Why were U.S. pursuit fighters at the start of WW2 of lower performance than European fighters?

[Thumpalumpacus]

I don't remember where I read this anecdote, probably here, that American aircraft had to at least make it from one end of Texas to the other.
It's a big country. I doubt there was a requirement written as such but thought along those lines must have been there. That might explain why American fighters were larger than their European counterparts.

Los Angeles is closer to El Paso than Texarkana. Texarkana is closer to Charlotte, NC than it is to El Paso.

 

[Greg Boeser]

I don't remember where I read this anecdote, probably here, that American aircraft had to at least make it from one end of Texas to the other.
It's a big country. I doubt there was a requirement written as such but thought along those lines must have been there. That might explain why American fighters were larger than their European counterparts.

Not only that, but they had to perform in environments from the Alaskan tundra to the jungles of the Canal Zone.

 

[marathag]

The P-40s were sort of in no man's land in 1940, they could perform just about as well as any European fighter except the Spitfire but they weren't actually combat ready.

Was the A6M Model 21 Zero of 1940 'Combat ready'?
It didn't have self-sealing tanks, armorglass or even armorplate for the seatback like the P-40B had. Sometimes even the Radio was removed.
It did have 950 hp and 156 US gallons of fuel internally, two MGs and two 20mm cannons, and pilot had good visibility.
Not all that fast, but maneuverable and had long range.

I like to bring up that the French Hawk 75s, fairly similar to the Zero in being lightly armed, was also long ranged and maneuverable and lacking armor and self-sealing tanks, did very well against the Luftwaffe in 1939-40

 

[pbehn]

I don't remember where I read this anecdote, probably here, that American aircraft had to at least make it from one end of Texas to the other.
It's a big country. I doubt there was a requirement written as such but thought along those lines must have been there. That might explain why American fighters were larger than their European counterparts.

Europe is almost comically small compared to other theatres. I spent years driving to the Hanover region (site of many ww2 air battles) from the north of England . The US "bomber country of Cambridgeshire and East Anglia are 3-4 hours south while the whole journey took 11 to 13 hours depending on traffic and the tunnel. A few times I drove to and from Milan which was just over a days driving. On one job I drove from Rouen to Duisburg every Thursday afternoon and back on the Sunday in time to watch the Rugby. One time I checked out of the hotel in France stopped in Belgium for petrol,, Netherlands for food and went to the bank machine in Duisburg, my bank put a hold on the card because it had been used in 4 countries in one day.. London Berlin is 580 miles, Paris Berlin 212 miles, Paris Berlin 550 miles. Paris to Moscow is 1550 miles which shows how stupid Napoleon was.

 

[MIflyer]

Note that almost all US fighters had substantially longer ranges than comparable European counterparts. The reason for this is simple. The USA is an enormous country by European standards. A typical European single seat fighter could not make it across TEXAS without running out of gas. The range requirement made most US fighter larger and heavier.

Brewster F2A: Normal range 950 miles, maximum range 1680 miles.
RAF Buffalo I: Normal range 520 miles, max range 840 miles.
Curtiss P-36C: 820 miles
Hawk 75A-4/Mohawk IV: 603 miles
P-35: Normal range 600 miles, with full fuel 950 miles,
P-40B: Normal range 730 miles, max range, 945 miles
P-40E: Normal range 650 miles, with a 50 gal drop tank, 850 miles,
P-40N: Normal range 750 miles, with a 75 gal drop tank, 1080 miles
F4F-3: Normal range 845 miles
P-38F: Normal range 900 miles at 10,000 ft, with two 160 gal drop tanks at 10,000 ft, 1750 miles
P-43: Range with a 200 lb bomb, 650 miles, Max ferry range, 1450 miles
P-47C: 640 miles with no drop tanks
P-51A: Normal range 1000 miles at 10,000 ft, with two 150 gal drop tanks 2000 miles

Note that the export versions of some US fighters had much shorter ranges; the Europeans did not seem to want anything more. And US fighters used drop tanks for years before the war started and many could also carry bombs.

I heartily agree with Snowygrouch's comments on US supercharging. The USAAF focused on turbosuperchargers, which were the correct soultion purely in technical terms but proved to be impossible to implement except in a few cases. The failure of the US to adopt liquid cooled inter/aftercoolers I find to be inexplicable, but then again I took too much thermodynamics in college.

