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Dec 25, 2013, 05:31 AM
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Quote:
Originally Posted by mbpetri
Sorry, I can't find 400 gms of chopped tomatoes here in Thailand, but this is a test I did awhile back

The weight used is a sharpening stone, probably in excess of 16 oz.
Marty
That is impressive - & even better I have a roll of it in the garage. I hadn't realised what you meant until you posted the picture.
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Dec 25, 2013, 05:39 AM
gpw
gpw
“There’s no place like Foam”
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Not to be too OT here , the present circumstances find us with yards of leftover gift wrapping ribbon .... very lightweight , Strong , and it’s Red ..... Wondering if we can use this to same effect on wings ... Hmmmmm?
Latest blog entry: Lost plans
Dec 25, 2013, 05:42 AM
Marty Petri Sr.
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Try it, please report back with your results, and if you have some, duplicate the test with Pallet strapping, also compare the weight between the 2.

Thanks,
Marty
Dec 25, 2013, 06:35 AM
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Quote:
Originally Posted by gpw
Not to be too OT here , the present circumstances find us with yards of leftover gift wrapping ribbon .... very lightweight , Strong , and it’s Red ..... Wondering if we can use this to same effect on wings ... Hmmmmm?
As ribbon has no natural kink resistance might it need to be "soaked" in epoxy & then it might be heavy...............

A test piece?

I can see a difficulty here that all these reinforcements work to some extent but some will work better than others, some will be heavier than others, some wings need more help than others, the choice of glue will make a significant difference, etc etc etc. How to choose?
Dec 25, 2013, 07:59 AM
gpw
gpw
“There’s no place like Foam”
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Chris , just thinking about it on the top and bottom as a “spar” -ish’ device ( Tension only) , much as we used fiberglass strapping tape in the earlier foamie' years ... The glue is, as you say, the determining factor ...
Latest blog entry: Lost plans
Dec 25, 2013, 09:59 AM
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Agree about the "tension". I am cautious about compression though as many years ago I did have a 1.5in thick brown paper covered white foam wing fold on me. Neither surface was torn but failure resulted from a kink that in essence compressed the top surface and foam - just like pushing in the middle of an empty beans can.

In the good old days of strapping tape I always had much thicker wings than the 3mm or 6mm often discussed here. I guess that the extra thickness might have lessened the need for compression strength. As you have vastly more experience with thin foams than I do I wonder if you consider the kink resistance of the strap as important?
Dec 25, 2013, 11:01 AM
gpw
gpw
“There’s no place like Foam”
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What we found on thin wings was the compression (and tension) stress raised drastically towards the center of the wing , where it meets the fuselage. Easy enough to add a bit of extra reinforcement there with a kabob stick or two ... The wingtips needed very little reinforcing , if any ...
The thicker foam wings were nice adding a bit of distance between the layers of tape .. making everything much stronger...

Just trying to do a bit of Holiday re-cycling into planes .... Might be fatuous ?
Latest blog entry: Lost plans
Dec 25, 2013, 03:05 PM
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Quote:
Originally Posted by gpw
What we found on thin wings was the compression (and tension) stress raised drastically towards the center of the wing , where it meets the fuselage. Easy enough to add a bit of extra reinforcement there with a kabob stick or two ... The wingtips needed very little reinforcing , if any ...
The thicker foam wings were nice adding a bit of distance between the layers of tape .. making everything much stronger...

Just trying to do a bit of Holiday re-cycling into planes .... Might be fatuous ?
Might be fatuous but interesting. Adding extra reinforcement is making life overcomplicated I think.
Dec 25, 2013, 05:37 PM
gpw
gpw
“There’s no place like Foam”
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Problem is, over complication adds weight... usually unnecessary ...
We’ve learned for "ultimate lightness", we build to the very minimum at first and if something breaks , we reinforce that area only ... That way , you don’t add what’s not needed..

well then... on the other hand, while we’re discussing packing bands and wing reinforcement ... Consider a short length of metal packing band across the very wing center... that “should” make this area almost unbreakable , when used in conjunction with the plastic bands on rest... crumbs for thought ...
Latest blog entry: Lost plans
Dec 25, 2013, 07:49 PM
Marty Petri Sr.
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Just for clarity here, the Main Wing spar I am using the mesh tape on is 16.4 mm tall, 6 mm wide. I also laminate the rear spar which is only 11 mm at the LE sloping down to 8 mm at the TE, also 6 mm wide. So there is ample thickness to help with the compression. Nice thing is the tape is buried under the 3 mm skin, leaving an unblemished surface.

