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Old 09-12-2013, 01:03 PM
  #39  
MTK
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Originally Posted by serious power
Hi Matt,
I will be sticking with balsa skins.
If the skins are stiff enough I can lighten the foam cores more.
Then once built I will/should have stiff wings.
The issue with these thin bipe wings is not really that of load carrying.
Resistance to twist is what I'm after.

I have read your derivative thread.
I also taper skin thickness to the tip - you don't miss many tricks !
I'm hoping to pull a little chord-wise curve in the skins while applying the veil to the inside.
Based on your thread the internal applied veil will weigh approx 15g so say 20g for both wings.
The veil itself will weigh 10g.
I estimate the foam cores at 63g to 85g per panel depending on foam used - will be either 15Kg/m\3 or 20Kg/m\3.
Using the 15Kg variety the total for cores will be 250g.
Removing ; 30% = 75g - 50% = 125g
I will remove at least 30%. - but because of the mount system/ boxed lay-out of the bipe wings (ie the model in the middle and then the out-rigger struts working in both tension and compression) I should get close to 50% out.
The plane will not only be electric it will be contra driven- no vibes,torques, or asymmetric thrust issues to deal with - just flight loads as applied.

Perhaps you could check my inside applied veil weight estimates in case I got you wrong !?
I will do test samples anyway.
Thanks again.

Brian
Brian

I assume that your two wings will have an area of about 1400 squares, or roughly 10 square feet. For skinning or veiling purposes, the actual area is twice that. That's equal to about 2.3 square yards of area so veil alone (assume your veil is 0.2-0.3 ozs per sq yard) should weigh about 14-18 grams total. Add roughly 10 grams total each wing for dope to help affix the veil to each skin. The affixed veil should add about 35-40 grams total to both wings. Epoxy or gorilla will add its own weight of course which will likely be around 25- 30 grams each panel (two sheets, around 350 squares each). The balsa should weigh around 30 grams each sheet.

If my rithmetic is right, 175 grams for cores, 240 grams for sheets, 110 grams for epoxy, 40 grams for veil. Less than 570 grams for two wings with no substructure added.

The heaviest parts are the sheets. Have you considered 0.75mm thick balsa? With the veil inside, it will be strong enough especially for E-power. No need for tapering. That's what I used on the stab of my DLE55 powered Delta...just an idea unless you've purchased the wood already

Last edited by MTK; 09-12-2013 at 01:09 PM.