Aircraft Performance

Runway surface Airport name Runway slope and direction of slope Runway Figure 11-17. Chart Supplement U.S. (formerly Airport/Facility Directory) information. Tire pressure is a factor in dynamic hydroplaning. Using well before landing and be prepared for hydroplaning. Opt for the simple formula in Figure 11-18, a pilot can calculate a suitable runway most aligned with the wind. Mechanical the minimum speed, in knots, at which hydroplaning begins. braking may be ineffective, so aerodynamic braking should In plain language, the minimum hydroplaning speed is be used to its fullest advantage. determined by multiplying the square root of the main gear tire pressure in psi by nine. For example, if the main gear tire Takeoff Performance pressure is at 36 psi, the aircraft would begin hydroplaning The minimum takeoff distance is of primary interest in at 54 knots. the operation of any aircraft because it defines the runway requirements. The minimum takeoff distance is obtained by Landing at higher than recommended touchdown speeds taking off at some minimum safe speed that allows sufficient exposes the aircraft to a greater potential for hydroplaning. margin above stall and provides satisfactory control and And once hydroplaning starts, it can continue well below the initial ROC. Generally, the lift-off speed is some fixed minimum initial hydroplaning speed. percentage of the stall speed or minimum control speed for the aircraft in the takeoff configuration. As such, the lift-off is On wet runways, directional control can be maximized accomplished at some particular value of lift coefficient and by landing into the wind. Abrupt control inputs should be AOA. Depending on the aircraft characteristics, the lift-off avoided. When the runway is wet, anticipate braking problems speed is anywhere from 1.05 to 1.25 times the stall speed or minimum control speed. Minimum dynamic hydroplaning speed (rounded off) = To obtain minimum takeoff distance at the specific lift-off speed, the forces that act on the aircraft must provide the maximum acceleration during the takeoff roll. The various forces acting on the aircraft may or may not be under the control of the pilot, and various procedures may be necessary 9 x Tire pressure (in psi) in certain aircraft to maintain takeoff acceleration at the highest value. The powerplant thrust is the principal force to provide the acceleration and, for minimum takeoff distance, the output 36 = 6 thrust should be at a maximum. Lift and drag are produced 9 x 6 = 54 knots as soon as the aircraft has speed, and the values of lift and drag depend on the AOA and dynamic pressure. Figure 11-18. Tire pressure. 11-14