What if the Americans never made any mistakes in their procurement decisions.

[XBe02Drvr]

Same hp, same top speed. Would that mean the same drag?
looking forward to your response

I would say that the P38's inherent induced drag is probably less, as it achieves the same speed at the same HP, but at 3,000 pounds more weight. If you could get it down to the rocket's weight, I suspect it would be faster. Also, comparisons of raw HP don't always translate directly to effective thrust, as there are other factors such as propeller efficiency, exhaust thrust, and with a radial especially, percent of the prop disk blanked by the cowling. Just a few more ingredients for the stew.
Cheers,
Wes

 

[MiTasol]

And with a twin, you can't go with Vstall alone, you have to consider Vmc, minimum engine-out control speed, which is generally considerably higher.
Wes

And VMC on the F5F will be very high.
Look at the Hudson, many of which used the same R-1820 engines - AP 1690F gives the Hudson stall speed gear and flaps up as 80kts at MTOW. VMC (safety speed as it was called then) is 120kts or 50% faster. Given that the Hudson has a much larger keel area than the F5F I would expect the F5F to have a far far higher VMC.
Keel area is best summarized as the amount of surface area of the fuselage as that makes the aircraft tend to stay in a straight line. Look at how they fixed directional instability on the Mustangs and Kittyhawks - increased keel area by adding fillets and/or fuselage extensions.
On the F5F keel area was as small as Grumman could make it so as to maximize maneuverability. The Hudson has a lot of keel forward of the wing and the F5F a minute amount. And the Hudson proportionally has probably three times as much behind the wing. Add to that the inertia (weight) of the Hudson is far higher so again it has a lower tendency to swing when an engine fails. With its twin booms the P-38 also has a much larger keel area and weighs in some 40-50% heavier than your projected F5F. I do not know its VMC/safety speed.

 

[swampyankee]

A much simpler procurement problem was with the USN's torpedoes. Its aircraft torpedoes had a quite poor reputation, in comparison with those of Japan, Britain, and Italy. While the USN got its torpedoes via an arsenal system, they did not have the same sort of failures of design with their ships built in naval dockyards and aircraft built at the NAF. I suspect part of the problem was that the USN had decided that torpedoes weren't important. This makes it pretty hard to have an effective submarine force and also tends to severely limit destroyers' value in surface warfare.

 

[pinsog]

And VMC on the F5F will be very high.
Look at the Hudson, many of which used the same R-1820 engines - AP 1690F gives the Hudson stall speed gear and flaps up as 80kts at MTOW. VMC (safety speed as it was called then) is 120kts or 50% faster. Given that the Hudson has a much larger keel area than the F5F I would expect the F5F to have a far far higher VMC.
Keel area is best summarized as the amount of surface area of the fuselage as that makes the aircraft tend to stay in a straight line. Look at how they fixed directional instability on the Mustangs and Kittyhawks - increased keel area by adding fillets and/or fuselage extensions.
On the F5F keel area was as small as Grumman could make it so as to maximize maneuverability. The Hudson has a lot of keel forward of the wing and the F5F a minute amount. And the Hudson proportionally has probably three times as much behind the wing. Add to that the inertia (weight) of the Hudson is far higher so again it has a lower tendency to swing when an engine fails. With its twin booms the P-38 also has a much larger keel area and weighs in some 40-50% heavier than your projected F5F. I do not know its VMC/safety speed.

The actual tests from the pilots that flew it said it would be a carrier pilots dream since the rudders were directly behind each engine. They also said with the engines close together that it aided in single engine handling. If, with one engine out, you had to pin the rudder to the opposite side, it wouldn't be unlike many single engine fighters on takeoff, the Wildcat had to use full rudder to counteract torque on takeoff. I would also point out that it flew a lot better with one engine out than a Wildcat, Hellcat or Corsair. At least it could maybe get back to the ship and let the pilot bail out over his own fleet.

 

[pinsog]

I would say that the P38's inherent induced drag is probably less, as it achieves the same speed at the same HP, but at 3,000 pounds more weight. If you could get it down to the rocket's weight, I suspect it would be faster. Also, comparisons of raw HP don't always translate directly to effective thrust, as there are other factors such as propeller efficiency, exhaust thrust, and with a radial especially, percent of the prop disk blanked by the cowling. Just a few more ingredients for the stew.
Cheers,
Wes

Interesting. One thing I have a question about is, many airplanes top speed isn't affected that much by an increase in weight, the Mustang for example only differed a few mph from full load of fuel and ammo to nearly empty of fuel and ammo(all internal of course). Climb of course was severely affected.

