twybrow
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| posted on 10/4/08 at 07:53 PM |
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quote:
I use carbon a great deal in my RC heli's - making a blade with a weave in one direction over another can be the difference between a
sweet flying machine or something that struggles to get off the ground and then is a mare to control with blades bending left right and centre.
Try 65:25:5:5 for your fibre orientation ratio (0,90,+45,-45)
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Delinquent
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| posted on 10/4/08 at 09:30 PM |
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quote:
Originally posted by twybrow
quote:
I use carbon a great deal in my RC heli's - making a blade with a weave in one direction over another can be the difference between a
sweet flying machine or something that struggles to get off the ground and then is a mare to control with blades bending left right and centre.
Try 65:25:5:5 for your fibre orientation ratio (0,90,+45,-45)
co-incidentally, that's exactly what I ended up with as my preferred layup 
It's also what I intended to use on the majority of my car tub, as it's what I've had most success with - then was going to try and
work out what to do with load paths in the more highly stressed area's, such as suspension mounts etc. Haven't quite worked out what
I'm going to do there yet (read: got fed up through sleep deprivation and will re-address once new baby has started to sleep for more than an
hour each night...)
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rpmagazine
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| posted on 10/4/08 at 09:47 PM |
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For a wet layup the devil is in the deatil in some respects. If you use a polyester resin then you are asking for trouble and frankly need a good
slapping...particularly if you use carbon/kevlar.
Wet layup is unlikely to meet the same performance standards of prepeg or zpreg, however the simple solution is that you use more.
You can always vacuum bag the wet layup too.
An autoclave is not required, work with the resin supplier and get a low/mod temp cure vynalester/epoxy and you can successfully cure it in a paint
oven over night. It will cure without the heat, but the post cure can add an extra 10-15% and more crucially make the resin less susceptible to hot
days.
This last bit is important...the resin WILL lose performance when it gets hot, vynalester is perhaps better than most wet layup epoxies...but check
with the resin supplier...they will know what is best.
FWIW my Rochdale Olympic is 4500lb/ft torsionally
www.racemagazine.com.au
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nitram38
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| posted on 10/4/08 at 09:49 PM |
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Monocoque carbon or fibreglass structures are rich man's toys. Come to that even Aluminium monocoques have a limited life span.
Good old steel spaceframe chassis will last longer and be easier to repair.
That is why most DIY car builders go down this route.
If you take aircraft as an example, their airframes are the biggest reason for limited life span and their eventual scrapping.
Nothing lasts forever but you should get more life and easier repairs with steel.
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Puk
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| posted on 11/4/08 at 06:43 AM |
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Nitram - I agree that most people build steel space frames because they are easier to design & fabricate (relative to any type of monocoque or
Elise type twin spar). But I don't agree that there is any engineering consideration for it to stay like that. Whilst there are plenty of steel
truss plans to follow or examples to copy from it is pretty hard for any one but a trained engineer to do anything else.
In the last 10-15 years the other materials have come to the for in the in formula where they are not prohibited, or put it another way, steel trusses
are not competitive when alternatives are permitted. F3, which doesn't have F1 budgets by any means, went CF years ago, hill climb is dominated
by CF or al alloy chassis. Elise, Jag XK and XJ, Audi, Renault Spider all have adopted structural al chassis. And bear in mind there are not cars with
a "drive before by dates" or Maclaren price tags. But to not do a steel truss requires the determination to learn how to design it your
self (i.e. more reading and more prototyping) and I guess that most folk would be happier driving!
Before you judge a guy, walk a mile in his shoes. Then when you judge him, you're a mile a way and you've nicked his shoes.
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iank
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| posted on 11/4/08 at 08:20 AM |
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quote:
Elise, Jag XK and XJ, Audi, Renault Spider all have adopted structural al chassis.
One of the main reasons spaceframes, and indeed almost all separate chassis, have been phased out in production cars is because of cost. They are
labour intensive to make as they don't lend themselves to automated manufacture. Any people involved in the process need to be skilled welders
so cost more than unskilled people.
On your points regarding racing cars moving to CF and monocoques. Yes they have, for a lot of reasons, not all technical (I'm always amazed how
much herd instinct and fashion have to do with what is used), but no-one here has said CF and monocoques aren't better than spaceframe. Just
they are harder to design and make and any additional performance you can theoretically get just isn't worth the money and time.
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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Delinquent
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| posted on 11/4/08 at 08:49 AM |
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There is another reason to use a composite chassis - economic use of space.
