Miata Flat Underbody
 

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
https://www.miataturbo.net/attachmen...ine=1355002824

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.
https://www.miataturbo.net/attachmen...ine=1355002824

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
https://www.miataturbo.net/attachmen...ine=1355088677
https://www.miataturbo.net/attachmen...ine=1355088677

Ground down the tar for weld prep
https://www.miataturbo.net/attachmen...ine=1355088677

After welding and with a little bit of black paint
https://www.miataturbo.net/attachmen...ine=1355088677

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

https://www.miataturbo.net/attachmen...ine=1358060826

https://www.miataturbo.net/attachmen...ine=1358060826

https://www.miataturbo.net/attachmen...ine=1358060826

https://www.miataturbo.net/attachmen...ine=1358060826

https://www.miataturbo.net/attachmen...ine=1358060826

https://www.miataturbo.net/attachmen...ine=1358060826

https://www.miataturbo.net/attachmen...ine=1358060826

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:

https://www.miataturbo.net/attachmen...ine=1358078137

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.

It came on a pallet with a wood bottom, (2) 12 foot long steel C channel on the length and cardboard top and bottom of the sheet.

Im guessing what I have cut is about 30 lbs.



Here it is mostly finished, next up is the splitter/front diffuser

https://www.miataturbo.net/attachmen...ine=1358122324

https://www.miataturbo.net/attachmen...ine=1358122324

https://www.miataturbo.net/attachmen...ine=1358122324

Wow, that is a flat bottom !!

So ... where does the heat go?

Wouldn't air coming in the front grill still get trapped above the flat bottom?

The heat goes out the back above the diffuser.

There is a about a 1" gap between the panel and the steering box, which will have a opening in the front air dam to channel the air into this space.

The air trapped under the hood will be going out vents in the hood, I haven't got to working on yet due to the cold temps outside. I will be mocking it up to match the vents on the German Touring Car. I also have a 1" hood spacer with the rear hood seal removed.

To give an idea of how much air is going through the channel (4 inch space between the frame rails) I will put wind speed guage in there then drive to 60, 80, then 100 mph. I'm guessing 5 to 1 would be a goal for now(100 mph speed with 20 mph air speed)

Assuming you are intending to use the car competetively, it's key to make things as light as possible. 30+ lbs is a lot for the flat panel, before even adding brackets and hardware.

For reference, my flat underbody is 11 lbs including all hardware and brackets.
(I just did a redesign for the brackets and hardware to save weight - now <200 grams total)

Not trying to detract at all from what you're doing, I'm really encouraged to see people getting deep into aero development for miatas. Just trying to inspire you/everyone to try to make the best pieces they can.

-Ryan

That is darn light. At lest it is at the lowest point. My goal is 2100 lbs w/driver. I will be making dry carbon wide body panels and a possible V8 swap, if you wanta know more click here ( https://www.miataturbo.net/general-m...her-car-61236/ ) for the specs I'm going with

This is a very bad idea that will hinder more than help. if you remove the rubber strip, the hood actually sucks air in and hinders flow through the rad.

All you need is a vent just in front of the engine.

Since the topic of aluminum is going on. Has anyone heard of 3003? I don't have much knowledge on metals. I bought a sheet of 3003 that I need bent and every fabrication shop I talk to has no clue what I'm talking about.

http://www.metalsuppliersonline.com/...metals/411.asp

Not nearly as popular as the 50xx, 60xx, and 70xx aluminums. "Applications: cooking utensils, decorative trim, awnings, siding, storage tanks, chemical equipment."

+1 The air at the base of the windshield is very high pressure and will enter through the rear of the hood and into the engine bay. Look at race cars for inspiration and their outlets through the hood just behind the radiator. Ricer fanbois do many things wrong and lifting the rear of the hood is one of them. Don't use them for inspiration.

Some people have them to lower their engine bay temps when they are having trouble melting shit. Not useful on a grip car, but maybe on a drift car.

Then they need to properly isolate the parts that are melting from the heat source. By raising the rear of the hood, you increase pressure under the hood and decrease the amount of heat that can escape. Unless your firewall directly underneath the hood is the issue, it will hurt things.

This. Higher pressure builds at the top of the hood at the windshield. Higher pressure areas are not where you should try to exit air; it is where you should have inlets. Looking below you can see the science...


Attachment 185669

Good CAD model, do you have any more models or do you have the program

It is my CAD model of the miata. I have more models of other vehicles. I use them for cfd.

How do so many aero theads divert into trying to explain to someone that hood risers are utterly useless? By how many times its been gone over by now, I'm surprised it even comes up any more.

-Ryan

Ban. Just ban.

I guessing its a 3D flow model. Do you have any CAD models of any Dive Planes (Canards). One other thing I was wondering is, If the Dive Plane is to low. Will the vortices shove more air under the car or will it do its job better by keeping the air from going under the car from the side?

I consider them cfd models since they are simplified models. I have not analyzed canards on a miata because I have never been ask to help design aero for a miata that wanted to use canards. I have done them before on another project.


"Will the vortices shove more air under the car or will it do its job better by keeping the air from going under the car from the side?"

It depends like all generic aerodynamic questions lol. You can design aero bits that can cause vortices that "seal" the sides to prevent air from spilling under the car. The vortices will act like skirts to seal the bottom ;) If you have an actual design you are thinking of, I might be able to give you a better answer than depends.

I wanted to see the efficiency of SlickAutos dive planes APR Carbon Fiber 3D Canards $285 or $355 | Slick Auto and how does the splitter effect it (with the distance between them)

shouldn't affect the splitter, they're doing 2 opposite things.

