Some Trim Drag Considerations for Maneuvering Aircraft

The results of a preliminary analytical and experimental study of trim drag characteristics at maneuvering lift coefficients have been summarized. The study included aft-tail configurations at subsonic and supersonic speeds and canard configurations at subsonic speeds. It is shown that the tail load required to minimize trim drag is highly dependent on the wingbody drag-due-to-lift characteristics with examples presented for both the full and zero leading-edge suction cases. For the high drag case (corresponding to zero leading-edge suction), which tends to be typical at high maneuvering lift coefficients and high speeds, rather large uploads on the tail are required to reduce the trim drag problem. The analytical predictions of trim drag characteristics compare well with the experiment for the aft-tail configuration. At supersonic speeds, reductions in down tail load required to trim, obtained by increasing tail volume and thereby allowing a favorable rebalancing of the aircraft, result in relatively large reductions in trim drag for aft-tail configurations. At subsonic speeds, the experimental studies for the canard configuration exhibit considerably higher trim drag than the analytical prediction as a result of canard stall.