Many thanks for the offer Don, but I think I'm ok sourcing suitable aluminium locally. I have a friend who can mill it to shape and drill the holes for me. I'll post more when the repair and re-test is done - hopefully next week.
Thanks Don - it would indeed be useful to see your calculations so I can compare them to mine.
To answer an earlier query in post
- the bearing strength of the 195gsm carbon twill that I used throughout my build is 80,000psi according to Jim Marske's Composite Design Manual.
You can find my original load/stress calculations
- pages F4 and F5 detail how the carbon Load Transfer Bars and wing root metal fittings (for a 2-part wing) are calculated. In my calculations they need to be a minimum of 17 layers of cloth thick to carry the loads. I made my root section LTBs from 21 layers of CF cloth, encapsulated into the spar by a further 5 layers of CF cloth.
The LTBs transfer the spar cap loads from the pultruded carbon rods that run the length of the wing to the metal fittings. The page numbers (F4 & F5) refer directly to the corresponding pages in Marske's Composite Design Manual.
Yes indeed - I got all the repairs completed before I headed off to France for the summer but I haven't had a moment to myself since I got home again (busy boxing up my mother's house for a big move... and now unboxing!) Now that things have settled down again, I'm waiting for a suitable weather window to set up and repeat the load test... but I will have to be patient, as the winter weather fronts have started their usual monkey business already - sun, wind, rain, every five minutes!
I ended up fabricating a pair of 1m long x 50mm wide carbon bars using biaxial carbon and laminating them onto the front surface of the centre section of spar (top and bottom) and encapsulating them in several more layers of bi-axial carbon cloth (see pic below.) These carbon bars extend well beyond the two #1 ribs and are tapered towards their ends. A pair of 10mm x 50mm x ~500mm aluminium plates, bolted through these carbon bars, add further stiffness to the unsupported centre 17" section of spar (I've no photos of them yet.)
There am I happy! During the summer I was wondering if and how you would solve the problem, but didn't want to ask. I slowly got the feeling you were discouraged and stopped. Happy to hear that it was the season. I just started building again, for the same reason you could't do the load test, unflyable weather.
Btw, where do you fly in the south of France, Laragne? Your profile photo is Monte Cucco, isn't it?
Keep my fingers crossed for your next test, but the construction you made looks very promissing.
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