Aerodynamics

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Old 11-13-2015, 03:36 PM
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Default Aerodynamics

In the hopes of having a great debate about aero devices we use on our cars I created this thread.
Please no unfounded claims or "I don't like what others do with their cars".


So, my experience with different bodies in 1/10th buggies is limited to a Team C TC02 with the standard body, which looks like one of those old Venom bodies and then switching to a Kyosho RB5 Finisher mounted on the same car.
Other cars I had (or have) I didn't try other bodies, like currently the B5 and the XXX (yes Team Losi XXX).

On the other hand I can get some facts with 1/8th buggies, I have a MBX6 with the standard body and the MBX7 body, which is a cab forward body. My intentions are to determine weight bias and if possible CG height changes. Then it's into the wind tunnel (work in progress).

DIYs:
- http://www.tomcarlone.com/WindTunnel...nnelReport.pdf
- http://www.instructables.com/id/Cardboard-Wind-Tunnel/
- http://makezine.com/projects/model-wind-tunnel/

Software:
- http://www.openfoam.org/

Universities/Colleges with available Wind Tunnel:
- http://www.sandiegowindtunnel.com/
- NC (North Carolina?)
- http://www.engin.umich.edu/aero/rese...s/wind-tunnels
- http://www.southampton.ac.uk/windtunnels
- http://www.cranfield.ac.uk/About/Peo...ll-wind-tunnel
- https://www.uwal.org/
- http://www.ati.org.uk/technology/wind-tunnels/

Resources:
- https://www.grc.nasa.gov/www/K-12/airplane/bgt.html

Last edited by 30Tooth; 11-15-2015 at 07:55 AM.
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Old 11-13-2015, 05:27 PM
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I would say if a wind tunnel is involved, you need to measure downforce as well. For instance, my Losi 8/2 JConcepts illusion body (1/8th) was inspired by Drake, for the flat upper surfaces for driving down the backside of a jump. Then they came out with the front cab, for increased downforce on the front end using the cab windshield. Lots of variables imo.
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Old 11-13-2015, 05:37 PM
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I'm not aware of any of the makers doing any wind tunnel testing, despite the easy availability of low speed wind tunnels (San Diego, NC..). There are significant inconsistencies in the marketing pitch and the shapes chosen. I say prove it, the way other sports marketing companies do.
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Old 11-13-2015, 06:52 PM
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It would be pretty simple to make a wind tunnel and test that way. Personally id like to put some scales in there and see the amount of drag and downforce. Smoke is a great way to see how the air moves around the body as well
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Old 11-13-2015, 07:01 PM
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I'd be interested in some tests on 8th scale rear wings aswell.
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Old 11-13-2015, 07:02 PM
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I say go for it. I would find it extremely interesting. I highly suspect that is why the Losi 3.0 had a more narrow chassis than a 2.0. To cut through the air more efficiently, less drag. Measuring downforce would be easy, use scales under the tires during the test. Or a weight measurement from above for the suspended truck, for tilting the body to measure forces in a wind tunnels.

I like Drake, he thinks outside the box.
A quick search for his Losi vids on YT
https://www.youtube.com/results?sear...th+losi&page=1

Eta: Haha Gokarter beat me to the scales comment lol. Some guys figured out on the XO1, that if they remove the rear wing, it actually goes faster, and that's a pretty flat wing. I know on my 8, as the car goes by me, the high downforce wing creates a huge disturbance by the feel of the air and leaves moving at full throttle. A less downforce wing, would mean less downforce and more streamlined flat movement, less pitch up of the front. But less downforce at higher speeds. Yes, I'm in Wings 101 right now lol.

Eta 2, It would be cool to see some smoke tests of different force wings on video.
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Old 11-13-2015, 07:16 PM
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This may be something i look into, ill have to get some plywood and plexiglass, i could hook up a potentiometer to control airspeed, a cheap smoke machine for smoke testing and i may have to make some rollers that sit on scales under the car. ( i could use one of those weight distribution scales and put the roller assembly's on them)

Im really interested to check up on this new front wing fad
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Old 11-13-2015, 07:40 PM
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Haha I'm looking at tunnel smoke testing on YT. This car below (the superbird) was actually banned from competing in Nascar due to it's superior aerodynamics. While some may say this has no effect on rc cars, if you could outrun the fastest car coming down the straights, that's a major deal.

Wind Tunnel Test: "43" 1971 Petty Superbird
https://www.youtube.com/watch?v=zl7jk85D2sE
+ YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.


About 4 minutes in on this one, they discuss wings/ spoilers and their different effects, downforce VS turbulence. Made by MIT.
https://www.youtube.com/watch?v=TKH1DyV9vNU
+ YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.
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Old 11-13-2015, 08:00 PM
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Good subject 30tooth! I am a professional aerodynamicist and I have been looking at car bodies with some interest recently. A wind tunnel test could be very enlightening, as could some very basic computational fluid dynamics (CFD) runs.

Just applying some basic knowledge to the body design has a lot of potential for improvement over what we have today. In my opinion the cab forward design is a positive step in helping race cars behave in a more desirable way while on the track. If you were to take a real engineering look at these designs, there might be significant performance improvements to be had. To my eye, the Schumacher KF body is very attractive because it is both cab-forward and appears to have very low drag. I don't have any numbers to back that up, just intuition based on the overall shape.

