Over and Under or around the sides

[greenpower dude reloaded]

Flyn I'm purely after a shell for this car as we are too far along as it's an upgrade rather than a new build but it is certainly something I will look into next year.
No reason to stop us using that as a plug to create a female mould other than time.

I just realised james I meant to say earlier on that the male mould would then be used to make a female mould which needn't take tooo much longer.

When I mentioned moulding the rough shape out of foam in other posts, this is what I meant



Although that would be minus roll bar and probably crash helmet fairing.

[flynfrog]

You can use the foam to make your shell cheap and easy. Think of the plywood as the mold. you need enough cross sections to bend the foam into place. use sandbags to hold it then glue in ribs.once the ribs are in place glass and go.

http://www.opencortex.org/cn00000313
http://www.opencortex.org/cn00000309
http://www.opencortex.org/cn00000317
http://www.opencortex.org/cn00000312
http://www.opencortex.org/cn00000314 this one shows the ply wood supports

here is an example of what im talking about

[flynfrog]

also you need to rethink your driver fairing you dont want to out in the middle like that taper it back down to the body.

maybe fair in the roll hoop as well

[Michiba]

How about RB5 style ridges on the sides of the nose?
I'm thinking you can use this to reduce the angle of the nose whilst accomodating the wheels.
Just thinking aloud here. Anyone care to explain how this might impact on the drag?

[lkocev]

I would have though that using ridges to accomodate the front wheels could potentially decrease the frontal area, possibly decreasing drag. Would probably be a cunt to make though... I guess you could possibly make a tub and then make kind of like fairings and bond them??

[Michiba]

I'm not sure that doing so reduces the frontal area. My idea is just to improve the flow over the car, where there is likely to be a lot of turbulence/drag over the drivers helmet.

[greenpower dude reloaded]

^ Last years car had massive ridges for accomodating the wheels and reducing frontal area. But believe it or not this years car has roughly the same frontal area and is already 4.5mph faster than last years car and I suspect this body modification could provide something of a substanstial improvement on that.

Having said that I do keep thinking about one day making a proper all out version of that car.

The helmet fairing is likely to be altered substantially it was just a quick and easy visual representation.

The roll bar you can see is an aerofoil section one, the problem is the chassis has to be that way because of the way everything has been packaged. It's far from ideal but it's positioning could be worse i feel.

Sorry for the late reply everybody, I was at a VSCC event at Prescott fri-mon

[greenpower dude reloaded]

Right quick update,

I've had some CFD analysis done and have been told the Cd of the new car is..... 0.17 the original shape being 0.39 then the updated (fences etc.) was 0.37 clearly this would be a quantum leap BUT does anybody know what sort of jump we should expect in speed?

When the Cd was 0.37 we could average 33mph (which is a pretty high average speed, top 5 cars maybe) now it'll be at least 20points better should we expect much of a rise in speed?

[RH1300S]

I thought you could calculate drag expressed as pounds of force (or whatever units you need) just as long as you know the CD & the Frontal Area. You must be close to knowing the theoretical answer.

[greenpower dude reloaded]

I know Cd and FA just not the formula... any clues??

[tomislavp4]

Drag (N)= drag (cd) * referens area (m²) * 0,5 * air density (kg/m3) * velocity squared (m/s)

Roling resistance = rolling resistance coefficient (0,03 for tyre on sphalt) * weight (kg) * gravity (m/s2)

Power (w) = (force (N)* distance (m)) / 3600

Hope it helps

[greenpower dude reloaded]

very helpful! I've basically established that this is one of the most efficient shapes compared to anything thats ever raced and nothing has looked quite like this

[tok-tokkie]

I have been following this thread with great interest. To have halved the CD is dramatic. Your shape adheres to the advice given on this thread & to see it so dramatically confirmed by threoretical analysis is great. The proof of the pudding should also be great even if it undershoots a little.

[flynfrog]

you should do a coast down test with the Cd data from your current car to correlate the data other wise you are just guessing.


http://www.physicsforums.com/archive/in ... 27550.html
http://www.landracing.com/formula/coastdown.htm
http://ecomodder.com/forum/showthread.p ... -2992.html

[greenpower dude reloaded]

Great idea Flyn, i'll be really interested in trying that, but it might not be until the winter.

We ran the original shape and then the slightly tweaked shape as well all within the same parameters so even if it's totally wrong Cd wise we've at least got a comparison of all three.

The Original had a Cd of 0.39 the then modified shape had a Cd of 0.37 and the new one 0.17. Frontal area has dropped a fraction as well with big rounded edges etc.

I'm hoping to test one with an improved crash helmet faring, but it all comes down to time doesn't it...

I ought to get on with building it really!