S-56, S-60, Cypher-2
Shawn,
From before my time the S-56, and the S-60 were both dual engine recips. And, I think I remember reading somewhere that the Cypher-2 UAV had dual recips as well.
But, if you think it through, what's the big deal? Pretend some mechanic mis-rigs the throttles in your dual engine recip such that one of them has 25% of the displacement compared to the other. Now head off into the wild blue yonder. As you pull pitch, the engine with its throttle more advanced will do all the heavy lifting. You have significant collective pitch, and significant throttle on both engines even though they are mis-matched. What happens to the engine with the retarded throttle? It doesn't just stay at idle. It will rev up until it hits the brick wall of the rotor system, then it won't accelerate any more. Everything will stay at the same RPM, both engines and the rotor system. Equivalent rotor RPM, that is. So none of your 3 needles will split. But, the engine with the retarded throttle is adding a lot less torque to keep the rotor turning, the other engine is adding a lot of torque. Not good for the hard working engine, or the input shaft/gears/bearings it is hooked to, but it will work.
A good analogy is a tandem bike. Similar overrunning clutches and everything. The guy in the front works hard, pedals up the hill. The guy in the back spins his pedals just as fast, but doesn't put any effort into it. Works fine until the guy in the front has a coronary.
How do you balance out the torque between the engines? I don't know how they do it, if the pilot has 2 throttles or if they do it in rigging. But either a torque measurement or manifold pressure should be close enough of a measurement to keep everybody happy.
-- IFMU