Originally Posted by cityevader

....................................
Then again, my interests are heavy slopers, so my perspective is likely biased...................

Then I suggest you use my wood insert method.
(I think I described it above).

I've done that before, but it is fiddly as you said. I like the concept of a foam wedge but am confident i cannot cut a perfect one.

Originally Posted by cityevader

I've done that before, but it is fiddly as you said. I like the concept of a foam wedge but am confident i cannot cut a perfect one.

Ok.
Then you are stuck deliberating between the two...........until you decide on an alternative.
Keep us posted on what you come up with.

I think the key to making sure your hingeline is solid is to keep the support structure for the hinge material as close to the mechanical hinge pivot as possible.

I'm not sure how to calculate the stresses exactly because I don't know the loads / speeds involved, but I would say that if they're THAT extreme, you may want to consider making the wing and control surface separately, then hinging with silicone.

I've tried both Jim's and Tom's way. Both are fiddly in their own way. Fitting the wood strip accurately is a challenge. Joe Mach1 details his method for this on one of his recent build threads. With Tom's way I struggle to get the little strips of facing fiberglass positioned right, the foam strip back in place, then wet out and bagged without things sliding out of position. That was with the 3m77 mist method; I'll have to try it with transfer tape. The cutting of the hinge line actually is not too hard Chad....you don't actually 'cut' the triangle out. The foam strip is rectangular. You make a vertical slice through the center of the foam strip down to the kevlar, fold open the hinge, then use a sanding block to create the bevel.

I have some worry about the skin/hinge pulling away from what's left of the foam strip on a slope plane that lives a rough life. Typical slopers have a thicker wing than a DLG so the strip/bevel needs to be wider. In that situation it seems like actually cutting a triangle (so the facing comes right to the hinge line) would be stronger. And like Chad says, cutting that triangle accurately can be a challenge.
But I usually wreck them long before weak hinge design becomes an issue

I saw an older dlg thread where a triangle was cut out, versus Tom's rectangular strip.
I like the idea of Tom's way better for construction ease.
If worried too much, i guess a carbon doubler could be added over the hinge line.

Originally Posted by tom43004

..................... then hinging with silicone.

I have also used silicone hinges very successfully on foam, built up and composite wings.
In this case...........EPP tape covered...............I have built in a timber (Pauwlonia.......but what ever you have) drag spar and control surface LE spar. Tape up, cover, then last of all run the silicone hinge.
I have an instructional video on silicone hinges somewhere. If you want, I will find it.

Silicone hinges are good!

Jim.

Originally Posted by Jim.Thompson

My favourite method of getting around this problem is to insert a balsa strip into the core before bagging. This is wide enough to provide both a drag spar for the wing and a leading edge spar for the control surface. I do the same for the ends. After the vac bagging process, the hinge is cut along this strip.
It' s a bit fiddly getting just the right size and thickness, but it does produce a a good result.

Jim,

When you insert the balsa into the core, is it a single piece of balsa that is later cut and beveled, or is it two separate pieces of balsa that create a drag spar and leading edge of aileron spar? I recently did the 2-piece method, and it seemed to be a LOT of work.

https://www.rcgroups.com/forums/show...&postcount=426

Tom moved his videos to a different provider.
https://www.rcgroups.com/forums/show...7#post46457457

Thanks for that Duane.

I think there may be some confusion about my method... and how it has been explained in the past. The video makes it crystal clear. You're never wrapping the little sliver of foam removed for the hinge. You're actually just wrapping the flapperon and the aft wing square edges, then performing normal hinging in the space between the facings after the wing is completed. I'm working on a new project that uses this same type of technique in extremes to "box" several spars and the hingeline all in the same wing. It really couldn't be simpler. After I release that project publicly, I'll put out some videos showing how it's made. The process isn't new, but I'm always using it in new ways.

Start about 6 minutes into this video:

https://rumble.com/vdi95d-nxt-sport-...=hcef9&mrefc=2

Originally Posted by spectra

Jim,

When you insert the balsa into the core, is it a single piece of balsa that is later cut and beveled, ............................

It is one piece. The actual hinge line cut and bevel is done after the wing has been bagged.

Toms's videos are highly instructive an look forward to season 2.

Cutting a triangle of foam is going to be very challenging ... but a truncated wedge should be much easier. You just have to cut from the bottom surface where the width will be constant.
Mark hinge-line ... with a medium size sharpie?
Cut leading edge of flapperon with blade angled* around 30deg towards the t.e. Straight edge 0.5mm behind the hinge line. You could calculate the angle to allow the amount of upward movement at the root of the surface you want {=flapperon chord * sin(angle*)}.
Then cut the trailing edge of the wing with the straight edge 1mm away from the first cut and the blade perpendicular to the wing (lower) surface. This should free up a wedge shape that is a constant 1mm wide on the lower surface - or whatever you decide is appropriate - and tapers from 4-2mm on the upper surface.
After this it's Tom's method all the way. It is going to be slightly more difficult to free up the surface since you need to start exactly on the hinge line and will need to remove all the foam and top skin between the facings. I think if you can accurately track where the facings are you should be OK. The width of the wedge on the top surface varies in line with the thickness of the wing. It shouldn't be difficult to keep a constant cut angle.

Need to find a wing core to practice on.

Originally Posted by pg10003

Toms's videos are highly instructive an look forward to season 2.

Cutting a triangle of foam is going to be very challenging ... but a truncated wedge should be much easier. You just have to cut from the bottom surface where the width will be constant.
Mark hinge-line ... with a medium size sharpie?
Cut leading edge of flapperon with blade angled* around 30deg towards the t.e. Straight edge 0.5mm behind the hinge line. You could calculate the angle to allow the amount of upward movement at the root of the surface you want {=flapperon chord * sin(angle*)}.
Then cut the trailing edge of the wing with the straight edge 1mm away from the first cut and the blade perpendicular to the wing (lower) surface. This should free up a wedge shape that is a constant 1mm wide on the lower surface - or whatever you decide is appropriate - and tapers from 4-2mm on the upper surface.
After this it's Tom's method all the way. It is going to be slightly more difficult to free up the surface since you need to start exactly on the hinge line and will need to remove all the foam and top skin between the facings. I think if you can accurately track where the facings are you should be OK. The width of the wedge on the top surface varies in line with the thickness of the wing. It shouldn't be difficult to keep a constant cut angle.

Need to find a wing core to practice on.

I've done this. It works fine. To get the angle I made a block with an angled face that I attach the blade to. I make the cut in several passes with the blade set to increasing depths. Works fine. For the wedge, I wrap it in packing tape and removal is pretty straight forward. If you are really careful/clever, you can use the flap of skin at the top of the wedge as a gap seal. Requires a precise single cut on the top at the leading edge of the control surface. Then you have to carefully round the top faced corner of the control surface so it doesn't get caught on the skin that makes the gap seal. It isn't easy to do, but when you get it right, it makes a really nice looking gap seal. With no gap seal, it is pretty easy. Just slice the skin in the middle of the gap, and after you make the hinge you can pop the surface free and the tape allows you to pull the foam wedge cleanly from the wing. Then you can trim/sand the rest of the skin up to the facing.