines.

The HeS30 had a diameter of 24", which was three inches smaller than the BMW003 and weighed 860 pounds with a Thrust to Weight Ratio of 2.20 (unlike the BMW003' weight of 1,375 pounds and TtWR of 1.13) making it the most powerful of the Class 1 jet engines.

 

[10020070122]

The HeS011 was a hybrid design that incorporated both centrifugal and axial function.

In regards to thrust, you need to take "Thrust to Weight Ratio" into consideration rather than final thrust output.

The HeS8 was actually smaller than the Jumo004 at 30" in diameter opposed to the 004's 32" diameter.

The Jumo weighed 1,585 pounds with a Thrust to Weight Ratio of 1.25 where the HeS8 weighed 838 pounds with a Thrust to Weight Ratio of 1.61 which means the HeS8 was producing more power per pound than the 004.

The He280 performed extremely well with it's HeS8 engines and would have been performing at a higher level if it had been allowed to be installed with the intended HeS30 engines.

The HeS30 had a diameter of 24", which was three inches smaller than the BMW003 and weighed 860 pounds with a Thrust to Weight Ratio of 2.20 (unlike the BMW003' weight of 1,375 pounds and TtWR of 1.13) making it the most powerful of the Class 1 jet engines.

HeS 8 was underpowered overall, and in any case trying to squeeze a centrifugal compressor down to the size of an axial compressor isn't worth it; its pressure ratio is also insufficient, and the HeS 8 seems to have never reached its target thrust. (Of course, I don't deny that the HeS 8 was still excellent for its era.) It would have been better to develop an axial engine directly. Since Whittle also developed the LR1, von Ohain shouldn't have had a "can't design this" problem, especially after absorbing Müller's team. As for the HeS 011, the problem is that it failed to grow quickly to 4000 lbs by 1945, which I consider a sign of failure.

 

[z42]

It would have been better to develop an axial engine directly.

For the reverse argument we had a thread not terribly long ago Germany goes for centrifugal flow turbojet engines?

 

[GrauGeist]

HeS 8 was underpowered overall, and in any case trying to squeeze a centrifugal compressor down to the size of an axial compressor isn't worth it; its pressure ratio is also insufficient, and the HeS 8 seems to have never reached its target thrust. (Of course, I don't deny that the HeS 8 was still excellent for its era.) It would have been better to develop an axial engine directly. Since Whittle also developed the LR1, von Ohain shouldn't have had a "can't design this" problem, especially after absorbing Müller's team. As for the HeS 011, the problem is that it failed to grow quickly to 4000 lbs by 1945, which I consider a sign of failure.

Once again, use the Thrust to Weight Ratio to determine the engine's performance, not final thrust output.

And as I mentioned earlier, the diameter of the Centrifugal engines matched the Axial engine's diameter closely. They were not bulky, but rather less complex and weighed half that of the Axials.

For example, the HeS30 had a diameter of 24" (62cm), an overall length of 8' 11" (2.7m) and weighed 860 pounds (390kg).

Compare this to the BMW003, which had a diameter of 27" (69cm), an overall length of 11' 11" (360cm) and weighed 1,375 pounds (623kg).

Now let's compare these two, performance-wise:

The BMW003's maximum thrust was 1,760 lbf (7.8kn) with a TtWR of 1.13

The HeS30's maximum thrust was 1,896 lbf (8.4kn) with a TtWR of 2.20

Even the HeS8's TtWR was more than the 003, at 1.61

So the bottom line is that Germany's Centrifugal engines were not bulky nor poor performers.

 

[10020070122]

Once again, use the Thrust to Weight Ratio to determine the engine's performance, not final thrust output.

And as I mentioned earlier, the diameter of the Centrifugal engines matched the Axial engine's diameter closely. They were not bulky, but rather less complex and weighed half that of the Axials.

For example, the HeS30 had a diameter of 24" (62cm), an overall length of 8' 11" (2.7m) and weighed 860 pounds (390kg).

Compare this to the BMW003, which had a diameter of 27" (69cm), an overall length of 11' 11" (360cm) and weighed 1,375 pounds (623kg).

Now let's compare these two, performance-wise:

The BMW003's maximum thrust was 1,760 lbf (7.8kn) with a TtWR of 1.13

The HeS30's maximum thrust was 1,896 lbf (8.4kn) with a TtWR of 2.20

Even the HeS8's TtWR was more than the 003, at 1.61

So the bottom line is that Germany's Centrifugal engines were not bulky nor poor performers.

Thanks，you've made a convincing case that Germany's centrifugal line really wasn't weak. So does von Ohain's centrifugal line have a future going forward? I'm more interested in whether the Class I results could carry over into Class II and actually make a breakthrough.

 

[z42]

Once again, use the Thrust to Weight Ratio to determine the engine's performance, not final thrust output.

And as I mentioned earlier, the diameter of the Centrifugal engines matched the Axial engine's diameter closely. They were not bulky, but rather less complex and weighed half that of the Axials.

For example, the HeS30 had a diameter of 24" (62cm), an overall length of 8' 11" (2.7m) and weighed 860 pounds (390kg).

