Guest author Steve Pomroy offers insights into one of flight training’s most challenging topics, the power curve.
When learning basic (and advanced!) aircraft handling, it helps to know and understand how much of a power reserve you have, and what that means to you as a pilot. It’s also useful to understand how the power required by the aircraft varies with airspeed and load factor. Building this understanding is where the power curve comes in. Learning the nuances of the power curve helps us develop an understanding of aircraft behavior and control response while we’re still on the ground. This ultimately makes our in-flight training much more efficient and effective.
The power curve is actually two curves plotted on the same axis: the Power-Required curve, and the Power-Available curve. Both represent power (required or available) as functions of airspeed.
Power required is defined as the power we need to be providing (from the engine) in order for the aircraft to maintain a constant airspeed and constant altitude. The power required is a function of the drag being produced by the airframe and our true airspeed.
Power available is the maximum power that we can produce with the engine. Although engines are normally rated for a fixed maximum brake-horsepower, the power available curve doesn’t show us constant power available—there is significant variation with airspeed. This is because the curve accounts for the efficiency of our propeller—which changes with airspeed—and as such represents thrust horsepower, not brake horsepower.
The difference between our power-available and power-required is our excess power, power margin, or power reserve. It’s possible for this value to be negative at high speeds and/or altitudes, but it is normally positive—indicating that we have access to more power than we need to maintain a constant airspeed and altitude. Our power reserve is important, since it’s an indication of how well we can accelerate and/or climb…