So as you can tell I'm writing about a theoretical. But I want the input of the board. I've done a bit of mechanical engineering (mostly mounts for dynamic loads that sort of thing) but I've been reading about the spaceships they've had in F1 (Figuratively but you know) and the Sebastian Loeb record on Pikes Peak. His car had 850hp for 850 kilos. Great. Peugeot and Loeb should be very proud. Really I mean it. I'm not being a smart ass. But I want to take it further. A carbon fiber space frame based on the Ariel Atom, Replace as many parts as possible on a Porsche 3.5 with carbon fiber while developing 850 hp. Use a Sadev transverse 4wd tranny. The goal is a 4wd vehicle with 1hp/lb coming in at no more than 850 lbs. Replacing a steel frame with carbon fiber will do a lot. But where else can weight be cut? Again. I do not have the money to make this a reality. But hey why not let imaginations run wild? (ps I know I have one post and registered today but I've been lurking for a while). A bonus would be that it develops half its weight in downforce.
My only input is that a carbon space frame is the wrong way to go. Composites don't respond well to point loads or localised loads which is what will be the case at every tube intersection. Would be throwing away a lot of stiffness and for what benefit?
Ok, Honestly something I don't know enough to argue with. The point was for lightness. The plan was to almost literally widen an Ariel Atom frame and replace the steel with carbon fiber. So would a titanium carbon fiber weave be better? Like Pagani are using? And thanks for the response. I really mean a stupid idea. I have no idea what I'm doing with carbon fiber. I've worked entirely in aluminum and steel.
Or Kevlar which obviously is more flexible.
And if I were to specify the weave so that the fibers were laid through each joint to make sure it was in tension the majority of the time, would I be further ahead? I'm really thinking what I need is a structure that is basically a monocoque. I use a space frame as an example because of the lack of material between the struts. But I am looking to avoid the inherent weaknesses of joining separate pieces.
I was thinking in a two part set up, split axially. Use the motor mounts and front differential/ aerodynamics as part of the chassis. So you're saying forget the space frame, set it up as a true monocoque with a real body? I could build more of the aero into the body that way.
Carbon fibre space frame has been tried before, at least experimental. So not totally new but it has to be asked what benefits it can bring. Don’t expect it to be automatically lighter. Carbon structures can turn out heavier than steel ones. It might also require more volume which occupies space for other parts. A steel frame might be easier to handle, weld able etc.
OK. This is why I asked for ideas (help really). So I need to rethink the body at least. I am going to figure out how to get a car under half a ton with a 1hp/ lb pw ratio. Dream big or sit down right?
You might have some things in common with Gordon Murray. Here's an article written by a fellow I hold in the highest esteem that focuses on what Murray is thinking when he thinks about cars these days.
Seems to me you should send off your resume and a good cover letter to Gordon Murray Design!
Some men go crazy; some men go slow. Some men go just where they want; some men never go.
my take on this :
reduce parts Count as much as possible .
so first step would be to make up a full BOM (Bill Of Materials ) and look where the weight really is and what the single parts use is and what it could do additionally .
Chapman once said he would simply omit parts which would not have at least two Tasks to fullfil ...maybe that´s a good starting Point to shed weight .
This will leed to a highly integrated design which in efffect will lead to less weight.
sure a cf tub will come out lighter and stronger than a spaceframe cladded with bodywork a nd a pletora of brackets to Mount all the bits and pieces.
but then again you will not be able to design the ultimate without ever having done something like this .It´s impossible to leapfrog all the accumulated experience with the help of a few interested forumm memebers and say 10 hours of brainfade.
some might say a spaceframe implies proportions such that buckling strength is matched to conventional strengths eg Lotus 8 ?
and dodgy cheap kitcars/replicas
with frames of this type magnesium alloy could be much lighter (eg Porsche 908s 917s) than steel
but modern spaceframes are not so proportioned so would not benefit
arguably the most efficient structures are such 'spaceframe' structures as in human-powered aircraft
cfc struts/booms with end fittings and cf or similar 'wire' ties with end fittings
the lightest way to a given stiffness or strength is the 'true' spaceframe
the most compact way to a given high stiffness is the modern 'monocoque'
though very heavy if made from steel
If it's all just in your imagination and you have no budget, why bother with a carbon space frame? may as well mould monocoque, it'll probably be lighter.
If all you want is 1hp/lb then thats not hard at all. F1 cars from the 80s were in that range. The recipe is:
Stressed engine + gearbox (to cut out rear chassis weight)
Turbo + tune such that it will only last one race
Flimsy chassis
No surplus auxiliary systems like hydraulic diffs, active aero
Small fuel tank
This gave circa 1000hp and 540kg in 1986.
In addition to this the main places to find weight are:
Smallest wheels possible
Carbon brakes are a big weight saver
Simple drivetrain
Power to weight is not the only thing you want though (otherwise why bother with the extra weight of the 4WD?). If you want increased crash performance you need a stronger chassis and impact zones. If you want a better top speed, you should run a closed body work instead of an open wheel design. Then if you want to go around corners quickly some downforce will be needed. All of these things add weight of course - so you really need to ask yourself: is power to weight the most important part or can we sacrifice some weight for performance in other areas.
By the way, the Gumpert Apollo is approaching what you want. cira 700hp and 1100kg. And that is with a steel spaceframe
So what you are asking is not entirely unrealistic, though there are some good reasons why it hasn't been done yet, at least on a production road car.
Think about issue from different direction-- You want to be traction limited up to what speed? Then figure what power to weight that requires. This also requires the intermediate step of deciding what tires (grip) and downforce, etc. you want to have.
I think around 3 lbs per hp, combined with no downforce and 1G grip, and combined with rear-drive, will be grip limited up to around 125 mph. So 1 lb per hp with same downforce and grip would be traction limited up to 375 mph. Do typical calcs for yourself and I think you will create similar numbers from realistic inputs. The point is don't kill yourself worrying about power to weight if you can't ever use it. Are you driving at Le Mans without the chicanes? When would you get to 375 mph?
To answer your question more directly you could save weight by having no multi-speed transmission, just a single direct drive of some kind. With 1 lb per hp there is no need for multiple gears.
It is very hard to reduce the mass of an existing design, it is far simpler to start with one that is too light and carefully add all the essential features, including perhaps an uprated spaceframe.
You need a weight budget, a piecemeal approach will just result in endless handwaving.
Given that your unsprung mass alone is likely to total 160 kg, I think you have a bit of a challenge to meet your 380 kg target.
Unsprung mass per corner
tire 11kg
wheel 4 kg
hub, wheel nuts 1 kg
CV joint 2 kg
brake disc 2kg
calliper 1kg
half of halfshaft, suspension arms, spring, shock 6kg
upright 2 kg
that's 29kg per corner with wheels that'll last 5 seconds.