When I started my design, the first thing I did was draw out a spaceframe chassis. Then I started trying to fit things in and around it. Every
approach I took resulted in compromises due to large bits of steel sticking out where they weren't ideal, but moving the bits of steel resulted
in a less than ideal chassis.
Then when you consider that to create a decent ergonomic environment inside, you need to skin all this spaceframe... if it's a complex shape
(which as a three seater mine is) you end up choosing a composite... if you are going to the trouble of making moulds for the composite, why bother
with the steel at all? Just make the composites structural.
One route I am considering at the moment to overcome the SVA issues is a mix of the two - a very simple steel roll cage to pick up the most stressed
points, with a sort of semi-structural composite tub around it.
Of course that brings up more issues in itself. Ho hum!
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smart51
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| posted on 11/4/08 at 09:05 AM |
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I built a recumbent tricycle out of carbon fibre a few years ago. It is no more tricky to wet lay carbon than to do GRP. West Epoxy takes about 8
hours to cure at room temperature. Every 10° C halves the cure time, so 60°C cures in about 30 minutes, 70°C in 15. I used a domestic oven on its
lowest setting. You're limited to the size of parts you can cure though. I'm told a heat gun and a poly tunnel are good.
I found when destruction testing early prototypes that CFRP is much tougher than GRP and stands up to knocks better, even in thinner section. when
you stress it too much, it just snaps. I didn't use vacuum bagging either. I was careful when laying up, rolling the laminate very thoroughly
to take out excess resin and air bubbles.
That was before the A380 and the doubling of price of carbon cloth. I wouldn't do it now.
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Delinquent
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| posted on 11/4/08 at 09:11 AM |
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quote:
Originally posted by smart51
West Epoxy takes about 8 hours to cure at room temperature. Every 10° C halves the cure time, so 60°C cures in about 30 minutes, 70°C in 15. I used
a domestic oven on its lowest setting. You're limited to the size of parts you can cure though. I'm told a heat gun and a poly tunnel
are good.
Friend of my father used to make masts for racing yatchs, they used to make thick poly tents over them and stick an industrial heater under it with a
thermostat!
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Puk
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| posted on 11/4/08 at 09:13 AM |
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Iank, I don't think that we disagree, particularly your point about the importance of herd instinct. My mail was to pick up on Nitram's
point:
quote:
Originally posted by nitram38
Monocoque carbon or fibreglass structures are rich man's toys. Come to that even Aluminium monocoques have a limited life span.
Good old steel spaceframe chassis will last longer and be easier to repair.
That is why most DIY car builders go down this route.
I agree that a steel space frame is easier to get right for most of us (they're tried and tested, loads of examples to copy from). But the
disadvantages listed for the alternatives are look more like opinions than facts.
So I don't agree that is an argument to reject alternatives. Only that alternatives do require more effort / stubbornness / research to get
right.
The CF mono alternative to the space frame isn't theoretically better - its been proven on the track - take F3 - there is no rule compelling
people to stop using space frames. But if they don't have a chance of winning they may as well pack up and go home - hence the move to CF.
But personally I'm not going the CF route, I don't feel comfortable about being able to design it right, or build it in a garage. Al
composite panels and structural adhesive on the other hand . . . 
Before you judge a guy, walk a mile in his shoes. Then when you judge him, you're a mile a way and you've nicked his shoes.
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nitram38
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| posted on 11/4/08 at 09:20 AM |
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Puk, just because something can be done, doesn't mean it should.
Cost and longevity is going to stop most people from going this route.
In my ideal world, I too would have a CF car, but my finances, facilities and my time limit this.
If you already have access to these materials and facilities, then go for it.
There are a lot of builders that don't even finish a steel car, so getting them all excited about a project that is more difficult to create is
what I am talking about.
Most people building cars on here are going to use them on un-even roads, race cars are generally on smooth tarmac circuits.
Also most racers will buy their cars, not build them.
They leave the building to people with the facilities and experience.
As I said, Rich Man's Toys.
[Edited on 11/4/2008 by nitram38]
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Puk
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| posted on 11/4/08 at 09:31 AM |
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Fair point. I'm not saying go ahead abandon steel, but I am saying to abandon steel is a hard thing - so be aware of what you're getting
into. I disagree that steel alternatives inherently have short life spans or are more difficult to fabricate. CF is harder to fabricate, but al
composite is not.
