smchale

My Feedback: (67)

I'm looking for a little direction on some carbon fiber sheet, and a source. I'm looking to use it to act as a fuselage bulkhead and an integral wing spar in one piece. Where can I source such material, and can I get it cut? I'll layout the dwg in CAD, but can it be water jet cut? I think 1/8" thick should be sufficient. The fuse is fiberglass, and I assume that a glue like hysol or aeropoxy would work? Thanks for any suggestions someone can offer.

ByLoudDesign

http://www.cstsales.com/products.html
http://www.acp-composites.com/home.php
http://www.fiberglasssupply.com/Prod...t_catalog.html

smchale

My Feedback: (67)

Do you think I may be better off with a Carbon Fiber composite with a birch core? http://dragonplate.com/ecart/categories.asp?cID=3
Looks like these guys will also cut it for me. I'm sure just having this part made will cost a small fortune, but worth it.

daven

My Feedback: (1)

would you consider doing it yourself?

laminate a piece of 1/8" lite ply on both sides with 5oz carbon should be strong enough for just about anything our models could put out.

I've done this with lighter carbon and it adds amazing strength to the ply. I like to cover a board of 3/4" mdf with waxed paper that is slightly larger than the piece your are to laminate. Wet the carbon out on the wax papered board and then put your piece on top of the wet carbon. Apply carbon and epoxy laminating resin to the top side, add peel ply, paper towels, and breether cloth and toss in a vacumn bag and suck it down to the wood at 23-25" of mercury for 24 hours.

Take it out of the bag and trim away the excess material to the wood. I use lighter carbon so I can get away with a xacto blade, you may not be able to do that with thicker carbon.

I really think solid plate would be overkill, and extremely expensive. I might make sense to laminate a slightly oversized piece of wood carbon, and THEN have the piece cut out by laser. Would make clean up, much easier.

smchale

My Feedback: (67)

Dave, thanks kindly for taking a few moments to weigh in on this. Certainly seems like you've been down this road before. Unfortunately i don't have the vacuum bag gear and don't want to invest in it for so few applications I run into. I'll take some time to draw up what I'm looking to do and then post back here to see if there are other ways to skin this cat.
In the meantime if anyone has any suggestions on what to look at, i'm all ears.

Magne

If the fuselage is fiberglass, then why do you need such a massive internal former?

Almost all the pre-fabricated carbon composite plates (solid carbon or carbon/wood laminates) will be manufactured by wowen carbon (0deg/90deg).
For a wing spar, 50% of this is just dead weight.
You can easily make a wing spar from unidirectional fibres, optimising the strength/weight ratio.
(Or buy a PBG composites carbon wing tube which is more suited for the job.)

Just an opinion.

Regards,
Magne

apereira

  HobbyKing has them on 1, 1.5,2 ,2.5mm and are around $12

smchale

My Feedback: (67)

The goal is to create a strong fuse bulkhead with an integral plug in wing spar. The model is a Hawker Hunter jet and going with a wing traditional wing tube arrangement would have the tube going right through the intake ducts spoiling the flow of air into the fan. My original thought was to use ply bulkheads in the fuse and bolt a custom aluminum plate former/spar to it, but now I'm thinking of saving the weight and making the former/spar out of a laminate sheet and bond it inside the fuse. Here's a quick sketch of my plan when it was with the aluminum plate....this is the direction I'm headed and am looking for a good composite material for the job, as well as a source to purchase and cut it to my AutoCAD dwg (which I'm working on).

invertmast

My Feedback: (23)

I believe the plywood piece and covering it with carbon will be your best most economical option. I've got some of the 1/16" and 3/32" dragonplate and the stuff is STRONG. But i wouldn't want to rely on it completely for a wing spare.  and you dont "have" to vacuum bad the ply/carbon laminate.  you can just do a normal wet layup like described earlier and apply some peel-ply (100% pure polyester cloth works great and is cheaper) and just let the part air dry..  The trim the excess carbon and your off to the races.

Bob.R

My Feedback: (2)

As others have said, vacuum bagging CF over ply is not necessary - a simple wet layup of CF onto the ply will work OK for your application, although it will be a bit heavier. Makes for a very strong composite plate.

