The aircraft winglet case is a little bit different than what we are playing with for our wings.

The goal with winglets is to get better fuel burn through increasing the effective aspect ratio of the wing (wingspan / wing chord) without physically increasing it to stay within gating sizes. Additionally they are operating in a region where the business cased doesn't benefit quickly from increasing flight speeds due to the supercritical airfoils performance degrading quickly, but rather minimizing the drag at a specific cruise condition that the majority of time is spent at.

If you imagine a wing section in a wind tunnel that spans from wall to wall the effective aspect ratio is infinite, and the sectional properties match that of the 2d analysis case of the airfoil. As you move away from that case the span efficiency term drops due to the mixing of the low and high pressure zones.

We're trying to get the greatest amount of downforce with a minimal drag penalty from our wings, where the optimal configuration will be track dependent. As has likely been mentioned before the end plate shape is usually driven by the thicker boundary layer on the upper side of the airfoil (closer to the ground in our case) cause by the low pressure region driving a taller endplate on the low pressure side relative to the high pressure side (3:1 ratio). The distance that the endplate projects forward into flow being a smaller fraction (less than .1) of the chord, with the optimal varying based on the loading & Re of the section, and aft driven to around .15 of the chord.

For our design points the induced drag (drag due to downforce) is substantially larger than the parasitic drag (skin friction drag) from the wetted surface area of the wing and endplates, with this trade growing quickly at increasing velocities.

Bit of a rant but I hope the info helps somebody make a logical choice with their DIY aero work!

I have made 3 splitters to date. The mounts I use are here KazeSpec Engineering splitter hardware kits - MiataRoadster - High-performance customer service...and parts for Roadsters

Version 1 - 9.7 kg (ABS Plastic)

Version 2 - 7.2 kg was made from ply 10mm with 2 layers of fibreglass on the bottom and 1 on the top. It has lasted quite well to be honest.

Version 3 - 5 kg is made from 17mm Monopan Sandwich Panel ? MonoPan » Lavender CE Pty Ltd. This stuff is strong and light! However the edge does not take drilling too well. I'm getting some 1.6mm x 17mm U channel aluminium to put around the leading edge to protect it. Enough Monopan to make 2 splitters cost about $250. It is easy to cut but a bit painful to shape and trim. In the end I got an air angle grinder out and this worked well. Note this is also a bit bigger than the other 2 but weights LESS.

Version 3...

Monopan under the front after V2 splitter removed
https://www.miataturbo.net/attachmen...ine=1436690571DSCN2609 by Eipeip, on Flickr

Version 2 - after about 18 months of use.
https://www.miataturbo.net/attachmen...ine=1436690571DSCN2607 by Eipeip, on Flickr

Starting to mark out (the red dot in the middle is in the flash shadow)
https://www.miataturbo.net/attachmen...ine=1436690571DSCN2613 by Eipeip, on Flickr

https://www.miataturbo.net/attachmen...ine=1436690571DSCN2612 by Eipeip, on Flickr

https://www.miataturbo.net/attachmen...ine=1436690571DSCN2615 by Eipeip, on Flickr

Cutting Plan. Made some changes to this version, an arch for the wheel turn radius.
https://www.miataturbo.net/attachmen...ine=1436690571DSCN2606 by Eipeip, on Flickr

https://www.miataturbo.net/attachmen...ine=1436690571DSCN2608 by Eipeip, on Flickr

Cut out (used an air panel saw, like a knife through butter)
https://www.miataturbo.net/attachmen...ine=1436690571DSCN2616 by Eipeip, on Flickr

https://www.miataturbo.net/attachmen...ine=1436690571DSCN2617 by Eipeip, on Flickr

https://www.miataturbo.net/attachmen...ine=1436690571DSCN2610 by Eipeip, on Flickr

https://www.miataturbo.net/attachmen...ine=1436690571DSCN2611 by Eipeip, on Flickr

https://www.miataturbo.net/attachmen...ine=1436690571DSCN2619 by Eipeip, on Flickr

Close up of edge after a bit of a clean up. Started with a die grinder, not very effective. Then a 3" grinder that worked a treat. I used more clark rubber foam to fill up the air gap. A more permanent solution is needed, a work in progress. The gap is caused by the GV Lip not being perfectly flat/level.
https://www.miataturbo.net/attachmen...ine=1436690571DSCN2626 by Eipeip, on Flickr

A great tool to clean up the edges after the grinder.
https://www.miataturbo.net/attachmen...ine=1436690571DSCN2625 by Eipeip, on Flickr

This is what the edge looks like close up with a bit of flat black paint.
https://www.miataturbo.net/attachmen...ine=1436690571DSCN2624 by Eipeip, on Flickr

This is where it stayed for a few weeks, until I could do the edge protection. I attached some rubber seal from Clark Rubber to protect it a bit. Monopan does not hold very well to screws put into the honeycomb middle structure. Fastners need to go perpendicular to the surface not horizontal.

https://www.miataturbo.net/attachmen...ine=1436690571DSCN2665 by Eipeip, on Flickr

