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maya.ayoub.32

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Hey all!

We have some updates regarding the leading edge! You can find all our updates and research on our blog post.

We decided to try the masking paper idea first because of its simplicity, where we used 3M High Strength 90 Contact Spray Adhesive to attach our masking paper. We also bought proper cargo straps for the test and to use on the final wing construction. We used just random rope we found on the last test, which we thought may have been part of the attachment problem.

We were originally unsure about which adhesive to use, so below is our comments and research

AdhesiveSpecialty SurfacesStrength (psi)Time to cure/bondPrice/ozNotes
3M High Strength 90 Contact Spray AdhesiveWood, laminates, metal, plastics, concrete23010 minutes$0.80Highest Strength 3M Spray-on.
3M Super 77 Multipurpose AdhesivePaper, plastics, cardboard16010 minutes$0.65General Purpose.
Loctite Premium MAX 9 Construction AdhesiveBrick, ceramic, drywall, to a lesser extent: metaln/a for metal24 hours$1.05Outdoor repair.
JB Weld MarineWeld™ Twin Tube - 2 ozAluminum, Fiberglass, Plastics, Metal502024 hours$4Aluminum centered
KwikWeld™ Syringe - 25 mlMetal, Wood, Plastic, Automotive, Ceramic, Aluminum24241 hour$9.40Metals

The full 3M adhesive chart can be found here, and it details spray (aerosol), cylinder, and bulk products.

We thought the 3M High Strength 90 would be the best for our purpose, as although it has a considerably lower psi than the LB weld brands’ products, it is 4x cheaper. Because the aluminum will not have a considerable amount of pull against the paper, it’s high strength of 230 psi should be more than enough for our purpose.


3M spray on the prototype aluminum LE.


We were pleasantly surprised that the masking paper idea worked independently!

These were done in a rush on extra foam that we lost the dimensions to so it’s obviously not perfect.

Good things:
It stuck!! The 3M Super 90 Contact Spray Adhesive was an experiment in itself, so we can use it on future tests now that we know it adheres very well to the slick aluminum.

Problems:
We used wood scraps to better distribute the force of the clamps, but unfortunately, we got too much epoxy on them so they wouldn’t remove unless physically ripped off (which is where the crack in the foam comes from). In the future to solve this problem, we’re going to put parchment paper between the wood and epoxy.

Improvements:
To make the leading edge sheet metal lighter, we’re going to implement a “finger” style design. We'll be testing it this weekend and will update everyone on the validity of the idea.

 
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proppastie

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That glue to paper is new to me.....great idea..... a further thought for "maybe" better.....might try to vacuum bend the aluminum/paper assembly.....over bend a little and then maybe you will not need much more than the straps to position the aluminum when you glue it to the foam ribs......b sure to bend a larger piece and trim after bending....from the looks of the last sketch you may want to bend it when it is maybe 2x the size of the final part.
 

maya.ayoub.32

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Any thought on how the glue and aluminum will act with temperature change?
Great thing to test out! The spray says its heat resistant up to 250 F, but we'll try heating it up while attached to the aluminum/paper to find the heat required to tear off.
 

maya.ayoub.32

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That glue to paper is new to me.....great idea..... a further thought for "maybe" better.....might try to vacuum bend the aluminum/paper assembly.....over bend a little and then maybe you will not need much more than the straps to position the aluminum when you glue it to the foam ribs......b sure to bend a larger piece and trim after bending....from the looks of the last sketch you may want to bend it when it is maybe 2x the size of the final part.
Interesting! We looked into it a bit but were under the impression it would be either the vacuum method or straps, which deterred us since, as you mentioned, it would not bend to our exact shape. Now that we know they can be used in tandem, it would definitely help us alleviate some pressure off the foam itself while strapping. We'll test it out this weekend and post some updates- thank you!
 

jedi

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As noted in a prior thread I have had issues with aluminum bonded to EPS foam. It may test OK after construction but in a short while when subjected to thermal changes the foam Al bond delaminates. You should use a tile like surface to limit thermal expansion problems.

My test piece was an Al cap strip with EPS shear web. Stored inside over the winter with Michigan heat cycling on and off the spar was scrap in the spring.

A one piece leading edge in summer sun would be brutal. I would advise one foot Al spanwise sections centered on the rib. Your bond may not be critical after the wing is covered.
 

maya.ayoub.32

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I'm presuming foam ahead of the spar. And the aft edge of these little tabs should be flange to keep the free edge from buckling.

