What of the Republic P-47 Turbo-Supercharger

[Husky]

The P-51A and Mustang Mk 1 had a single stage supercharger as did the early Spitfires. Later they had a two stage supercharger to give altitude performance. The P-47 and P-38 used an exhaust turbo for one stage and then and engine driven supercharger for the other stage, this works very well but is hard to fit in a single seat fighter. When Rolls Royce were asked to produce an engine for a high altitude Wellington bomber they discounted the use of a turbo just because of the difficulty in adapting it for anything else especially single engine fighters.

I don't see, or missed, any mention of engine driven on the P-47. All exhaust gas managed by variable ducting ...just didn't see any text to 'engine driven' in that manuals.

Seems, P-47 pilots were taught to manage duct work air flow to and from the turbo-supercharger to maximize engine performance.

 

[pbehn]

I don't see, or missed, any mention of engine driven on the P-47. All exhaust gas managed by variable ducting ...just didn't see any text to 'engine driven' in that manuals.

Seems, P-47 pilots were taught to manage duct work air flow to and from the turbo-supercharger to maximize engine performance.

Here, from Wiki. "The R-2800 powered several types of fighters and medium bombers during the war, including the U.S. Navy's Vought F4U Corsair, with the XF4U-1 first prototype Corsair becoming the first airframe to fly (as originally designed) with the Double Wasp[7] in its XR-2800-4 prototype version on May 29, 1940,[8] and the first single-engine American fighter plane to exceed 400 mph (640 km/h) in level flight during October 1940. The R-2800 also powered the Corsair's naval rival, the Grumman F6F Hellcat, the U.S. Army Air Forces' Republic P-47 Thunderbolt (which uniquely, for single-engined aircraft, used a General Electric turbocharger), the twin-engine Martin B-26 Marauder and Douglas A-26 Invader, as well as the first purpose-built twin-engine radar-equipped night fighter, the Northrop P-61 Black Widow. When the US entered the war in December 1941, designs advanced rapidly, and long-established engines such as the Wright Cyclone and Double Wasp were re-rated on fuel of much higher octane rating (anti-knock value) to give considerably more power. By 1944, versions of the R-2800 powering late-model P-47s (and other aircraft) had a rating (experimental) of 2,800 hp (2,100 kW) on 115-grade fuel with water injection.[4]"

 

[Husky]

Seems, P-47 pilots were taught to manage duct work air flow to and from the turbo-supercharger to maximize engine performance.

Don't know your aircraft and systems; don't understand critical relationships of power; in relation to density altitude, pressure altitude, indicated airspeed, true airspeed, super-turbine speeds at what altitude.......then...you fail.

No need to be a mathematician and intersect every point on every performance chart...but, understanding the theory behind the chart and/or knowing those specific areas of performance where one operates by memory can really save your ass.

 

[Husky]

Here, from Wiki. "The R-2800 powered several types of fighters and medium bombers during the war, including the U.S. Navy's Vought F4U Corsair, with the XF4U-1 first prototype Corsair becoming the first airframe to fly (as originally designed) with the Double Wasp[7] in its XR-2800-4 prototype version on May 29, 1940,[8] and the first single-engine American fighter plane to exceed 400 mph (640 km/h) in level flight during October 1940. The R-2800 also powered the Corsair's naval rival, the Grumman F6F Hellcat, the U.S. Army Air Forces' Republic P-47 Thunderbolt (which uniquely, for single-engined aircraft, used a General Electric turbocharger), the twin-engine Martin B-26 Marauder and Douglas A-26 Invader, as well as the first purpose-built twin-engine radar-equipped night fighter, the Northrop P-61 Black Widow. When the US entered the war in December 1941, designs advanced rapidly, and long-established engines such as the Wright Cyclone and Double Wasp were re-rated on fuel of much higher octane rating (anti-knock value) to give considerably more power. By 1944, versions of the R-2800 powering late-model P-47s (and other aircraft) had a rating (experimental) of 2,800 hp (2,100 kW) on 115-grade fuel with water injection.[4]"

I got all that sir. But what other aircraft has a turbo-supercharging system like the P-47? And, why not?