 

[special ed]

The isolationist thinking in the 1930s is what gave us the Bell YFM-1. The idea that the bombers would come in over the ocean unescorted meant that the YFM-1 could simply cruise up and blast them.

 

[buffnut453]

Note that almost all US fighters had substantially longer ranges than comparable European counterparts. The reason for this is simple. The USA is an enormous country by European standards. A typical European single seat fighter could not make it across TEXAS without running out of gas. The range requirement made most US fighter larger and heavier.

Brewster F2A: Normal range 950 miles, maximum range 1680 miles.
RAF Buffalo I: Normal range 520 miles, max range 840 miles.

Note that the export versions of some US fighters had much shorter ranges; the Europeans did not seem to want anything more.

The F2A/Buffalo range data are your only example of "the Europeans did not seem to want anything more." Unfortunately, your conclusion isn't correct.

You're comparing the range of an F2A-3 with that of the Buffalo which was based on the F2A-2. It wasn't that the Brits "wanted" shorter range from the Buffalo, it's simply that they were procuring a variant of the F2A-2 which had shorter range than the -3.

The -3 wasn't available when the RAF order was agreed. The first USN order for the -3 was in January 1941, by which time the production of RAF Buffalo MkIs was well advanced. First Buffalos arrived in Singapore in February 1941 and were with squadrons the following month.

The Belgian order for the F2A predated that of the RAF so it, too, had to be based on the F2A-2 which was the only variant in production at the time.

It's also worth considering that RAF-procured airframes in 1940 required self-sealing fuel tanks when many US aircraft didn't have that capability. Self-sealing tanks reduced fuel capacity and hence range of the RAF equivalents of existing US airframes.

Apologies for the Buffalo diversion...let's get back to the main topic.

 

[SaparotRob]

No apology necessary.

 

[tomo pauk]

Was the A6M Model 21 Zero of 1940 'Combat ready'?
It didn't have self-sealing tanks, armorglass or even armorplate for the seatback like the P-40B had. Sometimes even the Radio was removed.
It did have 950 hp and 156 US gallons of fuel internally, two MGs and two 20mm cannons, and pilot had good visibility.
Not all that fast, but maneuverable and had long range.

I'd say that Zero 21 was combat ready, regardless the imperfections.
P-40B was 1st delivered in January 1941. It was preceded with P-40 and P-40A - these two versions sported no protection for pilot or fuel.

 

[buffnut453]

Was the A6M Model 21 Zero of 1940 'Combat ready'?
It didn't have self-sealing tanks, armorglass or even armorplate for the seatback like the P-40B had. Sometimes even the Radio was removed.
It did have 950 hp and 156 US gallons of fuel internally, two MGs and two 20mm cannons, and pilot had good visibility.
Not all that fast, but maneuverable and had long range.

Depends whose definition of combat ready you're using. By RAF standards, most in-service US fighter aircraft weren't combat ready in 1940 due to lack of armour/self sealing fuel tanks.

Given that the IJN made quite extensive use of the Model 21 operationally, it's fair to assume it was combat ready from that service's perspective.

 

[Shortround6]

The US fighters were designed for more range/fuel capacity. But it was for transfers, not combat.

The change to self sealing fuel tanks hurt some planes more than others.
To modify MIflyer's list

Brewster F2A: 160 US gallons for all types until the F2A-3. Then it was still 160 gallons unless you filled the old unused tank under special orders.
RAF Buffalo I: 160 US gallons.
Curtiss P-36C: 105 US gallons normal, 160-163 gallons overload.
Hawk 75A-4/Mohawk IV: 105 US gallons normal, 160-163 gallons overload
P-35: Normal???? max 200 US gallons?
P-40B: 120 US gallons normal, 160 gallons overload
P-40E: Self sealing tanks, 148 US gallons normal (all three tanks were filled) 52 gallon drop tank
P-40N-5: 160 US gallons? change in type of tanks, larger drop tank.
F4F-3: 160 US gallon unprotected/147 gallons protected.
YP-38: 410 US gallons unprotected
P-38D: 300 US gallons protected
P-39C: 170 US gallons, unprotected
P-39D: 120 US gallons protected plus drop tank
P-43: Capacity ????
P-47C: 305 US gallons protected
P-51A: 180 US gallons protected.