Also, you can trim the excess CF with a knife before the epoxy fully cures - much easier than waiting for full cure to trim.

timrob

Invertmast (and others), what does peel ply do, and how do you use it (it is the last layer in the laminate?

Tim

invertmast

My Feedback: (23)

basically, it soaks up the "amine bloom" (shiney waxey looking) layer that the resin gives off when it cures, making the surface ready to bond practically (Istill go over the area w/ some coarse sandpaper and clean it well just for the extra piece of mind). if you are going to just do a wet layup w/o any vacuum bagging, you can go wet out the carbon and apply it to the bulkhead, and then the side not in contact with the wax paper, you can put the peeplply on it and remove the air bubbles.

I have used 100% polyester cloth (available at walmart for $1 a yard)before, instead of spending the $3-5 for actual "peel ply".

timrob

Thomas,

Thanks for the info.

Tim.

smchale

My Feedback: (67)

As I want to use part of my piece as a plug into a socket in the wing, wouldn't a premade piece cut to the correct shape be better and smoother than doing a wet lay up myself? I'm still working up my template and will post some more pics soon.

timrob

Hi Guys,

This is a little off topic, but seeing we are talking about CF, I thought I would ask:

I was wondering how CF parts such as hatch latches, control horns etc. are made. I know they put the CF into a mold, but how do they mix it in powered form in the resin to put into (say) a silicone rubber mold? Would love to know what the process is.

Tim

flyintexan

My Feedback: (1)

Sean,

Sounds like an interesting project.

I would recommend getting this part first laser cut from aircraft ply....not sure what thickness you wanted to use but perhaps you could use two pieces and laminate them together with c.f. between.  Layout some holes that can be used simply to join the two pieces with pins or small screws.  This may serve only as an experiment for your final part, but it sounds like it might be worth the investment.

I can highly recommend ak models for laser cutting.  Alex's work is very professional.

Good luck,

Mark

smchale

My Feedback: (67)

Spent a little more time working on my wing attaching arrangement. Cut sample templates out of 1/4" thick poster board after drawing them up in AutoCAD.

The distance from the tip of the 'stub' to the C/L of the fuse is 18".

Below is the shape I'm going for....allowing a solid bond to the fuse and ample area to run some ducting back to the fan from the inlet on each side.

invertmast

My Feedback: (23)

smoothness is just a asthetics part, typically the "glass look" you see on most carbon parts is just a layer of extra resin to make it more asthetically pleasing and has little to nothing to do with the strength of the part.

smchale

My Feedback: (67)

Thomas, for my purpose can you recomend a source and product for the carbon cloth, resin, etc that I would require? I'm wondering if 2 pcs of 1/8 thk aircraft grade ply, with carbon cloth on each side and in between the sheets would work form my use? I could let cure between two pcs of glass if that would help with keeping it flat and smooth. Anything else I would need?

invertmast

My Feedback: (23)

since that particular bulkhead is basically going to be "do or die" for your airplane, I would personally build it up using 3/16 or 1/4" aircraft ply (such as a 10ply wood) w/ a layer of carbon on either side and then possibly a 1/8" aircraft ply "doubler" on either side of the carbon for the outer 1/4 of the bulkhead. this would give you an extremely strong and probly extremely overbuilt bulkhead.... I would probly go w/ the 2.9oz plain weave fabric p/n # WF-18A from ACP composites.
http://www.acp-composites.com/home.php?cat=251

and US composites has a laminating epoxy resin system # 635 that i have heard is extremely good for the money, but have no experience with it personally.

racingjeff1

Hey Sean,

Email me Ithink Ican help you. This is something we do, I am in the process right now of making carbon fiber ducting for my 90mm fan in my scratch built DH-100 Vampire. I had a very similar issue on re-designing my F-101 spar for EDF use, the plans were for a pusher.

Regards,
Jeff
[email protected]

Magne

Sean.

A couple of points regarding carbon fiber.  This material is strong along the direction of the fibres, but week in all other directions.  (Bending strength at 45 degrees to the fiber direction is about 10% (yes!) of the strength in the fiber direction.)

