Ground sealing...

Recently I've been having these rather perverse ideas about itty bitty sports racers (think big FSAE with a LeGrand body and you're about there), and noticed something curious in the A-mod rules; movable side skirts ARE allowed, meaning some sort of ground sealing could be achieved. The more I think about it, the more I feel like flexible side skirts might be easier to set up, and strangely enough, I keep coming back to the idea of a door sweep. You know, that thing that looks like one row of bristles from a big push broom? Or, perhaps actually cannibalizing a push broom and using individual rows of bristles. It seems to me that something like that would be VERY easy to adapt to existing cars, especially ones with very little suspension travel. The real question is, would it work? I mean assuming you could get an AX car to work with VERY low amounts of body movement in roll and pitch and only an inch or so of bump travel, it seems like this would work very well, especially if you had a diffuser that extended into the sidepod area (ala Porsche 962) and made the skirt follow the outer edge of the tunnel rather than just running along the edge of the bodywork between the front and rear tires. This might also have the advantage of sweeping the course directly in front of the driven wheels, which can only help things I'd imagine. Of course, you'd have to periodically replace the bristles as they wore down, but I can't imagine that would be too expensive, just buy a pair of broom heads and you've got enough material to skirt at least one LeGrand or with some creativity, a few formula cars.

Am I starting to go certifiably insane, or could this actually work, at least for an AX/hillclimb application? If nothing else, your competitors couldn't complain but so much, on one hand you might have a serious aero advantage, but on the other hand, you're the autocross equivalent of a Zamboni

I've always wondered what they used when skirts were F1 legal, its been long enough that it can't be too exotic anymore.

Look into the Chapparals. Lexan skirts, with a cool little mechanism tied to the suspension to maintain a 1/4" clearance.

Bristles might be an easy thing to try. What the heck, right?

At typical autox speeds, I'm not sure you'll gain anything appreciable from such ground effects.

I do see the broom types in use, on semi trucks. At higher speeds, they move quite a bit. Seem to be not holding a vacuum, just guiding air around the truck.

In the case of a very light car, impacting the broom fibers onto the ground could have a very pronounced effect on the handling. Those fibers, en masse, are quite strong. When you sweep with a broom, the bristles hold the broom head up off the floor. You very well could end up with the car lifted off its suspension, if not completely at least partially. That is normally not good for handling and control.

Just some random thoughts.

A solution like a row of bristles could provide you with some downforce. It would be less than actually sealing with solid materials, but still most of the gain is there.
As far as how to keep different systems sealed:
You could use something like a soft door sweep mounted at an aggressive angle to reduce the skirt loading, but it would wear quickly (faster with more downforce trying to pull it under the car).
Rows of bristle type material will flex back and laterally with car motion, so unloading the rest of the car is less of an issues than proposed above. Bristles would work better on sides than the front. The wear of the bristles will be minimal and if the car is setup the same for most events any wear would be limited to roughly the same max roll/heave.
Lexan skirts (or other plastics) can be made to slide and pivot in channels on the sides of the bodywork and diffusers. That gives the advantage of a complete seal, wear adjustment and body motion all in one package.
The low speeds of AX do not necessarily mean low downforce. If you were able to generate even 0.1 psi of vacuum under a typical BMod size car you are talking about nearly 500 pounds (96in50in0.1psi=480pounds) of downforce. Keep in mind that a little suction spread over a large area adds up quickly.
Steve Stafford

Look up Brush Seals.

They are used extensively in the aerospace industry as "flexible" seals. With that said, they aren't exactly flexible, but if properly designed can create a very good seal.

Plus the guys at the autocross would really love you for sweeping the track for them!!!