I wish we had more tests of the XF5F.

Obviously they didn't build it, but since it had the room in the nacelles for the turbochargers and extra fuel, it doesn't require any outer changes that would add major drag (like the P39 for instance. No room to add a much needed turbo) it looks to me like it would be easy to do and work well. They mounted it on the XP50 which the wing and nacelles were virtually the same. To me, NOT adding turbochargers or at least 2 speed 2 stage engines, would be like removing the turbochargers from a P38, P43 or P47. The room was there so why not do it?

Does that line of thinking make sense?

 

[pbehn]

Interesting. One thing I have a question about is, many airplanes top speed isn't affected that much by an increase in weight, the Mustang for example only differed a few mph from full load of fuel and ammo to nearly empty of fuel and ammo(all internal of course). Climb of course was severely affected.

I wish we had more tests of the XF5F.

Obviously they didn't build it, but since it had the room in the nacelles for the turbochargers and extra fuel, it doesn't require any outer changes that would add major drag (like the P39 for instance. No room to add a much needed turbo) it looks to me like it would be easy to do and work well. They mounted it on the XP50 which the wing and nacelles were virtually the same. To me, NOT adding turbochargers or at least 2 speed 2 stage engines, would be like removing the turbochargers from a P38, P43 or P47. The room was there so why not do it?

Does that line of thinking make sense?

Because weight has a decreasing effect on speed as the top speed increases, with an increase in speed drag increases but the weight remains constant so the force required to provide lift remains as a constant while drag increases as an exponent. The P-51 was approx. 1 ton heavier than a similarly engined Spitfire but was 30MPH faster.

 

[Shortround6]

I can tell you that the installed 1820's were not the highest power available and they were never upgraded during the tests, the 2 speed Wright 1820's installed in the British Martlets were rated 1,200 hp at 4200 feet and 1,000 hp at 14,000 instead of 1,000 hp at 4200 and 900 hp at 14,000. That alone would increase performance from 312 mph at SL to 331 mph at SL and from 345 mph at 14,000 to 357 mph at 14,000.

From what I can find the engines in the XF5F were the same as the ones in the Martlets/US Buffaloes. They were the highest powered ones available at the start of the tests, even if never replaced as interest waned. Higher powered R-1820s with mechanical superchargers don't show up until late 1942 or early 1943. These were the basis for the very late war(and post war) 1425hp engines which used almost no interchangeable parts with 1200hp Cyclones.

Later on (post war?) the FAA approved the 1200hp rating for this series of engines for take-off at 2500rpm/44.5in for 5 minutes if using the 7.14 supercharger gear.
However max continuous (or Normal) was 1000hp at 6900ft at 2300rpm/37.2in.

try this page: https://rgl.faa.gov/Regulatory_and_...1fb9c650f34d78525676a006354ef/$FILE/5E-10.pdf

There appear to be a few hitches in the ratings? like high supercharger gear being limited to a minimum altitude? and the engine making about 200hp less in high gear at teh same rpm and nearly the same manifold pressure?

In the early part of the war the US often (but not always) used the take-off rating/s as the military power. And quite often they were a 5 minute rating. This is well before there was a WER rating.

My own opinion is that some of these performance numbers were achieved using military power(take-off) as some of them do not line up well.
The 4000fpm climb rate is a real puzzle as the plane in light condition is rated at 4.2 minutes to 10,000ft. or an average of 2380fpm.


The similar data sheet for the XF4U-2 night fighter

is here.
http://www.alternatewars.com/SAC/XF4U-2_Corsair_PD_-_17_December_1942.pdf
Please note the 4.3 minutes to 10,000ft using "normal" power of about 1650hp.
There is no way that the F5F with those two large Cyclone engines plus fuselage has less drag than the F4U.

I would note that the P-38 was actually pretty slick for a plane of it's size/weight. It's flat plate equivalent area for the J model falls between the F4U-1D and the F6F-3.

 

[pinsog]

From what I can find the engines in the XF5F were the same as the ones in the Martlets/US Buffaloes. They were the highest powered ones available at the start of the tests, even if never replaced as interest waned. Higher powered R-1820s with mechanical superchargers don't show up until late 1942 or early 1943. These were the basis for the very late war(and post war) 1425hp engines which used almost no interchangeable parts with 1200hp Cyclones.

