After a flight test, I determined I needed to raise my LO guide. During my hang test, this is what my plane looks like. Looks like that might be a lot of nose out. So far, I only changed the vertical. Should I just test fly it and see how it feels this time?
It's not yawed out that far in flight, for several reasons. The most important is that the lines don't make a straight line to your handle to the airplane - they lag behind, well behind in fact. It depends on the weight and the line size, but its on the order of 2-3 degrees. There was a paper written on the topic:
http://z6.ifrm.com/4811/197/0/p1016257/LineDrag2000.pdf which dates back to the 50s. A slightly erroneous version was published as nomographs by Wild Bill back in the 50's, later corrected with wind tunnel data (they didn't accomodate, or didn't correctly consider, the variation in the Reynolds number, as I recall). There is also a computer program floating around to calculated it, called LINEII, which was later ported to other versions of the unfortunate Microsoft Windows operating system by Bob Reeves as LINEIII.
My approach to trimming uses this calculation to set the (dry) leadout sweep to match the calculation of the line sag. I then adjust the rudder offset to get the minimum yaw reaction in the corners. That will yield a yaw angle that is tangent to the circle at the end of the flight, and will result in the leadouts not applying force to the guide. What you can't do, in my opinion, is try to control the yaw angle with the leadouts, unless you also adjust the rudder to get them in sync. Ancient trim techniques set the rudder however it was, left it alone, then try to adjust the leadouts for "best" performance - which usually resulted in the aerodynamics wanting to yaw the airplane nose-out in level flight, and the leadouts forcing it back close to tangent. That's swell as long as you only ever fly level at a constant speed.
As soon as the tension or speed changes (particularly, when the tension goes up entering a corner while the airplane slows down) you will get some sort of reaction in the lines - usually, dragging the nose inboard to start, but far more importantly, getting the lines swinging back and forth (line whip). It also tends to roll in at you, leading you to want to have a lot of tipweight for that condition. Of course, now the tip weight is excessive for less extreme conditions. We call that "Twister Disease" where if you set it up per the plans, tremendous rudder offset and "straight out" leadouts, you will find it essentially impossible to trim the roll axis.
Your angle might be too much for a heavy airplane on minimum-size short lines, it may be just right for a light airplane with heavy lines. A few minutes with a calculator or with LINEIII will let you know which.
Brett
p.s. I read some of the other responses. Your leadouts must be substantially aft of the CG (which is what you show) unless you have large amounts of rudder offset to fight it with, and that arrangement leads to "Twister Disease" as noted. I would guess 1" behind is about right assuming .015 x 60 lines. It cannot be level unless you also add a bunch of rudder offset because the line sag will make it try to yaw nose-in.
Topic: Yaw, how much is too much? (Read 1738 times)