HIGH-SPEED FLIGHT- MACH BUFFET BOUNDARIES

Thus far, only the Mach buffet that results from excessive speed has been addressed. It must be remembered that Mach buffet is a function of the speed of the airflow over the wing—not necessarily the speed of the airplane. Any time that too great a lift demand is made on the wing, whether from too fast an airspeed or from too high an angle of attack near the MMO, the "high-speed" buffet will occur.

However, there are also occasions when the buffet can be experienced at much lower speeds known as the "low-speed Mach buffet." The most likely situation that could cause the low speed buffet would be when the airplane is flown at too slow a speed for its weight and altitude necessitating a high angle of attack. This very high angle of attack would have the effect of increasing airflow velocity over the upper surface of the wing to the point that all of the same effects of the shock waves and buffet would occur as in the high-speed buffet situation. The angle of attack of the wing has the greatest effect on inducing the Mach buffet at either the high-speed or low-speed boundaries for the airplane. The conditions that increase the angle of attack, hence the speed of the airflow over the wing and chances of Mach buffet are as follows:

- High Altitudes—The higher an airplane flies, the thinner the air and the greater the angle of attack required to produce the lift needed to maintain level flight.
- Heavy Weights—The heavier the airplane, the greater the lift required of the wing, and all other things being equal, the greater the angle of attack.
- "G" Loading—An increase in the "G" loading on the airplane has the same effect as increasing the weight of the airplane. Whether turns, rough control usage, or turbulence causes the increase in "G" forces, the effect of increasing the wing's angle of attack is the same.