Curtiss XP-37/YP-37

[KJ_Lesnick]

The Curtiss X/YP-37 was an interesting concept that had a lot of potential, but the application was of course severely flawed

• The turbocharger was unreliable
  
• The ducting required for the turbocharger took up an obscene amount of space in the nose, seemingly to the exclusion of everything else except obviously the engine and propeller
  
• Fuel capacity appeared to be low
  
• Visibility was terrible
  

I know turbochargers are not themselves heavy, or necessarily large: I do know, however that all the ducting involved produced bulk when designers were not careful.

I'm curious exactly what causes the bulk?

• Is it the need for the exhaust flow path from the engine to the turbo to be good?
  
• Is it the connection between the turbine and the turbocharger?
  
• Is it the air-to-air intercooling system (and the resulting torturous airflow path)?
  
• Is it some combination of the previous?
  

[tomo pauk]

As a combat aircraft, the XP-37 have had no potential, unless the USAC settles for 50 gal fuel tank and four .30s (if even so much could be crammed in). The layout of powerplant took away the best place for fuel, while moving the pilot too much aft. The P-43 got the layout of the powerplant right (and the P-47B after it), but 'wrong' engine was choosen.

The tubocompressor needed to be somewhat remote from the engine itself (for the state of the art of late 1930s), so the temperature peaks don't destroy the turbine. The remote location then demands an amout of tubing/piping: most commonly a pair of exhaust manifolds, the intake manifold to bring the fresh air to the compressor, at least one manifold that 'transports' compressed air to the intercooler, then anothe one from intercooler to the carburetor. Plus the intercooler, plus there was also a manifold for cooling the turbocompressor itself.

[KJ_Lesnick]

tomo pauk

As a combat aircraft, the XP-37 have had no potential

It was an interesting concept in that it was an early inline-fighter with a turbo.  My curiosity largely around why the turbochargers were so bulky and why the screwed up so bad on the YP-37.

The P-43 got the layout of the powerplant right (and the P-47B after it), but 'wrong' engine was choosen.

You mean it wasn't powerful enough?

The tubocompressor needed to be somewhat remote from the engine itself (for the state of the art of late 1930s), so the temperature peaks don't destroy the turbine.

You mean the exhaust gasses had to cool a little before it touched the turbine?

The remote location then demands an amout of tubing/piping: most commonly a pair of exhaust manifolds

Which drives the turbine...

the intake manifold to bring the fresh air to the compressor

Which feeds it...

at least one manifold that 'transports' compressed air to the intercooler

You mean air that comes off the compressor and then through the cooler?

then anothe one from intercooler to the carburetor.

Which then is where it all meets the engine...

Plus the intercooler

You're talking an air/air cooled intercooler?

plus there was also a manifold for cooling the turbocompressor itself.

Turbine cooling?

I'm curious as to the ability of the V-1710 (or any engine of ours) early on to accommodate a liquid/air intercooler?

[tomo pauk]

The R-1830 didn't receive much of the upgrade through the ww2, hence my comment on the P-43. The 1200 HP, as-is, will be the only level of power probably until the end of 1943/early 1944. Then we have the drag, where the R-1830 is worse than the V-1710, even once we account for the drag of liquid cooling system. The R-1830 will be a bit lighter, though.
Yes - it was air-to-air intercooler as used on all of the turboed US designs worth their money.

Turbine cooling?

Indeed. Might want to check the diagram (this is for P-38): http://legendsintheirowntime.com/Content/1944/P38_Av_4408_DA_turbo_p146_W.png

[jcf]

YP-37

[KJ_Lesnick]

tomo pauk

The R-1830 didn't receive much of the upgrade through the ww2, hence my comment on the P-43. The 1200 HP, as-is, will be the only level of power probably until the end of 1943/early 1944.

Weird...

Then we have the drag, where the R-1830 is worse than the V-1710

Yeah more frontal area and shorter in length... as for the drag of the coolant system, that might not be as bad since you have more versatility where the radiators can be put.

Yes - it was air-to-air intercooler as used on all of the turboed US designs worth their money.

Generally the air cooled design is lighter but it's kind of like comparing 10 pounds of cotton to 12 pounds of brick: One is lighter definitely but it takes up more space and while 10 pounds is better than 12, sometimes less space is better...

Indeed. Might want to check the diagram (this is for P-38): http://legendsintheirowntime.com/Content/1944/P38_Av_4408_DA_turbo_p146_W.png

Yeah, I see it.


joncarrfarrelly

YP-37

Looking at the diagram it gives me the vibe of some stuff being rather "loosely" laid out though I could very well be wrong: I'm still surprised that they had to move the cockpit so far back.  You'd figure the radio and battery could be packed behind the pilot.

