Delinquent
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| posted on 10/10/07 at 10:01 AM |
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"how long is a piece of string" type SVA question
I have a somewhat out of date copy of the SVA requirements (think it's about 2003?) which I do intend to get around to reading properly sometime
before I start construction - maybe even going all flash and buying (  ) a later copy... but WHY do they have to use 25 pages to draw out something
that could be said in 3 words!!! It's headache inducing at the best of times.
While I'm still in denial of the need to fully read this piece of fictional literature, are there "key" elements of SVA that if
picked up on are likely to make me burst into tears and break out the petrol and lighter?
My main concern is the monocoque shell - cocking this up would effectively write the project off after considerable expense, bodywork issues are
trivial in comparison. All front suspension, steering, seatbelts - in fact everything forward of the engine - is going to be hung on it, and
internally all surfaces will be just the carbon - no coverings. How exactly do the SVA people "judge" the structure?
I can accept that a chap in a white jacket can tell the difference between a 25mm round 3mm wall tube chassis and a 15mm round 1mm wall tube
chassis.... but is he going to know the difference between 2mm of wet laid carbon and 10mm of aluminium honeycomb pre preg sandwich?!
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stevec
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| posted on 10/10/07 at 10:14 AM |
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No disrespect but if you are going to build what you say then surely it is a must that you become a authority on the current SVA manual.
The testers know how, and have the equipment to check your car very thoroughly.
All the best.
Steve.
[Edited on 10/10/07 by stevec]
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Delinquent
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| posted on 10/10/07 at 10:19 AM |
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LOL, yeah I know, as I say I do intend to double check everything thoroughly before I start construction - my fear is after reading various horror
stories about the person SVA'ing the car - I can convince myself that I've made something strong enough (mostly because I'm not
making those decisions, have a nice chap from the supplier who's had plenty of experience) but more how does one convince an SVA chap?!
quote:
Originally posted by stevec
No disrespect but if you are going to build what you say then surely it is a must that you become a authority on the current SVA manual.
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nick205
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| posted on 10/10/07 at 10:24 AM |
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I don't know how they would inspect/judge such a car when it's preseted to them. I would contact VOSA and your chosen SVA centre and
start taling to them about it before you make anything though. If they're going to want destructive testing of some kind (not that
they're equipped to do it) then I guess it's game over.
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Hammerhead
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| posted on 10/10/07 at 10:25 AM |
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You should possibly document your layup process with pics and explainations and data as to why you have constructed the chassis in the way you
have.
I have some pics of the porsche gt carbon chassis and a few others if you need them.
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Delinquent
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| posted on 10/10/07 at 10:27 AM |
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quote:
Originally posted by Hammerhead
You should possibly document your layup process with pics and explainations and data as to why you have constructed the chassis in the way you
have.
I have some pics of the porsche gt carbon chassis and a few others if you need them.
would be very handy - please! At least 50% of my time so far (over 2 years!) has been researching bits so the more info I can get the better -
I'll U2U you my email addy.
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Agriv8
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| posted on 10/10/07 at 10:30 AM |
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int the GTM a monocoque ( fiberglass ? regards
Agriv8
Taller than your average Guy !
Management is like a tree of monkeys. - Those at the top look down and see a tree full of smiling faces. BUT Those at the bottom look up and see a
tree full of a*seholes .............
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BenB
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| posted on 10/10/07 at 10:54 AM |
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They don't destruction test a tubular chassis why would they decide to do so with a GRP monocoque? Basically they will assess the chassis (ie
get a gut feeling!) and decide whether it's up to the job....
SVA is mainly a safety thing. If the monocoque is that flexible that SVA fail it then its going to drive like a bag of jelly anyway!!!! You'll
need to be careful about how you mount your seats, harnesses, axle mounts etc but then you'll want to do that anyway if you're going to
sit in it and drive it!!! It would be worth having pictures of any support bracketry that isn't visable from the outside.
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Delinquent
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| posted on 10/10/07 at 10:57 AM |
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quote:
Originally posted by Agriv8
int the GTM a monocoque ( fiberglass ? regards
Agriv8
Indeed - it's one of the cars that inspired me to continue on these lines.
BenB - good point on the destruction testing. It's that "gut feeling" thing that worries me, want to make sure that I can do all to
avoid an upset stomach for the SVA man.
Thinking photo's are definitely a good idea - plenty of area's will have aluminium and steel re-enforcing in the layup, and certainly not
be visible upon completion.
