Was the Republic P-47's turbo-supercharger system unique to only the P-47?

[Husky]

As a kid reading Robert S. Johnsons' "Thunderbolt", I was captured by his exploits and the aircraft he flew. I really became fond of the P-47; I found out it was huge for a fighter, didn't climb all well (not counting zoom climbs), wasn't all that good maneuvering (depending upon profiles of flight). But, was extremely durable, had powerful armament, was very one of the fastest WW2 aircraft at 25K alt and above, could dive like a home sick demon (and not break apart)...and, the top European Theater aces (Gabraski, Johnson, Muhurin) all flew P-47's and survived.

I used to wonder why there where no engine exhaust stacks from the massive PW R-2800 engine on the P-47? Those two portals on either side just in front and a little lower of the wings was the exhaust? Huh? I gather those two ports where called "Waste Gates"? Doesn't seem right compared to other supercharged aircraft where their exhaust stacks are all but clear to the eye.

So, what's up with the turbo-supercharger system of the P-47? Why so unique? Why valuable?

 

[MiTasol]

Your question is a little ambiguos in that you could mean was it the only turbocharged fighter (no, so was the P-38) or the only one with the wastegates between the engine and the turbocharger, which is probably correct as I cannot think of another built that way.

Why is it so? My guess would be that having the wastegate forward of the cockpit was necessary to keep the cockpit cool in hot climates. Reducing the volume of the exhaust passing below cockpit would significantly reduce the radiant heat on the cockpit and the resulting cooling needed but the down side is that when instant power is called for the lag between closing the wastegates and the turbo speeding up would be significantly longer than on an installation where the wastegate is downstream of the turbo. Two wastegates also doubles the chances of failure.
I do not know if you have the P-47 PTM so I am attaching one version and a P-38 version so you can see how the "normal" layout (P-38/B-17/B-24) is. In all those cases there is no exhaust near the cockpit.
I can add another, later, P-47 PTM if you want.

 

[Shortround6]

I used to wonder why there where no engine exhaust stacks from the massive PW R-2800 engine on the P-47?

Many radial engines in the early part of the war had less than prominent exhaust "stacks".
Try finding the exhaust "stacks" on an Early F4U, two groups of three, just below the wing and flush with the fuselage.
It has to do with how much thrust they thought they could get vrs how much drag the stacks would cause See the lumps and bumps on a B-25 cowl.

 

[swampyankee]

Ideally, one would expand the aircraft exhaust in such a way that the energy would be applied to the propeller, providing much more thrust than one would get from a jet effect. This was (and is) done in turbo-compounded engines (which exist outside aviation). A turbocharger recovers the energy in the exhaust and uses it to drive a compressor to supercharge the engine; there won't be any wasted energy to recover as jet thrust from the exhaust.

 

[Husky]

Your question is a little ambiguos in that you could mean was it the only turbocharged fighter (no, so was the P-38) or the only one with the wastegates between the engine and the turbocharger, which is probably correct as I cannot think of another built that way.

Why is it so? My guess would be that having the wastegate forward of the cockpit was necessary to keep the cockpit cool in hot climates. Reducing the volume of the exhaust passing below cockpit would significantly reduce the radiant heat on the cockpit and the resulting cooling needed but the down side is that when instant power is called for the lag between closing the wastegates and the turbo speeding up would be significantly longer than on an installation where the wastegate is downstream of the turbo. Two wastegates also doubles the chances of failure.
I do not know if you have the P-47 PTM so I am attaching one version and a P-38 version so you can see how the "normal" layout (P-38/B-17/B-24) is. In all those cases there is no exhaust near the cockpit.
I can add another, later, P-47 PTM if you want.

Thanks MiTasol. Just browsing the P-47...funny read; the language used, reads like a novel. LOL. Far from my UH-60 Operators manual from the 1980's.

 

[Dash119]

Your question is a little ambiguos in that you could mean was it the only turbocharged fighter (no, so was the P-38) or the only one with the wastegates between the engine and the turbocharger, which is probably correct as I cannot think of another built that way.

I was under the impression that if a Turbocharged engine has a wastegate, it is always located between the engine and the Turbocharger. The job of the wastegate is to regulate the flow of exhaust gasses to the Turbocharger. It not only to limits the total flow to prevent over-boost, but reduces back-pressure in the exhaust manifold during acceleration caused by turbo lag in some applications.

While I suppose some of this could be accomplished by placing the wastegate after the Turbocharger, through back-pressure, that seems incredibly inefficient. Can you sight an example of any powerplant that uses a wastegate after the turbocharger instead of before?

 

[Shortround6]

Can you sight an example of any powerplant that uses a wastegate after the turbocharger instead of before?

B-17, B-24, P-38, P-43, B-29. perhaps some others.

Granted the waste gate is very close to the turbo,

 

[MiTasol]

Can you sight an example of any powerplant that uses a wastegate after the turbocharger instead of before?

The P-38, the prototype P-39, B-17, B-24, B-29 for beginners.

