- by Niladri Roy
One of the more difficult concepts to grasp in learning to fly light propeller aircraft is that attitude controls airspeed while power controls rate of climb (or descent). The reason why this causes so much confusion among student pilots is that we are so used to the fact that the speed of an automobile increases when we step on the gas. The concept of maintaining the same airspeed but changing only the rate of descent (ROD) by varying power seems totally counterintuitive.
One way to convince ourselves that attitude controls airspeed is experimenting with various attitudes at constant power, and with various power settings at the same attitude. At constant power, it is possible to indefinitely hold, say, 85 knots by holding a particular attitude constant, and equally possible to indefinitely hold 75 knots at a slightly more nose-up attitude. Similarly, by scanning the attitude indicator, airspeed indicator and rate of climb indicator it is possible to confirm that for a particular attitude, different power settings only produce different ROD.
It is important to realize that there will be a period of adjustment after making an attitude or power change before the aircraft settles down. It is perfectly possible that an initial increase in power might result in an initial increase in airspeed (just as lowering the nose will initially result in increased ROD). However, the aircraft will soon settle down to the airspeed determined by its attitude and a ROD determined by its power setting.
Aircraft are designed to be inherently stable. The phenomena described above are no different from the phenomenon of phugoid oscillations observed when an aircraft flying straight and level is momentarily disturbed nose up or nose down and then the disturbing control input is removed. Phugoid oscillations describe the behavior of the aircraft of oscillating between alternate shallower and shallower nose up and nose down attitudes about a median flight path before settling down to equal the median flight path again.
