Properties of a Downforce Fan

[marcush.]

I have proposed something already :

a flat frame hinged by a paralellogramme type set of levers giving you a set distance to the ground .the gap between the frame and the car is taken up by a air filled rubber tube so the frame is always preloaded and can move up when hitting a bump but will be pushed back quickly.

You could link the corners of the sealing frame to the unsprung parts (suspension uprights) and keep the gap to the road constant whatever your spring compression (rideheight).

[MIKEY_!]

Is this going towards a lotus 88 double chassis concept?

[marcush.]

not quite ,would of course be the ultimate to put the downforce into the uprights but I think you need to design the car for that from scratch.my concpt would link the four corners of the closed skirt to the appropriate suspension corner forcing the sealing frame to follow suspension bump movements to avoid excessive rubbing on the ground ,one problem surely that as you suck air from the inner chamber the car springs will compress ,lowering the car by doing this -reducing the air gap -increasing the downforce even more ,compressing the sprngs more....I think without something adjusting the gap to the road to be as constant as possible you will run into a feedback loop wich is leading to unwanted fluctuiations of downforce-something that can only be controlled by massive springs that will not really compress under the force levels you will see ..... so you put all into the tyres..
with my proposal you still have the tyre squash varying your seal gap but you will surely get away with softer springs .

[MIKEY_!]

Ok a get you.

[xpensive]

...
Hmm let me think here....
...

Post deleted by better judgement as I'm posting under a suspended sentence.

[thisisatest]

judging from the arguments, although Mikey has read about the Cheaparral, others havent.
its underside was sealed on four sides to 1/2" clearance, and ran CASTERS(!) on the corners of the seals. rubber bellows connected this sealed square frame to the car itself. powerful fan. snowmobile engine driving it. it was all mounted in a Corvette (a road car, not built from scratch), won its autocross by a lot (and some other competitions since, i think). it was built with a total of $2000 in parts.
the seal can follow the ground as the car goes through its suspension travel and undulations, so sudden loss of downforce is not likely without really getting airborne (but you'd have other issues then, like landing)

minus the gravel issue, most concepts here could be applied to Mikey's project...

[MIKEY_!]

If it ever passes the concept stage

Heres a simple solution to the handling issues around clipping the apex from earlier, have a narrower sealed floor section. Or will this reduce DF. Also means the skirts don't have to move as much.

[machin]

A smaller floor area means you need a higher pressure differential to achieve the same level of downforce -either better sealing or a more powerful fan, or a combination of the two... I'm with you though -I think a narrower "floor" between the wheels is the easiest way to go as you haven't got to worry about sealing wheel arches etc....

[MIKEY_!]

This was always going to be an open wheeler. Probably never said that but what i really meant is about not having the bit of step plane that is normally visible from above on an F1 car. That way the floor is less likely to overhang the gravel verge (normally resulting in sudden DF loss)when the car clips an apex.

[marcush.]

If its allowed (or you allow it yourself to do) the linking of the movable frame facing the ground to the uprights should be enough to get rid of those casters .I think you could almost use the drop link and mount of the ARB achieving this.So if your sealingframe edges are close to the axle centreline only very pronounced bulges in the ground giving single wheel bump inputs could give you headaches.

the design goal is really not to allow the frame to hook into something at speed.so a set of wide rollers not touching the ground at the leading edge and the sides (to avoid hookin when slipping sideways) and you are ok.
(that holds true as well for the inside leading edges btw..--- happens and the worst thing is to rip of the nice work on the way from parc ferme to the start..

[MIKEY_!]

Thx

[xpensive]

The 1970 Chaparral 2J had Lexan (Polycarbonate) skirts, which were connected to the uprights somehow and thus maintained a constant gap regarless of the chassis ground-clearance.

http://www.youtube.com/watch?v=rj9JGORfZes&NR=1

Notice the squating when fans comes on!

http://www.youtube.com/watch?v=HZkUr5cG6wE&NR=1

[machin]

The 1970 Chaparral 2J had Lexan (Polycarbonate) skirts, which were connected to the uprights somehow and thus maintained a constant gap regarless of the chassis ground-clearance.

Is that what the "rocker" objects are in this drawing? One in front of the rear wheel (centre of the picture, and one behind the front wheel)?

[machin]

Bear with this a second... how about using some high density bristle-type draught excluders???!! It might sound a bit naff, but they're easy to source, cheap and mould perfectly to undulations in the road! Afterall, this is exactly the approach that hoovers use to give good suction when used on hard floors.....

[xpensive]

That's it, great pic machine! Not as effective as sliding-skirts with a ceramic contact rail, but good enough.

Btw, that strange looking belt-cover over the fan-exits was soon nick-named "the martian brassiere".

Great days they were.