Hi Widewing,
>As to adding 20mm cannon... The M2 cannon was nearly 40 inches longer than the BMG .50, which would have resulted in the guns protruding nearly four feet beyond the leading edge.
This seems to have been typical for successful Hispano installations ;-)
>The difference in weight between 8 Brownings and 4 Hispanos amounts to just over 100 lbs.
The difference is more pronounced if you look at the weights of the complete batteries as posted above:
4x Hispano II - 154 rpg - 352 kg - 187% firepower
8x ,50 Browning M2 - 375 rpg - 562 kg - 100% firepower
2x Hispano II - 308 rpg - 252 kg - 94% firepower
(Including ammunition and belt links, ammunition supply of equal energy in each setup.)
The advantage of the 4x Hispano battery is 110 kg (243 lbs - your figure is 235 lbs, so we're in good agreement here), and the advantage of the 2x Hispano battery is 310 kg (684 lbs).
A 310 kg advantage is equal to 413 L additional fuel - 110 gallons, or 38 min of endurance at 42" Hg/2550 RPM. My guess (we could tell more accurate with the manual data) is that this would result in a cruise speed of about 300 mph, so we have a gain of about 190 miles range or 95 miles combat radius.
According to Williamson Murray, "War in the Air", the P-47 had a combat radius of about 375 miles in August 1943, meaning that it could reach about as far as Wiesbaden. From Wiesbaden to Schweinfurt, we've got a distance of 88 miles, or slightly less than the gain from the different armament.
That should, at the very least, be food for serious thought :-)
(Of course, we wouldn't able to assign the full 310 kg to fuel, as tanks and fuel lines have their own weight as well. On the other hand, my P-47D-25 to D-35 Power Plan Chart indicates that Maximum Cruise Power is a bit lower than the setting I used above (which is about equivalent to Maximum Continuous in that chart), so we might get a bit more range out of it anyway. The 310 kg are about 4.9% of the loaded weight, so on the return leg, the P-47 will be markedly lighter than usual which helps combat radius, too. So there are some conservative factors along with the initial optimistic assumption that make the 95 mile combat radius extension a reasonable approximation. Conservative factors includes my map reading as Wiesbaden is not at the extreme limit of Murray's range circle, and somewhat south of the direct route to Schweinfurt, too :-)
>Now, the question begs, would the major level of modification required be worth the time, money and production delays associated with retooling? I think that the USAAF and War Production Board would say "hell no!"
With the benefit of hindsight, I'd say the answer in early 1943 should certainly have been an unambiguous "Yes"! Without this benefit, I'd expect that this suggestion would have been turned down since neither the USAAF nor the War Production Board had a clear idea at that time of how hard the fight was going to be for the 8th Air Force.
>To meet the need for additional range, the P-47D-25 introduced an enlarged internal aux tank, adding 65 gallons. With this, there was no more volume within the fuselage for additional fuel.
As pointed out above, the F4U-1 had tanks in the outer wings, which might have been an option for the P-47 as well, especially as we'd gain some volume from switching to 2x Hispano cannon.
To gain room in the fuselage, it would have been an option to remove the turbo-supercharger :-) The P-47 already had the intercooler that was required for high altitude performance, and replacing the turbo-supercharger with a mechanically driven one would have freed up the rear fuselage and the lower fuselage as well, creating plenty of room for enlarged fuel tanks.
Sounds like heresy, but actually two-stage mechanically-driven superchargers were doing quite well at high altitude, too, and while the P-47 would have lost a bit of power at the propeller, it would have gained some through exhaust thrust while being lighter overall (at an equivalent fuel load).
Regards,
Henning (HoHun)
