OK some explanation is in order. First, what Matt said is absolutely corect. He's been doing this longer than most of us! LOL There are many ways to get the job done, and a few of them are correct. Pick your poison. I ran into this problem when I was building a World Models Groovy 90 ARF. I had no reference line of any kind. No plans either. I called up the distributor and they told me that the Groovy 90 had 2 degrees of downthrust built in. Don't hold me to that number - it was a while ago. Whatever it was, I used the method I described for "if you know exactly what the thrust angle is supposed to be". The firewall was angled so that when you installed the engine, it gave you 2 degrees of downthrust relative to the "invisible" fuselage datum line that they forgot to show in the instructions (probably on the Master plan somehwere in China). All I did was use the "known" parameter to establish my reference point. This is one method and it works. Like I said, You're working primarily with 3 things: thrust angle, wing incidence and stab. incidence. When you have plans thst show a datum line on the fuse, you can just align everything relative to that. Works great. If you don't have that important piece of information, you can find it as long as you know one of the other key pieces. If you don't you can get fairly close by making some observations. On ariplanes that don't have adjusable stab's, the stab is a good reference point. What I'll usually do is zero my meter on the stab then measure the thrust angle. If that looks reasonable I'll set the wings realtive to the stab - about .5 positive. This gets you started. Remember, you need to fly it to dial everything in. The bench setup is just to get you started.

It's important to make sure the plane doesn't move when you're taking all of these measurements. If you put it on a cradle, make sure it's strapped in really well. You don't want anything to move while you're making adjustments (other than the part you're trying to adjust) or else your measurements will be inconsitent.

John Pavlick
Team Black Magic, Tech-Aero Designs