Flew several successful flights today with one mishap on landing . Came in outa gas and low reciever battery. Question I have is I was flying in varying wind so trimming was tricky but several times during flybyes I noticed the tail was wagging left to right alittle. It was when I was headed into the wind at about 100 ft up at half throttle. Its a SPAD FNS with 48" wing 5" dehidral, 30" fuse, 8" tall x 10" rudder. With the SPAD design theres only about 6" max of the rudder above the wing and fuse. Do I need to make the rudder taller? Or is this just caused from flying into a head wind.

Hi cj I have experienced the same with all my planes with the wind, spads, easy sport, advance 40, all get what I call tail wiggles from the wind. It gets real interesting with gusts to 30mph.

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.

Thanks for the insight FH I always thought the wiggles were caused by the wind. One thing though my planes tracking stays straight as an arrow when there is no wind even at full throttle.would the bamboo trick work for ailerons too ? thanks Bob

The stiffeners would help.

For the coroplast hinging method normally done on SPADs (inserting the ailern stock between the upper and lower skins) I carry the upper wing skin back to cover 2/3 of the hinge flute. This reduces the flexible section from 4 mm to appx 1 mm. Then aftter the CA is cured, I crease the hinge line up and down to 90 deg deflection a few times, so the hinge line moves freely. The stiffer hinge line gives reduced flutter tendancies.

Unfortunately, I have not found a good method to stiffen the coro hinge line at the tailplanes when using a single thickness of 4 mm. I've been considerng putting up with the added weight of 2 layer 2 mm to do an airfoiled shape tailplane and get the stiffer hinges... There are some aerodynamic benefits. But my coroplast planes tend to come out tailheavy already and I hate adding ballast. I may try this when I make my replacement fuselage for my 4*60 though... it has fairly large surfaces and needs more stiffness than 1 layer of 4 mm