Compare this to the BMW003, which had a diameter of 27" (69cm), an overall length of 11' 11" (360cm) and weighed 1,375 pounds (623kg).

Now let's compare these two, performance-wise:

The BMW003's maximum thrust was 1,760 lbf (7.8kn) with a TtWR of 1.13

The HeS30's maximum thrust was 1,896 lbf (8.4kn) with a TtWR of 2.20

Even the HeS8's TtWR was more than the 003, at 1.61

So the bottom line is that Germany's Centrifugal engines were not bulky nor poor performers.

The HeS 30 was an all-axial design, AFAIU.

 

[10020070122]

The BMW003's maximum thrust was 1,760 lbf (7.8kn) with a TtWR of 1.13

Was the BMW 003A-0's production version derated to lower thrust due to material shortages

It seems the HeS 8 was more of a stopgap design by von Ohain, meant to address the fact that the HeS 30 couldn't be used on the He 280 (at least not at that time).

 

[z42]

I'm more interested in whether the Class I results could carry over into Class II and actually make a breakthrough.

None of the class II engines had much, if any, prospects of reaching service, much less actually making an impact, before the Third Reich was overrun.

A bigger impact could have been achieved by starting to seriously finance jet R&D earlier. But the Germans were planning on a short victorious war, so jet engines weren't seen as that important. By the time this changed, it was too late. Of course, Whittle also had finance problems early on, so this wasn't a uniquely German failure.

 

[10020070122]

None of the class II engines had much, if any, prospects of reaching service, much less actually making an impact, before the Third Reich was overrun.

A bigger impact could have been achieved by starting to seriously finance jet R&D earlier. But the Germans were planning on a short victorious war, so jet engines weren't seen as that important. By the time this changed, it was too late. Of course, Whittle also had finance problems early on, so this wasn't a uniquely German failure.

I think this was mainly because the HeS 011 was overly complex and they didn't abandon that path in time. By contrast, the BMW P.3306 looks like a much more successful approach. If they had stuck with the HeS 8 line and the HeS 30 line instead, how do you think things would have played out?

 

[z42]

I think this was mainly because the HeS 011 was overly complex and they didn't abandon that path in time. By contrast, the BMW P.3306 looks like a much more successful approach. If they had stuck with the HeS 8 line and the HeS 30 line instead, how do you think things would have played out?

The diagonal compressor has received some interest in the past few decades, but today we know a lot more about turbomachinery, we can simulate with CFD, etc. Seems it was a step too far at the dawn of the jet age.

Also, contemporary turbines using both axial and centrifugal compressors invariably(?) have the axial stages first, followed by a final centrifugal stage. The HeS 11 was backwards, starting with the diagonal stage followed by axial stages.

Telling Heinkel they couldn't do engines was a mistake that cost valuable time to rectify.

Who knows, maybe HeS 8 and/or 30 could have been developed into production earlier had they not been canceled.

Also, focusing on improving the existing engines instead of developing new ones from scratch might have been useful. E.g. later versions (G/H) of the Jumo 004 developed ~17kN, about double that of the 004B. Similarly the latter 003 versions substantially increased thrust.

 

[10020070122]

The diagonal compressor has received some interest in the past few decades, but today we know a lot more about turbomachinery, we can simulate with CFD, etc. Seems it was a step too far at the dawn of the jet age.

Using a mixed/diagonal compressor to avoid variable geometry ended up creating problems that were even harder to solve than variable geometry itself.

Also, contemporary turbines using both axial and centrifugal compressors invariably(?) have the axial stages first, followed by a final centrifugal stage. The HeS 11 was backwards, starting with the diagonal stage followed by axial stages.

The diagonal/mixed-flow approach basically dragged Heinkel's engine development down. If the HeS 011 hadn't happened, maybe von Ohain or Bentele could have produced something more advanced—something along the lines of the LR1.

Also, focusing on improving the existing engines instead of developing new ones from scratch might have been useful. E.g. later versions (G/H) of the Jumo 004 developed ~17kN, about double that of the 004B. Similarly the latter 003 versions substantially increased thrust.

The HeS 8 was more of a temporary substitute for the HeS 30 to address the He 280's powerplant issue. Even if its thrust-to-weight was very good, it didn't seem to have much room for further improvement. As for the HeS 30, after Müller left, whether it could have been developed further is anyone's guess.

 

[10020070122]

So did von Ohain or Bentele ever have a pure axial turbojet design on the table, or not?

 

[ThomasP]

My understanding is that von Ohain etal never did more than 'pencil' studies of pure axial flow engines.

 

[10020070122]

My understanding is that von Ohain etal never did more than 'pencil' studies of pure axial flow engines.

What I mean is that, since a contemporary and similarly placed jet-engine designer like Whittle did pursue pure axial-flow concepts, von Ohain, as a pioneer of roughly the same standing, should in theory also have been capable of proposing a pure axial-flow conceptual design. Even if it never developed into a formal project, it seems possible that he may have left behind some sketch-like ideas in his spare time during the HeS 011 program. If it turns out that there was truly nothing at all, that would be quite a pity.