Adverse Yaw
Adverse yaw is defined as the tendency of the aircraft to yaw or roll away from the intended turn. In the F-100, this condition is present in the sub-sonic speed range, and is especially noticeable in high-angle-of attack maneuvering. If proper technique is not employed to counteract adverse yaw in high-angle-of-attack maneuvers, aircraft maneuverability is seriously compromised. In fighter-versus-fighter combat, since maneuverability is a key to success, inability to handle adverse yaw will produce disastrous results. We can see this upon examining the defensive turn. In defending against an AIM-9B attack, the speed and G which we were pulling produce a low angle of attack. Defending against a follow-up gun attack, however, produced a high angle of attack. If conventional technique is attempted when max performance is necessary, the result will not be maximum performance. To preclude performance degradation, the pilot must develop two entirely different techniques to control the F-100 under low-angle-of-attack and high-angle-of-attack conditions.
In low-angle-of-attack maneuvers, conventional technique will be employed. That is, ailerons will be primary control for directional change, in either turn or a roll, and rudder will be secondary. It will be used to counter the small amount of adverse yaw to keep the turn or roll coordinated. Back pressure will be employed to control the rate of turn or the intensity of the roll.
In high-angle-of-attack maneuvers, the following techniques will be employed: Rudder will be used to control directional change. Ailerons will be moved to the neutral position and back pressure will be employed to control the rate of turn or intensity of the roll. In a high-angle-of-attack situation, if the pilot employs aileron as primary for directional change, he will induce a roll-off in the direction away from the intended turn. The more aileron he applies, the faster the roll-away. This is true because, in a turn, the induced drag on the inboard wing is less than that on the outboard wing. If aileron is employed, the inboard aileron is deflected up and the outboard aileron is deflected down. This condition imposes an additional increment of drag upon the outboard wing. As a result, the aircraft yaws toward the high-drag area, or in a direction away from the intended turn. In low-angle-of-attack maneuvers, this yaw can be corrected by applying rudder until the ball is centered. In a high-angle-of-attack maneuver with the F-100, this technique is not satisfactory. As the angle of attack increases, the amount of adverse yaw generated by the induced drag and deflected ailerons increases. The yaw increase causes the outboard wing to meet the relative wind at a velocity less than the inboard wing. The decrease in velocity, plus the downward deflection of the outboard aileron, causes the aileron to stall out, consequently, there will be less lift over the outboard wing. The aircraft will roll in the direction of the yaw. If additional aileron is applied to correct this roll-off, the rate of roll will increase and the adverse yaw and stall conditions will be magnified. If rudder is employed – along with aileron – the adverse yaw generated may be cancelled by the favorable yaw induce by the rudder. However, as the angle of attack builds up, the adverse yaw generated by induced drag and deflected aileron become greater than the favorable yaw generated by the rudder. Thus, a roll-off will still occur, however, at a slightly higher angle of attack. On the other hand, if we neutralize aileron and employ rudder as primary for directional control, we can generate a maximum performance turn without a subsequent roll-off.
To determine whether we should use conventional techniques or the rudder technique, we need only recognize the “feel” of the aircraft. The moment the outboard wing appears to be heavy, the pilot should neutralize aileron and apply rudder to control the turn or roll. Full rudder should not be employed, otherwise the pilot will experience a loss of directional control. Instead, apply rudder smoothly and as needed to maintain directional control. If this is accomplished, the ball will be centered and a max-performance maneuver is possible. Do not arbitrarily use full rudder and opposite aileron to achieve a max-performance turn. If this is accomplished, a large amount of favorable yaw will be generated and a snap-roll or spin will probably occur.