Hi All,

I have heard people talking about using wings on the cars to generate down force, some say this is a waste of time because the cars aren't travelling fast enough.

What are the facts in this situation?

I know that miseli used an upside-down aeroplane wing on the front of his 2009 demo car, what did you find?

I thought a thread on this could be interesting / helpful.

Cheers.
David.

Short answer? Bugger all. Downforce increases with speed, and the speeds aren't high enough. Putting wings on the car simply to create downforce will only really create drag, and if they do create downforce, it will only add to the car's rolling resistance. When you only have one driven wheel (not two like in F1) there is going to be hardly any 'useful' rolling resistance added, and it's far easier to simply use a tire to get more grip.

With regard's to marc's car, he appears to have simply been streamlining his car to reduce drag on the axles.

I'm no aero expert though, but if I have some spare time next year I might pop over to the BHHS wind tunnel and do some tests on down force there.

PWK wrote:Downforce increases with speed, and the speeds aren't high enough.

I saw this on Wikipedia:

"The same principle that allows an airplane to rise off the ground by creating lift under its wings is used in reverse to apply force that presses the race car against the surface of the track"

If the speeds aren't high enough, how do paper planes fly? I guess because everything is scaled down?

We know that at 30km'h sticking wings on the family sedan will not create downforce but what happens when it's a small model car travelling at the same speed?

A paper aeroplane has a very low weight and a large relative area for that weight. As a solar car has a very limited area to work with for a wing, and a compulsory high relative weight of at least a kilogram in general, you will need high speed.

You could try to make a car that is almost completely a reverse aerofoil to get downforce, which would be a very interesting idea to look into, but the gains will probably still not going too be enough to compensate for extra weight in materials to get the shape and drag created. It's probably a feasible idea, but at the moment for teams that have a hard time getting axle alignment and electrical wiring right, it's impractical.

Redlands wrote:You could try to make a car that is almost completely a reverse aerofoil to get downforce, which would be a very interesting idea to look into, but the gains will probably still not going too be enough to compensate for extra weight in materials to get the shape and drag created.

It would be very difficult with the current heights of the cars, it would have been practical in the 1990s when the cars were just made from sticks.

You mentioned you have a wind-tunnel at Box Hill, how much does it get used?

The wind-tunnel gets used a little bit by the senior teams early on in the year for testing, and sometimes later so that we have accurate aero data for Ian Gardner's simulator spreadsheet. In the last couple of years the cars have actually been slightly too wide to fit in the tunnel as it currently stands, but we're going to remedy that soon. In future it will hopefully be used a lot more.

Also, from wikipedia: Downforce formula is D= (1/2)x(WSx H x AoA) x F x p x V^2 . As you can see, major limiting factors for downforce in a solar car are height, wingspan and velocity, especially wingspan given next year's expected rule changes re: width.

Do you have pictures of the wind tunnel?
Im interested in seeing what it looks like.

PWK wrote:The wind-tunnel gets used a little bit by the senior teams early on in the year for testing,

How many teams does Box Hill actually run each year?

TonyB wrote:Do you have pictures of the wind tunnel?
Im interested in seeing what it looks like.

As am I, it's amazing that model solar car racing has brought this sort of technology to high schools. Even if it is a basic setup.

This year Box Hill High School entered 16 teams into the Victorian event (From years 7 through to 12).

I'll try to get some photos of the wind tunnel for you. The wind tunnel doesn't belong to the school, but is on (very) long term loan from RMIT University. It isn't used by many teams, but in the senior years teams start thinking more about things like aerodynamics, and then it gets a workout.

unussapiens wrote:This year Box Hill High School entered 16 teams into the Victorian event (From years 7 through to 12).

Do the teams work together or are they all independent?

That reminds me unussapiens, how did you get that tube shape for Nigresta? How did you make it?

The teams are all independant, although we're friendly enough that we'll ask each other for help if we need it.

The tube shape for Nigresta was made in three parts. The middle section which was just a cylinder was a sheet of plastic (1/4mm thick, from memory) wrapped around a couple of aluminium rings. These rings held the car together, axles went through them, guides and panel were attached to them. The nose and tail were mading by lathing blocks of wood to the correct shape and then vacuum forming plastic over the top. We estimated that between 15 and 20 hours went into the nose and tail. We had to outsource the plastic forming to a local company (Acron Plastics, for any Victorians) since we couldn't get it strong enough at the base.

Redlands wrote:Do the teams work together or are they all independent?

As unussapiens said, we're generally independent, but help each other out occasionally as you do. Sometimes the independence is good (great ideas stem from competition) and sometimes it's bad, case in point this year, where we had so many teams that the teachers and mentors had a very hard time keeping track of them and getting them on track.

PWK wrote:where we had so many teams that the teachers and mentors had a very hard time keeping track of them and getting them on track.

Yes, that is understandable. It must be difficult managing all the resources.

And thank you unussapiens for explaining how the tube was built.

Sorry to Tony for getting a bit off-track from the original topic. Perhaps we should start a 'Box Hill' thread

TonyB wrote:Do you have pictures of the wind tunnel?
Im interested in seeing what it looks like.

I have a pic or 2 of the BHHS wind tunnel that Ian sent me I think. I'll see if I can dig them up. As PWK pointed out, the cars are slightly too wide for it which isn't ideal but Ian has said that it is going to be flipped on its side which should fix things up.

As was mentioned with regards to the test car, the main reason for the airfoil was to streamline the front axle. It is only very slightly shaped like an upside down wing.
The downforce produced will be next to nothing at the speeds the cars are going at, particularly in relation to weights of the cars.

I could also stick a few pics up of the Utas wind tunnel if you like.

miseli wrote:As was mentioned with regards to the test car, the main reason for the airfoil was to streamline the front axle. It is only very slightly shaped like an upside down wing.
The downforce produced will be next to nothing at the speeds the cars are going at, particularly in relation to weights of the cars.

Thanks for clearing that up Marc.

miseli wrote:I could also stick a few pics up of the Utas wind tunnel if you like.

Funny you mention uni and wind tunnels. I don't know if you went to the talk on Aurora after the seeding on Saturday, but the man giving the talk mentioned a crew member who had studied aerodynamics at the University of Melbourne.

Can you still study aerodynamics individually in Australia or is it just a small part of an engineering course? As an engineering student perhaps you could shed some light on this Marc??

You may need to study Aeronautical Engineering.
They have that degree at Sydney uni, but not to sure about other uni's.

Aeronautical Engineering is available at Monash and RMIT Unis in Melbourne. You could probably also do something relating to aerodynamics as a breadth subject as Melbourne, but I couldn't be sure.

TonyB wrote:You may need to study Aeronautical Engineering.

Yeah, you'd have to do something like that I'd expect. They don't run it at Utas and aerodynamics is just covered some way in the mechanical degree, but a number of the Universities around the country are bound to have it.

Unfortunately, I was sorting out the seeding and draw at the time of the Aurora talk and so didn't get a chance to go. I was a bit disappointed about that.

miseli wrote:but a number of the Universities around the country are bound to have it.

I think it's only UNSW, Monash and RMIT.

Don't think you can do it at University of Melbourne

Surely there must a few Fluid Mechanics/Dynamics subjects at all unis offering engineering?