Some of the more complex skin sections on the control surfaces and the wing fillets were focused on this month. The electrical system and radios also received their share of attention.
The P-47 has some unusually formed skin sections that join with a seam that has numerous curved indentations. Where the skins overlap in those areas, joggles must be created so that the skin surface remains smooth.
The wing fillets are always an exercise in intricate forming of complex curves in the aluminum skin. Randy Carlson came over from his shop, Carlson Metal Shaping in Fargo, to take care of this specialized work.
Aaron continues to complete the restoration of the aircraft systems, including the radios and instruments, as the P-47’s completion date gets closer.
A restoration milestone arrived as Aaron powered up the Thunderbolt’s electrical system for the first time this month.
The electrical circuits weren’t the only system to receive attention this month. The fuel system plumbing and antenna relay were installed in the upper rear fuselage.
The P-47 was a versatile and very successful WWII fighter. The Thunderbolt was effective operating both at high-altitude as a long-range bomber escort and down low as a fighter bomber. Much of that success and versatility can be attributed to the Pratt & Whitney R-2800 radial engine that powered the Thunderbolt.
Graham White, in his important book “Allied Aircraft Piston Engines’‘ called the R-2800 “the most significant aircraft engine built in the United States during WWII”1. Also called the “Double Wasp”, others have named the R-2800 the best radial engine ever built.
Those superlatives are opinions and are open to disagreement, but what isn’t debatable is that a great variety of significant WWII aircraft fighters and medium bombers were powered by the R-2800. In fact, it powered more different US aircraft types in WWII than any other engine.
Among the most well known are the F4U Corsair, Martin B-26 Marauder and PBM Mariner, Grumman F6F Hellcat and F7F Tigercat, Curtis C-46 Commando, Northrop P-61 Black Widow, Lockheed PV-1 Ventura and PV-2 Harpoon, Douglas A-26 Invader, and, of course, the P-47 Thunderbolt.
A total of 125,334 R-2800 engines were produced between 1939 and 1960 with 114,073 of those completed between 1941 and 1945 during the war.2
Production of the big double row radial continued after 1945. The Martin 404, Convair CV 240 and 340, C-123 Provider, and the Douglas DC-6 all used the R-2800.
Design of what became the Double Wasp began in 1936. The original design displaced 2600 cubic inches, but upon learning that Wright Aeronautical was developing a double row radial of 2600 cubic inch displacement, Pratt & Whitney increased the displacement to 2804 cubic inches by adding just over 11 cubic inches to each cylinder’s displacement.
One major challenge to the success of this first US double row, 18 cylinder engine was heat dissipation. The problem was solved by using aluminum cooling muffs with very thin and numerous cooling fins shrunk around the chrome molybdenum cylinder forgings.
A prime example of the collective commitment of American industry to support the Allied war effort was that Ford, Chevrolet, General Motors, and other US companies built R-2800s as subcontractors to Pratt & Whitney.
1 Graham White, Allied Aircraft Piston Engines, Society of Automotive Engineers, Inc, 1995, page 222
2 Graham White, Allied Aircraft Piston Engines, Society of Automotive Engineers, Inc, 1995, page 260
The R-2800 was turned out in over 40 variants, but the version used in the P-47D-23RA was the R-2800-59. Supplied with an improved General Electric C-23 turbosupercharger, the dash 59 could supply 2,000 hp at takeoff and 2,300 hp War Emergency Power in combat, with the use of water injection.
Later versions, the C series engines, attained 2500 hp and were used in the M and N model P-47s.
During WWII, R-2800s became renowned for surviving damage that would have stopped any other engine. P-47 pilots came back from missions knowing their R-2800 was down on power but still running. It wasn’t until they landed that they found out that one or even two cylinders had been shot out, but the trusty Pratt & Whitney had brought them safely home anyway.