Now the P-35/P-43 and P-39 employed a very popular "trick" of US designers in the late 30s, integral fuel tanks. Take part of the structure, seal it off and use as fuel tank/s saving the weight of a separate tank/s. Used on everything from the Vought Kingfisher to the Catalina and the very early B-24s. Trouble was that they often could not get them to stay sealed in use (flying hundreds of hours) even without the enemy trying to shoot holes in them. Once the enemy started shooting holes in them repairs were much more difficult.

We can also see that the drop tanks for the P-38, P-39, P-40 were initially to restore original intended range and not to extend range. at least on the P-39 and P-40.

What we don't know is why the original " no drop tanks" order was given.
1, The "Bomber Mafia" didn't want long range fighters stealing their glory?
2, A few companies used drop tanks to scam the requirements? Plane just missed required speed and range so they cut the fuel capacity and squeaked by the performance requirement and then met the range requirement with a drop tank?
3. In the days of very few planes being bought they had a few too many accidents in planes using drop tanks?

The last is somewhat brought out by a number of naval officers who were senior officers in the late 30s but had been flyers in the 1920s when a number of navy planes used water cooled engines. A number of them had made forced landings in the water due to cooing problems (leaks) with the water cooled engines. One is supposed to have said (the Navy will use water cooled engines in AIrcraft when the Navy starts using air cooled engines in submarines"

 

[Shortround6]

I'd say that Zero 21 was combat ready, regardless the imperfections.
P-40B was 1st delivered in January 1941. It was preceded with P-40 and P-40A - these two versions sported no protection for pilot or fuel.

The Tomahawk I had no protection.
The Tomahawk IIA had some armor and external coating on the fuel tanks.
The Tomahawk IIB and the same or more armor and used internal liners in the fuel tanks.

The US and the British had had a meeting in Sept of 1940 to try to agree to the minimum number of differences between the Tomahawks and the P-40 series to make change over from batch to batch easier. Does not mean that both parties immedialty got the agreed to changes.

 

[ThomasP]

F2A-3 had 3x SSFT added. There were 2x 20 USgal SSFT (1x in each inboard wing leading edge) and 1x 40 USgal SSFT in the fuselage. The original 2x 80 USgal integrated non-SSFT were retained. So total protected fuel was only 80 USgal out of the 240 USgal total. They also had serious problems with the self-sealing part of the new tanks.

Somewhere on the internet . . . there is a copy of a document describing the problems with the Buffalo's SSFT.

The F2A-3 PD lists the protected and unprotected fuel volume, just over half way down on the left of the 2nd page.

 

[buffnut453]

Brewster F2A: 160 US gallons for all types until the F2A-3. Then it was still 160 gallons unless you filled the old unused tank under special orders.

SR6, you often make this comment about the F2A-3. However, is it fair to ignore the capacity of that tank?

When the F2A-3 entered service, the US was still at peace with peacetime rules for flight authorizations. As such, it makes perfect sense for there to be stencils on an overload tank warning that it should only be filled under certain authorized circumstances.

Take the P-51 as a comparison. It, too, had an overload tank that negatively impacted aircraft handling during take-off and climb-out. During WW2, under wartime flight authorizations, filling that tank was driven solely by mission tasking. I'd bet good money that, in 1946 under peacetime authorizations, that overload tank would only be filled "under special orders." Yet nobody quotes the P-51's maximum range by caveating "special orders" use conditions for the overload tank.

Seems like there's a double standard at play here when comparing the much-loved P-51 and the unloved F2A-3.

 

[GrauGeist]

I beleive the P-43A had a total fuel capacity of 218 gallons.

Now I'm not sure if this capacity was a total for it's wet-wing tanks or if it included the 50 gallon drop tank: 168/50.

 

[ThomasP]

The P-43/P-43A manual lists 220 USgal total internal in 2x 110 USgal non-SSFT (1x in each wing).

 

[Shortround6]

SR6, you often make this comment about the F2A-3. However, is it fair to ignore the capacity of that tank?

