Have received some preliminary information on the next wing for the car... This was the reason for the wool tuft test on the underside of the GTC200. Modeling of the current wing suggests about 1,500 newtons at 180 kmh for a cd of 0.12.

The new wing at 180 kmh has 854 newtons of downforce for 0.03 cd or by adjusting the second element I can have 1984 newtons of downforce for 0.11 cd. Hence the new design has more downforce for less drag.
Old GTC 200 endplate on top of the new wing design. You can see the shape of the old wing profile on the endplate.

 

With so much talk about endplates recently, I wonder how many people have read the articles by Simon McBeath on CFD studies on endplate depth vs chord length.

Here is one: http://www.sm-designs.co.uk/pdfs/rearendplates.pdf

 

also plenty of rulesets with limits on the area of endplates.

 

you don't need to count this as part of the end plates. I made it 2 pieces as the enplates where already made, plus it gives more adjustment if need be.

 

I did an LS1 swap, so couldn't use the OEM undertray since the mounting points are gone. In another effort to make the car more stable at speed in anticipation of track days, and to protect some of the fragile parts underneath.

I removed the little air dam that runs a few inches behind the front of the lower spoiler or "lip". I had cut it up to give room for the lower radiator mounting I made. It removes with 5 10mm screws and the little self tapping clips. Keep the screws and clips.

I reinstalled the clips and made some marks where the holes are so I'd know where they were when the spoiler was boing mocked up. You'll even notice that there is a little step where the air dam was, which will be perfect to fit in the new undertray and make a nice, even transition.



I used some cardboard to make a template. I just used the cardboard that the aluminum sheet came with. Some drawing, cutting, and recutting got it close enough. Then I used a screwdrive to poke holes in the cardboard to find the 5 mounting holes.



For the tray itself I found some pretty reasonably priced metals online. I bought a 24" x 48" sheet of .080" thick 3030 aluminum. This is a good thickness I think, stiff, still somewhat flexible, will not add much weight (it's aluminum) and affordable.

I ordered the metal from Metal Remnants - Custom Cut To Size Metal for $33.00 + $17 shipping for a $50 total which I thought was pretty reasonable.

The 24" width would represent the distance from the front of undertray and reach to approximately where the front of the oil pan and main tube of the subframe is. This would give me a good point to create the rear mounting locations by using the subframe to weld to. It wouldn't interfere with any oil changes either.

I just used some 3/16" steel to bend some tabs, installed some 8mm nutsert/rivnuts and then welded them to the boxed tubing part of the subframe where the control arms attach. Cleaned up the welds and touched up with spray paint.



Here is the tray removed from the car. I removed any sharp, 90 degree corners on the final piece.




Final installed product. Took it for a quick test drive and didn't hear or notice any issues.



One thing I did was to make the mounting tabs such that the tray would make a slight bend as it touches the subframe in the middle of the tray with the hope that it would keep it tight and prevent any "flapping" or rubbing at speed, without add'l mounting tabs. If that didn't work out, at least I'd have room to add some spacers or washers to bring the tray down a bit until everything was good.

 

Not really aero related, but I'd never use rivnuts for anything that I don't absolutely have to.
Rivnuts are ****, and if you're going to add threads to something that you have access to a weld nut is a much better solution.

 

+1

Rivnuts are really useful sometimes (where you need captured threads but there's no access to the backside during construction), I use them in several places myself, but they have a lot of weaknesses. They are much better with loads in shear (force is in parallel with the mounting surface). A tension load like that is asking the rivet nut to work at its weakest. Rotating the mating surfaces 90° would be a lot stronger, but so would just having a weld nut on the back side of the tab instead of a riv nut like Moti said.

 

project binky doesn't use rivnuts, but there are captive nuts all over that unit.

 

A few pics showing how we quickly cobbed together the front end for Super Lap Battle in November 2017. We ended up winning Unlimited RWD and dropping the Miata lap record on 13CW by about 7s. As you can see, nothing the least bit exotic. Sign material and Home Depot FTW. I asked John to use the flat aluminum stock for the struts to make it easier to install, reduce drag a bit and also be a bit more robust. Note how we cut the back of the splitter as close to the target tires as possible. This improves lift/drag ratio.

In a perfect world, the entire splitter would have been about 1.5" lower and a slightly different angle. We would also make it easier to install and build an entire spare nose. As it was, we only had time to build one so we made it really high. This gave it some off road survivability at the cost of some efficiency. We pushed the air dam out much farther than the tires. The idea being that the yaw rates we knew it would be capable of meant really high steering angles at 100mph. This high steering angle exposes a large portion of the tire to the airstream. I knew from experience that the steering angle in Riverside at 100+mph with a manual rack was 90°. So we turned the wheel 90° and pushed the air dam out until it shrouded the tire. That in turn dictated how wide the splitter would be as we needed a certain gap between the end plates and air dam. This gap was our best guess at a balance between trapping air mass on the spliiter to raise local pressure and create downforce against the drag created by slowing the mass down too much. That intentional blockage makes the pressure bubble on the nose a bit larger which in turn raises the efficiency of the center area of the splitter. This in turn allows a smaller splitter which reduces drag a tiny bit.

So while crude, it was designed with known best practices in mind.

 

Great result and thanks for the overview.

 

Not sure why I reached for the rivnuts when I could've welded a nut, but I may rethink that before the undertray sees track stuff. Especially since it seems I installed one rivnut so that the bolt threads in at not quite 90 degrees - possible recipe for a cross-threading incident.

I could see how the rivnut could slowly loosen and turn and unthread the bolt, or pull through if under enough stress. But if the bolt is tight enough then I'd think that would keep both the rotation and the rivet "squish" under control for most situations.

 

emillio, what thickness alupanel (or alumalite) is that?

 

10mm total thickness.

 

If you re using a quality Rivnut and are installing it correctly, they can withstand substantial loads. Those 8mm Rivnuts that he used for his application are each rated at 450-500 pounds of pull-out force. I doubt that Emilio's whole front splitter on bullet made that much downforce.

If you are using cheap China made aluminum knock-offs then you get what you pay for.

 

Did you just assume that we're using low quality rivnuts AND installing them improperly at the same time?!

 

A safe rule of thumb is "Always assume the worst!" :P

 

Actually, if you are having issues with them when using them inside their design parameters, yes.

 

Nvm please delete. Found the answer

 

Age old discussion - diffuser without a flat floor. Was originally planning a flat floor in the RX7, but am anticipate running Track Mod at Gridlife, which only permits splitters/diffusers to the wheel centerline - flat floors are prohibited. V8 car, COT wing, splitter/dam, and looking to induce a bit of understeer for stability. Should I attempt the diffuser? I can feed the mouth of the diffuser from just below the exhaust (side exit).

 

I would not do it.