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Author Topic: Electric Trim issues  (Read 8241 times)

Offline Jeff Prosser

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Electric Trim issues
« on: April 12, 2016, 12:55:59 AM »
I have 2 electric stunters, Legacy and Trivial Persuit, and neither of them will groove in level flight. Upright or inverted it's the same. The motor direction is the reverse of an IC engine which should be an advantage in some ways. One has a 2 blade prop and the other a 3 blade. Both have balance points in the recommended position.  Some flyers have gone to prop rotation in the IC direction, does this help this problem?  Does anyone have any suggestions that may help solve this ?  Is it an electric issue or another problem common to all models regardless of power used.

Offline Alan Resinger

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Re: Electric Trim issues
« Reply #1 on: April 12, 2016, 08:05:12 AM »
Jeff,
This is a fairly common problem with electric stunters.  I've been flying electric for 6 years now and noticed the problem with my first electric ship.  I've been able to cure the problem by making sure that there is absolutely no place in your control system that rubs against any interior structure.  Lead outs cannot touch any ribs , spars or wing landing gear mounts going through the wing.  The controls themselves must be silky smooth in their action.  I even change my lines frequently as any roughness or minor kinks will bind on the other line once you have done a loop and have a twist in them.  Even if the lines seem like they are alright, I change them after about 60-75 flights as I start detecting the lack of tracking in level flight just due to the roughness of the lines themselves.
You might want to try flying with a further forward CG than what the plans recommend.  Most electric flyers use a more forward CG location.
The general theory about the lack of tracking is that electrics lack the vibration of an IC motor which probably tends to prevent the tendency for the model to not hunt in level flight.   
Alan Resinger

Offline Tim Wescott

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Re: Electric Trim issues
« Reply #2 on: April 12, 2016, 09:33:47 AM »
The general theory about the lack of tracking is that electrics lack the vibration of an IC motor which probably tends to prevent the tendency for the model to not hunt in level flight.   

Reason being (goes the theory) that when you have a motor shaking the bejesus out of the plane, any "sticky" spot in the control system will get shaken loose.

Note that the "shake the bejesus out of it to eliminate sticky spots" is a recognized phenomenon and there's actually industrial systems that do this on purpose.  The theory part is only about whether that's actually what's going on with an electric.  No one's been willing to purposely put an out-of-balance prop on one to see if that helps.

You probably want to try all of the other usual solutions to hunting before you whack the airplane apart to reduce hunting.  Rig the controls so the elevator trails down (or is it up, when you have reverse rotation?), experiment with the center of gravity, etc.  If you're not a member of PAMPA it might be worth it to joint just for Paul Walker's trim articles, or read his articles in Flying Lines.
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Offline Igor Burger

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Re: Electric Trim issues
« Reply #3 on: April 12, 2016, 10:04:25 AM »
That problem can be caused by almost any trim misalighment, I just trimmed my new model and it was terrible in level before I cleaned all trim issues. Now it goes like on rails and I did not need to concentrate to just "that". It leads to that prop choice. Many flyers already found that pusher is not fully trimable prop on classic models (wing and landing gears under the thrust line), so my recomendation (if mentioned friction problesm are solved) is to use normal prop and concentrate to trim the model. Then you will see if there is still that problem or not.

However there are still few tricks which SOMETIMES help in this case.

Try motor downthrust ~1 deg (if it does not hurt figures)

If you have front line up, try to exchange them in LO guide, front line down stabilizes model (WITH TRACTOR PROP), and keep line spacing ~1" or even more.

If you have moderate stab LE diameter, try turbulators on stab, or try to deflect elevator little bit down. (if it does not hurt figures)

If you do any of those changes or if you change the prop, and if you have PW chard front of you, you will see that before judging whether it helps or not, you will need completaly retrim the model, only then you can say if it helps or not.

