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Making your own Carbon Fibre Undercarriages and other ‘... - 5/31/2002 1:51:35 PM   
zippo



Posts: 98
Joined: 5/29/2002
From: Oxfordshire, UNITED KINGDOM
Status: offline 		Making your own Carbon Fibre Undercarriages and other ‘trick’ bits

I don’t know what it is about CF laminates, but they look just so good. I think it’s the almost 3-d appearance of the cloth under that shiny resin finish that does it for me.

I’m not saying that the following techniques are unique, but the work for me and produce bits that are perfectly acceptable in appearance.

Rather than use carbon fibre cloth, which is hugely expensive, I’ve used Carbon Fibre tape 100mm wide. This is significantly cheaper to buy and significantly reduces waste. I’ve used West System Epoxy resin and harderner,

I guess the technique I have been using can best be described as ‘cold pressing’. The laminate is sandwiched between two layers of 3M OHP polyester film, left to go green, cut to shape using a template and then pressed or formed over a template and then left to harden. It is significantly less messy than other methods I have used.

I first trace around a template using thin card; the template can be an existing dural undercarriage. I then cut the carbon tape to approximate size. I have used 8 layers of CF and this appears to be adequate for a .40 sized aircraft. You might need more depending upon the weight of your aircraft.

On a flat piece of glass (I use a tempered glass shelf, bought quite cheaply from my local DIY store), lay down a strip of the OHP film. I have found that smoothing it down with a cloth gets it to stick down quite well (possibly by the static charge that builds up).

Onto the film lay the first piece of CF and apply a liberal coat of resin.

Add each layer of CF, each time coating with a liberal amount of resin.

When the laminate is built up, cover with a second piece of the OHP film.

Now consolidate the laminate with a hard roller. This will remove air bubbles and will squeeze out excess epoxy. This bit can be messy, so be warned.

Leave for two hours so that the laminate goes ‘green’.

With a very sharp knife, cut around the template. I have found that while the laminate is in the green state, it cuts very easily. The semi-cured laminate will be quite flexible, but is easily handled due to the polyester film covering.

Carefully lift the CF blank you have produced and place over your U/C template. Form it over the template and clamp in position. I use scraps of balsa sheet to spread the clamping loads. If you don’t do this you can get localised points where the laminate is squeezed a little thinner than the rest.

Leave the whole thing alone for 24 hours.

When the epoxy is fully set, remove the clamps, release the formed under carriage and just peel off the film covering. The result is a nice home made CF undercarriage.

I have also used the same technique to form ‘L’ sections (using aluminium channel as a former) which can be easily be used for servo mounts. Also if you tape a piece of the green laminate over and around the LE of your wing, it make a very good LE band protector for fun fly’s planes.
       Post #: 1

Making your own Carbon Fibre Undercarriages and other ‘... - 5/31/2002 11:51:09 PM   
Logan


 

Posts: 30
Joined: 1/7/2002
From: Salem, OR
Status: offline 		What is "3M OHP polyester film" and where would you get? I have used teflon with good results but it leaves a bit of texture on the finished part which is OK, it just requires extra sanding. I like your method of working with a green layup to form some basic shapes.

L-

(in reply to zippo)
       Post #: 2

Making your own Carbon Fibre Undercarriages and other ‘... - 6/1/2002 10:24:05 AM   
TT2



Posts: 648
Joined: 3/19/2002
From: Osborn, MO, USA
Status: offline 		zippo, that seems too easy! Why didn't I think of that?!?!

I've been working with composites for YEARS and have toiled with the conventional methods of mold-making for wet lay-ups (a tedious process to say the least), but it never occured to me to form simple bends / curves after the layup while the laminate is in a 'green' state.

