Control Failure Brings Down Sopwith

Location: Van Alstyne, TX Accident Number: CEN20LA259
Date & Time: 07/03/2020, 1000 CDT Registration: N5539
Aircraft: LANKENAU Sopwith 9400 Injuries: 1 Minor, 1 None
Flight Conducted Under: Part 91: General Aviation – Flight Test

On July 3, 2020, a Sopwith 9400 experimental airplane, N5539, was destroyed when it was involved in an accident near Van Alstyne, Texas. The pilot received minor injuries and the passenger was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 test flight.

According to the pilot this was the 23rd test flight of the airplane, which was built following original design drawings. The flight was scheduled to be a short flight to confirm flying and landing wire deflections, flight control synchronization while under air loading, and to perform an aerial reconnoiter for potential obstacles at the approach end of the runway. A second crewmember was also on-board, responsible for monitoring cable deflections and vibrations, control surface positions during flight (ie; drooping aileron, elevator or etc.), and communicating with the ground crew via cell phone text.

The airplane performed normally through the first overflight of the airfield and a series of turns. As the pilot conducted a left turn he moved the control stick to the right to bring the wings level. There was no noticeable resistance and the control stick continued until it had reached its maximum travel. The pilot recognized this as a failure in the lower aileron circuit.

Not knowing the exact location or cause of the failure, the pilot maintained the control stick at it’s far right extent and waited for the effects of the dihedral to slowly bring the wings back to level, all the while maintaining marginal control with back pressure on the elevator and right rudder to keep the nose from falling off. The airplane eventually settled wings level with a slight nose down attitude on a northeasterly heading about 350′ AGL and 75 IAS.

The pilot elected to perform an emergency landing in the cornfield in front of the airplane. The pilot cut power to the engine during approach, and after cutting the engine power he was unable to clear trees during the emergency descent. The airplane brushed a tree and descended into the ground nose down and in a turn.

The pilot examined the wreckage and determined the cause of the failure. There is a rocking tube that connects the front of the front cockpit to the rear control stick. The aileron cables connect to a horn which is affixed to this tube. The tube had worked its’ way rearward about 1″, which was sufficient for the front part of the tube to come loose from its’ socket. The pilot found a flaw in the design of the original dual control configuration that allowed the tube to move rearward and cause the separateion.