Micro Aero Dynamics

[Crooked H]

Well friends just got off of the ignorance filled HPI Board and one of their hot topics is whether wings on micros are functional. Not surprising one of the most thoughtless answers came from one of their moderators saying that aerodynamics plays little to no part with micros because of their size. If he had only said it was due to the speed of stock micros, I may have been able to overlook it and leave their board without posting. They even started in on Front wheel drive cars with spoilers. AAAARRRRRRGGGGGH! Anyway thought we could get some intelligent discussion of the subject going here so I figured I'd post my response from their board here.

Here's my post:
Hate to be the bearer of bad news, but for anyone that has raced a speed 300 powered micro, it is a know fact that rear downforce is important. Believe me, after a few laps with the spoiler intact, trying to follow up with the spoiler removed is a frustrating experience. In the case of the micros, only fast moving stock and mod motored micros will notice any effect from spoilers. The effect seen will mostly be in straightline stability and initial entry into a tight corner. You tend to lose most of the downforce generated if you have to slow down to apex a turn properly (same thing happens to fullscale cars). Although a micro may only be travelling at speeds ranging from 17-40 mph depending on its powerplant, due to its small size, air molecules effect it as they would if the micro were fullsize travelling at the same proportional speed (which would be well in excess of 75mph which is a known start threshold of aerodynamic stability tuning). If air molcules didn't effect small vehicles in the same scale-like manner they do their larger counterparts, model aircraft would never leave the ground. Just think about parkflyers which can cruise at 5-10 mph. I haven't seen a full-size aircraft fly that slow yet.

HPI, being the racing freaks they are, addressed the issue of effective rear downforce with the black plastic wing set they made for the micro. This is also addressed in the wing and body design on many of the aftermarket companies such as ARM, RAD and Pro-Line (350Z and F360). Although it may not seem like a lot, any amount of downforce created will get transfered to the chassis. Although the rear body mounts flex under manual pressure from a human hand, the amount of downforce needed to make a micro "stick" to the ground is considerably less. The main thing is to determine the aerodynamic threshold for the micro, determine if you are able to travel above it, and tune accordingly.

As far as wings on a front wheel drive go. I can't vouch for the oversized wings seen on many Sport Compacts (these morons give us all a bad name), but I can vouch for their use in racing as Front Drives tend to have most of their weight over the front axle. This excess in weight is what causes the understeer and extremely twitchy steering at speed found in most front drives. To easily and effectively counter this, a spoiler is added to "weigh" down the rear end at speed and balance out the weight of the car as it begins decelerating into a turn until it has reached the point of apex in a turn and can use weight transfer to effectively ride the proper line out of a turn often faster than a comparable rear drive (This is why the Acura Integra was very effective on tight tracks with lots of turns in the Speedvision/Speed Touring Championship) .

[Crooked H]

To help get the ball going just thought I would give my impressions of the RAD Imprezza WRC since it went through its first race this past weekend. I found that this body has a balanced feel much like that described with the 10th scale Stratus body (though I know alot of that can also be attributed to my special wing). I have also found that this body does quite well when drafting another car and then swinging out to overtake them as well.:)

[ScottMcLeod]

I don't know about the micros yet because I haven't done too much research, but if you give me about 5 minutes, I can hunt down a calculation from the mini-zracer forums that we discovered proves that mini-Z wings are useless.

I'll get back to you with a wing size that would prove effective on a micro.

[ScottMcLeod]

Unfortunately, Maybe no one ever posted the equation, but for a Mini-Z (1/28th scale, approaching 15-20 mph lightly modded)

Here's the quote (from a guy named "DHS")

For the scale and speed of these models, you'll have to fasten a substantially large wing (e.g. > 25 cm^2) in order to have any appreciable aerodynamic effect.

That's just my back-of-the-envelope opinion as someone who just got a degree in mechanical engineering, if that means anything.

Anyways... Can someone who's got a degree in aerodynamics shine some light?

[jw_j]

the bigger the wing the better right? maybe i should go hunt down one of my model airplane wings lol

[Ghost]

Originally posted by jw_j
the bigger the wing the better right? maybe i should go hunt down one of my model airplane wings lol

Well it would certainly effect the aero on a micro, Just remember to mount it upside down. Otherwise it will generate Lift and you will have a very interesting ride.

