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maya.ayoub.32

Active Member
Joined
Apr 6, 2020
Messages
43
I model the rivet locations 2d in autocad convert holes to regions then union all the holes .
Do mass properties to find the centroid.....move the centroid to 0,0,0 and coordinate dimension the holes.

Looking at load each rivet and bearing strength each thickness and shear each rivet.
I would not of thought of using a type of simulation- I will definitely learn how to use auto cad, and get some good stress data! Thank you!
 

proppastie

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Feb 19, 2012
Messages
4,762
Location
NJ
I would not of thought of using a type of simulation- I will definitely learn how to use auto cad, and get some good stress data! Thank you!
Autocad 14 is what I use....rather old version, any cad program that can give "mass properties" will work.....I will look at some of my others programs.....I would think SW would do it....but I do not have that.
 

Rudy Lee

Member
Joined
Apr 26, 2020
Messages
11
I'm so glad you guys noticed our AOPA article and video! We are super proud of everything we've done and we're glad we can spread the word. You guys have been with us since the beginning so y'all deserve some thanks!
 

Rudy Lee

Member
Joined
Apr 26, 2020
Messages
11
Also... Howdy y’all! Its been a while since we checked in with you guys on the forum, so I want to give you a little update on what progress we’ve made recently. I also have a quick question for y’all that I’ll get to later.
In terms of progress, we are currently ready to construct our wing. We have done several rib tests and determined that our best bet is to use xps foam, but instead of doing wood rib caps as we had planned, to use e glass composite caps, which will increase both strength and ease of construction. We also had issues with our spar tearing through the foam, so we manufactured metal washers to go around the attachment hole and increase the foam’s tearout strength. All of the materials needed to manufacture our wing have arrived, so all that’s left to do is check our numbers and roll.
That’s where you guys come in and the question I have - we were doing some number checks, which led us down a rabbit hole of stall lift coefficient / velocities. We were looking over the Legal Eagle’s specs and comparing them to our own, and something didn’t seem right: their stall/max lift coefficient would need to be 1.9! (givens: dry weight = 246 lbs [plus pilot and whatever else we estimate to be similar to our own craft at around 508 lbs], stall velocity = 27 mph, wing area = 120 sq ft, and air density = 0.0765 lb/ft^3 [based on our own calculations]) Combine that with the standard equation for lift coefficient and you get around 1.64! If you run the same numbers for our current model (508 lbs weight, stall velocity = 24 kts, wing area = 186 sq ft, and air density = 0.0765 lb/ft^3) you get stall lift coefficient = 1.386, which is just under the max for the Clark Y, so that’s all good. (feel free to either trust us on that math or check it yourself, up to you, note: we arent 100% sure those numbers are correct but we are confident, also our numbers check our with this EAA provided ‘calculate your stall speed advisory,’ but theirs doesn’t [see page 21 of attached pdf]) Our one confusion is how does the Legal Eagle get away with that 1.64 lift coefficient? It doesn’t seem like their airfoil has that high of a max CL, so are we missing something? We are totally fine with using our current 186 sq ft wingspan as is, but ideally we can drop it down to somewhere near their 120, as it would save a large amount of weight. Our other specs are right on par with theirs, so can you guys see a reason why they can get away with a 1.64 CL and therefore a 120 sq ft wing? Thanks so much for all you help.
 

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Dana

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Two things: first, many ultralight manufacturers understate their stall speed and nobody really cares. Second, if you use the stall speed calculations in the AC103-7 appendices, which are very conservative, it's accepted as "proof" that it complies even if in reality it doesn't.
 

Ollie Krause

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Joined
Feb 26, 2020
Messages
103
Hey y'all,

It sure has been a while and things are going along nicely for our project. We've started construction and just today laid out all our ribs onto our two spars. We still have a long ways to go but we're hoping to have our wings built before the end of the year! Our blog is a little out of date but I recently published an article detailing how to use our parametric wing generator which some of you might find useful.

When I was reading into the PolyFiber fabric covering system, I noticed that the Poly-Tak will attack foam ribs (I assume XPS is included in the broader definition of "foam"). The affordable fixes this issue by covering all the ribs with a polyurethane coating (I assume water-based) but I'd be concerned that this could lead to adhesion issues between the foam and the fiberglass cap strips. Are there any other methods to protect foam ribs from Poly-Tak glue? Thanks as always for all of your help!
 

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pwood66889

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Joined
Feb 10, 2007
Messages
1,731
Location
Sopchoppy, Florida, USA
What you must remember, Ollie, is that you are working with a covering "System." That means all the chemicals have been tested with one another, and play well together. One does not just "mix and match." That means you may want to re-evaluate your rib material, or...
On the Independence Flyer, wood strips were glued to the foam ribs. They had a jig made up, and I assembled some of the "false ribs." I do not really know what "System" was used for covering, but the Poly products could have been it. Hope it is not too late in your game to change.
 

Protech Racing

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Joined
Jul 10, 2020
Messages
187
I ran into the same issue when building my UL. I did lots of glue test. The contact glue is worthless on foam. You can epoxy a fiberglass cap strip and glue to that if you wish.
The best method, I that I found , is to use a "wood pecker" Top Flite Woodpecker Perforating Tool
Run this down the area to be covered on the ribs. This allows the glue to penetrate the foam and increase the square inches of involvement .
I was a little hesitant to only use Gorrilla glue( youre gunna die!!) , so I used epoxy in the center line and gorrilla glue on the edges and mixed it a little with the epoxy. Worked swell. The failure point will be a 1/4- 1/2 in into the foam . Without the gorrilla glue, the failure point will be the epoxy to foam joint.
The tug test is at least 3x what simply epoxied to the foam is .** do your own test!!)

