TABLE OF CONTENTS In the theory of aircraft flight mechanics, it is well known that, for a conventional aircraft with wing and horizontal tail, the most significant effect of the wing on the tail is the downward deflection of the flow due to wing circulation, which can be aerodynamically modeled as a downwash angle ?.7 10 Such effects are present even under the assumption of quasi-steady flow and need to be properly accounted for. As the downwash is caused by circulation, it changes anytime the circulation changes; for example 1) changes in the wing lift due to changes in the angle of attack, 2) deflection of direct-lift-control flaps which are a modified part of the landing flaps on the wings, and 3) operation of wing-mounted speed brakes in flight. The modified flow at the wing, however, reaches the empennage after a time interval ? = r H/ V, where V is the airspeed and r H the tail length. Thus, the effective angle of attack at the tail is changed only after a time delay of ? s. The same transit time effect is also applicable to cases considering vertical wind based on Taylor s hypothesis of treating turbulence as a frozen pattern. Similarly, slipstream transit time effects result from dynamic thrust variations from wingmounted engines, particularly for propeller aircraft. In this section we investigate the estimation of the transit time lag effects originating from the aforementioned different cases.
