Pinnacle of Piston fighter: XP-72 vs Spiteful Mk XVI?

Shortround6 said:

Time machine.

From page 443 of "Vees for Victory"
"V-1710-41 2550+ bhp, turbo-compound w/separate 2-stage S/C and 2-stage air-cooled turbine, 50% aftercooler and port injection, 1947.

Also on Page 280, short description. Based on the G-10 which was a modified E-30 derived from the E-27.
E-27 engine
View attachment 796412
Just take of the engine driven supercharger, replace the single stage aux supercharger with a 2 stage supercharger, replace the single stage exhaust turbine with a two stage exhaust turbine. Install an after cooler, install port fuel injection, already has water injection.

Easy-peasy to put in a Spitfire in 1940

Click to expand...

You Know a clam shell type bubble canopy like the F-16 has was technically feasible for a 1936 fighter. Are going to make some silly comment about needing fly-by-wire and advanced composites and CAD to make it happen? Obviously a 1936 clam shell bubble canopy wouldn't be the exact same design or materials. The same goes for a "turbo Spitfire"
And I do believe two-stage impellers and turbines predate 1940. I want to say the French for both of those but I can't remember.

Jugman said:

You Know a clam shell type bubble canopy like the F-16 has was technically feasible for a 1936 fighter. Are going to make some silly comment about needing fly-by-wire and advanced composites and CAD to make it happen? Obviously a 1936 clam shell bubble canopy wouldn't be the exact same design or materials. The same goes for a "turbo Spitfire"
And I do believe two-stage impellers and turbines predate 1940. I want to say the French for both of those but I can't remember.

Click to expand...

Who knew how to make a large blown canopy in 1936? Perspex and Plexiglass were brand new materials in 1936. As far as I can tell the first use was in the Spitfire. Everyone else was building birdcage canopies until production techniques had evolved enough to produce large blown Plexiglas in mass quantities

You have to learn to crawl before you learn to walk. The conceit that you can jump straight to the final result without the hard work of development is nonsense.

As for turbo chargers materials were the main issue. GE didn't get their turbine materials sorted until 1941. From


"Cooperative research by Haynes Stellite and General Electric into the possibility of using Hastelloy alloy A, B, or C as a material for turbosupercharger buckets was begun in 1937. Forging was extremely difficult because of the great hardness and strength of these alloys at high temperature, but GE eventually developed a successful technique, the first one to succeed in drop-forging a Hastelloy alloy into any finished shape. Tests were also made of buckets which were cast to size by Austenal, but they were not liked so well as the
forged buckets, both because it was extremely difficult to produce sound, accurate castings and because the casting process gave a much larger grain than forging, while experience to date was believed to indicate that fine grain was essential for turbine buckets. The result was that by the middle of 1941 GE had decided that the best available method of producing turbo buckets was to forge them of Hastelloy alloy B. Eventually research done by GE on cast and forged Hastelloy buckets led to the discovery that at the 1,500°F-1 ,600°F blade temperature of the turbo the large grain of castings actually gave superior strength after 200 or 300 hours of life, but it would seem that this had not yet been fully realized by the middle of 1941.
By this time, however, it was clear that because of the war, buckets for turbosuperchargers would have to be made in enormous quantities, and that there was not nearly enough forging capacity in the United States for the use of that method of production, particularly since Hastelloy alloy B was so hard at the forging temperatures that the dies wore out very quickly. The result was that Austenal set to work in cooperation with GE to develop its lost-wax casting process to be really satisfactory for casting turbo buckets, and to make it suitable to true mass production. Austenal found it much easier to produce good castings of the Haynes Stellite alloy closely related to Stellite No. 6 which Austenal sold in dentures under the name Vitallium than of any of the other alloys tried. It was only then that tests were made by GE which revealed that Vitallium had really superior properties as a bucket material. The casting process had been developed to the point where it was satisfactory for buckets by the end of 1941, and Austenal then developed from the denture alloy a slightly modified composition which contained less carbon and hence was less brittle and better suited for turbine buckets. As soon as this casting process and alloy were approved for production by the Army, the Haynes Stellite Company was called on to assist in working out methods for mass production. The modified denture alloy was further improved by Haynes Stellite; the resulting material was designated Stellite alloy No. 21. This proved an excellent material for the purpose and actually far better than Hastelloy alloy B would have been, since the latter material contained no chromium and had very poor resistance to oxidation above about 1,400°F. "

Shortround6 said:

Time machine.

From page 443 of "Vees for Victory"
"V-1710-41 2550+ bhp, turbo-compound w/separate 2-stage S/C and 2-stage air-cooled turbine, 50% aftercooler and port injection, 1947.

