Pinnacle of Piston fighter: XP-72 vs Spiteful Mk XVI?

[tonycat77]

i'd fly the corsair for ground attack, the xp-72 for a long range escort mission and the spiteful for the kind of air superiority missions that were in vogue in holland/north germany by late 1944-45

 

[mig-31bm]

i'd fly the corsair for ground attack, the xp-72 for a long range escort mission

Isn't XP-72 better for ground attack? since it based on P-47 which supposed to be the most durable aircraft of WW 2?

 

[don4331]

I am intrigued by the decision to change from a turbocharger to mechanical drive. Was turbo lag a problem for the P 47?

I would suggest more issues with turbocharger availability.

For whatever reason, GE was slow off the mark in creating the BH-1 and it had quality problems = service problems = poor reliability. And the CH-7 which was little more than a souped-up CH-5 which was the turbocharger for the R-2800 in the P-47M; not really up to powering the R-4360 at altitude for extended durations.​

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As J Jugman indicates - if you don't pipe the exhaust back to the turbocharger, you can use that area for:

a. extra air to the supercharger​

b. extra cooling air to the intercoolers.​

c. extra air from the supercharger to the carburetor​

R-4360 being 5/9ths bigger than the R-2800, it needs a bunch more air.

The numbers for the XP-72 are mfrs estimates;

The P-47M made 473mph @ 32k', at which altitude, the R-2800-57 could make 2,800hp in WER (and I believe that is with 115/145 fuel). But to keep apples to apples, the R-2800-57 makes 2,100hp@2,800rpm@28,500' on military power burning 100/130 fuel.​

Now, the R-4360-33 (XB-44 engine) has basically the same 1st stage supercharger as in the XP-72. The R-4360-33 makes 2,400hp@2,700rpm@25,000' on military power burning 100/130 fuel.​

​

So, the 64¢ question is: Was there any potential left in the 1st stage mechanical supercharger as it existed or not? Or did P&W need to get a bigger boat?? There was definitely more potential in the R-4360.

 

[Reluctant Poster]

I would suggest more issues with turbocharger availability.

For whatever reason, GE was slow off the mark in creating the BH-1 and it had quality problems = service problems = poor reliability. And the CH-7 which was little more than a souped-up CH-5 which was the turbocharger for the R-2800 in the P-47M; not really up to powering the R-4360 at altitude for extended durations.
​

As J Jugman indicates - if you don't pipe the exhaust back to the turbocharger, you can use that area for:

a. extra air to the supercharger
b. extra cooling air to the intercoolers.
c. extra air from the supercharger to the carburetor​

R-4360 being 5/9ths bigger than the R-2800, it needs a bunch more air.

The numbers for the XP-72 are mfrs estimates;

The P-47M made 473mph @ 32k', at which altitude, the R-2800-57 could make 2,800hp in WER (and I believe that is with 115/145 fuel). But to keep apples to apples, the R-2800-57 makes 2,100hp@2,800rpm@28,500' on military power burning 100/130 fuel.
Now, the R-4360-33 (XB-44 engine) has basically the same 1st stage supercharger as in the XP-72. The R-4360-33 makes 2,400hp@2,700rpm@25,000' on military power burning 100/130 fuel.
​

So, the 64¢ question is: Was there any potential left in the 1st stage mechanical supercharger as it existed or not? Or did P&W need to get a bigger boat?? There was definitely more potential in the R-4360.

 

[Reluctant Poster]

The exhaust pipe is tiny compared to the intake air system. Look at the following diagram.

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Not much space is freed

 

[mig-31bm]

Apparently this is layout of XP-72

 

[mig-31bm]

Spiteful technical drawing and different between each prototype

 

[Peter Gunn]

i'd fly the corsair for ground attack, the xp-72 for a long range escort mission and the spiteful for the kind of air superiority missions that were in vogue in holland/north germany by late 1944-45

I doubt the XP-72 would have the range of a Mustang equivalent.

Personally, I'd opt for the P-80 for all three missions and when the P-84 came online later use it for ground attack.

 

[mig-31bm]

On spiteful Mk XIV, the cooling inlet is right behind the propeller , such as on this RB517

On Spiteful Mk XVI, the cooling inlet moved further back near the landing gear such as on this RB518

And apparently, this is RB518 when it is still a spiteful XIV?

 

[don4331]

On spiteful Mk XIV, the cooling inlet is right behind the propeller , such as on this RB517



On Spiteful Mk XVI, the cooling inlet moved further back near the landing gear such as on this RB518


And apparently, this is RB518 when it is still a spiteful XIV?

That is the engine air intake, not the cooling intake.

They were playing around with ram effect vs drag.​

The cooling intakes for the radiators (intercoolers, radiators and oil) are still slightly aft of centerline on lower surface of wings.

