Pinnacle of Piston fighter: XP-72 vs Spiteful Mk XVI? (2 Viewers)

[mig-31bm]

The NA-117 P-51H was the XP-51F with 1650-9 and proposed with 4x20mm for interceptor.

I think I just found the chart, but I'm not sure whether this is estimated or actual data measured in test
Also It seem that XP-51F were ever only tested with four 0.5 cal, the option with 4x20mm maybe suggested but never actually install or tested (I think their longer barrel likely cause some drag as well)

The P-51H was completely redesigned to NA-126 because of the fuel fraction requirements.

The NA-126 chart also seem faster than the operational P-51H SAC chart, maybe this chart is only estimated performance?

 

[mig-31bm]

Quick comparison:
XP-51F
Sea level speed: 420 mph ( 676 km/h)
Top speed: 491 mph (790 km/h) at 22,700 ft
Climb rate: 6530 ft/min (33.17 m/s) at sea level, 5730 ft/min at 20,000 feet
Engine horsepower:
Merlin V-1650-9 engine with 2218 HP at WEP
Normal take off weight: 7553 lbs (3426 kg)
Wing area: 21.6 m2 (233.3 ft2)
Wing loading: 158.1 kg/m2
Power to weight: 0.647 hp/kg (0.29 hp/lbs)
Weapons:
four 0.50 caliber machine gun

vs

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

vs

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 and 483 mph (777 km/h) at 21,000 ft (6,401 m)
Climb rate of Spiteful F.14 is 4890 ft/min (24.8 m/s) at 2000 ft, the Spiteful F.16 probably around 5000 ft/min thanks to more powerful engine
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).
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.

 

[mig-31bm]

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

I mistakenly gave wrong climb rate for the hornet haha, damm, I was wondering why it has such insane rate of climb at 5450 ft/min
turn out the rate of climb at sea level is only 4700 ft/min, took about 4.89min to reach 20kft.
Seem a lot more reasonable

P/S

wait a sec, I also found this, so what data is correct???

de Havilland Hornet Performance

WWII Aircraft Performance, wartime flight trials and reports of D.H. Hornet aircraft. Hornet data.

www.wwiiaircraftperformance.org

 

[drgondog]

I think I just found the chart, but I'm not sure whether this is estimated or actual data measured in test
Also It seem that XP-51F were ever only tested with four 0.5 cal, the option with 4x20mm maybe suggested but never actually install or tested (I think their longer barrel likely cause some drag as well)
View attachment 883591



The NA-126 chart also seem faster than the operational P-51H SAC chart, maybe this chart is only estimated performance?
View attachment 883592

Yes, estimated performance for NA-126 with original Packard V-1650-9 performance charts - and estimates are for clean P-51H without wing racks and a fully functioning speed density pump. There were issues in 1945 flight testing, resulting in design change to metered fuel carburetor and the lower top speed.

The four barrel 20mm was in fact part of NA-8900 P-51H Airplane Specification - and Never configured to my knowledge for flight test, and yes top speed estimates were reduced by 5mph.

 

[mig-31bm]

Yes, estimated performance for NA-126 with original Packard V-1650-9 performance charts - and estimates are for clean P-51H without wing racks and a fully functioning speed density pump. There were issues in 1945 flight testing, resulting in design change to metered fuel carburetor and the lower top speed.

The four barrel 20mm was in fact part of NA-8900 P-51H Airplane Specification - and Never configured to my knowledge for flight test, and yes top speed estimates were reduced by 5mph.

I'm slightly confuse, how to know NA-117 is tested and NA-126 is estimated?
btw do you know why the hornet Mk1 seemingly have 2 different contradict climb rate?

 

[drgondog]

btw do you know why the hornet Mk1 seemingly have 2 different contradict climb rate?

No, but very common for Performance analysis be made on a 'fighter' configuration with partial internal fuel and subsequent gross weight below a fully combat loaded airplane. NAA standardized on 105-gal internal fuel loading for 'fighter' configuration for all Merlin/Packard powered variants.

In the chart above for the Mustang III at 15lbs, the internal fuel load was 184-gal - fully loaded but without installed 85-gal fuse tank. FWIIW the Mustang III with Merlin 100 installed was in mid 4,000's ROC and IIRC 409mph at 5000 feet.

The P-51B with 1560-7 and 145 octane fuel and 25lbs was equivalent.

 

[mig-31bm]

No, but very common for Performance analysis be made on a 'fighter' configuration with partial internal fuel and subsequent gross weight below a fully combat loaded airplane. NAA standardized on 105-gal internal fuel loading for 'fighter' configuration for all Merlin/Packard powered variants.