I was getting ready to order some CF landing gear for a H9 Edge but now I'm going to make them myself. I've got a 10 yard roll of 60" wide plain weave 5.7 oz. carbon fiber cloth and over a gallon of West Systems 105/206 sitting in my workshop. By using the method you described, a simple form made out of wood (or even hot-wire cut foam) could be fabricated in a FRACTION of the time that it would take to make a conventional mold for a wet layup.

I might try to vacuum bag the 'green state' laminate over a hot-wire cut form to see what happens. Are you using the 205(fast) or 206(slow) hardener?

I don't know what 3M OHP polyester film is (Overhead Projector?). I use 0.014" mylar for vacuum bagging carbon fiber and fiberglass wing skins among other things. What you describe must be thinner if it is easily cut with a knife. If I can't find the OHP film I might try using 0.007" Lexan polycarbonate (waxed) as a carrier to be peeled off later.

Thank you for sharing such a fantastic idea! I will start experimenting with this very soon. If my results are favorable, I'm going to make new landing gear for every plane I have!

-Tom

_____________________________

As complexity approaches infinity, mean time before failure approaches zero...

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       Post #: 3

Questions - 6/2/2002 5:05:57 PM   
DennisS


 

Posts: 53
Joined: 3/9/2002
From: Woodbury, MN,
Status: offline 		Zippo,

What is 3M OHP Polyester film?
Where is a good supplier of Carbon Fibre Tape?

Thanks, like your post, great ideas.

Dennis

(in reply to zippo)
       Post #: 4

Making your own Carbon Fibre Undercarriages and other ‘... - 6/5/2002 1:17:21 PM   
zippo



Posts: 98
Joined: 5/29/2002
From: Oxfordshire, UNITED KINGDOM
Status: offline 		Tom & Denis

I'm using polyester Over Head Projector film ... comes in rolls of 50 ft by about 8.5". I use it because its very cheap and easily available via any office supplies outlet. Here in the UK it is significantly cheaper than mylar film.

The Carbon tape I'm using is 10cm wide/200g a square metre bought from a boat building supply company here in the UK. I also think that West Systems have it as a stock item.

I have been using West Systems 105/205 epoxy and hardener. I find this gives me plenty of working time (but then again, being in the UK the average tempurature isn't that great most of the time!).

I quite like the idea of using hot wire cut foam templates - also vacum bagging sounds good. Let me know how you get on.

Cheers


Tony

(in reply to zippo)
       Post #: 5

Making your own Carbon Fibre Undercarriages and other ‘... - 6/5/2002 4:38:53 PM   
DennisS


 

Posts: 53
Joined: 3/9/2002
From: Woodbury, MN,
Status: offline 		Tony, looks like a grand celebration going on "across the pond". Wish I was there. Thanks for the prompt reply.

Dennis

(in reply to zippo)
       Post #: 6

Making your own Carbon Fibre Undercarriages and other ‘... - 6/6/2002 4:51:56 AM   
bipeaddict



Posts: 393
Joined: 2/19/2002
From: Montpelier, VA, USA
Status: offline 		There is also an article that was published in RCM on how to make your own CF landing gear. If you are a subscriber you can access the article online at [url]www.rcmmagazine.com[/url]

Other places for supplies:

[url]www.cstsales.com[/url]
[url]www.fibreglast.com[/url]
[url]www.arts-hobby.com[/url]

(in reply to zippo)
       Post #: 7

Making your own Carbon Fibre Undercarriages and other ‘... - 6/6/2002 9:15:42 PM   
TT2



Posts: 648
Joined: 3/19/2002
From: Osborn, MO, USA
Status: offline 		zippo

I made forms from hotwire-cut extruded foam (Dow Grayboard) and vacuum-bagged 8 layers of 1.5 oz fiberglass to the form surface to strengthen it and to leave a glass-smooth finish. I used .014" waxed mylar as a carrier for the glass.

My first attempt at making gear for a World Models Extra 300s went OK, but I experienced some buckling on one of the gear legs during layup which resulted in a slight delamination at that point. The buckling was caused by beginning to shape the laminate from the END of one leg instead of forming it from the center...duh!

