Mini-Z Aero Development

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Been a long time since I've been back here, so I thought I should make this post worthwhile by telling you guys and gals about some uber-cool stuff I/GSR have been up to in the last year or so:

Aerodynamics.

People used to tell me that aero did not matter at 1/28, that a body's weight balance was more important than the downforce it produces. We've long suspected that's wrong, but some recent developments have completely blown it out of the water -- aero matters, and a lot! I'll start off from the top to cover all the aero devices we've been playing with and just how well they work.

First thing on my to-do list was the Gurney flap -- these work on 1/1 cars, sometimes on 1/10 cars, do they work at 1/28? I had no idea. So I did some calculations based on some research papers, and, assuming the entire bodyshell was to be treated as a wing, came up with a measurement of between 3 and 4mm as the optimal height for a Mini-Z-sized Gurney flap. Here it is:



And as you guys may know, a Gurney flap needs some airflow underneath it to work. So I opened up the rear of my shell and gave it some air.



Track test: the Gurney flap weighs about 0.2g -- confirmed on a scale. That's a negligible amount of weight, so the effect on handling (where weight distribution is most obvious) should have been unaffected if there's no aero effect.

However, to my pleasure this was not true. The Gurney flap adds a little bit of traction from medium speeds and up! That little bit of extra traction makes the car a lot more stable. On the other hand, the Gurney flap is rather fragile, one touch and it cracks due to the plastic I used, and also didn't provide enough downforce to handle a more powerful (43t, neo magnets) motor. So eventually I went back to a "traditional" scoop wing, especially after seeing some analysis of flap spoilers vs. raised wings (credit to ruf on MZR for finding this pic, the actual picture is on www.auto123.com):



You can see that the airflow is definitely smoother with the raised wing model vs the flap spoiler, which means the raised wing is likely more efficient and will produce the same drag for more downforce, or the same downforce for less drag. This was my main motivation for dumping the Gurney flap and switching to a scoop wing. More later.

The next aero device I tried was a LeMans-style front diffuser. Making it was not terribly hard, but also not the easiest task on earth as you need to be PRECISE if you don't want to screw up your handling.



The front diffuser's job is to smoothly route the air upwards from underneath the bumper, thus generating downforce. Here are 2 shots with the diffuser installed that should make the point clear:





Track test: The diffuser weighs in at about 1 gram. This isn't a negligible weight, however I do know that if there's no aero effect, at high speeds the added weight will actually make the car understeer. So I tested out the diffuser bearing this in mind.

Turns out to be Absolutely not the case. The front diffuser on its own added so much front grip that I could not stop traction rolling! Any full steering input with the intent to negotiate a corner would see the car hunker down, turn really fast, and then either spin out or flip on its lid. This was at almost every corner too, not just the high speed ones. The Gurney flap was definitely not enough downforce to handle the front grip, I had to put a scoop wing on my car to balance it out. And afterwards the handling became incredible. Have you ever gone from being a mid-pack racer to lapping the field twice in 5 minutes? Yeah, that's what happened as soon as I paired a rear wing with the front diffuser. I've never seen such a ridiculous improvement before, and from then on I was convinced that aero is going to play a very important role in Mini-Z racing.

Now if front diffusers work, what about rear diffusers? I hadn't been able to test it out 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. No laptime or race data as of yet but he notes a marked improvement in rear traction, without the car feeling like it's any heavier (his underfloor + diffuser weigh 1.8g). This to me is amazing, knowing that we can adapt existing designs that others have given up long ago and through good execution, make it work! We've made underbody aero tuning 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 doing two things right now: 1) Building a wind tunnel to try and get some numbers on the aero devices installed on my car, and 2) Trying to get legitimate wind tunnel (hey, I'm a college student now!) time or simulation software to see if there is a way to visualize the airflow going through the shell. It's 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 pictures of the entire car I'm currently campaigning, 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! ) This car has definitely 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.