In level turns, the required additional thrust is proportional to the angle of bank.

In level turns, the required additional thrust is proportional to the angle of bank.

• A. True
• B. False
• C. Only at high speed
• D. Only at low speed

Answer: (A)

In a level turn, keeping the aircraft at the same altitude means the lift must increase as you bank. The vertical balance requires L cos(phi) = W, so as the bank angle phi grows, lift must rise roughly as L = W / cos(phi). That extra lift brings more drag—especially induced drag tied to lift—so you must increase thrust to overcome the added drag and maintain the same speed. Because the lift increase (and the associated drag rise) grows with the bank angle, the additional thrust needed is roughly proportional to how much you bank, at least for small to moderate angles. Remember, the turn is produced mainly by the horizontal component of lift, while thrust mainly counters drag to keep speed. At very large bank angles, the relationship becomes non-linear, but for typical turns the proportionality is a useful approximation.

In a level turn, keeping the aircraft at the same altitude means the lift must increase as you bank. The vertical balance requires L cos(phi) = W, so as the bank angle phi grows, lift must rise roughly as L = W / cos(phi). That extra lift brings more drag—especially induced drag tied to lift—so you must increase thrust to overcome the added drag and maintain the same speed. Because the lift increase (and the associated drag rise) grows with the bank angle, the additional thrust needed is roughly proportional to how much you bank, at least for small to moderate angles. Remember, the turn is produced mainly by the horizontal component of lift, while thrust mainly counters drag to keep speed. At very large bank angles, the relationship becomes non-linear, but for typical turns the proportionality is a useful approximation.