When the F2A-3 entered service, the US was still at peace with peacetime rules for flight authorizations. As such, it makes perfect sense for there to be stencils on an overload tank warning that it should only be filled under certain authorized circumstances.

Take the P-51 as a comparison. It, too, had an overload tank that negatively impacted aircraft handling during take-off and climb-out. During WW2, under wartime flight authorizations, filling that tank was driven solely by mission tasking. I'd bet good money that, in 1946 under peacetime authorizations, that overload tank would only be filled "under special orders." Yet nobody quotes the P-51's maximum range by caveating "special orders" use conditions for the overload tank.

Seems like there's a double standard at play here when comparing the much-loved P-51 and the unloved F2A-3.

There is no real CG issue with filling the old tank on the Buffalo. the problem is that you are adding about 480lbs of weight to a plane that already had weight issues.
There is no way to dump the weight/fuel in an emergency, either mechanical or by surprise enemy attack.
The F2A-3 was almost 300lbs heavier heavier than the F2A-2 with the same fuel and armament. Adding more fuel just makes the performance worse.
If there was a special mission that required extra fuel then perhaps it could be used.
The F2A-3 was an under 7000lb plane, adding 480 lbs to it makes a difference.
P-51Ds were about 9600lbs with just the internal wing tanks and about 10200lbs with the rear tank.
Interesting note I just ran across, P-51D with rockets, rear tank and drop tank was limited to 1100lb of fuel in the drop tanks or the combat ceiling would be under 25,000ft.
What does that extra 480lbs do to the F2A-3 climb and ceiling? Or take-Off roll?

But the long range recon scenario sometimes put out makes no sense.
As mentioned above with all tanks full only 1/3 of the fuel is protected. The Navy was using SPD as scouts, not fighters, the SPD could carry 260 gal all protected.
The Navy in many of of their weight and load lists would claim they were going the ferry the planes without guns. Maybe they did.

I have a reprint of a post war F-51 manual. They advise not filling the rear tank more than 55 gallons but there are cautions if filled more. They also want 30 gallons to stay in the rear tank for landing (I have no idea what they may have done to radios or other equipment) but they wanted that 30 gallons to be used last after all other tanks were dry.

 

[Shortround6]

The P-43/P-43A manual lists 220 USgal total internal in 2x 110 USgal non-SSFT (1x in each wing).

Thank you,

P-43 Performance

the performance numbers are for 145 US gallons of fuel but as I have said, that was common for the time.

 

[drgondog]

There was a wide consensus in U.S. military circles ~1939-1940 that U.S. pursuit fighters were substantially less capable in terms of performance than their equivalent European counterparts. Specifically, in Germany, the BF109-E (the first version to use the Daimler-Benz DB-601 engine) began production in 1938, while the original airframe was designed in 1934. In Britain, the Spitfire airframe was designed in 1935 and the airplane went into production in 1938. The single-engined fighters which were being developed in the U.S. at the same time included the Seversky P-35, Bell P-39, and Curtiss P-40 (derived from the P-36). There was wide belief - confirmable by various performance metrics - that the U.S. fighters were inferior.

The Lockheed P-38 was spawned by available funds for an Interceptor in 1937. The RFP defined "In line engines, heavy firepower and Turbo supercharging to achieve high altitude performance". Two contractors were selected by Ben Kelsey/Oliver Echols at Wright Patterson Field - home of Materiel Command and R&D functions for AAC. Both received contracts in mid-late 1937. One achieved success, the XP-39 tested poorly - majority reasons surrounding the turbo supercharger/Allison installation and performance.

First production orders for YP-38 in April 1939, despite crash of XP-38 in Jan 1939. Production ordered for YP-39 also in April. First Production orders for Mustang I in May 1940. So by the end of 1940, the YP-38 has been flown; 24 P-39C delivered; the Prototype NA-73X has flown - and all three or producing to fill orders by AFPC, and in the case of P-38 and P-39 orderd by AAC.

If 1940 is the date "in which wide concensus in US Miitary circles" I would ask you for a citation from senior 'US military circles'.

If you re-frame the question to "Why didn't the P-40 and P-39 maintain PACE with performance attained by Bf 109K and Spit XIV".

