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Color0's Micro RC Blog -- A technical brain dump from the mind of yours truly...
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Mini-Z Aero Development, Pt. 2

Posted 03-02-2011 at 01:44 AM by color0
Updated 03-08-2011 at 10:29 AM by color0
So if you recall a couple weeks ago, I posted that front diffuser work, and surprisingly well too considering the size and actual speed of these little cars. So if we can get away with front diffusers, what about rear diffusers? I hadn't even finished making one yet before a fellow MZR member made a beautiful underfloor and rear diffuser for his Mini-Z (credits to Rune on MZR):

I had been wondering how effective this could possibly be, since our Mini-Z's are run at very low ground clearances and air might not even make it to the back of the car in a smooth manner. But I was mistaken, Rune has since reported back that the rear diffuser also works. Meanwhile, I got mine assembled...

Neither of us have laptime or race data as of yet but Rune notes a marked improvement in rear traction, without the car feeling like it's any heavier (his underfloor + diffuser weigh 1.8g). I, on the other hand, felt that the car got more rear-heavy, indicating that mine wasn't working. There are many variables that we didn't really account for in this short experiment, ride height being one of them -- given that I run super low ride heights on RCP it's entirely possible that I was blocking off airflow to the rear diffuser. Or I might just suck at fabricating it, really anything could be possible. At least we've made some progress, and I think someday underbody aero tuning will be just another part of the process of setting up a Mini-Z.

Now I have one thing to discuss: basic aerodynamic theory applied to 1/1 cars dictates that aerodynamics scale with speed squared, so low speed aero effects are almost negligible and at high speeds they are far dominant to suspension settings. The rear scoop wing (see Rune's Supra above) feels like it works that way, the effect is minimal at low speeds (~3mph) and rises sharply as the speeds climb (say, to 15mph). But the front diffuser does NOT seem to work like that. Its effect was noticeable at ALL speeds high and low, and only noticeably lost its effect at the slowest one or two turns on the track where I race. The front downforce feels like it's "kicked in" in the entire rest of the layout, both infield and high speed section. This is mathematically not impossible, I know that as objects get smaller, the aerodynamic effect has been known to possibly scale with speed instead of speed squared (look up Reynolds Number and Viscous Flow if you're knowledgeable and curious). But is that the effect I'm seeing with these cars? I have no idea, and I'm not about to BS that it is without confirming that it is. Which is why we (GSR) are starting to build a wind tunnel to try and get some numbers on the aero devices installed on my car. It should be good stuff.

In the meantime, I've implemented one more aero mod for testing: ducting.

See the intake and the diffuser behind it? The diffuser scoops the air upwards and directs it through vents in the hood:

And you can see the pathway the air follows looking through the hood:

I myself used to think that it wouldn't work, especially if the holes were not large enough. Air forms a boundary layer around objects, so I was thinking that small intakes like the ones pictured would never be able to move enough air to make a noticeable aero difference. But if my last track results are anything to work with, I might have just proved myself wrong. The car gained a lot of front grip at high speed -- it was actually enough to almost overwhelm my rear wing. With the speed affecting front downforce more than before (i.e. purely front diffuser) I think that I could attribute the newfound front grip to the intake/vent system that I've cut into the body. More testing will tell, but it seems like it's got potential and would rock the boat by opening up MANY more areas of our bodies to aerodynamic modification.

I'd like to end this post by posting a picture of the entire car I did this work on, a Kyosho Mini-Z MR-03 with a 911 GT1 body stretched to 94mm wheelbase. (Also the only appearance of the scoop wing in this post, sorry for showing it so late!) Do note that the scoop wing is mounted HIGH: this improves the aerodynamic efficiency of the part, such that even though the wing profile is not as aggressive as, say, a Reflex wing, this small scoop wing actually works just as well. This car has been great to work with, and the aero mods have shown so much promise that I'm almost turning my hobby into an area of academic interest. Hope you guys enjoyed the read and I hope to have some more updates for everyone a couple months down the road.

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