Which statement about stall speeds is supported by the material?

Which statement about stall speeds is supported by the material?

• A. Stall speed is unaffected by weight changes.
• B. Stall speed is increased by weight increases.
• C. Stall speed decreases with increased weight.
• D. Stall speed is constant regardless of power setting.

Answer: (B)

Stall speed is the minimum airspeed needed to generate enough lift to support the airplane in level flight with the wing at its maximum lift coefficient. Since lift must equal weight in level flight, and lift increases with the square of velocity (L = 0.5 ρ V^2 S Cl), at the stall where Cl is at its maximum, the speed required is Vstall = sqrt[(2W) / (ρ S Clmax)]. This shows stall speed increases as weight W increases (and decreases with smaller weight, larger wing area, higher air density, or a higher Clmax). So heavier airplanes need to fly faster to avoid stalling. The other statements contradict this basic relationship: weight changes do affect stall speed, heavier weight does not reduce stall speed, and power setting does not set a fixed stall speed in level flight. Hence the statement that stall speed is increased by weight increases is the best choice.

Stall speed is the minimum airspeed needed to generate enough lift to support the airplane in level flight with the wing at its maximum lift coefficient. Since lift must equal weight in level flight, and lift increases with the square of velocity (L = 0.5 ρ V^2 S Cl), at the stall where Cl is at its maximum, the speed required is Vstall = sqrt[(2W) / (ρ S Clmax)]. This shows stall speed increases as weight W increases (and decreases with smaller weight, larger wing area, higher air density, or a higher Clmax). So heavier airplanes need to fly faster to avoid stalling. The other statements contradict this basic relationship: weight changes do affect stall speed, heavier weight does not reduce stall speed, and power setting does not set a fixed stall speed in level flight. Hence the statement that stall speed is increased by weight increases is the best choice.