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Darren_O

Aileron fouling wing

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Darren_O

Just setting up my Sigma II and I noticed the aileron servo wouldn't centre or go up much.

After inspection I can see the trailing edge has a depression fracture that fouls the aileron as it moves back inside the edge.

What's the best way of fixing this? Was thinking a little epoxy then a thin card holding it in position. But if there's a proper fix I'd appreciate your advice.

 

 

IMG_20161226_191540.jpg

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simon_t

You sometimes find the upper wing skin is too close to the surface (typically its the flaps that catch).  It is very easy to use a thin permagrit file or some medium carbide paper to cut back the upper skin trailing edge a bit.  In your picture, if you replace the playing card with carbide paper, face up, you can then take 0.5-1mm off the wing skin.  It doesn't take much to stop the problem, due to the geometry of wing skin to the aileron seal. (Crappy sketch attached)

Simon

IMG_0209.JPG

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isoaritfirst

Only addition I can make to Simon's excellent response is to check the hinge, and its supporting skin.

Most likely the solution lies in sanding - but just check,

Sometimes this can become weak and allow the aileron to move upwards (reference Simon's sketch) 

If it needs strengthening you could add some epoxy and microballoons to bridge it a little more to the rear spar.

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Austin

Same idea as Simon but I used to use a steel rule and scalpel and actually cut off 0.5 to 1mm of wing skin along the entire panel, I tried sanding but sometimes it gets an uneven finish, this sort of thing used to happen a lot on some designs. 

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Scram

I think it might be worth strengthening the breaks a little with some cyano.  I would slide a piece of thickish polythene in, in place of your card, so the cyano can't stick to the wiper etc.  Care not to use too much so it can run down into the hinge.

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Darren_O
On 12/26/2016 at 20:28, isoaritfirst said:

Only addition I can make to Simon's excellent response is to check the hinge, and its supporting skin.

Most likely the solution lies in sanding - but just check,

Sometimes this can become weak and allow the aileron to move upwards (reference Simon's sketch) 

If it needs strengthening you could add some epoxy and microballoons to bridge it a little more to the rear spar.

Bullseye, thank you :) Upon closer inspection the aileron is higher where it's catching. Part nearer fuse is seated right but the final third towards tip is slightly raised,looking at the wing I can see it's up by a mm or so.

Now, the hinge...my only experience is a plastic hinge on a balsa model. I can't even see a hinge here. Any tips? 

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isoaritfirst

Disconnect the clevises and fold the surface back to reveal the inside of the hinge line. 

Then if it seems necessary adds mix of micro balloons and epoxy to create a fillet up against the trailing edge spar. 

Leave to dry propped up so the epoxy wells into the right area, and hold the surface in place while it dries. Perhaps with the playing card jammed down the gap side. 

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Darren_O

Don't follow you, I've disconnected it and looked down the wing. It looks like about 50cm of the wing is depressed,aileron looks straight.  Out of my depth with this one and whilst I don't mind having a bash at my Ocelot and Banana I'm a bit wary of poking this with my uneducated paws it's far to pretty to cock up.

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Darren_O

 
Hard to see but Aileron raised/wing depressed mainly to the right of the cyano mark. 
I fixed the little crack, but this wasn't to blame for the fouling. 

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oipigface

Do you have any idea how large this problem is? If the fouling is slight, you could just sand away the underside of the wing skin. (Use a piece of 80 grit Aluminium Oxide paper glued onto a piece of 1mm glass fibre board.) if you need to strsighten the wiper or the false TE, you'll probably need to apply some heat. Protect areas of the wing and aileron from the heat, and blow a hair dryer at it. Go gently, you only need to spply as much heat as is necessary to soften the epoxy a little. Use a piece of GF board to apply even pressure along the length of the wiper or TE.

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Darren_O

It's the outer 20cm of the aileron towards wing tip

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oipigface

I was wondering more about the amount of material you would have to remove to free it up, rather than the length. Is there any visible distortion of the wing skin or of the wiper, when viewed from the tip?

 

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isoaritfirst

Hi Darren. If the top skin is depressed and fouling the wiper then one solution is to reposition the top skin slightly higher. 

To achieve this will require the fillet I discussed earlier. Thevfillet should just be Made to support the top skin to the trailing edge spar. The top skin should be propped against the wiper with some card to hold the gap while the fillet dries. 

Obviously the fillet should be small enough to not foul the wiper. 

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Darren_O

Viewed from tip it seems a little of both..

IMG_20170108_114844.jpg

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oipigface

In that case, I'd think about doing a bit of both. Thinning down the trailing edge is easy and comparatively safe. Mike's inserted fillet sounds as if it can also be done without much danger of damage. Whether or not it is a better solution than trying to actually bend the trailing edge as I suggested seems to me to depend on what the pattern of distortion is. If the skin bends down toards the wiper only behind the false TE, then putting a fillet in will not undistort it, even though it will stop the binding. On the other hand, taking a heat gun to a finished surface is a risky business.

I think I would see whether the problem can be solved with a bit of sandpaper first. If the trailing edge gets towards looking unacceptably thin, then try whichever of the other two methods you fancy, bearing in mind the various issues that have been raised in this discussion.

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Scram

If you are sanding the bottom of the wing skin, my feeling is that 80 grit paper is much too coarse.  Perhaps John omitted a leading 1  :huh:

I would use something finer myself, 240/280 or so.

I suspect that for Mike's fillet, it is intended that the epoxy is installed whilst the skin is lifted by a card between it and the wiper, just enough under the edge of the skin to lift it.  When the epoxy hardens the skin is fixed there.  Epoxy/micro balloons would be ideal for this as the balloons would stop the epoxy then settling back under a load from the stressed skin.

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oipigface
40 minutes ago, Scram said:

If you are sanding the bottom of the wing skin, my feeling is that 80 grit paper is much too coarse.  Perhaps John omitted a leading 1  :huh:

I would use something finer myself, 240/280 or so.

Well, I've used 80 myself in the past. The way trailing edges are built varies, and the particular job I was doing (an Air One, I think) was very resistant to anything finer. After all, the object is to remove material from the underside rather than polish it. I think you are right, though, that caution is desirable, and that seeing how it goes with something finer is worth the trouble. But I would definitely recommend gluing whatever paper is being used to a small piece of thin glass fibre board. The piece I use is about 50 x 25mm. It's a good idea to put a strip of masking tape along the aileron surface as well, to stop the GF scratching it. 

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