Low-altitude wind shear is a major cause of air carrier accidents in the United States. Most of these accidents have been caused by either microbursts (small-scale, low-altitude, intense thunderstorm downdrafts that impact the surface and cause strong divergent outflows of wind) or by the gust front at the leading edge of expanding thunderstorm outflows. A microburst encounter is a serious problem for either landing or departing aircraft, because the aircraft is at low altitudes and is traveling at just over 25% above its stall speed [12].
The design of the control of an aircraft encountering wind shear after takeoff may be treated as a problem of stabilizing the climb rate about a desired value of the climb rate. The resulting controller uses only climb rate information.
The standard negative unity feedback system of Figure 8.24 has a loop transfer function
Note the negative gain in Gc(s)G(s). This system represents the control system for the climb rate. Sketch the Bode diagram and determine gain (in dB) when the phase is -180°.