EDIT: and do not forget that IC model has tank with fuel which moves CG forward as mentioned in other posts, so if you have CG as per IC plan, you have it tail heavy
« Last Edit: April 12, 2016, 10:45:14 AM by Igor Burger »

Offline Mark Scarborough

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Re: Electric Trim issues
« Reply #4 on: April 12, 2016, 10:39:56 AM »
Jeff,
This is a fairly common problem with electric stunters.  I've been flying electric for 6 years now and noticed the problem with my first electric ship.  I've been able to cure the problem by making sure that there is absolutely no place in your control system that rubs against any interior structure.  Lead outs cannot touch any ribs , spars or wing landing gear mounts going through the wing.  The controls themselves must be silky smooth in their action.  I even change my lines frequently as any roughness or minor kinks will bind on the other line once you have done a loop and have a twist in them.  Even if the lines seem like they are alright, I change them after about 60-75 flights as I start detecting the lack of tracking in level flight just due to the roughness of the lines themselves.
You might want to try flying with a further forward CG than what the plans recommend.  Most electric flyers use a more forward CG location.
The general theory about the lack of tracking is that electrics lack the vibration of an IC motor which probably tends to prevent the tendency for the model to not hunt in level flight.   
Alan Resinger
As Alan said, its pretty common phenomenon with electrics, I am carrying my CG substantially forward of the GLow position

cant explain why, don't care why, just know its true,, and I still have more corner than I can reliably use even being my plane is 73 ounces,, and heavy,,
For years the rat race had me going around in circles, Now I do it for fun!
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Offline Randy Powell

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Re: Electric Trim issues
« Reply #5 on: April 12, 2016, 03:22:02 PM »
Yea, I've been shocked by how far forward the CG ends up and how far aft my leadouts end up. Seems like most things I learned about trimming are suddenly void.
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Offline Mark Scarborough

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Re: Electric Trim issues
« Reply #6 on: April 12, 2016, 08:58:25 PM »
Yea, I've been shocked by how far forward the CG ends up and how far aft my leadouts end up. Seems like most things I learned about trimming are suddenly void.
some of us tried to tell ya, we did,,
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Offline Jeff Prosser

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Re: Electric Trim issues
« Reply #7 on: April 13, 2016, 01:40:41 AM »
Wow, thats quite a response.  Thanks to Alan, Tim, Igor and Mark for your helpful comments.
The controls are quite free and smooth but the lines are getting a little old so I will change them and see if that helps a bit.
I have the leadout positions about as far forward as they will go so I will try moving them back again.
The Trivial Pursuit plan does not show a CG position but it is currently forward of the high point of the wing probably a little forward of the position for IC. I can try moving that further forward.
I have tried adjusting in different amounts of down elevator but that does not seem to have helped much. It currently has more down than it probably should.  It does not have motor down thrust, its at zero.  Turbulators may help.
The TP has front line up so that could be changed that but it's more difficult to do.
That's a lot of changes to work on.  I will need to do them do them one at a time to judge the effect.
As Igor has said that many flyers have found that a pusher prop is not fully trimable I will have to try a normal prop. 
I will let you know how it works out.

Offline Peter Germann

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Re: Electric Trim issues
« Reply #8 on: April 13, 2016, 04:52:26 AM »
I have just done the first three flights with a new model yesterday; Symmetria, built-up wing Polyspan/Silkspan covered, 683 sq.in., 61 oz. The airplane is all in-line and, in order to generate in-line drag, is equipped with a retracable landing gear. Flaps and elevators are set at zero deflection. C.G. is at 7.3 in from hingeline fwd. Following advice found here on stunthanger, the stabilizer leading edge is knife edge sharp and I use a lightweight 13 x 6 AeroNaut Carbon CAM pusher prop at 8'800 RPM. So far no level flight tracking problem.
Peter Germann

Offline Don Coe

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Re: Electric Trim issues
« Reply #9 on: April 13, 2016, 07:54:40 AM »
Great thread. Thanks to all.   H^^

Offline Jeff Prosser

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Re: Electric Trim issues
« Reply #10 on: April 27, 2016, 05:24:25 AM »
Hi
I have tried nearly all of the suggestions given and the model is now reasonably stable.
Some things didn't seem to make a lot of difference but others really helped.
Moving the leadouts back helped but I eventually went too far and had to come back a bit. Moving the CG forward helped but you can also can go too far.
Cleaning the lines a lot helped so I tried new lines and that was even better so the lines must become a bit rough with use and drag on each other. I didn't think this would be an issue as the model has good tension but it does make a difference.
I borrowed a tractor prop but it was too large and I couldn't slow the model enough to get a really good feel for it but on the last (slowest) attempt it felt a lot better so still some testing to be done there.
It seemed that there is no instant cure, just a lot of different things that each contribute a bit to get it right.


