NACA-RM-L58C11

Abstract

INTRODUCTION <br>One of the problems frequently encountered with supersonic aircraft is that of the lox-directional-stability level that occurs with increasing Mach number a d increasing angle of attack. This problem stems from two main sources; one source is the highly unstsble wing-body combinations that result from the use of high-fineness-ratio bodies and far rearward centers of gravity, and the other source is the decrease in vertical-tail effectiveness that results from a decrease in tail lift-curve slope with increasing Mach number and from the effects of forebody and wing vorticity with increasing angle of attack. <br>A logical way to attack the problem of low directional stability Would be to seek means whereby the level of instability of the wing-body combination night be reduced. In this way the tail size and load might be reduced. Another course to pursue would be to seek means of increasing the tail effectiveness other than by merely increasing the size of the vertical tail. <br>Recent tests at subsonic speeds have indicated that significant improvement in the stability level for wing-body continuations might be obtained at high angles of attack through the use of forebody fins or strakes. These strakes act in such a way as to provide a directionally stabilizing movement increment over the forebody and have been found to be useful as an aid to spin recovery (refs. 1 and 2) and as a means of increasing directional sta3ility et high angles of attack (ref. 3) . The strakes might also be expected to affect the forebody vorticity and thereby have an effect on the tail contribution. <br>In order to determine if the use of strakes night be advantageous at supersonic speeds, an investigation has been conducted at a Mach number of 2.01 in the Langley 4- by 4-foot supersonic pressure turrnel of various strake arrangements. The model used in the investigation was a tailless configuration and had a 60&#176; delta wing. Tests were made with both a single body-mounted vertical tail and twin wing-mounted tails in order to dtermine the effects of strakes on vertical-tail effectiveness. <br>The investigation included the effects or' strake length and radial position, the relative effects of windward and leeward strakes, and the effects of strake thickness and vertical location on two cylindrical body configurations. Subsequent to the completion of the force tests a forebody pressure model was tested to provide an insight into the charges in pressure on the forebody caused by the presence of the strakes. The results of Torte tests and an example of the results of pressure tests are presented.