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Old Jun 13, 2012, 07:51 PM
Detail Freak
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Harbor City, CA
Joined Oct 2003
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Idea
Aileron/Flap facing on bagged wings

I am wondering if anyone has tried what I am thinking of trying:

My thought is to hot wire a perfect circle the thickness of the foam wing core centered over the hinge line.
I would then use the foam "dowel" with a braided CF or GF sleeve over it, and wet it out and put it back in the core just prior to laying up the skins.

My intent is to split the circle in two, after bagging the cores, cutting completely loose the flying surfaces, so that I can easily add a wiper of some sort.

I intend to use a silicone hinge doing this.

The wing STE and the aileron/flap LE's would already be faced this way, and the back of the wing would have a nice smooth concave for a wiper to follow.

Also, the area where the silicone hinge will be will have a reinforcement of the braided sleeve meeting the skin material, giving a stiff lip for the silicone hinge....

Any thoughts/suggestions??

R,
Target
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Old Jun 14, 2012, 01:29 AM
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Quote:
Originally Posted by target View Post
I am wondering if anyone has tried what I am thinking of trying:

My thought is to hot wire a perfect circle the thickness of the foam wing core centered over the hinge line.
I would then use the foam "dowel" with a braided CF or GF sleeve over it, and wet it out and put it back in the core just prior to laying up the skins.

My intent is to after bagging the cores, split the circle in two, to cut completely loose the flying surfaces, so that I can easily add a wiper of some sort.

I intend to use a silicone hinge doing this.

The wing STE and the aileron/flap LE's would already be faced this way, and the back of the wing would have a nice smooth concave for a wiper to follow.

Also, the area where the silicone hinge will be will have a reinforcement of the braided sleeve meeting the skin material, giving a stiff lip for the silicone hinge....

Any thoughts/suggestions??

R,
Target
Why use a silicone hinge when you could use a live hinge?
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Old Jun 14, 2012, 06:25 AM
Father of Fr3aK, DLG Pilot
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USA, OH, Worthington
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If you can dream it, it's been tried. Similar methods using drinking straws and foam backer rods have been done. I like the drinking straw method because you can just use a razor blade to slit it and it's already hollowed for the attachment of the wiper if needed.

I kind of like live hinges too but I understand the appeal of silicone for the "go fast" crowd.
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Old Jun 14, 2012, 09:08 AM
Detail Freak
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Harbor City, CA
Joined Oct 2003
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Thanks Tom-

I'm wondering if the drinking straw will work when there is taper in the section. In other words, the thickness of the core along the hinge line will diminish as it gets closer to the tip...so, I would assume that either the straw would have to flatten and extend into the wing and aileron fore and aft more, making an oval, or it would have to be slit for some overlap allowing the straw to reduce its diameter as needed.

The reason I am wanting to use silicone hinges is that I can sand or otherwise adjust the wing TE or surface LE as needed easily; more easily than if the surfaces are live hinged.
Also, my intent was to do an all spread tow carbon layup, full chord, with no kevlar.

R,
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Old Jun 14, 2012, 11:46 AM
Father of Fr3aK, DLG Pilot
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You can still do live hinging even with carbon from LE to TE. You simply add a strip of kevlar to the layup in the hinge area and sand through to the kevlar. It's actually really easy. I do it all the time.
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Old Jun 14, 2012, 12:46 PM
Detail Freak
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Harbor City, CA
Joined Oct 2003
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I thought of doing that also, but for some reason I feel that live hinges on foam cores causes the skin not to bond as well to the core, or to have the tendency to be pryed away from the core...

Also, having the parts separated is an advantage (IMO) should they need any massaging in the area between them.

I haven't completely ruled out a skin hinge, but its one less thing to deal with until later, when everything is prefect, and the silicone is applied.

Also, we seem to have run off onto a tangent of debate of skin vs silicone hinges, and I'm more interested in facing methods other than what is used for the stock Supra design.
It seems to me that a rounded concave, at least on the back of the main panel, makes good sense if you want to incorporate either a molded splooge, or even a tape wiper.
Any good tried and true methods to suggest??

Thanks in advance.
R,
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Old Jun 14, 2012, 12:59 PM
Whisper Model Aircraft
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Greensburg, PA
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Someone here did a kevlar hinge, then used a window blind shade to mold to a wiper. Looks pretty awesome, too much work for me though....
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Old Jun 14, 2012, 01:17 PM
Detail Freak
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Harbor City, CA
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Is there a link you can send me down?
Or, do you remember which forum it was in??

I'd love to look at it.

R,
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Old Jun 14, 2012, 09:16 PM
yyz
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Target,

There might be something to be learned from my recent experiments and mistakes here and here.

How about the following....

In your case, replace the balsa with foam cut spanwise from your cores (the foam dowels in your idea). Wrap those in your favorite composite, wet and bag. Out of the bag, those drag spars go back in the wing before bagging the skins. I would make that wrap layup super dry and bagged with peel ply. You'll get some epoxy back from the skin layup and have a good surface to bond to.

That should give you the skin-to-skin bond that I think you're after. If you left some space between the spars (chord-wise), you could do the wiper thing. You'd obviously need to sand some height out of the foam pieces to compensate for the thickness of the wrap.

