XF5F and XP-50: how good they really were?

davebender said:

The F5F program was cancelled after a single prototype. Far too soon to answer that question. However it had potential to become a good design.

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Based on?

We've had some former Grumman people give talks at the Planes of Fame Museum and they mostly talked about main production types. In short digressions, they said the planes in question were both good. The F7F was designed with R-2800's, not R-1820's, and was "upsized" to handle the engines and props ... and everything else sort of flowed from the size and weight of the R-2800's, props, fuel require for the specified range, and armament requirments. The wing area was set for the required landing speed.

There were no specific performance numbers given for either the F5F or XP-50, but they were said to be good aircraft. I see some disparagement of them in here, but we weren't there and can't know. These were short-lived prototpes and are NOT well documented. All our speculation is for naught when in the presence of people who were there and KNOW. Corky Meyer is such a person.

As a volunteer at the Museum, we've had some spirited discussions of Grumman products and have heard from volunteers who have attended the monthly event where the actual pilots were talking for more than 20 years, and they have passed on the comments from the people and pilots who were there. I cannot recall any "bad" Grumman planes being spoken of and have heard specific GOOD things about these twins.

The F7F and P-65 were designed around the R-2600. From Joe Baugher's web site.

"Following the loss of the sole XP-50, Grumman succeeded in interesting the Army in a different proposal, named Design 46 by the company. Design 46 called for a somewhat larger twin-engined fighter powered by a pair of supercharged 1700-hp Wright R-2600 radials. Work had actually began on Design 46 in October of 1939, nearly two years before the loss of the XP-50. This initial work led to the company's Design 49, which was an export version proposed in February 1940 and to Design 51, a naval fighter adaptation which was submitted on March 24, 1941. "
"The Army ordered two prototypes of the Grumman-designed twin-engined fighter under the designation XP-65 on June 16, 1941. The Navy ordered two prototypes under the designation XF7F-1 two weeks later. However, both services eventually concluded that a single design would not actually be able to satisfy their individual requirements, and on January 16, 1942 the Army decided to back out of the project in order to permit Grumman to optimize their design to meet naval requirements."

The F5F and XP-50 may not have been "bad" airplanes but that does not mean that they meet their performance goals. Or ever would reach them. Again from Joe Baugher's web site "There were problems with the XF5F-1 almost from the very beginning-- engine oil cooling was inadequate, aerodynamic drag was excessive, and there were problems with the closing of the undercarriage doors. Sideward and downward visibility were both atrocious, owing to the forward location of the wings and the position and large diameter of the radial engines"

And
".... returned the aircraft to Grumman for some major modifications in an attempt to alleviate some of its more obvious shortcomings. The engine nacelles were lengthened and extended further aft, spinners were fitted to the propellers, the height of the canopy was reduced, wing fillets were added, and the fuselage nose was extended forward of the wing leading edge. However, when the plane was returned to Anacostia on July 24, 1941, it was found that the changes had not provided any significant improvements in the aerodynamic drag or in the engine cooling problems"

Now the cooling problems may have been able to be solved. Nobody mentions any "bad" handling characteristics. Flying a plane in 1941/42 that could climb at 4000fpm near sea level may have been a lot of fun but the prototypes carried no guns, no armor and no self-sealing fuel tanks. Climb and speed would have been reduced on service versions and since speed was lacking to begin with it doesn't look like this design would a viable fighter or substitute for the P-38 or any R-2800 powered single engine plane.

The first F5F prototype had problems. That's normal for almost every WWII era aircraft program.

That is true but it rather depends on what the problems are. Faulty landing gear doors, elevator needs modification or faulty drag estimates means the plane is 10% slower than anticipated? Somethings are lot easier to fix than others. Cooling problems on an already 'slow' plane are especially troubling because you can't trade improved cooling for extra drag like you could on a plane that tested faster than the "estimates".

I wonder how the XP-50 would have done with a pair of turbocharged Allison's in it.the V-1710-143 one.

So, would the XF5F have been a big enough improvement in performance over the P39, P40 and F4F to justify its existance in the 1942-43 time period when they were having so much trouble with the Zero?

If I may: it depends. If the turboed engines (be it Cyclone, T. Wasp of V-1710) are aboard, the plane should offer the performance on par with P-38, hence out flying the P-39/-40/F4F and Zero. The another engine choice could be the 2 stage Twin Wasp, or maybe single stage V-1710. Simpler choice, but not that good above 20000 ft (does it really matter in 1942/43?).

I do not believe that 420+ mph were possible with Cyclones, as one can read on many web sites. With V-1710? Maybe, some time 1943/44.

I wonder how the XP-50 would have done with a pair of turbocharged Allison's in it.the V-1710-143 one.

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Hi, John. Maybe better than the P-38?

