Density Altitude: Why Hot Days Make Your Airplane Feel Weak

Every pilot eventually has the same experience: the same airplane, the same runway, the same weight, and a takeoff roll that feels noticeably longer than it did in the cool of the morning. Nothing is wrong with the airplane. The air changed, and the air is what everything on the airplane, from the wings to the engine to the propeller, is working with.

That change has a name, and it's one of the most tested and most misunderstood ideas in private pilot training: density altitude.