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Old Jan 23, 2014, 12:20 AM
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Jim Deck's Avatar
Valparaiso, IN
Joined Apr 2005
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Thrust line Advice

For those struggling to get the trust line correct when converting to a "winch in the nose", I offer this sage piece of "advice" from another forum:
"Model airplanes need right engine offset to counter-act the exhaust push from gas engines which always have the exhaust blowing out the right side. Electric motors don't have an exhaust therefore have no need for the offset."
Now you know why electric power is growing in popularity
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Old Jan 23, 2014, 05:10 PM
AMA7224 LSF1832
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:Who don't know that?
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Old Jan 23, 2014, 05:13 PM
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Lenny970's Avatar
Greeley, Colorado, USA
Joined Feb 2000
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I guess left thrust would be in order then if the glow engine were inverted!
Lenny
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Old Jan 23, 2014, 08:27 PM
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Fly Wheel's Avatar
Blackstock, South Carolina
Joined Sep 2007
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Then why do most electric planes have down and side thrust in their plans? Isn't there a prop effect that requires this?
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Old Jan 23, 2014, 08:48 PM
Balsa addiction since age 3
ScottSails's Avatar
Upstate NY
Joined May 2005
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Quote:
Originally Posted by Fly Wheel View Post
Then why do most electric planes have down and side thrust in their plans? Isn't there a prop effect that requires this?
Yes, its due to torque from the motor from twisting the prop... Surprisingly even happens on rubber powered planes...

Scott
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Old Jan 24, 2014, 12:05 PM
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Joined Aug 2009
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ALL single engine/motor prop planes will have the following influencing how much left and down thrust the plane requires.

* P Factor (asymmetric propeller loading) is what has great influence on a single engine prop plane wanting to yaw to the left. RPM, Blade Size and Pitch of the blade will all influence the amount of P-Factor

* Propeller Wash causes a twisting helix pushes on the left side of the tail causing the plane to yaw left

* Propeller Torque Effect causes the plane to rotate ccw if the prop is spinning CW which induces adverse yaw to the left.

I would seriously doubt that the influence of open stack exhaust would be any where as much of an influence of the above to cause adverse yaw.

And as you all know this yaw can be overcome by right and down thrust of the motor/engine.

Terry
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Old Jan 24, 2014, 01:45 PM
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United States, AZ, Chino Valley
Joined Apr 2013
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dead on

Terry is dead on about P-factor. It wouldn't matter if the prop were driven by fuel, electricity, or a very strong hamster. It's the fact that if the downthrust is proper each blade operates at a slightly higher blade angle of attack as it descends compared to when it ascends. This produces slightly more thrust on the descending blade side, causing a tendency to yaw.

If we ran a counter-clockwise motor rotation with a prop designed for that rotation, with the descending blade on the left, we would find a tendency for the model to yaw right.

Go easy, lateral thrust-line offset is easy to overdo, and in my opinion much less critical that getting the vertical alignment right to prevent unintentional looping on launch.
Diane
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Old Jan 24, 2014, 02:22 PM
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War is Peace's Avatar
United States
Joined Mar 2012
425 Posts
I build in about 2.5 degrees down thrust and then use the radio to mix in some down elevator in proportion to the amount of throttle. It only takes a few flights to get it dialed in. I don't worry about left/right as I'm usually steering the model in a particular direction during climb anyway.
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Old Jan 24, 2014, 04:44 PM
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San Diego area
Joined Jul 2006
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For SAILPLANES I think it is simpler to just mount the motor straight.

Then, mix elevator and rudder to the motor as required.

Craig
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Old Jan 24, 2014, 08:01 PM
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dion9146's Avatar
United States, KY, La Grange
Joined Feb 2006
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Quote:
Originally Posted by craigrrr View Post
For SAILPLANES I think it is simpler to just mount the motor straight.

Then, mix elevator and rudder to the motor as required.

Craig
That's what I have done on all of my e-sailplanes, then I just fly it. No mixing required.

After all, the object is to get it to a spot at altitude not fly it like a sport plane, right?

Dion
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Old Jan 25, 2014, 07:30 AM
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Wallingford, Ct
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For sailplanes it is easy enough to make any mixing/corrections with the stick. That is what it is for.
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Old Jan 25, 2014, 07:49 AM
AMA7224 LSF1832
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United States, DE, Seaford
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Yup, thumb/brain interface works for me.
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