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

[mig-31bm]

Due to the jet age, various super props never go to production despite their high performance. Among those, it can be said that XP-72 and Spiteful F.16 were the most high capable design.
So let say if these prototype got to production stage, which would be the ultimate piston fighter?
XP-72

Performance of the XP-72 .
Sea level speed: 405mph (651 km/h)
Top speed: 490mph (788.5 km/h) at 25,000 feet
3.5 minutes to 15000 feet

Engine horsepower: R4360 engine
3450hp at SL
3000hp at 25000 feet
Normal take off weight: 14,760 lb (6,695 kg)
Wing area: 27.9 m2
Wing loading: 239.9 kg/m2
Power to weight: 0.515 hp/kg (0.233 hp/lbs)
Weapons:
Six 0.50 caliber machine gun

Spiteful Mk XVI (also known as Spiteful F.16)

Performance of Spiteful XVI (F.16)
Top speed: 494 mph (795 km/h) at 27,800 ft (8,473 m).
There is no information about low level top speed of Spiteful Mk XVI (F.16) however, Spiteful Mk.XIV (F.14) with pretty much same aerodynamic and a weaker 2,375 hp (1,771 kW) Rolls-Royce Griffon 69 could achieve: 409 mph (658 km/h) at sea level, 437 mph (703 km/h) at 5,500 ft (1,676 m) and and 483 mph (777 km/h) at 21,000 ft (6,401 m)
Engine horse power:
Spiteful number RB518 was fitted with a 2,420 hp (1,805 kW) Griffon 101 engine to become the sole Spiteful F.XVI (F.16). The Griffon 101 had a two-stage, three-speed supercharger and turned a five-blade, single rotation propeller.
Normal take off weight: 4513 kg
Wing area: 20 m2
Wing loading: 225.65 kg/m2
Power to weight: 0.536 hp/kg (0.24 hp/lbs)
Weapons:
Four 20 mm cannon.



Compare with some mass produced super props.
P-51H

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
Engine horsepower:
Merlin V-1650-9 engine with 2218 HP at WEP
Normal take off weight: 9450 lbs (4286 kg)
Wing area: 21.6 m2 (233.3 ft2)
Wing loading: 198.4 kg/m2
Power to weight: 0.517 hp/kg (0.234 hp/lbs)
Weapons:
Six 0.50 caliber machine gun




F4U-5

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
Engine horsepower:
R-2800-32W engine with 2760 HP at WEP
Normal take off weight: 12,901 lbs (5851.79 kg)
Wing area: 29.172 m2 ( 314 ft2)
Wing loading: 200.5 kg/m2
Power to weight: 0.47 hp/kg ( 0.213 hp/lbs)
Weapons:
Four 20 mm cannon

 

[PAT303]

The XP-72 was never a fighter unlike the other three.

 

[mig-31bm]

The XP-72 was never a fighter unlike the other three.

As I understand it, XP-72 was a prototype exactly same as Spiteful Mk XVI. There are two prototype made. The only different was that XP-72 prototype wasn't run at full potential (from what I have heard, they didn't turn on the supercharger while they tested its top speed?). Allegedly, with super charger turned on, XP-72 could have reached something like 540 mph which make it faster than early jet such as Meteor. Ofcourse, that is only an estimate and production version could be a lot slower, for example: XP-51G could reach 492 mph, however, production P-51H is limited to 474 mph
P/s: updated with new information

 

[Reluctant Poster]

Here is the most complete discussion of the XP 72 I have found

Left behind by the Jet Age - Republic's XP-72 Super Thunderbolt

The first Republic XP-72 prototype soon after being completed. The 14 ft 2 in (4.23 m) diameter Curtiss propeller was one of the largest used during World War II. In 1941, the Republic P-47 Thunderbolt had just entered production, and hundreds of the aircraft had been ordered. However, led by...

forums.spacebattles.com

 

[mig-31bm]

Here is the most complete discussion of the XP 72 I have found

Left behind by the Jet Age - Republic's XP-72 Super Thunderbolt

The first Republic XP-72 prototype soon after being completed. The 14 ft 2 in (4.23 m) diameter Curtiss propeller was one of the largest used during World War II. In 1941, the Republic P-47 Thunderbolt had just entered production, and hundreds of the aircraft had been ordered. However, led by...

forums.spacebattles.com

Thank you, that thread is pretty decent, which come as a big surprise to me because The war room of spacebattle is quite infamous for having low quality debate when it come to modern weapons. It is not that they don't have some well informed posters here and there. The issue is mainly vote there being used as a bully tactic. Members will up vote their favorite poster regardless of how wrong and nonsense their arguments are. Which lead to well informed posters leaving the forum.

 

[Shortround6]

May I suggest

Aircraft: World War II

Click to view all Aircraft: World War II articles starting with the most recent.

oldmachinepress.com

which may have the original article (seems to be dated a few days earlier?) and in any case has a host of interesting odd ball stuff with well researched articles.

It seems like forums.spacebattles may have lifted the whole thing.

