ORIGINAL: Premium2000
Rangerstl,
I have been thinking about your advice regarding the fin and the problem with stabilty when if it where to be located forward of the CG and CD. What if the fin/rudder were made solid/one piece which pivots around a vertical axis (rod), like a weather vain? Since it would offer little or no resistance then it should not affect yaw nor adversely affect stability. It is merely going along for the ride.
So where does rudder control come from? How about adding a set of wheel skirts? The trainer I have in mind would use tricycle landing gear. With skirts, the front wheel (normally) could perform double duty. On the ground, it would steer the plane as ussual (all be it in reverse). In the air, the skirt on the (what is now in the rear position) would act as the rudder. Perhaps the skirts on the main gear would also add to the overall stability of the plane, as well.
Regarding the orientaton of the main wing. Right now I'm not inclind to take the easy way out and just turn the wing around so that it operates in the way that it was designed. Assuming that ailerons on the effective leading edge won't work what about this? Make the main wing solid with a fair amount of dihedral (for roll stability) but use the last few inches of the wing tips for roll control. My idea is to make the wing tips so that they rotate (under control and in apposing directions) effectively turning them into the ailerons. Given the lever arm involved, small movements should have a big effect on roll. Obviously picking the right point of rotation is critical.
Finally, I expect that the main wing will need a significant amount of positive incidence in order to generate sufficient lift when flying backwards. What about the forward wing? How will the angle of the main wing affect the nominal angle of incidence of the forward wing?
Thanks for your thoughts!!!
Larry
This is all a non starter. Yes I suppose it's possible that your "fin" could be rigged to weathervane and thus not have much effect. But for the model to achieve the directional stability it would need you would need a WAAAAAYYYYY bigger vertical area than just the wheel skirt idea. The amount of effect of the stabilizers and fins are sort of like levers. You can use a small amount at the end of a long lever or a big amount at the end of a short lever. So if the trainer fin works OK with the lever it normally has to make it work with your backward plane it would need to be roughly twice as big (based on the canardly more middle CG location) than the regular fin. The model will look pretty darn silly with a huge fin on the "nose" but trust me, it will be needed.
There's a perfectly good reason why canard models don't look like backwards normal planes other than the areas of the lifting surfaces. You're running into this issue and you can't ignore it.