Was the F4U Seriously Considered for the European Theatre ?

JoeB said:

I don't see why we wouldn't assume the same for 2 as 1, that the USN sheet is correct. It clearly identifies those tanks on the diagram of fuel tanks as 'unprotected'.

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Quote from pilots manual.
"4.i WING TANK VAPOR DILUTION SYSTEM OPERATION. ----Provision is made, on airplanes having outer panel integral wing tanks, for making the atmosphere above the fuel inert, for protection from gunfire during combat, by admitting CO2 to the wing tanks."

There is a warning saying use of vapor dilution system while using the fuel from the tank will cause fuel flow interruption. However fuel is still useable. There is no warning regarding use of wing tanks in combat or of emptying wing tanks prior to combat.

I think combat with fuel in the wing tanks was initially anticipated and planned for. The AAF added a destabilizing 85 gallons to the P-51B and I think adding more internal fuel to the F4U would be less problematic. However, the same could be said for the P-47, which the AAF would have more likely chosen. The real problem was that the AAF did not acknowledge a need for a long range fighter until late and by then the P-51 was showing promise. Without using the wing tanks for combat either with CO2 or adding protection, the F4U-1 would not be able to perform deep escort, not even a well as the P-47.

As I said, if the USAAF wanted to use the F4U for long range land operations, if could always modify it any number of ways, but as for F4U's as actually equipped the USN assumption was as mentioned, that the wing tanks wouldn't be used to directly supplement the main tank.

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This was Navy procedures. Would it have been the AAF's if it was desperate to protect its bombers?

And to clarify the math of the ACP sheets, under the USN assumptions the 237 gal main tank was enough for combat (8.5 min at combat power, 11.5 at military) and a 60 minute cruising reserve at a radius of 340 miles; that's where 340 comes from and why the number is still 340 whether the wing and drop tanks were used or just the drop tank. Their assumption, not just mine, was that the internal wing and drop tanks couldn't be used for any of the combat, or thus return cruise, requirement.

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Not pertinent. As long as the comparison uses equal criteria, it is appropriate. I simply used fuel available at contact with enemy air, subtracted fuel required to return to overhead base 600 miles away, and calculated the max time at Mil power on remaining fuel. All other variables, such as min. at Combat, min. at Mil, would be proportional to this number when applied equally to each airframe. In addition since assembly and recovery would have to be the same these cancelled out. Some error in incurred because some aircraft will use more fuel than others for this effort.

3. I think with all due respect it may be too quick and simple. Again, if F4U's as actually equipped could easily fly 600 mile radius missions, then they would have flown from Munda directly against Rabaul from summer 1943, which is only around 475 miles one way (the Rabaul based Zero 21 missions in 1942 against G'canal were 650 miles one way; there was never any idea of US fighters of 42-43 flying that mission in the other direction). But they didn't fly against Rabaul until bases on Bouganville were secured around 250 miles from Rabaul. So I think F4U lack of 600 radius is demonstrated in real operations where it would have come in handy if it were actually true. But again Merlin/85gal tank P-51's could operate at 600 miles, again as shown by actual missions.

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Again, not pertinent. The aircraft could probably have performed the mission but Naval operational procedures apparently, maybe rightly so, felt the mission was not worth the risk. The Japanese would have readily accepted the risk, as they did with the Zero. And, maybe the AAF would have done the same over Germany to save their bombers, and maybe not.

This suggests to me there's something wrong with your calculations.

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Only because you don't recognize it is a comparison of equal scenarios and not an individual mission based operational plan. I did make some thumbnail assumptions such as using the P-47 cruise number for F4U numbers because I had good P-47 data and did not have good data for the F4U. The F4U is lighter and would probably have slightly better performance per gallon.