Some data seem somewhat skeptical, for example, this seem to suggest that Hornet can reach 490 mph

But this one chart seem to limit top speed to around 450 mph

This suggest around 475 mph, extremely good rate of climb though

whereas this one suggest top speed of 472 mph and normal climb rate of 4600 ft/min

https://www.wwiiaircraftperformance.org/Hornet/Hornet-Flight_24jan46.pdf

-------------------------------------------------------------------------------------
Interesting note about dive speed

 

[GregP]

Yup. They did make a few.

They powered some 29 aircraft, of whicj maybe 4 were fighters. The rest were transports, bombers, or other large aircraft. I don't think the engine was ever pushed for power since it churned out enough torque to spin a BIG prop. Would love to learn to run and fly one myself, but there aren't many left running today and I'm not rich enough to be able to afford to do so.

Sigh ...

 

[Howard Gibson]

Howard, what was the altitude at which 530mph was achieved? And which aircraft?

Look up Rare Bear, a highly modified Grumman Bearcat. According to Wikipedia, it did the 3 km World Speed Record of 528.33 mph (850.26 km/h) set August 21, 1989. There is no mention of altitude. A similar speed was achieved by Voodoo, a highly modified P51. Again, there is no mention of altitude.

The lightweight P47J did 505mph at 33,000ft.

 

[Shortround6]

They powered some 29 aircraft, of whicj maybe 4 were fighters. The rest were transports, bombers, or other large aircraft. I don't think the engine was ever pushed for power since it churned out enough torque to spin a BIG prop.

they don't seem to have gotten the supercharger situation sorted out. The rated power at 25,000ft with the rear supercharger in the XP-72 is not enough and the turbo installations the Bombers were not going to fit in the XP-72.

one of the 4300-4400hp versions with the two turbos.
You want over 4000hp at 25000ft you need a BIG supercharger.

 

[Howard Gibson]

Some data seem somewhat skeptical, for example, this seem to suggest that Hornet can reach 490 mph
View attachment 883618

But this one chart seem to limit top speed to around 450 mph
View attachment 883619

This suggest around 475 mph, extremely good rate of climb though
View attachment 883620

whereas this one suggest top speed of 472 mph and normal climb rate of 4600 ft/min

https://www.wwiiaircraftperformance.org/Hornet/Hornet-Flight_24jan46.pdf

-------------------------------------------------------------------------------------
Interesting note about dive speed
View attachment 883621

Those performance charts are at 18psi boost. The Hornet was supposed to use 150 octane fuel, which means boosts of 21 or 25psi. A P51H ought to not be much faster than a P51D. Again, the P51H is using 150 octane, and water injection.

 

[Sisu]

Look up Rare Bear, a highly modified Grumman Bearcat. According to Wikipedia, it did the 3 km World Speed Record of 528.33 mph (850.26 km/h) set August 21, 1989. There is no mention of altitude. A similar speed was achieved by Voodoo, a highly modified P51. Again, there is no mention of altitude.

The lightweight P47J did 505mph at 33,000ft.

The Bear's record and Voodoo's record were set at 4 or 5000 feet (Las Vegas N M and somewhere in Montana respectively). The Bear did passes of 540 mph or so -- all with healthy doses of Nitrous Oxide and a remarkable Frankenstein modified 3350...

At higher altitudes Dago Red set a record of 517 mph back in the 1980s with Rolls Royce rods at 10,000 feet or so. An Allison rod version ran over 540 mph at altitude in 1998 or so -- verified by Edwards AFB radar tracking.

 

[GregP]

they don't seem to have gotten the supercharger situation sorted out. The rated power at 25,000ft with the rear supercharger in the XP-72 is not enough and the turbo installations the Bombers were not going to fit in the XP-72.
View attachment 883670
one of the 4300-4400hp versions with the two turbos.
You want over 4000hp at 25000ft you need a BIG supercharger.

Seems like it would have required some engineering. Perhaps they figure that out and decided it wasn't worth the effort. I tend to think the advent of jets made the difference.

I could be mistaken. It's happened before ...

Great pic, Shortround6!

First green exhaust I ever saw ... Hope it is high-temp paint!

 

[don4331]

they don't seem to have gotten the supercharger situation sorted out. The rated power at 25,000ft with the rear supercharger in the XP-72 is not enough and the turbo installations the Bombers were not going to fit in the XP-72.
View attachment 883670
one of the 4300-4400hp versions with the two turbos.
You want over 4000hp at 25000ft you need a BIG supercharger.

