Aerodynamics of Flight

During the takeoff phase of flight, ground effect produces establishing a positive rate of climb and only after achieving some important relationships. An aircraft leaving ground a safe altitude. effect after takeoff encounters just the reverse of an aircraft entering ground effect during landing. The aircraft leaving If, during the landing phase of flight, the aircraft is brought ground effect will: into ground effect with a constant AOA, the aircraft experiences an increase in C and a reduction in the thrust • Require an increase in AOA to maintain the same C L L required, and a “floating” effect may occur. Because of the • Experience an increase in induced drag and thrust reduced drag and lack of power-off deceleration in ground required effect, any excess speed at the point of flare may incur a • Experience a decrease in stability and a nose-up considerable “float” distance. As the aircraft nears the point change in moment of touchdown, ground effect is most realized at altitudes less than the wingspan. During the final phases of the approach • Experience a reduction in static source pressure and as the aircraft nears the ground, a reduction of power is increase in indicated airspeed necessary to offset the increase in lift caused from ground effect otherwise the aircraft will have a tendency to climb Ground effect must be considered during takeoffs and landings. above the desired glidepath (GP). For example, if a pilot fails to understand the relationship between the aircraft and ground effect during takeoff, a Axes of an Aircraft hazardous situation is possible because the recommended takeoff speed may not be achieved. Due to the reduced drag The axes of an aircraft are three imaginary lines that pass in ground effect, the aircraft may seem capable of takeoff well through an aircraft’s CG. The axes can be considered as below the recommended speed. As the aircraft rises out of imaginary axles around which the aircraft turns. The three ground effect with a deficiency of speed, the greater induced axes pass through the CG at 90° angles to each other. The drag may result in marginal initial climb performance. In axis passes through the CG and parallel to a line from nose extreme conditions, such as high gross weight, high density to tail is the longitudinal axis, the axis that passes parallel altitude, and high temperature, a deficiency of airspeed during to a line from wingtip to wingtip is the lateral axis, and the takeoff may permit the aircraft to become airborne but be axis that passes through the CG at right angles to the other incapable of sustaining flight out of ground effect. In this case, two axes is the vertical axis. Whenever an aircraft changes the aircraft may become airborne initially with a deficiency its flight attitude or position in flight, it rotates about one or of speed and then settle back to the runway. more of the three axes. [Figure 5-18] A pilot should not attempt to force an aircraft to become The aircraft’s motion about its longitudinal axis resembles airborne with a deficiency of speed. The manufacturer’s the roll of a ship from side to side. In fact, the names recommended takeoff speed is necessary to provide adequate used to describe the motion about an aircraft’s three axes initial climb performance. It is also important that a definite were originally nautical terms. They have been adapted to climb be established before a pilot retracts the landing gear aeronautical terminology due to the similarity of motion of or flaps. Never retract the landing gear or flaps prior to aircraft and seagoing ships. The motion about the aircraft’s longitudinal axis is “roll,” the motion about its lateral axis is Pitching Rolling Yawing Lateral axis Longitudinal axis Vertical axis Figure 5-18. Axes of an airplane. 5-12