Last night was my second attempt. I used 17 layers of 5.7 oz CF plain weave and West Systems 105/205. After wetting out the CF, I stuck the sandwich in a vacuum bag between two sheets of plexiglass laminated to 3/4" thick melamine (particle board). After pulling a full vacuum (24" hg) for 2 hours, I pulled out the gear 'blank' to begin cutting the shape. I found that the epoxy had 'kicked' a bit more than expected, so cutting the shape was a very difficult task (during my first attempt, I found that cutting the shape was easy). I suppose that by having a thicker layup (I used 12 layers on my first attempt), the epoxy was more prone to exothermic reaction and cured a bit quicker.

After I cut the laminate shape I again sandwiched it between the plexiglass / melamine and shoved it back into the vacuum bag just long enough to pull a full 24" hg vacuum. This will smooth-out any deformation that was caused by cutting the laminate. I removed the gear 'blank', shaped it around the form (from the center this time!), and covered it with the same .014" mylar used to laminate the fiberglass to the form. At this point the CF laminate was fairly stiff and didn't conform to the form 100%, but after examining the results this morning, I found that it's still entirely useable and looks VERY nice.

A few thoughts:

1. I would have had much better results if I had not let the laminate cure so long. I think that the cure-time to laminate thickness is inversely proportional, and finding the right amount of cure-time will just require further experimentation.

2. I had used plain weave cloth from a 50" wide roll cut on a 45 degree bias. When using a plain weave cloth, orienting the fibers on a bias is nearly twice as strong as orienting them aligned with the gear lengthwise. Since you are using tape, I don't think that you can do this...unless you've found some bias-weave tape.

3. I am considering using uni-directional CF in the future. It's cheaper, easier to wet-out and the fibers would be optimally oriented. One could use a woven cloth on the first and last layers of the laminate to enhance appearance.

My process is evolving, and I'm sure that I'll be churning out 100% perfect gear within a few more attempts. I need some for my Cermark Pitts, H9 Edge 540, AeroWorks Freedom 3D, and Sig Fazer.

Thanks again for the tip! If you have any more suggestions or questions, please don't hesitate to discuss it here or offline.

-Tom

_____________________________

As complexity approaches infinity, mean time before failure approaches zero...

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       Post #: 8

Making your own Carbon Fibre Undercarriages and other ‘... - 6/7/2002 12:37:43 PM   
zippo



Posts: 98
Joined: 5/29/2002
From: Oxfordshire, UNITED KINGDOM
Status: offline 		Wow ... Tom you are really going for it!

I have made U/C legs for my Seduction and Hirobo Stream 50. Both are 40 sized planes and I have found that 8 layers of CF tape provides an light, but what I consider to be adequately strong gear.

You are dead right to point out that any epoxy "goes off" at different rates. As I said in an earlier posting - its quite cold here at the moment (typical UK weather) Damp, cold, windy ... I could continue moaning. I guess you really need to experiment with different combinations of epoxy/laminate thickness in order to work out what is the optimal time to wait before forming.

My next step is to buy some 200g cloth (I think this is equivilent to the 5oz you are using. Its hugely expensive over here, they sell it by the 1/4m for £7.50 - thats £30 a meter.

You have taken the technique way beyond my rather feble attempts ... as we say over here .. "more power to you elbow!". Its gratifying to see some one pick up an idea and run full speed with it .. thankyou.

Tony

(in reply to zippo)
       Post #: 9

Making your own Carbon Fibre Undercarriages and other ‘... - 10/18/2002 4:50:52 AM   
rsieminski



Posts: 1406
Joined: 4/24/2002
From: Sarasota, FL, USA
Status: offline 		1.) How can I get a gloss finish?
2.) With the Overhead Projector Film, do you still have to use a release agent?
3.) How do you smooth out the edges so they are nice and straight(lg width wise)? I would like to make gear that look nearly as good as the commercial stuff.
4.) If you were to use a layered mix of: s-glass, kevlar, carbon how should it be layered to exploit their strengths?


