Thrust is determined by which factor?

• A. Shape and age of the propeller blade
• B. Engine horsepower only
• C. Blade color
• D. Air temperature only

Answer: (A)

Thrust from a propeller is produced by how the blades move air backward. The blade shape (its design, camber, twist, and chord) and the blade’s condition determine how effectively that air is accelerated and how much lift the blade generates as it spins. A well-designed blade converts engine power into forward thrust efficiently, while aging or wear—nicks, erosion, or changes in the blade’s profile—degrades that efficiency and reduces thrust even if the engine is delivering the same power. The other options don’t directly set thrust: color has no aerodynamic effect, and while temperature can influence air density, it doesn’t determine thrust as directly as the blade’s geometry and condition. Engine power matters, but the actual thrust for a given power depends mainly on the blade shape and its current condition.