FF underbody aero

[stephen wilson]

This may be a silly question, but here goes: I have an 1/8" steel, full width "ballast plate" bolted under the middle of my FF floor-pan. Is there enough drag created by this lip to make it worth the effort of mounting the ballast inside the chassis?

A related question, can any noticable downforce be generated by the rake of a flat underbody only 15" wide? With the currently used 1" diffusers ?

Thanks,
Steve

[thomschoon]

Might want to check the GCR 9.3.8

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9.3.8. BALLAST

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Ballast may be added to all cars as required, to meet minimum weight,
provided it is securely mounted within the bodywork and serves no other

purpose.

Regards
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[racer27]

If you need weight down low, just use a heavier floor. A thicker floor is probably the safest place to add weight. It also adds stiffness to car and enhances performance. It also protects you behind, enhancing safety. Heavier Stainless floor will last allot longer then aluminum reducing replacement frequency. When done. you'll end up a nice smooth surface.

As for the 1" rule, not sure of downforce, but if you can accommodate it within the rules I'll add it, as that upkick could save your floor if you end up going over a curb backwards and may prevent you from high-siding the car.

[Joefisherff]

A few years ago the Purple Frog took some great shots at the Runoffs of different interpretations of the 1" rule. I don't know if anyone did anything similar last year I didn't see any pics.

[stephen wilson]

Well, I guess that answers one question! I managed to miss 9.3.8, though many cars have skid blocks under the front and rear to protect the pan. At what point does a skid block become ballast? A sturdier pan is good, but I need to adjust the weight to compensate for the number of cheeseburgers I've eaten!

Joe, those Runoffs pictures are exactly what I was thinking about, since they were deemed legal.

[ghickman]

In my opinion if you have anything extending below the belly pan such as you described it will "TRIP" the air flow and have some detriment. Hence the reason for going to great pains to use counter sunk rivets when installing belly pans and such.

Any type of diffuser will help no matter how small, down force with virtually no drag penalty is always a good thing.

Gary Hickman
FB #76

[preform resources]

Steve, it sounds as though you are using the steel sheet as a floor pan also, and you want to make it wider than the bottom of the chassis, I don't know why it would be illegal
as a floor pan,I also don't know the FF rules on width of the bottom of the car, having said that, if you have a flat bottom with a slight kickup for a quasi diffuser then ride height and rake would make a difference in downforce, the size of the flat area would determine the amount of downforce you could generate ultimately.
Dave Craddock

[stephen wilson]

The steel sheet is currently bolted under the riveted floor pan. There is a max. width of 95 cm, with no undertray extensions allowed, the body itself would have to be made wider.

[R. Pare]

There is nothing in the rules that would disallow the use of a steel sheet as an undertray below the floorpan - you can use almost anything you want material-wise for undertray construction as long as it does not run afoul of the material rules for bodywork ( which most likely that sheet would be declared to be)

The likelyhood of it being tossed because it is "ballast" that is not located within the cockpit interior could be another matter all together, but most likely if you never declare it as ballast, no one will ever bother to protest (unless you are beating them rather soundly!)

[problemchild]

You would need to have a pretty tricked-out car and be super-competitive to be worried about a 1/8" step half-way down your floor. Just start calling it an ass-protector instead of ballast!

If you must worry about it, chambfer the edges or fill in the step with tape, glue, bondo, silicone, plastic wood ....?

How many of your body panel seams fit perfectly?

[Art Smith]

Stephen-

one other concern to deal with; what rivet spacing was used for the steel plate AND what was it riveted to?? if it was riveted to the frame it would seem like the 6" minimum spacing rule would be in play...... if not and you riveted to the belly pan it's not clear to me you don't have the same problem!! once a compliant belly pan is attached to the frame in a compliant manner, is it "belly pan" or is it "frame"??? the courts were unwilling to provide a binding answer to the gramar question when asked via an 8.1.4 request about the post attachment status of "brackets" without a specific case/picture.................... it's a thorny question of which set of rules are in play; bodywork or frame. depending on your objective(s), you may have a preference!!! as a simple and silly example: there are no width constraints on frames........

Art
artesmith@earthlink.net

[Daryl DeArman]

On a related note, why is the following wording missing from the FF section? or did I miss it?

"No permitted component/modification shall additionally perform a prohibited
function."

There are other sections of the GCR that contain the above.

[stephen wilson]

The sheet is actually a shallow channel, bolted in 4 places to the outside of the frame rail.

Art, my ASSumption would be that closely spaced attachments would be legal, since the pan is allowed to be a stressed panel.

Greg, I agree, it is a very minute detail. But, I'm a bit anal-retentive, and tend to obsess about every detail! It doesn't help that I'm not racing right now, and have too much time on my hands to think about these things.

[racer27]

If you already have a pan there, this is not a pan, thus I think the 6" attachment rule might apply. It is serving an alternate purpose (ballest, skid block). I'd personally not want to be behind a car with something that large that has the potentiial to be dislodged.

[stephen wilson]

It's mounted with 4 large bolts, if I hit anything large enough to dislodge it, my frame would probably be broken in half! There's be a better chance of a car in front of you losing a wheel, or other significant part.

Steve

[GeoffRain]

I'd be more concerned about the extra 1/8" of ride height that you now need to run. You may be putting that (15?) lbs nice and low but aren't you effectively raising the other 1085?

[stephen wilson]

I agree, that's why I will be changing rub blocks on the front of the pan. The rear is not as much of an issue with the rake of the chassis.