How to bend the aluminium U channel that I planned on using. After loots of attempts I got a sheet of 18mm marine ply and cut out 1/2 of the splitter. I also attached a few hold down points to help it keep its shape.
https://www.miataturbo.net/attachmen...ine=1436690571DSCN2667 by Eipeip, on Flickr

After heating the aluminium and 'tapping, it against the mould, a test piece.
https://www.miataturbo.net/attachmen...ine=1436690571DSCN2669 by Eipeip, on Flickr

https://www.miataturbo.net/attachmen...ine=1436690571DSCN2666 by Eipeip, on Flickr

Final version. It is held on with Sikaflex and riveted from the underside. I would have preferred to use peel rivets however they are not available over the counter in my area.
https://www.miataturbo.net/attachmen...ine=1436690571DSCN2675 by Eipeip, on Flickr

A closeup of the edge inside the wheel well. A nice neat fit.
https://www.miataturbo.net/attachmen...ine=1436690571DSCN2676 by Eipeip, on Flickr

Finished
https://www.miataturbo.net/attachmen...ine=1436690571DSCN2680 by Eipeip, on Flickr

https://www.miataturbo.net/attachmen...ine=1436690571DSCN2679 by Eipeip, on Flickr

A few creases, I'll get better at shaping the aluminium, or sand it flat next time.
https://www.miataturbo.net/attachmen...ine=1436690571DSCN2681 by Eipeip, on Flickr

Is that a standard GV lip with optional side panels?


I don't think I've seen those in the States...

got this NASA splitter installed over the weekend. i remember someone telling me they won't fit.

https://www.miataturbo.net/attachmen...ine=1436809699

https://www.miataturbo.net/attachmen...ine=1436809699

I got the diagram from a buddy that works in the nationwide series. used 1"x1" .083 wall square stock. thing came out beef i would say it's close to 20 lbs. but i could use it as a bumper.

Johnny - looks like you're actually using at least a portion of the original NASCAR splitter frame?

Looks good. Obviously need to cut off the rear portion that extends into the wheel well, but don't trim any of the width down to make it narrower.

-Ryan

Yes it is. By the way the car is in Australia and I have not seen the side panels here yet either. Car also has the GV bonnet.

I just started to coppy the original nascar diagram. i'll post more pictures when i can get the car on the ground. Also i found out this is a cup car splitter, the nation wide splitters are larger. next time i order one i'll get the nation wide option. i trimmed the wheel wells with a sawzaw.

I have used a similar material for another project. I drilled small holes around the mount area, injected them with epeoxy, and then drilled the final size hole after it dried. Held fasteners much better. Cost some weight though....

Then I realized that I could drill the hole I wanted, then put a small Allen wrench in a drill and used it to sweep out the honeycomb around the hole. Then I filled that area with epoxy and micro balloon. Made a super strong hole/mount area. Then I used carbon tube on the leading edges to close that. Again removing the honeycomb in the way, and epoxy the tube in place.

Ryansmoneypit, thanks for the advice. I have another splitter to make so I will use your advice.

Random pic that popped up on my facebook. This was done by a cone. Aluminum splitter FTL. Birch splitter would have beheaded the cone, with nothing more than a smudge mark to show for it. I know, I've mowed down my fair share ;)


https://www.miataturbo.net/attachmen...ine=1438485341

I really like all of these splitter/undertray projects. I'm already taking advice from this thread to make a splitter for my miata, but I was wondering if my daily driven RSX would benefit from it considering gas mileage predominantly (mostly interstate) and maybe a little handling? For the return on investment, would it be an all or nothing kind of thing? For instance would you need to make a splitter, full flat undertray, and diffuser to make it worth it or would a splitter that extends to about the front axle be worth the time and money?

Post your DIY aero pics
 

In true MT fashion, you would need to run ALLOFIT.

says the guy currently running NONEOFIT :giggle:

a quick update i ran road Atlanta. it was 15* hotter then when i ran before and almost matched my best time. 1.39.5 vs 1:39.2. i think the splitter is too high off the ground. i'm going to lower it one inch.
i didn't notice much difference in the butt dyno, according to my Aim Solo i still pulled a peak of 1.2G.

What i did notice was in the braking zone, holy molly i could get way more into the pedal. I was straining at the harness. that's what leads me to think it needs to get lower. i noticed it when it got close to the ground.

The BRZ guys are seeing 2-4mpg increases in highway driving with just diffusers.

This sounds like....a 10-15% increase in fuel economy, fromantic a single part. Wouldn't every manufacturer put them on cars, with an increainincrease in mileage like that? I'm not sold on those numbers.

The only numbers on a brz that matter are the ones where the tq drops off like 20lb/ft.

Then don't be? I won't be able to report back until I get mine and see how it works. Keep in mind this is with a diffuser behind the diff and also panel/(s) that cover up all space between the control arms, in front of the diff up to the rear of the floor pan.

The BRZ has a relatively flat floor pan to begin with so.....no idea?

I could believe 2-4mpgs. From what I can gather, the biggest percentage of drag, after frontal area, is the suction produced by the car ending abruptly and disturbing laminar flow. Thats is why these exist:


https://www.miataturbo.net/attachmen...ine=1438904060

That's 2-4 mpg on a flying brick, with straight sides and a square end. Not an already aerodynamic car.