The First answer is powerplant. The Bf 109 had far more Cdt than the P-39 and more than the P-40 but the DB-601A to 605D performance evolution was superior to the Allison V-1710 in same volume - enabling the airframe to grow with it. When Allison introduced auxilary second stage, it was too bulky to drop into an existing airframe. Impossible for P-39, P-40, P-51 and P-38. To accomodate, basic fuselage/wing position (major re-design) required to install in P-39 (P-63), and P-40 (P-40Q). The Spitfire was blessed with the R-R Merlin evolution. That said, the P-39 was slighly lower drag. Had Bell enough foresight to realize that R-R engines would be available in near future (and politics not intervene) the slighly longer Fuse and change of CG version would have been very interesting as a point Interceptor with longer range that same Generation Spitfires.


The second answer is Fuel Fraction. US fighters always spec'd and developed with higher fuel fractions than Euro or Asian counterparts (Save A6M). The US defined Airframe Structures Standards set a higher limit for Limit and Ultimate Loads for given design full Gross Weight internally. The P-51H was the exception and the XP-51F/G were the progenitors of NAA Lightweight Fighter program. I am unclear what German aircraft structural standards were, but fuel fractions were lower. Obviously higher fuel fractions - all else exactly equal affect Induced Drag, Rate of climb, Acceleration.

What accounted for this difference in performance?
Of note: I am looking mostly for an engineering answer, and references would be greatly appreciated!

Advances in in aircraft performance are generally governed by developments in 1) aerodynamics 2) propulsion and/or 3) structures.

See above for power and structures. You missed 4.) basic airframe design --------> which trades increasing wing area for lower W/L versus more speed, trades airfoil selection from low T/C to reduce profile and Mcr vs internal stores capacity (fuel and armament). You might also consider trade offs between best practices production standards vs aerodynamic best practices (i.e. flush rivets, surface preparation standards including butt joints, puttying/painting forward surface of wing, paint selection (bad choice = more friction drag).

Of the ones discussed above (P-38, P-39, P-40, P-51, Spitfire, Bf 109) I would argue the aerodynamics superiority as follows:
1. Mustang - the rigid adherence to second order curves for fuselage, combined with dumping the dragy things aft of Lifing line (coolant/oil radiators) into fuselage, combined with Meredith Effect design to reduce cooling drag Hp, combined with Low Drag but subtantial fat T/C for high volume internal stores - made it the winner of the Puppy charm list. It grew to Wolfhound proportions mission-wise with Merlin engine upgrade.

2. Spitfire with a slight queasiness due to radiator design and carb scoop 'bumps'. Additionallythe top surface bumps on wing to accommodate te 20mm armament were parasite items of significance, What raised it above the P-38/P39 for me was the thinner wing compared to P-51, P-38 and P-39 with elliptical planform to reduce Induced drag over the others. Additional consideration beyond foundation aerodynamics was the wing area combined wit low weight to achieve low W/L and thus better climb and turn performance for given (Power Available less Power Required)/(W/L).

3. P-38 gets my third position for aerodynamics as the Parasite drag was higher - although it was extremely low for any twin engine Fighter. Additionally, while draggier than Spit, the NACA 23016 airfoil was only a little draggier than the NAA/NACA 45-100 Low Drag airfoil for the Mustang. Initially the intercooler was located on leading edge - absent scoops etc. Overall the aerodynamics were cleaner than Spit and P-39 and P-40, but suffered increased wetted drag due to size while offsetting with low Induced Drag of wing span (AR). All the turbo stuff located aft of lifting line. It's achilles heel was uncovered during wind tunnel testing after first dive test failures. The centerbody between the two booms created a venturi effect at Mcr, which created major problems until dive flaps in P-38J solved the initial acceleration into MCr at high altitudes. That said - not a factor save at medium high altitude.

4. Bf 109E but it was not a clean airframe in 0.029 range for low RN compared to P-51 (all until P-51H) at 0.017 at RN at 1.8x10^6. What made it slightly above Spitfire was that is was small, big engine and lower wetted drag. Scalable engine Hp increases overcame the draggier airframe. The Bf 109E had lower drag than the F and G but the F was a great performer.