Another idea: Scallop the free edges, top and bottom, of the leading edge aluminum, in between the attachment tabs, so that most of the free edge is supported on the spar. The tension of the fabric will hold it in place. ASCII Art follows
=======================| <= End rib
| | |L < tabs |
| | | ( <scalloped edge | <= Trailing edge
| | |L |
| | | ( |
| | |===================
| | | ^ full length rib^
| ^
^ s
L p
E a
r

you can also "tweak" the free edge ever so slightly to give it a little rigidity. This is a good tool to do this on long, straight edges 8 in. Sheet Metal Clamp or you can use a sheet metal brake, or use a piece of aluminum bar stock or hardwood with a .020" wide slot about 3/4" deep sawn into the end to give you enough leverage to put a 10 degree or less crease in the edge. Bend a little, move the tool, bend a little, move the tool.
Sorry I'm just setting this! It looks like the masking paper idea Protech Racing proposed works on its own so we may not need aluminum reinforcement. However, we will be bending aluminum for other parts of our plane and this sounds like a wonderful method for doing so- thank you!
 

proppastie

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so we may not need aluminum reinforcement
often the D-Nose is a structural part of the wing......if you are only holding the shape for the fabric you may not need a sheet metal LE. as was said/shown before often the front spar tube is all the way in the front to provide that shape.......and I know you do not want to re-design the wing.
 

maya.ayoub.32

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Yes, surface the glass tape .
You can hand paint the rib edges with latex.
Quick question here, by surfacing do you mean sanding? We are considering sanding the fiberglass to remove any sharp nibs + edges that would cut the fabric covering. If we do this, is there any structural concern with the fiberglass? The PolyTech manual mentions sanding the fiberglass with varieties of grit, but it has no mention of structural integrity.

If there structural concern, should we add another layer of epoxy on top of the fiberglass to smooth it instead of/in addition to sanding? If so, would we require micro-glass bubbles for this purpose as well?

As always, thank you in advance for your help.
 

Ollie Krause

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often the D-Nose is a structural part of the wing......if you are only holding the shape for the fabric you may not need a sheet metal LE. as was said/shown before often the front spar tube is all the way in the front to provide that shape.......and I know you do not want to re-design the wing.
Yeah we abandoned the leading edge spar design a while ago since it easily tore out from the rib when under load. In hindsight, I wish we'd tested some C shaped support washers to reinforce the leading spar attachment but the ribs are plenty strong with the leading spar placed back from the leading edge.
 

proppastie

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might need a mold for the fiberglass LE but maybe the paper will provide enough strength to support the fiberglass on the wing......I am not sure how strong the paper glued to foam ribs are, certainly not as strong as fiberglass......one thought is after the fiberglass is cured and you had mold release over the paper you could peal off the paper and glue the fiberglass to the ribs. this is all very experimental so load testing test panels is important...... and if the fiberglass LE is not structural the fabric should hold it on and no need to worry about the paper interface except for extra weight of resin soaking into the cardboard, which wax paper would solve.
 

Ollie Krause

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I'm presuming foam ahead of the spar. And the aft edge of these little tabs should be flange to keep the free edge from buckling.

Another idea: Scallop the free edges, top and bottom, of the leading edge aluminum, in between the attachment tabs, so that most of the free edge is supported on the spar. The tension of the fabric will hold it in place. ASCII Art follows
=======================| <= End rib
| | |L < tabs |
| | | ( <scalloped edge | <= Trailing edge
| | |L |
| | | ( |
| | |===================
| | | ^ full length rib^
| ^
^ s
L p
E a
r

you can also "tweak" the free edge ever so slightly to give it a little rigidity. This is a good tool to do this on long, straight edges 8 in. Sheet Metal Clamp or you can use a sheet metal brake, or use a piece of aluminum bar stock or hardwood with a .020" wide slot about 3/4" deep sawn into the end to give you enough leverage to put a 10 degree or less crease in the edge. Bend a little, move the tool, bend a little, move the tool.
Sorry but do you have a photo or drawing with more details on this configuration? The ASCII drawings are a bit hard to understand.

We were under the impression that scalloping was bad because it deformed the airfoil profile but this patent on leading edge scalloping seems to suggest otherwise. Does scalloping behind the leading negatively impact the airfoil? The Affordaplane has some severely scalloped wings but they aren't exactly the best example in terms of safety or best practices...

