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

tomo pauk · Oct 21, 2012

When one reads about the Grumman twins, the great speed is claimed, at least at Wikipedia. But how good they really were?
Was it possible for a plane with less HP than P-38, more drag (due to bulkier engines) to attain the speeds in excess of 420 mph (XP-50)? Or, the plane far far draggier than the P-47D, to almost as fast, on about the same HP?

ShVAK · Oct 21, 2012

They both looked like smaller lighter airframes than the P-38, which explains some of their performance. Both Grummans weighed about 10,000 pounds loaded with 42 ft wingspan, a P-38L by comparison was around 17,000 with 52 ft wingspan. That had to count for something.

GregP · Oct 21, 2012

If the R-2800 were used, then 400+ mph would be the result, if not in the early models, then perhaps in the later models. The XF5F was powered by the Wright 1820, but almost certainly would have been an R-2800 candidate later in development. Ditto the XP-50.

I have never seen the XF5F listed at above 400 mph. It is usally quoted at about 383 mph or so. The faster one was the XP-50 and it was half the weight of the F7F and had only about 60% of the wing area, so it was a MUCH smaller aircraft with a weight-to-power ratio similar to the F7F; in fact a bit better at combat weights (12,000 pounds for the XF5F and 22,000 for the F7F). I believe the 424 mph myself.

Recall the Navy bought the F4F. F6F, and commissioned the F8F. I tink both the twins were pretty good but the Navy wasn'r ready to commit EVERYTHING to Grumman. Hence, they passed on the big twins until the Tigercat came along.

Either could have been developed into a competent fighter ...

fastmongrel · Oct 22, 2012

That might have been an estimated speed, paper planes are always faster than the metal version. I suppose speeds calculated by a slide rule are always going to be high no one ever sold anything by undervaluing the merchandise.

drgondog · Oct 22, 2012

tomo pauk said:
When one reads about the Grumman twins, the great speed is claimed, at least at Wikipedia. But how good they really were?
Was it possible for a plane with less HP than P-38, more drag (due to bulkier engines) to attain the speeds in excess of 420 mph (XP-50)? Or, the plane far far draggier than the P-47D, to almost as fast, on about the same HP?

It is probable that the Total Drag expressed in pounds was less for both ships was less than the P-38 due to much smaller wetted area and wing size. I.E The Bf 109 was 'much draggier' than the Mustang with respect to CDo but the total drag expressed in pounds was close because the 109 wetted area and wing were much smaller.

tomo pauk · Oct 22, 2012

Wing area of the P-38L was 327.5 ft², the XP-50 had 304 ft² - the P-38 had some 8% more. The P-51 had 35% more wing area than the 109G-6.

johnbr · Oct 22, 2012

Here is a photo.
eneral characteristics
Crew: One
Length: 31 ft 11 in (9.73 m)
Wingspan: 42 ft (12.80 m)
Height: 12 ft (3.66 m)
Wing area: 304 ft² (28.24 m²)
Empty weight: 8,310 lb (3,770 kg)
Loaded weight: 10,500 lb (5250 kg)
Max. takeoff weight: 13,060 lb (6,530 kg)
Powerplant: 2 × Wright R-1820-67/69 9-cylinder air-cooled radial engines, 1,200 hp (895 kW) each
Performance
Maximum speed: 424 mph (680 km/h) at 25,000 ft (7,620 m)
Range: 1,250 mi (2,010 km)
Service ceiling: 40,000 ft (12,190 m)
Rate of climb: ft/min (m/s)
Wing loading: lb/ft² (kg/m²)
Armament
2 × 20 mm (.79 in) cannons
2 × 0.50 in (12.7 mm) machine guns
2 × 100 lb (50 kg) bombs

tomo pauk · Oct 23, 2012

Were those estimated performance figures or achieved? Was it armed when those 424mph were achieved?

Shortround6 · Oct 23, 2012

The 420mph (or 424 mph) was estimated. I don't believe the aircraft was armed.

The Plane first flew on the 18th of Feb. was damaged in a landing accident on the 14th of March, repaired and lost on the 14th of May when a turbo charger exploded. One source says 20 hours or less total flight time IIRC.

tomo pauk · Oct 23, 2012

The 420mph (or 424 mph) was estimated. I don't believe the aircraft was armed.

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?).

pinsog · Oct 23, 2012

Why not compare the F5F directly to the Westland Whirlwind. The F5F was slightly smaller, weighed the same, and had 1200 HP engines vs 885 HP engines in the Whirlwind. I would imagine the F5F would have been a pretty awesome little fighter at the time it would have been introduced. Certainly better than anything else America had in the inventory at the time.

tomo pauk · Oct 23, 2012

The F5F had greater wing area (304 vs 250 sq ft), it's engines were bulky radials, and it was 1100 HP vs 885 HP at altitude. Call it a draw, speed-wise?

Now, F5F with V-1710 - that would've been an airplane...

VBF-13 · Oct 23, 2012

Grumman wouldn't have got the job, anyway, once it went into production on the XF6F, as it couldn't spare the plant capacity. That's why its other aircraft went over to GM. And Lockheed had a lock (no pun intended) on that P-38, which was the incumbent.

Shortround6 · Oct 23, 2012

I think the document provided by Tomo pretty much puts "paid" to the XF5F-1's account and with it the XP-50.

Far from the "estimated" 383mph at sea level in some sources, even if we credit it with 312mph using 1000hp per engine 383mph is waaaaay out of reach. Even 383mph at somewhere between 15,000 and 20,000 feet seems out of reach.
Even if the 358mph at 17,300 was achieved with the 900hp "normal" rating and not 1000hp "military" the XF5F-1 would need 1100hp to hit 383mph according to the cube law. The 1350hp Cyclone 9 used in the later FM-2 Wildcats was good for 1000hp at 17,500ft military rating.

tomo pauk · Oct 23, 2012

The XP-50 was featuring the turbocharged Cyclones, so the speed ought to be higher, once the plane is at high altitude. But what kind of performance was to be expected? The P-38G was making, at 24,400 ft, 403.0 mph on 1175 HP.

davebender · Oct 23, 2012

An F5F powered by the latest model R1820 engines will be competative with most Pacific aircraft up to the end of WWII. So why mess with a good design? In 1945 it will be superceded by the larger F7F.

wuzak · Oct 23, 2012

Was it a "good design"?

Shortround6 · Oct 24, 2012

tomo pauk said:
The XP-50 was featuring the turbocharged Cyclones, so the speed ought to be higher, once the plane is at high altitude. But what kind of performance was to be expected? The P-38G was making, at 24,400 ft, 403.0 mph on 1175 HP.

True but the XP-50 only has 50hp more total and has a lot more drag.

Here are some interesting pictures of both planes.

S.A.M. #52: Grumman Skyrocket - Dieselpunks

Shortround6 · Oct 24, 2012

wuzak said:
Was it a "good design"?

According to one source the only help it was to the F7F design was showing them HOW NOT to do things.

davebender · Oct 24, 2012

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.

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

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