by Tommy H. Thomason

Monday, September 1, 2014

F-111B Envelope Expansion Wing

One of the remaining mysteries to me about the F-111B program was the presence of the four-segment flap wing (i.e. the F-111A wing) on F-111Bs #1 and 4. I didn't even notice it in the picture of #1 on the cover of my F-111B monograph until someone eventually pointed it out.

Note that the wings have the ferry tips so that the span is that of the F-111B.

This is the F-111B early five-segment flap wing.

Tim Lent pointed out that F-111B #4 also had a four-segment flap wing at one point.

(You can take my word for it - a lightened version of a high-resolution scan of a pretty good photograph shows that the fifth flap segment is not present.)

The reason for Tim's search for evidence of this wing on #4 was the desire to identify the third F-111B in this photo, the one with its back to the camera.
 I was pretty sure that it was #4 because it appeared to have the rotating glove flap on the fixed portion of the wing and did not have the pod on the fin tip. However, Tim noted that it had a four-segment flap with the ferry tip.

My speculation is that this set of wings was specifically instrumented for high-speed envelope expansion and the use of the ferry tips allowed it to be used by both General Dynamics on an F-111A and Grumman on an F-111B. In fact, #4 was used for flutter/envelope expansion in late 1966 and early 1967. After its crash, #1 was used for flutter/envelope expansion at Edwards in the fall of 1967, which is likely when the monograph cover picture was taken.

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