Improve the YP-37

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W

wuzak

Captain
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Jun 5, 2011
Hobart Tasmania
The Curtiss YP-37 was a precursor to the P-40 that became the US's main fighter in the early part of WW2.

The YP-37, Curtiss Model 81 evolved from the XP-37, Models 75I and 80. The main difference was the extension of the rear fuselage behind the cockpit.

The YP-37, as with the XP-37, used a turbocharged V-1710. In both cases the turbo was mounted beneath the engine, partly exposed to the air flow. The air to air intercooler was mounted in the fuselage behind the engine, as was the coolant radiator. It was this positioning of the coolers that forced Curtiss engineers to move the cockpit rearwards, this being the feature that led to the perception that the aircraft was unsuitable for combat, due to poor pilot view. I'm sure that the service prototypes didn't have any armaments or self sealing tanks either.

Can we reposition the radiator and intercooler to enable us to bring the cockpit forward to a reasonable position?

The P-40 radiator and oil cooler position could work. But where to put the intercooler?

http://farm9.staticflickr.com/8310/7883876544_a31b229ae3_z.jpg
http://www.palba.cz/forumfoto/albums/userpics/11965/YP-37.jpg
http://crimso.msk.ru/Images6/MM/MM-150/0112-01-2-1.jpg
 
Engine, along with the Prestone oil cooler, in front. Inter-cooler and turbocharger in tandem, aft low fuselage. Pilot between engine and turbo. The sqetch is for turbo P-51, but the idea is applicable.
 

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The Service prototypes were supposed to be carrying one .50 cal and one .30 cal.

The YP-37 were good for about 340mph at 20,000ft which is about 20mph slower than a P-40F with a Merlin so something is going on with drag. Adding more lumps, bumps and scoops might help but probably won't.
 

The radiator and intercooler drag in the YP-37 was high. More bumps may help if the bumps give more aerodynamic cooling systems.

The turbo sitting out in the breeze can't help either, so fairing somehow that in would help.
 
If yiou look at the P-47 Thunderbolt, you'll see the lower 1/3 of the belly is all air duct to get the turbocharger behind the pilot. You have to get the exhaust there, the fresh air there, and the intercooled and compressed air back to the carburetor. I don't think the sketch of the P-51 is possible and still have rooom for the pilot ... the air and exhaust has to go somewhere.

To the YP-37 ... I think it would be possible, but the fuselage would have to grow a little and that might make it slower ... so there's a tradoff to make it happen ... but it probably could be made to happen if they thought the visibility was more important than easy placement of the turbo and associated hardware. It probably WOULD have been made to happen if the War Materiel Board hadn't removed the turbo from the P-39 and P-40, but since they didn't have to do it due to the lack of a required turbo, why would they waste the money until the customer wanted the change?

Don't get me wrong, I think they SHOULD have ... but we simply not required to do so by the primary customer. If the British had asked for it, maybe they would have proceeded. By the time they found out they needed the trubo, other newer types were on the drawing boards with 2-stage superchargers. Maybe they should have tried THAT one, too with the XP-40Q. It is possible the drag would not make it any faster than it was, but it is also possible a 2-stage Merlin would have made enough difference at altitude to warrant some production consideration.

It's a "what if" that we'll never know I suppose, but an intriguing proposition. Good thread subject, Wuzak.

We currently have a P-40C at the Planes of Fame displayed before it goes to England and Stephen Gray. I cannot see where the associated hardware would fit without enlarging the fuselage ... it is a small fighter to be sure, smaller than the P-40N model we fly.
 
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I don't think anybody had any great success with the concept of powering a single engined fighter by a turbocharged liquid cooled engine. Unless you were willing to greatly increase the fuselage cross-sectional area, you either wound up with something like the XP-37 with its far rear mounted cockpit or you ended up with lots of external plumbing like the FW 190C. AFAIK the FW 190C prototypes with the external belly mounted turbocharger failed to demonstrate any significant performance gain. The situation was rather different for radial engined fighters, such as the P-47 - they had the benefit of having more capacious fuselages, and, even then, the P-47 had an exceptionally deep fuselage. Interestingly, Bell went with the mechanically driven two stage supercharger for the P-63.
 
