Lots of reading
 

Spent the last 3 days on and off getting through this thread. Damn, this thread perfectly defined why I went with a Miata.

Going for tried and true on my soon to be supercharged Ecotec swap. Cut lower half of bumper cover and do front air dam, already ordered the 0.1" plastic from Speedway. Plywood 4" splitter and under tray back to the subframe, 4" because at roughly post 1253 Emilio said 4" is when the magic starts happening. I'm going to add an APR wing in back, GTC-200, 200 because I found a decent price on one locally (Canada), have a line on a full COT wing but it's 50% more.

This all started after messaging Moti about one of his black spoilers, decided to do some research and here I am.

My car, Ecotec 2.4 with supercharger going in this spring. Xida Coils 800/500, upgraded front sway, stock rear. Full rebuilt control arms, delrin and sphericals, extended lower ball joints, 3.9 torsen. Kirkey seats, full 6 point harnesses roll bar (duh). No air, no PS oh and Track Spec hood vents about to go on.

https://cimg2.ibsrv.net/gimg/www.mia...514a04116b.jpgAeroless


That's about it.

So a quick sidetrack here. I've been researching what it would take to build one's own CF wing instead of buying a premade setup. In doing so, I stumbled across this older thread in a BMW forum about doing just that:
https://www.bimmerforums.com/forum/s...Fiber-Wing-DIY

The TL: DR of that thread is pretty standard, cuts foam core, layers with CF/epoxy, bolts on endplates, mounts to trunk lid and drops laptimes.

The part that surprised me was this, he skipped vacuum bagging altogether, and instead just did three crisscross layers of CF, baking each layer in an "oven"(car parked in hot sun) as he went.
From updates posted later in the thread, the OP states the wing "worked well for 6 years". And thats on an M3 that would see much higher straight line speed then a Miata. The wing was indeed producing appreciable downforce, as he stated his(aluminum) endplates were being sucked inwards.
SO my question is, can a decent quality/strength produce be produced even without vacuum bagging, especially for the lower loads that a N/A Miata would see?

Yes, I realize that vacuum bagging produces a stronger end product. My question is if a non-bagged item will be strong enough. Even on the back straight of RA I'm only seeing about 115mph.
Skipping the vacuum bagging would drop around $100 off the total project(which could go towards mounts, trackfees, tires, ect), as well as be less hassle, easier, and quicker. But is it worth it to do so?

From the research I've seen the biggest difference between bagged and not is weight. Sure bagged is slightly stronger, so do another layer of CF. I'm planning on building an aluminum tube structure to run inside the wing foam to give it strength and use a single layer of carbon to give it abrasion resistance.

Bagging is for weight. My wing is literally laser cut 0.75" Styrofoam profiles stacked on 3 thin wall aluminum tubes and 3 layers of fiberglass, not even crisscross. Simulation puts it at road race wing 140mph downforce at 60mph. And I've been over 100 with it. Mounts are the part that needs to be stronger than you think, especially side to side.

Mounting is where I think I'd turn to a local shop. I lack the ability to manipulate aluminum to that extent. But even with a generous shop estimate, I'm looking at less then half what Singular's GT250 setup would run me, with a very similar wing profile and custom endplates.

Vacuum bagging was a pain in the butt as I was building my splitter last weekend. Will share my wing when I make it in a few weeks.

Bagging is not for weight, unless you reduce the amount of resin in the fiber. The bagging is to compact the fibers, and reduce the amount of voids in the fiber. This improves your fatigue strength for one. Pretty much every composite part that is worth any money, is done with bagging, or compression molding. Now, that isn't to say you can't make a wing strong enough without bagging.

One solution I've used in the past (FSAE days), was to create a mold with the wing shape we needed, pour expanding foam in the mold, and wait for it to cure. You could then wrap that foam shape with carbon, put it back in the mold, and stack heavy weights on the mold while it cured. We used high temp cure resins, but if yours does not require it, wouldn't be needed.