Without the F5F, the Blackhawks would have had to walk!

tomo pauk said:

Yep, my thoughts exactly.

Here is a table covering the XF5F-1 ('Skyrocket') and XFL-1 ('Airabonita') The XF5F is tested as capable for 357-358 mph at 17300 ft, no guns, no ammo. The R-1820-G231 being a single stage supercharged engine, so no turbo here?
The data for the Airabonita has some typos, BTW (V-1210 engine?).

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This is an old post but oh well.

The XF5F was unarmed but I believe it was ballasted for weapons. It did have a radio installed.


Empty weight 7990
Normal Loaded weight 10,021 leaves 2,031 pounds for load.
178 gallons of fuel is 1,068 pounds
150 pounds of oil (P36 oil times 2)
200 pound pilot

Leaves 613 pounds for weapons
4 50's is 300 pounds
300 rounds per gun is 300 more pounds

Empty weight 7990
Overload weight 10,892 leaving 2902 for load
277 gas is 1662
150 pounds of oil
200 pound pilot
Leaves 890 pounds for weapons
4 50's is 300 pounds
500 rounds per gun is 500 pounds

Based on this, I think it was ballasted for weapons.

If anything you have underestimated the weight of the weapons and ammo, (US .50 cal is closer to 30lbs per hundred)
but something is there to account for the differences in weight besides just more fuel.

Shortround6 said:

If anything you have underestimated the weight of the weapons and ammo, (US .50 cal is closer to 30lbs per hundred)
but something is there to account for the differences in weight besides just more fuel.

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I used the listed weight of the 50 and it's ammo from the wwii performance P36. What ever weight a 50 and it's ammo are, the XF5F as tested was ballasted an extra 600 pounds on standard weight and an extra 900 pounds on overload weight after fuel, oil, radio and pilot, so it has to be ballast for future weapons weight.

Shortround, I realize you don't like the XF5F for whatever reason. But the test sheet provided by Tomo Pauk shows Hellcat performance all the way up until the air got too thin for the single stage Wright's. Smaller diameter, better performing P&W 1830's would be the obvious choice for even better performance due to less drag and much better power at altitude. The early 1941 Wildcat P&W was making 860 hp per engine at 25,000 feet. That's 1720 hp at 25,000 feet in a fighter the size of a Hellcat and 2,500 pounds lighter. It's 4,500 pounds lighter than an early P-38. All of this with engines available in January 1941, that's when the F4F-3 test was done in wwii performance. And even though the actual guns weren't in place, the weight for them apparently has been added

Check out the climb rate on a P-38 at 13,900 pounds, 1,200 hp per engine. Why is it hard to believe an XF5F would climb at 4,000 fpm on close to the same hp when it weighs 3,900 pounds less?

According to what little info in out there, the reason it wasn't adopted was the Navy thought it was too heavy and it used 2 engines so the parts supply was doubled.

pinsog said:

Shortround, I realize you don't like the XF5F for whatever reason. But the test sheet provided by Tomo Pauk shows Hellcat performance all the way up until the air got too thin for the single stage Wright's. Smaller diameter, better performing P&W 1830's would be the obvious choice for even better performance due to less drag and much better power at altitude. The early 1941 Wildcat P&W was making 860 hp per engine at 25,000 feet. That's 1720 hp at 25,000 feet in a fighter the size of a Hellcat and 2,500 pounds lighter. It's 4,500 pounds lighter than an early P-38. All of this with engines available in January 1941, that's when the F4F-3 test was done in wwii performance. And even though the actual guns weren't in place, the weight for them apparently has been added

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The timing for the XF5F is off and it really only has a very narrow window of opportunity.
It may well have been ballasted for armament as you have shown, however the probability of it being equipped with armor or self-sealing tanks are a lot lower.

There is no question that the P & W R-1830s are smaller in diameter and better performing. They are also about 195lb heavier per engine. This does not include the intercoolers. The intercoolers are included under "engine accessories" which for the F4F-3 are 242lbs. The Wright powered F2A and FM-2 have the engine accessories included in the engine weight so the actual difference is over 430lbs per engine. While the 25.6 sq ft of frontal area for the pair of R-1830s is certainly much smaller than the 33.6 sq ft of the two R-1820 Cyclones it is still much larger than the 14.8 sq ft of the R-2800 in the Hellcat. Hellcat also has the pilot behind the engine and not in a third body attached to the wing.

Then there is availability, In Dec of 1941 (11 months after the test) the US Navy and Marines had 181 F4F-3s and 65 F4F-3As. The 3As having single stage engines due to a lack of two stage engines. Granted form about then on there was no shortage of two stage engines but you are not going to get F5Fs in numbers until 1942 due the engine situation.

