less Carafino more hydrofoil

[Bradn]

Do you have a vacuum pump? I would recommend some pressure with the glass/carbon layers.
maybe since it's straight, just to get it working, clamp some thick rubber on top? will not be consistent but at least some pressure all around?

[zfennell]

this is my latest failure
4 layers 6 oz fiberglass very flexy .
70 kgs of load.
can i just lay 2 layer of carbon on top?
what shoud i do?

hi pedro,
save the carbon for a while.

it did not break because it wasn't STIFF enough.
it broke because it was not STRONG enough.

is the wood core damaged?
did the glass fail on both sides?
im assuming we're looking at the compression side, yes/no ?
how long did you cure the laminate?

your test does provide a pretty good map of where the stress is too high.
that's really the area that needed extra glass.
if the core is still intact, adding glass to the center half of the wing ( with smooth transitions) will keep the reinforcements where they are needed.
if you are still trying to minimise the amount of reinforcement , it was the span-wise fibers that failed. Perhaps a higher concentration of uni D if you can find it.

your pic shows enough xtra glass for another layer, try to minimise the waste and put it back on the foil.

when you finally have enough glass, you will be the first to know how much carbon you needed.
save it until then.
-bill

[windfreak74]

Hello Zfennell,
no core damage
only the compression side is damaged.
i have an 18oz. biax glass with mat(1.2 mm thick )i can reinforce the midlle part but it will change the profile of the wing dont know if its that relevant.
i was thinking 6oz carbon because of the stiffness and less material.
what if i put a layer of carbon on the bottom of the wingso it will fex less on he compression side?


Off topic but how much anhedral is good enough?
i was thinking something about 3cm anhedral to make a new wing.
its seems easier to make a small winglet mould and epoxi it to each side of the wing.
what do you guys think?
Pedro

[Bille]

this is my latest failure
4 layers 6 oz fiberglass very flexy .
70 kgs of load.
can i just lay 2 layer of carbon on top?
what shoud i do?

>> 4 layers 6 oz fiberglass very flexy .

Flexy enough to push anhedral without breaking it ?
If so, then jig your work up, and Mold it . Watch that Ya Don't screw up
your twist by doing that though !

With a Mold, you can build several of them. till it's Strong enough !

Bille

[zfennell]

Hello Zfennell,
no core damage
only the compression side is damaged.
i have an 18oz. biax glass with mat(1.2 mm thick )i can reinforce the midlle part but it will change the profile of the wing dont know if its that relevant.
i was thinking 6oz carbon because of the stiffness and less material.
what if i put a layer of carbon on the bottom of the wingso it will fex less on he compression side?


Off topic but how much anhedral is good enough?
i was thinking something about 3cm anhedral to make a new wing.
its seems easier to make a small winglet mould and epoxi it to each side of the wing.
what do you guys think?
Pedro

0-90 biax?
or
+/_ 45 biax?

matt?
that never sounds good.
if our definition is the same....little fibers in every direction.
that about the same as a lam with aluminum sheet

i think it broke due to lack of 0 deg fibers.
adding reinforcement to places that did not fail (other side) doesn't sound very efficient.

adding very stiff carbon to soft e-glass tends to negate any loads the glass 'used' to carry.
its a bit like starting over with just carbon

[ozchrisb]

the top laminate failed .should i try to save the wing or start over?
do i have to sand the part where is cracked?

It looks like it failed in compression on the top? i.e. did the wing bend up towards the board? Firstly, carbon doesn't work well to resist compression. If the top laminate is failing (even in glass) make sure you pay attention to the bottom of the wing. It's that side that you want to stop bending.
You can probably reuse the wing. If it cracked you might want to glue it back together. Think of what you're doing as make a fancy carbon tube with some wood in the middle. It's the skin that's providing the strength, not the wood. Grind of as much of the glass as you can. You don't want "floppy" broken glass in there, and you'll get better adhesion if you grind off as much of the cured epoxy as possible. Good luck, it's looking good and you're close.

[windfreak74]

Bill,
Its +-45° with a 2 oz mat.
i just wanted to know if it was worth saving.
the 6 oz. carbon i have is 0/90 or 16 oz carbon 0/60/60 triax.
maybe billys sugestion of making a plug with anhedral is good and use the carbon to make a new wing.
ozcrisb,
thanks for you sugestion!!
Pedro

[zfennell]

of course its worth saving.

but IMO.
its not worth saving in carbon (especially if you put it only on the tension side)
and
its not worth saving if you use +-45 cloth to solve span-wise bending
(twist may still be waiting for you)

maximise the use of 0 deg glass
add it to the failed side (in the middle, where stress is highest)

dont worry about thickness or stiffness until you solve the strength problem.
make sure you follow the manufactures directions for full cure to 'full strength"
( i doubt 48 hrs of cure will do the job unless proven otherwise)

once it works, you will have all the numbers to convert to desired amount of carbon, stiffness or thickness.
it will work.
sail it for a while while you think about what really needs to change.

BTW.
how much do you weigh?
and
how much did it bend?
and how thick is each layer of 6oz?
and how much epoxy ends up in the lam?
did you test the mixing cups for full cure?
there is enough material in your off cuts to do tensile tests ...maybe?
my point is keep track of the all the numbers, for everything. (weights, temp, time load, displacement)
the information you have is the best tool for predicting changes.

[WCH]

Try orienting you grain of wood different, think about a 2x4, carry,s a greater load on it,s edge.
You can also glue it together with a layer of 4oz cloth between the lamination, use 1"strips, using this technic, you can also cut your anheldral shapes, and after drying hand shape your leading edge and lifting foil shape, the bottom of the foil can be flat. After shaping, use a couple of layers of 6oz glass top and bottom, with a couple of patches around your bolt hole. When shaping your lifting foil, use a cut out pattern, of you choice of air foil you can find on the internet.

[windfreak74]

i did not wait 24 hours on the cure!
kept it on vaccum for 4 hours until the epoxy was hard enough.
i cooked it for an hour on oven at 60 degrees
that about it.
no scientific or tiiming method used.
ill keep track of everything from now on.
someone commented on a heat curing for several hours at 60 °C in a controled temp box.
i have to do the box.
i wil do both sabe the wing as experiment and do a new one dirrectly in carbón to see the diferences in construction and stregth.
thanks Bill i will adjust all parameters to have a superior build.

thanks guys for all the tips!
Pedro