Effect of forebody strake control technology on static directional stability

When static directional stability of an aircraft is unstable, the typical effectiveness of the vertical tail and rudder to the yawing moment falls off because the vertical tail gradually becomes enveloped in the wake of wing and fuselage. Meanwhile, the forebody remains in the undisturbed flow field, and therefore the static directional stability can be enhanced though addition of forebody strake at the forebody. From the results of a series of experiments on forebody strake, it was found that the angle of attack for static directional stability from stable to unstable was increased by about 8° when chord of the forebody strake being 3% of the length of the fuselage was used. Moreover, as the sideslip angle became smaller, the more angle of attack for static directional stability from stable to unstable rose. The positive effects of forebody strake on static directional stability is due to the vortices of the forebody strake, which could affect the front part of fuselage and thus result in the reduction of negative pressure value on leeward side of forebody. Hence, the unstable yawing moment of cross sections of forebody also decreases, and the static directional stability increases.