RE: Aileron Differential
Peter is an exceptional pilot and his article on trimming is the most informative that I have read.
The idea of checking differential on a 45-degree upline is excellent advice and a good means of avoiding unnecessary rudder and elevator input. However, unless I have misunderstood it, I believe that the section dealing with corrective action may contain a slip of the pen.
With no aileron differential, an aileron only turn is likely to cause an aircraft to yaw in the opposite direction to the roll i.e. a right roll would cause a yaw to the left and vice versa. This is because for equal aileron movements up and down, the downgoing aileron is likely to create more drag.
In simplified terms, the additional drag can be thought of as a trade off for the lift created by the downgoing surface. The affect is particularly noticeable flying full size older generation gliders. Many of these aircraft have insufficient differential and an aileron only turn to the left (say), produces a very noticeable â€˜adverseâ€™ yaw to the right. Glider instructors take great delight in pointing this out to converts from Cessnas and Pipers who are used to turning the aircraft without the need for co-ordinated rudder!
If consecutive rolls to the left cause an aircraft to go right, this is a sign that the downgoing aileron (i.e. the right aileron) is creating too much â€˜relativeâ€™ drag. This can be corrected â€“ at least to some extent â€“ by decreasing the throw of the downgoing aileron i.e. increasing the differential.
The recent generation of composite aircraft, with top hinged ailerons, can introduce an additional complication. Because of the top hinging, equal degrees of aileron movement up and down will cause the downgoing surface to present less surface area to the surrounding airflow and therefore less corresponding drag. In some cases, it can be necessary to counteract proverse yaw by introducing â€˜negativeâ€™ differential i.e. setting the ailerons to move further down than up.
In practice, with many F3A models, there seems to a limit to how much adverse yaw can be corrected by aileron differential. Some models will continue to exhibit adverse yaw even in situations where the down going throw has been reduced to zero. In such cases the best option is probably to dial in a smaller amount of differential and accept the imperfection.
Hope the post has helped to clarify rather than confuse!
With very best wishes and many thanks for taking the time to produce such an interesting and informative forum.