Dec 1941. Long range day fighter.

GrauGeist said:

The XP-50 was actually faster, using the "crappy" R-1820-67 instead of the R-1820-40
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Dave - what was the real speed of the XP-50?

A couple of points about the P-51/Mk I. Approximately 150 were produced and delivered in 1941. The production rate went from 78/mo to 104/mo by March 1. The wing rack/external fuel tank (unpressurized) was in detail design for the A-36 (future) in January 1942.

The P-51-1/Mk IA with Allison 1710-39 and four Hispano's at 8824 pounds (full internal combat load of ammo and 180 gallons of fuel) was tested with following fuel consumption:
291#/hour (~48gph) was burned at 2200 RPM Auto Lean at 13,200 feet resulting in 1200 miles straight line range at 314mph. Lower RPMs and Boost resulted in 1350 miles straight line range.

The MKI with same engine, 4x50 cal and 4x30 cal had slightly longer range at 10,000 feet (~1350 miles)

I have to dig a little more but IIRC Lockheed only delivered ~200 P-38E in the same timeframe.

The A-36/P-51A delivered in 1942 with extended performance, including the wing rack/wing tank/bomb carrying capabilities

tomo pauk said:

Dave - what was the real speed of the XP-50?

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Tomo, let me see if I can find my data sheets on the two, but from memory, the XP-50's max. speed was 42 miles an hour faster (67.5kph) than the XF5F at their mid-operating altitude of 20,000 feet (6km)

GrauGeist said:

Tomo, let me see if I can find my data sheets on the two, but from memory, the XP-50's max. speed was 42 miles an hour faster (67.5kph) than the XF5F at their mid-operating altitude of 20,000 feet (6km)

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So that should put it somewhere around 390-400 mph.

pinsog said:

So that should put it somewhere around 390-400 mph.

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At 20,000 feet, the XF5F was 383 mph, the XP-50 was 424.

Also, keep in mind that the XF5F's figures were for an un-armed (was to have two .30 MGs and two .50 MGs), unarmored airframe.

The XP-50 was tested without armament (was to have two 20mm cannon and two .50 MGs), but aparently at some point, had preliminary armor installed.

GrauGeist said:

At 20,000 feet, the XF5F was 383 mph, the XP-50 was 424.

Also, keep in mind that the XF5F's figures were for an un-armed (was to have two .30 MGs and two .50 MGs), unarmored airframe.

The XP-50 was tested without armament (was to have two 20mm cannon and two .50 MGs), but aparently at some point, had preliminary armor installed.

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Several people here have doubted the XF5F 383 mph speed results and the XP-50 424 mph (I don't have an opinion) so I just used the actual real test results we have showing the XF5F at 358 at 17,300 and added the 40 mph to it. Another 525 pounds for 4 50's and 400 rounds per gun, plus 150 pound armor plate behind the pilots seat shouldn't have much effect on level flight and with 2,400 hp the climb rate should still be very good also.

http://alternatewars.com/SAC/XF5F-1_and_XFL-1_PD_-_26_December_1942.pdf

I think you're way off on your armament weight, 1600 rounds of linked .50 cal. just by itself weighs more than 600 lbs., 4 .50 cals BMG with ammo cans, chutes, gun heaters and everything else required to install guns could easily add another 600 lbs.

pinsog said:

Several people here have doubted the XF5F 383 mph speed results and the XP-50 424 mph (I don't have an opinion) so I just used the actual real test results we have showing the XF5F at 358 at 17,300 and added the 40 mph to it. Another 525 pounds for 4 50's and 400 rounds per gun, plus 150 pound armor plate behind the pilots seat shouldn't have much effect on level flight and with 2,400 hp the climb rate should still be very good also.

http://alternatewars.com/SAC/XF5F-1_and_XFL-1_PD_-_26_December_1942.pdf

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I might point out that the XF5F first flew in 1940 (1 April) and last flew in 1944...while that's a good flight test report you posted, bear in mind that there were several other flight tests done.

The XP-50 first flew in 1941 (18 February) and crashed on 14 may 1941, after several tests as well.

And also keep in mind that as soon as you start loading an airframe down with weapon systems and armor, it will suffer a performance penalty.

GrauGeist said:

At 20,000 feet, the XF5F was 383 mph, the XP-50 was 424.

Also, keep in mind that the XF5F's figures were for an un-armed (was to have two .30 MGs and two .50 MGs), unarmored airframe.

The XP-50 was tested without armament (was to have two 20mm cannon and two .50 MGs), but aparently at some point, had preliminary armor installed.

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Unfortunately, the 383 mph is a figure 30 mph too big, the data sheet saying so. For comparison, the Whirlwind was good for 360 mph, on about same power, despite being far more streamlined affair. It was also smaller, that compensating for drag of armament installed.
The P-38 needed 1600 HP to beat 420 mph mark, I'm afraid there is no chance for the XP-50 to make that turn of speed on 1200 HP, with radial engines on board.

