How does stall speed Vs change with weight?

• A. Vs decreases as weight increases.
• B. Vs remains constant with weight.
• C. Vs increases with weight.
• D. Vs only changes with air density.

Answer: (C)

Stall speed is the minimum airspeed needed to generate enough lift to balance the aircraft’s weight when the wing is at its maximum lift coefficient. From Lift = 0.5 ρ V^2 S Cl, and setting L = W at stall (with Cl = Cl_max), you get Vs = sqrt[(2W) / (ρ S Cl_max)]. This shows Vs rises as weight W increases, since more lift is required to support more weight and the lift coefficient cannot exceed Cl_max. The relationship is proportional to the square root of weight, so heavier airplanes stall at higher speeds.

The other options don’t fit because increasing weight does not decrease stall speed, nor does stall speed stay constant with weight. While air density affects stall speed (lower density raises Vs), weight is also a factor, so it isn’t correct to say stall speed changes only with air density.