I'm well aware of why they dont work to lower water temps. I never said they did. Do people even read posts?
I've seen tests demonstrating lower engine bay temps because of them.
In a drift day you tend to spend a lot of time waiting in line with your car running and your bonnet down. There are people on here who are into drifting, I'm not really one of them, but it may help them.

The thing that always impresses me about this forum is the knowledge. And I think its better for people to know what they do and what they dont instead of just saying "They're shit."
I havent put enough research/thought into heat sheilds vs ventilation in this niche application to discuss it. And I dont think this is the appropriate place to do so.

Nobody fucking cares what drifters are doing.
This thread is about a guy building an undertray for the purpose of GOING FASTER. Why in the fuck are you talking about motherfucking drifting?! Hood risers make sense in drifting because hood risers are retarded and drifting is too. Being retarded has nothing to do with this thread.

Seriously, go away. I hate you.

Well I lol'd.

What Mr Boogie said.

Let me hit you with an idea, if this was air cooled VW drift forum, people here would give maybe even half a fuck about engine bay temperature, but its water cooled mazda performance forum, and here no one gives a dam about how warm the cam cover is, sorry bruh.

Dann

Sorry, but if the ambient heat in your engine bay is too much for your car to handle, stay out of the kitchen.

But what about my turbo manifold? Im not sure it can handle the hot air on it, and thats an expensive part!?

Dann

I wasn't talking about the canards affecting the splitter, I was talking the complete opposite. On a wing and most aero surfaces the top part of the wing pushes down about 1/3 of the force. 2/3 of it comes from the bottom being sucked down. So my question was if the canard was to close to the splitter would it be less effective?

Is there a way to lessen the low pressure area on top of the roof, but I;m guessing not since that is high speed air. Is that a small hint of blue on top of the hood just in front of the budge?

A canard is not profiled like a wing, however. The purpose of the canard is to create vortices along the side of the car, downforce gains are minimal from canards and are mainly used for balancing F/R bias.

Yes there is a hint of blue right where the hood opens and right in front of the bulge.

Race prep subsection, race prep thread. We have a BS subsection just perfect for drifting talk.

Those canards will increase drag. Flares that gently direct air out past the fronts of the wheels do not, but rather smooth the flow that would otherwise strike the tire directly and deflect into the wheel well.

As for the low pressure area over the roof, low pressure is created by the faster airflow over the surface (see mathematician Daniel Bernoulli).
https://www.miataturbo.net/attachmen...ine=1358352921

As for the low pressure area over the roof, low pressure is created by the faster airflow over the surface. [/QUOTE]

Yep and i was thinking is there a way to slow the air on the roof with out to much drag or turbulence, maybe a gurney flap

You can think of increasing the radius of the roof, making it less of a high speed area.
Removing the windshield+roof is one way :D
Fastback is another, less drastic way (but mostly even out the flow/pressure over the roof+trunk area, in my personal simplistic analysis).

PM me specifics if you want to set up an analysis.

Fastbacks still create a lot of lift and most of the time more than a coupe, because they have a much greater area where the lower pressure is effecting. Fastbacks will have lower drag however.

Note: the rear lip spoiler's function is to reduce the speed of the air above the trunk surface to reduce the lift on the rear of the car, and not actually to direct air upward and force the rear of the car downward as a dive plane would.

Disturbing the high speed laminar flow over the roof surface will indeed reduce lift, but will often create huge amounts of drag. If vortex generators were employed at the leading edge of the roof you would see this. Vortex generators at the rear of the roof, however, have been shown to be useful in reduction of the separation of the boundary layer from the rear glass and trunk lid surface and creating more effective use of spoilers and wings mounted at the rear of the car. But this thread is about flat underbodies. /threadjack

Not entirely off topic. The spoiler cleans up the airflow at the rear of the car and increases mass airflow underneath the car. These CFD plots are of a modern nascar-type car, without a flat underbody, and they showed 550lbs of downforce at 112mph. With a flat underbody, mass flow underneath the car would be made that much more effective, and the benefits of the spoiler would increase correspondingly. The combination of the two is much much more effective than either by itself.

https://www.miataturbo.net/attachmen...1&d=1358444926

I was going to show just "plucas" until it is done, but I guess I will show all of you now what my plans are for the under tray. This car is a Porsche race car I found on google, but don't know yet until after some testing.

https://www.miataturbo.net/attachmen...ine=1358931820

I know this was brought up before about the heat being trapped in the trani tunnel. I ordered a digital wind meter and will be placed in the tunnel in numerous places. The car will be driven at 60 mph, 80 mph and at 100 mph to see the ratio of speed of air moving in the tunnel.

Right now I am not as worried about heat since it gets no hotter than 50 deg F out side and that there is a 1" opening between the flat panel and the steering rack. I do not want to also just start cutting holes for NACA ducts in the floor in places where there shouldn't have been.

Keep in mind that Porsche obviously has no heat from engine bay, turbo, exhaust, etc. in the front 3/4 of the car - so managing heat with an underbody is incredibly simpler for them.

Ambient temp is really not a significant issue - your exhaust gasses are 1500 degrees either way, so whether it's 40* outside or 100*, if the heat in the transmission tunnel for example is going to overheat components, it will probably still happen. Since you're making yours out of all aluminum, you obviously don't have to worry about damaging the undertray itself with heat, but the general consensus seems to be that the differential relies a lot on air passing around it to cool it, so that's probably the most important area to either supply air to, or install a cooler for.

-Ryan

Hmmm, have the same thing with the roof down? :-) Guess you'd have to at least model seats and roll bar.... Once I made an amplifier cooler for my biggie stereo by running shop-van tubing in and out of the trunk. Seemed to work well though later I did it right.