Some accounts say the XP-50 was lost with less than 20 hours of flying time. Depending on how smoothly, or not, the test flight program was running this may not have been enough time to get peak performance numbers. Most accounts saying either the performance figures listed were either estimated or not achieved in tests. The XP-50 first flew just 4 days before the F5F-1 was delivered to the Navy and the F5F was still suffering from a host of problems and was returned to Grumman for rework which included (but not limited to) at least 5 different modifications to reduce drag. Even with modified nacelles, prop spinners, lowered canopy, pointed nose and new wing fillets the F5F failed to show a major reduction in drag. Hard to believe the XP-50 without most of these modifications would have done so much better.



Please remember that the F7F Tigercat used smaller diameter engines. 14.8 sq ft EACH vs 16.6 sq ft for frontal area.
The engines in an F7F-1 were claimed to be giving 1500hp at 25,000ft military power. The Tigercat is lot heavier and lot bigger but not all aircraft were created the same when it comes to drag. Bf 109E with 1100hp vs P-51 with 1100hp Allison?

tomo pauk said:

Unfortunately, the 383 mph is a figure 30 mph too big, the data sheet saying so. For comparison, the Whirlwind was good for 360 mph, on about same power, despite being far more streamlined affair. It was also smaller, that compensating for drag of armament installed.
The P-38 needed 1600 HP to beat 420 mph mark, I'm afraid there is no chance for the XP-50 to make that turn of speed on 1200 HP, with radial engines on board.

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Tomo, my point was that a single data sheet gives a good indication of it's performance but should not be used to form a final conclusion.

Also, the HP = speed comparison between the P-38 and either of the Grumman G-34 projects should also include the difference in empty/loaded weights, where the P-38 was much heavier (empty) than the XF5F (loaded).

To be fair, a weight comparison of the experimental P-38 versus the XF5F or XP-50:
YP-38:
Empty: 11,507 lbs/5,218 kg
Loaded: 13,964 lbs/6,332 kg

XF5F:
Empty: 8,107 lbs/3,600 kg
Loaded: 10,138 lbs/4,600 kg

XP-50:
Empty: 8,310 lbs/3,770 kg
Loaded: 10,500 lbs/5,250 kg

I've pulled the Whirlwind data exactly for the reason to either support or dispell the speed figure. We can also take a look at the IMAM Ro.57, another smaller aircraft with similar power, not able to make 320 mph. Or, Ki 45, 336 mph on almost 20% more power. Neither having the bulky 9 cylinder radial engine.

The weight indeed can impart the dent on speed, but we can recall that heavy P-51 was faster on same HP than the lighter Spitfire. The increase of weight by 1000 lbs for the clean P-51D imparted reduction of speed by just 3 mph (the RoC and time to height received much more of a hit), per 'America's hundred thousand', pg. 125.

Also, in comparing the two G-35 projects, I would suspect that the XP-50 was faster by virtue of it's nose configuration as the original XF5F design saw the rounded nose assembly situated behind the leading edge of the centerwing, which would not be clean at all.

The nose was "cleaned up" to a certain degree, seen in later photos, with a slight extension that brought the XF5F's nose foreward of the centerwing's leading edge, similar to the XP-50's, though a bit shorter and somewhat angular.

Increased weight for same airframe results in having to fly at a higher angle of attack to generate the Lift required to offset the GW for level flight - thereby increasing Induced Drag slightly. That is the sole reason the average top speed in a P-51D for same boost/same engine/same RPM was approximately 4mph TAS slower than the P-51B.

Increased weight is more of a serious problem for Climb and take off characteristics as well as range.

Unfortunately power to weight has little to do with speed. Speed is power vs drag.

Power to weight had much more to do with climb but only AFTER you subtract out the power needed to fly at the best climb speed for each aircraft.
Basically the F5F and XP-50 were flying barn doors (if not the whole barn) compared to the P-38.

I agree with both of you gentleman on the increased weight slowing the rate of climb, but, if you have 1,200 hp per engine (2,400 hp in total) up to 25,000 feet, then you have an airplane with 400 more hp than a mid war P47. An F6F-3 in May of 1944 had about 1,900 hp at sea level and 1650 hp at 25,000 feet. The XF5F with turbocharged engines, guns and armor is going to weigh about the same as an F6F, the wing size is about the same, but the XF5F will have 850 more hp the the F6F. I think climb rate will be great and top speed won't be too bad even considering the higher drag


F6F-3 May 1, 1944

Gross Weight (lbs.) 11506 12415
High Speed at sea level (MPH) 312 309
High Speed at 5500 ft. (MPH) 330 327
High Speed at 10500 ft. (MPH) 343 340
High Speed at 15000 ft. (MPH) 357 354
High Speed at 16100 ft. (MPH) 355 352

XF5F Skyrocket

10,892 pounds

Sea level 311 mph
4,500 ft 325
7,300 ft
14,000 ft 345
17,300 ft 357


The XF5F has the same performance in 1941 on 1,000 hp 0-4500 feet and 900 hp 7300-14000 as the F6F-3 had in 1944. Imagine turbocharged engines in 1941 on the XF5F….

