I know ThePass is just in the final testing of his Flat Underbody,
but I was going to do the same thing before I went to Afghanistan. ThePass: I read everything you had to say and all the input other people had on the topic. I also bought a few books: Aerodynamics Competition Car,
Suspension Competition Car and Composites Competition Car to give me
inspiration.

For the main throat I am going to have a 1 deg rake to provide the down
force and be held on by 16 Dzus Fasteners (8 on ea side). The rear
diffuser, of course, does not produce downforce, but the math i'm going
with is the front open area under the bumper plus 20%. The 20% added
will offset some of the air that comes in from the side of the car and
the rear tire.

I will add some pics here soon

 

Here are a couple of pics

These are the 16 Dzus fasteners that will be holding up the underbody, Plus there are 4 more to put up on the undertray/air dam


This diffuser is from 5 years ago for my 240sx project. This is not going to be the final piece, this is just to hold over until I have extra material to build another one. I had to shorten the width to fit on the Miata by about 8 in.

 

Dzus is baller. Good luck, let us know how it turns out!

-Ryan

 

What are you using down the sides of the car? Do you plan to cover the bottoms of the control arms? What's your plan to disapate heat?

 

I'm welding the Dzus fasteners to the frame rails. I am going to run the main sheet of the underbody under the control arms as far as I can. I was going to run a Naca duct right at the catalytic converter and diff, but not set in stone yet

So here was my idea of keeping the Dzus fastener brackets in line and level. I took the slotted angle steel and drilled it with a step drill bit to match the taper on the fasteners. Attached 8 of them to the angled steel and welded them up after I ensured the car was level. I put a rake to the fastener brackets.

How I have the steel angle set up. I left the other 2 Dzus to show how big the holes had to be



Ground down the tar for weld prep


After welding and with a little bit of black paint

 

Looks good.

Is that a cherry bomb?

 

Loving it, keen up the good work!

 

Anybody found the picture of the silver NB with a full underpan? I believe the car was local to VIR. It was posted around 2009-10, really good design.

 

Here is an update, but not done yet. More progress to come tomorrow

 

That's a purty big sheet of aluminum

What kind of thickness are you using?

Here's my version 2 flat bottom mid-section. Version one was mostly ABS, version 2 is more aluminum to resist heat:

 

Sections... I'd hate to remove that beast to change trans fluid, tighten a clamp, or something... good job on getting it square and notching though

 

It is a 12x5 foot piece of .063 6061 T6

 

That sounds heavy. Almost as thick as my endplates on my wing. What is the weight of the whole piece?

-Ryan

 

0.063 is pretty thin sheet aluminum imo. Curious why you went with 6061 instead of 5052? 5052 is easier to bend

 

+1 on the alloy. You already bought your sheet but for others a 5000 series aluminum is easier to bend and less likely to crack. At some point of thickness a 6061 sheet is hard/impossible to bend into sharp corners without cracking or at least making it weak, even with a proper sheet metal break.

0.063" may be OK. That's pretty thin. Or maybe you are not going to bend it at all.

 

I expect that that sheet at that thickness weighs 20 lbs, maybe a bit over. Curious if the OP can weigh it and find out. Then there's still the weight of hardware and additional brackets, etc. to add in.

 

53 pounds using the density of aluminum.

 

16ga aluminum (0.0625") is 0.717 lbs / ft^2. So a 5x12' sheet (60 ft ^2) would weigh 43.02 lbs.

What I want to know is how you ship something like that.

 

12ft x 5 ft = 60 ft^2

60 ft^2 x 144 in^2/ft^2 = 8640 in^2

8640 in^2 x 0.063in = 544.32 in^3

Density of 6061 T6 = 0.0975 lb/in^3
MatWeb - The Online Materials Information Resource

544.32 in^3 x 0.0975 lb/in^3 = 53.07 lb


We get our shipments of sheet aluminum by big trucks

 

Ah, yes. You're right. I used the wrong conversion from inches to gauge. 16ga stainless is .0625, however that does not translate properly into sheet aluminum sizing.