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Partially due to experience with the YP-37s and with the turbo Airacuda the Army thought that SERVICEABLE turbo equipped aircraft were about 2 years in the future while an Allison powered P-36 ( P-40) without turbo was only one year in the future. Given the world situation and the Army's lack of modern fighters, Holding out for turbo equipped fighters would have meant hundreds if not 1000-1500 fewer fighters in service (or delivered to allies) as of Dec 1941.

A turbo equipped P-40 would have been faster from 15,000 on up and really coming into it's own above 20,000ft, unfortunately it would have been 20-40 mph slower at sea level and have poorer climb at low levels. Unless you limit the armament to four .50s and a small quantity of ammo (200-235rpg?) it will be heavier than a P-40E once armor and protected tanks are fitted.
 

Yes, the belly of the P-47 has air ducts through it. But they don't all have to be there.

There are two exhaust pipes from the engine to the turbo, and two intake pipes from the intercooler to the carburettor deck. The latter aren't in the bottom of the airframe, but about half way up, around the perimeter. The most space is taken up by the duct that feeds air to the intercooler. This duct does not need to come from the very front of the aircraft, but could, in fact, be fed by a short duct which starts behind the wing. It may even be better aerodynamically that way.

The exhaust and intake air pipes are required, but they may be able to get away with a single one for each.

They certainly could for a V-1710, though two exhaust pipes would probably be easier for the V-12.


Could the intercooler for the YP-37 have been placed in a similar position to those on the P-38J/L? ie under the nose, ahead of where the Y-37's turbo was. Then all we have to do is relocate the coolant radiator(s). The belly position is out for them, since the turbo is under the engine and the hot exhaust would likely end up going through the radiator core.
 
Hi Wuzak,

If you go with a single one for each, you get exhaust crosstalk with backpressure issues that could be easily cured or be an engineering nightmare. That's why nobody did it. You can relayout the P-47, but they made a war winner out of it ... how much better would you make it than the designers did? I think it would have to be worth the effort to make is feasible.

I think you'd need some good calculations or a good wind tunnel to convince anyone to spend the time and money.
 

The XP-47J had the duct section set back from the nose, though not as far as I suggested, and it had improved performance.

I do not foresee any issues with having a single outlet on the R-2800. The cylinders fired in a sequence around the engine, so the issues suggest shouldn't be too much of an issue. Looking at the layout of the exhausts sytem for teh P-47 it seems they didn't do anything more clever than having the cylinders on the left half feed one pipe and the cylinders on the right half feeding the other.

The XP-37 and YP-37 both used single pipes to feed the turbo.

I have the benefit of hindsight to be able to suggest such improvements, however.
 
Methinks the front row might have one exhaust and I'm not too sure if the rear row has another exhaust that feeds farther downline (i think so)... but ... since this is Firday, I'll check it tomorrow since I'm putting new oil lines on our P-47 ... at least I THINK I am since I took them off and it is scheduled for a flight demo on the first Saturday in March. Lot's of tight areas to put cotter pins and safety wire ...
 
Hi Wuzak, Thanks for that ... it shows the belly WAS necessary since the ducts take up the space ... as they do in our P-47G (a P-47D built by Curtiss). If you rerouted the ducts around the cockpit the fusealge would be WAY too wide and increase wetted area (the pilot has to have a minimum width and the engine had more than that which needs to be streamlined). I can't see where you could make a difference in the drag by reducing it ... but it could be possible.

Drgondog might weigh in here.

To me, the P-47 as designed, seems pretty sound. If anything, I'd add enough wing area to bring the wing loading to 38 - 40 pounds per square foot and leave it alone after that. But ... I haven't done hard aerodynamics for 40+ years and could be wrong.

As a variant, I like the XP-72 ... seems to have it all except a jet engine.
 
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That's not what I said Greg.

