Wolf HR
|
| posted on 26/1/08 at 01:44 AM |
|
|
Something a tad different
Hi everyone. I'm currently in plan and design phase of my car, so I'd appreciate comments and suggestions.
As I've said elsewhere, I'm going a bit radical and have decided on something a bit more expensive (albeit, I'm hoping a rather
simpler) for my project. I'd use a cured GRP sandwich for main structure, instead of steel frame, to cut down weight, and hopefully cost. The
main tub structure would be reinforced by three 'tube' sections to provide stiffness.
The monocoque would have four Al alloy bulkheads glued to it (two box sections at the fore-most and aft-most parts to carry suspension mounts and rear
engine mounts, and two U-shaped in the middle section, one for steering/dashboard, 2nd just aft of driver to carry fore engine mounts and seat belt
installation).
Just for the fun of it, I've fiddled around and added Hayabusa engine (with dry sump conversion) which I'd dearly love to see used to
propel this car of mine... (the challenge was adding Solidworks based model of the engine to Autocad model of the monocoque... all done in 3rd party
program).
Sooo, whaddya think? TIA
P.S. The structure in the first pic should weigh around 23-24 kg. Similar GRP sandwich structure was used on some aircraft (although I use twice as
thick/strong GRP facesheets)
|
|
|
|
|
Rogue Se7ens
|
| posted on 26/1/08 at 03:14 AM |
|
|
Very nice design Wolf, the boxed members should provide much strength as long as the material thickness is appropriate. One concern that you may have
already considered is torsional stiffness. Maybe if the body parts which are not shown are stressed members you will be OK. Will the three boxed
structures be housing anything? If not filling them with expanding urethane foam should greatly increase the strength. Look forward to seeing more.
|
|
|
Ivan
|
| posted on 26/1/08 at 06:15 AM |
|
|
Very similar to what I would do if I where designing a rear engined car so I like your idea. Only I would look at getting the tub commercialy folded
out of Aluminium or stainless steel which I think might even be lighter (haven't done the maths).
Of course the tortional strength will be dependant on proper bulkheads at each end of the tub.
|
|
|
Confused but excited.
|
| posted on 26/1/08 at 02:40 PM |
|
|
quote:
Originally posted by Wolf HR
I'd use a cured GRP sandwich for main structure, instead of steel frame, to cut down weight, and hopefully cost. The main tub structure would be
reinforced by three 'tube' sections to provide stiffness.
Great for boats and planes, but have you ever seen a Robin Reliant after a crash?
Only my personal opinion of course.
Tell them about the bent treacle edges!
|
|
|
Volvorsport
|
| posted on 26/1/08 at 02:50 PM |
|
|
have you ever seen a darrian after a 100mph off ?
robin reliants have a seperate chassis - the body is there just to look at and isnt structural in a modern sense .
i think itll be good , but, you might make it easier/quicker in steel , i notice you have some compound curves , which youll need to make molds for -
time consuming but cheap , can you guarantee accuracy affter all that work ?
make it a bit easier to make and youll be on to a winner .
why not use something like this i nyour build , its very easy to use , and would suit your purpose .
http://www.teklam.com/
www.dbsmotorsport.co.uk
getting dirty under a bus
|
|
|
Wolf HR
|
| posted on 26/1/08 at 05:34 PM |
|
|
Volvosport, I was thinking of laying the core (10mm H-80) over set of equally spaced patterns since curvature is rather gentle. I'd use wet
lay-up (4 layers of 7781 cloth + gel coat on the outer, and 5 layer w/o gelcoat on the inner facesheet). Something like in this sketch, but I'd
be more inclined to use male patterns (instead of female shown)- to ensure perfect fit of 'subframes' (box sections that will be glued to
it).
How does that look?
[Edited on 26/1/08 by Wolf HR]
|
|
|
Puk
|
| posted on 27/1/08 at 02:46 PM |
|
|
Wolf you have great English vernacular for someone from Croatia  Are you in exile?
I considered a GRP structure versus aluminum composite and chose the latter partly because I was worried about being able to be certain of structural
integrity but mainly because I didn't fancy all the mold making and polishing involved with plastic.
Are you familiar with the moldless composite construction techniques that Burt Rutan popularized for home built aircraft construction? Basically carve
your shape in foam and cover with woven glass cloth and resin. Then polish. A lot. I would imagine that it would be the quickest way of building a one
off.
How will you calculate the required shell thickness?
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.
|
|
|
Wolf HR
|
| posted on 28/1/08 at 04:49 PM |
|
|
Thanks for kind words, Puk- I'm living in Croatia (but I did hone my english, eons ago, living for a month in Brighton), so it's practice,
practice, practice.
Current lay-up got a thumbs-up from someone in the know, but I'll try to do a FEA before I start making it. Comparable lay-up can be found on
Cirrus SR20 aircraft:
I'd use 4 plies (+ gel-coat) on the outer facesheet, and 5 plies on the inner, instead of 2. Luckily, I was able to lay my hands on some
'real data' for the material (a cured ply of 7781 8-harness satin with epoxy resin)- which is the hardest part, and it compares favourably
even to many kinds of steel (e.g. tensile strength in excess of 330 MPa)...
Yes, I'm aware of it, but I was hoping to use sandwich core as the 'mould'.
EDIT- Just wanted to add a sketch of how I hope the car would look like...
[Edited on 28/1/08 by Wolf HR]
|
|
|
