Vanes for Sensing Incidence Angles of the Air from an Aircraft

Abstract

Two types of vanes that were used to measure the angle of the airstream with respect to an aircraft are described, analyzed and compared. One type is a rotating vane that is free to align itself with the airstream and the angle is sensed by an angle transducer. The other type is constrained from rotating and the angle is obtained by measuring the force exerted on the vane by the airstream and dividing by the pitot-static pressure. The free vane measures the angle directly and is not sensitive to acceleration, while the constrained vane has a faster response time and has no bearing friction. At an aircraft speed of 70 m sec?1, both vanes are able to resolve changes in angle of less than 0.02°, which corresponds to a gust velocity of about 2 cm sec?1, and respond to within 5% of a step-function change in angle in a distance of less than 5 m. An inflight comparison between the two vanes indicates that they both measure the same angle with a correlation coefficient of 0.97.