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



## Husky (Jul 17, 2020)

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?


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## MiTasol (Jul 18, 2020)

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.


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## Shortround6 (Jul 18, 2020)

Husky said:


> 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.


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## swampyankee (Jul 18, 2020)

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.

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## Husky (Jul 18, 2020)

MiTasol said:


> 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.


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## Dash119 (Jul 18, 2020)

MiTasol said:


> 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?


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## Shortround6 (Jul 18, 2020)

Dash119 said:


> 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,


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## MiTasol (Jul 18, 2020)

Dash119 said:


> 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)

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## Dash119 (Jul 18, 2020)

Gentlemen,

I stand corrected.


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## wuzak (Jul 19, 2020)

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.


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## MiTasol (Jul 20, 2020)

wuzak said:


> 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.


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## Reluctant Poster (Jul 20, 2020)

Dash119 said:


> 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.


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## wuzak (Jul 20, 2020)

wuzak said:


> 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 said:


> 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.






Reluctant Poster said:


> 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.


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## Dash119 (Jul 20, 2020)

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?


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## mad_max (Jul 20, 2020)

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.


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## Dash119 (Jul 20, 2020)

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


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## mad_max (Jul 20, 2020)

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.


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## Dash119 (Jul 20, 2020)

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.


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## MiTasol (Jul 20, 2020)

This diagram shows the wastegate butterfly clearly

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## tommayer (Jul 23, 2020)

MiTasol said:


> 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
> ...


great visuals. thanks.


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## mad_max (Jul 23, 2020)

Dash119 said:


> 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.



I only know of one P-47 with a functioning turbo and that is Hun Hunter. All the rest are just using the single speed supercharger only as that's good for 10K alt.


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## stug3 (Jul 25, 2020)

P-47D

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## Big Jake (Aug 23, 2020)

Gentlemen, The waste gate on B turbos as mounted on B-17, B-24 and P-38 is located after the turbine. The turbos are the same for these 3 aircraft and they were made by either by GE or Allis-Chalmers. We use P-38 turbos on our B-17. The P-38 has one turbo per engine, the B-29 two. Re the P-47: There are always exhaust gases that go through the exhaust system and turbine, even when the waste gate is completely open. Thus the duct under the cockpit will always be "hot". I believe that the only reason that the waste gate was installed where it is at is the desire to "dump" much of the exhaust gases outboard as close to the engine as possible when boost is not needed. 

By the way, when it comes to exhaust stacks, one shouldn't forget the glare from the flames coming out of the exhaust at night. That was one of the main reasons for placing the stacks where they sometimes wound up at.


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## wuzak (Aug 23, 2020)

Big Jake said:


> Gentlemen, The waste gate on B turbos as mounted on B-17, B-24 and P-38 is located after the turbine.



No, it is not. The wastegate relieves the exhaust before it passes through the turbine.

On the B-series the wastegate is integral with the turbine housing, which directs the exhaust through the turbine.

Physically the wastegate is behind the turbine on those machines, but it could be placed in any orientation. In terms of the exhaust flow, the wastegate is before the turbine.


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## Big Jake (Aug 25, 2020)

wuzak said:


> No, it is not. The wastegate relieves the exhaust before it passes through the turbine.
> 
> Before it passes through the turbine? See below.
> 
> ...



So now it's behind the turbine? 

As someone who has personally replaced turbos on B-17 on a number of times, I should know my turbos... The wastegate is behind the turbine and after it is nothing - in a preflight inspection, you stick your hand into the wastegate and make sure that the flapper valve is loose and free. I do it often enough...


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## wuzak (Aug 25, 2020)

Big Jake said:


> So now it's behind the turbine?
> 
> As someone who has personally replaced turbos on B-17 on a number of times, I should know my turbos... The wastegate is behind the turbine and after it is nothing - in a preflight inspection, you stick your hand into the wastegate and make sure that the flapper valve is loose and free. I do it often enough...



The exhaust that exits the wastegate does not go, and has not been, through the turbine. It works exactly the same as the wastegates on the P-47, which are not mounted behind the turbine.

The wastegate is operationally between the engine and the turbine, even if physically is not.

If you turn the turbo 90° around its axis, is the wastegate now to the side?

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## Dash119 (Aug 26, 2020)

Big Jake said:


> So now it's behind the turbine?
> 
> As someone who has personally replaced turbos on B-17 on a number of times, I should know my turbos... The wastegate is behind the turbine and after it is nothing - in a preflight inspection, you stick your hand into the wastegate and make sure that the flapper valve is loose and free. I do it often enough...


The B series Turbo-Supercharger contains an integrated wastegate, not a separate wastegate like the C series found in the P-47. As wuzak points out above, while the butterfly valve of the wastegate and it's exhaust port are located at the back end of the unit, in operation it controls the flow of exhaust gases into the exhaust turbine. This was not clear to me or other members until wuzak explained the actual operation, so he gets the credit for the following.

The circular manifold which culminates in the wastegate has pathways to the exhaust turbine of the Turbo-Supercharger. So when the wastegate is closed, the exhaust gases are forced through the exhaust turbine and out the bottom of the Turbo-Supercharger itself. When the wastegate is open, the back pressure inherent in the exhaust turbine of the Turbo-Supercharger causes most of the exhaust gases to flow out past the butterfly valve.

So despite its physical location, the integrated wastegate on the B series Turbo-Supercharger provides a bypass and regulates the flow of exhaust gases into the exhaust turbine. All the wastegates I have ever heard of, in any application, control boost by regulating the flow of exhaust gasses to the *inlet* side of the exhaust turbine not the *outlet* side. Trying to control boost by regulating the flow of exhaust from the *outlet* side of the exhaust turbine creates a whole litany of issues, and would be very inefficient.

See the image of the B-24 manual in post #8 of this thread for a better visual. The B-17 manual image is somewhat deceptive as it doesn't show the flow out the bottom of the Turbo-Supercharger as it should.


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## wuzak (Aug 26, 2020)

Dash119 said:


> Trying to control boost by regulating the flow of exhaust from the *outlet* side of the exhaust turbine creates a whole litany of issues, and would be very inefficient.



That would be the Variable Discharge Turbine (VDT) that Pratt & Whitney tried for the R-2800 and R-4360, but abandoned due to control issues (and the coming of jets).


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