Flight Club - Ultralight Build Log

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proppastie

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repeatability of our design is now dependent on a single source
Well if you are like many of the suits I worked for you would be designing and building your production tooling before you have produced and tested the prototype. If the customer is Uncle Sam hire a bunch of "contract engineers" double the billing rate and make a bundle.
 

Rudy Lee

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Apr 26, 2020
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Where are you?

How much do you need?

When do you need it?


BJC
We are located in the Bay Area, and we can drive anywhere that wouldn't have large gas prices involves. We need enough for ideally 10 ribs to test, each one using around 1" x 12' of material (it's ok if it's broken down into smaller chunks). We would like to have it in the next week if possible, but if our best bet is to wait a bit, we at least need it within 3 weeks to a month.
 

proppastie

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I do not know much about wood, but this guy used "door veneer"...from Home Depot.

 

Ollie Krause

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Feb 26, 2020
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I’m only a 2 hour drive from Tampa Bay. Stop by for a visit. I have enough plywood for your testing, at no charge.


BJC
Thanks for the generous offer but we're in the San Francisco Bay Area 😆
 

jedi

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All this Bay Talk try a marine plywood. Check your waterfront chandlery and related lumber yards or suppliers.

I would prefer a white foam block over the Home Depo blue extruded insulation. The smooth extruded skin is not a good bonding surface. You can easily hot wire slice thin sheets from a foam block. That should be available from marine supplies as it is used for dock flotation. I prefer thinner sections of the higher density foam and have cut 1/16 inch sheets. Ask me how if you go that route.
 

mcrae0104

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I have done exactly zero calculations for an ultralight wing rib but I have a hunch you could lighten up the proposed design. Have you read NACA reports 344 & 345?
 

Ollie Krause

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I have done exactly zero calculations for an ultralight wing rib but I have a hunch you could lighten up the proposed design. Have you read NACA reports 344 & 345?
I skimmed through both NACA reports but they seem to focus more on plywood and truss rib construction and I'm not sure how applicable they could be to our foam and plywood designs. I get the feeling that we just need to eat the $200 freight surcharge and just do the tests ourselves. Unless someone else has done the exact tests we plan to do, I imagine it would take some serious FEA, CFD, and experience to accurately predict how our wing ribs would fail under loading. By doing the tests ourselves, we'll be certain of our rib strength and can optimize our wing accordingly.
 

mcrae0104

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You're right, they may not be directly applicable. But if you can make a rib using a single plywood shear web (as in some of their designs), then it seems that skinning two sides of a foam rib with plywood may be heavier than it needs to be. Just food for thought.
 

Aerowerx

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You're right, they may not be directly applicable. But if you can make a rib using a single plywood shear web (as in some of their designs), then it seems that skinning two sides of a foam rib with plywood may be heavier than it needs to be. Just food for thought.
What is the weight vs strength comparison of a rib with, for example, 1/8th plywood web and a rib with 1/16th inch ply over 1/4 inch foam?
 

D_limiter

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Fritz did some experiments about relative strength of foam and stick ribs. He even stood on some sample ribs to test the strength. Interesting details in this thread on this page:

 

Ollie Krause

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Quick update: now it’s summer, we’re all off school and are regularly putting in 8-12 hour days and making some great progress with our calculations and truss analysis. One issue that we’ve just run into is selecting the proper XPS foam for our ribs. I’ve read through all the HBA threads I could find discussing the use of different house insulation foams but I couldn’t find any information discussing the differences between the different versions of XPS foams. It seems like there’s two main manufacturers: Dow and Owens Cornering with Dow being slightly preferred due to its history of usage in home built airplanes. The R value refers to its insulation ability but I’m unsure how it affects its strength. In addition, they seem to come in different densities (1.30lb/ft^3 - 3.00lb/ft^3) which in certain affect the strength but I’m curious if anyone has done any tests to determine the one with the highest strength to weight ratio or how the density affects its rigidity and brittleness (a stress/strain graph would be great here haha). I was just wondering if what your informed experiences have been with different XPS foams and if there’s any testing data available anywhere. If not, we’d be more than happy to do some detailed tests of our own to help out the community. Thanks again for all the help!
 

jedi

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I did some building in the early 70's with both blue and white foam and the white foam in both low and high density.

I left the wing spar under the bed thru a Michigan winter and at night I could hear the aluminum wing spar delaiminating from the blue foam shear web as the forced air heat cycled on and off. Spars were load tested after completion in the fall and in the spring they were complete junk. They lost more than 50% of their strength as the foam failed next to the glue line.

The skin on the extruded blue foam was a demonstrated week spot even more so than the hot wire cut foam edge.