5. The P-39 and P-40 were about equal wrt to CDt, both about 10% lower than P-38 but 10% higher than Spit. What makes the P-40 ultimately superior IMO was the wing design and the overall internal fuel capacity compared to P-39. Although both were 15% T/C airfoils, the P-39 wing was 10% smaller in span, MAC and internal volume available. Additionally the rearward retraction of main gear while slightly draggier, provided room for main armament with disposable weight in ammo less impactful to Cg issues than nose armament scheme of P-39. That said, the power loading of the P-38 was superior to all the existing fighters globally above 20,000 feet

The P-39, P-40, P-38 and Mustang I airframes at end of 1940 were inferior dogfighters (inherent capability) to Spit, (IMO), but roughly equivalent to the Bf 109E and Hurricane. The Mustang through the altitude limitations of lower FTH to the Spitfire was inferior in turn and climb to Spit but accelerated, dived and superior in speed. The Bf 109E was marginally superior in climb to Mustang, equal in turn and slower in speed and dive - Spit, P-39, Bf 109E far inferior to tactical footprint of P-38 and P-51, slightly inferior to P-40. ALL of the ones mentioned were inferior to P-38 in speed and celiling and high altitude performance at close of 1940. That said, only the P-40 and P-39 were neing delivered to operational units in spring 1941.

Keeping this in mind, the most obvious causal factor in the superior performance of European fighters is that the European engines available for use in the 1935-40 timeframe were of higher performance in terms of P/W ratio (particularly at altitude) than similar engines then available in the U.S. The German DB-601 and British Rolls Royce Merlin engines were both superior to the American Allison engine, the only serious V12 the U.S. produced in the late 1930s. It would take until 1940 for the U.S. radial engine makers to launch high-output versions of their radial engines (e.g. supercharged R-2800s) and of course the U.S. capitalized on the high-performance, liquid-cooled Merlin for use in the P-51.

So the question is, was the entire scope of the performance difference due to powerplants alone or whether there were other salient developments in aircraft aerodynamics and/or structures that help account for the superior performance of British and German fighters to start the war.

Would take exception to that generality, beginning with V-1710-39 or equivalent for P-39, P-40 and Mustang I. Would also point out that V-1710-29/31 with GE turbo was far superior in Hp to weight above 20,000 feet, producing the same HP at 25000 feet as the R-R and DB 601A at 15,000 feet.

Additionally, the R-1830-76 w/ 2stage/2 speed supercharger for F4F-3 was delivering 1000 hp at 19000 feet, in production Feb 1940 and deployed at end of year. Fully loaded heavy fighter weight = 7500 pounds. That said, except for superior turn ability the F4F-3 was inferior to all the above mentioned in-line fighters.

To your question however, growth in performance (or lack thereof) are the successive engine improvements in Hp/weight without drastic changes to the airframes mentioned. Fo the Bf 109 for example it was two steps forward for one step back, as bulges to accomodate the bigger engine on same airframe, protuberances such as cooling system scoops relocated under wing increased drag due to larger cooling system requirements. The installation of the Packard 1650-1 increased Hp and FTH at the expense of greater weight and increased coolant radiator size. The change to 1650-3/-7 for P-51B/D dramatically improved performance above 15,000 ft compared to P-51A with Allison V-1710-81 - but the WI capability of the final P-51A enabled superior speed, turn and climb over the B/C below 12,000 feet. Why?, basically the same airframe but lower GW and equal/greater available HP

I think the best way to do this comparison is to compare three specific aircraft c. 1940: 1) The BF-109E 2) The Spitfire Mk1 (or Mk2) 3) The Curtiss P-40 (alternatively, substitute the P-39).

See above - combat operations for P-38, P-40, P-39 and Mustang I were essentially the same. ALL the Euro fighter you name are in combat before serial production of any of the P-40/P-39/P-51 or P-38 types.

Note - I am being very specific to the timeframe of 1935 - 1940 because later U.S. developments, such as the P-51 Mustang, F6F, etc., largely corrected much of the performance deficit. While one could still argue on the margins about the superiority of one design over the other, there was no longer a consensus amongst the U.S. military officials that their pursuit fighters were inferior.

