RE: Aircraft rolls with up elevator  
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All Forums >> RC Airplanes >> Aerodynamics >> RE: Aircraft rolls with up elevator
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RE: Aircraft rolls with up elevator - 9/23/2007 8:53:31 PM   
KurtS


 

Posts: 48
Joined: 1/14/2007
From: Roseville, CA, USA
Status: offline 		I think you were asking me since I was the one who started the thread. As you can see, it's nothing fancy, in fact it's pretty small and simple. 46" span, 4lbs, not an ARF.

K


quote:

ORIGINAL: da Rock

I've not been able to find where you identify the model. What is the airplane?





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(in reply to da Rock)
       Post #: 26

RE: Aircraft rolls with up elevator - 9/24/2007 12:28:25 AM   
da Rock



Posts: 6980
Joined: 10/11/2005
From: western, NC, USA
Status: offline 		That non-tapered wing is the best layout to resist tip stalls. Although flaring ailerons for looks screws that up a bit.

How much aileron trim is there on the airplane? Are both ailerons pointing straight back?

Look at the wing for warps.

Not an ARF..... if you built that, you did a very nice job.

(in reply to KurtS)
       Post #: 27

RE: Aircraft rolls with up elevator - 9/24/2007 12:40:35 AM   
KurtS


 

Posts: 48
Joined: 1/14/2007
From: Roseville, CA, USA
Status: offline 		Thanks! Built it from a lazer cut short kit of an old Midwest Little Stik.

Ailerons are dead even in level flight and man, I don't see any warps and believe me, I have looked and looked.

K

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       Post #: 28

RE: Aircraft rolls with up elevator - 9/24/2007 1:47:22 AM   
BMatthews



Posts: 9011
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		What's the engine on it? It seems terribly big for the size of the model. If it's a 40 as I suspect it may just be that you're getting some torque rolling effect.

And another hearty WELL DONE! She looks great.

< Message edited by BMatthews -- 9/24/2007 1:48:24 AM >

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       Post #: 29

RE: Aircraft rolls with up elevator - 9/24/2007 1:48:57 AM   
Kreag


 

Posts: 4
Joined: 12/31/2006
From: Kirkland, WA, USA
Status: offline 		Mine is a Seagull Extra 260 (90 size with a Saito 125)

Sometimes just pulling back to correct attitude will drop the right wing a little (which is the part that frightens me). Speed of the aircraft doesn't seem to be a factor, fast.. slow.. doesn't matter. I have flown the Seagull Yak54 same size plane almost the same thing, and I know what this plane *should* be capable in general. This is nothing fancy just a gentle pulling up to point the nose towards the sky will start the process. If I take off and let the speed bring the nose up (along with some very gentle up elevator) everything is just fine. I should note that I have quite a bit of expo on the elevators, and I also have the throws set very low to begin with.

(in reply to KurtS)
       Post #: 30

RE: Aircraft rolls with up elevator - 9/24/2007 2:02:33 AM   
KurtS


 

Posts: 48
Joined: 1/14/2007
From: Roseville, CA, USA
Status: offline 		That engine is a .45 FSR and it never flew with it. It has an Evolution .36 on it now.


quote:

ORIGINAL: BMatthews

What's the engine on it? It seems terribly big for the size of the model. If it's a 40 as I suspect it may just be that you're getting some torque rolling effect.

And another hearty WELL DONE! She looks great.


(in reply to BMatthews)
       Post #: 31

RE: Aircraft rolls with up elevator - 9/24/2007 6:23:36 AM   
BMatthews



Posts: 9011
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		Try doing some loops with the engine at about 1/3 power and dive to get the speed needed to do your loops. If it tracks straight or at least straighter than at full or near full throttle then you may have your answer.

Some fine tuning of side thrust may help a lot but in the end that size of engine just has a lot of torque on a model of that size.

