Accident Overview
On September 5, 2017, about 1430 Pacific daylight time, an experimental Cobalt Co50 Valkyrie airplane, registration N523CA, sustained substantial damage during a hard landing at Castle Airport in Atwater, California. The airline transport pilot was not injured. The aircraft, serial number PX-04, was manufactured in October 2016 and registered under an Experimental Research and Development airworthiness certificate. Operated by Cobalt Aircraft Industries, Inc. as a Title 14 Code of Federal Regulations Part 91 test flight, the local flight originated from Atwater about 1405. Visual meteorological conditions prevailed, and no flight plan was filed.
Flight Details
The accident flight was the pilot's first in a Cobalt aircraft. The purpose was to evaluate handling qualities at various configurations per the test card. Before departure, the pilot conducted two test runs down the runway, briefly lifting off to check rotation performance. On both attempts, full aft back pressure on the control stick did not rotate the airplane. The pilot determined the center of gravity was too far aft, prompting ground crew to add 2° to the adjustable ground trim (total 10°). The pilot then configured for departure from runway 31, planning a rotation speed of 75 knots.
In-Flight Control Issues
After rotation at about 50 feet above ground level, the pilot experienced extreme difficulty controlling the airplane. As airspeed increased, some controllability returned, and he climbed to about 1,400 feet. The ailerons were ineffective, but rudder provided directional control. Pitch stability was sporadic with intermittent pitch up and down movements. After about 20 minutes of manipulating controls and practicing climbs and descents using trim, the pilot stabilized the airplane around 90 knots. He planned to land at increased airspeed using steady thrust and rudder for directional control.
Landing and Damage
During landing, about 10 feet above the runway, the airplane experienced a loss of lift and landed hard. The right landing-gear leg separated, and the airplane made a 180° turn. The right-wing spar sustained damage.
Company Findings
A Cobalt representative stated that review of video and onboard recorders revealed that after a faster-than-expected rotation speed between 80-85 knots, the airplane had no roll control. For the test flight, the aircraft had increased weight and a changed winglet position, which contributed to a loss of aileron effectiveness.