Also on Page 280, short description. Based on the G-10 which was a modified E-30 derived from the E-27.
E-27 engine
View attachment 796412
Just take of the engine driven supercharger, replace the single stage aux supercharger with a 2 stage supercharger, replace the single stage exhaust turbine with a two stage exhaust turbine. Install an after cooler, install port fuel injection, already has water injection.

Easy-peasy to put in a Spitfire in 1940

Click to expand...

Detailed article on turbo compounding

Jugman said:

You Know a clam shell type bubble canopy like the F-16 has was technically feasible for a 1936 fighter. Are going to make some silly comment about needing fly-by-wire and advanced composites and CAD to make it happen? Obviously a 1936 clam shell bubble canopy wouldn't be the exact same design or materials. The same goes for a "turbo Spitfire"
And I do believe two-stage impellers and turbines predate 1940. I want to say the French for both of those but I can't remember.

Click to expand...

We are confusing two different things. What is technically feasible from a materials and fabrication point of view and what is feasible practical from point of view of just fitting the desired "stuff" in the air frame.
By the time you get to 1945-46 piston fighters with high altitude engines the supercharger system takes nearly the same volume as the basic engine.
Even if you have the idea for such a supercharger and the materials to make it it won't fit in a Spitfire or even a P-51.
You might be able to build your prototype engine and fit it into a single seat fighter. But it won't be anything somebody would recognize as a Spitfire or P-51.
Engine text book of the time estimated a turbo or mechanical 2 stage engine for a 1000hp engine needed about 10 cu ft of space. A 2000hp engine would get some benifit of scaling but it was going to be closer to 20cu ft than to 10 cu ft.
What was not said was what altitude. The Super Allison, the P&W Sidewinder and the Wright turbo compound engines were made for higher altitudes than even the 2 stage Merlins and they need the space/volume to deal with the thinner air.
Once again the earlier simpler Allison than the H-1.

and no aftercooler or any ducting for an after cooler.

Jugman said:

Shortround6 described the V-1710H. Bell had a P-63 proposal for Wright turbo mounted behind the engine at ~60° from horizontal. Both of these fit in the same space as the regular V-1710 two stage.

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SR6 described the V-1710E-27, not a V-1710H. It was Bell's XP-63H paper projest that was supposed to be powered by that engine. The E-27 will not fit in the same space as the regular V-1710 with 2 stages of supercharging, since there is another perhaps 1.5ft required for the power recovery turbine to fit, and the exit of the spent gasses also requires some free volume.
Added to this, the 2-stage supercharged V-1710 was already a long engine, longer than the 2-stage Merlin, let alone the 1-stage Merlin.

Jugman said:

GE turbos had two major problems that impacted compactness.
1. Their impeller efficiency was god awful.
2. Turbine cooling.

Pretty much anybody else's supercharger fixes one.
Two can be improved by air-cooled turbine blades. BMW had some success with them in 1938. There were other methods to improve cooling that could be employed. Such as the "turbo Snout" used in the P-61C. Most of these methods require better coordination between GE and the engine and airframe manufacturers.

Click to expand...

If you'd be so kind to post some info about the air-cooled turbine blades by BMW, that would've been cool.
List of companies that made 'bad' impellers, and further messed up the intake to lower the compressor abilities:
- P&W (rectified by the C series R-2800s of mid/late 1944)
- BMW (rectified by late 1942 801E that went nowhere, repeated the succes with 801S in late 1944 by that time it was too late)
- Bristol (rectified by mid/late 1944, for the Centaurus and 100 series Hercules)

There is no doubt that GE would've made a better stuff with more pressure by the military, as well as with more support by the military and NACA. As for the usage of turbochargers in the British aircraft, that ain't gonna happen unless indeed some kind of time travel is used.

Jugman said:

The XH-2600 engine X-95 This engine had two 13in diameter impellers. The first stage had an eye diameter of 9.625 and a van height of 3in. 8.25in and 1.25 for the second stage.
The XH-3130 engine X-96

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Thank you
Unfortunately, P&W's 2-stage superchargers once installed on R-1830s were about as good as other people's 1-stage superchargers, leaving out the question of just how good were the superchargers on these P&W engines.
FWIW, RR (and other companies) were free to look at Farman's 2-stage S/C as depicted in open press in 1937, or even the earlier devices on the Junkers and Bristol engines in order to make a 2-stage S/C even earlier.

Shortround6 said:

Time machine.

From page 443 of "Vees for Victory"
"V-1710-41 2550+ bhp, turbo-compound w/separate 2-stage S/C and 2-stage air-cooled turbine, 50% aftercooler and port injection, 1947.