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       Post #: 32

RE: Aircraft rolls with up elevator - 9/25/2007 4:25:52 PM   
cncswiss1


 

Posts: 210
Joined: 7/15/2004
From: Indianapolis, IN, USA
Status: online 		the right side 'ron looks like it's drooping a bit to me.

check the wing torsional strength for evenness from side to side, if the wing twists under load you might have "incedence on demand" going on here. do this with the wing mounted in the plane to check the mounting system as well.

if it drops the right wing while upright and elevator is added, what wing does it drop while inverted and you pull negative? (down elevator while inverted) if the same wing drops (on the other side) I'd say lateral balance needs checked.

and for yucks raise the TE of both rons 1/16 to 1/8 above center, this will help reduce the snap happy problem.


another note, single 1 part elevators have been known to flex and have an "aileron" effect depending on where the horn is mounted.

(in reply to BMatthews)
       Post #: 33

RE: Aircraft rolls with up elevator - 9/25/2007 4:49:02 PM   
daven



Posts: 7020
Joined: 12/7/2001
From: Andover, MN, USA
Status: online 		Don't know whats causing it, but I know what I would do to fix it.

I would mix counter acting aileron to up elevator. Start with about 5% and increase it in small increments until the mix takes out the unwanted roll.

Start small as it may cause other issues and is only masking the real problem (which we don't know what is).

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(in reply to cncswiss1)
       Post #: 34

RE: Aircraft rolls with up elevator - 9/25/2007 10:28:00 PM   
mflander


 

Posts: 245
Joined: 5/23/2005
From: Elk River, MN, USA
Status: offline 		I have seen this exact problem in a single piece elevator before as mentioned above. If it is rolling to the right and the elevator was flexing, I would assume the control horn was on the left side of the elevator(when looking from tail to nose). It doesn't take much flex on the elevator to cause a roll, especially if you have an aft cg.

Hope this helps!

(in reply to daven)
       Post #: 35

RE: Aircraft rolls with up elevator - 9/25/2007 10:32:36 PM   
daven



Posts: 7020
Joined: 12/7/2001
From: Andover, MN, USA
Status: online 		Elk River, Minnesota!

My home town!

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(in reply to mflander)
       Post #: 36

RE: Aircraft rolls with up elevator - 9/25/2007 11:31:46 PM   
KurtS


 

Posts: 48
Joined: 1/14/2007
From: Roseville, CA, USA
Status: offline 		Interesting idea. Here's a shot from the other side. The control horn isn't that far off center but I suppose the elevator could be flexing. And since the horn is on the right side of the elevator, when giving up elevator the right side would be under a stronger pulling force from the pushrod than the left side and that would possible make the aircraft roll to the right which is exactly what it does when you give it up elevator. And the more up elevator the worse the roll. As stated in an earlier post of mine, if the elevator input is large, the airplane comes out of a loop on a 90 degree different heading than when it started.

More to look into but this theory sounds plausible.

K




quote:

ORIGINAL: trixer

I have seen this exact problem in a single piece elevator before as mentioned above. If it is rolling to the right and the elevator was flexing, I would assume the control horn was on the left side of the elevator(when looking from tail to nose). It doesn't take much flex on the elevator to cause a roll, especially if you have an aft cg.

Hope this helps!



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< Message edited by KurtS -- 9/25/2007 11:32:26 PM >

(in reply to mflander)
       Post #: 37

RE: Aircraft rolls with up elevator - 9/25/2007 11:34:38 PM   
KurtS


 

Posts: 48
Joined: 1/14/2007
From: Roseville, CA, USA
Status: offline 		Yeah, perhaps a bit. It hadn't yet flown when those pictures were taken. Before the first flight I had all the clevises loose and tweaked all the surfaces to be neutral. Good eye though!

K

quote:

ORIGINAL: cncswiss1

the right side 'ron looks like it's drooping a bit to me.



(in reply to cncswiss1)
       Post #: 38

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