Dakota Territory Air Museum – P-47D Restoration Update – August/September 2021

Aaron is in the cockpit testing the electrical system. (photo via AirCorps Aviation)

Warbird Digest has received the August/September, 2021 report from Chuck Cravens concerning the restoration of the Dakota Territory Air Museum’s P-47D Thunderbolt 42-27609 at AirCorps Aviation in Bemidji, Minnesota. We thought our readers would be very interested to see how the project has progressed since our last article on this important project. So without further ado, here it goes!


The team focused on some of the more complex skin sections for the control surfaces and wing fillets this month. The electrical system and radios also received their share of attention.

Complex Skin Forming 

The P-47 has some unusually formed skin sections that join with a seam which has numerous, curved indentations. Where the skins overlap in those areas, joggles must be formed in the sheet metal so that the skin surface remains smooth.

Wing Fillets

The wing fillets are always an exercise in intricate forming of complex curves in the aluminum skin. Randy Carlson came over from his shop in Fargo, North Dakota, Carlson Metal Shaping, to take care of this specialized work.

Instruments and Radio 

Aaron continues to complete the restoration of the aircraft systems, including the radios and instruments, as the P-47’s completion date gets closer.


Electrical System 

A restoration milestone arrived this month; Aaron powered up the Thunderbolt’s electrical system for the first time!

The intercooler doors are another electrically powered system. This is the motor and jackscrew which operates those doors. It worked perfectly in the electrical tests. (photo via AirCorps Aviation)

The Mark VIII gunsight lights up! The Mark 8 reflector gunsight as installed in the D-23 Thunderbolt was used in USAAF fighters prior to the development of the K-14 gunsight. Originally developed by the U.S. Navy, who used it in aircraft such as the F4U Corsair, F6F, and F8F, the Mark VIII reflector gunsight was also used in the P-47D Thunderbolt. Reflector gun sights worked by projecting a reticle (also called a pipper) onto a slanted piece of glass through which the pilot aimed. (photo via AirCorps Aviation)

The light for the pilot’s main switch box is working. (photo via AirCorps Aviation)

Internal Fuselage Systems 

The electrical circuits weren’t the only system to receive attention this month. The fuel system plumbing and the antenna relay were installed in the upper rear fuselage.

Pratt&Whitney R-2800 Double Wasp

The P-47 Thunderbolt was a versatile and highly successful fighter during WWII. The type 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 is attributable to the Pratt & Whitney R-2800 radial engine which powered the Thunderbolt.

The Pratt & Whitney R-2800-59 which will power the P-47 awaits installation. (photo via AirCorps Aviation)

Graham White, in his seminal book, Allied Aircraft Piston Engines, described the R-2800 as “the most significant aircraft engine built in the United States during WWII.”1 Known as the Double Wasp, the R-2800 has often been referred to as the best radial engine ever built.

Those superlatives are opinions and are open to disagreement, of course, but what isn’t debatable is that a great variety of significant, WWII-era fighters and medium bombers used the R-2800. In fact, the Double Wasp powered more different US aircraft types in WWII than any other engine!

The most well-known types to use this powerplant include the Vought F4U Corsair, Martin B-26 Marauder and PBM Mariner, Grumman F6F Hellcat, F7F Tigercat, F8F Bearcat, Curtiss 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 1945.2

Production of the big double row radial continued after 1945. The Martin 404, Convair CV 240 and 340, Fairchild C-123 Provider, and the Douglas DC-6 all used the R-2800.

The design for what became the Double Wasp began in 1936. The original concept displaced just 2,600 cubic inches, but upon learning that Wright Aeronautical was developing a double row radial of 2,600 cubic inch displacement, Pratt & Whitney increased their design’s displacement up to 2,804 cubic inches by adding just over 11 cubic inches to each cylinder.

Heat dissipation proved to be one of the major challenges which the engineers had to tackle in making the R-2800, America’s first double-row, 18-cylinder engine, successful. Pratt&Whitney solved the problem by using aluminum cooling muffs with numerous very thin, cooling fins shrunk around the chrome molybdenum cylinder forgings.

A prime example regarding the collective commitment of American industry in supporting the Allied war effort was the fact that so many U.S. companies, including fierce competitors such as Ford, Chevrolet and General Motors, were willing to build 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

A WWII Chevrolet advertisement mentioning the R-2800. (photo from The Truth About Cars website, accessed 9/30/2021)

Cooling fins on a R-2800 cylinder were thin and precisely designed to maximize airflow over the two banks of 9 cylinders. (photo via AirCorps Aviation)

There were more than 40 variants of the R-2800; the version which the P-47D-23RA used 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 up to 2,300 hp War Emergency Power in combat, with the use of water injection. Later, C-series variants of the engine (which M and N model P-47s employed) could attain up to 2,500 hp.

The R-2800-59 used General Electric magnetos; they are the black painted assemblies in this image. Briggs & Stratton also built many of these magnetos during WWII; just another example of US industrial commitment to the “Arsenal of Democracy”. (photo via AirCorps Aviation)

The single stage supercharger mounts on the rear of the crankcase and, in conjunction with the C-23 turbosupercharger, provides excellent high altitude performance. (photo via AirCorps Aviation)

During WWII, R-2800s became renowned for surviving damage which would have crippled any other engine. P-47 pilots could come back from missions with their R-2800’s 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.

And that’s all for this month. We wish to thank AirCorps Aviation, Chuck Cravens for making this report possible! We look forwards to bringing more restoration reports on progress with this rare machine in the coming months. Be safe, and be well


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