IHS ESDU Contribution of tailplane-mounted twin fins to sideforce, yawing moment and rolling moment derivatives due to sideslip at subsonic speeds. 92007

ESDU 92007 gives a semi-empirical method applying to fins of small sweep (up to 20 degrees) for small sideslip angles up to Mach 0.7. From an analysis of limited experimental data extracted from the literature, a fin effective aspect ratio was determined as a function of fin vertical height on the tailplane that allows for the endplate effect of the tailplane. The lift-curve slope for the effective aspect ratio is then corrected for the effect of fuselage sidewash by a factor that depends on fuselage height/width at the tail and the exposed tailplane span. To determine the moment derivatives, the sideforce is assumed to be divided according to the areas above and below the tailplane, and to act at a point 0.424 of the height of each portion from the tailplane (assuming half elliptical loading on each portion). For the rolling derivative an additional correction is made to allow for the asymmetric loading on the tailplane induced by the fins in sideslip. Sketches compare experimental and predicted results and show the sideforce, rolling and yawing derivatives to be predicted within 0.03, 0.005 and 0.012 respectively. The ranges of geometry considered are tabulated, and a worked example illustrates the use of the data.