You would be hard pressed to source any US Military senior commander claiming that US fighters were inferior. You wold also be hard pressed to find a senior officer in 1940 advcating the P-51. (Or junior officer)

Note 2 - there is a difference between a design choice & a technical advance. German and British fighters also may have had higher performance on the metrics I mentioned above not because German's had specific ideas that were more advanced than the U.S.'s designers, but also because they were designed to do with different goals in mind. I have tried to equalize by not comparing aircraft designed for obviously different goals (eg, a twin-engined interceptor vs. a single-engined fighter). But there still might be some differences. For example, U.S. fighters might have been heavier (thus reducing climb rates) because the USAAC put more emphasis on armor protection than the RAF did. If that is the answer, happy to hear that too. Just want to know!

I mentioned the AAC Materiel Command handbook for strutural design, in which you may find anomalies compared to Brit/French/USSR/Italy in context of Limt and Ultimate Loads. Specifically the Brit standard vs US design standards that I am aware of include lower landing gear, lower side load and lower Angle attack G factors. All point to lower weights in airframe given equal competency of structural design engineers.

One glaring diference was landing gear design. Both Spit and Bf 109 chose main support near or at primary fuselage longeron WS, while All the US designs were farther outboad for wider landing track. That decidion influences design consideration for spar/wing design.

Lower lateral loading considerations lead to smaller cross sectional fuselage areas, smaller longeron/stringer design, and thinner shear panel thickess for aft fuselage.

Lower AoA design limits drive smaller Spar Moment of Inertia for primary and secondary spars.

Exchange of sealed fuel tanks for un-sealed steel tanks drove increases in weight and reductions in internal volumes available for improved capacities.

The airplanes with initial high fuel fractions and primary fuel storage in wings (P-51, P-38) thrived when asked to increase internal fuel to increase range when compared to P-39, P-40, P-47, Spitfire, Bf 109, Fw 190, etc

 

[buffnut453]

There is no real CG issue with filling the old tank on the Buffalo. the problem is that you are adding about 480lbs of weight to a plane that already had weight issues.
There is no way to dump the weight/fuel in an emergency, either mechanical or by surprise enemy attack.
The F2A-3 was almost 300lbs heavier heavier than the F2A-2 with the same fuel and armament. Adding more fuel just makes the performance worse.
If there was a special mission that required extra fuel then perhaps it could be used.
The F2A-3 was an under 7000lb plane, adding 480 lbs to it makes a difference.
P-51Ds were about 9600lbs with just the internal wing tanks and about 10200lbs with the rear tank.
Interesting note I just ran across, P-51D with rockets, rear tank and drop tank was limited to 1100lb of fuel in the drop tanks or the combat ceiling would be under 25,000ft.
What does that extra 480lbs do to the F2A-3 climb and ceiling? Or take-Off roll?

But the long range recon scenario sometimes put out makes no sense.
As mentioned above with all tanks full only 1/3 of the fuel is protected. The Navy was using SPD as scouts, not fighters, the SPD could carry 260 gal all protected.
The Navy in many of of their weight and load lists would claim they were going the ferry the planes without guns. Maybe they did.

I have a reprint of a post war F-51 manual. They advise not filling the rear tank more than 55 gallons but there are cautions if filled more. They also want 30 gallons to stay in the rear tank for landing (I have no idea what they may have done to radios or other equipment) but they wanted that 30 gallons to be used last after all other tanks were dry.

Authorization restrictions are put in place for a whole host of reasons, not just instability. In the case of the F2A-3, it seems that weight was likely a primary driver.

Agree adding more fuel makes the porcine F2A-3's performance even worse. That said, the impact would reduce over time...assuming the old tank was emptied first. Not sure the "surprise attack" scenario is particularly valid. The same problem would occur for overloaded P-51s if they were bounced just after take-off. Yes, the P-51 could jettison drop tanks but that would make the CofG issue even worse...unless the pilot could selectively dump fuel from the overload tank. I don't know if the latter was possible.

I agree entirely about the long-range reconnaissance scenario. Indeed, the requirements for the F2A-3 seem entirely muddled. The F2A-2 was an adequate platform overall and there seemed little reason to add all the extra fuel and oil. The RAF managed with the -2 design and protected tanks so why not an upgraded F2A-2? A conspiracy theorist might suggest the -3 was simply a means for the USN to get rid of the type and replace it with the F4F.