As a result I started working with the white foam blocks and decided that thin sections of 3.00lb/ft^3 foam bonded better than thicker sections of the lighter/weaker low density foam. The foam will not help in tensil or compressive loads. The only benefit is to prevent buckling in the primary structure and to form nice aerodynamic surfaces.

I spent many hours burning scraps of the blue foam before I found out that the difference between white and blue is that the blue is fire retardant. Hold a burning piece four feet off the floor and the foam melts and makes flaming drops that sound like a minature buzz bomb.

The best use was using 1/4 inch thick or less sheets of HD foam bonded to a strong light tensile film (Tyvek) on one surface. The sheet could be bent to form a clean, light weight, smooth leading edge profile with the foam uniformly yielding in compression as the composite was bent.

Another method uses thicker sheets (1/2" or less) for larger radius curves and stronger skin. Bond a thin layer of fiber glass to the flat sheet on a workbench and let cure. Score the foam side of the sheet with a razor blade perpendicular to the planned bend. As the sheet is bent (fiber glassed side against the rib) the foam fails in tension as it is bent over the ribs or against a mold. A light sanding will convert the straight foam surface sections into a smooth curve that can then have a wet layup applied to make a double surface skin.

Of course the first method could have a concave inner skin bonded but I did not find that necessary.

Contact me for more details as necessary.
 

Ollie Krause

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Feb 26, 2020
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94
I did some building in the early 70's with both blue and white foam and the white foam in both low and high density.

I left the wing spar under the bed thru a Michigan winter and at night I could hear the aluminum wing spar delaiminating from the blue foam shear web as the forced air heat cycled on and off. Spars were load tested after completion in the fall and in the spring they were complete junk. They lost more than 50% of their strength as the foam failed next to the glue line.

The skin on the extruded blue foam was a demonstrated week spot even more so than the hot wire cut foam edge.

As a result I started working with the white foam blocks and decided that thin sections of 3.00lb/ft^3 foam bonded better than thicker sections of the lighter/weaker low density foam. The foam will not help in tensil or compressive loads. The only benefit is to prevent buckling in the primary structure and to form nice aerodynamic surfaces.

I spent many hours burning scraps of the blue foam before I found out that the difference between white and blue is that the blue is fire retardant. Hold a burning piece four feet off the floor and the foam melts and makes flaming drops that sound like a minature buzz bomb.

The best use was using 1/4 inch thick or less sheets of HD foam bonded to a strong light tensile film (Tyvek) on one surface. The sheet could be bent to form a clean, light weight, smooth leading edge profile with the foam uniformly yielding in compression as the composite was bent.

Another method uses thicker sheets (1/2" or less) for larger radius curves and stronger skin. Bond a thin layer of fiber glass to the flat sheet on a workbench and let cure. Score the foam side of the sheet with a razor blade perpendicular to the planned bend. As the sheet is bent (fiber glassed side against the rib) the foam fails in tension as it is bent over the ribs or against a mold. A light sanding will convert the straight foam surface sections into a smooth curve that can then have a wet layup applied to make a double surface skin.

Of course the first method could have a concave inner skin bonded but I did not find that necessary.

Contact me for more details as necessary.
Thank you for all the great insights! Would you be able to provide some photos or drawings of these two methods? I remember reading about them in some other thread but I was still a little confused on how exactly they worked. What would their primary benefits be over the plywood capped foam ribs we're currently planning on using? Also, just to make sure we're both on the same page, could you provide some links to the white and blue foams you're talking about? Thanks again for all for all of the help!

The best use was using 1/4 inch thick or less sheets of HD foam bonded to a strong light tensile film (Tyvek) on one surface. The sheet could be bent to form a clean, light weight, smooth leading edge profile with the foam uniformly yielding in compression as the composite was bent.

Another method uses thicker sheets (1/2" or less) for larger radius curves and stronger skin. Bond a thin layer of fiber glass to the flat sheet on a workbench and let cure. Score the foam side of the sheet with a razor blade perpendicular to the planned bend. As the sheet is bent (fiber glassed side against the rib) the foam fails in tension as it is bent over the ribs or against a mold. A light sanding will convert the straight foam surface sections into a smooth curve that can then have a wet layup applied to make a double surface skin.
 

cluttonfred

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This might be useful, Ollie.

 

Victor Bravo

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The pink colored Owens Corning "Foamular" will make a pretty good foam rib I believe. Blue Dow foam is also good. For wing ribs (instead of entire hot-wired wing cores) I would suggest the 3.00 pound density foam would likely be more appropriate than 1.3 or 1.5 pound density. The R value is probably a reflection of material density, which is very likely a direct relation to compressive strength.
 

Dana

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The R value for foam boards takes into account thickness as well, a 2" thick board will have double the R value of a 1".

Blue or pink, no difference.Just don't use the white EPS (expanded polystyrene) "bead board".
 
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