I built a Zenith 40 sometime back, which was a plans built 40 size pattern style airplane. I remember the designer stating that he had to redesign parts of the airplane to eliminate the roll coupling. In other words, the airplane would not roll when rudder was applied. My current flyer, the RCM Hot Dawg, also has very little roll coupling. Other airplanes, such as the GP Decathlon, have a lot of roll associated with the rudder. So much so that I almost lost it on takeoff a few times trying to maintain the heading on the ground with rudder.

My questions - What quality in an airplane design either introduces roll coupling or reduces it? What do designers do to eliminate it? How can you put an airplane into a stall/spin where the rudder will not drop a wing?

Mervin Friesen
http://mefriese.hsd.ca