I'm not able to open your link at work, but here is what I think. Cut wing core out of desired core material, strengthening with aluminum tube or chunks of balsa or other wood is an option too. I would suggest bagging the core, and there are some ghetto ways you can do it. Obtain serial killer plastic, make seal with 2 sided foam tape or tacky tape, create or purchase venturi, and rig up air compressor to pull vacuum on your newly created vacuum bag. The quality of the part will be better, and it will look nicer than just plastering layers of fiber on a core. My :2cents:

This isn't outside of my ability, but it's another ~$100 to add to the project costs, added complexity, and also looks to beThink what I might just do is wrap a test run of a 3ft segment of foam or plastic and see how strong it comes out, then make the call if I want to go to the hassle of bagging at that point.

No no, have you never watched Dexter?

I made this (crappy) test piece back in the fall: https://cimg7.ibsrv.net/gimg/www.mia...efcc51fbce.jpg

I could put every bit of strength into it and could not break or bend it. That was just two layers, not alternating. Ignore the collapse shape. I had a hole drilled in that foam core that I was going to put a rod through, and the vacuum bagging collapse the empty hole.

Exactly. Keep your work space clean!

I'm a bit surprised a ghetto way costs that much, but I guess I have not researched prices on this in a bit. Just be cognizant on the "what is strong enough?" issue. The last thing you want is a wing falling apart on the track.

And yes, serial killer plastic is a technical term.

When you figure $80 of that hundred bucks is the harbor freight vacuum pump it makes sense, then theres the $50 of misc fittings, valves, gauges and hose, the $10 in sealing putty and its easy to see how they $100 ghetto way costs $140.

Yep, what Leafy said. I did it the HF vacuum pump way. I used cheap hose, no valve (just let the pump run and keep it full of oil). Amazon cheapo bag connector that works okay.

Expensive part is the consumables...breather ply, release film, bagging material. Of course if you're only doing one thing, it's meh.

Unless you use a venturi with your air compressor, I've made many parts that way, including an FSAE monocoque, it pulls enough vacuum. You don't need all that fancy stuff if your just doing a part or two as well.

Consumables are certainly expensive, but some careful thought can mitigate that. You all should take a look through some of the DIY composites forums, there is some sketchy stuff being done on boat hulls, and air planes.

What kind of compressor did you have at school? We had a pretty sweet screw compressor with a chiller, that could easily keep up with a venturi. But if someone is balking at $100 in tools they probably dont have even a larger home model compressor, and even that is going to struggle to do the 6-8 cfm required to run a ventrui especially not for like 8-16 hours straight. I guess if you're super particular about eliminating all leaks and are willing to babysit the bag setup for most of the curing time you could probably get away with it.

First of all, I wouldn't hesitate to skip vacuum bagging if I had to make a part from scratch track side or in an apartment parking lot. I would also not hesitate to make the parts out of fiberglass if I was broke. I still experiment and make bucks out of cheap random strand glass mat. Some times those parts see actual use. If you don't have time for loads of experimentation or access to reliable composites oriented FEA, you'll never make use of the additional strength available from carbon.

As far as hood rat tools, I have used the HF brake bleeder as an emergency vacuum pot. It won't pull a super deep vacuum and you definitely have to baby sit it, but it works, and it's cheap. You don't have to maintain the vacuum for the whole cure process, only until the epoxy sets, which is usually only 1-3 hours. I like to splash a little bit on my Freekoted work table so I know when it's full hard.

I typically use a salvaged refrigerator compressor. They're cheap/ free, quiet, and fairly reliable, and they'll pull a VERY deep vacuum. I bought a vacuum relay on ebay for ~$50 to control them, and have only burned up about 3 compressors over the course of ~10 years on and off making composite parts.

My next vacuum pump will probably be a commercial AC maintenance pump. They don't move much volume, so you absolutely have to be a fanatic about leaks.

Hey all, first post here. I actually track a 98 M3 instead of a Miata, but this seems like far and away the best real-world DIY car aero resource!

I am in the midst of manufacturing a rear wing for my car. I selected a Selig 1223 airfoil and am 3D printing interlocking sections at work about 5 inches at a time. The plan is for a 65 inch wide wing with an ~11 inch chord.

I plan to carbon wrap the sections once bonded together. What is the go-to carbon fabric total thickness for a rear wing? I'm trying to determine if I can get away with fewer plies by going heavier fabric weight. I've never worked with cf before and minimizing layers is probably a good idea for me!