If you have the Futaba radio, 8 channel, Don Ed???? has a book about how to program it. In the back of the book, he talks about how to do this program,,,,,,,,BUT!!!!!!!! Do not follow it exactly!!!
Per the instructions, the mix works from IDLE up. DO NOT DO THIS!!!
The problem is that while taxiing to the runway, every time you hit the rudder, one engine will speed up.This causes the plane to vere off to one side, now you counter and the other engine comes on the opposite way, and on and on!!!!!! You end up chasing the plane........NOT GOOD.
I cannot tell you exactly how to program each radio, but only allow it to happen above 50% throttle and retard one engine. Must set max limits to avoid over driving the servos.
Basically, using mixes, if the plane is going to turn right, as a hammer head, you input rudder to the right and the right engine retards a given amount. This gives left engine more authority to pull the plane to the right, and visa versa.
Imagine now a knife edge flight, the lower engine is at full throttle and the upper engine is 60% or whatever. This helps hold the plane in knife edge beyond only aerodynamic lift.
Now, imagine the flat spin. One engine pulling the plane round faster than a single engine couple do........worried to get out of the spin?.......reverse the rudder direction, and the thrust stops the spin and out you fly as the engines now are pulling in opposite direction to the spin. Neat!!!!!
I now use it on all of my aerobatic planes, but not warbirds.
It will work best on the twin fuse type bashes, but my Ultra Sport 100(2) also uses it. Now, in the past, I have warned against wide engine spacing, and still do for most planes and learning to fly twins, due to engine out problems, but with a plane that you plan to do aerobatics, the farther apart the engines, the more this mix will benefit the performance. There is of course a trade off with control with wide spacing. Choice is up to you.
One more idea, Morris Hobbies has an electrical mixer to do just this mix without the aid of a computer radio. Have not tried it, but have seen the instructions. He sells it for his fun fly twins.
Good Luck,
Twinman