maximum lift flap setting

There is a concern about the use of flaps for takeoff from a backcountry strip among many pilots. Should flaps be used or not, and if used, how much flap should be used?

The majority of mountain pilots agree ... flaps should be used for takeoff.

How much flaps? The POH or Owner's Manual may give a recommendation, in which case you are obligated to use their wisdom. But, if there is no blessing listed, the following procedure will provide the maximum lift from any particular airfoil section.

Begin by making full control deflection, aileron control (wheel or stick) moved full left in this picture. This represents the maximum lift for the airfoil design. Remember, lift and drag are directly proportional. Increase lift and you increase drag. Here the manufacturer determined the maximum lift for the aileron deflection is obtained at the particular angle formed.

Next, match the flap deflection to the aileron deflection. This provides the maximum amount of lift for the airfoil (considering the effect of drag). This works for normally aspirated engines. With the Cessna-type airplanes, it is necessary to parallel the flap deflection to match the aileron deflection since they are not side-by-side. This will result, for example, in about 12-degrees flap extension in the Cessna 150-170 series airplanes.

If your airplane happens to be a turbo-super charged wild duck, or some such derivative, the flaps will probably be set at 50 percent because you are not as concerned with the balance of engine power and lift.