Carbon fins project

General Discussion
1
Hello people,
I'm new here and I've been watching this great forum for a while now.
Hope u'd exuse me for few spelling mistakes that I might have...
Wasn't born in the Usa\Aus or Britain....
Anyway I'll get to the point, here it comes:
A few weeks ago I was planning to make a hollow composite board
With a mold. ("Mould" for you british guys...ha ha)
After I had a nice idea in mind I decided to make a small search in the net...
Lucky me, I found this forum and fell directly on lpcdefg's thread
About his unblievely beautiful "Hollow Carbon Shell Board".
Good job man!
I was amazed to see how much we have in common.
My plan and design were very similar to his and in addition, I also "play" with
r/c models as he does. This "playing" period is about 15 years now and actually
this is what I do for my living.
I design and fly UAV's (Unmanned Aerial Vehicles) which are made
Of composite materials.
After I saw lpcdefg's project, I decided to put mine on hold and make carbon fins instead.
I hope u guys will accept me to your comunity and let me enjoy from
Your designing tips ( which I really need right now) .
Before I start being a nag and asking too-much questions I wanna share my small
Carbon-fins project.
.
Enjoy,
Sorry, I Wasn't able to upload the pic's so here is a link to
My G-mail Album...( pics+explanations)

http://picasaweb.google.com/JordanDotan

then click on the "“carbon fin project” pic/icon

2

sweet post dude

cheers

3

Great!

Any thoughts on how to make the back fin?

So far my plan is to make 2 molds, exactly how you have done, but each mold is half of the rear fin.

Then you pour in the microballoons, and let it set.

Then the microballoons get sanded down until it’s level, like I think you did.

Now the two halves can be glued together, making a complete rear fin.

The seam where they join can be sealed and hidden by brushing on resin with graphite powder for colour.

Great post man, those fins look awesome!

Kit

4

wow! very nice!

5

10x guys.

KKSurf, I’ll be back home in two weeks and I’m looking

forward to complete this project and make that back fin.

and ofcourse…there will be pictures…lots of them…too many I suppose!!! :slight_smile:

In the mean time, your way sounds good but there are some rules in composite-materials that might help u, spare u time and make your final product perfect .

one of these rules is -

parts should stay as much as possible in the mold

and if u make a TWO-part product (e.g backfin),

both sides should be all the time in their mold,

when u finish working on each side whilst still in its mold, u can fill it in “whatever u want” , microbaloon slurry for example, and then clamp the two molds together,

then u let it cure , separate the two molds and release the final product from them.

in that case the fin will get out of the mold in its final

form, no trims needed and ready for use.

b.t.w- there is a good way for asuring that the two halfs will be centered but I don’t know how to explain it by words.

U’ll have to wait for the pic’s+explanations.

good luck.

6

Welcome Lee.

Nice work and photos.

What was the finished weight of the fins in grams?

Do they float?

Cheers

7

Awesome!! I wanted to do the same thing for my composite board. I just have to have matching fins. I planned on adding some pluming into my fin molds so I could vacuum infuse the microbaloon slurry into the fin while in the mold. I still need to figure out the many details. Im not a big fan of sanding, so any technique to reduce sanding is a plus. First I have to make a board that I’m satisfied with before I take the time to make some fins. I plan on taking the first ride this evening. By the way, I love my R/C. I think it’s the best thing ever. The only thing that has been getting me down is that people are not building their own planes anymore. ARFS… What kind of planes are you flying?? I’d like to get into UAV’s when I get my engineering degree. Do you post on any r/c forums?

8

Thanks again…did my best so u guys have a colorfull thread.

Craftee- I didn’t check their floataion abilities but I’ll surely do when I get home (14 days)

        skin weight ( Fabrics+resin) was around 10 grams for each fin (if I remember good)  and 

        the total weight depens on the filling that u choose. 

        sinse I just made an experimental fin I really did'nt care for minimizing the weight 

        so I poured inside quite thin slurry .  a 50/50  epoxy/microbaloon ratio. 

        total weight is 32gram per fin while the original FCS is 60 !!!
9

welcome Lee

great thread!

inspirational!

