RE: Aviastar 46?
My buddy, "Flaps" Laffert and I have built 25 twins, so we are pretty familiar with how to make them work. Problems with twins come from inexperience and letting your buddies who have no knowledge of twins help you.
Use some out thrust on your plane if you can. It works. 8 degrees is ideal, but it looks like way too much. You don't notice it in flight. Any amount is better than nothing. I built and tested a plane with 8 degrees out thrust and took off with one tank half full and the other topped off. I did this with both engines and flew acro until the one with the low tank quit. The only way I could tell is the plane slowed down. Just to prove a point, I removed the original engines and installed a Thunder Tiger .46Pro/11-6 and a Thunder Tiger GP.42/10-6 and flew it that way. Couldn't tell a difference.
1. Break in your engines on a single engine plane first and get the needle settings right before putting them on a twin.
2. Use a mid range prop on the .46, something like an 11-6. Don't go for a small prop for speed or a large prop until you get things sorted out.
3. Set your engines individually. Crank one and set it, hold the nose up for a good 20 seconds, then shut down. Crank the other engine and set it. Top off tanks and start both and fly. Do not tweak the needles. You will probably get one too lean and have an in-flight failure. Trust me on this, 1,000 rpm difference is much better than 10,000 difference. Your best setting for a twin is slightly richer than for a single engine plane.
4. Forget a tach and syncing your engines. set both for reliable running and fly. Your flight setting should be SLIGHTLY RICHER than normal. With 2 engines running, they will tend to run leaner in flight. Don't go peaking them out or let your buddy peak them out.
5. Pull-pull is best for rudder. And also a strong servo-80-90 in-oz torque. If the plane comes with a rudder pushrod, install another control horn on the other side of the rudder and run a cable to the servo. Hold full rudder stick and try to straighten out the rudder both directions. If you can do it easily, you need a stronger servo or to stiffen the pushrod or install pull-pull. The rudder is going to save your *****, so get it right.
6. If the plane goes goofy in flight, or sounds funny, chop the throttle, get it under control and slowly add power, checking if you need rudder. I have seen to many guys try to stay at full power and lose it. You may not be able to hold the plane with full power on one engine. Setting it down level in the weeds is better than rolling over and dieing with one engine at full power.