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

[PAT303]

It's heavy and can't climb like the others, any good pilot facing the Jug will go into a vertical fight and get above it, the Spitfire and Ta 152 would defiantly do a climbing turn then reverse and boom and zoom it.

 

[mig-31bm]

It's heavy and can't climb like the others, any good pilot facing the Jug will go into a vertical fight and get above it, the Spitfire and Ta 152 would defiantly do a climbing turn then reverse and boom and zoom it.

Number wise (if we asume engineer estimate of XP-72 is correct), then it is the one with highest rate of climb. Even higher than XP-51G

Spiteful: 4890 ft/min (24.8 m/s) at 2000 ft. No additional information

XP-72 with twin props: 5250 ft/min (26.67 m/s) at sea level, take 3.8 min to climb to 20,000 ft

P-51H: 5120 ft/min (26 m/s) at sea level, take 4.58 min to climb to 20,000 ft

XP-51G: take 3.58 min to climb to 20,000 ft

F4U-5: 4840 ft/min (24.58 m/s) at sea level, take 4.7 min to climb to 20,000 ft

 

[PAT303]

Number wise (if we asume engineer estimate of XP-72 is correct), then it is the one with highest rate of climb. Even higher than XP-51G

Spiteful: 4890 ft/min (24.8 m/s) at 2000 ft. No additional information

XP-72 with twin props: 5250 ft/min (26.67 m/s) at sea level, take 3.8 min to climb to 20,000 ft

P-51H: 5120 ft/min (26 m/s) at sea level, take 4.58 min to climb to 20,000 ft

XP-51G: take 3.58 min to climb to 20,000 ft

F4U-5: 4840 ft/min (24.58 m/s) at sea level, take 4.7 min to climb to 20,000 ft

It's not good to assume, I'd like to see hard evidence on the XP-72 instead of theoretical. It's a heavy aircraft.

 

[hobbes154]

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

https://i.pinimg.com/originals/ae/a4/f6/aea4f68bbd489e9845cf8b33207edc97.jpg

Not much space is freed

A little OT but I never understood why the P-47 air intake was at the front of the plane requiring all that bulky ductwork underneath the pilot? The air is first "used" in the turbocharger behind the pilot so why not a scoop at rear similar to the Mustang radiator?

As shown in post #26 the intake was moved back a bit on the XP-72 but still underneath the pilot rather than behind (I don't think the mechanical 2nd stage vs the turbo should make any difference, that only replaces exhaust ducting with a driveshaft).

From this thread perhaps a rear intake would suck up too much dust etc (presumably engines are more sensitive than radiators)?

 

[mig-31bm]

Someone OT but similar, would Spitfire XIV better than Spiteful?, given that it has much lower wing loading and very competitive Hp/ mass

Performance of the Spitfire XIVe .
Sea level speed: 397 mph (638.9 km/h)
Top speed: 449 mph (722 km/h) at 24,500 ft (7,468 m)
Climb to 20,000 ft in 5 minutes
Engine horsepower: Griffon 65 engine
2,050 hp
Normal take off weight: 8,574 lbs (3,889 kg)
Wing area: 22.5 m2
Wing loading: 172.8 kg/m2
Power to weight: 0.527 hp/kg (0.239 hp/lbs)
Weapons:
two 0.50 caliber machine gun
two 20 mm cannon

 

[Reluctant Poster]

A little OT but I never understood why the P-47 air intake was at the front of the plane requiring all that bulky ductwork underneath the pilot? The air is first "used" in the turbocharger behind the pilot so why not a scoop at rear similar to the Mustang radiator?

As shown in post #26 the intake was moved back a bit on the XP-72 but still underneath the pilot rather than behind (I don't think the mechanical 2nd stage vs the turbo should make any difference, that only replaces exhaust ducting with a driveshaft).

From this thread perhaps a rear intake would suck up too much dust etc (presumably engines are more sensitive than radiators)?

Picture a B50 nacelle with a pilot stuck on top

 

[Jugman]

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

Not at all! Highly compact and weight efficient turbo installations (the V-1710H or Bell's turbosupercharged P-63 are good examples) that could fit a Spitfire or P-51 were very feasible even in 1940. The problem was no one firm had all the knowledge or resources necessary to accomplish this at that time. The USAAF had far to few eggs in far to many baskets nor was the US procurement system really set up to deal with component R&D.

Even before the 60 series Merlin was a success P&W had the same arrangement on the XH-2600 and XH-3130. There really wasn't anything novel or eye opening about it. It was the fastest, simplest and cheapest way to improve performance and given the situation at the time it was unquestionably the right call.