If scalloping on the leading edge isn't an issue, we have no need for the leading edge sheet metal. Our calculations and testing data shows our current rib and spar configuration is capable of a maximum load factor of 3.8g so we have no need for the additional strength provided by a metal leading edge. Removing the leading edge sheet metal from both wings would also save a total of 6lb.

I'd also have concerns the leading edge would separate from the ribs at high loads if it were just glued in place. The upwards bending of the wing would put the bottom of the leading edge in tension and the top in compression. The C shape of the leading edge sheet metal would resist this bending causing it to separate from the ribs and buckle.
 

proppastie

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Does scalloping behind the leading negatively impact the airfoil?
My understanding of scalloping is as shown in your post #241, except the fingers are longer with radius to the rest of the LE. ...I do not understand how that might effect to airfoil unless the fabric was not shrunk tight and/or if glued to the whole LE rather than the recommended 2" overlap at the LE. which might cause a ridge where the fabric balloons up in flight.
 

Ollie Krause

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My understanding of scalloping is as shown in your post #241, except the fingers are longer with radius to the rest of the LE. ...I do not understand how that might effect to airfoil unless the fabric was not shrunk tight and/or if glued to the whole LE rather than the recommended 2" overlap at the LE. which might cause a ridge where the fabric balloons up in flight.
Inkedunnamed_LI.jpg

Hmmmm... This is my understanding of scalloping based on the definition provided in the Poly-Fiber covering manual:

"Scallops are troughs that form between the ribs, more so with modern polyester fabrics than classic Grade A Cotton. Although they present no aerodynamic problems, for cosmetic reasons, some prefer fabric that is more level to the ribs with little scalloping."

I would assume that's referring to the swoops highlighted in red in the Affordaplane photo above. If the fabric doesn't match the airfoil exactly because of scalloping I'd assume the wing wouldn't match our calculations...
 

proppastie

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thanks.....I did not see that in the Poly-Fiber manual, they are the experts.....that does make more sense.....I am not very good at aerodynamics, how ever
Although they present no aerodynamic problems,
is what they are saying.

Maybe our aero nerds can chime in.
 

karmarepair

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Sorry but do you have a photo or drawing with more details on this configuration? The ASCII drawings are a bit hard to understand.
Forget I even suggested it - I didn't understand your spars. What I was suggesting will not work with your arrangement.
We were under the impression that scalloping was bad because it deformed the airfoil profile but this patent on leading edge scalloping seems to suggest otherwise. Does scalloping behind the leading edge negatively impact the airfoil? The Affordaplane has some severely scalloped wings but they aren't exactly the best example in terms of safety or best practices...
If you could section the wing at the deepest scallop, I think you'd find a thinner, lower camber, sharper leading edge airfoil.
 

proppastie

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obviously you have different airfoil shapes,....maybe run some numbers for "average" shape, assuming you can come up with a reasonable average. You might need to increase the height of the ribs if your average is not to your liking.

having a LE edge that does not allow that much scalloping as you show in your sample picture would also be a solution.
 

Protech Racing

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As prior posted. I gave up on the nose cap. I disliked the hard edge at the rear . I removed the paper and used extra half ribs. I like my airfoil imperfections in line with airflow .
The paper is glued on very well with Gorilla glue . Better than epoxy. Either will work . Scallop the rear of the paper if you use it and cover.
 

Rudy Lee

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Hi all - I have a few questions about our wing as I get ready to start attaching the fabric. 1. do we need to attach the fabric to our false ribs? (see first photo below, false ribs in red, normal ribs in green.) It would add a bit of extra weight to cover our false ribs with epoxy such that the fabric glue wouldn't melt them - do you think it is necessary to adhere the fabric to the false ribs when it will already be adhered to the other ribs? and 2. We recently had some concerns about hinge moment breaking our aileron ribs off of their torque tube. Is there an equation/method to determine maximum aileron hinge moment (or just a standard number) so we will know if our current design is strong enough/if we need reinforcement. (see aileron in second photo below)
IMG_1283.jpgIMG_1282.jpg
 

Protech Racing

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Gorrila glue the places that are not protected. The short ribs will be fine.
As far as the aileron ribs, maybe running some drywall taped all the way around will stiffen it up enough .

You may also not like the hard crease of the covering at the false spar. You should hang some covering on it and think about trimming it .
 
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