Grumman Design 25

Tailspin Turtle

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6 December 2007
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Unfortunately, the great people at the Grumman Aircraft History Center haven't yet found a drawing of Design 25, but they did come up with the submittal letter dated 28 May 1937. We therefore know that it was powered by two Allison V-1710 engines of 1,000 horsepower each and was very similar in configuration to the Lockheed P-38 Lightning. (Ironically, Lockheed submitted a Lightning derivative powered by two air-cooled R-1535 engines.)

"It is believed that the greatest advantage in performance can be gained for the twin engined fighter by fully utilizing the possibility of doubling the maximum horsepower available for a single engine plane. This consideration, coupled with the desire for the minimum practical frontal area, led to the selection of the Allison 1710 liquid cooled engines for this airplane. This engine is rated at 1000 horsepower at sea level (1150 horsepower for take-off) and with a turbo-supercharger installation, this power may be maintained up to 25,000 feet. It is estimated that the maximum speed of this airplane at 25,000 feet will be 360 m.p.h. and that it will climb to 20,000 feet in eight (8) minutes."

Other configuration facts from the letter:

The pilot is located in the fuselage forward of the wing and the rear end of the fuselage terminates a short distance aft of the wing. There was volume for a second crew position aft of the pilot.

The engines drove three-blade tractor propellers of the controllable type thru extension shafts. (My guess is that this was a center of gravity consideration because of the forward location of the cockpit; the other possibility is that the propellers were located fairly far forward, but the nacelles would then create a field of view problem so that doesn't seem likely.)

There was a small bomb bay sized for two 110# or one 500# bombs.

Armament was four 50 cal machine guns with an alternate installation of two 20mm Oerlikons or one 37 mm cannon.

The wings folded. Folded width was 23' and overall length was 38' 6". (My guess is that the aspect ratio was higher than in Grumman's designs up to that point because or since the wings folded.)

A clever fellow could use the Design 29 and 30 drawings prepared that same year and already posted to create something that meets this description. Note that the Design 29 had twin booms and a tricycle landing gear and the Design 30 had a forward cockpit and a propeller driven by an extension shaft. Both had rounded wing tips unlike Grumman designs after the XF4F. I'd guess that the wing span was about 42 to 44'.
A Grumman twin-V-1710 looking like a twin-boom P-38? Wonderful! This could be a contest subject for our friends the What-if modelers... Thanks!
“Grumman G-25 High altitude single-seat Navy fighter with twin Allison engines, 5,37. Not built.” is only briefly mentioned (page 261) in Tony Butler and Alan Griffith’s book “American Secret Projects: Fighters, Bombers and Attack Aircraft/ 1937 - 1945.” (Crecy, Manchester, 2015) with no illustration.
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