I am making a rotorcraft that has two petrol engine powered rotors. Obviously to prevent torque induced spinning I need the two rotors to spin in opposite directions. Can I simply start one engine in the opposite direction without any problems? From what I have gathered this is possible with two-stroke engines but not four-stroke. Plan B is to duct them and use control vanes.
>This because you can't reverse even a two stroke engine.
I think you can with total-loss 2 strokes, if you can change the ignition timing. With small engines it's just a dynamo. There may be ventilation issues but that's minor.
The reason you can't do it with 4-strokes is because the valve order is basically fixed by the camshaft. Simple 2-strokes got no cams, just reed valves
"Modern" 2-strokes are closed-crankcase, and have tappet valves (with a camshaft). Stuff like (US) marine/outboard engines--but then, none of them are cheap $$$$$$$$
You can still drive *vintage* road-legal 2-stroke cars and motorcycles in the US, but nothing sold now with a 2-stroke is street-legal.
The last motorcycle that is legal is a Yamaha 2-stroke ricebike, from 1982 I thinks?... a long time ago. And the last car was even earlier, late-1960's / early-1970's I think.
Wouldn't the far simpler solution be to split the output of a single engine and reverse one with gearing?
You don't have to worry about power output being unbalanced, you don't have to worry about twinning the throttle and you'd be generally cutting your moving parts almost in half.
I can't promise you, but I'm also pretty sure that you can get a significantly better power to weight ratio from a single engine versus twin.
>There's no reason you can't run a 4 stoke on reverse if you have control of the spark and injection, just purposely misfire to skip cylinders.
when there is no fuel or spark and the engine is spun in the normal direction, a 4-stroke engine acts like an air pump: it sucks air in through the intake, and expels it out the exhaust....
to get it to run backwards, you would either need to switch the intake & exhaust connections, or you would need to make another camshaft
the 2-strokes that just use reed valves & expansion chamber pipes will do this tho. all you change is the ignition coil and spin the other way to start them
there is at least one aircraft engine that you can get like this--you can order it to spin either direction.
the ones some people used on Cri-cris are like this.
too heavy and complex.
Also from my own research small engines give better power to weight ratio. Probably because bigger engines need thicker cylinder walls and volume increases weight by a power of three. I dunno though maybe I just found shit engines.
Unfortunately it is something that I wish to patent. That is the entire reason for this build; to test that control system. However to titillate your tastebuds I'll share some of the failed ideas. Idea 1 was hydraulic, failed because to work it would need custom lightweight pumps whoch was way beyond my engineering capability. Idea 2 was continuous variable transmission, failed because the good ones are too heavy and complex and the simple ones are ridiculously inefficient. Idea 3 was retractable propellers, failed because centripetal force was too great for servos, also no less complex than a swash. Finally the last failed idea was to run the engine throuh a fluid coupling and eddy-current brake. Failed because heavy and inefficient. This current top secret idea is so far working well, this could be it, flying car time.
You should probably make sure your radical ideas aren't already incorporated into the V22 Osprey.
>You should probably make sure your radical ideas aren't already incorporated into the V22 Osprey.
I don't know shit about rotorcraft, but have you considered variable pitch rotors? I'd imagine it would be responsive and easy to translate to an electronic controller using a servo. If you are looking to scale this up beyond small drones you are going to be using larger and less responsive engines that won't be suitable for fine/quick control.