Shortround6 said:

True but many of the "bench mark" or theoretical ranges for navy planes are at speeds under 200mph and sometimes altitudes of 5000ft. Now this might or might not be a realistic cruise condition returning from a carrier strike or Island raid over open water with no flak guns and little or no pursuit. Defending enemy planes having to return to the ship or Island for fuel and so are unlikely to pursue far. Army fighters, at least in Europe, would almost be committing suicide to cruise back over France at such a speed and altitude. Aside from the Flak guns, such a speed and altitude gives up too much initiative to defending fighters. Over Germany and France the defending fighters can pursue allied aircraft away from their own base with the knowledge that they can land at another airfield to refuel. Granted the German fighters did not have the range of the Japanese fighters to begin with but after the British losses of 1941/42 the standard survival tactic was to "cruise" as fast as possible over enemy territory, fuel consumption permitting. Planning an operation with a cruise of 200mph in 1943 probably would not have been given the go ahead.
A Corsair burned roughly twice the fuel per minute as max lean power as it did at it's most economical settings. The reserve for "looking for the carrier" was figured at the economical settings.

I would want a double check on that dog fighting with a 150 gal tank still attached to the plane. Corsairs were big, tough airplanes but 150 gals of fuel is 900lbs, add the tank and you are darn close to 1000lbs. Add the drag of the tank and it is going to cut into climb and speed a significant amount.

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In fact if you look at the consumption curves of the A6M-3 you can see that it achieved its long range by using very low throttle settings (which also implies very low altitude):
http://www.wwiiaircraftperformance.org/japan/Zeke-32-TAIC-102C.pdf

At ~280 mph, range falls to about 260 miles, or probably less than an Me109e at the same speed, but at about 150mph range is nearly 900 miles (all ranges on internal fuel).

Timmy raises an interesting point and very good photos. The F14 carried most of (or all) of it's missles, bombs in the tunnel and carrying it there was called conformally. That allegedly meant that there was no drag penalty and the air plane was as fast with the missles as without. I wonder if there was a somewhat similar situation with the Corsair and that the twin external 150 gallon tanks carried in the inverted gull section did not extract as much drag penalty as twin tanks did on an AC with a conventional wing?

OK, I went to the Williams site and here is the data observed from the 1-12-06 posting on the F4U1D Perfomance section.
This is fighter load with 2400 rds of ammo and this is the AC with pylons for rockets or bombs.
The AC has two 150 gallon drop tanks one protected and one not for a fuel load of 534 gallons. The protected tank is retained.
Warm up-20 minutes
Take off -one minute
Rendesvous- at SL-20 minutes
Cruise at 15000 feet set for max range
Combat-20 minutes @ 15000 feet 8.5 minutes WEP, 11.5 minutes Military and descend
Cruise back at 1500 feet at 170 knots TAS
Reserve one hour
Subtract 5.7 gallons for cruise at 215 knots
Subtract 9.5 gallons for cruise at 237 knots
Combat radius is 555 miles and this from a carrier and it is based on flight test
I think that is what I read

as a comparison a P-47C with 305 gallons in the internal tank could use Emergency max power (2000hp) for 5 minutes and max continuous power (1625hp) for 20 minutes and burn a total of 93 gallons. 175 gallons was supposed to be good for 580 miles at 200-205mph IAS at under 12,000ft. leaving a 37 gallon reserve (36 minutes give or take 5 minutes depending on altitude). This from the charts.

Obviously the Army wasn't planning on using a 200mph IAS cruise at under 12,000ft to get the fighters back to base or the P-47 could have done the job with 305 gallons internal and a couple of drop tanks.

Increasing the cruise to 200mph IAS (300mph true) at 25,000ft increases the fuel burn to 95 gallons an hour and shortens the "range" to 485 miles.

Increasing the cruise to 225mph IAS (338mph true) at 25,000ft increases the fuel burn to 145 gallons an hour and shortens the "range" to 380 miles.

Most (all?) fighters did not take off on the drop tanks but used internal fuel for warm up, taxing, take-off and climb to a low but safe altitude to change over to the drop tanks. this 12-40 gallon take-off 'allowance" has to be subtracted from the "return" range.