Offline Tim Wescott

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Re: Electric Trim issues
« Reply #11 on: April 27, 2016, 09:26:41 AM »
Have you read Paul Walker's trim articles?  Paul's philosophy is to trim the airplane so well that it flies itself, and then go add your bit on contest day.  It seems to work fairly well for him.

Paul Walker on Stunt.
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Offline Randy Powell

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Re: Electric Trim issues
« Reply #12 on: April 27, 2016, 03:03:19 PM »
Mark,

Yo Mama!
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Offline Tim Wescott

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Re: Electric Trim issues
« Reply #13 on: April 27, 2016, 03:06:18 PM »
Perhaps the answer is a big electric motor in the nose, and a Cox 049 on each wing, with enough fuel for 6 minutes of flight.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Randy Powell

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Re: Electric Trim issues
« Reply #14 on: April 27, 2016, 03:14:16 PM »
Tim, only you could come up with that.
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Offline Mark Scarborough

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Re: Electric Trim issues
« Reply #15 on: April 27, 2016, 03:42:42 PM »
Mark,

Yo Mama!
hey you leave my momma out of this,,

move your cg forward,, leadouts back, and increase your elevator to flap ratio,, all will be golden,,

or dont,, then I can smoke ya in Roseburg muah hahahaha S?P
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Offline Tim Wescott

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Re: Electric Trim issues
« Reply #16 on: April 27, 2016, 04:36:09 PM »
Tim, only you could come up with that.

That's why they pay me the big bucks.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Jeff Prosser

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Re: Electric Trim issues
« Reply #17 on: April 28, 2016, 05:36:45 AM »
(Have you read Paul Walker's trim articles?  Paul's philosophy is to trim the airplane so well that it flies itself, and then go add your bit on contest day.  It seems to work fairly well for him.)

Thanks for the link Tim.  I will go thru that.  There's a lot there to absorb and it will take some time to read and understand.


Offline Randy Powell

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Re: Electric Trim issues
« Reply #18 on: April 29, 2016, 11:18:38 AM »
Mark,

We'll see.

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Offline Mark Scarborough

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Re: Electric Trim issues
« Reply #19 on: April 29, 2016, 02:02:33 PM »
Mark,

We'll see.


yepper,, looking forward to it Randy,, really looking forward to it, its been awhile since we were both at a contest, especially with Pat there,,
For years the rat race had me going around in circles, Now I do it for fun!
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Offline Dean Pappas

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Re: Electric Trim issues
« Reply #20 on: May 03, 2016, 08:58:48 PM »
Hello Jeff,
I'd strongly suspect that the pusher prop discussion is a red herring.
There are sooo many way to end up with an otherwise nice flying plane with a groove or tracking problem, and I have seen many planes with pusher props that were trimmed to an excellent state.

Regards and let us know your progress,
  Dean P.

"Nirvana is a state of trim."
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Offline Jeff Prosser

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Re: Electric Trim issues
« Reply #21 on: July 20, 2016, 01:26:40 AM »
I have finally managed to get the Trivial Pursuit tracking really well.  I tried pretty well all the suggestions here - except Tim's idea using the Cox 0.49s - so thanks for everyone's input.  There were many idesa that helped a bit but there were 2 things that made a significant difference.
Keeping the lines clean and using new lines was one thing and changing over to a tractor prop was the most significant. I bought a 2 blade carbon  prop from Brian Eather which is beautifully made and that really did the trick. It uses less battery too, so that's a bonus.
I have gradually retrimmed the model and many things like balance points and leadout positions and elevator "droop" have gone back to similar positions to when I started out but the model now grooves really well.
I am still unsure why propellor rotation has so much effect but that's what fixed this model.  At the World Champs in Perth I saw quite a few competitors with well trimmed models using pusher props so maybe there are other options but for me, with this model, it was mostly prop rotatation that fixed it.
It's been a worthwhile exercise as I have learnt so much about trimming a model and the effect that various items have.

