THE HANDLING QUALITIES OF A LARGE JET TRANSPORT AIRCRAFT IN SEVERE WIND SHEAR AND TURBULENCE (RAIN)

An examination of the affects of a variable wind field and heavy rain on the flying qualities of a large wide-body multiengine jet transport was performed by developing a six-degree-of-freedom rigid-body simulation with a yaw damper control system. The simulation included nonlinear aerodynamics with aeroelastic, Mach, and load factor effects. The aircraft model was verified by comparison to previous simulations and flight test results.;Linear analysis was performed by using small perturbation theory. The linearized aerodynamic coefficients were determined by small motion analysis of the full model about a trimmed flight condition. These results indicate that at low frequencies, the aircraft will follow the wave motion and act as a kinematic point mass. For wave motions with frequencies about the phugoid mode, the transport is highly susceptible to external stimulus, such as wind shear, which acts to drive the altitude and altitude rate while only slightly affecting the other dynamic variables of the aircraft, including airspeed, angle-of-attack, pitch rate and angle, and load factor. As the frequency of the wave motion is increased above the short-period frequency, the gust response results in normal and lateral accelerations of the aircraft.;By running time histories of atmospheric wave and gust responses, the linear analysis was verified form small motions. Large motions revealed phugoid mode instabilities and divergences not indicated by linear analysis. Heavy rain was determined to significantly degrade the performance of the aircraft by excitating the phugoid mode, increasing the drag and the trim angle-of-attack, and decreasing the stall angle.;Turbulence was found to contribute to wind shear problems by increasing the time required for a pilot to recognize the shear. Moderate to severe turbulence can contribute to the wind shear problem by frequency summing. The wind shear and long wave length turbulence may add together to create an additive shear greater than the effects of either of the components.