Mock up of XF5F


Picture of R-1830 installation in first F4F-3

Everybody wants the extra power of the "trick" engine installations, few people want to pay the cost in weight and volume.

Yes the P&W would add weight, but the P&W Wilcat was at least 15 mph faster than the Wright. The XF5F would probably gain more since it had 2 of those engines so drag should drop considerably. But still, using the barn door sized Wright's it was faster than a Sptitfire II at any altitude, 22 mph faster at sea level. It basically equaled Hellcat performance several years earlier with current engines. It never had armor or self sealing tanks, armor being an easy fix, self sealing tanks were not on this particular plane. But still, adding P&W engines, armor and self sealing tanks and it will still weigh less than a Hellcat, and actually have more power at all altitudes with the same sized wing. Also, the wings folded, which they didn't on the first Wildcat and it was 30+ mph faster at sea level than the P&W F4F3. As far as engines, they would have to use what's available like the Wildcat did. But even with the Wrights it still had very good performance. Also, didn't we give the first 150 Wildcats to the British? (I might be wrong) the Corsair and Hellcat were great, but they simply weren't there for the first 21 months when we needed them. The XF5F could have been.

The British got a fair number of early WIldcats but they were NOT given to them, First 100 were ex French contract aircraft with Cyclone 9s (essentially same engine as used in late model Buffaloes) then 50 British aircraft with single stage R-1830s , a number of these had folding wings. Then some ex-Greek aircraft show up in 1941 ( also with single stage R-1830s)

The XF5F was designed for a projected two stage R-1535 which was never built. The R-1820 was much fatter but not very different in weight (single speed/single stage R-1535s went around 1120lbs) making conversion somewhat easy. It is the further change to two stage R-1830 engines that may pose problems.

Ballast helps equalize things but internal ballast does not simulate the drag of gun barrels/ gun ports or cartridge/link slots. Spitfire may not have had just a radio but also IFF aerials.

I didn't mean they gave Britain the Wildcats for free, but the US didn't keep the first 160 or so.

I agree that ballast doesn't tell the whole story, but it also wasn't being tested 1,000 pounds underweight, so at least the climb numbers would be relatively in line.

Would you have an educated guess on speed gain at sea level just by using smaller diameter P&W engines? 10 mph? 20? (I really have no idea, thought you might)

The US didn't keep those 180 or so planes because the US didn't order them or pay for them. The US had allowed some aircraft to be sold overseas or for foreign deliveries to made sooner than US deliveries, this was not purely altruistic. The US often allowed current production aircraft to be exported while the replacement aircraft for the US Forces would be of later, improved models. This ended Dec 7th 1941 when the US took over quite a few aircraft. The 180 or so WIldcats the British got were delivered before Dec 7th. The 100 planes on the French order got commercial Wright Cyclones.

I would note that the "powerplant" of the R-1830 powered super F5F would weigh just over 5000lbs (engine section, engine, accessories, controls, propellers, starters and oil system) This from doubling the weights from the F4F-3 For the F6F the power plant is 3917lbs or about 1100 lbs lighter.

If the super F5F is going to be significantly lighter than the F6F what is NOT being put into the Super F5F?

I would note also the the powerplant on the FM-2 was about 300lbs lighter than than on the F4F-3 but the FM-2 used a heavier Cyclone than the XF5F, it used a propellor about 25% heavier than the F4F and used a much heavier oil system.

I kind of like the XF5F but then I like the Whirlwind too, I just don't think you could stick Merlins in a Whirlwind without designing almost a whole new plane and I don't think you could stick two stage R-1830s in the XF5F without a LOT of redesign. So much that trying use the performance figures for the XF5F as a base gets very iffy.


BTW the British figured that their Cyclone powered Martlet I was only about 4-5mph slower than an R-1830 powered Marlet II at about 14,000ft.
Martlet I had 1000hp at 14,000ft and did 313 at 14,500ft. Martlet II had 1050hp at 13,100ft and did 317mph at 14,000ft. Granted there is a whole lot of drag on the Wildcat that has nothing to do with the engines.

The comparison on the Spitfire is not valid as you are comparing an in service fighter to a prototype. The Spitfire III flew before the XF5F but was never place in production, retractable tail wheel, clipped wings and a Merlin XX engine.

I looked at it a bit closer. If you add the 860 pounds of extra engine you talked about, 140 pounds of armor, that leave 300 pounds for self sealing tanks and the Hellcat and XF5F would weigh the same.

Do you know the max hp of the Wright engine the XF5F at 20,000? I can't find anything on the Wright that isn't turbocharged.

The performance is pretty good with the Wright engine. Maybe they go with a single stage 2 speed P&W to save weight, but still lose a significant amount of frontal area to keep changes to a minimum.

Do you have a best guess on speed increase by switching to smaller diameter P&W if hp at all altitudes stays the same?