According to Gordon Elliot White's book on the Wasp Major the contra-prop gearbox and drive system for the XB-35 worked fine on the test stand, the problems started when it was mounted on the aircraft. White posits that the issues were caused by where they were mounted and that they were a pusher configuration. Being mounted with the thrustline above the surface of the wing, which put the propellers in clean air at the top of their arc but at the bottom subject to the assymetrical airflow off of the wing that resulted from the changing thickness of the airfoil and the sweep of the trailing edge, which meant that the speed of the air traveling over the surface changed as you went outboard from the centerline of the aicraft. As a result, as the propellers rotated, the loading was constantly changing. It's possible that staggered positioning of the propeller assemblies, the inboard being forward of the outboard, may have played a role. He also points out that changing to the single rotation four-bladed propellers didn't eliminate the vibration, it just reduced the performane of the aircraft.
something I forgot to add, the P-47 at 72" of MAP was good for 2800hp, but there is evidence that they ran more power than this in combat. At minimum the P-47Ms got juiced up to a documented 76" (to their apparent detriment) and I've heard more than one tale of Jugs running 90-100 inches of mercury in the direst conditions. the R-2800 is easily past 3000hp at such a setting. Republic tested the R-2800 on an engine stand at 3600hp for some 250 hours straight
Probably a P-47 could have carried at least 6 but it would have required a redesign of the wing internals and I don't think it was ever a priority. 8 fifties is getting to be quite a lot to even consider upgrading, especially when you consider the jug had nearly infinite ammo and the M3 browning at ~1200rpm came out late in the war. Furthermore the US Navy was enamored with them but by the time the USAF decided to pursue 20mm cannons the P-47's successor's successor's successor (F-100) was already underway. Here was a one-off experiment with 2 under the wings.
Looking at the photos of the wing structure of this restoration back in 2020 it doesn't appear to me that converting to 20mm cannon would be a big deal.Probably a P-47 could have carried at least 6 but it would have required a redesign of the wing internals and I don't think it was ever a priority. 8 fifties is getting to be quite a lot to even consider upgrading, especially when you consider the jug had nearly infinite ammo and the M3 browning at ~1200rpm came out late in the war. Furthermore the US Navy was enamored with them but by the time the USAF decided to pursue 20mm cannons the P-47's successor's successor's successor (F-100) was already underway. Here was a one-off experiment with 2 under the wings.
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here is the room in the wings for them to play around with. the wing spars seem to be designed around the length of a .50 bmg shell
I doubt that the combination was especially successful. The succeeding P-60E used a conventional propellor with the R-2800. If a simpler. lighter, cheaper, more readily available four-bladed standard propellor could handle the R-2800's power, the contrarotating type would not seem to offer any advantages.,
Ab ad about Curtiss electric propellers in "Aviation" February 1942
6 fifties of the new M3 variant had the firepower of 8 of the old M2 guns. That would make the P-47 lighter and maybe increase its roll rate since the outer 4th gun and its ammo would be deleted. The XP-72 was to carry 6 M3 guns or 4 37mm cannons.
Maybe, but in practice P-47 pilots always elected to carry 8 guns, even when allegedly some P-47Ns received the M3 in the final days of the war. There's no such thing as overkill!
planehistoria.com
I like this teasing in early 1942. Hyping up their new product.
Eaker asked for the Republic ferry tank - Jan/Feb 1943. Republic had a proprietary 4 point attach scheme for the P-47C-2 skid plate.
I think around 1200 delivered between February and June 1943.
True - first test by LtC Cass Hough July 13. Issues with non-pressurization limited ability to draw fuel above 22000 feet. Very draggy, 'uncomfortable flying characteristics, often hit empennage when dropped' - recommended using but limit to 100gal and use primarily for climb to 20000 feet then drop.
February 24 1942 Fighter Conference. Ordered Wright Field to Increase Range of Fighter, Attack and Light Bomber aircraft". This initiated the start of drop tank development. Lockheed also gave their pylon design already being produced for drop tanks and bombs, to all pursuit manufacturers, incl, Republic.
No, it only had provision for the four point skid mount and Republic 200 gal tank. The Brisbane tank could also be mounted on the C, D-2 and D-4. The new Keel and B-7 rack installed on the D-6 was retrofitted to all previous models at end of August, 1943. Until the B-7 no tank from US could be mounted.
True, but the 150gal flat tank began arriving in January - just not enough to replace the 108gal Bowater or US mad 110gal steel tank.
Wing pylon kits were sent to ETO and SWP in December for retrofit on D-11. Very lengthy mod. The D-15 arrived in sufficient numbers to complete a mission on March 18th.
The result was Bowater-Lloyd paper composite 108gal tank, but the original 100gal steel tank design at Langford Lodge was denied steel priority by Brit War Ministry in April/May.
The first 108/110gal steel tank from US was also tested in July but found to require improvements, finally delivered in December.
Those 108/110 gal tanks Were Pressurized and driven by slaving exhaust vacuum pump from engine. Valves ordered locally.
oldmachinepress.com
The Materiel Command was opposed to changing to another standard 20mm logistics imposition. The P-38 and P-400 were the only two - and the P-400 only because the Brits insisted.
I don't think the logistics of supplying more 20mm ammo or the necessary parts would have been a problem for the USAAF, but the fact is the American built 20mm Hispanos were having rather severe reliability issues. Tony Williams has written on this before but most if it seems to have been due to some minor dimensional changes made in manufacturing that caused a huge headache. The 20mm cannons also weren't being built to the same tolerances that smaller caliber MGs were because anything larger than .60 caliber (15.2mm) had different standards. That threshold being decided upon in a seemingly arbitrary manner. The mass-produced 20mm Oerlikon didn't have a problem here since it was a somewhat simpler and more robust design, but the lighter and faster firing 20mm Hispano needed very precise workmanship to function well.
I'm not sure they were anything special with regard to firepower per weight or per volume, but they certainly were important to USAAF planning, and were one of the cannon types used in the post-war ballistic trials, indicating that USAAF interest in the weapon was still high, which I'd count as a vote of confidence in the value of the weapon, including its usefulness for the future. The 37 mm shells turned out to be a bit more destructive against "hard" aircraft components than the German 30 mm mine shells that were also trialed, and less destructive against the "soft" aircraft components. (Which probably was just what one would have suspected anyway, but they proved it to a good level of statistical significance.)