Later on (post war?) the FAA approved the 1200hp rating for this series of engines for take-off at 2500rpm/44.5in for 5 minutes if using the 7.14 supercharger gear.
However max continuous (or Normal) was 1000hp at 6900ft at 2300rpm/37.2in.

try this page: https://rgl.faa.gov/Regulatory_and_...1fb9c650f34d78525676a006354ef/$FILE/5E-10.pdf

There appear to be a few hitches in the ratings? like high supercharger gear being limited to a minimum altitude? and the engine making about 200hp less in high gear at teh same rpm and nearly the same manifold pressure?

In the early part of the war the US often (but not always) used the take-off rating/s as the military power. And quite often they were a 5 minute rating. This is well before there was a WER rating.

My own opinion is that some of these performance numbers were achieved using military power(take-off) as some of them do not line up well.
The 4000fpm climb rate is a real puzzle as the plane in light condition is rated at 4.2 minutes to 10,000ft. or an average of 2380fpm.


The similar data sheet for the XF4U-2 night fighter
View attachment 571983
is here.
http://www.alternatewars.com/SAC/XF4U-2_Corsair_PD_-_17_December_1942.pdf
Please note the 4.3 minutes to 10,000ft using "normal" power of about 1650hp.
There is no way that the F5F with those two large Cyclone engines plus fuselage has less drag than the F4U.

I would note that the P-38 was actually pretty slick for a plane of it's size/weight. It's flat plate equivalent area for the J model falls between the F4U-1D and the F6F-3.

Nice info/data sheet on the F4U. I guess I'm looking at the data a bit different than you. When comparing the climb of the Corsair at normal power (1675 hp) it is close on time 4.3 minutes to what the test on the XF5F is at normal power 4.2 minutes. Agree 100% that the XF5F has a lot more drag than the F4U. So the F4U at 1675 hp for normal power and 11,500 pounds has about the same climb as the XF5F at 10,900 and normal power 2000 hp (1000 hp X 2 ). That would show higher drag for the XF5F. Of course both lose power as they climb. The F4U at military power adds 325 hp and climbs a little better than 3000 fpm, the XF5F if it used takeoff power would add 400 hp down low up to I don't know what altitude. There are so many sources that quote the 4000 fpm climb of the Skyrocket, hence the name. But the F4F-3 is quoted as having an initial climb of 3,300 fpm but it doesn't hold that rate very long. Obviously the Wrights get winded pretty quickly at altitude not being 2 stage or turbocharged.

Did you see the example a couple of posts ago that at around 5000 feet if you adjust the hp of the XF5F to 1150 hp per engine it is almost exactly the same speed as a P38? I thought that was interesting considering the P38 is considered slick and the XF5F is considered high drag.

I actually think of many of your posts when making a case for the XF5F. You have stated on many threads that: you can't build a P47N in 1942 or 1943 because you don't have enough power (or propeller). You also said you can't build a long range P51 in 1941 because you don't have enough power. In my opinion the XF5F is in the same boat, except it COULD have been done by adding turbochargers.

FWIW I know the US Navy would not have ever specced this plane out like I have. 2 stage P&W yes, turbocharged never, but it COULD have been done. They had all the pieces they just needed to put them all in the same plane.

 

[XBe02Drvr]

They also said with the engines close together that it aided in single engine handling.

As long as you're above single engine safety speed, which is probably in the 120-125 MPH range, as pointed out by MiTasol above. Good luck getting it aboard at that speed. You do understand what happens if you get below that speed on one engine?

 

[XBe02Drvr]

The P-51 was approx. 1 ton heavier than a similarly engined Spitfire but was 30MPH faster.

Thanks to some cutting edge aerodynamic wizardry that the Spit didn't have.

 

[pinsog]

As long as you're above single engine safety speed, which is probably in the 120-125 MPH range, as pointed out by MiTasol above. Good luck getting it aboard at that speed. You do understand what happens if you get below that speed on one engine?

Tends to make dents that won't buff out doesn't it?

 

[pbehn]

Thanks to some cutting edge aerodynamic wizardry that the Spit didn't have.

Well yes, but that was my point, at the top speed of these type of aircraft small improvements in aerodynamics have a big effect. Also absolute top speed wasn't always the top priority, the cannon on the Spitfire were known to cost about 5-8MPH I believe, but reverting to 0.303 MGs wasn't considered. Sticking a rear view mirror on the outside of the cockpit has an effect out of all proportion to its weight. and nothing like fitting extra tanks and guns inside.

