DIY Strut to board plate failure report

[revhed]

This is for the D I Y guys to hopefully learn from like I now have.
4th build using a 1.1 cm factory pultruded, extruded carbon plate for the strut, fuse.
7 mm same style for board plate.
Both surfaces factory prepaired for epoxy lay up, textured.
Strut meticulousy cut L E and T E to fit into slot in board plate like this example at the strut to fuse.

Flown for 2 seasons, hundreds of sessions.
Almost never run aground.
fuse and wings, strut to fuse mono block

Complete failure

So now to repair much stronger hopefully.
I will get the top of the strut straight and level.
The board plate will also be completely flat.
The failer used 3 layers of 300g on each side over a 3 cm dia fillet, finley chopped carbon epoxy mix, vac sacked.
I will texture all surfaces to allow the best bonding and then use 3 layers uni in line with the strut and 3 layers bibias on each side over 4 cm dia fillet vac sacked and cooked of course.
The problem as prooved here is a mechanical bond as opposed to a chemical one.
So if possible either layup your strut to board plate continusouly as most mold guys do, or make sure you join parts BEFORE the chemical "Keys" are cured, check your epoxy.
QUESTION?
I have read that on board repairs to go increasing surface area lay ups for best mechanical strength. First 3 cm dia for example followed by a 4 cm dia. ect...
Shall I do the same, meaning each sucessive lay up will over lap the previous by about a cm or so onto the strut top and board plate.
OR,
Start with the longest layup and reduce each succesive layer.
So for all you epoxy carbon lay up gurus, which is best and why please?
And or any other ideas.
My third build was done exactly like the 4th and no sign of weakness or failure, yet, and she is my high wind friend so used a lot more where I live seeing much more stress.

Side note,
A new Ozone R1 17m2 on long lines was the only kite on the water all day
at the MDV flying a Radical KBHF.
Big slow kite loops flown both for water starts AND turns, every one!
Needless to say ultralite wind, I did not have my calibrated meter with me but we all agreed about 6-8 knots, and at times less untill it would not get the pilot up.
R H

[tkettlepoint]

that sucks REV but after all those sessions it is a great DIY.

for the lay up I would go smaller and over lapping bigger each time.. it will spread the load better is the way I see it

That is the way I fix all boards if boxes and such are pulled.

Terrie

[Bille]

...

That is the way I fix all boards if boxes and such are pulled.

Terrie

I have a Way Better idea :

Package the body , pylon , and both wings up ; and send it to Me ; and i will fix it .
I'll even pay shipping ; of course you won't be getting it Back !!

On a more serious note :
You see the plane-weave carbon on the Right side of your above picture ?
The weave is running the Wrong way ; it should have bin turned ( + - 45-deg)
so the actual contact on "All" the tows at the junction , was giving strength to the joint.

The way it is ; only 1/2 the carbon tows are adding strength to the pylon
and plate connection, and the other 1/2 are doing nothing. I made that same mistake
with one of my carbon legs, and it broke right away.

Bille

Ps :
Glad to see your using 1.1 cm factory pultruded, extruded carbon plate for the strut, fuse.
7 mm same style for board plate. That stuff adds Gobs of strength !!!

[Bigdog]

How did you shape that mast? Is it all uni? How is the torsional stiffness?

Stan

[revhed]

How did you shape that mast? Is it all uni? How is the torsional stiffness?

Stan

A lot of time!
The plate my good friend gave me was about 1m 20 X 68 X 1.1 cm
Heavy, dense, brittle, but with quad ultra thin factory lay ups.
Cut with diamond blade jig saw, slow.
Shaped with diamond dust angle grinder, slow.
I really should do the FK24 twist and length flew test to know for sure.
I made 2 with this using different designs for the fuses.
I think the strut twist and flex compair to most factory set ups, but for sure not as stiff as Sword 1, or any alus.
Off to grind.....almost nuclear work gear needed to not come in contact with nasty carbon dust, but I have the habit.
R H