Phat wind tunnel
 

It all started off with a a hair dryer, a wing, a piece of plywood and set of digital scales .... not exactly hi-tech but it was pretty clear from the readings we got on the scales that there was some potential in building a slightly more sophisticated wind tunnel ....

So we did ... it's not finished yet by some way and we're learning what does and doesn't work as we build it but the final version should allow us a good insight into what aerodynamics do on a RC car :)

Piccies ....

http://img40.imageshack.us/img40/731/dsc04320j.jpg

http://img201.imageshack.us/img201/860/dsc04319u.jpg

http://img692.imageshack.us/img692/5732/dsc04318jq.jpg

http://img40.imageshack.us/img40/734/dsc04316q.jpg

http://img29.imageshack.us/img29/1824/dsc04347q.jpg

http://img26.imageshack.us/img26/5871/dsc04345s.jpg

http://img201.imageshack.us/img201/9070/dsc04343n.jpg

http://img405.imageshack.us/img405/7661/dsc04341c.jpg

http://img826.imageshack.us/img826/3844/dsc04350z.jpg

http://img100.imageshack.us/img100/7518/dsc04351i.jpg

http://img825.imageshack.us/img825/1674/dsc04352j.jpg

http://img407.imageshack.us/img407/2082/dsc04353e.jpg

http://img269.imageshack.us/img269/4286/dsc04429li.jpg

http://img163.imageshack.us/img163/805/dsc04430h.jpg

More pics and details to follow :thumbsup:

Nice work!:)
Looks ace and interesting results should follow
Excellent Mr speedy
You can get smoke pellets or smoke matches for chimney testing at most plumbing stores
Hth's

your one busy man!! looks brilliant :):)

I used to build lots of small wind tunnels. Believe me smoke is not the way to go. We tried allsorts of smoke from burning cardboard to that smoke mixture for stage productions. All of these end up filling the room with smoke quite quickly. In the end we used the finest thread attached to a thin piece of steel wire.

HTH

Sparky

Or you could just vent it outside

We've only done a few basic trial runs with the wind tunnel and the data collected so far is from the digital scales mounted under the front and rear axles and is proving reasonable accurate ...

I'm pretty sure we will test some sort of smoke .... was actually thinking of a smoke pellet in a barrel with a small bore flexible line to draw the smoke up to some sort of wand in the wind tunnel ...

I don't think the smoke will hang around in the workshop too long tho, the fan at the end of the wind tunnel is around 16" dia and draws air at 25mph !!! :D

Cheeky little MK1 Golf in the back ground what year is it?.

Great project!

Ask Dan as its his and i think he has two of them and a polo.
Its so low he has trouble getting it off the drive:lol:

se this for controled smoke

http://www.tlc-direct.co.uk/Products...FUNTfAodgkIAaQ

hi there.

I'm really liking the wind tunnel, it's a great project.

Just one question, have you thought about pointing the car towards the fan which would give you aerodynamic loads for the car going forward not backwards??

If you look at the fan blades, Si is drawing the air in from the multi-tube end over the car and out through the fan, not blowing it directly over the car from the fan end. This would cause turbulence and localised areas of higher pressure, unless the fan was further away and/or the air was channeled to smooth out the airflow. What he's done is the best way for the working area & the fan he has.

Nice going Si, you've talked about it for ages, good to see it working :)

Can only see two sets of scales. Why arent you measuring drag too. Almost as important as downforce!

Or is that on the long list of things to do?

Si does indeed have the fan sucking air throo and not blowing and its abloody big fan aswell as seen it for real. Imagin the size of your dustbin lid and you got an idea.

Ace! I did my Uni degree project on RC aerodynamics using a wind tunnel. You'll be amazed at what happens to the air as it hits the car.

I chopped a shell in half lengthways and mounted it to a board. I used special fluro paint that stuck to the board showing the affects of the aerodynamics.

http://i10.photobucket.com/albums/a1...b/DSCF0021.jpg

I saw people at force India using what looks like the same stuff when I was there on work experiance, its really amazing what shapes and patterns it leaves.
would love to see any results, especially if you test any forward cabs to see what the difference is? :thumbsup:

Don't buy this stuff, it's for testing smoke detectors. You can hardly see it when it comes out the can. I use it just about every day of the week.

how about removing the pinion, and the back stop, and replacing it with a small spring gauge, and a small wire to teather the car, and measure drag liek this http://www.ebay.co.uk/itm/Newton-met...item3a60847f50

F1 uses the paint approach so why not go that route applying it to key areas of the shell ecetera and see results as it can be studied before cleaning as smoke is instantanious so you may miss something?