Don't forget guys, the angle of the wing makes a great deal of difference in the effectiveness of any wing.

[Crooked H]

Basically, a good wing should be at least the width of the ****pit area of a body and should have a rear surface at a height very close to that of the roofline of the vehicle. A good example of this is the black plastic wing kit that HPI makes for the micro and supplies with the RTR Kits.The reason for the close proximity to the roofline is to try to catch as much air flowing over the body as possible while still remaining within body rules at many tracks which don't allow a spoiler to be taller than the roofline of the car and receive "clean air".

Another factor is the "angle of attack" of the airfoil of a spoiler. This is a fine line that must be established through trial and error. Too little angle yields very little downforce;whereas too much angle equates to a drastic increase in drag and can hurt the vehicles overall speed. A common example of this can be seen in the wings supplied with some of the HPI Bodies. To make up for the lack in good airfoil shape and usable size of the wing, a greater "angle of attack" is used to compensate for this as well as compensate for a sloped mounting surface for the wing mounts.

The last factor I will touch on is the forward speed of the micro. Though I have not been able to attain any accurate speed reading of micros racing, I have hypothesized that based on the size of the micros, and some initial impressions of driving several different micros, that they would have to reach about 16-17 actual miles per hour to begin to experience downforce generation from a rear spoiler. While this may seem like a trivial speed, it is estimated that the average box stock micro will reach speeds between 10-15 mph which makes them fall short of this threshold. Most of the micros that I found to be unstable at speed and inital entry into a corner, seemed to travel fairly slower than micros that I found quite stable and seemed to surpass the threshold quite well.

Hopefully I will be able to get my hands on a HPI wing set and be able to get some impressions of it to discuss with you all. :)

[ScottMcLeod]

and the censored word, ladies and gentlemen, is:

*drumroll*

c o c k p i t !

:D

[Crooked H]

:D Rotflmao

Can't imagine why they wouldn't want to use a lovely word like c o c k p i t, can you?

[The Thunderer]

Its probably done automatically. I know I wouldn't touch (or "fix") that word. LOL.

[jw_j]

ok ill find my trainer airplane, and rig the wing up so it can take off, then ill get a nitro engine and fuel tank and put it on the wing so i can fly the thing

[ettsn]

A 1/18 scale car has a much higher Reynolds number than it's 1/1 scale counterpart. What that means is if the fullsize wing is effective, the scale wing cannot be at the exact same scale (ie it should be larger than exactly 1/18 scale to provide the same effects at scale speeds). A perfect scale wing would have the same total effect (in scale) if the speeds were 5.6 times (inverse of 1/18 scale) as high. Example:

fullsize car going 100mph produces 300lb of DF
1/18 scale model must go 556 real mph to produce 16.67lb of DF (roughly equal in scale - 300/18=16.67)

Where this excercise fails is that the Micro is not 1/18th of the overall mass of the 1/1 car. Nor are the dimensions or angle of attack for the scale wing exact.

Therefore, they are correct that scale aero doesn't work as planned. Rather a different approach should be taken. If you want real DF, skip the hokey HPI wing. It's more for cosmetics. Go get a slotcar wing set and you'll be glued. If you leave it clear, you might not even notice that your Micro looks like a scale farm combine now! :)

The best wing I've seen with a Micro body lately is the one that comes in the Proline F360 kit. Cut correctly, it should offer some pretty decent DF at realistic speeds (noticeable).

BTW, I'm not an aerodynamicist, nor am I degreed in fluid dynamics, but I do mess around with it as a hobby. Maybe one day I'll go get that MME-CFD degree to sit next to my MBA. :)

HTH
-Paul

[Crooked H]

The thing about micros is that the wing doens't neccessarily need to be huge, but just large enough and shaped properly to be exposed to airflow and actually be affected by it.

I currently have the HPI Black Racing Wing Kit on its way to me, so I should be able to test it at our next race and get some impressions of it.

[urq435]

Aren't those wings identical to RTR one? Keep us inform on their effectiveness. :D

[hpidriver]

yes, the rtr's come with the bigger plastic wings

[FishBone]

This is strictly my personal opinion. I do not believe that wings will make too much of a difference in a bone stock car racing. The body, on the other hand will. When I started racing my micro, I ran a Beetle. I was horrible. I ran the body only 2 times. Then i changed to the Pro-Line Ferrari F-390 Modena body. Instead of getting lapped about 5 times in a race, I was up with the leader. Altough I got lapped sometimes by first place, I still got second every time that guy was their. After he moved to North Carolina, I think, I bagan to get first over and over. My season ended with one second place and the rest first. I even managed to get 3rd in super stock one night with my bone stock car.