Now that huge radiator -- now there's a case for putting that underneath the aircraft like the XP-46, XP-60B/-D.

The turbocharger itself was fundamentally unreliable, correct?

[wuzak]

Looking at the diagram it gives me the vibe of some stuff being rather "loosely" laid out though I could very well be wrong: I'm still surprised that they had to move the cockpit so far back.  You'd figure the radio and battery could be packed behind the pilot.[/quote]

The drawing is an indication of where the components were, not an accurate representation.

The locations were most likely chosen for centre of gravity considerations.

Now that huge radiator -- now there's a case for putting that underneath the aircraft like the XP-46, XP-60B/-D.

It's not an overly large radiator, though what is actually shown is the inlet duct.

Part of the reason why it took up so much space was that the air had to be guided into and out of the duct, and that needed some longitudinal space in order to limit the duct losses.

Logically speaking, placing the radiator and coolers on the centreline behind the turbine and wastegate outlets does not make much sense.

It is the same reason why single stage Merlins in Mosquitoes used only 5 exhaust stubs instead of 6.

The turbocharger itself was fundamentally unreliable, correct?

Yes, the turbo was unreliable, being an early version.

[KJ_Lesnick]

Wuzak

The drawing is an indication of where the components were, not an accurate representation.

Okay, I gotcha

The locations were most likely chosen for centre of gravity considerations.

Makes enough sense, though I'm not sure how much weight the batteries, radios, and baggage compartment weights would be.  

Though a strange question: Why would a fighter pilot need a baggage compartment and flares?  There weren't heat-seeking missiles in those days so the only thing I could think of would be a flare gun, and if you are talking about emergency supplies: A crash of an aircraft would destroy the aircraft leaving the pilot only what he could carry on his person when he bailed out (parachute, sidearm and a mag or two, rations, a flare-gun).

It's not an overly large radiator, though what is actually shown is the inlet duct.

True enough, plus underneath the aircraft would basically mean it'd ingest air from the turbo exhaust unless it was placed on one or either the wings (though that could encroach upon fuel load).

It is the same reason why single stage Merlins in Mosquitoes used only 5 exhaust stubs instead of 6.

So two pipes fed one stack?

Yes, the turbo was unreliable, being an early version.

I'm curious about three things

• What model turbocharger was used on the XP-37 and YP-37?
  
• Was turbochargers kind of a crap-shoot in that era?
  
• Didn't the Y1B-17A fly after the XP-37 did with a turbo?
  

[wuzak]

Though a strange question: Why would a fighter pilot need a baggage compartment and flares?  There weren't heat-seeking missiles in those days so the only thing I could think of would be a flare gun, and if you are talking about emergency supplies: A crash of an aircraft would destroy the aircraft leaving the pilot only what he could carry on his person when he bailed out (parachute, sidearm and a mag or two, rations, a flare-gun).

Not all crashes result in the destruction of the aircraft.

A pilot may have to make a forced landing away from his base or even in enemy territory. The luggage area could store some basic survival gear. Sometimes it may contain a lift raft for water landings.

Flares are used for signalling, obviously.

In bombers the flare would be often used for signalling the base that the aircraft was in trouble. I'm not sure about fighters, but it is possible that the same situation applies.

It's not an overly large radiator, though what is actually shown is the inlet duct.

True enough, plus underneath the aircraft would basically mean it'd ingest air from the turbo exhaust unless it was placed on one or either the wings (though that could encroach upon fuel load).

Which is what I said above.

It is the same reason why single stage Merlins in Mosquitoes used only 5 exhaust stubs instead of 6.

So two pipes fed one stack?

Yes. Do a Google search and you will doubtless find a picture of the arranegment

Yes, the turbo was unreliable, being an early version.

I'm curious about three things

• What model turbocharger was used on the XP-37 and YP-37?
  
• Was turbochargers kind of a crap-shoot in that era?
  
• Didn't the Y1B-17A fly after the XP-37 did with a turbo?
  

The YP-37 used the Form F10 turbo, renamed as a B series.

I believe the XP-37 used an earlier turbo, which had a different layout to the ones that went into mass production.

Crap shoot? Well, the Allison V-1710 was not tested in conjunction with the turbo before the XP-37 flew. The V-1710 may not have been tested with a turbo on the bench before the YP-37 flew either. In that way, it was an excursion into the unknown.

Yes, the Y1B-17A did fly after the XP-37 with turbos. The original installation of that didn't work too well either.

There may be a few different reasons why the turbo was less reliable in the YP-37 than the early B-17s. One of which is that it is quite probable that the V-1710 had hotter exhausts, stressing the materials more.

