Playing with a twin.

[Sparky Paul]

With a nudge from a question on another forum here, I took my long suffering Gentle Lady kludge and made it a twin.
The purpose is to investigate the flight control situation with the (rare in electric) single motor situation.
Using 2 GWs 300-E, 11x8 GWS props, Wattage 30s ESCs.. one for each motor, 8x800 nicad.. channels 3 (left motor) and 6 (right motor) mixed, with the knob on channel 6 used to cut that motor.
Flying weight 45 oz.

Not unexpectedly, with full power on the left motor and the right motor off, the amount of turning to the right while holding the plane in one hand on the ground is significant.
Goodly performance on both motors.
In flight, after a few "comforting" passes, with the power on both pulled back to maybe 30%, then cutting the right motor, the plane can fly, and turn left.
Any more power than that minimal amount and there isn't sufficient rudder authority to prevent a right turn.
I plan to add a co-pilot to the rudder, but don't expect to see any change in controllability at higher power levels.

[Ollie]

Paul,
I recall, you had a designed twin that carried a ~5 to 8 pound load. Could you help?
http://www.rcgroups.com/forums/showthread.php?t=399796

[HELModels]

Sparky, how about trying smaller diameter props? Why? To see if smaller prop disc radius can raise the rudder authority limit, by reducing the band of asymmetry. An appropriate smaller prop would have to put out as much as original test prop to get a good comparison, n'est pas?

[Sparky Paul]

Electro, smaller diameter and closer in works fine for control after one motor stops.. it's the initial stoppage at power that creates the problem, with the sudden change in flight attitude and violent manuvering.
Fingering out which motor quit and correcting that before impact.
My Co-pilot is broke... no response in roll, non-linear in pitch (which could be used in the roll axis by mounting it 90 degrees off, I'm not worried about pitch) and the remote channel is always on. Drat!

[Tom Harper]

Looks spiffy in the air. Must be a real floater.

[Sparky Paul]

Several flights today with and without the co-pilot..
The lateral channel's gain had no effect on the full throw of the rudder, the plane rocking back and forth the same at 3 different settings..
Took the co-pilot off (due to popular demand from the observers) and got a good flight with manual control.
With the right motor stopped, and the left motor at about 30% power, there's still enough rudder authority available to turn the plane to the left, which I feel is a reasonable criteria as the photo shows. Max throw is 35 degrees.
Much more power than 30%, and it goes straight, and more power, right only.
Which is expected.
Tony F suggested a lateral thrust change.. may try that.
The co-pilot needs some TLC.. :(

[biber]

If the two motors/props are squinting the plane will be forced to slightly slip towards the dead engine at single engine mode. That would give the tendency to roll against the yaw induced by the asymmetric thrust and might help the rudder to maintain authority.

biber

[Sparky Paul]

I tried some outthrust on both motors.. only a subjective improvement in the amount of power the left motor could have before the plane couldn't turn right.

[Sparky Paul]

And in a moment of sanity... decided to put the right motor on the front.
No reason, just because... :)
Flies the same.

[Tom Harper]

Sparky,

In #8 shouldn't the out thrust point the other way?

[biber]

Yes, Sparky, the very same thought came to me aswell, just like Tom said. Maybe you will have to try some bigger angle and into the other direction. That angles on the pic seems to be very little. To really get an effect you might have to try 10 degrees each or so. Even that won't hurt it too much.

biber

[Sparky Paul]

"..10 degrees.."
Wouldn't want it to look odd.. :)
As I can't get the operating motor much more than 40-50% power before the plane goes right irretrieveably except by powering up the right motor, I suspect with electrics, when one motor fails, saving the plane would be to cut power to idle, then determine which motor has quit, and adjust power/rudder to get the thing back.

[biber]

Hm, isn't it looking odd already :rolleyes: ? :D

biber

[Sparky Paul]

I skootched the motors out some more today.
With cruise power it handles well with either motor cut, turning in both directions without losing lateral control.

[Sparky Paul]

A secondary reason for moving the right motor forward other than just to do it actually prompted the move.
With the right motor pushing, the prop is very close to my left ear, which I am attached to, when launching the thing with my left hand.
Launching it today with my right hand, the left motor could go forward as well. :)
Twin pushers may be practical if it ROGs...

[tommy321]

That is awesome. That’s one of the things I love about this hobby… if you can think of it, you can try it out ;)

That looks identical to my gentle lady…. The plane that taught me and my dad to fly…. That is… a patchwork quilt of whatever covering we had left… filled with “aftermarket” gussets and braces. :D:D Brings back memories.

My gentle lady is in the basement rafters at the moment… perhaps I should resurrect it.

Tom