Twinstar wing strengthening

[Steve W-O]

The Twinstar wings seem very flexible, I have read of people putting a strip of fibreglass tape along the bottom of the wing for strengthening.

I tried this on pieces of loose foam, and found that although it did add a bit of strength, the top part compressed, and the foam folded because of the top compressing instead of the bottom tearing. This happened on my depron sonicboom, which is why I tried it.

What I am thinking of now is embedding a 2mm diameter carbon rod in the top of the wing to take the compressive forces.  Testing on foam, the tape on one side and the carbon on the other is immensely strong.

 

Wonder if anyone has any comments or other ideas? 

[Simon Chaddock]

Steve

I don't think this post is in the right place but never mind.

An adhesive glass fibre tape fixed to the foam will be pretty efficient at resisting the tensile forces but to effectively resist the compression forces the carbon rod should also be securely fixed to the foam rather than just embedded in it.

 

With such a small diameter rod this will be difficult to achieve which means the wing would fail long before the rod reached it limit. You would do better to use a lighter material but in a larger size to give more area to glue to the foam.

 

I have found hard balsa works well as both the tension and compression elements, it glues well to the foam and has the benefit that the wing is equally strong in both directions.

This shows the detail of my balsa (red) reinforcement on my "built up" Depron wing.

The wing centre section under construction. Apart from the balsa top and bottom spars all the rest is 4mm Depron sheet.

I have used this technique right up to the 60" wing on my Giant Dragon.

I hope this helps

 

[Steve W-O]

Thanks Simon,

Just the kind of info I was hoping for.

 

I did it yesterday, and I am happy that it will give the added strength I am hoping for.

 

There is a difference from yours in as much that the wing has a 10mm carbon spar for half its span, so hopefully it will be OK.

 

I have overlapped the 2mm rod by about 10cm over the main spar. I cut a slot (single cut, no material removed) 6mm deep, pushed the rod into it with CA.

 

I tried it on 3 layers of 6mm depron and the rod stayed fixed, so it looks promising.

 

If I was to start a wing from scratch, I would use a more conventional  method as you show, however the wing is basically strong enough as it is, but some people have had problems when the plane is heavily loaded, and as I want it for a camera, I just wanted to do all the probable necessities first.

 

Out of interest, I almost always use ramin for my wing spars, it is only fractionally heavier than balsa, but quite a bit stronger.

 

Also use it for fuselage frameworks then cover with depron.