June 8, 1983

We have had two known cases of wing distortion in flight. In each case, the wing tip was damaged and partially repaired prior to the inflight distortion which ultimately caused emergency landings. Although neither pilot was injured in the emergency landings, both planes did suffer significant damage and therefore, we believe it is important to inform you of the circumstances leading to the distortions and to recommend a method of avoiding such a problem with your aircraft.

In the first incident, an FP-101 builder sustained a hard landing in his craft during which he dragged a wing tip when the plane ground looped. The resulting side loads from the ground loop

collasped the landing gear. After replacing the gear and visually inspecting the wing, which appeared to have suffered only minor damage, he returned to the air. During a subsequent flight, approximately 2 flight hours after the accident in which the wing tip was dragged, the main spar twisted about 1/2” near the aileron control horn causing a partial loss of aileron control, and an emergency landing which substantially damaged his FP-101.

The second incident occurred with the factory Clip Wing FP-101. This aircraft had previously sustained severe damage to the right win; after striking a tree at the Sun’n Fun Fly-In which resulted in crushed wing ribs, bent attach fittings, bent struts, and a broken rear spar. After replacing the ribs, splicing the rear spar, repairing the broken geodetic and straightening the attach fittings, the wing appeared visually to be sound. Subsequent flights of the repaired aircraft showed far more inflight vibration than we had ever experienced in the FP-101’s. We were unable to immediately pinpoint the problem because when we repaired the aircraft we also charged the span of the horizontal stabilizer and the pilot believed the vibration to be coming from the tail section indicating a problem with the new stabilizer rather than the wing. Finally the wind flexing, which was the actual cause of the vibration became severe enough that the pilot made a forced landing in an extremely soft, recently plowed field which caused the airplane to nose over. The pilot noted that prior to the forced landing he could see the wing moving back and forth and the covering was flexing quite significantly. Evidently the spar attach block had been fractured in the earilier accident but the fracture was not visually apparent. However, during flight loads the fractured block allowed, the wing to flex