What I am saying, in stock, the downforce will not make too much difference, not as much as the body. In my personal opinion, I beleive that people in stock should stop trying to make their cars go oh so fast, and work more on their driving techniques and styles. After you learn how to drive the car, then go for the speed and power. I am racing currently right now with Crooked H at my local track. During our practice running, my first time I got to try my Super Stock setup, we matched our cars up and let 'em rip. Our cars where the same speed.

During the race the following day, I would one way or another, get the lead, almost get it, or fight him off. To my surprise, our driving styles were close to being the same. We had some very interesting battles for first, sort of like Nascar racing. In the end, I got 2nd all night in my heats and Crooked H got first. In the mains, I started off second, Crooked H first, and a friend in third(which was getting first all night in the other set of heats). Right off the line I managed to get and hold first for about 2 minutes of the race, with Crooked trailing close, planning his kill. After one hard race of passing, crashing, and ploting our passes, our freind that started 3rd got first. His driving style was just so unique. When he got pressure put on to him, some how he would pull away. It was almost like we couldn't pass him no madder how hard we tried. He just kept getting better as we got closer. That night was a lot of fun.

What I am saying is to first learn how to drive the car at its full potential stock, and then go for the mods to make it go faster and handle more precise.

[ScottMcLeod]

Where can this proline wing be obtained?

[Crooked H]

Scott- The Pro-Line wing comes with the 350Z and 360 Modena bodies.

Fish-while driving skill is an absolutely paramount weapon to have in your armada, lets not forget the other reason our cars are blazing fast; total race weight. Another thing is that yes bodies play as big a role in handling as wings do, but the two can work effectively to compliment eachother and create a neutral handling car. And we all know that a slow stock car won't be able to use any aerodynamic help since it doesn't move fast enough to create any. Just remember your car has always been faster than the rest of the stock and super stock racers, which meant that your car got up to the speed that it needed aerodynamic help, which explains your beetle body nightmares. Notice what you said, you switched to the 360 Modena body and you were up there with the leader. Remember just as a crappy driver can't do much with a good car, a good driver can't do much with a crappy car either.

Just to help out things alittle more here is my definition of what a neutral handling car is.
- A vehicle that displays neither oversteer nor understeer when pushed hard into a turn. Handles as such that a novice driver can master the basics of the vehicle after only a few minutes of driving it or can be driven by various drivers with various driving styles for full effect.

[Crooked H]

Well gang, my wing arrived early Monday morning. Pretty amazing since I ordered it Thursday evening. Anyways I'll be able to get some initial impressions of it Friday evening but probably won't be near my computer until sometime Sunday. Darn, I still need to find something to do until then. Guess I'll paint my new 10th scale body.:D

[M@rk]

I have tried the CLK, M3 and Skyline body on my micro and there is a big difference.... The CLK was the best.

It is the same in 1/10 Touring car... Most drivers have the Stratus, Vektra and 156 to use in races depending on the track and the weather.

[Mondo]

My experiences are as follows:

Last week I partook in my first Micro race which is an indoor event on carpet.
I used a Protoform Dodge Dakota (truck) bodyshell with no wing.
The results were disasterous.
I blame this on the car being set up incorrectly.
Even on top speed, it was shaky as hell.
Another driver side slammed me and my (GPM) rear axle bent, putting me out of contention.
The Protoform body didn't offer any protection as the Lexan is thin.

Last night I raced again.
I had set the car up a lot better than my debut race last week.
This time I used the CLK boyshell with the HPI Micro Rear Wing set large wing.
What a difference, it was handling like a babe.
The CLK bodyshell does make a difference and due to the track having a long straight, the large rear wing kept the back wheels behind the front wheels.

Here's a pic (http://mini-zracer.com/forums/attachment.php?s=&postid=43298) of the rear wing.

All the other Micros use standard rear wings and 150mm bodyshells.
The most popular by far is the M3. Almost all the Micros use them.
The top driver uses a Dodge Stratus and there are also Skylines and one C5-R.