Video.

To answer a few questions ...

... the Golf is a '83 series 2 mk1, is currently under restoration and belongs to Dan ...

Like Matt said, the tunnel is a sucker not a blower ... don't think that's the technical term tho !!

The drag question ... um .. well not sure on that one just yet. For now I want to keep the wind tunnel as simple as poss and try to get it working as consistently as we can so that we can measure downforce with some degree of accuracy from model to model. Thanks for the ebay link, its on my 'watch' list !!

Thanks to everyone for the tips and links, I look at all of them .... it's been a steep learning curve so far and I think the hardest part will be collecting the data and applying it to something useful that can be used positively on track .... again any suggestions are much appreciated !!

Very cool project! I work in the aerodynamics department at Mercedes F1 and have always wanted my own tunnel for RC testing. This one looks superb.

Have you tried using 4 scales (one for each wheel)? That's how most real tunnels work.

What sort of repeatability do you get? This is always the hard part ;-)

Thanks !! Very cool job :woot:

To be honest I haven't even finished building it properly yet ... should really get off the PC and go do it !!! ....

Whats the advantage to having a set of scales per wheel instead of just one per axle ?

I can't really answer about the repeatability, when the tunnel is finished we can test parts a bit more seriously and will find out how accurate it is :D

My experience with these little scales is that they can be a bit inaccurate if the load isn't centred on them. If your car isn't totally balanced and centred on the scales, you might get some issues. Or it may work just fine, so probably just something to think about if any issues do come up.

With a real tunnel one pad per wheel is just easier to engineer I guess, plus there's usually a rolling road in the way to complicate things!

Keep us updated, look forward to seeing some results :)

After having a long chat with Si & Dan at WORM yesterday about their basic initial tests & findings with F & R wings and their positions, i think people are going to be suprised at just how efficient certain wing and body shells are ( or arent ) and what they do to the airflow for F & R lift and downforce. Or dont do, as the case may be.... :woot:

Roll on winter when they have more time to do some more testing and show some spreadsheet results :)

There is another method I've used which is great for photography but only good for stuff that doesn't mind getting wet, like bodyshells. If you've got a white bath, rig up a cheap adjustable strobe light, and move the bodyshell slowly along the bottom of the bath in just enough water to cover it. (glue a small stick to the roof) Adjust the strobe light until you see a nice flow stream over the bodyshell. You will see where the vortex's are forming but obviously you won't be able to measure the downforce. A nice angle without any turbulence will be between 12 and 20 degrees.

Nice tunnel have a look at this

http://www.youtube.com/watch?v=mpMOpyLbjcA

Uses 5 digital scales. open fan design with boundary layer suction very cool. But then the guy did the gesign work on the nissan P35 and Nissan r35 gtr so it probably child play for him.

http://www.suzukaracing.com/

Thanks for the input guys ... already studies the vids ... this ones interesting - http://www.youtube.com/watch?v=DpzRP...hannel&list=UL

We're on a re-build at the moment, nothing too technical, just a little more accurate construction than the first version. Hopefully with a stepped speed controller to change the wind speed as its fixed at 25mph right now. Seemed a good idea at the time, but on reflection, this is prob a little on the high side to be a good representation of an buggies average speed.

Anyone got a good idea of a buggies speed around a track ?

Track length at WORM is about the 145m mark from memory (might be longer now, but can't remember precisely...must get Kev to walk it again with his wheel sometime!)...best laptimes shown on our website results come in at around the 25 secs mark...do some simple maths to get a rough idea of an average speed!

145/25=5 metres per sec

5x60=300 metres per minute

300x60=18,000 metres per hour = 18km/hr = 11mph average over a lap!

Maybe you should start out by finding out what speed the aero design actually comes into play and is effective! That would tell you at which points on a lap it could have the biggest impact.

Wow that's low ... not what I expected. Sounds like 25mph is too high for a relative downforce reading really ... maybe on the straight ... but won't really apply to majority of the track.

We're looking into an Iphone app that determines speed ... think it's for mountain biking ... could be useful !!

Aren't wings really to stablise the car in the jumps?
You would need the launch angle peak height and mass and a equation of a projectile http://en.wikipedia.org/wiki/Trajectory_of_a_projectile
if you know what the drag is you can resolve for launch speed fairly accuratly.