 

[pbehn]

I got all that sir. But what other aircraft has a turbo-supercharging system like the P-47? And, why not?

Apart from the aircraft listed in my post many other American bombers, the problem comes with a single engine fighter because the logical place for the turbo is where the pilot or fuel are. On the allied side the RR Merlin with a two stage two speed supercharger was found to be best, especially with regard to the P-51 because it bolted almost straight in with few modifications. A Turbo version would have the turbo where the P-51s cooling system is.

 

[Shortround6]

OK,

Diagram leaves out the waste gates which are right behind the oil cooler shutters. there is an arrow but no caption.

At low altitude where the turbo was needed the wastegates dumped the majority of the exhaust out just behind the oil cooler doors. as the plane climbed the waste gates shut and routed more of the exhaust gas to the turbo, after passing through the turbo the exhaust exited the aircraft though the duct in the bottom of the plane.

Underneath the star in the insignia. at high altitude most of the exhaust was exiting the aircraft though that duct. I am not sure if it gave any forward thrust or not.
I would note that all other US turbos just dumped the exhaust gas from the turbo out into open air. In part to expose the turbine blades to cool air to keep the temperature down.

as to why? It is what the customer wanted.
The US army liked turbo chargers. And compared to the two stage mechanical superchargers used in the F4U and F6F the turbo offered much more power at the higher altitudes.
They were not small airplanes either. Please remember that when these planes (P-47 and the F4U) were first conceived and flown 100/130 fuel did not exist and 100/100 was about as good as it got in the US. There was a limit to how much you could compress the intake charge before detonation set in and you needed to cool the intake charge with intercoolers to prevent detonation.

 

[Dash119]

I don't see, or missed, any mention of engine driven on the P-47. All exhaust gas managed by variable ducting ...just didn't see any text to 'engine driven' in that manuals.

Seems, P-47 pilots were taught to manage duct work air flow to and from the turbo-supercharger to maximize engine performance.

Unless the Supercharger is two-speed and requires the pilot to manually change speeds, there is no need for the pilot to interact with the Supercharger. Some Superchargers shifted from low speed to high speed automatically, others required the pilot to make the change manually. I'm not sure if the single stage Supercharger on the P-47 was single speed or two speed.

I had not heard of variable ducting, usually the Waste Gates regulate the flow of exhaust to the Turbo-Supercharger. There may have been some kind of manual control for the adjustment of the Waste Gates on the P-47.

 

[Dash119]

Underneath the star in the insignia. at high altitude most of the exhaust was exiting the aircraft though that duct. I am not sure if it gave any forward thrust or not.
I would note that all other US turbos just dumped the exhaust gas from the turbo out into open air. In part to expose the turbine blades to cool air to keep the temperature down.

I don't believe there was enough forward thrust to offset the drag of outlet duct on the P-47. In most cases the energy contained in the exhaust gases is greatly reduced as it is converted to mechanical energy in the Turbocharger. The loss of thrust from the exhaust is one of the downsides of the Turbo-Supercharger.

 

[Dash119]

I got all that sir. But what other aircraft has a turbo-supercharging system like the P-47? And, why not?

As previously mentioned the P-38, and additionally the B-17 and B-29. Once again, the bulk of the system was not well suited for use in a single engine fighter. Additionally it was the U.S.A.A.F. that were true advocates of the Turbo-Supercharger. The U.S.N. and most other countries primarily relied on the Two Stage Supercharger for high altitude performance.

 

[GregP]

Hi Husky, just in case you don't know what "waste gates" are I'll post this. No insult intended.

A turbocharger has a compressor the same as a supercharger. In WWII, turbochargers were called "turbosuperchargers" leading to modern-day confusion by many people. There are several types of compressors, but the ones in the P-47 look very similar to a supercharger compressor. Both the supercharger and the turbocharger compressors need to be rotated mechanically by something to work. In the case of a supercharger, the compressor is connected to the crankshaft via a gear and the engine supplies the power to turn the compressor. it cnn be 0 - 300 or so horsepower, depending on rpm and boost.

