The roll torque created by dihedral or anhedral is not strongly dependent on angle-of-attack

The roll torque created by dihedral or anhedral is not strongly dependent on the angle-of-attack of the wing as whole

Steve Seibel
www.aeroexperiments.org

September 16, 2006 edition

 

The roll torque created by dihedral or anhedral does not depend strongly on the angle-of-attack of the wing as a whole. More precisely, for a given airspeed and a given yaw (slip) angle between the aircraft's heading and the actual direction of the flight path and relative wind, the roll torque created by dihedral or anhedral is not strongly dependent on the angle-of-attack of the wing as a whole. Or to put it even more precisely, to the extent that the wing's lift curve is linear, for a given airspeed and a given yaw (slip) angle, the roll torque created by the difference in angle-of-attack between the two wings arising from the wing's dihedral or anhedral geometry will be independent of the average angle-of-attack of the wing as a whole.

The upper aircraft in this photo is designed to fly with the rudder as the sole means of roll control. Therefore the aircraft has lots of dihedral. On this aircraft, a left rudder input creates a left roll torque in the aircraft's own reference frame, regardless of whether the wing as a whole is flying at a positive angle-of-attack, the zero-lift angle-of-attack, or a negative angle-of-attack. The aircraft can be controlled with the rudder with no reduction of roll response or reversal of roll response even during 0-G manuevers and negative-G maneuvers, including sustained inverted (negative-G) flight. (The aircraft is extremely unstable in roll during sustained inverted flight, but that's another story!)

In flight at a given G-loading (e.g. normal 1-G flight), for a given yaw (slip) angle between the aircraft's heading and the actual direction of the flight path and relative wind, the roll torque created by dihedral or anhedral will be greater at high airspeeds than at low airspeeds, because the aerodynamic forces created by a difference in angle-of-attack between the left and right wings will be proportional to the square of the airspeed.

For example, in the case of the RC model sailplane illustrated above that uses the rudder as the sole means of roll control, the roll response to rudder inputs is greater at high airspeeds than at low airspeeds.

 

Advance to "Competing effects of sweep and anhedral"

Skip to "The main cause of adverse yaw during rolling motions: the 'twist' in the relative wind"

Up to the Aerophysics Exploration Pages index

Up to the Aeroexperiments site map

Copyright © 2004 aeroexperiments.org