Originally posted by cabanestrut2002
just dont get your ground speed confused with your airspeed, ie; if you are flying at 20 mph ground speed into a 10mph headwind then the airspeed is 30mph.
if you are flying downwind with the 10mph wind up your arse then your plane is only doing 10mph and likely to be close to stalling speed this is what catches people out.....the bitter voice of experience 
This isn't exactly right. When the airplane is trimmed for level flight and say has 30 mph
airspeed, the plane doesn't care about the wind. The airplane will maintain the 30 mph
airspeed in a 10 mph headwind or tailwind. In the head wind the
groundspeed will be airspeed - wind speed (30 - 10 = 20mph
groundspeed). In the tailwind situation the
groundspeed will be airspeed + wind speed (30 + 10 = 40mph
groundspeed). The airplane will always maintain the desired
airspeed no matter how fast the wind is blowing. Even if the wind is blowing faster than the airplane's normal cruise airspeed, the airplane will maintain its airspeed. ie. wind = 50mph, AS = 30, groundspeed (headwind) = -20mph (airplane going backward 20 mph); groundspeed(tailwind) = 80 mph!