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Building Tips and technical articles. => Building techniques => Topic started by: Jonathan Chivers on April 29, 2013, 01:12:12 PM
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Hello all,
looking at planes and build logs for competition stunt planes, I see that they all make provision to move the position where the leadouts exit the inside wing to move backwards and forwards.
What is the impact on the planes handling when you do this?
If this has been covered before, please point me at the right link.
Jonathan
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a quick search netted over 12 pages of results on "adjustable leadouts"
short version,
moving the leadouts allows you to trim the yaw position of the airplane in flight,
in a VERY simplified explenation, you want the leadouts to leave the wingtip so that they align with the lines from the handle whilst the airframe is tangent to the flight path...
moving them forward typically will assist in gaining line tension overhead ( to a point)
moving them back will typically bias line tension towards level flight,, ( to a point)
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To a point -- when you start experimenting with leadout position you find that as you move them in one direction or the other your overhead tension will get better and better, then start getting worse. It just ends up being cut and try.
Edit: Mark already mentioned searching, and Paul Walker's trim chart in another reply to one of your questions. Both are valid -- figure out how to do searches here and you'll find lots and lots of material on each one of your questions. And, maybe you'll find a copy of Paul's trim chart, too. IIRC Paul's chart doesn't tell you how to change things, but it does point to what to change first, then next, etc.
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As a general rule of thumb for a "typical" stunt ship of "normal" dimensions and weight and power say like a Vector with a stunt 40 at 45 oz or so: set the center of the leadout guides about 3/8" rearward from the CG position for every 10 inches of inboard span. (from Bill Netzeband's articles more than 45 years ago.) For slightly bigger and slightly smaller ships, this same parameter applies. Then with your adjustable leadout guides, you will find an optimum position, but this will get you in the ball park without a disaster.
Or do what Mark, suggested, you can be entertained for hours if you do a search on this stuff.
Keith
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You can get very close to the optimal position by using Bob Reeves's Line III: http://www.tulsacl.com/Linelll.html .
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When I first started using adjustable lead outs I just fumbled with it until the airplane flew acceptably. Then (quite a few years back) Kaz Minato told me to hang the airplane by the lead outs and shuffle the slide until the nose hung one degree down. Although I usually go 1 1/4 to 1 1/2 degrees it always works for me and is almost always the final position. When you see that the lead out position is always in direct relation to the CG, you'll also understand that if you make a CG adjustment you'll also need a linear lead out adjustment if it was in the right spot to begin with.
Dave
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Tho I agree entirely with all the above, at one contest it was suggested to me (wrongly, it turned out) that I should move my LO's forward. I did. It didn't help, but before I moved them back again, I thought I'd try moving the CG forward a bit, to make a match with the more forward LO's. THAT helped. Like Brett says, put the CG where it needs to be, and don't worry about the added weight. You have to trim the airplane, regardless. This also suggests that if you can't build light, at least lengthen the nose 1" or more, to prevent tailheavy planes from happening again and again. FYI, most electrics are coming out tailheavy, if that applies to your new project. S?P Steve
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When I move leadouts, I move them at most 1/8 inch at a time. Yes, I am an incrimentalist. S?P
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Thank you for everybody's replies.
Jonathan