[tomo pauk]

The compressor of the turbo on the XP-37 took the fresh air from inbetween the compressor and turbine, intention being that shaft's bearing housing will receive some cooling in the process. That meant the shaft, connecting the turbine and compressor was too long, also necessitating an outer bearing. The name of the turbo in the XP-37 was 'Form F-10'. Installation so close to the engine will not going to improve the situation. The turbo controls were also of 1st generation, it took the GE until 1942 (!) to come out with new controls that remained for the rest of the war.
For the YP-37, the new turbo was specified, the 'Form F-13'. It have had the fresh air entering from the shaft end into the compressor, in an 'usual' way we might say. That allowed for shorter and stiffer shaft, while dispensing with external bering. Some plumbing was necessary to cool off the bearings, though. The new turbo also allowed the increase in rated altitude to 25000 ft, vs. 20000 ft for the old turbo. It was soon named as 'Type B-1'. In the actual 13 of YP-37, the B-2 turbo was installed. The YP-37s still experienced problems with controls and low turbine bucket life, since both controls and installation remained basically the same as with XP-37.

[KJ_Lesnick]

wuzak

Not all crashes result in the destruction of the aircraft.

True, but I wouldn't bet on it... admittedly in the jet-era landing speeds are much faster

The luggage area could store some basic survival gear. Sometimes it may contain a lift raft for water landings.

Did any of the following other aircraft have these features: F4F, P-38, P-39, P-40, F4U, P-47, and P-51?

I didn't know bombers ejected flares while in flight to signal they're in trouble after takeoff...

The YP-37 used the Form F10 turbo, renamed as a B series.

I believe the XP-37 used an earlier turbo, which had a different layout to the ones that went into mass production.

Which would explain reliability...

Crap shoot? Well, the Allison V-1710 was not tested in conjunction with the turbo before the XP-37 flew. The V-1710 may not have been tested with a turbo on the bench before the YP-37 flew either. In that way, it was an excursion into the unknown.

Understood.  If I may ask: Why didn't they test a V-1710 with a turbo during the bench testing?

Yes, the Y1B-17A did fly after the XP-37 with turbos. The original installation of that didn't work too well either.

So it required some work as well?

There may be a few different reasons why the turbo was less reliable in the YP-37 than the early B-17s. One of which is that it is quite probable that the V-1710 had hotter exhausts, stressing the materials more.

That would do it...

[wuzak]

The luggage area could store some basic survival gear. Sometimes it may contain a lift raft for water landings.

I didn't know bombers ejected flares while in flight to signal they're in trouble after takeoff...

Bombers had crew members who could fire a very pistol.

And it wasn't just on take-off. More likely on return, when crew members were injured.

A story I read a while back was that on a Tallboy mission a bomber from either 9 or 617 squadron found itself alone and could not call the escorting fighters (Mustangs) on the R/T. So one of the crew fired a flare to alert the fighters, which was claimed to have gone into the chasing Fw 190A and forced it to, at least, break off.

[tomo pauk]

Re. the turboed V-1710 not being tested prior installation: plenty of factors involved. 1st is that Allison with V-1710 was trying to do plenty with small resources, having 1st the bench test would've slowed the XP-37 project that was already behind the schedule. 2nd, US Army wasted plenty of money with 'hi-perf' engines that went nowhere, while delaying some payments to the Allison (it was 900 000 $ in some moment) instead to pour some money in the V-1710 development. 3rd, there was no 'system integrator' person/institution for a complex thing of combining a new engine, new type of supercharging and new installation.
No wonder the XP-37 suffered wrecked turbos, while pilots reporting the unbereable heat with engine running.

[Captain Canada]

Never knew that thing existed ! great pics, thanks. And as for the 5 stubs....you learn something new everyday !

[KJ_Lesnick]

tomo pauk

the turboed V-1710 not being tested prior installation: plenty of factors involved. 1st is that Allison with V-1710 was trying to do plenty with small resources, having 1st the bench test would've slowed the XP-37 project that was already behind the schedule. 2nd, US Army wasted plenty of money with 'hi-perf' engines that went nowhere, while delaying some payments to the Allison (it was 900 000 $ in some moment) instead to pour some money in the V-1710 development.

What engines proved to be a waste?

3rd, there was no 'system integrator' person/institution for a complex thing of combining a new engine, new type of supercharging and new installation.

Did the USN, RAF, or Luftwaffe have this?


wuzak

Bombers had crew members who could fire a very pistol.

Yes, but a fighter isn't a bomber; if you did carry a pistol, wouldn't you want to carry it ON your person?

And it wasn't just on take-off. More likely on return, when crew members were injured.

A story I read a while back was that on a Tallboy mission a bomber from either 9 or 617 squadron found itself alone and could not call the escorting fighters (Mustangs) on the R/T. So one of the crew fired a flare to alert the fighters, which was claimed to have gone into the chasing Fw 190A and forced it to, at least, break off.

That's actually pretty cool.