F4U Corsair vs P-51 Mustang

[Shortround6]

I would guess that if you at max continuous or below (1625hp?) then the turbo would be idling.

however.

Without giving any speeds it says that the turbine was required for take-off (2000hp 52in but no ram)
At what point it crossed over I don't know, and don't know if the p-47 was going full tilt on the deck if the RAM was enough to get the turbo down to idle from the 5,600rpm needed for climb (P-47 be with early control and turbo)

 

[J.A.W.]

Unless the turbo had a bypass* ( like some mech-supercharged R-2800's - with a 'neutral' setting)
then surely - the turbine was always going to be hot 'n' spinning..

So hence the take-off 'surge' warning advisement in P-47 'Pilot's Notes'..


Edit: Addit;
*Was the 'waste gate' intended - to do this?

 

[wuzak]

Unless the turbo had a bypass* ( like some mech-supercharged R-2800's - with a 'neutral' setting)
then surely - the turbine was always going to be hot 'n' spinning..

So hence the take-off 'surge' warning advisement in P-47 'Pilot's Notes'..


Edit: Addit;
*Was the 'waste gate' intended - to do this?

I doubt all the exhaust bypassed the turbo. It would need to have some flow through and maintain some rpm to reeuce spooling time when it was needed.

Also, the temperature of the turbo must have some influence on the lubrication, seals, etc. If it sat for a while and became cold it may not lubricate properly for a short period.

 

[DarrenW]

Great discussion guys but I'm now a little confused about when the turbo was actually used. I was under the impression that when boost was demanded (controlled by the booster lever on the throttle quadrant) the turbo portion of the turbo-supercharger was always utilized to some extent, and that when climbing to altitude the turbine wheel connected to the supercharger unit would spin faster from the increase of exhaust gases sent to it by a closing of the waste gates. This action is what took up the slack as the supercharger's boost pressures dropped off during the climb, thus maintaining it at the current setting. How else could the engine maintain a nearly constant military power output all the way up to critical altitude? A standard supercharger alone will not give you this. Are you saying that it was only used while operating at or above military power levels and flying at high altitudes?

http://www.wwiiaircraftperformance.org/p-47/P-47D_42-26167_Power.jpg

 

[GregP]

Whether or not it was always used depends entirely on whether or not the waste gate could be completely opened and completely closed.

If the waste gate is all the way open, then all the exhaust is diverted out the exhaust pipe. If the waste gate is completely closed, then all the exhaust is diverted to the turbocharger. Any "in between" setting would allow some exhaust to escape and some to get to the turbo. I'm inclined to believe it always allowed enough exhaust to get to the turbo to keep it at least at "idle," which is spinning relatively slowly ,about 10% max rpm in fact. That speed produces no boost and keeps the turbo warm. I'd think you'd have to have enough heat going through the intercooler to keep it from freezing, but maybe not.

Seems like a fun thing to investigate. I'll ask someone who knows and get back in a week or so.

 

[wuzak]

Great discussion guys but I'm now a little confused about when the turbo was actually used. I was under the impression that when boost was demanded (controlled by the booster lever on the throttle quadrant) the turbo portion of the turbo-supercharger was always utilized to some extent, and that when climbing to altitude the turbine wheel connected to the supercharger unit would spin faster from the increase of exhaust gases sent to it by a closing of the waste gates. This action is what took up the slack as the supercharger's boost pressures dropped off during the climb, thus maintaining it at the current setting. How else could the engine maintain a nearly constant military power output all the way up to critical altitude? A standard supercharger alone will not give you this. Are you saying that it was only used while operating at or above military power levels and flying at high altitudes?

http://www.wwiiaircraftperformance.org/p-47/P-47D_42-26167_Power.jpg

The turbo, generally speaking, only produced enough boost so that the engine itself thinks it was at sea level. Hence the constant power rating to the critical altitude - which, if I am not mistaken, coincided with the maximum turbo rpm.

 

[Shortround6]

As a theory let me throw out the idea that there was always some gases going through the turbo.

There is one on each side. They do not block the exhaust gases from going to the rear of the plane and the turbo. They do offer a lower resistance path to the outside air and the pressurized gasses will tend to follow the path of least resistance. Or at least will try to equalize which is what happens when the gate is in a middle position.
Some warbirds flying now have no turbos and the waste gate is removed making these the only exhaust outlet. Simplified maintenance for one thing, no exhaust gases running another 20 ft through the fuselage and no potential for exhaust leaks into the fuselage.

