A National Advisory Committee for Aeronautics specialist proposed cutting holes in the XBT-1's flaps to divide large vortices into smaller ones. The team had considered the idea but rejected it as too radical. Heinemann also feared that the holes would increase stalling speed beyond the 60-knot requirement dictated by carrier landings. Mechanics first cut three-inch holes in the inner third of the flaps and added more after successful tests. Once the perforations extended along the full flap, the flutter disappeared and the aircraft could descend vertically in stable flight at 250 knots. Acceptance still required persuading the Navy's bureau that the unusual perforated surfaces were satisfactory, which the project officer handled.
Notable Point · 2:23:03-2:24:52
NACA's perforated-flap solution restores a stable vertical dive
Three-inch holes broke up the vortices behind the dive brakes, curing flutter while raising a separate concern about carrier landing speed.