10
Quote:

Awesome!! I wanted to do the same thing for my composite board. I just have to have matching fins. I planned on adding some pluming into my fin molds so I could vacuum infuse the microbaloon slurry into the fin while in the mold. I still need to figure out the many details. Im not a big fan of sanding, so any technique to reduce sanding is a plus. First I have to make a board that I’m satisfied with before I take the time to make some fins. I plan on taking the first ride this evening. By the way, I love my R/C. I think it’s the best thing ever. The only thing that has been getting me down is that people are not building their own planes anymore. ARFS… What kind of planes are you flying?? I’d like to get into UAV’s when I get my engineering degree. Do you post on any r/c forums?

Unlike u I am a big fan of sanding …as long as we are speaking of balsa!!! ha ha ha

composite works should be as clean , precise and profesional as possible …definatly not carpentry! ( again ha ha ha)

GOOOOD LUCK…test ride…Hmmmm sounds like heaven in its best. have fun , hope the board works as u wanted.

ARF’s are for lazy spoiled rich children!!! I’m with u on this one!

Along the years , I have built my planes or from a scratch or from my own design.

only two kits in my record and one small electric F-16 arf ( still ashamed of this!).

this F-16 should take around 3 hours to finish…hmmmm…it took me 3 days! I tried to customize it, add rudder,flaps, landing gear etc.

then I came to a conclusion- never buy ARFs again. they have no soul!

I’m flying praticaly everything and anything. external pilots should have this ability…

three years ago I began flying mostly slope gliders and some thermal…I find it much more exiting and pure than the noisy Nitros.

only me , the model and the wind.

well I better stop talking of R/C before I get kicked out from this forum.

p.s

was participating in R/C GROUPS but not anymore…just lack of time.

11

I really like your pictures, you do nice clean precise work!

Yeah thats good advice about leaving the parts in the mold until finished.

The problem is, the fin will turn out wider that the original fin.

When you lay the carbon fibre in the mold, the cloth laps out of the cavity, onto the surrounding mold faces.

So when the two parts are put together (aligned by using “keys”, thats the word in english :slight_smile: ), the two molds are seperated by the carbon fibre that is sandwiched between them, meaning that the finished fin will be too wide, not a perfect copy of the original.

I was planning on removing the part from the mold, cutting back the carbon cloth roughly and sanding back the microballoons, then putting them back in the mold to be glued together accurately. Thats why the join would need to be disguised with black coloured resin.

I think pouring the microballoons in then putting the mold peices together would be difficult, very hard to get the right amount of mixture to perfectly fill the cavity.

Some air voids inside would be fine (carbon will probably be stiff enough), but if you use two much, the microballoons will squeeze out, and force the molds apart even more!

My plan is to try using foaming PU glue (Gorilla Glue), and mist some water over it to increase the expansion. (it cures with moisture).

Then the glue will expand perfectly to fill the cavity, resulting in a very light weight fin, with a well filled supporting core.

The glue won’t squeeze between the mold surfaces at all. The glue will be measured on a digital scale so each fin is equal, and it should be much lighter that using microballoons.

This will work well for carbon fibre because you can’t see through it.

Clear glass with wooden cores will be harder to work with cosmetically.

Kit

12

Good idea Kit for the super light weight core, the foaming would make some amount of pressure in the mold, don’t know if it would be enouph to distort or break the mold but pressure escape routes could be drilled thru to the top of the fin to let excess foam escape. Trimming the cured laminate in the mold can be done but the mold edge might suffer from normal trimming snags and slip ups which would make the next layup not as pretty, maybe some aluminum oxide, available from West System, could be added in that area of the mold to harden it.

13

very nice !!

thanks for the photos

welcome to swaylocks !

cheers

ben

14
Quote:

then I came to a conclusion- never buy ARFs again. they have no soul!

HA HA HA !!!

ARF’s are like R/C popouts right?!

that quote is too funny

15

Thanks GTFD.

Some care would have to be taken not to over fill will glue.

But i’d be pretty suprised if the hydraulics of the glue foaming overcame the vac pressure. Maybe increasing pressure with time as the glue reacts. High pressure at the start may be able to collapse the mold, when the inside is not filled with foam yet. May take some experimentation to get it right, but weighing the glue accurately should allow me to adjust and get it right in a couple of trys.