This chassis cost half the price of a FF space frame, because although the components are more expensive you spend a day bolting them together rather
than a week welding steel tubes.
Linky to picture
Its tougher in a crash too.
[Edited on 11/4/08 by Puk] Bloody hell adding pictures is an art! Lets go back to fax!
[Edited on 11/4/08 by Puk]
 
Formula Lotus Chassis
[Edited on 14/4/08 by Puk]
Before you judge a guy, walk a mile in his shoes. Then when you judge him, you're a mile a way and you've nicked his shoes.
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Delinquent
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| posted on 11/4/08 at 09:42 AM |
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quote:
Originally posted by nitram38
Puk, just because something can be done, doesn't mean it should.
Cost and longevity is going to stop most people from going this route.
In my ideal world, I too would have a CF car, but my finances, facilities and my time limit this.
If you already have access to these materials and facilities, then go for it.
There are a lot of builders that don't even finish a steel car, so getting them all excited about a project that is more difficult to create is
what I am talking about.
Most people building cars on here are going to use them on un-even roads, race cars are generally on smooth tarmac circuits.
Also most racers will buy their cars, not build them.
They leave the building to people with the facilities and experience.
As I said, Rich Man's Toys.
[Edited on 11/4/2008 by nitram38]
I'm most definitely not rich by even the average persons standards - not even well off. About the only thing that looking at a composite
monocoque has cost me so far is time and reading researching it - which although incredibly frustrating at times I've enjoyed for the most part,
and have learned skills that can be used elsewhere in the build.
Will it cost more than a steel spaceframe to build? of course it will, but for me building this car is about pushing my boundaries, learning new
skills and achieving something I've not done before. If I welded together a load of steel tubes and dropped a body over it I'll have
achieved nothing new, just spent my time doing "another" project for the sake of another project.
It may well end up that way if the extension costs keep spiraling as they are, but it's something to aim for...
[Edited on 11/4/08 by Delinquent]
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Alan B
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| posted on 11/4/08 at 12:07 PM |
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quote:
Originally posted by nitram38
............. There are a lot of builders that don't even finish a steel car, so getting them all excited about a project that is more difficult
to create is what I am talking about.........
Excellent point.
Those with the knowledge, determination and cash will do it, and do it well I'm sure. I admire and applaud you for that.
It's the new guys reading this thread and thinking "Oh, I might have a go at that" that I'd really advise to stick with
simple, proven and cheap.....and ultimately way more achievable.
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Doug68
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| posted on 11/4/08 at 12:27 PM |
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Some observations:
1. A Porsche 917 frame weighs 42kg the Bentley LMP from 2003 weighs
~70Kg which do you think is better and why?
2. CF and other processes "novel" to the home builder won't be widely accepted until they are widely understood. One day someone
will write "How to build a Carbon Fibre Hypercar for less than 5000 quid" then all of a sudden 100,00 people will be "experts"
on the subject (Just like we all are with steel frames  ), but until then...
3. These processes and techniques are not widely understood today (least of all by me) hence all the "Burn the Witch" posts that are
generated every time this subject comes up.
Doug. 1TG
Sports Car Builders WA
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chunkytfg
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| posted on 14/4/08 at 03:16 PM |
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quote:
Originally posted by Gakes
Like I said before, this must be the best site ever. Anything is possible and this forum has all the right members
I thought it was possible, not just wetting myself How does the vacuum bag work??
Not sure if you have had an answer to this yet as i havnt read the whole thread but have a look at this for insiration and help
http://www.bayarearidersforum.com/forums/showthread.php?t=145975&pp=15
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Benonymous
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| posted on 16/4/08 at 11:50 AM |
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Interesting thread on the BARF forum.
Just read the whole thread on BARF. Very interesting. However, let's not forget that a motorcycle fuel tank is not a structural part as such.
I admit it has a critical role and has to be strong enough not to split and spew fuel everywhere in the event of an accident but it's not
carrying any load.
Another very interesting point to be learned from the above thread (link) is the actual amount of work involved in making a part. The effort required
to get a nice shiny (out of the mold) CF part is pretty high even for a relatively small part like this.
Finally, the builder remarked several times on the availability of 'certified' CF cloth. The last time I checked, there was little in the
2K or 4K area available thanks to the abundance of demand (aerospace) and the lack of CF manufacturing facilities. For a chassis, you'd have to
use certified cloth unless you just want the cosmetic look rather than the strength. This kind of shortage drives up prices.
