carbon fiber splitter/undertray help

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#1

Hello all,

I had good luck on my last inquiry, so I will try again and hope for similar results.

I am developing an adjustable splitter/undertray for the racecar that I am building. I am finishing up the prototype that I had waterjet cut and I ultimately want it to be in CF to reduce the weight by a solid 15 pounds. The prototype is constructed of HDPE. In its maximum dimensions, it is roughly 65"x36"

It is a completely flat piece and I will have the template printed full scale to trace out any foam, etc. It mounts at 4 points in the front and two in the rear by means of tubular stanchions which are fixed, and then the splitter is adjustable by means of loosening the bolts and sliding it in the slotted holes. The mounting systems is very rigid and distributes the load very well.

This will be used for road racing and in a very functional manner, so I am shooting for a very high quality product. I anticipate it to seen 150MPH at peak speeds. It will be protruding a maximum of 4" in the center and up to 5" on the sides where it has a broader radius than that of the front bumper itself.

My questions are as follows.

What type of foam core is recommended? What thickness would you recommend?

Should I do this by means of vacuum bagging or compression molding between thick smooth sheets of plastic?

Should I approach it by doing x amount of layers on the top, overlap the edges from top to bottom, and then layers on the bottom?

In regards to achieving a good surface edge, should I try and make some type of mold to go around it in the shape of a C to keep things squeezed/tight?

I want to integrate some type of aluminum reinforcing plates where the adjustment slots are, any thoughts on the best way to integrate them is appreciated.

lastly, how many layers of CF would you recommend to achieve a nice stiff product, and any suggestions on techniques for utilizing something like colloidal silica would be great!

Here are some pictures of the prototype being fitted for reference.

Any info on some/all of these questions would be greatly appreciated!

Thanks!


CF brake ducts shown here

Thank you!!!

#2

1: depends on the air pressure, and shape of the tray. You want it thin, so 1/8" would be good. Plus if you make it FLAT, then, along with 6, more layers, thicker core will mean more stiffness. If you add ribs to stiffen the shape, less core, less layers.

2: VARTM/RTM is the best.

3: Depends on your mold, and how much post-work you want to do. As long as you have the top and bottom face sheets laminated with each other, say 1", you can just cut the edge. No need to wrap. If you want the core TO the edge, you should think about wrapping the fabric around the core.

4: Molding with an edge would help. Simple 1/8-1/4" radius would be fine I think. Remember not to have draft, so You can pull the part out. Any negative draft will just mean your part is now part of the mold!

5: A: treat/anodize the aluminum or B: coat with layer of resin and fiberglass. CF + metal = corrosion many times. Depends on your part, but if there is core, just take out the core, replace with the metal. If just a bolt, maybe 2x the dia of the bolt would be fine. Point is, you don’t want to crush the core.

6: depends on the size, bolt locations, etc. If the part is a flt stock the size of the car, bolting around the edge, and down the middle might be enough. This is just for airflow, not structure, right? If you only do the front of the car, and can not bolt the middle somehow, you will need it stiff on that unsupported side.

ps: images don’t work.

#3

Sounds like a nice project, I’ve done a few splitters and under trays, though somewhat different dimensions. I typically make a mold for the piece so that the part can be vac bagged. The mold will typically have an 1/8 to 1/4 inch radius forming the leading and side edges of the part so that the part has a nice clean appearance. The last couple I did used one layer of 5.7oz twill for the cosmetic surface and one layer of 8 HS for strength and then 1/4 balsa core with another layer of 8 HS and a final layer of twill for the exposed bottom surface of the part. This has worked well for me.