P-38 (from the Allison service school handbook)

From the GE Turbocharger handbook

From the -2 (E&M) manual

B-17 (from the B-17 Pilot Training Manual.)

B-24 (from the B-24 Pilot Training Manual). Yes the B-24 uses the twin row R-1830 but this is the diagram in the B-24 manual.

B-29 (from the GE Turbocharger handbook)

 

[Dash119]

Gentlemen,

I stand corrected.

 

[wuzak]

The wastegate on the B-series turbos was in the housing and released exhaust before the turbine.

As you can see in the picture from Shortround, there is no exhaust ducting or wastegate after the turbine on the P-38.

 

[MiTasol]

As you can see in the picture from Shortround, there is no exhaust ducting or wastegate after the turbine on the P-38.

Actually the wastegate is in the photo provided by Shortround. The arrow points to the pivot shaft for the wastegate butterfly as shown in the graphic from the manual below it.

I will try and find a link to that GE turbocharger book - I got my copy from Welcome to AviationShoppe - Aviation Blueprints work includes presenting aviation and military history but I cannot find the link at present. It clearly shows the actual mechanisms quite clearly.

And incidentally the B-32 used the same basic B series turbo as the P-38/B-17/B-24/B-29 but used two like on the B-29 installation. In fact both the B-29 and the B-32 used the same model B-31 turbos.
Unlike the P-38 etc the wastegate mechanism on the B-32 was blanked off and a separate wastegate was installed just before the turbo.

 

[Reluctant Poster]

I was under the impression that if a Turbocharged engine has a wastegate, it is always located between the engine and the Turbocharger. The job of the wastegate is to regulate the flow of exhaust gasses to the Turbocharger. It not only to limits the total flow to prevent over-boost, but reduces back-pressure in the exhaust manifold during acceleration caused by turbo lag in some applications.

While I suppose some of this could be accomplished by placing the wastegate after the Turbocharger, through back-pressure, that seems incredibly inefficient. Can you sight an example of any powerplant that uses a wastegate after the turbocharger instead of before?

Yes the wastegate dumps the exhaust before it passes through the turbocharger.

 

[wuzak]

The wastegate on the B-series turbos was in the housing and released exhaust before the turbine.

As you can see in the picture from Shortround, there is no exhaust ducting or wastegate after the turbine on the P-38.

Actually the wastegate is in the photo provided by Shortround. The arrow points to the pivot shaft for the wastegate as shown in the graphic from the manual below it.

Yes the wastegate dumps the exhaust before it passes through the turbocharger.

As I said, the wastegate is not after the turbine.

And there is no exhaust housing/pipe after the turbo on the P-38.

 

[Dash119]

In some of the photos and diagrams the Wastegate seems to be a simple flapper valve at the exhaust outlet of the Turbo-Supercharger. While it is possible this is the actual wastegate, it not only seems like a very inefficient placement in the system, it seems like a very inefficient valve in and of itself.

In modern Turbochargers some of them are built with an integral wastegate, while other still rely on the standalone wastegate. Is it possible that some of the WWII Turbo-Supercharger have an integral wastegate.

I know we have seen pilots manuals that describe the valve after the Turbo-Supercharger as the wastegate, but does anyone have access to a maintenance manual or manufactures diagrams?

 

[mad_max]

I worked on a rebuild of a P-47 ( Sad Sack) at Air Heritage back in the day. Butch Schroeder ended up buying it from David Tallichet's heirs. The waste gate is right close to where the firewall meets the cockpit. Here's the system.

 

[Dash119]

mad_max,

When you worked on that P-47 did you get a good look at the wastegate itself? Was it a simple flapper valve, or something more sophisticated? It just seems like some of the flapper style valves they show in the diagrams and pictures would be very inefficient wastegates.

Kim

 

[mad_max]

It looked like a butterfly valve in a carb. Real simple device, but we didn't hook up the turbo as usually they don't fly them over 10,000 ft as warbirds today, so full power is produced up to that alt. by just the supercharger that the turbo fed. A man developed the exhaust system that is about as efficient as can be done and the exhaust now exits through where the waste gate dumped out the exhaust normally.

 

[Dash119]

Butterfly valve is a much better description than flapper valve...

I think only one of the flying P-38's actually has functioning turbos, not sure about the flyable P-47's.

 

[MiTasol]

This diagram shows the wastegate butterfly clearly

 

[tommayer]

The P-38, the prototype P-39, B-17, B-24, B-29 for beginners.

P-38 (from the Allison service school handbook)
View attachment 588639
From the GE Turbocharger handbook
View attachment 588641

From the -2 (E&M) manual
View attachment 588648


B-17 (from the B-17 Pilot Training Manual.)
View attachment 588636

B-24 (from the B-24 Pilot Training Manual). Yes the B-24 uses the twin row R-1830 but this is the diagram in the B-24 manual.
View attachment 588635

B-29 (from the GE Turbocharger handbook)
View attachment 588640

great visuals. thanks.