What must wings and propellers do to generate the same amount of lift in lower air density?

To generate the same amount of lift in lower air density, wings and propellers must move through the air faster. Lift is generated according to the principles outlined in the lift equation, which states that lift is proportional to the air density, the square of the velocity of the air over the wings, and the wing area.

In conditions of lower air density, such as at higher altitudes, there is less air for the wings and propellers to interact with, which means that to maintain the same lift, the velocity must increase. Moving faster compensates for the reduced density of the air, allowing the aircraft to generate enough lift to remain airborne at the desired performance level.

Other options, such as moving slower, increasing engine power, or using larger wing surfaces, may alter lift to some extent, but increasing speed is the most effective way to directly counteract the effects of reduced air density on lift generation.