Carbon Fibre

Judders

Judders

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Where does one purchase the stuff?

The boat we're working toward has a few nice touches in the stuff but I can see great potential for weight saving. Not complicated moulds, just areas where flat ply could be replaced with it, but I've no idea where to get hold of it or how much its going to cost.
 
It's expensive.I usually get it from a resin and glass supplier.Last time I asked it cost about €80 per sqmeter.
 
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CF is lovely stuff and it has actually been around for twenty years+. There are many weights of cloth just like there is fibre glass. Therefore the weight is dependant on what you plan to do with it. typically 100grm/m2 or heavy duty would be 200grm/m2. There are many different weaves typically twill. some will fall into compound curves some wont. you can also get unidirectional or bidirectional where say kevlar runs in one direction and carbon at right angles to it! There is pre preg which needs an autoclave to cure it but I presume you thought of two pack epoxy resin. It is very nice to work with unlike kevlar! Lots of model aeroplane flyers use it and would be happy to tell you where to get it. Model shops for small quantities but before you start with it read lots ! hope that helps!!! Nik
 
Matata said:
CF is lovely stuff and it has actually been around for twenty years+.
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'The high potential strength of carbon fiber was realized in 1963 in a process developed at the Royal Aircraft Establishment at Farnborough, Hampshire. The process was patented by the UK Ministry of Defence then licensed by the NRDC to three British companies: Rolls-Royce, already making carbon fiber, Morganite and Courtaulds. They were able to establish industrial carbon fiber production facilities within a few years, and Rolls-Royce took advantage of the new material's properties to break into the American market with its RB-211 aero-engine'

Almost a British success story, save that the RB-211 carbon fiber blades couldn't withstand a bird strike.
 
This is obviously a different style to what I was used to a while ago !

What about 'baking' in autoclaves ?

When I worked for BAe, the Harrier II wing was the largest C F structure in the world; and everyone was scared to death by it, I must say for what seemed good reason to me.

From the start the hollow wing ( containing fuel tanks and backings fof hard points - pylons- ) and the tailplane horizontal stabilisers - elevators - were treated very gently, any 'strike' on the rear fuselage by ammunition links was treated seriously, our development Harrier for the trials had the aft fuselage painted matt - soft - white to show hits.

It was reckoned a carbon fibre structure could take a hard hit and not show it, but be delaminated inside like smashed plywood...

This was a serious worry, as was the time a Harrier GR5 was hit by lightning !

As the wing is a sort of graphite, the arc had tracked down from the fuselage spine to almost the wingtip.

I was sent to go and photograph it, and guys with Ultrasound kit were going all over it.

A solution was come up with; also a colleague did a study on carbon fibre repairs which got him some sort of an industry advanced degree, I photographed his stuff, but to be honest it all seemed common sense repairs to me, while using U/V curing etc.

Anyway I decided that Carbon Fibre while strong is brittle; and I don't want that on a boat going offshore, even if it is racing ( I've raced in plenty of dinghies with the stuff, but I expect largely because of the boat designs I'm not a fan.

Attached below shots of the first UK Harrier II on first takeoff; the green bits are carbon fibre ( baked in a huge autovlave ) the yellow bits are mainly L72 Duralumin alloy.

1sttakeoffUKHarrier2GR5.jpg
 
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The first big problem with carbon fibre is that it's extremely stiff and undergoes brittle fracture at very low strains.

The second big problem with carbon fibre is that as a result of the first big problem it absorbs very little energy when breaking.

The third big problem with carbon fibre is that as a result of the first and second big problems it tends to shatter into a huge number of fragments when it breaks.

The fourth big problem with carbon fibre is that as a result of the first, second and third big problems the surfaces of broken carbon fibre structures tend to be lethally jagged.

In gliders, for example, carbon fibre fuselages have a couple of layers of glass as well around the cockpit to add impact strength and to keep the pilot safe from fast moving sharp edges in an accident.

Unless you are absolutely certain that you need a light, stiff structure and don't mind poor impact resistance, carbon is a waste of time and money. This is particularly true if you're making flat panels: if you use a thick enough layup to get bending stiffness the structure will be far stronger and heavier than it needs to be, and if you use just what you need for strength the panel will be very flexible. The sensible way to go is a layer composite with honeycomb in the middle, but that's complicated, time consuming and expensive to do.
 
