Hi,On some, perhaps all, of the default autopilots in FS9, are the usual array of buttons to push..hdgaltnav etc,etcbut what does 'yd' stand for..in fact the light has gone on and I think it stands for 'yaw damper', which sounds Cornish but perhaps stops the plane twisting on it's axis in flight.Maybe someone really knows!Andy.

Yaw Damper is to help keep the wings level in rough air conditions, sometimes works and sometimes not. Might help for approach to landing, but never tried it.Part of the secret of success in life is to eat what you like -M.Twain

A yaw damper is used to reduce the rolling and yawing oscillations due to Dutch roll mode. Dutch roll is anaircraft motion, consisting of an out-of-phase combination of yawing and rolling. It's normally well damped in most light aircraft, though some aircraft with well-damped Dutch roll modes can experience a degradation in damping as airspeed and altitude increase. Wings placed well above the center of mass, swept wings and dihedral wings tend to increase the tendency to Dutch roll.

Hi,Thank you both. I'm not entirely convinced by the Dutch Roll explanation as I can't quite figure out what they might have to do with it. Early Fokkers?:+ They had high wings, but too early for autopilots.CheersAndy.

"Yaw Damping is provided by two completely independent dampers which can be operated singly or simultaneously. The prime function of the system is to minimise Duch Roll by providing automatic rudder displacement proportional to and opposing the amount of yaw experienced."http://www.boeing-727.com/Data/systems/infoyawdampers.htmlA Fokker EIII weighed 1100 lb empty and had a maximum speed of less than 100 mph. Comparing that with a B747 weighing some 800,000 lb with a maximum speed of about 600 mph isn't really of much value - the flight dynamics are a little bit different.

Hi,thanks again; it was the Dutch part I didn't get the drift of, why 'Dutch' and that set me thinking of Anton Fokker and that his planes were way too early for 'yaw damping' autopilots, if they had any sort of autopilot at all, which I don't think they did.I'll d/l that Boeing html and thanks for going into this for me:-beerchug Andy.edit: from Dutch skaters!!

.