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Spektrum DX18 variable mix

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Old 05-10-2017, 06:19 AM
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mlr53
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Default Spektrum DX18 variable mix

I have my plane trimmed to fly level at a throttle setting of about 1/3 stick. Is it possible to set a varying throttle elevator mix from there that would add down elevator as the throttle is increased so that the plane would continue to fly level as the throttle is advanced? Do you have to set multiple mixes for each advanced throttle position or is there a way to have the mix vary the amount of down elevator as the throttle is advanced?
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Old 05-10-2017, 08:24 AM
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You most likely have either a CG problem or an engine thrust angle problem. Generally speaking, if the nose comes up when power is added, it's a thrust angle problem. Best to get that fixed before trying to compensate with radio mixes.
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Old 05-10-2017, 10:16 AM
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Zeeb, a plane flies from lift generated by the wings either from airfoil generated lift or angle of attack. Either way if you trim it to fly level at one airspeed, then increasing the airspeed will generate more lift and the plane will climb. Slowing the airspeed it will generate less lift and therefore descend.
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Old 05-10-2017, 11:08 AM
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If your plane is a high wing configuration and the nose pitches up with an increased throttle, it is a thrust vector problem as Zeeb stated. Every high wing plane I’ve had either does this or would if the engine weren’t angled down. If the airplane climbs because the lift increases as the speed increases, that is what airplanes suppose to do.

Yes, you could set up a program mix to add down elevator as the throttle increase. But you have to be extremely careful in not having too much down-elevator mix. I’ve done this on my electric powered sailplanes where it wasn’t possible to alter the thrust line. It is very disconcerting to launch a plane and it dives to the ground when giving it power and drops to the ground when letting up on the throttle.

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Old 05-10-2017, 05:50 PM
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Originally Posted by mlr53 View Post
Zeeb, a plane flies from lift generated by the wings either from airfoil generated lift or angle of attack. Either way if you trim it to fly level at one airspeed, then increasing the airspeed will generate more lift and the plane will climb. Slowing the airspeed it will generate less lift and therefore descend.
Hmmm....

"Monte
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Four digit AMA number, District 6 Pattern VP, CK Aero Team, how in the world could I question those credentials?

Would you like me to show you my credentials? Commercial Pilot License with Instrument and Multi-Engine ratings? How about my A&P Mechanic licenses for full scale?

You should not make such assumptions regarding another member's post as you did with mine.
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Old 05-10-2017, 07:51 PM
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Zeeb, Sorry I upset you. Let me add to my credentials as well. Pvt Pilot single engine land, Instrument and glider rating. Also a certified Louisiana ultralight instructor. But I take your point. My issue is not a thrust issue as the plane does not pitch up at the addition of throttle, it climbs gently as speed increases. It has 0.5 degrees of down thrust in the engine, is a low wing symmetrical airfoil with 0.5 degrees of incidence in the wings.. My apologies as I did present the situation by saying when I add power instead of as the speed of the plane increases. Thanks for your input.
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Old 05-11-2017, 05:51 AM
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Yes, a mix of THR > ELE will give you an elevator trim change with throttle changes.

I would set it up first on a switch so that I can turn off the mix and revert to normal flying until I get the amount right. You can also use the Offset function to adjust where the mix starts to apply.

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Old 05-11-2017, 10:06 AM
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My Motion RC RocHobby Strega foamy does that at high sped i just fly it with the down elevator
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