I used CF for the first time last year as part of a dagger board.I sheathed the whole board doing one side at a time.The board also had another two layers of FG on top.I found it reasonably easy to work.It wet out in a similar way to the FG.Cutting the cloth was difficult,but there is info/tips on google.(I think,IIRC, you pull a thread out of the weave and cut down the line)There are different type weaves available.I can't remember the chord,but the board is 6 foot long.The CF to do the job was about £60.I used epoxy for the build,no smell, so was done in the workshop.The job worked really well,the cured CF (extreamy sharp and very very painfull at the ragged edges-wear gloves) looked absolutly stunning,a bit like a spoiler off a race car,it was a shame to recover it and paint.
If using CF,watch out for splinters in the cured state.When sanding,wear a mask.
I intend using CF in the rudder I'm planning building.
If you intend to make light panels,then a foam core sandwich would be the way to go.Expensive in CF though.How strong do you need it?
Cheers
 
2Tizwoz said:
Almost a British success story, save that the RB-211 carbon fiber blades couldn't withstand a bird strike.
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Correct, but RR were faced with a revolution in materials technology at that time. Ceramics were their favoured option during design/development, but Carbon deserved a look see.

You would be astonished to know where the patented/secret materials in the subsequent RB211/Trent engines came from and how their use is managed/licensed/controlled.


The jury is still out on CF. A little known factoid is that CF expands at low temps - doesn't sit well in a metal/CF composition. It's highly electrically conductive, but the glue burns.
 
boguing said:
You would be astonished to know where the patented/secret materials in the subsequent RB211/Trent engines came from and how their use is managed/licensed/controlled.
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Point of information. If they are patented they can't be secret. The whole point of patenting is that you give up secrecy in return for exclusivity.

We now return you to your fascinating slice of aviation history ...
 
A lot of negatives about CF which i don't agree with.
CF can be used like glass with any resin system. It does not have to autoclaved or vacuum molded. These 2 options however give the best strength to weight ratio by minimising the amount of resin.
In itself CF is very stiff. I use a bit for the fin of a home made wind pointer. One layer has enough stiffness for the job. I also used it to cover foam as a floor in the little boat. Here I wanted lower floor / more headroom so CF was good.
It is not tough and is as easy to cut as fibreglass both as a cloth and as a hardened sheet with any resin.
It can be damaged by impact or abrasion.
The trick is to use Kevlar in the layup. (this stuff is hard to cut) An outside layer can provide longitudinal strength and resistance to cutting or abrasion. However as said a honeycomb or foam sandwich construction gives the best stiffness by simply making the board thicker. (geometrical strength)
NB CF in a layup is not insulating to electricity but with a relatively high resistance will get very hot with current flow. Hence lightning concerns.
CF is stiffest along the fibre axis. So using a twill weave while enabling it to follow curves would negate its stiffness value. Vacuum molding is the way to get it to bend into corners.
So really the trick in using CF Kevlar honey comb and f/g is in the design of the end product.
Give it a go and have fun olewill
 
Ubergeekian said:
Point of information. If they are patented they can't be secret. The whole point of patenting is that you give up secrecy in return for exclusivity.

We now return you to your fascinating slice of aviation history ...
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Ah, if it were so simple.

Get a Patent and who polices it? The holder. Publish and stand by for worldwide copying and astonomical legal fees.

Or - don't go down the Patent route. Supply your customer with ready to install bits. Have a contract that says "you want them - we fit them". And no, you can't have spares, we'll fit them when needed.

I've just described the hold that Sweden's 'intelligent' metals industry have over RR.

Truly incredible technology, but even RR don't know exactly what and how goes into the cauldrons.
 
boguing said:
Ah, if it were so simple.

Get a Patent and who polices it? The holder. Publish and stand by for worldwide copying and astonomical legal fees.

Or - don't go down the Patent route. Supply your customer with ready to install bits. Have a contract that says "you want them - we fit them". And no, you can't have spares, we'll fit them when needed.
Click to expand...

Just as I said, then. Patented or secret, but not both.
 
Having worked around carbon fibre, and photographed such structures under high load and impacts, plus working with a colleague on a Masters Degree on carbon fibre repair schemes, I will only say this;

If on anything larger or further traveling than a racing dinghy, I would pay good money NOT to have anything significant like rudder, mast etc made of carbon fibre !
 
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