-Aaron
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Old 11-14-2015, 06:36 AM
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For those of you thinking about building a wind tunnel, this link will provide good information.

https://www.grc.nasa.gov/www/K-12/airplane/bgt.html
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Old 11-14-2015, 07:32 AM
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Creating a wind tunnel is something that I have considered. I talked to some air flow guys I work with, and one thing you definitely need to have is a flow straightener for the wind. This can be as simple as a bunch of standard straight plastic straws packed in a box. Just a little tip to keep the test rig simple and inexpensive.
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Old 11-14-2015, 07:39 AM
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Thanks for the nice replies.

Originally Posted by spookie View Post
I would say if a wind tunnel is involved, you need to measure downforce as well. For instance, my Losi 8/2 JConcepts illusion body (1/8th) was inspired by Drake, for the flat upper surfaces for driving down the backside of a jump. Then they came out with the front cab, for increased downforce on the front end using the cab windshield. Lots of variables imo.
That's the goal, to have at least downforce distribution forces calculated by simple scales in each end of the car and a third to measure drag (or Cx if it's more correct to say). You touch on a very delicate subject, the shape of the wind shield might not provide enough downforce to be felt, as you know air "bleeds" if it's not correctly streamed.

Originally Posted by R1Joel View Post
I'd be interested in some tests on 8th scale rear wings aswell.
I'll do my best Joel, I have the Mugen and Kyosho wings, the JQ one and a double plane no name (will be interesting to test this one).

Originally Posted by gokarter64 View Post
This may be something i look into, ill have to get some plywood and plexiglass, i could hook up a potentiometer to control airspeed, a cheap smoke machine for smoke testing and i may have to make some rollers that sit on scales under the car. ( i could use one of those weight distribution scales and put the roller assembly's on them)

Im really interested to check up on this new front wing fad
Here's some DIYs:
- http://www.instructables.com/id/Cardboard-Wind-Tunnel/;
- with a covered hole to put the scales like this one http://makezine.com/projects/model-wind-tunnel/

Are we on a race to see which one of us is the first to finish making the wind tunnel?

Originally Posted by avaldes View Post
Good subject 30tooth! I am a professional aerodynamicist and I have been looking at car bodies with some interest recently. A wind tunnel test could be very enlightening, as could some very basic computational fluid dynamics (CFD) runs.

Just applying some basic knowledge to the body design has a lot of potential for improvement over what we have today. In my opinion the cab forward design is a positive step in helping race cars behave in a more desirable way while on the track. If you were to take a real engineering look at these designs, there might be significant performance improvements to be had. To my eye, the Schumacher KF body is very attractive because it is both cab-forward and appears to have very low drag. I don't have any numbers to back that up, just intuition based on the overall shape.

-Aaron
Guess the wind tunnel runs are easier to do, CFD seems like it would need the complete CAD model and I don't see any brand sending those.

Originally Posted by Fastforward View Post
For those of you thinking about building a wind tunnel, this link will provide good information.

https://www.grc.nasa.gov/www/K-12/airplane/bgt.html
Very helpful! Thank you.

Originally Posted by icecyc1 View Post
Creating a wind tunnel is something that I have considered. I talked to some air flow guys I work with, and one thing you definitely need to have is a flow straightener for the wind. This can be as simple as a bunch of standard straight plastic straws packed in a box. Just a little tip to keep the test rig simple and inexpensive.
Does the wing straightener has to have certain measurements? Didn't find anything about it in the NASA site.
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Old 11-14-2015, 08:02 AM
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Originally Posted by icecyc1 View Post
Creating a wind tunnel is something that I have considered. I talked to some air flow guys I work with, and one thing you definitely need to have is a flow straightener for the wind. This can be as simple as a bunch of standard straight plastic straws packed in a box. Just a little tip to keep the test rig simple and inexpensive.
Originally Posted by 30Tooth View Post
Thanks for the nice replies.


Does the wing straightener has to have certain measurements? Didn't find anything about it in the NASA site.
Unless the goal is a continuous loop design as shown on the NASA site, the power source (fan) can be positioned to draw still air over the test object from behind. No need for vanes to straighten the airflow coming from a fan.

If the fan must be in front of the object, a cylindrical fan might have an airflow that's easier to control.

Best bet- don't attempt to build a wind tunnel. Just rent time at an existing one where they have everything figured out. You can tell them what you want to study and they can design the testing protocol.

In San Diego and NC they can measure fractions of grams of drag on cyclists. This stuff would be really easy for them.
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Old 11-14-2015, 08:10 AM
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Good pointers, I still have to make a wind tunnel because I don't have access to one nationally but I will ask the local university.
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Old 11-14-2015, 09:21 AM
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Originally Posted by icecyc1 View Post
Creating a wind tunnel is something that I have considered. I talked to some air flow guys I work with, and one thing you definitely need to have is a flow straightener for the wind. This can be as simple as a bunch of standard straight plastic straws packed in a box. Just a little tip to keep the test rig simple and inexpensive.

Yes, an air flow straightener is needed. I would think length needed would be a function of diameter, but I don't know the magic L/D. Plastic straws are not as cheap as you would think.

http://www.mrtakeoutbags.com/mm5/mer...RoGxoCcOLw_wcB
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