Nukem said:Any recommendations on where to get CF / general composites supplies? I've got a few little carbon fiber projects in the backlog of my brain that I'd like to tackle soon.
Also, this thing is Rad
Thank you both!
I personally use Composites envision and Fiberglast. By the way, fabric prices became insane as of late...
Thanks for both of your suggestions!
In reply to madmax98 :
Can I solicit you for a more detailed write-up of your CF skinning process in the tech tips section perhaps? (https://grassrootsmotorsports.com/forum/tech-tips/)
You've already given a lovely amount of detail but I'm about to ask like 30 pretty specific questions and I don't want to derail your thread too much :)
I think I'd like to borrow your CF over-FDM process pretty much exactly for a couple of parts for my MG build (an air box and a duct pretty similar to your oil cooler duct to start, both of which I've already got CAD and printed parts).
Nukem said:Thanks for both of your suggestions!
In reply to madmax98 :
Can I solicit you for a more detailed write-up of your CF skinning process in the tech tips section perhaps? (https://grassrootsmotorsports.com/forum/tech-tips/)
You've already given a lovely amount of detail but I'm about to ask like 30 pretty specific questions and I don't want to derail your thread too much :)
I think I'd like to borrow your CF over-FDM process pretty much exactly for a couple of parts for my MG build (an air box and a duct pretty similar to your oil cooler duct to start, both of which I've already got CAD and printed parts).
I have no problem doing that! Go ahead and ask whatever you need anyway. That way I know what details are needed.
In reply to madmax98 :
Nukem said:In reply to madmax98 :
- Any recommendations on vacuum pumps that are relatively budget friendly?
- What materials are you printing in typically? From what I've heard PETG doesn't bond very readily with most resins.
- If you are using PETG, are you using any particular resin or doing any special surface prep to get the layup to bond to the prints?
- Is there are CF weight / weave that you prefer for laying up directly over printed parts?
For vacuum pumps I just use the Harbor Freight one (used for AC work). I typically make sure I have a good seal on the vacuum bag. If you do that, you would only need to pull initial vacuum (few seconds depending on the size of the part) then clamp the hose and turn off the pump. A few times my bag didn't hold vacuum very well and I had to leave the pump on for a couple of hours. It became noisy, from overheating i concluded, so I just put a box fan next to the pump. It was fine after that. I've had the same pump for the last 12 years. It was 70 or so bucks. 500 bucks for a "proper" composites vacuum pump is an overkill for a hobbyist in my opinion.
I still use PLA. I find it easiest to work with and faster to print. I have the Creality printer so I can only go so far with this printer. Ideally you want ABS as a base, but a man can only dream. PLA will do. Not great for high temp applications, and obviously it shouldn't be/have a structural function. I just rough it really well with an 80 grit or similar. Clean with alcohol or Acetone. Acetone dissolves PLA so you have to be careful and quick with it. Then, proceed with the layup. Make sure the first layer gets plenty of epoxy in order to flow through to the 3d print. Otherwise it will delaminate.
PS: I use a bit of filler on my prints to have a smoother surface/finish, but I don't think it makes a huge difference. All the aesthetic work happens in the end any way, AKA sanding lol.
Typically, I use 3K, 5.7 Oz, 2x2 twill. Easy fabric to work with (relatively speaking). Some geometries are still tricky for the fabric to conform to, regardless. For difficult areas and sharp corners, I use a SMALL bit of 3m adhesive to help the fabric conform. Too much adhesive and it will delaminate since it prevents epoxy from getting to these spots. Epoxy is really good in bonding to almost anything, but try not to push it lol
Let me know if you have any other questions.
In reply to madmax98 :
I certainly will have more, but this helps loads!
Nukem said:In reply to madmax98 :
I certainly will have more, but this helps loads!
No problem, send them.
By the way, why were you asking about the vacuum pump? What kind of project are you looking at anyway?
In reply to madmax98 :
First up is probably doing a layup over this this air box, which I've still got to make some updates on in my thread.
Oh interesting!
By the way, something I didn't mention is I usually stitch the 3D print pieces with a cheap solder iron. Basically, I go a long the seam and create overlap between the pieces to form the bond. Sorta like plastic welding. Goodluck planning your project. Let me know if you have any questions.
Alright... my last update was about 5 weeks ago. Since then I have been working with the CAD model to get it to be usable for CFD (Computational Fluid Dynamics). Pretty much worked on it everyday for 4-5 hours, more on weekends. Getting surfaces to be used for CFD is a pain in the butt. Additionally I tried to streamline a workflow so I can easily test a few ideas without having to start from scratch. So there was a lot of trial and error, iterations and re-do's.
I initially excluded the radiator and intercooler just to make sure I have a working model. The CFD model was incredibly unstable and problematic. I improved things a bit by tuning some parameters and implementing some tricks I learned in the past. However, it was still strangely unstable numerically. So I looked at the physics of flow and it all made sense. The flow itself was incredibly unstable and complicated, which in turn set the numerics ablaze.
The two areas which showed their importance and effect on the whole field (instability) were the front-bumper area right ahead of the tire, and the back of the deck lid/ trunk. Initially my bumper was open to the front wheels, sort of like not having wheel well plastic trim/liner. This caused a lot of unstable turbulence. Also my decklid did not have a spoiler on it. The effect was dramatic behind the car presenting in the form of very strong unstable turbulence as well. I added a 1" gurney flap/spoiler back there, and covered the bottom of the bumper ahead of the front wheel. The problems disappeared! By these 2 simple modifications, the car exhibited a much better flow field, and aerodynamic drag went down by 10%. So if you don't have a wheel well liner, get one. I think "naked" trunks are ugly (my personal opinion), and apparently they're very draggy as well lol OEM's know what they're doing when they put either spoilers or small lips on the trunk. It's not just for looks.
Front-bumper problem area:
And the trunk gurney shown here:
I then introduced the radiator and intercooler. I made some assumptions regarding how much of a blockage the intercooler is. This was eye opening! The intercooler really blocks a lot of the flow to the radiator. A lot more than perceived.
Putting the intercooler and radiator in series is not optimal... Far from it! On top of that, although the high beam opening (I took out the high beams) directs a lot of fresh air directly to the radiator, it causes a lot of circulation in front of the radiator. This really counters the benefits.
Although I made some assumptions, it's obvious that this area needs some more work and re-design. I'm now rethinking leaving the radiator at this location!
Below is a view showing the circulation ahead of the radiator
Another thing is a lot of air ends up leaking to the sides to avoid going through the intercooler (half view):
More problems: This shows the air is hitting the vent area, as opposed to flowing over it. The strakes are not aggressive enough (stickout). I already have a solution designed and made, just haven't put it on yet (good to know it's actually needed).
Areas in yellow/red indicate high pressure. Not what you want here.
The solution I made (a year ago now) is a lip that goes here (ahead of the vent)
Wheels are a major area/source of drag (Hot wheelz)
Zooming out a bit, this one is telling about a few things. From front to back, leakage around intercooler, leakage from the high beam openings, flow from the front tire sneaking under the car, strong vortex along the A-pillar.
Front view streamlines:
Side View:
Rear View: it's a mess. Not sure what to do about this yet.
I call this one the "horned owl"
Well, that's it on the initial model. This model is OEM except for a flat floor. To be continued.
Any updates on this?
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