The overall length of the P-72 was less than six inches longer but had to accommodate an engine some two feet longer and 1000lbs heavier. The accessory section became engine and the main fuel tank was reduced to 155US. gal. to make space for the oil tank and accessories. If you want to fit a turbo, reduction in size or removal of the auxiliary fuel tank would be necessary to provide space to route ducting efficiently. With only 255gal* total the P-72 was projected to have an endurance of only .62 hours at rated power. Well below the 1hr minimum and 1.5hr standard. Reducing this another 100gal. would have crippled its already poor endurance.


*At some later point 370gal became the listed fuel capacity. I don't known if that was for comparative purposes or if Republic actually managed to get fuel capacity up to the same level as the P-47D-RE-25. If they did the latter there is definitely fuel tanks in the wings.

 

[AMCKen]

Not quite relevant but when I was going to the Reno Races in the late 1970s I had a t-shirt that said "Spiteful XV Racing Team".
The XV had the Griffon 85 engine with contra-props. Spiteful wings were used on the Supermarine Attacker jet fighter.

 

[hobbes154]

Picture a B50 nacelle with a pilot stuck on top

The intake position looks fairly similar to the XP-72 but not sure what point you are trying to make?

What I'm wondering is, seeing as the pilot on both P-47 and XP-72 was in between the engine and 2nd stage turbo/supercharger + intercooler, why the intake was not moved back (relative to the engine) along with those accessories? Only reason I can think of is it would ingest too much crud on takeoff? (Probably less of a problem on a B-50 since it's operating on paved runways and the engine is further off the ground.)

 

[don4331]

View attachment 796286
The intake position looks fairly similar to the XP-72 but not sure what point you are trying to make?

What I'm wondering is, seeing as the pilot on both P-47 and XP-72 was in between the engine and 2nd stage turbo/supercharger + intercooler, why the intake was not moved back (relative to the engine) along with those accessories? Only reason I can think of is it would ingest too much crud on takeoff? (Probably less of a problem on a B-50 since it's operating on paved runways and the engine is further off the ground.)

I would Republic had learned more about boundary/ram air. There's a progression from P-43 Lancer have slightly ovoid cowl with intake at bottom, to P-47B thru D enlarged ovoid with both intake and intercooler air. Then for the XP-47H, you have the air intakes on the rear fuselage* and the cooling air intake slightly back from propeller.

Having the intake close to the propeller helps get air forced into the intake/cooling - important for a steep climbing interceptor? Maybe not so much for plane already operating at high speed (or with engine cooling fan) The XP-47J builds on this. So, not surprising that the XP-72 has moved it further back.

It is surprising that compared to other late aircraft Boeing (B-50). N.A. (P-51), Lockheed (P38 Late) and even Bf.109F & later, that the intake wasn't separated from the boundary layer.

*P-47H is interesting: When Republic installed the intake scoops, the engine could get enough air to make full power; but the drag of the scoop resulted in plane being slower...

 

[hobbes154]

... Then for the XP-47H, you have the air intakes on the rear fuselage*

Really? Where? It looks very similar to the XP-72 to me. Уголок неба ¦ Republic P-47H Thunderbolt

Do you mean those two little scoops on the upper rear fuselage either side of the "razorback" behind the canopy? They seem so small.

*P-47H is interesting: When Republic installed the intake scoops, the engine could get enough air to make full power; but the drag of the scoop resulted in plane being slower...

Slower compared to what? Not having scoops and just having holes flush with the skin in the same place (less drag but less power)? Sort of like the exhausts below the scoops but turned around?

 

[don4331]

Really? Where? It looks very similar to the XP-72 to me. Уголок неба ¦ Republic P-47H Thunderbolt

Do you mean those two little scoops on the upper rear fuselage either side of the "razorback" behind the canopy? They seem so small.

Slower compared to what? Not having scoops and just having holes flush with the skin in the same place (less drag but less power)? Sort of like the exhausts below the scoops but turned around?

The 2 "little" scoops are larger combined than single one on say Bf.109 which powered ~1,500 DB engine..

You got it - flush holes less power but even less drag.

 

[Jugman]

A little OT but I never understood why the P-47 air intake was at the front of the plane requiring all that bulky ductwork underneath the pilot? The air is first "used" in the turbocharger behind the pilot so why not a scoop at rear similar to the Mustang radiator?

As shown in post #26 the intake was moved back a bit on the XP-72 but still underneath the pilot rather than behind (I don't think the mechanical 2nd stage vs the turbo should make any difference, that only replaces exhaust ducting with a driveshaft).

From this thread perhaps a rear intake would suck up too much dust etc (presumably engines are more sensitive than radiators)?