 

[PAT303]

As I understand it, XP-72 was a prototype exactly same as Spiteful Mk XVI. There are two prototype made. The only different was that XP-72 prototype wasn't run at full potential (from what I have heard, they didn't turn on the supercharger while they tested its top speed?). Allegedly, with super charger turned on, XP-72 could have reached something like 540 mph which make it faster than early jet such as Meteor. Ofcourse, that is only an estimate and production version could be a lot slower, for example: XP-51G could reach 492 mph, however, production P-51H is limited to 474 mph

The Spitefuls, the MkXIV and XVI were operational fighters ready for production, but jets were the future. The XP-72 reaching 540mph is pure fantasy

 

[mig-31bm]

May I suggest

Aircraft: World War II

Click to view all Aircraft: World War II articles starting with the most recent.

oldmachinepress.com

which may have the original article (seems to be dated a few days earlier?) and in any case has a host of interesting odd ball stuff with well researched articles.

It seems like forums.spacebattles may have lifted the whole thing.

Thank you, always good to find the original source
So to summary:
1- Unlike P-47, the XP-72 does not have a turbocharger but instead used a two stage supercharger
2- The first XP-72 prototype (serial number 43-36598) was completed with a single-rotation propeller and a P&W R-4360-13 engine. The R-4360-13 engine could accommodate the remote, variable-speed supercharger, but sources disagree regarding whether or not the remote supercharger was installed in the XP-72. Without the remote supercharger, the R-4360-13 engine basically an engine with a single stage supercharger. The -13 engine produced 3,450 hp (2,573 kW) with the remote supercharger and 3,000 hp (2,237 kW) without it
3- Some sources claim a 3,000 hp (2,237 kW) R-4360-3 engine was used on the second XP-72. The -3 had a single-speed, single-stage (non-remote) supercharger and accommodated contra-rotating propellers, but the -3 engine used SAE #60-80 spline shafts. The Aeroproducts propeller used SAE #50-70 spline shafts, so it seems unlikely that the -3 engine was used. Many sources state the second XP-72 used a R-4360-13 engine, the same type fitted to the first prototype. The -13 engine was single-rotation with a SAE #60 spline shaft and could not accommodate contra-rotating propellers. However, it is possible that a contra-rotating gear case from another engine could have been fitted to the -13.
4- Almost all sources indicate that both XP-72 prototypes achieved 490 mph (789 km/h) at 25,000 ft (7,620 m).An order for 100 P-72 aircraft was placed in late 1944. Production P-72s were to be powered by the P&W R-4360-19 engine, which used the Aeroproducts contra-rotating propeller and had an engine-driven, variable-speed, remote supercharger similar to the one used on the -13. The -19 engine was planned to provide 3,650 hp (2,722 kW) at sea level and 3,000 hp (2,237 kW) at 25,000 ft (7,620 m), allowing the P-72 to attain an estimated speed of 504 mph (811 km/h) at 25,000 ft (7,620 m).
5-Further engine development resulting in 4,000 hp (2,983 kW) would reportedly enable the P-72 to reach a speed of 540 mph (869 km/h) at 25,000 ft (7,620 m) in theory.

So basically the prototype reached 490 mph, not sure with or without the second stage supercharger installed on aircraft. And with the more powerful P&W R-4360-19 planned, the aircraft is projected to reach 505 mph. But since that were neither build or demonstrated, the better comparison to the proven Spiteful XVI would be the version of XP-72 with P&W R-4360-13 engine.

 

[mig-31bm]

Data from Republic:

 

[Reluctant Poster]

Data from Republic:
View attachment 795512
View attachment 795513

As always the Maximum Speed quoted is not a real number

 

[mig-31bm]

The Spitefuls, the MkXIV and XVI were operational fighters ready for production, but jets were the future. The XP-72 reaching 540mph is pure fantasy

I can see that Spiteful Mark XIV were operation since there are about 18 of them. But isn't spiteful mark XVI is only prototype similar to XP-72 since there is only a single unit (RB518) tested with Griffon 101 engine

 

[mig-31bm]

As always the Maximum Speed quoted is not a real number

So the 550 mph and 505 mph are just hypothetical value, but isn't 490 mph the actual value that the prototype reached in the test?

 

[mig-31bm]

I don't have a lot of data for spiteful F.16 so I have no choice but to merged that speed of spiteful F.14 at lower altitude with the speed record of spiteful F.16 at high altitude. Afterall, they have some aerodynamic with slightly different engine

P/s: does anyone know why P-51H top speed chart has a sharp reduction at middle altitude while F4U-5 has such smooth curve

 

[Tom Fey]

The laminar flow wing as used on the Spiteful was reportedly very unforgiving with essentially no warning before the stall either in low-speed flight or accelerated flight. If the mission profile includes dogfighting, this would be a serious disadvantage for the Spiteful. The Republic S-3 airfoil on the P-47 was well respected for its performance in all aspects of flight.

 

[PAT303]

I can see that Spiteful Mark XIV were operation since there are about 18 of them. But isn't spiteful mark XVI is only prototype similar to XP-72 since there is only a single unit (RB518) tested with Griffon 101 engine

They only made one but the Spitefuls were fighters, not prototypes.

 

[Reluctant Poster]

So the 550 mph and 505 mph are just hypothetical value, but isn't 490 mph the actual value that the prototype reached in the test?

The data sheets are the manufacturers estimates they are not a proper test. The list of aircraft that did not live up to the manufacturer's estimates is very extensive indeed. Any articles have read about the XP72 will say sources state a top speed of 490 but I have yet to see the actual source.

 

[Reluctant Poster]

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