Which law explains the equal and opposite reaction to the engine torque on the airframe in a propeller-driven airplane?

• A. Newton's Third Law
• B. Bernoulli's Principle
• C. Pascal's Law
• D. Lenz's Law

Answer: (A)

Newton's Third Law explains the equal and opposite reaction to the engine torque on the airframe. When the engine drives the propeller, it applies a torque to spin the propeller; the propeller, in turn, applies an equal and opposite torque on the engine and airframe. That reaction torque tends to rotate the aircraft in the opposite sense to the propeller’s rotation, producing a tendency to roll about the longitudinal axis as power is applied. Other concepts don’t describe this mechanical reaction: Bernoulli's principle relates to lift from pressure differences, Pascal's law concerns pressure transmission in fluids, and Lenz's law deals with the direction of induced currents in magnetic fields.