Two factors.
The intake would sit much closer to the ground and the air would be more turbulent greatly increasing the risk of FOD.
The exhaust pipes ain't moving so you're not saving much depth. The main air duct was ~14.5in. deep vs ~8in. across for the exhaust shrouds.

 

[mig-31bm]

I just realized that I forget to mention the Hornet F.1. It is the only twin engine super props with practically the same high speed performance of P-51H but much better climb rate
In term of speed, it almost overlapped with P-51H at high altitude. There is almost no different

Performance of the de Havilland Hornet:

Sea level speed: 392 mph ( 630.8 km/h)
Top speed: 472 mph (759 km/h) at 22,000 ft
Climb rate: 5450 ft/min ( 27.68 m/s) at sea level
take 4 min to climb to 20,000 ft
Engine horsepower:
2 x Merlin 130/131 engine with 2,070 HP each at WEP
Normal take off weight: 16,100 lbs (7302.8 kg)
Wing area: 33.538 m2 ( 361 ft2)
Wing loading: 217.74 kg/m2
Power to weight: 0.566 hp/kg ( 0.257 hp/lbs)
Weapons:
Four 20 mm cannon

 

[mig-31bm]

There are some conflict information about the Hornet climb rate. Some source seem to indicate the climb rate to be > 5450 ft/minute at sea level , some other source indicate the climb rate to be 4500 ft/minute at sea level. Iam not sure which is correct

 

[tomo pauk]

Not at all! Highly compact and weight efficient turbo installations (the V-1710H or Bell's turbosupercharged P-63 are good examples) that could fit a Spitfire or P-51 were very feasible even in 1940.

I would like to learn more about the V-1710H, as well as about the turbocharged P-63, as well as how that was feasible in 1940.

Even before the 60 series Merlin was a success P&W had the same arrangement on the XH-2600 and XH-3130. There really wasn't anything novel or eye opening about it. It was the fastest, simplest and cheapest way to improve performance and given the situation at the time it was unquestionably the right call.

Care to elaborate about the 2-stage superchargers as designed for these P&W engines?

 

[Shortround6]

I would like to learn more about the V-1710H, as well as about the turbocharged P-63, as well as how that was feasible in 1940.

Time machine.

From page 443 of "Vees for Victory"
"V-1710-41 2550+ bhp, turbo-compound w/separate 2-stage S/C and 2-stage air-cooled turbine, 50% aftercooler and port injection, 1947.

Also on Page 280, short description. Based on the G-10 which was a modified E-30 derived from the E-27.
E-27 engine

Just take of the engine driven supercharger, replace the single stage aux supercharger with a 2 stage supercharger, replace the single stage exhaust turbine with a two stage exhaust turbine. Install an after cooler, install port fuel injection, already has water injection.

Easy-peasy to put in a Spitfire in 1940

 

[Reluctant Poster]

Not at all! Highly compact and weight efficient turbo installations (the V-1710H or Bell's turbosupercharged P-63 are good examples) that could fit a Spitfire or P-51 were very feasible even in 1940.

Bell couldn't come up with a compact and highly efficient turbo installation in 1940 that actually worked.

 

[Reluctant Poster]

View attachment 796286
The intake position looks fairly similar to the XP-72 but not sure what point you are trying to make?

What I'm wondering is, seeing as the pilot on both P-47 and XP-72 was in between the engine and 2nd stage turbo/supercharger + intercooler, why the intake was not moved back (relative to the engine) along with those accessories? Only reason I can think of is it would ingest too much crud on takeoff? (Probably less of a problem on a B-50 since it's operating on paved runways and the engine is further off the ground.)

To visualize what substituting a turbocharger for a mechanical drive would due to the installation

 

[Jugman]

I would like to learn more about the V-1710H, as well as about the turbocharged P-63, as well as how that was feasible in 1940.

Shortround6 described the V-1710H. Bell had a P-63 proposal for Wright turbo mounted behind the engine at ~60° from horizontal. Both of these fit in the same space as the regular V-1710 two stage.

GE turbos had two major problems that impacted compactness.
1. Their impeller efficiency was god awful.
2. Turbine cooling.

Pretty much anybody else's supercharger fixes one.
Two can be improved by air-cooled turbine blades. BMW had some success with them in 1938. There were other methods to improve cooling that could be employed. Such as the "turbo Snout" used in the P-61C. Most of these methods require better coordination between GE and the engine and airframe manufacturers.

Care to elaborate about the 2-stage superchargers as designed for these P&W engines?

The XH-2600 engine X-95 This engine had two 13in diameter impellers. The first stage had an eye diameter of 9.625 and a van height of 3in. 8.25in and 1.25 for the second stage.

The XH-3130 engine X-96