trampbike said:
At first I thought about starting a new thread for my next question, but I'm not too sure it deserved it, so I'll ask it here.
An aileron roll is a pretty basic maneuver. A 360 degrees turn around the longitudinal axis of an airplane. When done properly, the entry and exit altitude should be the same (raise the nose high enough considering your roll rate and entry speed). I do not doubt that any military pilot can do it easily, yet on EVERY single video I saw of a military airplane performing an aileron roll (except for airshows), it exits at a lower altitude. Why is that?
Asymmetrical drag coupling of the ailerons inducing a yaw rate, exacerbated by offset of the aircraft flight path from the extended longitudinal axis.
If you just use ailerons without blended rudder and elevator, the nose will drop by the time the roll is completed. If you are rolling right, for example, the left (upgoing) wing's aileron will increase the local angle of attack due to increased effective camber as the trailing edge of the aileron moves downwards, which causes greater induced and form drag over portion of the wing with the aileron. There is at the same time an opposite effect on the right (downgoing) wing (reduced AOA in the region of the upturned aileron). The overall effect is yaw to the left, so to keep the nose "bullet straight" you would feed in a slight amount of right rudder....until, that is, the vertical axis of the airplane departed from the vertical enough that balanced flight forces between lift and gravity would reduce due to a reduced vertical component of (perpendicular) lift because of the bank angle, which would require compensation with aft stick to raise the elevator to increase perpendicular lift to keep the vertical component balanced with gravity, which requires left rudder to compensate against the rightwards lateral component of the aircraft's banked wings. Uncorrected, the nose will drop, resulting in unintended descent. The plane hasn't even gotten to 90 degrees of its 360 degree roll, and the pilot has been blending all the controls to keep the center of mass going straight forward along a level trajectory. Keep rolling, adjusting for the varying yawing coupled forced with roll and pitch component through 270 more degrees, and if you've done everything right, you might be reasonably close to the original, pre-roll flight path. The less symmetrical an aircraft is along its lateral and vertical axes, the greater the unintended coupling forces will be, and the greater coordinated compensation required to be input by the pilot during the conduct of the roll.
Purpose-built aerobatic aircraft, like the Pitts Special, Su-26, CAP 21, Christen Eagle, Xtra 300, etc... have relative aerodynamic symmetry (drag-wise) about their axes, so there is less unintended coupling between the controls than with other aircraft. Even these aircraft will barrel slightly, but are relatively small, so the airshow crowd doesn't really pick up the slight gyrations of the aircraft's longitudinal axis during the roll (or other similar manoeuvres, for that matter).
The closest I've seen to a perfect roll other than an aerobatic aircraft is the 'Widow Maker', a.k.a. F-104 Starfighter...probably helped by the fact that at 90 degrees, the F-104's vertical fin is damn near as big as the two wings.
Anyway, just because something appears simple or "basic" externally, doesn't mean it isn't complicated inside the cockpit.
Regards
G2G