I would note that the P-47 seems to be the only plane with the waste gate/s before the turbo charger.
edit. cut away of turbo

gasses come through the duct on the right and go into the turbo housing with the wast gate at the end. The majority of the gas will go through the open waste gate and as it closes more will go out through the turbine blades.
There was no way to "shut off" the turbine totally.

 

[wuzak]

I would note that the P-47 seems to be the only plane with the waste gate/s before the turbo charger.
Picture of model but seems to be correct

Schematically, all wastegates are before the turbo.

It just so happens that the B-series turbo had the wastegate integral with the turbine housing.

GE B-series turbo cutaway

 

[DarrenW]

Oh ok, now it's making more sense to me. So I suspect that when the supercharger regulator sensed a drop in these exhaust gases (which would happen as the engine loses power) it would close the waste gates even further, which allowed the turbine to spin even faster and provide more boost to the carburetor. This action would increase engine power accordingly. Does this seem plausible?

 

[wuzak]

Oh ok, now it's making more sense to me. So I suspect that when the supercharger regulator sensed a drop in these exhaust gases (which would happen as the engine loses power) it would close the waste gates even further, which allowed the turbine to spin even faster and provide more boost to the carburetor. This action would increase engine power accordingly. Does this seem plausible?

I believe the regulator used the pressure of the compressed air to control it. Maybe early P-38s used the exhaust back pressure? Along with an rpm limit.

 

[Builder 2010]

Closing the waste gate would reduce flow through the exhaust turbine, not increase it. The most turbine action would happen with the gate wide open… at least that's how I set it. Why was the ram cooling scoop adjustable on the turbine face. It seems that it can be mounted at differing angles. I've never seen a real up one up close to see how this actually works.

 

[Shortround6]

Oh ok, now it's making more sense to me. So I suspect that when the supercharger regulator sensed a drop in these exhaust gases (which would happen as the engine loses power) it would close the waste gates even further, which allowed the turbine to spin even faster and provide more boost to the carburetor. This action would increase engine power accordingly. Does this seem plausible?

That was how the first turbo regulators worked but they weren't very successful. The later ones shifted to measuring the air pressure at some point in the inlet duct and regulated the waste gate to try to maintain that value.

 

[pbehn]

I would think that even if the turbo isn't needed or even providing any boost it is best to keep it spinning to keep it warm and reduce the lag if it is needed urgently.

 

[Milosh]

The GE turbo, The Turbosupercharger and the Airplane Power Plant

 

[DarrenW]

Closing the waste gate would reduce flow through the exhaust turbine, not increase it.

But don't most of the exhaust gases escape out the waste gates into the open air when they are wide open? Closing them forces these same gases to travel back to the turbine wheel which increases it's rpm.

 

[Shortround6]

But don't most of the exhaust gases escape out the waste gates into the open air when they are wide open? Closing them forces these same gases to travel back to the turbine wheel which increases it's rpm.

You are correct, In the case of the P-47 it is only slightly different, the waste gate does not close off the passage/duct to the turbocharger, it merely opens a variable sized hole in the side of the pipe/duct.

 

[GregP]

Great pics, Shortround. I was going to go look at "Dottie Mae," but I see I don't have to.

 

[YF12A]

Closing the waste gate would reduce flow through the exhaust turbine, not increase it. The most turbine action would happen with the gate wide open… at least that's how I set it. Why was the ram cooling scoop adjustable on the turbine face. It seems that it can be mounted at differing angles. I've never seen a real up one up close to see how this actually works.

Umm, closing the waste gate will, depending on the design of the system, force most or all of the exhaust through the turbine bucket, not the other way around, that's why it is called a waste gate.

 

[Barrett]

There was a real-world, single-elimination contest between Mustangs and Corsairs: Honduras v. El Salvador summer of 69, the so-called "Football War" because both were in the World Cup (or whatever.) All air to air successes were scored by a sr. HAF F4U-4 piloto who downed two El Sal FG-1s and a P-51D. Fernando Soto--he's in my Naval Institute Corsair book thanks to an exchange pilot who knew him.

 

[DarrenW]

Anyone know what the turbo-supercharger unit used by the P-47 weighed in total? I recall a discussion about it but for the life of me can't remember what thread....