Shortround, the test for the XF5F shows it to have a top speed at 4,500 feet of 325 mph at 1,000 hp per engine. Top speed of the Whirlwind at 5,000 feet is 315. So an extra 230 hp or so in the XF5F gives it a 10 mph speed advantage right down on the deck. Install turbocharged engines and the "barn door" will have 630 hp more than a Whirlwind and hold it all the way up to 25,000 feet.


Whirlwind

Weights:
Empty 8,310 lb. Loaded as fighter 10,356 lb.


Performance:Max. speed (light): 5,000 ft 315 mph
10,000 ft 335
15,000 ft 360
20,000 ft 350

Skyrocket

Empty 7,990 Normal load 10,021
Sea level 312 mph
4,500 ft 326
7,300 ft 324
14,000 ft 346
17,300 ft 358

Trouble is the Whirlwind didn't have 885hp on the deck or at 4,500ft. It had 885hp per engine at 15,000ft.

For take-off it had 765hp per engine at 43.7in of boost (or about 6 3/4lbs boost.)

"assuming" a straight forward progression in power (throttle was opened up progressively as the aircraft rose in altitude) the Whirlwinds engines will give about 805hp at 5,000ft and 845hp at 10,000ft.

Gee, the F5F was 10mph faster with 25% more power at 5,000ft. I'm impressed

BTW. the engines in the F5F had two speed superchargers and were rated at (or about) 1000hp at 2300rpm, max continuous at 6900ft and 900hp at 2300rpm max continuous at 15,200ft, exact height may vary due to intake ram effect. These ratings were on 91 octane fuel. Take-off was 1200hp at 2500rpm.
Later versions of the R-1820 were rated at 1200hp military (NOT WEP) at 2500rpm at 4,200ft and 1000hp at 2500rpm at 14,200ft using 100 octane fuel.
The F5F had some issues with cooling which may (or may not have) played into the poor climb numbers. 9.3 minutes to 20,000ft with 178 gallons of fuel on board? No guns, ammo or protection?
There seems to be a discrepancy between the climb numbers and the level speed numbers as far as power used goes.

BTW II. The P-38 according to one table had a flat plate area equivalent for drag about 1/2 way between the Corsair and the Hellcat.

YP-38s seemed to need 1000hp per engine make 334mph at 5000ft. Without torque meters on the engines people were depending on charts from dyno testing on the ground to figure out power.
P-38E at 14,458lbs could make 20,000ft over 2 minutes quicker than the F5F and that is after dropping the engine rpm from 3000rpm to 2600rpm at 14,600ft.

One might also note that in one test an F6F made it to 20,000ft in 10 minutes using normal power for the entire climb at a weight of 12,243lbs. Normal power being about 1675-1600hp from sea level to 20,000ft as the supercharger engaged the second stage ( 1550hp at 21500ft.)

Turbos were not "free",figure over 200lbs per turbo (or closer to 250lbs) for ducts, mounts,piping and the intercoolers, figure about 10-12 cubic feet per turbo for volume needed. Now figure in the extra drag of the intercooler installation

On the B-17

The innermost air intake in the wing root was the intake for the engine combustion air, the next intake was for the intercooler air and the intake just outboard of the engine nacelle was for the oil cooler. outer engines reversed the layout. Granted B-17s had a lot of room to spread things out in. Adding a turbocharger installation could actually hurt performance under 15,000ft.

XF5F did 358 mph at 17,300 in an actual test with 1,800 hp. Add 500 pounds for 2 turbos now giving you a total of 2,400 hp 8,000 feet higher up. Would you add 500 pounds for an extra 600 hp and 8,000 feet more altitude? As I said above, 2,400 hp is 750 hp more than a Hellcat or Corsair had at the same altitude. It's 400 hp more than a mid war P47. All of this is available with 1939 technology that we already had. We had already been running these engines for several years, surely somebody at Grumman could figure out how to fit a cowling on an airplane, maybe walk across the runway and look at an F4F-3. The AP4 (P43 Lancer prototype) had been flying since early 1939.

The turbo technology was still not 'fool proof' in 1939. We know that XP-50 was lost due to explosion of the turbocharger, and that was in 1941. The turbo regulators were not sorted out until 1942. The turbo, used on XP-37, was trouble spot, it took GE to design a new unit to be installed in YP-37s and subsequent aircraft that have the turbos.
With that said, IMO, a Skyrocket, or P-50 with turboed Cyclones ( =1200 HP at 25000 ft), 'core' intercoolers and with armament should be probably good for 380 mph at 25000 ft, but probably not for 400 mph, let alone 420 mph.