***I have to restest the 3M 5200 in place of the Gorrilla glue.** I doubt that it will work into the foam as well but it may be OK and be more permanent. Not sure until I test it.

The procedure is to wood pecker, rub some water down the edges, run your gloved fingers down the rib to even up the moisture. Dripp some epoxy in the centerline , , run a small bead of Glue up the edges , set the glass tape cap strip and add some epoxy brushed and rolled into the tape .
Now you can use the contact glue if you wish.
I used Gorrilla glue to cover my plane, as the tug /break value is way above the contact glue. Looking back, I could have glued the dacron straight to the ribs, but I like the glass cap strip idea. You can add a rib stitch just behind the fat part of the foil for added insurance.
Please do your own glue test!!. I did . The Gorrilla glue will be stable for 5-10 yrs in the wing unpainted. But take the time to paint all of it and it seems to pass the exterior 10yrs test no problem . Exposed to air and sun it will degrade inside of 2 yrs.
Latex paint works perfect on the glue and covering .
This plane was built 12 yrs ago and the painted glue areas are still sound . The unpainted glue areas are failed.
 
Last edited:

Ollie Krause

Well-Known Member
Joined
Feb 26, 2020
Messages
103
Hey y'all,

It sure has been a while and things are going along nicely for our project. We've started construction and just today laid out all our ribs onto our two spars. We still have a long ways to go but we're hoping to have our wings built before the end of the year! Our blog is a little out of date but I recently published an article detailing how to use our parametric wing generator which some of you might find useful.

When I was reading into the PolyFiber fabric covering system, I noticed that the Poly-Tak will attack foam ribs (I assume XPS is included in the broader definition of "foam"). The affordable fixes this issue by covering all the ribs with a polyurethane coating (I assume water-based) but I'd be concerned that this could lead to adhesion issues between the foam and the fiberglass cap strips. Are there any other methods to protect foam ribs from Poly-Tak glue? Thanks as always for all of your help!
Yeah, we're using fiberglass cap strips as well but I'd be concerned that the Poly-Tak might drip around the edge of the fiberglass and start dissolving the rib. We could use masking tape along the cap strip and then spray a coat of polyurethane varnish on the sides of the ribs. That way the polyurethane varnish doesn't come between the Poly-Tak and the fiberglass cap strip.

Completely separate question but would you suggest lightly sanding the fiberglass cap strips before gluing down our fabric? There are some small irregularities and bumps especially on the edges of the 1" fiberglass tape which might cut into the fabric.
 

Victor Bravo

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Joined
Jul 30, 2014
Messages
8,065
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KWHP, Los Angeles CA, USA
Is there a reason you have to glue the fabric to the ribs? Tens of thousands of certified airplanes were built without gluing the fabric to the ribs. The fabric is tied around the ribs using "rib stitching", and no glue is used at those locations.

SOOOO.... if you put something glue-proof onto the leading edge, you can glue the fabric to that, and then stitch it to the other 80-90% of the length of the rib. It will be a little lighter than the glue probably, and definitely lighter than epoxy or fiberglass caps on the ribs. It can also be removed without damaging the ribs, which you will not be able to do if the fabric is glued down.

I am not 100% sure this is the right solution for your project, but I am 100% sure you should look into it, balance the pros and cons, and you may find it gives you more pros than cons.
 

Dana

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Apr 3, 2007
Messages
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CT, USA
Use Stewart System instead of Poly-Fiber, it uses a waterbone adhesive instead of the MEK based Poly-Tak.

Or to save some money, use 3M Fastbond 30NF which is the same thing as the Stewart adhesive, and paint using acrylic latex house paint.
 

Ollie Krause

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Joined
Feb 26, 2020
Messages
103
The fabric is tied around the ribs using "rib stitching", and no glue is used at those locations.
We'll definitely look into fabric stitching some more. I always thought it was used for planes with wooden wings, though, and I'd have concerns that the string would tear through the foam. Anyways, I'll do some more research and report back what I find.

In terms of fiberglass cap strips, they are a necessary structural component of the ribs. The cap strips and support washers (which reinforce the attachment of the spars to the rib) increase the maximum rib load from around 80lb to over 250lb.
 

Protech Racing

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Joined
Jul 10, 2020
Messages
187
I have never seen rib stitched on foam ribs . Every plane with foam ribs has been glued AFAIK. The wood cap strips , or even the glass tape may allow stitching tho . The glue also uses the covering to stabilize the wing IMHO.
 

karmarepair

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HBA Supporter
Joined
Jan 13, 2011
Messages
283
Location
United States
Two things: first, many ultralight manufacturers understate their stall speed and nobody really cares.
They MAY actually believe their numbers, due to pitot static errors at low speeds and high angles of attack. Getting the P/S system right on certified airplanes is a major big deal. I doubt that ultralights get that level of detailed development.
 

Dana

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Apr 3, 2007
Messages
9,449
Location
CT, USA
Rib stitching doesn't go through the rib, foam or otherwise; it goes through the fabric, down alongside the rib, out through the fabric on the otherwise, across the rib, back in and up the other side, then exits out the top where it's tied to the starting end.

But many ultralights use only glue with no stitching.
 
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