hi..id like to confirm that the idea of wood for core material is good....my test determined that with thin laminates.....taking into acount the home builder,cost,strenth weight......a core of no lighter than 200 kg 2m was best in the 6mm pannel range.....hunny come is bad news as is end grain balsa..balsa is good...simple ply is a winner eaven when it is thinner.....the lighter the ply the better..
id also like to add that 2 oz glass is the same weight as 6 oz carbon once laid up...i know it sounds wrong ...and it surprized me too...i have here a tail boom skin of bothe and they weigh the same...try a sample.....the conclusion was i might as well use carbon.

russ.


On Sun, Oct 16, 2011 at 11:34 AM, Bill <This email address is being protected from spambots. You need JavaScript enabled to view it.> wrote:


That was the thinking in the building of the Millennium wing D-tube. Carbon-Kevlar-foam-Carbon-Kevlar. That was for the first couple dozen wings then they decided the pro/con arguments for Kevlar wasn't all that great and replaced it with all Carbon so, Carbon-Carbon-Foam-Carbon-Carbon was used on the later wings.

Billj3cub
Millennium #12
Beaverton, Oregon



On 10/15/2011 3:44 PM, Philip Lardner wrote:


If a D-skin made of a couple of layers of plain carbon is strong enough but too vulnerable to puncturing then could a couple of lams of carbon/kevlar mixed cloth or one layer of kevlar over one layer of carbon give us the strength and impact resistance we're looking for?

Phil.

www.easycomposites.co.uk/products/carbon...r-22-Twill-1-2m.aspx

---

From: This email address is being protected from spambots. You need JavaScript enabled to view it. [This email address is being protected from spambots. You need JavaScript enabled to view it.] On Behalf Of Daniel Armstrong
Sent: 15 October 2011 21:21
To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Subject: [Carbondragonbuildersandpilots] Alternate D-Tube Skin Concepts




A while back, I built some skin samples using 3 oz/yd2 fiberglass face sheets and 1/4" thick 3 lb/ft3 divinycel. The parts came out very stiff and smooth. The part was about 50% heavier than the combination of skin, core and epoxy individual weights. I vacuum bagged the part, but the core absorbed a lot of epoxy that didn't add to the strength. The skins were easy to puncture and probably not damage tolerant enough.

The 1/32" birch ply core is pretty resistant to punctures and the 1.45 oz/yd2 face sheets will take all of the torsion loads.

The 2 ply carbon (282 style) samples were pretty brittle and easy to puncture.

Nomex core is difficult as you note. The skin is easy to puncture between the cell walls, it requires a mold and probably an oven and film adhesive to get good bonds. For my experiments, I have been keeping to relatively simple technologies. Since the glass plys are adequate for the loads, the core could be something like dense balsa or cedar. The core has to take out of plane compressive loads without denting easily. The samples I made with balsa cores dented too easily. The core was about 6-8 lb/ft3 balsa. 12 lb/ft3 balsa might work, but I haven't tried it. The core wouldn't have to be plywood since the face sheets are adequate for the shear loads. If you have ever seen a cedar strip kayak, this would make some beautiful gliders. Northern white cedar can be found with density of about 19 lb/ft3. A .05" or .06" thick core would allow around 5" rib spacing in the d-tube.

These notes are from some work I was doing in the late 1990's, but are probably still possibilities.

Dan