[biggusditchus]

In my experience having tried corvette, clk and m3, the largest difference is the overall track... the m3 is awfull at standard I ended up lifting the body and widening the track which helped. But seeing as I didnt want to race a monster truck I bought a corvette which at 150 wheelbase and widest track handles pretty well. the corvette is also less 'pointy than the m3' i.e. it doesnt produce as much front end grip, another reason it tends not to grip roll. The wing isnt the only thing on the car producing downforce.

[DrFelix]

Beautiful car, Mondo!
I´m also very glad to hear the CLK handling so well because of my Viper handling so crappy, at least on carpet. Will upgrade to Epic soon and not sure about the body to buy. But didn´t have much time to experiment with the set up. Have you tried the CLK with the normal wing? Is there any difference in comparison with the wing you´re using currently?

Thanks in advance

Felix

[Mondo]

DrFelix,

Thanks for the compliment.

To be honest, I didn't even bother with the standard wing.
When I went shopping I bought the Micro wing set made by HPI.
It comes with two wings, the one on the CLK is the larger of the two.
Some racers did comment about its size. I don't care about looks at race meetings, I care about results.
As you see it in the pic, it's set at the 10° angle.
Compared to the ProLine Dakota bodyshell, on top end down the straight, the CLK is on rails, as straight as an arrow.
The ProLine Dakota bodyshell was as twitchy as hell, and if when I went through the chicane, it would just spin.
With the CLK bodyshell I can get through the same chicane flat out.

When I raced with the Dakota I had a rigid suspension setup, with CLK I fitted a high-roll suspension plate (Penguin 3500LM chassis)
I don't believe that one change could be the sole reason I am getting at least 200% more stability down the straight and into the chicane.
I am racing on medium grip carpet.

[Crooked H]

Well gang, just got back from the track. All I can say is wow. I have like some major pitbull, kung-fu style grip on this thing. I got some impressions of this thing running with both foam and rubber; rear grip and straight line stability were second to none. It was funny to watch the rear of the car skipping and bouncing on the carpet trying to break lose when I went into a turn hot. It was also nice not having the car all over the place if I had to change my line and get out of the "black groove" to overtake someone on any part of the track. I'll post some post-race impressions sometime between late tomorrow night and Sunday morning if I'm not to buzzed from celebrating if I end up on the podium tomorrow. :D

Here's a few pics of the wing installed on the car.

[Crooked H]

Another view. The wing set comes with 2 wings. One wide and one narrow. This is the narrow one.

[Crooked H]

Last one. Another nice thing is that the wing screws onto the mounts so you can change the mounts to suit your downforce needs on different tracks. Definitely a must have part for serious racers. I myself doubted this until having used the thing.

[Crooked H]

The results are in. Although I finished 2nd in the A-Main, the car performed flawlessly. My result was due to errors in judgemnt as a driver (over-driving the car on cold tires). The wing was instrumental in helping the car remain stable on the straights until my tires got up to temp. Another thing I noticed is during a few fast hairpin turns I performed, my car used to have a tendency to tip up on two wheels, but now it remains flat. Not really sure if this is aerodynamically related or not.:confused:

One more point I would like to bring up is aero-tuning as a part of tuning the whole car. Basically this is to look at it as tuning the downforce on the car can help make up sure that other stuff on the car does what it is supposed to do or make up for shortcomings in tuning elsewhere. One example of this is weight distribution. In my car I have a slight bias to the front which I estimate to be about 50.5/49.5 when using my heaviest racing battery pack. This tends to make a car very, if not overly responsive to steering input. But with aero-tuning at speed this can be balanced out or biased slightly rear with downforce to make the car less twitchy at speed. (A example is the Ford Focus WRC with a 52/48 balance).

A good side note to all of this is that no matter how well tuned your car is, no amount of tuning will overcome bad driving.

Oh well, maybe next weekend I'll get to be top dog at the track.:p

[shznit65]

i was interested in this subject ,so i've done some research! i think the wing size definately effects the handling.............ehhh:p

[jw_j]

lol no!

[Chaos Chao]

Would the "big" wing effect anything on ARM or RAD bodies like the ARM Porsche GTP or the RAD CLK-GTR, or are those bad bodies to use in general.