Need to know about thrust angles (post # 1)

Ok. So I'm flyin my Pico Tiger Moth And BAM! nose first into the dirt. Busts the motor stick off flush at the cowl. So I hog out the busted stick from the fuse and in the process inlarge the hole to about twice the size as it was. No problem, get a new stick and a
can-o-foam,fill in the hole,cram the new stick in and kinda eyeballed it to where it looked right. (pointed slightly down from horizontal). Back to the park we go, give it a toss. Its flyin but man,I really got to work the stick hard to get any air. So I guess my ? is; Is there a standard formula for calculating thust angles? Or
Is it hit or miss? thx DJ

Well, I'm guessing your tiger moth is a park flyer and has a flat bottom wing or maybe an under cambered wing. Therefore it would usually require down thrust. 2 or 3 degrees. Also , it will require that the engine be offset slightly to the right, say 2 or 3 degrees. These are just sort of rules of thumb. They are good starting points. Don't be surprised if your model turns a little better to the left. That is normal. There is torque, precession, and be cause your park flyer flys so very slow, I would guess that it is flying a little nose up, like it is struggling along a little. This introduces something called "P" factor. The right blade, (facing forward) , generally refered to as the "descending blade" will have more apparent pitch then the left blade. The result is an asymetrical thrust causing a yaw to the left. It helps if your turning left, it hurts if your turning right. I hope that makes sence.

OK...Thx for that KWB... Think I kinda figgered out...The hardway

The answer to your ? is, there is no standard formula. There is theory, but the only way to get any particular model set up with the "correct" offsets is to fly it, see how it flies, adjust right or down thrust if you think it's called for, and fly it again. I say "correct" because it's a matter of flyer judgment whether it looks and feels right or not. KWB cites the standard rule of thumb, 2-3' right and 2-3' down as a starting point. High wing requires more downthrust, mid-wing & low-wing less or none at all.

It's usually not practical to produce offsets at any precise angle. It's normally done with one or two or three metal washers under the appropriate mounting holes. So if one washer isn't enough, and three is too much, you're stuck with two. I have on occasion sorted a pile of washers by thickness, or shaved a washer with a file.

Some kits will have offsets built into the firewall, which in my book is a mark of a well developed design, but even that only works well if your engine is similar to the prototype.

Lots of guys fly happily with zero thrust offsets, and for sport flying you can get away with it on most models. But some designs coupled with some engines produce an extreme reaction at high torque/low airspeed. I have seen models snap-roll right over and into the ground on take-off, which is the worst scenario. Once you have good airspeed, the effect subsides to unnoticeable.

With G2 you can edit your offsets by tenths of a degree and observe the simulated effect. Try the Dazzler with 52 4-stroke. Fooling around with that for a few sessions will help you a lot more than theory.