Aileron augmented directional control and braking

Papadopoulos, Christopher A. (2000) Aileron augmented directional control and braking. (PhD thesis), Kingston University, .


Current landing and braking systems are associated with the approach, flare and rollout. Automatic and independent brake systems prevent skidding but do not restore the aircraft to the original trajectory. None use the normal aerodynamic surfaces to augment braking effectiveness to steer the aircraft during sudden changes in runway surface conditions. Many aircraft accidents occur during landing. The task of bringing the aircraft to a safe taxing speed from touchdown in variable weather conditions is the most difficult manoeuvre that a pilot has to make. There is no opportunity to recover or reattempt the manoeuvre. It is the only phase of the aircraft operation that has not been effectively improved through the use of autopilot control systems. Improving this regime of operation through the use of formally redundant aerodynamic control surfaces is the subject of this thesis. This thesis describes the development and testing of a controller, auto-pilot and ABS combination that uses ailerons to control the normal loading differential between the main gear of a B747-100 for the purpose of increasing the directional control so that is it possible to either minimising the centre line off-set or to maintain heading of a landing aircraft. The aileron based differential normal loading controller uses the brake line pressure differential as an input variable to control the ailerons during touchdown. During the maximum braking case, the brake line pressure is proportional to the difference in runway friction coefficient, normal loading, and brake disk stack friction coefficient. Landing aircraft are extremely non-linear in function. To overcome this, a model and controller that generates the appropriate non-linear mathematical description of the aircraft during the landing phase and generates an effective controller that effectively generates an increase in normal gear force on touch down of 100% and thereby allowing the aircraft to be controlled in direction during hazardous conditions was developed. The outcome of the work is that the use of a control scheme and unconventional use of ailerons can significantly improve aircraft landing characteristics during adverse landing weather conditions and reduce the number of accidents. Current advances in future aircraft design are tending towards tailless aircraft such as Boeing's Blended Wing Body aircraft and a similar study by Airbus. These aircraft do not have sufficient rudder or engine yaw control at landing speeds. This work provides a method of steering the aircraft from touchdown to taxi speed through normal force and brake augmentation.

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