Offline Igor Burger

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Re: Electric Trim issues
« Reply #22 on: July 20, 2016, 05:02:47 AM »
Thrust line over the wing and landig gear drag pushes nose down, while precession of the tractor compensates it. That is result of 50+ years evolution. The pusher does it just opposite. That is the difference.

Offline Randy Powell

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Re: Electric Trim issues
« Reply #23 on: July 20, 2016, 01:10:02 PM »
Mark,

"then I can smoke ya in Roseburg muah hahahaha  S?P "

How's that work out for you?
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Offline Mark Scarborough

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Re: Electric Trim issues
« Reply #24 on: July 20, 2016, 01:37:25 PM »
Mark,

"then I can smoke ya in Roseburg muah hahahaha  S?P "

How's that work out for you?
well see its like this,,,,,,,,,

that was all part of the plot to get you complacent,, and then I will p0ounce,,  D>K
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Offline Randy Powell

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Re: Electric Trim issues
« Reply #25 on: July 20, 2016, 01:43:48 PM »
Should be fun.
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Offline Jeff Prosser

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Re: Electric Trim issues
« Reply #26 on: July 20, 2016, 07:26:45 PM »
Thrust line over the wing and landig gear drag pushes nose down, while precession of the tractor compensates it. That is result of 50+ years evolution. The pusher does it just opposite. That is the difference.

Thanks Igor, that seems logical.

Offline Mark Scarborough

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Re: Electric Trim issues
« Reply #27 on: July 20, 2016, 08:02:23 PM »
Should be fun.
Hey its my fantasy,, I can live there if I want to LOL
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Offline Keith Renecle

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Re: Electric Trim issues
« Reply #28 on: July 21, 2016, 12:27:33 AM »
I have just done the first three flights with a new model yesterday; Symmetria, built-up wing Polyspan/Silkspan covered, 683 sq.in., 61 oz. The airplane is all in-line and, in order to generate in-line drag, is equipped with a retracable landing gear. Flaps and elevators are set at zero deflection. C.G. is at 7.3 in from hingeline fwd. Following advice found here on stunthanger, the stabilizer leading edge is knife edge sharp and I use a lightweight 13 x 6 AeroNaut Carbon CAM pusher prop at 8'800 RPM. So far no level flight tracking problem.
Hi Peter,

Your Symmetria design sounds very interesting. Adding retracts to an in-line model is something that I would like to try as well.......just for fun! Could you please post a few pictures if you don't mind? Thanks a lot.

Keith R
Keith R

Offline Peter Germann

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Re: Electric Trim issues
« Reply #29 on: July 26, 2016, 07:30:58 AM »
Hi Peter,
Your Symmetria design sounds very interesting. Adding retracts to an in-line model is something that I would like to try as well.......just for fun! Could you please post a few pictures if you don't mind? Thanks a lot.
Keith R

As the loss of a prop blade in flight resulted in me having to build a now nose section now, I am sorry to have no pix, Keith. I believe to remember Tim Wescott publishing a related video here somewhere.
The total weight of the retractable gear components was 84 Grams and, despite it looks fine in flight, its up or down effect on flight characteristics was (for me...) hardly noticable and as far as energy saving is concerned it's hardly worth the effort. However, the looks are hot, indeed.
Peter Germann

Offline Dean Pappas

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Re: Electric Trim issues
« Reply #30 on: July 26, 2016, 10:22:34 AM »
Yes, Peter ...
We forget that Stunt is a beauty contest with technical sub-text! S?P
Best Regards,
  Dean P.

P.S. I would have liked to have seen a picture of the Symmetria, too.
Dean Pappas

Offline Keith Renecle

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Re: Electric Trim issues
« Reply #31 on: July 26, 2016, 11:24:31 PM »
Thanks anyway Peter, that's a pity because it's always nice to see your projects. I agree with the hot looks as well.

Keith R
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