The duct for the intercoolers doesn't need to come from the front. It could, in fact, be as coop near the trailing edge of the wing. The intercooler ducting that is required is in orange. The yellow bit isn't really needed.

The air going from the intercoolers to the engine, shown in purple, do go around the cockpit sides.
 

The exhaust pipes (2 total) go each side of pilot's cabin. Air gets into after-cooler as it did on historical P-51, the turbo fresh air intake can be located next to the after-cooler intake.


The P-40 never had the turbo.

wuzak said:
The XP-47J had the duct section set back from the nose, though not as far as I suggested, and it had improved performance.
...
Click to expand...

The XP-47J was using the C series R-2800, 2800 HP, at higher altitude than B series. 2 guns less, plus shorter fuselage. The fan cooled, tightly cowled engine should have less drag.
 
It was estimated that a 1000hp engine would need about 10 cubic feet of space/volume to fit a turbo-intercooler-ducting. While the turbo may stay the same size a 1500hp engine may need bigger ducting ( or have higher pressure losses in the ducts) and a bigger inter-cooler. The P-38s suffered from this problem for quite a while.

I don't know if there is a minimum distance between the engine and the turbo. the exhaust gas temperature as it leaves the engine MAY be too hot for the turbo. A few extra feet of exhaust duct (exposed to the outside air) may be all that is needed. P-47 used internal pipes but used a lot of feet.

Allison, when they tried a turbo-compound engine resorted to injecting ADI (water/alcohol) directly into the exhaust manifolds to keep the exhaust gas temperature inside the limits for the turbine unit.

You may also have CG issues, was the pilot shifted to the rear of the YP-37 for space reasons or to help balance the the turbo under the nose? or both? late model P-38s got bigger/ heavier radiators which may have helped balance out larger props and inter-coolers? perhaps it can be done with ballast?



Lumps and bumps moved around and changed shape.



perhaps the radio and battery could go behind the cockpit with the cockpit moved up a bit.

on early P-40s the auxiliary fuel tank and oil tank were behind the cockpit instead of on the CG but then they didn't have a few hundred pounds of turbo sitting several feet in front of the CG.
 
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Hi Tomo, the exhaust pipes on the P-47 do NOT go down the side of the cockpit. We happen to have one and they go down the lower third of the belly under the cockpit ... and are stainless steel. They take up part of the "lower one-third of the belly." If you doubt that, come visit and see it in person. I know where they are by virue of having secured the Dzus fasteners when required.

Don Berlin was allowed to make one turbo P-40. It performed very well at 30,000+ feet, if you can believe the reports that have been dissiminated. I don't have one of the reports but have heard a synopsis from our P-40 pilots and they say it was a good bird that was never built. I have little reason to doubt it simply because the turbo P-38's were good at altitude ... so why not another turbo Allison? Probably used the same systems but I don't really know and it didn't make production, so it is an historical footnote of no consequence.

But I am assured it DID exist and fl quite well. There certainly was no production turbo P-40 ... but I think there was a prototype that was not proceeded with. That is from heresay around the museum from people who werre there at the time ... but I can't say for sure. I wasn't there at the time. Never saw a pic of it to date.

I think the XP-37 drawing above is quite obviously mislabeled. The part labeled "supercharger " is NOT supercharger. It is a turbocharger. The supercharger was integral within the Allison V-1710 and is located between the carburetor and the intake manifold, right behind the crankshaft-accessory case joint. The carb feeds directly into the supercharger impeller. ALL Allison V-1710's were supercharged except maybe the ones used for tanks, which didn't need supercharging because they didn't need 1,000+ HP to be effective; 750 HP was just fine. The Allisons used in PT boats were all supercharged. We have one if anyone wants a FAST boat, and all the parts are on it, ready for overhaul including the flywheel. You should find your own Vee-Drive. If we have to find it, we can, but you'll do better (it will be cheaper) if you find your own.
 
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Hey Greg, there was a turbocharged Allison powered P-60 prototype, so maybe that is the one that you have heard about? Not exactly a P-40 development, though. That was developed from the XP-53 and had laminar flow wings.
 
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