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flap mod
Bob, you weren't looking well enough. Remember Keven has an early 337, and A model
Quoting from the history page:
In an effort to increase the downwash over the horizontal tail for minimizing nose-down pitch with flap deflection and increasing elevator power for landings, a unique differential flap travel arrangement was installed in the early production airplanes. Those flap sections between the fuselage and booms would be deflected 40° while the outboard flaps would be deflected to a maximum of 25°. This worked very effectively. However, an ice-laden C-337 making an instrument approach at night in Cleveland, Ohio experienced a sudden nose-down pitching motion when the flaps were extended. This resulted in a crash into a home near the airport which was survived miraculously by all occupants of the airplane. It was apparent that an ice build-up on the leading edge of the horizontal stabilizer could not tolerate the increased localized downwash angle due to 40° of flaps. Thus the underside of the tail stalled, causing the loss of elevator control when the airplane pitched downward.
Since it was inappropriate to install a deicing boot on all C-337s, a decision was made to simply remove the differential flap feature. Cessna Service Letter 65-43 dated April 19, 1965 stated, "to improve the stall characteristics of the Model Super Skyrnaster, the inboard flap travel has been reduced from 40° to 25°. This change provides for a much smoother stall recovery under a gear down, flap down and partial power configuration." This was a mandatory change that involved the modification of the existing inboard flap bellcranks, replacement of the existing flap push-pull rod, and adjustment of the rods, bellcranks, and cables
Just an FYI
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