Suitability of a fighter to under take certain missions depends on the actual conditions of the mission/s. Not a "benchmark" estimate of range.

renrich said:

Timmy raises an interesting point and very good photos. The F14 carried most of (or all) of it's missles, bombs in the tunnel and carrying it there was called conformally. That allegedly meant that there was no drag penalty and the air plane was as fast with the missles as without. I wonder if there was a somewhat similar situation with the Corsair and that the twin external 150 gallon tanks carried in the inverted gull section did not extract as much drag penalty as twin tanks did on an AC with a conventional wing?

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There must be a real drag penalty having tanks behind the propeller line

Now North American Aviation which I guess had a very good understanding of the importance of good aerodynamics
Went as far as mounting the drop tanks on the p82 mostly on the outer edge of each wing of that aircraft
Which to me does not make any sense when they could have them all along the centre wing, as there is no under carriage in the way

So my guess was that NAA thought those tanks would cause too much drag behind the propeller line?

renrich said:

Timmy raises an interesting point and very good photos. The F14 carried most of (or all) of it's missles, bombs in the tunnel and carrying it there was called conformally. That allegedly meant that there was no drag penalty and the air plane was as fast with the missles as without. I wonder if there was a somewhat similar situation with the Corsair and that the twin external 150 gallon tanks carried in the inverted gull section did not extract as much drag penalty as twin tanks did on an AC with a conventional wing?

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Yeah, that's what I surmised. Figure the JATO units hung there, as well. That was a stable spot on that aircraft. Those units looked not unlike those fuel tanks in Timmy's picture. Look at the yellow tips on those, how they're pointed to reduce the overall in-flight drag. Same went for any drag from the prop-wash, I'd imagine. That had to be negligible, at best.

The chart did not say what the cruise speed was but an escort fighter is not going to cruise faster than the bomber being escorted. The four engined bombers cruised at around 175 MPH when loaded I think. The Navy fighters after disengaging from combat, if they knew where the carrier was going to be, would begin to slowly descend all the way back to the carrier, to save fuel and still maintain good airspeed. I expect that the AAF fighters would do the same if conditions allowed.

The escort fighters DID cruise faster than the bombers. It takes too long to accelerate from 175-200mph up to 350mph to engage the enemy fighters when bounced. The escort fighters did "S" turns to keep speed up and still stay with the bombers. Even after the initial combat the escort fighters went home (at least a good part of the way) at high cruise speeds in case they were bounced again. Cruising at 175-200mph at under 15,000ft over western Germany or most of France gives the Luftwaffe too much of an advantage. Once over the Channel the speeds would be reduced and/or altitude lost.

timmy said:

I'm sure I have read some where on this forum that if you had any protrusions like drop tanks behind the propeller line, it produced so much more wind resistance meaning less range. While mounting drop tanks outside the propeller line (P51) produces a lot less wind resistance, better range

Now I understand why Vought mounted the external tanks under the fuselage as it produces less stress on the wings. But if Vought was serious in adding range to the f4u wouldn't it be better mounting those tanks on the outer wings ? An F4U wing would certainly be strong enough

Anyway just wanted to add my thouhts

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a little OT but the tanks on the 51 gave the plane ( and i imagine other ac with the same set up ) another occasional quirk. i remember stories from some 51 pilots to said the tanks created a little suction on the gear covers and every so often make the gear hard to retract. the fix was after taking off they would wag the wings or slip it side to side slightly to break the gear free to retract. i didnt think about too much until read in an old with franz stigler who said they did the same thing to 262 ( skid of slip it ) but on landing ...to lock the gear down. and i wondered if that had to do with the turbulence between the engine and the gear cover???

Luftwaffe Aces: Franz Stigler - HOGS Forum

You weren't in the 262 for very long were you? How many missions?

I had the 262 for over half a year…you know they build 'em… one down in America.

Yeah! They flew one few months ago!

They got it up…I was there. If the pilot would have done what I told him…he wouldn't have grounded it...

The wrecked the landing gear didn't they?

Yeah, the undercarriage collapsed…

What did he do wrong?

What we always did…when we came in for a landing, and we were high yet, we sideslipped so the undercarriage would really lock.

And he didn't?

It was common that it did that, you know…automatically. We had the same problem. Thing is, if we didn't get the wheels even, you know, because the airplane exploded right there......