enderw88
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| posted on 26/8/05 at 09:11 PM |
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Why not bend the longerons?
Starting to think about my chassic design and I am wondering why the book chassis doesn't bend the longeron to keep them a single pice, vice
several short straing runs. Is it just to avoid needing a tubing bender?
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Liam
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| posted on 26/8/05 at 09:44 PM |
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Uuuuuurrrrrrrrr???????
What's a longeron???
liam
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Liam
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| posted on 26/8/05 at 09:46 PM |
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10 seconds of internet research later...
Aaaaahhhh! Yeah that's probably the reason. Might look quite nice with a bend instead of a kink in the side of the chassis...
Liam
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Hellfire
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| posted on 26/8/05 at 10:13 PM |
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quote:
Originally posted by Liam
Uuuuuurrrrrrrrr???????
What's a longeron???
liam
Are you mystified Liam by a longeron - that'll be a "Mysteron" then 
Sorry - I'll get me coat 
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Liam
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| posted on 26/8/05 at 11:01 PM |
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I'm surprised you'd face people for the time it takes to get your coat. I think you should just leave as soon as possible.
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smart51
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| posted on 27/8/05 at 07:54 AM |
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curved would look stunning, especially if it looked like an aerial atom. With a pipe bender you get one radius, so you would end up with a
straight-bend-straight type tube. It would look like a normal seven. Isn't there an opinion that a bent tube isn't as strong as two
straight tubes welded together?
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britishtrident
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| posted on 27/8/05 at 08:59 AM |
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Not a good idea for pretty obvious reasons framed structures should be made of only perfectly straight struts and ties.
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Triton
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| posted on 27/8/05 at 09:07 AM |
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Cut n shut welded tubes in a chassis is stronger........bending tube weakens it especially rhs as it crushes on the inside of the bend and stretches
on the outside.
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JoelP
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| posted on 27/8/05 at 09:11 AM |
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my solution to this one is to have the chassis straight from front to back, as i believe that the bend in the side just near the scuttle, is probably
one of the worst features, as its not triangulared in all directions.
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quattromike
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| posted on 27/8/05 at 12:31 PM |
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If you look in my photo archive you see a picture of the slight curve I have put in my chasis sides.
You'll never know how it's gonna work if no one actually does it.
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quattromike
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| posted on 27/8/05 at 12:44 PM |
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Or look here
link to picture
I'm gonna make the tunnel stronger to try and stop some of the twisting about, if there is any
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smart51
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| posted on 27/8/05 at 03:06 PM |
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The front wheels on my sierra based VortX don't go anywhere near the bodywork even at full lock. The nose doesn't have to be as narrow as
it usually is, except for convention on narrow axled cars.
The VortX is wider in the body by 60 or 70mm than a book locost chassis. A "book" locost with Sierra running gear may be able to have a
straight chassis, or close to it. You might even get a bike engine in without having it at an angle to the propshaft.
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britishtrident
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| posted on 27/8/05 at 04:27 PM |
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quote:
Originally posted by quattromike
Or look here
link to picture
I'm gonna make the tunnel stronger to try and stop some of the twisting about, if there is any
Try thinking in terms of stiffness not strength --- stiffness to weight ratio is the key to chassis design.
Because the tunnel is much closer to the neutral axis you won't get anything like the stiffeness back from stiffenning the tunnel. It would also
require substantial stiffening of the rear cockpit bulkhead area to transfer torsional loads to the tunnel.
Any structural engineer will tell you even a slight bend in a slim strut type member is a really bad design causing a drastic reduction in
the load at buckling failure as well as a major reduction in stiffness.
The effect on members in tension eg ties is confined to a reduction in stiffness but it is significant.
Ariel get around it as did the early 1960s Cooper F1 cars by using subtantially bigger diameter tube for the main structural members the wall
thickness is also a believe increased.
This will regain some of the lost stiffness but at the price of doubling the weight.
[Edited on 27/8/05 by britishtrident]
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Hugh Paterson
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| posted on 27/8/05 at 05:03 PM |
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bending tube
Try building it in CDS instead of RHS, looks good and sexy if u weld it with TIG while your at it. Fish mouths and bent CDS is far superior to cut n
shut RHS, but then again as the locost chassis is prob as stiff as Strawberry jelly why bother!
I really must get out more often and mix with normal people
Shug.
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Liam
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| posted on 27/8/05 at 06:10 PM |
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Dax rush chassis is straight sided - tapering from the back of the cabin all the way to the front without a kink. It's no wider at the cabin
than a book locost and consequently even narrower in the footwell area. They can still take a V8 though.
I thought by a bend that enderw88 was suggesting producing the normal shaped chassis with a small bend instead of two tubes, rather than one continous
curve all the way along, which is certainly not good structurally. I would have thought the former would be fine - just a more convenient method of
construction (if you have a tube bender). MK get away with a lot of bent tubes, even in the rear suspension mount area.
Limam
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Liam
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| posted on 27/8/05 at 06:12 PM |
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Oh wow!!! I appear to have found islam and changed my name to Limam today! Great!
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Peteff
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| posted on 27/8/05 at 06:43 PM |
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Salaam Alaikum Limam.
Please leave your shoes at the door.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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quattromike
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| posted on 27/8/05 at 06:52 PM |
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Yeah I do agree it'd be much stronger if the sides were dead straight, BUT , The minute you put a bend (or a kink) in it that's all the
strength lost again, I don't think there would be a great difference with a straight a bend and a straight compaired to an even curve down the
length. What I'm trying to say is if the side bars went from one point at the rear of the chasis to a point at the front and in the middle it
was 50mm out off the straight, what's the difference if it go's straight to the middle and then straight to the front compaired to going
through the points in a smooth arc? I'd like to say it'd actually be better in an arc but I get the feeling someone with more brains would
correct me so I wont. So do you get where I'm comming from?
Mike
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MikeRJ
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| posted on 27/8/05 at 08:38 PM |
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The point is that the top chassis rails are in compression just taking the weight of the car. A bent tube in compression is far, far weaker than a
straight one.
Or think of it another way, spaceframes rely on triangulation to form a rigid and strong structure. A triangle has straight sides....
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JoelP
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| posted on 27/8/05 at 08:57 PM |
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yup, best avoided IMHO. Ive just finished sketching a dedicated BEC chassis today, only simple lines, spacing and triangulation, but i hope to make a
balsa model shortly. The basics though, 22" at the front to 42" at the back, and 8" high at the front, 21" at the back, the
sides being totally straight with a gentle slop up.
Im thinking that this will increase the rigidity a bit, and i might use lighter tubing. Im torn between fishmouthing rounds tubes, or using regular
square. Seems a ball ache doing it in square though. So probably end up using 25x1.6mm round.
The other plus side, is thats its 16" shorter than a locost, due to the small bike engine, and the passanger loosing some footwell for it.
This was the reason for me starting that recent thread 'fancy wishbones', because you dont end up with any nice parallel edges at the
front to mount regular bones onto.
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kreb
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| posted on 28/8/05 at 03:55 PM |
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I've been tossing out version after version of this idea. (My poor employer, little does he know!)
Ultimately my take is that to get that sexy curve without comprimizing strength, your best bet is to curve your skin, not the frame. Do a search on
"stitch-and-glue construction" like the kayak builders do, and you'll see what I mean.
https://www.supercars.net/blog/wp-content/uploads/2016/04/1966_FiatAbarth_1000SP1.jpg
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