What effect does increasing density altitude have on aircraft performance?

• A. Density altitude higher increases engine power
• B. Higher density altitude reduces engine power, lift, and aerodynamic efficiency
• C. Density altitude has no effect
• D. Density altitude higher increases lift

Answer: (B)

As density altitude increases, the air becomes thinner. That thinning air means the engine has fewer oxygen molecules to burn, so the available power from the engine drops. The propeller also moves less air, so thrust is reduced. Lift depends on air density through the equation L ∝ ρV²S; with lower air density, the wing produces less lift at the same speed and angle of attack. Aerodynamic efficiency falls as the thinner air provides less reaction for both the wing and the propulsion system. Put together, higher density altitude leads to less engine power, less lift, and overall reduced aerodynamic efficiency, which is why performance like takeoff distance, rate of climb, and climb speed suffer on hot days or at high elevations.