On the same note, if you were to use flat carbon, let's say, 6 mm wide, 1/2 mm thick, you would have the same compression issues. Pallet strapping too!

Marty
Dec 26, 2013, 04:36 AM
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Quote:
Originally Posted by mbpetri
Just for clarity here, the Main Wing spar I am using the mesh tape on is 16.4 mm tall, 6 mm wide. I also laminate the rear spar which is only 11 mm at the LE sloping down to 8 mm at the TE, also 6 mm wide. So there is ample thickness to help with the compression. Nice thing is the tape is buried under the 3 mm skin, leaving an unblemished surface.

On the same note, if you were to use flat carbon, let's say, 6 mm wide, 1/2 mm thick, you would have the same compression issues. Pallet strapping too!

Marty
I hadn't realised that you also had 2 spars and a 3mm skin. That makes comparison with just a thin bit of foam very difficult.
Dec 26, 2013, 06:57 PM
Marty Petri Sr.
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Quote:
Originally Posted by ChrisE
I hadn't realised that you also had 2 spars and a 3mm skin. That makes comparison with just a thin bit of foam very difficult.
The test will still be valid, just take some scrap foam, cut 3 identical pieces, say 2"x12". 1 for strapping tape, 1 for mesh tape, 1 for ribbon, an laminate both sides with 1/4" or 1/2" wide material using the same type glue, then test all 3. Log the weights and strength comparisons.

Marty
Last edited by mbpetri; Dec 26, 2013 at 07:09 PM.
Dec 27, 2013, 01:49 AM
Registered User
I looked at using strapping some time back when I was throwing lots of it away
The problem I had with the few experiments I made was as usual glueing it to Epp
I have yet to find a suitable thin glue for Epp I have tried UHU por, epoxy resin, 3M reinforced packing tape, sail cloth repair reinforced tape, double sided mounting tape etc and all have been found wanting to me
Hot glue works for me but it is thick and heavy
The best glue I have found that really sticks is the glue that is on the velcro I use
If we could find out what that stuff is Voila ! I think we will have cracked it
I hope to try and find that out
Dec 27, 2013, 02:00 AM
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Quote:
Originally Posted by ChrisE
Agree about the "tension". I am cautious about compression though as many years ago I did have a 1.5in thick brown paper covered white foam wing fold on me. Neither surface was torn but failure resulted from a kink that in essence compressed the top surface and foam - just like pushing in the middle of an empty beans can.

In the good old days of strapping tape I always had much thicker wings than the 3mm or 6mm often discussed here. I guess that the extra thickness might have lessened the need for compression strength. As you have vastly more experience with thin foams than I do I wonder if you consider the kink resistance of the strap as important?
that is why the strapping is suggested as a replacement for CF.. small diameter CF rods fixed on the wing like a sandwich work much the same way.. the bottom resists stretch the top resisting compression and kinking.. which makes for a strong wing..

for thin foams its better to have both working for you...
I havn't played with many proper tests yet.. but I would think 6mm is likely the lower limit for getting good results , whilst using the strap horizontal on just foam sheets..
I think thinner sheets will likely compress and kink too easily, so perhaps a different construction might help...
Obviously a simple 3mm CF rod will work as a spar, but...
What I have also tried is a strap/balsa/strap sandwich spar at 1/8"- 3mm thick ,plus the straps... that gives a strong result
Held horizontally, holding just 2" in my hand on an 8" stick length and pushing the tip down on some kitchen scales, its been taking 22oz, bending and feeling like its near its limits and likely wont go much further. later horizontal failure occurred at 24oz
All the stress and then the break was at the point where my thumb was doing the pressing down on the top of the stick...

Hold the same spar construct vertically and I got it up to near 60oz when it became a pain, (literally) , to hold. so I gave up ..
I managed to destroy that by using two hands... the balsa core broke as the strap became unstuck from both surfaces, right on the spot where the pressure was being applied by my thumbs...
In a wing you are unlikely to have all the pressure or forces applied at one spot, and likely you would also have the foam either side of the spar to keep the strap in better contact ... my hand hold was loose at the sides
Last edited by davereap; Dec 27, 2013 at 02:45 AM.
Dec 27, 2013, 02:41 AM
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UHU seems best on EPP but you cant apply it thinly.. and when applied thick its solvents go into the foam and take a long time to clear out...
I always iron it to get it sticking better, that helps remove the excess solvents...
EPP is a B***** to stick well...thick UHU and cool melt glue is what I use..
even the Velcro glue is not so clever.. I always spread uhu on the EPP surface before I add the Velcro..


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