Tailhook Topics: Grumman XF4F-2

4 May Update: I revised the top-view wing-tip shape and added the wing gun ammo doors based on a relook at the wind tunnel photos. I'm not convinced that I got the wing-tip shape correct.
25 April Update: Reduced the chord on the ailerons on the top view
25 April Update: Revised side and top views and added side view.
24 April Update: Revised side view and added top view.
19 April Update: Added annotated side-view pictures of the early and late configurations.

Grumman initially lost the competition with Brewster for production of the Navy's first monoplane fighter. However, the Navy continued to fund development of the F4F and then ordered it into production as well. For a bit more, see http://thanlont.blogspot.com/2011/12/grumman-comes-from-behind-to-win.html

Jack Alvrus wrote an excellent conversion article on the XF4F-2 and -3 that appeared in the IPMS Quarterly Volume 4, Number 4. It detailed configuration differences with the production F4F, including several of the changes that were made in flight test. However, the side-view and planform drawings are not accurate in my opinion. The Lloyd Jones multi-view drawing also appears to be suspect as Rick Koehnen discovered when he compared it to published dimensions. However, there is a pencil sketch, almost certainly by a Grumman engineer, that compares the XF4F-2, F4F-3, and an early layout for what was to become the F6F. It is incomplete and contains one major and at least one minor discrepancy, but it provides the foundation for a pretty good drawing of the XF4F-2 configuration.

The major discrepancy is the location of the wing tip. The XF4F-2 had a wingspan of 34 feet; the production F4Fs, 38 feet. The -2 wing tip is clearly located too far outboard on the drawing. I’m not sure where Jones went wrong on his side view.

Dana Bell's F4F monograph is now available (see http://www.cybermodeler.com/hobby/ref/cw/book_cw_f4f.shtml). He said that it doesn't include much on the XF4F-2 but kindly provided me with high resolution side views of the early and late XF4F-2 configurations, which I have annotated to show the changes made between November 1937 and March 1938.

Two subtle difference are the open canopy side brace that was added, probably to minimize canopy buffeting when it was open, and the change to a single exhaust stack located directly in front of the landing gear attach-points fairing, apparently to reduce drag. The gun barrels were also shortened significantly.

As you can see, there were a number of changes made during flight test and it would be easy to mix them up. Note also that the backside of the propeller blades on the March 1938 version has the extended blue section to reduce glare. It also doesn't have the gun sight installed for some reason.

The following side and top views of the final configuration are based on the engineering sketch and the photos. Noting that the aft tip of the -2 fuselage appears to end a bit sooner than that of the production Wildcats, I came up with a drawing that has an overall length, including the spinner shown, of 26’ 5”, which matches the published dimension.

Note that the drawings do not include the wing guns or the bomb shackles. In any event, the details shown are approximately sized, shaped, and located since they were added by reference to photographs.

For excellent pictures of this particular configuration, see http://crgis.ndc.nasa.gov/historic/643_Test_92_-_XF4F-2. Note that some represent a configuration that was for drag evaluation in the wind tunnel only, such as the removal of the cooling air scoop under the inboard port wing and the addition of a fairing over the main landing gear wheel well.

Another difference between the prototype and production Wildcats was the shape of the sides of the turtleback. The prototype's was definitely concave and the aft edge of the canopy curved to match.

This was changed to be mostly straight in production. Its likely that manufacturing cost trumped any aerodynamic benefit that the concave shape might provided. It certainly simplified the canopy construction and that of the life-raft access doors that were added for production (the original concept was that the raft be stored in a large tube behind the pilots headrest).

Another potential point of confusion with the XF4F-2 configuration is that after its initial Navy trials were substantially completed, it was crash landed following an engine failure.

Grumman rebuilt it with a more powerful engine, extended wings, and new vertical fin/rudder and horizontal tail. Although it retained the -2s Bureau Number, it was redesignated XF4F-3 in recognition of the engine change.

For more on the production F4Fs (and a few photographs of details applicable to the XF4F-2), I can't recommend Dana Bell's latest monograph too highly. It includes large photographs, many previously unpublished, on quality paper illustrating the differences and details among the various production aircraft, including the one-off seaplane, as well as illustrations of the major color schemes and markings.