In the case of the P-47 turbocharger, the exhaust is routed through a fanlike arrangement (looks like a turbojet engine turbine blade set) and the flow of the exhaust makes it turn. It is connected via a solid shaft to the compressor and it's sort of like driving a fan with compressed air. If the entire exhaust is routed through the fan at all times, the compressor would be working all the time at maximum boost, which is not desirable. So, they have a pivoting flap (pivots on pins) in the exhaust pipe that opens and closes to let all or any portion of the exhaust flow out the exhaust pipe or through the turbocharger. If the flap closes off the exhaust pipe, all the exhaust goes to the turbo fan. If the flap closes off the fan, the entire exhaust goes out the exhaust pipe and the extra power that could be gained from using it for boost is "wasted" by the waste gate. If the flap is anywhere in between fully open or closed, some portion flows out the exhaust pipe and the rest flows to the turbo fan to spin it and generate boost via the compressor connected to the fan. They use a pressure regulator to control the boost to some desired set point by moving the waste gate.

In the case of the P-47 turbo system above, the exhaust pipe is up near the front and the pipe to the turbo runs along the lower left fuselage in a stainless tunnel to the turbo fan, which is located behind the cockpit just over the belly bump on the bottom rear of the fuselage in front of the tailwheel. The compression generated heats up the air and it goes through a radiator before flowing back forward through aluminum pipes that are routed on either side of the cockpit at about elbow height and back to the pressure carburetor.

Hope that helps. Cheers.

 

[Shortround6]

The P-47 used a single speed supercharger on the engine.

There was a turbo control that was supposed to maintain a constant value (pressure) in either the exhaust manifold/system (early control) or in the intake system before the carb on the engine driven supercharger. This control was supposed to open or close the wastegate/s automatically to a preset value. Like sea level air pressure to the inlet of the carburetor.

 

[Husky]

Appreciate all your all's inputs.

I understand the technical (well kinda, but theory I get)

But why a big huge unproven fighter with massive

Hi Husky, just in case you don't know what "waste gates" are I'll post this. No insult intended.

A turbocharger has a compressor the same as a supercharger. In WWII, turbochargers were called "turbosuperchargers" leading to modern-day confusion by many people. There are several types of compressors, but the ones in the P-47 look very similar to a supercharger compressor. Both the supercharger and the turbocharger compressors need to be rotated mechanically by something to work. In the case of a supercharger, the compressor is connected to the crankshaft via a gear and the engine supplies the power to turn the compressor. it cnn be 0 - 300 or so horsepower, depending on rpm and boost.

In the case of the P-47 turbocharger, the exhaust is routed through a fanlike arrangement (looks like a turbojet engine turbine blade set) and the flow of the exhaust makes it turn. It is connected via a solid shaft to the compressor and it's sort of like driving a fan with compressed air. If the entire exhaust is routed through the fan at all times, the compressor would be working all the time at maximum boost, which is not desirable. So, they have a pivoting flap (pivots on pins) in the exhaust pipe that opens and closes to let all or any portion of the exhaust flow out the exhaust pipe or through the turbocharger. If the flap closes off the exhaust pipe, all the exhaust goes to the turbo fan. If the flap closes off the fan, the entire exhaust goes out the exhaust pipe and the extra power that could be gained from using it for boost is "wasted" by the waste gate. If the flap is anywhere in between fully open or closed, some portion flows out the exhaust pipe and the rest flows to the turbo fan to spin it and generate boost via the compressor connected to the fan. They use a pressure regulator to control the boost to some desired set point by moving the waste gate.

In the case of the P-47 turbo system above, the exhaust pipe is up near the front and the pipe to the turbo runs along the lower left fuselage in a stainless tunnel to the turbo fan, which is located behind the cockpit just over the belly bump on the bottom rear of the fuselage in front of the tailwheel. The compression generated heats up the air and it goes through a radiator before flowing back forward through aluminum pipes that are routed on either side of the cockpit at about elbow height and back to the pressure carburetor.