Isn't that the mere 3,500 HP version out of a B-50?

And the CH-7 turbo-superchargers gave nothing but grief in the B-50s. Also note the huge intercooler between the turbochargers and the throttle body. The R-4360 is moving 50% more air than the R-2800 requires -> means it need to be 50% larger than the P-47s intercooler.*

The remote mechanical supercharger on the XP-72 is limited to providing enough air for 3k hp at 25k' minus the 600hp, it is absorbing = 2,400hp.** About 400hp less than the R-2800-57 equipped P-47M was making at that altitude.

*CH-7 turbo compressor might be more efficient than the C-23 in the P-47 which would allow a reduction in intercooler area.

**The R-4360-13 used in the XP-72 was rated on 100/130, so later engines which used 115/145 fuel might have made more power at lower altitude, but I'm not sure the Republic fighter would go faster..

 

[mig-31bm]

Those performance charts are at 18psi boost. The Hornet was supposed to use 150 octane fuel, which means boosts of 21 or 25psi. A P51H ought to not be much faster than a P51D. Again, the P51H is using 150 octane, and water injection.

Hmm, you are right, the speed chart is at 20 psi boost rather than 25psi
Merlin 130/131 was rated at about 2,060 hp at +25 psi boost, so at 20 psi boost it probably generated roughly 1800 hp
For a piston fighter at top speed, speed varies roughly with the cube root of power, so
if the Hornet's Merlin 130/131 power drops from:

• Max power = 2060 hp at +25 psi (150 octane fuel)
• Reduced power = 1800 hp at +20 psi (130 octane fuel)

then

• Reduced power / Max power =1800/ 2060=0.874

and

• Reduced velocity / Max velocity = 0.8741/3 = 0.956

So top speed falls by about 4.4%.
If a Hornet can do about 472 mph at +25 psi then reduced velocity would be 451 mph.
Matching quite well with what in the graph
On a side note, the spitfire XIV with Griffon 65 running on 18 psi boost seem to out speed the Hornet from 25kft and above. Why is that?. What is the key reason?. I would have expect Merlin to work better at high altitude

 

[mig-31bm]

On a side note, does anyone know whether Griffon 101 reached 2,420 hp with 20 psi boost or 25 psi?, for an engine that that has 36% larger displacement than the Merlin 130, the power generated only seem to be 17% better. I also wonder if the 3 speed super charger would help much compared to the 2 speed super charger on Merlin

 

[mig-31bm]

Hornet has higher dive limit than P-51D at high altitude but P-51D has higher dive limit down low, why that so?

This source indicate even higher diving speed for P-51D but not sure why

https://www.wwiiaircraftperformance.org/mustang/p-51d-dive-27-feb-45.pdf

 

[drgondog]

Look up Rare Bear, a highly modified Grumman Bearcat. According to Wikipedia, it did the 3 km World Speed Record of 528.33 mph (850.26 km/h) set August 21, 1989. There is no mention of altitude. A similar speed was achieved by Voodoo, a highly modified P51. Again, there is no mention of altitude.

The lightweight P47J did 505mph at 33,000ft.

I 'know' Rare Bear'. Greenamer set the record that stood until Hinton, jr beat it with Voodoo. I thought you were referring to stock/prototype WWII fighter.

 

[drgondog]

Hornet has higher dive limit than P-51D at high altitude but P-51D has higher dive limit down low, why that so?
View attachment 883726

This source indicate even higher diving speed for P-51D but not sure why
View attachment 883729

https://www.wwiiaircraftperformance.org/mustang/p-51d-dive-27-feb-45.pdf

All the velocities are calculated and predicted versus Qmax applied to Limit G loads. I suspect a mistake in the T.O. presentation or a different applied analysis. It makes zero sense that the comparative values favor the Hornet in any altitude envelope. The data you extracted from Mike Williams is in the Pilot Operating Manual for P-51D.

The actual Limit Dive speed is 0.75Mach throughout for True air speed for the P-51D. The not to exceed true airspeed in 0.80Mach and the highest recorded dive speed (with some structural damage) was 0.85Mach. Comparing against instrument displays with dissimilar static and dynamic pressure sensors could account for the difference.

 

[mig-31bm]

. It makes zero sense that the comparative values favor the Hornet in any altitude envelope.

Why is that so?, isn't Hornet extremely fast? Its top speed is pretty much comparable to P-51H and much faster than P-51D, shouldn't dive limit also quite high?