SIG Witch Doctor 1/2 A F.F.

High performance free flight models tend to have a center of gravity that is insanely far back for just about any other type of model -- it turns out that a stable airplane is a plane that wants to loop under power. Given that a competition free flight airplane needs a fast climb and a floating glide, that means that it needs to be hanging by its little fingernails to the edge of the stability.

An R/C plane on the other hand -- particularly one for a beginner -- wants to be much more stable.

You _could_ make it work with some redesign -- basically you want to bring the C/G forward by at least an inch or two, which means building it with a significantly longer nose. The pylon is superfluous if you have elevator control, and the fuselage is way too skinny for a radio and battery. You'd want to find a web page that shows you how to do stability calculations -- it'll have a great big horizontal stabilizer which will let you place the C/G way farther back than normal; that's not something that's easily "rule of thumb"-able.

I could see this as a fun building project for someone whose an experienced builder, who knows how to figure out the correct center of gravity for a nice flying plane, and who is willing to spend some time shoehorning a radio in there and tweaking the result.

If you just want to go fly then you may want to start with something else. If you _really_ want to make this work then consider building a fat pylon big enough for all the electrical stuff, figure out how to mount the motor forward, and go for it.

Thanks, Tim. Guess it was a bad idea.

If I could write the Characteristic Equation, I could check stability with Routh, Root Locus, or Nyquist. Just kidding.

Perhaps my unbuilt Goldberg 1/2 A "Blazer" would have been a better choice. Fuse is hollow aout 1-1/2 by 1-1/2 or so. Cof G (desired) is shown on the plan and I guess if I matched that I might have a chance.

" Blazer" has 40 in. WS, and 19 in. stab. Weight is 6 oz with 1/2 A gas engine. Guess wing area is about 240 sq. in. O.A.L. is 29 in.

Are there other issues with mounting components on the pylon than drag? Thanks, Jim

Not _bad_, just really involved. The Blazer sounds like a better candidate -- that fuse is still a bit tight, but with planning you should be able to shoehorn the necessary equipment in there.

I take it that while you haven't done R/C you've done plenty of F/F -- I envy you; I fly R/C because I just can't get my F/F planes trimmed out, and because there's a whole lot of trees here in the hills.

You will still have to move the CG forward, I'll bet. Don't, and you'll have a hairy ride. This page,

should help out with figuring where you want to put it. You _will_ have to do some math, but it's all laid out for you so you'll just need to plug the right numbers into a calculator. I've used his formula before for my own designs and for kits that didn't have the balance points right, and it's worked very well.

The formula he gives will put the CG about as far forward as you'd ever want -- which is probably just right for a trainer. As you get more proficient at flying you'll want to move it back for better maneuverability and for less drag -- so plan your battery and motor installation accordingly, and give yourself room to move the battery back later on.

If you want a relaxing glider-like thing, I would suggest you put the elevator hinge line somewhere between 3/4 to 5/6 of the horizontal stabilizer back from the leading edge. If you really want to hot dog it later put it smack in the middle, but keep in mind that you'll be amplifying any slop in your linkage. At any rate for a model that size and with you a beginner you probably want the trailing edge of the elevator to go about 1/4 of an inch each way -- that should be enough to get you out of most trouble, and keep you out of the rest. Give it lots of rudder area or you won't be able to steer it when it's going slow -- I'd put the hinge line no more than 1/2 way back, and for the floater that the thing ought to be making the rudder area 75% of the total vertical area is not overkill.

Don't bother with ailerons. It'd be a sin on a model like one of those.

As far as putting components on the pylon, it's just the obvious considerations: drag, looks, and structural integrity. If you've modified kits before without the results falling apart you'll be fine.

If you have the money you can get some very small radio gear. I've been thinking about converting a Guillows or Sterling I have laying around to RC. mk who needs a round-tu-it