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Agriv8
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| posted on 10/10/07 at 11:24 AM |
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Sorry Ill finish what I meant to type not what I was thinking the GTM is Monocque and that passes SVA.
I would start by looking at that and see how they have tied the relevant structures together. GRP thickness ect.
regards
Agriv8
Taller than your average Guy !
Management is like a tree of monkeys. - Those at the top look down and see a tree full of smiling faces. BUT Those at the bottom look up and see a
tree full of a*seholes .............
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Delinquent
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| posted on 10/10/07 at 12:38 PM |
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quote:
I would start by looking at that and see how they have tied the relevant structures together. GRP thickness ect.
regards
Agriv8
Indeed - unfortunately I don't know of any in the area, and find most enthusiasts are reluctant to let me start pulling their car apart 
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DarrenW
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| posted on 10/10/07 at 01:52 PM |
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As mentioned already id try and talk to one of the SVA guys. I found them quite helpful during the build. Most are car mad so may afford you some time
for a chat if you provide the coffee and biccies.
Might also be worth researching the woes of the RH lightweight builders to remind yourself what SVA's main concern was with that car (i hope i
havent propomted a digression by saying that ).
Sounds like a great plan you have so dont let anything put you off. If Lotus can get the Elise type approved then im sure you can do a amateur built
one. If you are fortunate to have access to computer gear for the design side then it wont harm having a portfolio of design calculations and FMEA
print outs should the questions be raised.
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britishtrident
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| posted on 10/10/07 at 02:59 PM |
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Best to deal with seat belt mounts is locate them on a steel roll cage and bond the roll cage into the structure. Davrian/Darrian used bonded in
roll cages with great success.
Suspension and engine mounts need to be designed to feed the loads into the structure in shear ----- with a double wisbone set up this might require
a steel subframe.
Again a look a Darrian or a Mk7 or Mk8 Davrian will give you clues on proven best practice.
Document & photograph any safety critical item the inspector can't see.
[Edited on 10/10/07 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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Syd Bridge
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| posted on 10/10/07 at 03:36 PM |
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quote:
Originally posted by britishtrident
Suspension and engine mounts need to be designed to feed the loads into the structure in shear -----
[Edited on 10/10/07 by britishtrident]
That quote is not true, and poor engineering at best, particularly with composites. Davrian and Darrian might get away with it with massive overdoing
of the layups, but it can be done infinitely more elegantly and sensibly with correct and proper use of the relevant materials.
The loads need to go into the monocoque as tensile or compressive loads.
I've been down this road with SVA. Best I can say is 'Good Luck'.
They'll want to see metal plates (yes, metal!!) set into the composite at areas of stress. ie. wishbone mounts and seatbelt mounts. The sizes
are laid out in the sva manual. If you haven't got one, get the latest. It's a small cost in the overall picture, and can be your best
friend in a build of your type.
You'll need to put solid sections in the core, and take pics as proof.
It's not up to the SVA man to pass it at will, you will have to prove its safety and engineering.
Sadly, a steel tube chassis is what they want to see from a one off amateur build.
Do take as many pics as possible, and be ready to show the engineering calcs you've made to back up your design and execution of it.
Cheers,
Syd.
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Delinquent
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| posted on 10/10/07 at 03:48 PM |
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Cheers Syd, suppose I best get the new SVA book before I go any further then... more reading!
Metal inserts into the laminate construction are planned wherever something structural is going to be mounted, and I was thinking of re-inforcing with
clamping plates either side of the composite just to give something "visual" as it were.
LOL - the "good luck" bit sounds ominous though. Having said that, I only intend to do this once, and it's as much an
"achieving a life goal" task than actually building the car, so I must keep on track... it's the "engineering
calculations" bit that worries me most. Rusty would not even come close to describing my position there.
Think I'll see if I can push my handy pro to put something on paper that looks fancy - even if it's beyond my comprehension!
Just one question - you mention solid core - do you mean in relation to the metal inserts, or are you just talking generally? I'm torn between
nomex / aluminium honeycomb and poly foam at the moment - my helpful chappy uses poly foam exclusively in the boat building side. Slightly heavier
admittedly but he reckons on impact protection it far surpasses aluminium 'comb.
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blakep82
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| posted on 10/10/07 at 05:56 PM |
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haven't read other posts, but i think it would be important to make a full build diary to take along for the test, showing all the bits in
detail that the tester can't physically see.
plenty of photos showing how the structure is made.
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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