ORIGINAL: bjr_93tz
ORIGINAL: tony0707
i have always set my wing , stab and engine at zero degrees to each other on all my airframes on jigs in my shop-my stuff flys on rails
You've answered your own questions. If all your planes fly on rails then you don't need to change your engine thrustline settings.
Changes to engine thrust line angles are only used to correct faults where engine thrust is the predominate cause/cure. ie vertical upline tracking in the pitch plane is trimmed with engine downthrust/upthrust, while straight and level flight tracking (upright and inverted) is trimmed using centre of gravity and decalage.
Sidethrust is a matter of personal preference in that not enough causes some problems, just right causes less problems and too much causes different problems, so you have to decide which problems you can live with and which ones you can't. Generally if you can pull to an upline and your plane doesn't deviate left or right as you slow down while still under power then you're pretty close.
The above are generalisations and I've never seen a zero-zero setup fly straight yet but they fly straighter than a really crooked plane.
For 3D work, if your holding in a heap of right rudder and down elevator in a hover I'd be tempted in add right thrust and downthrust. If your plane needed up elevator and left rudder to hold a hover I'd be temted to add up thrust and left thrust. Every plane is different.
Flies on rails....not particularly demanding of the flight envelope; sounds like it's sport flying and for that, 0-0 is fine. For demanding pattern performance in the highest level of competition, a bit of down, as much a 1 1/2 degrees and a bit of right, as much as 2 degrees for prop sizes up to around 20" is fairly typical of the current crop of fuse designs. What you are after is straight flight with application of rudder, and pure response in any attitude from any control input. This is the holy grail but unlike the biblical sense, this is achievable, without e-mixing much of anything
For true 0-0 set-ups you have got to eliminate the spiralling airstream. This also is not a particularly tough problem but you have got to be able to think outside the "normal" box when designing.
MattK