Stressed vs. Non-stressed Engine/Gearbox

[NewyorkKopter]

ah I see, wait so can you use a tubular chassis with a stressed layout?

[drunken monkey]

well... you can do what you like.
it also depends on some other things too.
dimensions of the engine, what ancillaries there are, what kind of body you are working with, construction method of body etc etc.

the old F1 cars of the 60s-70s were more or less an engine (that held the rear suspension) bolted onto a tubular framed main chassis that had body panels attached (onto the frame).

[Carbon Fibre]

Drunken monkey's right. Monoque is like a boat's design. The ribs help the cored hull.
I would like to know why the McLaren F-1 doesn't use this type of construction. It uses a cad designed 4130 chromoly steel frame to support it's highly touted carbon fiber body. All the body does is transfer downforce to the chassis. But it weighs something like 4.000lbs. This is probably due to using a large v-12 motor. It's output is approximately 600hp, so, o.k., it's good at top speed.
If a carbon fiber unibody (monoque) chassis was used, along with a more efficient 4-banger like a modified VW direct injection turbo motor, 2000lbs with over 400hp. could be easily acheived. This, with similar downforce charachteristics incorporated into the design would yeild a MUCH better product.

[drunken monkey]

s far as i know, the F1 does have a monocoque chassis at its heart and uses secondary structures (also made from carbon fibre) attached to the monocoque (mainly at the front) to serve as crumple areas.
it also weights 1140 kgs which is not 4000lbs.

you're thinking of the SLR.
but then that doesn't have a V12 so i now have no idea what you're talking about.

[NewyorkKopter]

yea man, what car are you talking about? The F1 was made all in Carbon Fiber, no steel frames were used. About the stressed engine layout with a Tubluar chassis, wouldn't it just depend on the chassis being a bit stiffer than usual, and the engine/gearbox being beefed up to support the weight? Also back in '89 Mercedes used a stressed chassis layout with a Tubular frame in thier LeMans winning Sauber C9.

[drunken monkey]

not sure what you mean.
the point is, the teams aim to have lowest posible weight but this is not the only determining factor. Weight, weight distribution, centre of mass, polar axis, aerodynamics (allowed and not allowed) location of large masses all play a part in how you make the car.

you don't need to beef up the engine/gearbox because it is more or less a solid bit of metal. It is rigid enough as it is.

as i said, there is no single best way.
you do what you need to do to acheive what you want.

[TheSilentChamber]

Something nobody mentioned, that may have played a part in the design process is that some of these cars are designed to break appart into pieces when wrecked.

[NewyorkKopter]

oh true. What I meant about stiffening up the chassis was that you would probably need to make a tubular chassis abit more stiffer and stronger in a stressed layout than in a non-stressed layout, so it can support the wieight of the entire powertrain of the car. And then I gave an example of a car with a tubular chassis that used a stressed engine/gearbox layout...the Sauber C9.

here's a pic of the chassis

[drunken monkey]

oh, that pic is of something else entirely.
that's more of a reinforced tub with roll-over bars.
a tub chassis can be taken to be a more fancy tubular frame but the way it deals with shear forces is different enough to make a different type of chassis.

it isn't really the engine you aim to support;
you make sure that the connection between the engine and the main chassis is solid and that any forces that acts between the two are diverted safely.
look at the roll-ever structure and where it connects on the main tub and you'll see what i mean.

[Moppie]

Up untill the late 60s all a cars chassis had to do was keep the engine off the ground, and make sure all 4 wheels stayed in the right place relative to each other.
Then someone decieded race drivers were valuable and a chassis had to be able to protect them in a crash, and things started to get complicated.
So most of the strength in a chassis now days is aimed at protecting the occupants during a crash, with only a small part aimed at the basic job of keeping the engine off the road, and the wheels on it.

Add in all the different class rules in differnt types of racing, and there is no longer one type of chassis design that is superior to any other.
Start talking about road cars and it gets even more complicated as you have to start thinking about things like pedestrian safety and noise and vibration.

Throw the incrediabl versatility of modern materials like carbon fibre and bonded aluminuim and you can build what ever structure you like designed to behave in what ever way you like.

[NewyorkKopter]

oh sorry for the late reply, but yea good point, you can do alot with modern matierials.

[drunken monkey]

and going slightly differently, the porsche carera Gt has a full carbon fibre monocoque passenger cell and carbon fibre frame on the front and rear; essentially a chassis made of different ways for different parts for different features.

[NewyorkKopter]

Yea I heard about that. Isn't it like the 1st car ever to incorporate plastic into the chassis