Smoothie Tracking Problem

LAST EDITED ON Aug-04-03 AT 04:16 PM (CDT)
 
I've got an '52 Air Trails plans version Smoothie that I just can't seem to get to track level. There is a yaw problem that appears to me to be a result of weather vaning but I'm at a loss as to what to do to trim it out. Can anyone advise me on how to approach this without an adjustable rudder or leadout guide. It's a reasonably attractive little ship and it's about to be relegated to the status of "decoration" but I'd rather be flying it. I will certainly use the "cut and glue" method of adjustments if it comes to that but I'm not sufficiently proficient at trimming to start hacking away without some expert advice. Any and all information offered here will be greatly appreciated.

Do you have offset on the engine? There are a lot of things here that are hard to change, since everything is "hard". But, with offset, that would cause some of your yawing problems.

It would have been nice to have adjustable leadouts. Then you just move them until you find the best position. Not having that, check your balance. Do you want to change it? It sounds loke you need to move the leadouts forward, but if you move the CG back that does the same thing. Only move the CG if you want to (need to). You cold add a little tail weight (solder wrapped around the tail wheel strut) to see what it does. But, ultimately, once you have adjusted the weight situation, you may have to move the leadouts to improve the situation.

I would suggest that if you do cut in to move the leadouts, that you do it and don't patch things until you find the best spot. That way you can make little improvements by cutting and gluing and then patch the tip when you are done.

Leonard,

Thanks for the reply. The CG is pretty far back now - killer corner, but there is offset in the rudder and a tiny bit in the engine too. I'm observing no "obvious" problems in the corners that I would expect from excessively rearward line rake or outward yaw but that might be because I have not yet developed the appropriate observational skills. Line tension is pretty equal everywhere and there seems to me to be no consistent yaw but when I'm flying "level" I can see the tension moving from one line to the other causing the plane to "hunt." That led me to the conclusion, perhaps mistakenly, that it's somehow weather vaning. Maybe rather than butchering the wingtip, I might benefit from hinging the rudder and experimenting with that? Unfortunately, the stock Smoothie wingtips are particularly unfriendly when it comes to repositioning the leadouts so I was hoping the "magic bullet" would be found somewhere in the CG/tip weight/rudder offset mix. I'm also wondering if I might be missing something in regard to how line length figures into this. I'm hoping Brett will share some of his highly regarded trim insights on this as well.

Thanks,

Dave,

What, is McClave out of town? It was his Smoothie which attracted me to Classic--and a Smoothie of my own--a few years ago. Neither his nor my models did anything weird...

Dan,

Don and I applied all manner of straight edges, squares, and measuring devices to the Smoothie to see if we could find a missalignment that would account for the tracking problem but found nada. We had pretty much given up on it, my thinking it must be some kind of leading edge shape voodoo, but when I was using it to test a three blade on the Fox I caught an unusually clear view of what it was doing(looks like weather vaning) and thought I might "mine" the forum for some new ideas. Don just probably thinks I'm crazy for fooling around instead of just building an Oriental.

Dave

Dave,

Not sure if this will help but I have ran into two airplanes that hunted somewhat like you are describing. One had controls that were too stiff and the other had the CG to far aft. If your control system is reasonably free but solid I would add some nose weight and see what happens.

Good Luck
Bob

Dave,

We all think you're crazy and don't need this episode for proof.

Give Alice a big kiss for me. Wait! I'll do it myself...

Tracking problem’s comes from misalignment. Clean lines, engine thrust line, wing to stab, leadout position, and engine offset. DAVE is an expert builder. HOWEVER, something is off. I’ve seen this plane fly and I stand there wishing I could fly it to give some input. Up right engine, light, silkspan-dope finish, no lead out adjustment, and no wig tip adjustment. I’ll say that it’s one of two problems. Engine has up in the thrust line. AND the lead-outs need to go forward a little.

Scott (not Johnny five) Riese

Scott,

All you had to do was ask! I'd be happy to have you take a flight on the Smoothie. Already tried shimming in downthrust though and there was no improvement, just lost the inside corner with no tracking improvement. The CG was originally much further back, which would seem to me to suggest that if the leadouts should be further forward now, there would have been some evidence then. Perhaps I have that wrong. I put the leadouts where Don McClave indicated on the plans I got from him and I'm pretty sure they were ahead of where the originals were. You can bet I won't build another airplane without adjustable leadouts! I have loaded up the nose with weight in the past and ofcourse that eventually dulls out the hunting a lot but it's at the sacrifice of too many other good things(like a corner) to be the "real" solution. I wish I could have made it up to Arlington to have both Don and Paul scutinize it.

I had a ship two years ago that did not track well when the CG was far enough back so it would turn well. When the CG was forward the tracking was there but not the turning. I taped the elevator hinge line (not the flaps)and the elevators became powerful enough to allow me to move the CG forward. Now I have both good tracking and good turning. You might give it a try.

Dee