 

[wuzak]

The only possible mistake that I can see is:-
1. Not making any F5F Skyrockets.

Is the XF5F the new Fw 187?

 

[wuzak]

I think the biggest mistake the USAAC/F made was the delay in ordering the P-51.

 

[Shortround6]

Did you see the example a couple of posts ago that at around 5000 feet if you adjust the hp of the XF5F to 1150 hp per engine it is almost exactly the same speed as a P38? I thought that was interesting considering the P38 is considered slick and the XF5F is considered high drag.

We are back to what power they were really using on the Xf5F.
the 1000hp rating was normal power but normal power was not military power, Normal power was the same as max continuous. An early P-38 made 1000hp at "normal" power. 2600rpm and 37-38 in of manifold pressure.

See; http://www.alternatewars.com/SAC/F2A-3_Buffalo_PD_-_1_December_1942.pdf

If you believe the performance of the XF5F was done at "normal" power then you have to believe the F2A-3 Buffalo could make 320mph at 14,500ft on 900hp or that the max speed of the B-17 was done at 2300rpm and 39.2in MAP (1000hp ) instead of 2500rpm and 45.5in MAP (1200hp).

 

[Kevin J]

Is the XF5F the new Fw 187?

Having seen the latest figures for the production F5F-1, I think the Seafire was the best option for the FAA for 1942/43.

 

[Kevin J]

I think the biggest mistake the USAAC/F made was the delay in ordering the P-51.

If you're just comparing speeds for the Mustang I and Kittyhawk I then there's very little difference, it's 372 vs 362 mph and the later was a better dogfighter. For the Mustang Ia then you're up to 392/382 mph with 2/4 cannon. So the Mustang begins to look like a better bet. The A-36A brings in the plumbing for fuel tanks and bombs which is carried over into the P-51A, so perhaps the P-51A should have been built with the V-1650-1 rather than being used in the P-40L?

 

[pinsog]

We are back to what power they were really using on the Xf5F.
the 1000hp rating was normal power but normal power was not military power, Normal power was the same as max continuous. An early P-38 made 1000hp at "normal" power. 2600rpm and 37-38 in of manifold pressure.

See; http://www.alternatewars.com/SAC/F2A-3_Buffalo_PD_-_1_December_1942.pdf

If you believe the performance of the XF5F was done at "normal" power then you have to believe the F2A-3 Buffalo could make 320mph at 14,500ft on 900hp or that the max speed of the B-17 was done at 2300rpm and 39.2in MAP (1000hp ) instead of 2500rpm and 45.5in MAP (1200hp).

That's a real head scratcher Shortround. I don't know. I certainly understand what your saying, but I don't see the point in listing the exact hp at several different altitudes and then testing the airplane at that exact altitude and using a different hp than you listed. "Engine makes 900 hp at 14,000 feet, does 345 mph at 14,000 feet" (but we actually ran engine at 1100 hp, shhh don't tell them) The Buffalo did have a rather small wing area which might contribute to the higher speed at less hp, only 209 square feet vs 260 for the F4F. Personally, I think we need to assume the things listen in a test are factual (unless it's an obvious typing error) if we reject the facts listed in a test such as hp at a given altitude, then we can simply reject any and all tests that we don't like the results from. Yes I do like the XF5F and I'm a bit of a fan, but, it was a rather small aircraft, 5 feet shorter than a Hellcat, same size wing as a Corsair, but there wasn't much to it except for the 2 windmill sized engines and yet it took at least 200 more hp to equal the Hellcat at sea level. It seems legit to me. My main suggestion for the XF5F is that you could add turbochargers into the engine nacelles and hold takeoff power up to 25,000 feet. No one would want to take a P38, P43 or P47 into combat without a turbocharger, I feel the same about the XF5F.

I appreciate your responses. Thank you

 

[wuzak]

Having seen the latest figures for the production F5F-1, I think the Seafire was the best option for the FAA for 1942/43.

You may have joined after the period of much Fw 187 love.

Seems like we are in a period of XF5F love!

 

[jetcal1]

You may have joined after the period of much Fw 187 love.

Seems like we are in a period of XF5F love!

Without knowing the actual VMC of the aircraft or how its weight issues were going to be solved along with other problems Grumman didn't want to mess with, it's kind of hard to call the F5F the be all end all of naval fighters in 1941.
Even Grumman was trying to wash their hands of the project by the end of March 1942 with a memo to BuAer stating they had no further interest in the F5F.