Which surface is designed to obtain lift, or negative lift, as it moves through the air?

Which surface is designed to obtain lift, or negative lift, as it moves through the air?

• A. Airfoil
• B. Airworthiness Directive
• C. Altimeter
• D. Advancing Blade

Answer: (A)

An airfoil is the surface designed to create lift (or downward force, i.e., negative lift) as it moves through air. Its shape—typically a curved upper surface and a flatter lower surface—causes air to flow faster over the top than underneath. This speeds up the air and lowers pressure above the surface while the pressure underneath remains higher, producing a net force that acts perpendicular to the oncoming air flow. In a helicopter, rotor blades are built with airfoil cross-sections, and by changing the angle of attack and rotational speed, they generate the lift (or downward force when configured for negative lift) that turns the rotor into thrust. The other options aren’t surfaces designed to produce lift: a regulatory directive, an instrument that measures altitude, and a term describing the forward-moving portion of a rotor blade.

An airfoil is the surface designed to create lift (or downward force, i.e., negative lift) as it moves through air. Its shape—typically a curved upper surface and a flatter lower surface—causes air to flow faster over the top than underneath. This speeds up the air and lowers pressure above the surface while the pressure underneath remains higher, producing a net force that acts perpendicular to the oncoming air flow. In a helicopter, rotor blades are built with airfoil cross-sections, and by changing the angle of attack and rotational speed, they generate the lift (or downward force when configured for negative lift) that turns the rotor into thrust. The other options aren’t surfaces designed to produce lift: a regulatory directive, an instrument that measures altitude, and a term describing the forward-moving portion of a rotor blade.