AFH 6-10

The most common errors made while performing crosswind takeoffs include the following: ⦁ Failure to review AFM/POH performance and charts prior to takeoff. ⦁ Failure to adequately clear the area prior to taxiing onto the active runway. ⦁ Using less than full aileron pressure into the wind initially on the takeoff roll. ⦁ Mechanical use of aileron control rather than judging lateral position of airplane on runway from visual clues and applying sufficient aileron to keep airplane centered laterally on runway. ⦁ Side-skipping due to improper aileron application. ⦁ Inadequate rudder control to maintain airplane parallel to centerline and pointed straight ahead in alignment with visual references. ⦁ Excessive aileron input in the latter stage of the takeoff roll resulting in a steep bank into the wind at lift-off. ⦁ Inadequate drift correction after lift-off. Ground Effect on Takeoff Ground effect is a condition of improved performance encountered when the airplane is operating very close to the ground. Ground effect can be detected and normally occurs up to an altitude equal to one wingspan above the surface. [Figure 6-7] Ground effect is most significant when the airplane maintains a constant attitude at low airspeed at low altitude (for example, during takeoff when the airplane lifts off and accelerates to climb speed, and during the landing flare before touchdown). Figure 6-7. Takeoff in ground effect area. When the wing is under the influence of ground effect, there is a reduction in upwash, downwash, and wingtip vortices. As a result of the reduced wingtip vortices, induced drag is reduced. When the wing is at a height equal to 1/4 the span, the reduction in induced drag is about 25 percent. When the wing is at a height equal to 1/10 the span, the reduction in induced drag is about 50 percent. At high speeds where parasite drag dominates, induced drag is a small part of the total drag. Consequently, ground effect is a greater concern during takeoff and landing. At takeoff, the takeoff roll, lift-off, and the beginning of the initial climb are accomplished within the ground effect area. The ground effect causes local increases in static pressure, which cause the airspeed indicator and altimeter to indicate slightly lower values than they should and usually cause the vertical speed indicator to indicate a descent. As the airplane lifts off and climbs out of the ground effect area, the following occurs: ⦁ The airplane requires an increase in AOA to maintain lift coefficient. ⦁ The airplane experiences an increase in induced drag and thrust required. ⦁ The airplane experiences a pitch-up tendency and requires less elevator travel because of an increase in downwash at the horizontal tail. ⦁ The airplane experiences a reduction in static source pressure and a corresponding increase in indicated airspeed. VX is the speed at which the airplane achieves the greatest gain in altitude for a given distance over the ground. It is usually slightly less than VY, which is the greatest gain in altitude per unit of time. The specific speeds to be used for a given airplane are stated in the FAA-approved AFM/POH. The pilot should be aware that, in some airplanes, a deviation of 5 knots from the recommended speed may result in a significant reduction in climb performance; therefore, the pilot should maintain precise control of the airspeed to ensure the maneuver is executed safely and successfully.