It's not uncommon to see poorly attached spoiler/splitters "pumping" (sucked to the ground and then back up again when the df is lost) and then giving quite a varying result.
Flex can be used as an advantage, if you know what you are doing, so it's much easier to keep things firm.

Many hobby racers get really surprised when aero actually work (diffusers ripping pop-rivets etc).

 

jpreston - Thanks for pointing that out. I had to go back and refresh my memory on force/energy in elastic deformations. Sometimes it's easy to fall into the trap of repeating what you've heard a million times. The misconception is not confined only to forums or to the amateur level, I've seen this 'knowledge' reiterated by guys involved in IMSA, Grand Am, etc.

There are other negative effects of flex due to downforce, as Leafy and NiklasFalk have touched on. I've heard of diffusers deforming to the point of becoming completely ineffective, and have seen several examples of deformation at speed completely changing the profiles or attitudes of parts.
On a pro level flex can be intentional and tuned - wings decreasing aoa and rear bodywork depressing to reduce drag (LMP), winglets deflecting to shift the center of pressure (F1), etc. etc. but on an amateur level it is almost always unintentional and detrimental except for a few specific cases I can think of where it was cleverly used to a benefit, albeit a blunt one.

The other ugly byproduct that can arise in aeroelasticity is 'flutter' or oscillations, and this is in nearly every instance detrimental.

So for more than one reason, it is ideal to fix aero components as solidly as possible.

-Ryan

 

Agreed with all of that- especially this part. I tried to write something similar but it started dragging on into TL;DR territory, so I just deleted it.

Another reason flex should be avoided at our level is that, in general, any part allowed to flex will eventually fail. The pros that are designing significant flex into aero components are also calculating cycle life and throwing parts in the trash after a certain number of hours.

 

the delta wing is copping us.

 

If you were going to make one of the "EP" styled air dams out of aluminum sheet, what thickness would you choose? It seems Emilio prefers 0.100" HDPE, so aluminum I should choose something <0.100"?

 

Anything close to 0.100 would be ridiculously heavy. In basic sheet form, there's a fine line between lightweight and too flexible with aluminum. Why would you want to use aluminum anyways? These aren't dirt circle track cars, think beyond just sheet metal options, ABS is much better in this application.

-Ryan

 

Agreed.

Aluminum is a poor choice for EP style dam. Thick enough to resist dents and its both hard to work with and heavy, besides costing more. HDPE is flexible, super easy to work with, reasonably light and most of all, dirt cheap. I buy mine from Amazon, All Star sheet plastic.

 

Will be testing this aero package next weekend. Large front and rear spoilers, and fastback. Will make side skirts if I get time.


image hosting 30 mb

 

I know Al is a bad choice for this...I'm not doing it because I think it's a good idea but because of a rule set.

So...I'm definitely going to use Aluminum, just don't know what thickness to use.

 

HDPE covered by alu foil?

Whats the rule exact wording?

 

What organization and class?
Link to rules?

I'd suggest a thin skin, .049 or maybe .030 with supports underneath. I think it's uncharted territory though since no one ever bothers with al for that structure. You will eventually become the expert and tell us what does and doesn't work.

 

Someone on here did try the thin aluminum EP air damn. Might actually be in this thread, it was an EPIC FAIL. I think 1/16th inch might work without bracing. I think .050 is going to be the minimum you could use at all without it flopping everywhere.

What the **** is your rule set?

 

ChumpCar

Homemade aero is allowed on a point per sq-ft basis.

Wood (up to 0.5" t) = 1pt / sq-ft

Sheet Steel or Aluminum (up to 0.25" t) = 2pts / sq-ft

Sheet Plastic or Polycarbonate (up to 0.38" t) = 3pts / sq-ft

Carbon Fiber = 5 pts / sq-ft


Points are few and very precious. Since plastic is 150% the point cost of aluminum I thought I'd try aluminum for the air-dam and rear spoiler. Some sort of splitter will be made out of wood.

So it's not that the rules don't allow plastic, just that they favor aluminum.

 

Why would you not use thin plywood for the air damn instead? The right plywood would take the curves fine, it works for boats.

Or failing that I'd pick steel over aluminum.

 

I would use veneer then.

 

I hadn't thought of using wood...sounds super ghetto. Of course, it's ChumpCar so I guess that's the point?

 

Get some thin 1/8" birch ply and cut vertical grooves with a table saw. Very flexible yet rigid. Add horizontal grooves where compound curves are required.

Furniture and cabinet makes do this all the time with great results. Not ghetto at all if one executes properly.

 

That was me. Epic fail can be seen at the top of page 11.

http://www.miataturbo.net/race-prep-...11/#post929111

 

Cool...thanks for the link.

It seems I'll make the first attemp with nature's composite!

 

The rules you posted don't say anything about fiberglass or resin. What about using the thinnest/lightest wood you can find and then adding a fiberglass skin to the front side after the wood is shaped onto the car?