FAA Flight Instructor Airplane (FIA)Performance, Weight and BalanceHard
An airplane has a calibrated stall speed of 50 knots at a gross weight of 2,000 lb. If the airplane is loaded to 2,420 lb, what is the approximate new stall speed?
- A53 knots
- B55 knots
- C52 knots
- D58 knots
Show answer & explanationAnswer & explanation
Correct answer: B. 55 knots
Stall speed varies with the square root of the weight ratio: New Vs = Old Vs × √(New Weight ÷ Old Weight) = 50 × √(2,420 ÷ 2,000) = 50 × √1.21 = 50 × 1.1 = 55 knots.
Why the other options are wrong
- A. Does not match the square root of the weight ratio.
- C. Too low; underestimates the weight-to-stall-speed relationship.
- D. Too high; overestimates the effect of the weight increase.
Stall Speed vs. Weight
Stall speed increases with the square root of the ratio of new weight to old weight, since lift required to sustain flight increases with weight.
- Formula: New Vs = Old Vs × √(New Weight / Old Weight)
- A 21% weight increase raises stall speed by about 10%
- Heavier airplanes always stall at a higher indicated airspeed at 1G
Memory trick: Square root the weight ratio to find the new stall gate