Also on Page 280, short description. Based on the G-10 which was a modified E-30 derived from the E-27.
E-27 engine
View attachment 796412
Just take of the engine driven supercharger, replace the single stage aux supercharger with a 2 stage supercharger, replace the single stage exhaust turbine with a two stage exhaust turbine. Install an after cooler, install port fuel injection, already has water injection.

Easy-peasy to put in a Spitfire in 1940..

Click to expand...

I was thinking Hurricane, myself. P-39?

SaparotRob said:

I was thinking Hurricane, myself. P-39?

Click to expand...

With or without nose armor?

Shortround6 said:

We are confusing two different things. What is technically feasible from a materials and fabrication point of view and what is feasible practical from point of view of just fitting the desired "stuff" in the air frame.
By the time you get to 1945-46 piston fighters with high altitude engines the supercharger system takes nearly the same volume as the basic engine.
Even if you have the idea for such a supercharger and the materials to make it it won't fit in a Spitfire or even a P-51.
You might be able to build your prototype engine and fit it into a single seat fighter. But it won't be anything somebody would recognize as a Spitfire or P-51.
Engine text book of the time estimated a turbo or mechanical 2 stage engine for a 1000hp engine needed about 10 cu ft of space. A 2000hp engine would get some benifit of scaling but it was going to be closer to 20cu ft than to 10 cu ft.
What was not said was what altitude. The Super Allison, the P&W Sidewinder and the Wright turbo compound engines were made for higher altitudes than even the 2 stage Merlins and they need the space/volume to deal with the thinner air.
Once again the earlier simpler Allison than the H-1.
View attachment 796494
and no aftercooler or any ducting for an after cooler.

Click to expand...

Nothing technical to add, but man, that thing would have sounded awesome I bet.

Jugman said:

The XH-2600 engine X-95 This engine had two 13in diameter impellers. The first stage had an eye diameter of 9.625 and a van height of 3in. 8.25in and 1.25 for the second stage.
View attachment 796420
The XH-3130 engine X-96
View attachment 796421

Click to expand...

The induction system looks very poor. Extreme right angle turns and dramatic changes in duct aspect ratios will negate a lot of the pressure increase developed by the superchager which will be compounded by the resulting increase in charge air temperature. Also the supercharger design looks like the typical poor GE design without the scroll seen on a well designed supercharger.

mig-31bm said:

I just realized that I forget to mention the Hornet F.1. It is the only twin engine super props with practically the same high speed performance of P-51H but much better climb rate. In term of speed, it almost overlapped with P-51H at high altitude. There is almost no difference

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Wouldn't the Do.335A be another twin super prop in same realm? 673 km/h @ 6,500m on B4 fuel; maybe a little more with MW50. If he snuck in behind you, there would be some tense moments if you tried running straight and level to distance your Allied Superprop from the 30mm cannon.

Shortround6 said:

What was not said was what altitude. The Super Allison, the P&W Sidewinder and the Wright turbo compound engines were made for higher altitudes than even the 2 stage Merlins and they need the space/volume to deal with the thinner air.
Once again the earlier simpler Allison than the H-1.
View attachment 796494
and no aftercooler or any ducting for an after cooler.

Click to expand...

Isn't the big advantage of the Super Allison and the Wright turbo compound, that the exhaust turbine(s) are adding 100s of hp to the crankshaft?

p.s. Wouldn't it sound more/less like a P-38? All the nice V-12 rumble ducted away to the turbine... It would be like the current F1 engines - very efficient, but not the wail of the V-10 and 12s.

don4331 said:

Wouldn't the Do.335A be another twin super prop in same realm? 673 km/h @ 6,500m on B4 fuel; maybe a little more with MW50. If he snuck in behind you, there would be some tense moments if you tried running straight and level to distance your Allied Superprop from the 30mm cannon.

Click to expand...

Do335A has high wing loading of 249 kg/m2 and much lower power to weight of 0.197 hp/kg

Reluctant Poster said:

Who knew how to make a large blown canopy in 1936? Perspex and Plexiglass were brand new materials in 1936. As far as I can tell the first use was in the Spitfire. Everyone else was building birdcage canopies until production techniques had evolved enough to produce large blown Plexiglas in mass quantities

Click to expand...

