A Proposed Solution to the Longitudinal Instabilities of the Ball-Bartoe Jetwing Through the Addition of a Thin, Fixed Slat to the Horizontal Tail

The Ball-Bartoe Jetwing research aircraft was developed as a STOL demonstrator vehicle employing single engine powered lift by means of upper surface blowing. Unfortunately, the aircraft has been plagued by longitudinal instabilities since the first flight. These instabilities have prevented an exploration of the full STOL potential of the aircraft since the problem becomes more severe during low airspeed flight.

A review of the historical data indicated that the instabilities may be attributed to the downwash flow that blanketed the horizontal tail in certain flight conditions. As the blown flaps were deflected to increase lift at low airspeeds, the resulting downwash inhibited the tail effectiveness and eventually caused the tail to stall. The small planform area and relatively thin NACA 0008 airfoil of the horizontal tail have been identified as contributing factors in the instability problem.

An evaluation of the current applications of high lift devices determined that the thin, fixed slat was the most appropriate solution for the insufficiencies of the horizontal tail. The design of the slat was optimized to simplify fabrication and installation. The projected results indicate that the slat should provide some measure of stall resistance and increase the tail effectiveness.