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Old Aug 19, 2015, 08:32 PM
pzanni is online now
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Australia, ACT, Canberra
Joined Feb 2013
198 Posts
Help!
Wing joining techniques - Carbon tube

Hi all.

Plan to build a 2.3m powered glider.

As it's a twin boom pusher, the centre section of wing, 420mm, will be permanently attached to fuse and house tail booms and elevator/rudder servos.

Each wing will be removable.

Plan to use tapered carbon fibre shafts approx 900mm long in each wing, protruding 100mm from wing to sleeve inside aluminum tube located in centre section.

The CF tube at root has OD of 12mm whereas the airfoil, Eppler 205, calls for 18mm (which is the profile minus the 2.5 mm corflute top and bottom wing skins).

To make up the difference in height, increase strength and to create a better surface area for glueing spar to wing, I plan to make a spar box from 3mm corflute, 18mm square and length of CF spar or until the taper of wing allows.

Given the alum tube in centre piece will be larger diameter, I plan to make the box for that section from 2.5mm corflute. I may need to crush the box upper and lower sections around the tube a little to get the depth right.

Obviously I'll need some smaller locator tabs/rods on LE and TE as well. Will probably use BEX 3m glider techniques for that.

QUESTIONS ARE:

- will this approach be strong enough/work?
- is there a better way? Perhaps ply rib ends for wing and centre piece to receive corresponding tubes? I could do foam cores as well but want to try without for the first wing.
- open to opinions on how much overlap I need where the carbon tube sleeves to central tube too. I read somewhere that the overlap should be at least 4 times the diameter of the tube so 100mm should be plenty?

Would like to keep weight down where possible. Rough calcs puts my corflute box idea at less than half the weight of a ply box.


Root Chord: 220mm
Spar height root: 18mm

Tip Chord: 160mm
Spar height tip: 11mm

Any/all constructive comments welcome!

Many thanks, P
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Last edited by pzanni; Aug 20, 2015 at 04:03 PM.
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