It's one thing to want to do a CF chassis but another to commit the time and money to achieve it. At the present time it looks like its a
project for the well heeled, not the Locost builder.
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Ferg
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| posted on 26/4/08 at 05:07 PM |
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quote:
Originally posted by tegwin
Have you looked at how the GTM libra is made?...
That's a GRP monocoque with steel front and rear subframes.,.....
Actually it's a GRP monococque with a frame that holds the engine. The suspension is simply bolted through the GRP with a small plate on the
inside. It has no additional strength barring two 2" square steel plates in the 'B' pillar for the upper seat-belt mounting. No
coremat, no laminated in metal etc.
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robroy
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| posted on 16/5/08 at 05:12 PM |
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Hello everyone. Great thread on a great forum! I salute you all.
I've been thinking about my next project, a single seater road/track car and its chassis construction. I'm hoping it'll be 500kg
with driver and fuel and will have maybe 100bhp so we're not talking massive speed here.
I've been looking into the cheap side of composite construction and there hasn't been much information on the net and I still have many
thoughts on the subject. I have found this interesting old article though:
http://www.rqriley.com/frp-foam.htm
Here is a sketch of my project:
One of the advantages over spaceframe I see is that I can achieve a finished surface on the outside of the tub without creating bodywork for the mid
section. Some time and effort saved.
I have incorporated 'gentle' curves into the panels - will this substantially reduce the strength?
I guess I could always combine the two, and build a spaceframe chassis and fit a lightweight core between the tubing around the tub before glassing
around it for extra strength. Heavier but should have impressive rigidity and crash protection, and can again use the outside of the tub as a finished
surface.
Also, I notice that no one has mentioned end grain balsa as a core, although much used by airplane or boat builders where it can achieve impressive
rigidity in half inch panels. Anyone have any concerns about using this core?
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Puk
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| posted on 16/5/08 at 05:21 PM |
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I think that Elden built some formula cars in the 70s using end grain balsa core with al skins. I worked there one summer way after their hey day and
the boss had a desk made out of the stuff. Any one know anything more about them?
Before you judge a guy, walk a mile in his shoes. Then when you judge him, you're a mile a way and you've nicked his shoes.
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Wolf HR
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| posted on 17/5/08 at 08:57 PM |
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Puk, it was called Mallite and was IIRC pioneered by McLaren in Formula 1 in late sixties...
I imagine it would be suitable for flat surfaces or with very little curvature, whereas foam core would be more suitable for cars because it allows
compond curves (and the benefit of using lighter but thicker core would be stiffer structure)...
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Puk
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| posted on 18/5/08 at 05:32 AM |
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Google threw up:
"Formula 1, works team Mallite monocoques intended for Ford Indy V8 power, also used Serenissima V8"
So can be done. As with all these discussions about alternative chassis materials - if you want to go that route you need to know how to use the
materials. Which doesn't necessarily imply a degree in engineering, just a good head for reading. Allan Staniforth writes about a single seater
hill climb car that was built by a school teacher from carbon in the late 80's IIRC. The chap modeled it on an F1 Jordan and the chassis is
still being raced. A good starting point would be to ferret out the design guides that Hexcel used to provide some for using the composite panels that
they used to supply.
wooden linky
Cheers,
Puk
Before you judge a guy, walk a mile in his shoes. Then when you judge him, you're a mile a way and you've nicked his shoes.
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rpmagazine
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| posted on 18/5/08 at 07:16 AM |
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have a look at www.ayrescom.com
www.racemagazine.com.au
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Ians
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| posted on 18/5/08 at 02:38 PM |
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grp chassis
I am the teacher mentioned in PUK's last post, I can only add that for the last 15 years composite construction has been my chosen method of
build, it does require a lot more design preparation prior to starting (any changes or design flaws can often render produced moulds ineffective, it
will always be easier to cut and move tubes and modify a space frame). There are obviously many more pitfalls and avenues of failure when dealing
with monocoque constructions and priorities must lay in defining load paths. I personally feel whilst it may not have an advantage over a spaceframe
for the amateur or first time builders it offers a challenge that some may find worth the effort. Ians.
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Puk
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| posted on 18/5/08 at 03:15 PM |
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Ians - nice to "meet you" thank goodness I wasn't disrespectful in my post.
Before you judge a guy, walk a mile in his shoes. Then when you judge him, you're a mile a way and you've nicked his shoes.
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