heli_headcase
Key Veteran
Location: Hovering around Atlanta
| Going both ways...The rotational running direction depends on the intake porting timing. Most 2 strokes for model aircraft have a unidirectional, asymmetrical intake timing, meaning the period of induction is optimized to draw the greatest 'gulp' of fuel/air mix in one revolution of the crankshaft in one direction only. Examples of this type engine are ones with a rotary valve intake system, commonly through a port drilled through the crankshaft or via a rotating disk valve in the rear of the crankcase. This optimized intake timing is completely wrong for the strong air/fuel draw if rotated in reverse. Yes, some engines that are timed "wild" (very late closing intake timing) can run in reverse if conditions are right but their torque is low and can't easily sustain operation.
Other engines with symmetrical intake timing, reed valve and piston-port are key examples, will run equably well both directions as long as there's no issues with ignition timing. Glow or diesel ignition is symmetrical; spark ignition is not. It's easy to make the ignition timing work for reversed rotation if the means of triggering the spark are via an outside trigger sensor but if the trigger is part of a flywheel magneto system, reversing can be problematic.
Hope this helps.
HHC
So many heli's - too little time... |
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