Looking at your spar design, you have a problem area at the transition between the fuselage and the wing.  Although you have drawn some fillets to partially remove stress concentrations, you still have an area there where the stress will go "across" the fibers, if you only lay up the fibers (cloth) aligned with the spar.  Adding a few layers at +/-45 degrees would significantly improve the strength of the spar.  Having unidirectional fibers follow the outer contour of the spar would be much better, but a bit more work to do.  Still quite feasible, though.  (I can write a suggestion for how to do this, if are interested.)

As long as the bending of the spar is in the up/down direction, increasing the thickness of the plywood between the carbon layers is not improving the strength of the spar significantly, as you are only increasing the width of the "softest" material.  (It will however be stiffer in forward/rearwards bending by increasing the shear web thickness, but this is not helping you.)  Remember that the plywood in such a built up spar structure is there primarily to hold the carbon in place, and is not really contributing much to the total strength per se.

Regards,

Magne

smchale

My Feedback: (67)

Magne,

Thanks for weighing in on this. Yes, I'd be interested in what you mean by having unidirectional fibers follow the contour of the spar. Do you mean that when I lay a couply pcs of carbon that they should be 45 degrees to each other? So it's like x+x ?

My plan is to bolt (not just pin) the wing panel to the fuse near the leading a trailing edges to keep it secure and prevent and rotational stress, etc.

Do you think 2 pieces of 1/8" thk ply laminated together is too much? At the moment I'm thinking of a wet lay up of carbon cloth, 1/8 aircraft ply, carbon cloth, 1/8 ply, and carbon cloth. All squished between 2 pieces of 3/4" plate glass and left to cure. I'd like a relatively smooth surface as it will plug into a box in the wing which I plan to make out of 2 pieces of ply sides (likely 1/8th lite ply) with hardwood top and bottom of the box, pinned and wrapped in a few areas with carbon thread or perhaps even cloth.

Thanks again for everyone who has weighed in with suggestions....it's a big help!

Magne

Hi Sean.

This is of course just a suggestion, just like everybody here have their own idea about how to go about things.

A couple of alternatives:

1.  One option would be to do just what you said, laying the cloth like +x+x+.  This will ensure that at least some of the fibers are located along the direction of stress.  This is much better than just +++, considering the shape of your former.  (Imagine the stress as lines along the outer contour of your former.  The highest stress will always be in the outer fibers, following the shape of the former.  Ideally these lines should not cross the carbon fibers.  Typically, and quite surprisingly, if the strength along the carbon fibers is 100%, then it will be about 50% at as little as 15 degrees misalignment, and 10% at 45 degrees.)

2. This is what I would do:  (Dimensions etc. have to be adjusted according to the size of the component, I don't know how big your plane is.)  I would start with a sheet of 1/8" plywood, with carbon cloth laminated on both sides.  (Either like +ply+ or +xplyx+)  You can make this yourself, or buy ready made.  (Probably only available in +ply+ configuration.)  DO NOT cut the former to the right shape yet.  Then, as step two, I would make a "channel" from 1/8" balsa, by cutting out pieces of balsa sheet, and gluing to one side of the carbon/ply plate.  The outer edge of the channel should correspond to the outer contour of the finished former, and the inner edge of the channel should be e.g. 1/4" inside the outer contour.  (You are filling the whole area between the channels at this stage.)  Then you fill this channel with wetted carbon tow (rowing) and press down under your glass plate.  (There is of course one channel along the top edge of the former, and one channel along the bottom edge of the former.)  When cured, turn over and repeat on the other side. (One difficulty is to judge exactly how much carbon tow  to fill in the channels, you are probably better off by slightly overfilling them, any excess carbon will squeeze out on top of the balsa and can easily be trimmed off/sanded.)  Finally you cut the outer contour flush with the outer edge of the channel, and also cut the internal holes in the former. The most difficult, and critical area, is still the transition at the inner edge of the wing, you have to make sure that the carbon fibers have a nice, smooth "flow" with no sharp corners. 

Do you follow?  It's not very easy for me to describe this even though I have a picture in my mind about what this could look like.

Magne

smchale

My Feedback: (67)

Mange, option 1 certainly seems more straight forward. I'll proably go with something like that or close to it. I'm not sure I totally follow option 2, but it sounds like you are building a lip around the perimeter of the bulkhead in the fuse correct? won't the fillet that is formed on each side of the former when attaching it to the fuse serve a similar purpose?