I may just make the mold super strong, so I can crank full vac and not worry.

I keep all off cuts form glassing a board, and use poly resin cos it’s cheap, and you can make the molds really quick with UV cure. Just add another 10+ layers of 4 ounce and nothing will break it! Anyway, it’s good to have a sturdy permanent mold that will last.

I was thi nking that i’d remove the fin halves from the mold to trim them, there should be a well defined line to cut along, and that will avoid damage to the mold.

Then just place them back into the mold, ready to fill with whatever.

16

KKsurf-

I quote you:

"the problem is, the fin will turn out wider that the original fin.

When you lay the carbon fibre in the mold, the cloth laps out of the cavity, onto the surrounding mold faces. "

there is another aspect that u haven’t thought about!

I learnt it by trial and erorr !

when u leave “extras” or as u call them , laps out of the cavity, they cause anoter problem…

the thick fabrics are not able to take the sharp corners between the cavity and the surrounding faces.

even vacuum bagging doesn’t solve this problem and is not

powerful enough to press the fabric onto the mould.

the result is an air buble that ruins the leading and trailing edge of the fin.

the painful truth about composite materials is called

PREPARATION!!!

it means that if u prepare the materials , fabrics and whatever u need , in advance, it will make your work easier

when its time. and its never to much!

and sinse this is not an easy work specially when the epoxy is allready mixed and the clock is ticking,

every singel thing might help u.

cutting the fabric into its exact size prior to the epoxy mixing will help u in three things:

  1. save u time in triming the “extras” later.

  2. prevent that air buble and fabric separation in the

    edges.

  3. solves the problem of a thicker_than_the_original final

    product.

there is a very good method for cutting the fabrics, that makes your life easy.

its called “wet layout”.

basically u take a nylon layer , lay all the fabrics u want

(e.g , I used 1 layer of microglass and one layer of carbon)

then u wet them with mixed epoxy and lay another nylon layer on top.

now we have a 4 ply “somthing”

( I don’t know how to call it)

ok i’ll try better- N.C.C.S

Nylon Carbon Cancer Sandwich…hahahaha

now if u were smart enough to prepare a cutting template shaped like the desired element,

now u can easily and cleanly cut those wet, nylon covered, fab’s into the shape.

peel one nylon layer from the side that u want lay on the mold, you can play with it, re-fit it, peel it and put it again etc.

then peel the other nylon layer and proceed with the next

stages of vacuum bagging.

huuuhhhhhhh…how much I wrote!!!

I hope all of this nonesense helps u in somthing.

there is a lot more to say but i’ll save some ,before my fingers faint. :slight_smile:

B.t.w

thanks for -

“(aligned by using “keys”, thats the word in english :slight_smile: )”

it will take me some time to improve my english …

this is a good experiance!

17

That process you descibe sounds like it will be faster as well.

I’ll give that a try, thanks!

Putting a gel coat into the mold first might help the bubble at the edges? The resin could flow in to fill the voids?

I have a huge tub of milled fibreglass, it’s useful for making the mold surfaces strong and chip-resistant.

I’ll add some to the gel coat of the fins, so the outer layer of resin will be strong and hard. Then it will be ok to build up the sharp edges a little with resin only.

The resin that forms the sharp corners of the FCS tabs will be much stronger with the milled fibre also. I assume that the carbon cloth can’t fold into the sharp corners of the tabs?

Kit

18

This is really brilliant, I love it. A small step on and you can do the whole thing using infusion or RTM (resin transfer moulding) , ah god here I go again!. That way there’ll be no bubbles and you can put in a core at the same time. Lay it all up dry, hold the layers in place with frame mount spray adhesive, close the mould halves, evacuate, suck in the resin. This is how some of the big producers must do it??

19

Wait a minute…is that sarcasm in your voise???

or u are serious and I misunderstood u…

anyway, yup , the pros’ do it almost as u described!

20

NO,no,no sarcasm, really. I’m playing with this all the time at a boatbuilding school, it’s a great way to go…