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Trim Settings Change While Flying

Old 10-23-2017, 05:49 PM
  #1  
garyp1029
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Default Trim Settings Change While Flying

I have been flying my GWS Formosa for over two years. The last few times the trim settings, particularly the elevator, change without my touching the trim switches. Have made successful emergency landings so far. Have checked the servos--they seem OK---and done a successful range check. What could be causing this--Transmitter, ESC, Receiver, Servos??? Which would be the most likely suspect? the least likely? Thanks. Gary
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Old 10-23-2017, 06:19 PM
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Wildflyer
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I have had the same thing happen.
I finally realized it wasn't the radio system at all. It was the way I was storing the plane.

My plane was all EPP foam, and during storage, one or more control surfaces were touching or laying on something. This caused a slight warp, but during flight the warp relaxed.

Of course I would trim the plane at the start of the flight and then have to retrim later.

I changed how I stored the plane, being careful not to put stress on things and it flew fine.

I don't know if this is what is happening to your plane.
I would try to look at exact servo positions before and after the trim changes if possible.
That would tell you if the servo is moving.

I hope this might help
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Old 10-23-2017, 06:26 PM
  #3  
firemanbill
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Agreed, especially with older foam, they just don't last forever. A little bit of softness and going from heat to cool or cool to heat causes fluctuations in the foam. Doubt you have any issues with your radio. you just need to check it as soon as you get airborne and adjust.

Now on the other hand you say emergency landings... is it so bad it is not flyable? if so you have bigger issues somewhere.
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Old 10-23-2017, 06:29 PM
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solentlife
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I have the Hobby King version of the Formosa .... and I noted the foam hinging was getting 'imprecise' ... so I cut and refitted. Later when I covered with 'nylon and PVA' giving it a really rock hard but light skin - the hinge areas were left free of PVA but the nylon helped as well.

Then I didn't have trim problems.

I would check those hinge lines and see if any cracks or splits are starting. If they are - then as you go through manoeuvres / attitude changes - they let surfaces 'adjust' !!

Just a thought.

Another is servo arms ... I've had a number of servo arm screws loosen .. then arm can 'slip' a spline ... need check they are tight every so often.

If you have the original internal servos ... check that the control rod runs are not flexing ...

Nigel
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Old 10-23-2017, 08:39 PM
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formontoya
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I have a wing that the hinge is a little stiff...if I do a full throw roll it will hang a bit in that direction. do a full roll in the opposite direction to center it and it's fine again...
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Old 10-24-2017, 12:18 AM
  #6  
birdDog
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Check your servo arms very well.
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Old 10-24-2017, 07:17 AM
  #7  
solentlife
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Originally Posted by formontoya View Post
I have a wing that the hinge is a little stiff...if I do a full throw roll it will hang a bit in that direction. do a full roll in the opposite direction to center it and it's fine again...
That's common with foam hinged models when the surface is not worked well before connecting up. I always work my surfaces back and forth a lot till they free up before setting up. If it doesnt- free up - then its cut both surfaces and hinge properly.

I would be inclined to disconnect control rod .... flex that surface till its free ....

Stiff hinge can create crazy trimming !

Nigel
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