How to Calculate Stall Speed

Stall speed is a very important value for a pilot to know. It is the speed where the airflow over the wings can no longer generate the lift necessary to keep the airplane aloft. Many crashes that occur just after takeoff or just before landing are either directly or indirectly caused by stall, as these are the times when the airplane flies the slowest. Stall speed is an air-speed value, not a ground-speed value.

Things You'll Need

• Standard atmosphere chart
• Lift chart of your aircraft

Instructions

1. Obtain the weight of the aircraft and double it. This is the numerator for the equation to calculate stall speed. The value for the weight should be the in-flight weight, or the weight of the aircraft with pilot, passengers and luggage.

2. Look up the standard atmosphere value for density at the altitude you are calculating the stall speed. Find the maximum value for the coefficient of lift for your aircraft's wing. Finally, look up the wing planform area. Multiply these three values together to obtain the denominator of the stall speed equation.

3. Divide the numerator from Step 1 by the denominator from Step 2 and calculate the square root of the result. This is the stall speed.

Tips & Warnings

• If you would rather see the equation written out, it is: V = sqrt[ 2W / (rho*S*Cl,max)]

• Make sure your units are consistent. For example, don't use "kg/m^3" if you are measuring weight in pounds. Also, use "lb/ft^3" for density in English units, as most weight measures assume that "feet" is being used instead of "inches."

References

• Fundamentals of Aerodynamics, John D. Anderson, Jr., 1991