Positive coupling between yaw (slip) and roll

Definition of a "positive coupling between yaw (slip) and roll"

Steve Seibel
www.aeroexperiments.org

This page was last modified on August 22, 2006

 

In "Oblique and side views of aircraft with dihedral", we saw how an aircraft with dihedral experiences an increase in the angle-of-attack of the "upwind" wing, and a decrease in the angle-of-attack of the "downwind" wing, and a roll torque in the "downwind" direction, whenever there is a sideways component in the relative wind or airflow over the aircraft.

Whenever practical in these tutorial pages, we'll use the phrase "downwind roll torque" to describe these dynamics. However, another phrase that can be used describe the same dynamics is a "positive coupling between yaw (slip) and roll". For the purposes of these tutorial pages, we'll define this phrase as follows: an aircraft, wing, or other set of aerodynamic surfaces exhibits a "positive coupling between yaw (slip) and roll" if a sideways component in the relative wind interacts with the aircraft, wing, or other set of surfaces to create a roll torque in the "downwind" direction.

For example, if an aircraft is flying along with the nose yawed to point to the left of the actual direction of the flight path and relative wind at any given moment, and the resulting right-to-left component in the airflow over over the aircraft generates a roll torque toward the left, we'll say that the aircraft exhibits a "positive coupling between yaw (slip) and roll".

This phrase is slightly ambiguous, but most alternative phrases are either extremely awkward or are even more ambiguous. We'll avoid any ambiguity by sticking religiously to the definition given above!

 

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