Hope that helps. Cheers.

Helps in plain language - much thanks.

So, I have a fair idea of the mechanics and theory...but why and intricate ducted system that is heavy when an F4U, P-51 or Spit charger could be used at a lot less weight?

 

[Shortround6]

F4U R-2800 engine 1650hp at 21,000ft no ram and 23,000ft with ram with 2 stage mechanical supercharger with the aux stage in high gear. Has inter coolers. 53in MAP.
P-47 R-2800 engine 2000hp at 27000 ft with turbo, 52in of MAP.

F4U is using 350hp to drive the auxiliary supercharger (1st stage)

P-51 or Spitfire supercharger is too small to feed an R-2800.

 

[Dash119]

At low altitude where the turbo was needed the wastegates dumped the majority of the exhaust out just behind the oil cooler doors. as the plane climbed the waste gates shut and routed more of the exhaust gas to the turbo, after passing through the turbo the exhaust exited the aircraft though the duct in the bottom of the plane.

I think you meant to say "At low altitude where the turbo was not needed..."

So there was no boost provided by the Turbo-Supercharger during take off, it was strictly altitude compensating? That would seem to be a disadvantage down low when compared to a two stage Supercharger. Did the Corsair have more horsepower available at take off than the P-47?

 

[GregP]

The U.S.A. preferred the boost for it's engine during WWII came from a turbocharger. There were 2-stage supercharged R-2800, but they were for the Navy, not the USAAF. The Thunderbolt had a single-stage supercharger for low-altitude boost and an additional turbocharger for boost at higher altitudes. The P-47 was perhaps less than wonderful down low but, up high, above 25,000 feet, it was one of the best, if not the best, fighter that was mass-produced for WWII.

There was little decent competition against it at 30,000 feet and above. The much-vaunted Ta-152H, the high-altitude version of the Ta-152, never got to fight up there to speak of and was produced in numbers too small to be of any impact in any case. Aside from that airplane, there were damned few equals or better for the P-47 at 35,000 feet.

 

[Acheron]

IIRC, aircrafts without superchargers had to be optimized for either low- or high-altitude and would suffer in performance if flying at the wrong altitude. Please correct me if I am wrong.

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).

From what I read, they later introduced a new propeller to the P-47 that ENORMOUSLY improved the aircraft's climbing ability. Must have been a nasty shock to the Germans.

 

[Dash119]

There were 2-stage supercharged R-2800, but they were for the Navy, not the USAAF. The Thunderbolt had a single-stage supercharger for low-altitude boost and an additional turbocharger for boost at higher altitudes.

I think the USAAF also used two stage Supercharged R-2800's in the A-26, B-26, C-46 and early versions of the P-61 but I could be wrong maybe they were single stage.

 

[pbehn]

Just wanting a turbo charger set up doesn't mean you get one. The Turbo operates in a very severe environment with very high temperatures and RPM so need special alloys bearings and lubricants. The supercharger and turbocharger were steps towards the jet engine, eventually they connected one to the other and cut out the middle man.

 

[Shortround6]

That would seem to be a disadvantage down low when compared to a two stage Supercharger. Did the Corsair have more horsepower available at take off than the P-47?

Not in the early versions, WEP wasn't approved until late 1943 for these aircraft, that changed things a bit. The F4U (and F6F) didn't engage the auxiliary supercharger low gear until they were at several thousand feet. The Corsair and Hellcat(and any other plane using the two stage P&W R-2800) could disengage the aux stage (put it in neutral) and ran on just the engine driven single speed supercharger. The engine in an F4U weighed 215lbs more than the engine in the P-47 due to the weight of the auxiliary supercharger.

I think the USAAF also used two stage Supercharged R-2800's in the A-26, B-26, C-46 and early versions of the P-61 but I could be wrong maybe they were single stage.

The P-61 had the two stage engine, the others were single stage but had two speeds.

 

[swampyankee]

Was the weight of the turbocharger system in the P-47 charged to the engine or airframe?