 

[spicmart]

What would Germany's riposte to these superprops have been?
Fw 190D-12/13 with Jumo 213EB and about 780 km/h?

 

[Jugman]

The exhaust pipe is tiny compared to the intake air system. Look at the following diagram.

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Not much space is freed

For clarity, those images ignore the exhaust shrouds that surround most of the exhaust piping. They take up more space than those images let on. Removal of the carb intakes from the wing leading edge of the F4U and the P-61 didn't save a huge amount of space but it saved just enough.

If the P-72 were to be fitted it with a turbo it would most likely fallow the supercharger i n front of the intercooler arrangement of the XP-47J and the XP-72. This would probably make space even tighter.

By the time the P-72 was ordered it was understood that there was a limit to how fast a propeller driven aircaft could go. If a mechanical supercharger will get you to that limits a turbo is mostly pointless.
There are some added benefits to a mechanical supercharger.
Exhaust pumping to improve airflow through the cowling.
Less weight.
Less back pressure improving cylinder head temperature.
Less cost.

 

[PAT303]

What would Germany's riposte to these superprops have been?
Fw 190D-12/13 with Jumo 213EB and about 780 km/h?

TA 152, it absolutely deserves to be in this group.

 

[don4331]

TA 152, it absolutely deserves to be in this group.

Ta152C with Jumo 222D?

 

[Reluctant Poster]

For clarity, those images ignore the exhaust shrouds that surround most of the exhaust piping. They take up more space than those images let on. Removal of the carb intakes from the wing leading edge of the F4U and the P-61 didn't save a huge amount of space but it saved just enough.

If the P-72 were to be fitted it with a turbo it would most likely fallow the supercharger i n front of the intercooler arrangement of the XP-47J and the XP-72. This would probably make space even tighter.

By the time the P-72 was ordered it was understood that there was a limit to how fast a propeller driven aircaft could go. If a mechanical supercharger will get you to that limits a turbo is mostly pointless.
There are some added benefits to a mechanical supercharger.
Exhaust pumping to improve airflow through the cowling.
Less weight.
Less back pressure improving cylinder head temperature.
Less cost.

Basically the argument is that the USAAF was barking up the wrong tree with turbochargers particularly for fighters. The USN certainly preferred mechanically driven 2 stage superchargers and I think the success of the 2 stage Merlin opened up a lot of eyes. I find it ironic that the P 47 found its niche at low level where a turbocharger is less effective

 

[GregP]

i'd fly the corsair for ground attack, the xp-72 for a long range escort mission and the spiteful for the kind of air superiority missions that were in vogue in holland/north germany by late 1944-45

In general, you only get one choice. You are assigned to a unit and you fly whatever aircraft that unit has in inventory.

It would be very nice if you had a choice , but nobody actually did.

 

[Reluctant Poster]

Some excellent images of the P47 turbocharger system

July/August Dakota Territory Air Museum P-47 Update | AirCorps Aviation

www.aircorpsaviation.com

Note that there are 2 exhaust pipes

 

[mig-31bm]

To be fair, there is not much different between top speed of XP-72 and Spiteful XIV.

 

[PAT303]

The XP 72 will do well until it turns because it won't hold it's altitude, then the Spitfire Spitfire P51H Ta 152 will have the advantage.

 

[mig-31bm]

The XP 72 will do well until it turns because it won't hold it's altitude, then the Spitfire Spitfire P51H Ta 152 will have the advantage.

How come? XP-72 only have slightly higher wing loading, but it got very high HP/weight (and it should hold that hp advantage ways higher than the others at high altitude)

Performance of the XP-72 .
Sea level speed: 405mph (651 km/h)
Top speed: 490mph (788.5 km/h) at 25,000 feet
CLmax 1.2
Wing loading: 239.9 kg/m2
Power to weight: 0.515 hp/kg (0.233 hp/lbs)

Performance of Spiteful XVI (F.16)
Top speed: 494 mph (795 km/h) at 27,800 ft (8,473 m).
Sea level top speed: 409 mph (658 km/h)
CLmax: 1.2
Wing loading: 225.65 kg/m2
Power to weight: 0.536 hp/kg (0.24 hp/lbs)

Performance of the P-51H
Sea level speed: 413 mph ( 664.6 km/h)
Top speed: 474 mph (762.8 km/h) at 22,700 ft
CLmax: 1.2
Wing loading: 198.4 kg/m2
Power to weight: 0.517 hp/kg (0.234 hp/lbs)

Performance of the F4U-5
Sea level speed: 347 knots = 399 mph (642 km/h)
Top speed: 408 knots = 469.5 mph (755.6 km/h) at 27,000 ft
CLmax: 1.7
Wing loading: 200.5 kg/m2
Power to weight: 0.47 hp/kg ( 0.213 hp/lbs)