The tail wagging is NOT the wind unless your wheels are 0n the ground or you are wagging the stick trying to decide what amount of rudder to use.

the 2 major causes of tail wag:

1) Dutch roll. Thi is a design imbalance causing the airplane to yaw and roll (usually the roll is smaller than the yaw) at some airspeed, power and angle of attack combination. You can cure it by changing any one of the 3. For example my Tiger 60 will wag its tail at full power at appx 20 deg climb from take-off. Reduce power to about 70% and no wag. (I have lots more power than I need) It also goes away if I use a 13X6 instead of a 14X6... (less static thrust at full throttle) but that is actually too small a prop for the engine.

2) Rudder flutter. This is the more common cause with SPAD designs at high speed. The rudder is too flexible. Too eliminate the flutter in these, you stiffen the rudder by inserting bamboo 90 deg to the flutes (poking a lot of holes as you penetrate the surface from fromt to rear) and put 1/2 round (I cut bamboo skewers in half the long way. Some people use 3/32 or 1/8 inch dowels) on the leading edges of the tailplanes.

You CAN cure it in either case.