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[link]http://mywebpages.comcast.net/webmaster01/[/link]

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       Post #: 10

Making your own Carbon Fibre Undercarriages and other ‘... - 10/18/2002 1:58:22 PM   
zippo



Posts: 98
Joined: 5/29/2002
From: Oxfordshire, UNITED KINGDOM
Status: offline 		I have found that you do not need any type of release agent if you use the polyester OHP film. It just peels off really easy when the resin is fully cured.

The finished items are actually pretty good in the 'gloss' finish department. In fact after having seen several commercial items, I'd go as far as saying .. almost as good and in some cases - better. However, because this technique doesn't use a proper mould as such - the actual surface finish can (and does) have surface ripples. Bit difficult to describe .. but on the ones I have done it really doesn't look too bad.

Not sure about your comment about smooth edges - So I'm guessing here. If you cut the laminate with a sharp knife, them proceed to form it around a template, the edges get a bit rough. But I havce found that you can trim this off (again) with a sharp knife and really tidy up with a sanding block.

As for the use of other materials .. can't comment because I've only ever used carbon!

(in reply to zippo)
       Post #: 11

Making your own Carbon Fibre Undercarriages and other ‘... - 10/18/2002 7:27:51 PM   
TT2



Posts: 648
Joined: 3/19/2002
From: Osborn, MO, USA
Status: offline 		rsieminski:
1. Very simple. Spread a thin layer of resin on the plastic film before laying any carbon on it. Do the same for the other layer of plastic film (the top 'bread' of the sandwich) before applying it to the layup. This will eliminate epoxy starvation and leave a perfect finish. There will be a slight amount of indentations in the weave of the carbon like zippo described, but they are unavoidable without using a mold...certainly nothing to worry about, the pieces still look fantastic!

2. I don't even know what kind of plastic I'm using. I bought it at the hardware store. They have it on a roll by the window plastic. It is quite similar to OHP film...fairly stiff and very glossy. No release agent or wax is required...it peels off easily after the epoxy is cured.

3. A few seconds on the belt sander does the trick.

4. Why use S-Glass? Kevlar is a pain in the neck to work with, though in LG applications I suppose alternating layers of unidirectional carbon / kevlar could be optimal. Haven't tried it yet. The most important factor in composite structures is fiber orientation. I wasn't too happy with the gear I had made with bidirectional cloth, but the unidirectional stuff is GREAT! The reason the bidirectional cloth isn't optimal is because the fibers oriented width-wise on the piece (in LG applications) don't do anything to increase the strength or stiffness of the part. Of course you can use bidirectional cloth as the first and last layers for appearance...or a hybrid kevlar/carbon for appearance like some of the commercial stuff. Get some West Systems unidirectional tape. I bought some 13" wide and fold it over on itself to build up multiple layers...you can't really 'rip' the stuff to a different width because the fibers then separate. The 13" wide stuff is BY FAR the cheapest by volume.

Hope this helps....

**************************************************

Zippo:
I can't thank you enough! I'm using the 'cold forming' method for soooo many things. What a great idea!!!

-Tom

_____________________________

As complexity approaches infinity, mean time before failure approaches zero...

(in reply to zippo)
       Post #: 12

Making your own Carbon Fibre Undercarriages and other ‘... - 10/19/2002 10:56:09 PM   
Kasper



Posts: 84
Joined: 10/19/2002
From: Denmark
Status: offline 		ooooops... well i just got some large areas of GFK/BALSA/CFK layer. and ONLY used a peice of glass. But NOW its STUCK!

Any meathod i can remove the glas...?

How about using a HEAT GUN?

Regards



Homepage: [url]www.modelfly.dk[/url]

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