Masters Theses

Mark A. Werth

Date of Award

8-1999

Degree Type

Thesis

Degree Name

Master of Science

Major

Aviation Systems

Major Professor

William Lewis

Committee Members

Fred Stellar, W. R. Lawrence

Abstract

During flight test of the AV8B nose wheel steering system, gyroscopic precession was inadvertently encountered. Following a touch and go landing with a 180 degree turn to downwind, the spinning nose wheel caused the nose landing gear strut to process away from a centered conditioned. The physical properties of nose wheel's angular momentum coupled with the pilot's technique can easily be seen to have caused the precession however, this phenomenon had never been seen during the previous 13 years of the Harrier's existence. Toquantify this behavior, a study of gyroscopic precession as it applies to aircraft landing gear is presented. Understanding how the aircraft nose landing system works in conjunction with the operational procedures employed is critical to understanding why this precession had not previously been detected in other aircraft either. Accordingly, a discussion is presented. Following that, a data presentation section describes the test aircraft and limitations to data collection during the flight test events. A mathematical.model was also developed to show how the flight test results conformed to gyroscopic theory.Analysis of the test data and the mathematical model provided insights about gyroscopic precession in the AV8B nose landing gear system. The data indicated that gyroscopic precession of the nose strut was a function of several variables. Contributing factors were the nose wheel rotational velocity, the aircraft roll rate, and the aircraft roll acceleration. The gyroscopic precession appeared to be mostly due to high rotational wheel speed velocity at the point of aircraft maneuver however, it was discovered that there was a large dependency on aircraft initial roll rate and roll acceleration. The data also revealed that although precession trends can be predicted, an absolute solution is quite unpredictable. The single most important factor during this study of nose wheel gyroscopic precession was pilot technique since this defined the aircraft roll rate,roll acceleration, and nose wheel rotational velocity that generated the precessional moment on the nose strut. It is highly recommended that landing gear design engineers find a method to inhibit nose landing gear strut precession thereby ensuring that pilots do not have to contend with this dangerous phenomenon.

Download
Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS