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May 22, 2019, 09:49 AM
flyin' fool
goldguy's Avatar
You have the wrong density EPP. My builds are way lighter than $TF even with 'stiffiners' or most other foams I've used. MPF is the best of the rest as most other foams found in $$ stores are too brittle.

What's the span of your deltas?
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May 22, 2019, 10:00 AM
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Thread OP
30" span. Delta is cut one piece from a 20 x 30 board. When you say your EPP is lighter than $TF is that at equal thickness? Because this EPP is thicker than the $TF, so the difference per square inch is more due to thickness than density.

But even though the EPP is about twice as thick, it's way flexy compared to the thinner $TF and it's that flexibility that's causing me problems as the airframe is yielding to aero control forces.

Additional stiffening will be the answer, but now the weight penalty will be even higher.

I have some MPF samples coming. (thanks springer) Might have enough to piece together into a single layer test wing.
May 22, 2019, 10:35 AM
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One thing I can say is stay as far away from the $0.88 foam board at walmart.

It may look like DTFB but the paper is lousy on it. Even with a brand new #11 blade my paper "crinkled" rather than cut, and, if you want to remove the paper? Only way is with iso-propyl alcohol.
May 22, 2019, 10:47 AM
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Originally Posted by goldguy
You have the wrong density EPP.
Just measured and weighed a sheet. It's 1.3 lb/cu-ft. I think that is the lighter density. Choices are usually 1.3 and 1.9.

Here it is RTF with the carbon strut visible along aft centerline. But currently raining

We currently have about a dozen of these ($TF version) flying or in build. As I'm the combat series organizer, I'm continuously looking for improvements that add to the fun or at least durability without affecting cost or complexity. This is one of those experiments.
Last edited by hard line; May 22, 2019 at 11:04 AM.
May 22, 2019, 11:46 PM
flyin' fool
goldguy's Avatar
I never use 1.3#, way too floppy as you found out. I usually slice my sheets to 6, 8 and 10mm thick.

I always cut out and shape all the bits, and then go over each piece with my iron. That gives it a nice shiny finish, melts all the fuzzies together to add to the surface rigidity and needs less paint. Test iron first!

As concerns weight I've got a 30 wing that weighs 4.4 ounces RTF with a wing loading of 2.4 ounces per square foot and out performs all my other birds, even in big wind.
May 23, 2019, 09:22 AM
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4.4oz = 123g. Mine is about 400g. That might be a show-stopper.

You've got me stumped. You're using denser foam and getting 1/3 the AUW? We must have way different battery and electonics.
May 23, 2019, 12:09 PM
flyin' fool
goldguy's Avatar
That's probably the main difference for sure. I use smaller lighter gear. Over the years I found it worked for me.

But, just go with what you have on hand. I cycled (bought./sold) my gear many times to arrive at where I am now.
May 23, 2019, 12:23 PM
flyin' fool
goldguy's Avatar
I guess I'm a bit obsessive about building light, right from the choice by weight of items, from the prop to the control horns.

An example is a high quality small motor I have compared to a cheap one at half the price, but with the same weigh, stator size and kv. On the same voltage and prop the elcheapo one wins hands down on efficiency comparing the watts in. So, the expensive one gets sold and more of the cheap ones ordered.
May 23, 2019, 01:05 PM
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Ahh, your little guy is a Crack Wing, now I understand. I have one too, but it's stock. I see you've done a tractor version. Nice. Any videos?
May 23, 2019, 09:16 PM
flyin' fool
goldguy's Avatar
It's a tractor, with rudders and lots of CF rods to make it rigid. The most amazing wing I've ever flown, does everything and more. I can even shoot touch n' goes with mine. Note the skid under the nose and have CF rods at the wing tips. No broken props too.

No vids yet.

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