I was thinking more along the lines of the general concept of a large canopy not the dome itself. I'm well aware of the limitations of Plexiglass. The original F-16 wasn't even Plexiglass it was LEXAN. Modern ones are made out of ran outer layer of glass laminated to polycarbonate.

tomo pauk said:

SR6 described the V-1710E-27, not a V-1710H. It was Bell's XP-63H paper projest that was supposed to be powered by that engine. The E-27 will not fit in the same space as the regular V-1710 with 2 stages of supercharging, since there is another perhaps 1.5ft required for the power recovery turbine to fit, and the exit of the spent gasses also requires some free volume.
Added to this, the 2-stage supercharged V-1710 was already a long engine, longer than the 2-stage Merlin, let alone the 1-stage Merlin.

If you'd be so kind to post some info about the air-cooled turbine blades by BMW, that would've been cool.

Click to expand...

So he did.
Per "V-1710 and V-3420 designs and concepts"
The V-1710H
length ~101.6in
width 29.3in 36in. including exhaust pipes.
height 40.75in

This system was not geared to the crankshaft. It was pure turbo-supercharged engine consisting of a two-stage compressor driven by a two-stage turbine. The turbo axis was mounted transversely with the 2nd stage compressor discharge centered on the engine centerline. This turbo was ~25.5in in diameter and ~20in in height. For reference the type B-1 was 26.5in by 15in.

for comparison a two-stage griffon was
length ~91in 81in to rear propeller collet
width 29.5in
height 46in

Sorry I don't have any details on the BMW blades.

Jugman said:

I was thinking more along the lines of the general concept of a large canopy not the dome itself. I'm well aware of the limitations of Plexiglass. The original F-16 wasn't even Plexiglass it was LEXAN. Modern ones are made out of ran outer layer of glass laminated to polycarbonate.

So he did.
Per "V-1710 and V-3420 designs and concepts"
The V-1710H
length ~101.6in
width 29.3in 36in. including exhaust pipes.
height 40.75in

This system was not geared to the crankshaft. It was pure turbo-supercharged engine consisting of a two-stage compressor driven by a two-stage turbine. The turbo axis was mounted transversely with the 2nd stage compressor discharge centered on the engine centerline. This turbo was ~25.5in in diameter and ~20in in height. For reference the type B-1 was 26.5in by 15in.

for comparison a two-stage griffon was
length ~91in 81in to rear propeller collet
width 29.5in
height 46in

Sorry I don't have any details on the BMW blades.

Click to expand...

No charge cooling is a big minus.

Jugman said:

Not at all! Highly compact and weight efficient turbo installations (the V-1710H or Bell's turbosupercharged P-63 are good examples) that could fit a Spitfire or P-51 were very feasible even in 1940. The problem was no one firm had all the knowledge or resources necessary to accomplish this at that time. The USAAF had far to few eggs in far to many baskets nor was the US procurement system really set up to deal with component R&D.

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The level of experience with turbochargers in 1940 was extremely limited The number of aircraft equipped with turbochargers and actually flying was was small indeed. Note that post WWI experiments with Libertys and Renaults had been abandoned due to reliability issues. As far as I can ascertain the only aircraft in 1940 equipped with turbochargers were American. The following is the sum total of experience with actual flying turbo installations at the end of 1940.




As SR pointed out in a previous post the P-30 was a unique installation using the turbocharger as a direct replacement for a mechanical supercharger. The aircraft itself was not successful and had a very short service life. Information on the turbo installation is sparse. Although I did read that cooling was an issue, I have not found any proper documentation The first two stage system was the prototype P-37 which flew AFTER the prototype Spitfire flew so obviously it was too late to influence the Spitfire's design.
In sum, not counting losses (eg the first P-30 crashed fatality one month after is first flight) there were 158 examples of turbocharger flying in 1940, half of which were B-17s. A further third were were obsolete P-30s which were on the way out and offered no real experience of a useful turbo installation. The rest were prototypes, mostly unsuccessful. Hardy a level of experience to base the defense of the realm on.

Reluctant Poster said:

The level of experience with turbochargers in 1940 was extremely limited The number of aircraft equipped with turbochargers and actually flying was was small indeed. Note that post WWI experiments with Libertys and Renaults had been abandoned due to reliability issues. As far as I can ascertain the only aircraft in 1940 equipped with turbochargers were American. The following is the sum total of experience with actual flying turbo installations at the end of 1940.


View attachment 797246

As SR pointed out in a previous post the P-30 was a unique installation using the turbocharger as a direct replacement for a mechanical supercharger. The aircraft itself was not successful and had a very short service life. Information on the turbo installation is sparse. Although I did read that cooling was an issue, I have not found any proper documentation The first two stage system was the prototype P-37 which flew AFTER the prototype Spitfire flew so obviously it was too late to influence the Spitfire's design.
In sum, not counting losses (eg the first P-30 crashed fatality one month after is first flight) there were 158 examples of turbocharger flying in 1940, half of which were B-17s. A further third were were obsolete P-30s which were on the way out and offered no real experience of a useful turbo installation. The rest were prototypes, mostly unsuccessful. Hardy a level of experience to base the defense of the realm on.

