THE AERODYNAMIC DESIGN OF SAILPLANE TAIL ASSEMBLIES

Abstract

The aerodynamic design of a sailplane is dominated by its high aspect ratio unswept wing, which by itself is inherently unstable and uncontrollable in pitch and yaw. A tail assembly of minimum drag and weight must be provided which will permit the pilot to regulate the wing angles of attack and sideslip in normal flight, to overcome towline moments during launch, and to insure recovery from spins. Aerodynanic constraints upon stability and control are examined to determine minimum control surface size, and a simple method, based on biplane theory, is presented for estimation of the vortex drag penalty for tallplane trinming loads. It is concluded that small drag savings can be made with modest weight penalties by adopting longer tail moment arms and higher control surface aspect ratios.