_______“Adverse Yaw”
_______________________ ___________by M.TAJ

Introduction

I noticed with interest that there was thread started on our Forum talking about control of Adverse Yaw (sideways motion) in high wind conditions. Our guest assumes at the beginning that al reading know what “Adverse Yaw” is and how it is generated. Hmm I thought, I am sure that in the large numbers of readers we will get reading the thread the majority are not going to be aeronautical engineers hence this article explaining what Adverse Yaw is and its effect on the motion of an aircraft.

Definition of “Adverse Yaw”

"This is a Yaw motion generated when the ailerons are used. The profile drag increases on both wings when the ailerons are deflected, but the increase is equal when the ailerons are deflected by the same amount. However, the induced drag on each side is not equal, and a larger total drag force exists on the wing with the down aileron. This difference in drag creates a yawing motion in the opposite direction of the roll. Since the yaw motion partially counteracts the desired roll motion, this is what is known as the Adverse Yaw."


How Aircraft Counter Adverse Yaw

There are several methods employed to counter Adverse Yaw condition but I have selected two main methods used to counter and correct this aerodynamic effect.


The first method couples the ailerons and rudder together so that they deflect at the same time. As the ailerons create a Yaw motion in one direction the rudder automatically counters by creating a Yaw motion in the opposite direction. The two effects counteract each other eliminating the undesired yaw.

The second method is to bring the Spoilers into play. When partially raised on the wing with the up aileron the spoilers reduce lift and increase the profile drag on that particular wing. The wing with the Down aileron will experience a large increase in lift and only a small increase in drag. The combined effect will give the desired roll motion while at the same time creating a complimenting yaw motion known as the "Proverse Yaw".

The lifting of the spoilers in conjunction with the ailerons can be seen when Pilots go through the routine of checking the control surfaces whilst preparing to Taxi or are being pushed back. Sharp turns on the Yoke will show the ailerons move and the spoilers rise.

The question at Hand High Winds is, in my opinion, down to pilot training. The larger Aircraft are heavy and are most likely to be affected by this condition at lower speeds and lower altitude but again have an envelope operation that must be strictly adhered to i.e. weather condition operations for fleet type. The smaller ones your Cessna’s and Pipers etc, being mostly privately owned, not bound by company rules and policies in regards to the operation of company aircraft, away from the CAA or FAA regulations. Pilots need to monitor conditions much more closely High winds at low altitude give pilots less chance of recovery due to terrain proximity which goes without saying, hence if a pilots knows that the winds are gusting at 30 knots and he is in a Cessna then he should be planning an alternative rather than thinking my plane can handle the condition. Know and understand wind limitations for your aircraft, and how they apply in practical taxi, takeoff and landing situations, that is the guideline possibly you could say a lifeline.

COPYRIGHT M.TAJ 2003