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Thank you for putting that into chart form.

The US had built around 5-10 (?) planes powered with turbo Curtiss Conqueror engines like the P-30 which gave them the confidence to try the P-30. Many of these used a Grease gun to lubricate the turbo so long endurance flights were not being done


As a correction the turbo Curtiss Conqueror engines did not replace the the mechanical supercharger with the turbo unit. Curtiss Conqueror engines, in service, were un-supercharged, much like many Kestrels and other V-12s from the late 20s and early 30s.

The US also had several Airacudas with turbos although they had so much trouble with the first few planes very early and the majority of the contract were completed without the turbos.

This is just minor quibbling and the main point/s are not in question.
The US had much more experience with the turbo than the rest of the world put together.
The turbo was not ready for service use in fighters in 1940 (B-17s had a flight engineer and the B-17 didn't climb or dive as fast making it easier to regulate the turbo/s as the altitude changed). B-17s also had a lot more room to fit the turbo and the associated 'plumbing'.

Shortround6 said:

Thank you for putting that into chart form.

The US had built around 5-10 (?) planes powered with turbo Curtiss Conqueror engines like the P-30 which gave them the confidence to try the P-30. Many of these used a Grease gun to lubricate the turbo so long endurance flights were not being done
View attachment 797250

As a correction the turbo Curtiss Conqueror engines did not replace the the mechanical supercharger with the turbo unit. Curtiss Conqueror engines, in service, were un-supercharged, much like many Kestrels and other V-12s from the late 20s and early 30s.

The US also had several Airacudas with turbos although they had so much trouble with the first few planes very early and the majority of the contract were completed without the turbos.
View attachment 797251
This is just minor quibbling and the main point/s are not in question.
The US had much more experience with the turbo than the rest of the world put together.
The turbo was not ready for service use in fighters in 1940 (B-17s had a flight engineer and the B-17 didn't climb or dive as fast making it easier to regulate the turbo/s as the altitude changed). B-17s also had a lot more room to fit the turbo and the associated 'plumbing'.

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Thanks for the correction. I had expunged the Airacuda from my memory. Not the most attractive aircraft.
What is the biplane shown in the photo?

The Biplane is the Curtiss XP-6F.
However there 17 (?) P-36Ds (11 converted P-6 and 6 converted P-6As but, depending on sources, anywhere from 7 to 17 were so modified).

Exhaust crossover is at the front of the engine.

Things go back even further. At least one P-2 got a turbo D-12 engine which paved the way for the five P-5 Superhawks.

142mph at sea level, 166mph at 25,000ft. Curtiss D-12F engine.
This 'series' ended with the XP-23 (last P-6E)

Note the turbo has changed sides. Engine is the Conqueror and the engine was rated at 600hp at 15,000ft with the turbo.
This was the last biplane fighter ordered by the USAAC.
This "series" of turbo biplanes covered around 5 years.

Shortround6 said:

The Biplane is the Curtiss XP-6F.
However there 17 (?) P-36Ds (11 converted P-6 and 6 converted P-6As but, depending on sources, anywhere from 7 to 17 were so modified).
View attachment 797257
Exhaust crossover is at the front of the engine.

Things go back even further. At least one P-2 got a turbo D-12 engine which paved the way for the five P-5 Superhawks.
View attachment 797258
142mph at sea level, 166mph at 25,000ft. Curtiss D-12F engine.
This 'series' ended with the XP-23 (last P-6E)
View attachment 797259
Note the turbo has changed sides. Engine is the Conqueror and the engine was rated at 600hp at 15,000ft with the turbo.
This was the last biplane fighter ordered by the USAAC.
This "series" of turbo biplanes covered around 5 years.

Click to expand...

Article on record breaking turbocharged Hawk

Jugman said:

So he did.
Per "V-1710 and V-3420 designs and concepts"
The V-1710H
length ~101.6in
width 29.3in 36in. including exhaust pipes.
height 40.75in

This system was not geared to the crankshaft. It was pure turbo-supercharged engine consisting of a two-stage compressor driven by a two-stage turbine. The turbo axis was mounted transversely with the 2nd stage compressor discharge centered on the engine centerline. This turbo was ~25.5in in diameter and ~20in in height. For reference the type B-1 was 26.5in by 15in.

Click to expand...

Thanks for the details.
However, I'd say that there was none of these turboes available from manufacturer(s) in 1940, when the Spitfires and Mustangs were supposed to have them under the hood.