J'Motta,

I have two Twisters--both a bit kit bashed--and ended up with 2 degrees thrustline offset on both of them. With only 1-3 degrees of offset, it does not look funky to me. Even on a full fuse job with a closely fit cowling, you might have trouble casually seeing offset that small.

That said, you need to consider three trim adjustments in aggregate: leadout position, rudder offset, and engine offset. Probably should include a couple more, as explained below. But you want the plane to fly as close to tangent as possible with adequate line tension. That will result in the fewest secondary trim issues.

Since line tension also depends on speed, line length and weight you can see that a bunch of different things are involved. Finally, what one guy thinks is adequate line tension for his style of flying and weather conditions can vary a lot from the next guy. That is why you see people changing all of these parameters to find what works best for them.

On my two Twisters, I'm happy with the 2 degrees of outthrust, a bit of rudder on one, but none on the other, and lines about 62 feet (handle to centerline). Both use OS .46LA's. I tend to fly a bit faster as a bit more line tension gives me more confidence. The Twister with no rudder offset is significantly lighter than the one with offset.

The only place I would agonize over engine offset is with a full fuse job with a close spinner fit. On a profile, you can try whatever you want with no drama.

I might try a Twister without rudder offset, but I'd expect to have to cut into it to add some after a bit of testing. Maybe I'd get away without it, but....

Good luck with yours!

Dave

Thanks for the response. My build right now has 1 degree engine offset with no tail offset but am at the point where I can change it. Actually it would be easier to add more engine offset  than take it out. Do you think I知 good the way it is? Appreciate the valuable information.
                      Joe

I'd suggest putting in one degree of engine offset, then if you're curious, try adjusting that when you're trimming.

The advice that I've heard repeatedly, and that I just follow, is to install the fin/rudder with as close to zero offset as you can, but if you're going to screw it up, make it yaw to the outside.  This has served me well.

There are some slight advantages to be had from making the rudder ground adjustable, but (says the guy who took two years to build a Twister) that's getting too complicated for a profile.  I wouldn't suggest going there until you're flying Advanced and contemplating a jump to Expert, and if you subscribe to the Paul Walker school of trimming (meaning: trim obsessively, with the objective to make the plane fly itself as much as possible).  At that point, you should be building and flying full-fuselage planes.

Looking for input on engine offset. I知 building a Twister and wondering about engine/rudder offset. Is it needed? The plane has a nose ring and if I need offset can I get the same effect by putting it in the rudder instead of having the funky engine offset look?

My Twister was electric and Fancherized.  2 degrees offset 1 degree down thrust and 1/8" rudder offset.  IMHO motor offset is more effective than rudder, especially if it is a tall rudder.  However, effective means that which will not be named - (YAW shhh) so go gently.

Ken

THANK YOU DAN!  I have been asking where this article was since it was first brought up a while back!

Again - Thank You - Ken

   And I answered you over on the changing stab height thread, rather, Keith Trostle did, and then I did again on the SV-11 Incidence check thread!   Want me to read it to you!!!???
  Type at you later,
   Dan McEntee

We値l I appreciate the feedback. Right now the build is set up with 1 degree offset and about 1 degree down thrust. I think I値l leave it at that and continue the build. Thanks again.
Joe

JM,

Some (theoretical?) basics?

Our models should have least drag when they fly as nearly tangent to the flight circle as possible. But where do we want that tangent point to be? And to what?

Simplest, if you think about it, would be to put the tangent point at the CG and on the long axis of the fuselage, no? Our models fly at the edge of a circle. A straight fuselage axis, tangent at the CG, already has some out-thrust angle (at usual line lengths, about 1ｰ or less. A straight fin/rudder (usually about twice a far aft of CG as the prop is forward of it) has about twice that: maybe 1.5ｰ or so. This is not large enough to really worry about. It seems to me, and has worked on all my recent models, to - at most - have the fin/rudder mounted basically on the axis but airfoiled with the curve ONLY on the inboard face. IOW, a slight lifting airfoil tending to cause nose-out.

If everything is just about right, IMHO the only reason for more engine offset on a profile is if everything goes slack, it will try to steer the model back out to full length of the lines. It is easy on a profile to slip a washer under the front mounting lugs, or a degree shim under them all.

Tangency can be created with adjustable leadout guides, which point the line pull's trail angle to the CG. If that's off, the pull force will try to yaw the model to make it line up. Complicates trimming... Also, this varies slightly with changes to the CG location.

Just some musings trying to see some fundamentals before the truly adept (in science, math, building, trimming and flying) share with us the fine details that they find useful, and might baffle many of us mere mortals...

 /LOU

What you're doing with engine offset is basically gluing the wing in the fuselage cocked. So, anything you can do with engine offset you can do much easier with the lead out slider.

    No.   Offsetting the thrust vector of the engine is a very fundamentally different issue than adjusting the leadouts, it has multiple effects (at least, changing the relationship of the thrust vector WRT the CG, and changing the direction the propwash strikes the airplane) that are completely different from leadout sweep, and you certainly can't substitute one for the other.

    You cannot set the yaw angle with the leadout position, or at least, you shouldn't. You set the yaw angle with the rudder and to a very small extent, the engine offset. Anything else,  and you tend to create a mismatch between the aerodynamics and the line sweep effects, and that almost always leads to wild yaw motion in the maneuvers. Basically, you don't want to be applying any static torque to the airplane with the leadouts, and use it for the very least of dynamic stability you can manage.

     Brett

      Ditto. All of my rescued Ringmasters have the rudders cut off and put back straight.

     Type at you  later,
  Dan McEntee

  Of course - because you are reducing the effect of the leadouts "fighting" the rudder offset. It works even better on the green box Nobler.

    Brett