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Mar 09, 2013, 02:45 PM
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I got some front splitters made. I have no idea how much splitter I'll need, so I made a big one, and a small one. Given the shape of the body, even the small one might be too big and add unnecessary drag. About the only thing I could find for size reference is the XO-1, and it's splitter is pretty small compared to the size of the car. Comparatively speaking, mine are huge, but I'm fairly concerned with blowovers. If they prove to effective and the belly pan starts scraping, I'll make a smaller one. They're easy to change, the "tongue" just slides under the body and gets taped to the bellypan.
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Mar 09, 2013, 11:33 PM
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You probably already know this but you have a rather cool project going. Thank you for the vacuuming forming information as well, I have been interested in attempting it and they way you lay out and describe why you make the choices you make and how you actually do it is quite informative.
Mar 10, 2013, 06:50 PM
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Glad you're finding it informative Vacuum forming is fun to play with. While my former is a commercial unit, they're pretty easy to make DIY.

To the topic at hand, I've got a concurrent thread over on URC. We briefly discussed wind tunnels, and it was pointed out to me that I don't need a big elaborate wind tunnel to do some basic aero testing. I decided to give it a try with my leaf blower providing the high speed airstream, and some thread to observe the airflow. Right off the bat, I discovered that the lip of the pan vibrates very badly, and taping it to the body gets rid of the issue. I was planning on taping the whole perimeter anyway, but it's good to know.

Second, I was concerned that the big dips on the sides of the body would cause big drag, but the airstream down the side of the car largely flows right over them. The channel between the front fender humps and cockpit direct air right into them, helping fill the vacuum behind the front splitter to the rear fender.

Third, as you can see in the pic, air skims over the top of the body beautifully and exits off the kammback with minimal turbulence. There is a nice big high pressure zone above the front lip that should give me great downforce. The body posts were bugging me too, and I am going to trim them down, but they stay almost entirely in the high pressure zone on the nose, and are largely out of the airstream.
Mar 11, 2013, 12:49 AM
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I got my rear diffuser done. It needed a bit of clearancing for the back of the control arms to get full travel. It's a separate piece from the bellypan so if it doesn't work as expected, I can take it off. It's really hard to photograph clear stuff, so it didn't show up all that well. (Also, yes, my wheels are on backwards. I just threw them on temporarily.)

I should have mentioned too that PETG is fairly hard to glue. I did a lot of testing to figure out which glue works best, and I ended up with Devcon Weldit. If I were using Lexan, I'd use Shoe Goo.
Last edited by Bugman Jeff; Mar 11, 2013 at 12:55 AM.
Mar 11, 2013, 12:53 AM
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Here's one of my little secrets. I've been working on making my own Kevlar belted tires. I used a $7 set of e-bay tires, a $3 spool of Kevlar thread, and some glue. Lots of glue, and lots of testing later, this is what I came up with:

How to Kevlar belt your RC tires to prevent ballooning (2 min 17 sec)

Mar 11, 2013, 12:53 PM
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Not sure if it was just the video, but it looks like there's a bulge in the tire after spinning it up that could cause a vibration in the car and really upset the handling. Might just be an optical illusion with whatever is on the outside of the tire for the tach to pick it up though?
Mar 11, 2013, 01:11 PM
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I couldn't get the spindle exactly centered in the grinder, so the whole assembly wobbled very slightly. The faster it went, the more the wobble threw off the balance. I had it setup in a less powerful grinder that did allow prefect centering, and it was perfectly smooth and vibration free up to it's max of 13,000 RPM(about 80 MPH)
Mar 15, 2013, 06:05 PM
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I'm starting to build my rear wing, and I can't make up my mind on how. I'm using the Porsche 962 as inspiration for much of my design. It's got many different rear wing configurations, ranging from right on top of the body to extended well out past it. In addition, a wing low to the body can help the diffuser diffuse adding downforce without adding any extra drag. From a wiki on aerodynamics:
"The rear wing also affects the diffuser. When the wing is mounted low and close to the diffuser, the low pressure under the wing helps suck air through the diffuser. Cars, such as the Toyota Eagle MK. III and the Jaguar XJR-14 employed two-tier wings to enhance this effect. One profile was mounted high, in order to hit relatively clean air. The other profile was mounted almost flush with the bodywork behind the chassis. This wing's profile is used to drive the diffuser, creating that low pressure area to help move air from the underbody. According to Hiro Fujimori, aerodynamicist for the Toyota Eagle project, this bi-plane wing produced 18% more downforce for the same drag as a normal wing.[2] Conversely, equal downforce levels could be attained for significantly reduced drag with this "Red Baron" wing."

Here are some basic mockups I made, which direction do you think I should go?
Mar 16, 2013, 03:45 AM
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I like the first version best.
Mar 16, 2013, 04:09 PM
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I've made a few more wing mockups. These ones are much lower to the car, similar to the 962 #17 wing. I'll probably end up making a few interchangeable wings like I did with the front splitter.
Mar 18, 2013, 12:00 PM
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Man you have something great going on here. I like how you made your own belted tires, really great stuff. What kind of glue did you use?
Mar 18, 2013, 12:48 PM
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Power Poxy Super Cement. It's shown at :22 right in the video
Mar 22, 2013, 04:22 PM
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I got a couple wings made, again out of .050 PETG. I'll mount them to the body in such a way that they'll be adjustable. I'm using a KFm-1 airfoil because of it's simplicity, and mostly to add some strength to the wings so they don't deflect under load. I don't want to add a center pylon if I don't have to.
Mar 23, 2013, 04:29 PM
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Here's how the wings look on the car. They fit down through slots on the body, then will get taped to the inside. By moving them in the slots, I can adjust height, angle, and location. The second flatter wing in particular has a whole lot adjustment room, from tight to the body to extending well out past it.
Mar 23, 2013, 09:52 PM
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Okay. I know you're putting the storm troopers on the back!

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