Sep 20, 2012, 06:59 PM
Joined Sep 2010
I may have posted something similar to this in the past, but it's worth bringing back up for anyone that missed it...
Plenty of old FS twins that used identical rotation on both engines.
The problem with those was that you have a critical engine, and it occurs on the engine that swings a blade downward on the outside of the nacelle.
In other words, if you have CW rotation engines as viewed from the rear, the critical engine is on the RH side.
When you have positive AOA, the downward blade gets more of a bite and produces the majority of the thrust.
Since this downward blade is farthest from centerline, you get more adverse yaw when the LH engine quits than you would if it was the other way around.
Sometimes it's not a big problem, sometimes it's a very dicey situation.
That's the reason for so many twins to have opposing rotation engines, to eliminate a critical engine issue.
Quite a few twins out there that would be ridiculously unsafe if it weren't for counter rotating engines, so there's definitely a reason for it.
For the JPower, it's not an issue to be concerned with because you're pretty much screwed if EITHER engine quits LOL
I've had engines quit on both sides and I couldn't tell the difference in handling between the two...your only option is to cut throttle and hope you have some airspeed or altitude to play with.
Programming differential thrust only reinforced my idea that counter rotating props make very little to zero difference at this scale (or perhaps it's just this model?).
Reversing the mix on the diff. thrust so that the rudder works correctly and the motors work counter productively (ie left rudder normally spins up the right motor, but now it spins the left) had given me a great idea how much more overpowering the thrust from the motors was in comparison to the effectiveness of the rudders.
It was like the rudder was dumbed down to 50% rates, favoring thrust instead of rudder.
To make a long story short, if you lose a motor on the JPower and attempt to maintain level flight with full rudder deflection, it'll be like flying with 50% opposite rudder input until you chop power.
So, is there any advantage to having counter rotating props?
Sure, it's actually more efficient in both theory and practice.
You might not notice it, but the airframe is actually trimmed somewhat to mask the P-factor.
Eliminate the very slight deflections on the control surfaces and the airframe will be somewhat cleaner aerodynamically.
You'll also notice that there is some P-factor on takeoff, but not nearly as much as a single engine taildragger.
Imagine jamming the throttle from a standstill and not veering off even the tiniest bit, not favoring a wing during a powered stall, or rotating while attempting to hang it on the prop...there's an advantage to that as well.
All in all, there are advantages to counter rotation, but you have to weigh them against finding a scale prop to match or going with a non scale prop (which eliminates the scale advantage).
I was happy with mine just the way it was, but if I could find the same prop in opposite rotation just as easily I'd probably go that route instead.