Hopefully that made sense,

Mike
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Last edited by yyz; Jun 14, 2012 at 09:51 PM.
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Old Jun 14, 2012, 11:35 PM
working to the closest cm
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Quote:
Originally Posted by yyz View Post
Target,
snip.....

In your case, replace the balsa with foam cut spanwise from your cores (the foam dowels in your idea). Wrap those in your favorite composite, wet and bag. Out of the bag, those drag spars go back in the wing before bagging the skins. I would make that wrap layup super dry and bagged with peel ply. You'll get some epoxy back from the skin layup and have a good surface to bond to.

.....

Mike
Somewhere on the German forums I have seen similar.

A spanwise section of foam cut from the core. This is widw enough so that the front edge is the rear drag spar and the rear edge becomes the closeout on the aileron. This is wetout and bagged along with the remainder of the cores. I imagine in a similar manner to the supra facing methods. Core segments held together with 3m and 3/4oz glass.

The completed bagged rectangular section can be than split and hollwed out to create a wiper cavity. I imagine either silicon or kevlar hinge methods could be addapted.

Historically in my local club we have bagged the wing and separated surfaces then fitted closeouts onto the bare foam surfaces. This has included hollowing out the cavity for the wipers to drop into. This method has often resulted in some skin deformation along trh rear of the wing surface due to the curing epoxy.

cheers Jeff
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Old Jun 15, 2012, 09:20 AM
Detail Freak
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Harbor City, CA
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Thanks gents....
I did some sketches last night, and while I did come up with a way to do all of what I wanted in one shot, its more complicated than I want it to be.
I do have a plan and it will be tried out on some scrap cores first.
Thanks for the input.

R,
Target
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Old Jun 15, 2012, 11:30 AM
yyz
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Quote:
Originally Posted by jirvin_4505 View Post
Somewhere on the German forums I have seen similar.

The completed bagged rectangular section can be than split and hollwed out to create a wiper cavity. I imagine either silicon or kevlar hinge methods could be addapted.

cheers Jeff
That's close to what I was trying to articulate. I was actually thinking about creating two parallel drag spars. Those would be wrapped/socked and bagged separately and then placed back in the cores before continuing with the bagging of the skins. Some space between the two spars would give you the room to do the wipers and RDS if you wanted to go that route.

Having said that, I actually like your idea of the vertically-oriented C channel that gets hollowed out post-skin bagging. That could be made really strong w/ an integrated aramid hinge at the bottom of the channel.

The trick in doing all of that extra work is, as you pointed out, maintaining the airfoil fidelity which actually may not be that critical that far back on the section. I had an interesting discussion with the gentleman who CNC cut some cores for Mark Drela and he mentioned that Mark had tweaked the airfoil coordinates near the hinge line to allow for the extra wrap around the hinge line faces which tie the top and bottom skins together. Maybe the airfoils actually are sensitive to minor deformaties that far back.

Mike
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Old Jun 15, 2012, 01:57 PM
Just fly it!
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Cody, WY
Joined Nov 2007
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I cut the core into 3 segments. The hinge line would fall out right in the middle of the middle segment. I 3M bias cut materials onto the core like the diagram shows. I then put the 3 peices back together set the on the bottom bed and hard roll the area to dent the fabric into the cores so everything is still flush. Then I tack my kevlar hing material into place to hold everything together and hard roll again. Then I flip it over onto the top bed and hard roll the bottom. The hard rolling is only necessary if you are using thicker fabrics like 3K carbon. If you are using light glass then the rolling isn't necessary. I brush resin into these before putting it into the Mylar taco. Once you cut the hinge free you can clear the foam section out to make room for the wiper.
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Old Jun 17, 2012, 09:01 PM
yyz
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What's the verdict, Target?
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Old Jun 17, 2012, 09:15 PM
Detail Freak
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Harbor City, CA
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Guilty! :-)

I thought that I had responded to this, but I guess not.
I have an idea that I think will work as good, or better than the suggestions here, but it will have to be non-live hinged, and its un-proven. I'm not sure how painful it will be to execute, but I'm hoping not too bad, and that when I'm done it will make a nice wiper reciever.

Basically, the piece that I intend to cut out will need to be close to a tear drop shape (on its side, drop towards the TE), and have a curved top, radius the same as the core thickness at the hinge line.
The bottom of the "drop" will face the TE, and make up the aileron or flap LE.
The flat side of the drop will be the bottom of the core, from the hinge line, coming forward to the radiused side of the drop, meeting where a "point" of the drop would be.

My thought is to hotwire this out of the core with a second cut, wrap with tape, then slip over braided sock. This would be wet out just before the layup is, and inserted into the cores, and then they would be layed up.

After bagging, the rounded part of the drop (bottom of a drop, if you will) would be sliced off, and the taped foam removed.

What should be left, is a reinforced aileron/flap LE with a concave face, and a reinforced flat lip on the bottome skin, with a quarter rounded cavity to the top skin, perfect for a wiper to follow....

I have no CAD program or skills, only a hyper-active mind, so I hope that you could follow that?

VR,
target
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Last edited by target; Jun 17, 2012 at 09:25 PM. Reason: add crude picture
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