When I first encountered the Scalextric 4 Schools competition I was tempted to dismiss it. It initially seemed to me that they may be too small to allow deep engineering thinking. Three years further on I am starting to wonder if I will ever plumb it's depths.

From a teaching point of view it is manor from heaven unlike many projects it has been described as being an onion, you no sooner remove one layer then you discover another.

Although the wind tunnel was originally designed to enhance the scalextric for schools project it's is easily adaptable for stand alone use at all the key stages.

At keystage 3 I would have a series of simple cardboard shapes that could be introduced into the airstream, it may be advantageous to drill a hole half way down and half way up the clear panel, this would allow shapes to be rotated in the airstream to watch the change in turbulence.

At keystage 4 I would quickly revisit the keystage 3 demonstration with the shapes then give the pupils blocks of polystyrene for them to experiment with making their own shapes to try in the chamber to discover how each fair in the smoke stream.

Should I have a number of G&T pupils I would move on to the shapes of wings and analyse at what point the air stream breaks up to the point that would cause a stall in real life. If you have never seen the sudden change in how air flows over a wing and how it suddenly breaks up under stall conditions it is astounding.

Concept Cars

Concept Bikes

Future Design

Pagani Zonda F in a Wind Tunnel

Mercedes in a Wind Tunnel

Novitec Rosso Ferrari 458 Italia in Wind Tunnel

The Wind Tunnel with the Smoke Machine

The wind tunnel project came from an idea I saw in an advert to entice people to become student teachers.

The teacher had what I now know was a beautiful home made wind tunnel showing the students how the air moved over his model.

The engineer in me noticed that the teacher (In reality probably an actor) had used a block of straws to straighten the air out. Again with hindsight the tunnel was probably a prop made by someone who never got the credit.

I can now tell you that making a working Wind tunnel seems simplicity itself the truth is as follows.

Making smoke without fire or hazardous byproducts is not cheap. I tried using a scented oils burner with smoke oil with some success but it required the use of camping fire solid fuel tablets cut in half which if not monitored could escape the burner and start charring the wind tunnel. A full tablet would probably give you more smoke than you could handle and require a new build of the school. So the burner will work but is by no means safe or very good at producing smoke.

The second option is smoke matches used to test flues (I purchased a box of 75 for under £3 from Screwfix) the trouble is that the fumes are not good for the human body and continued exposure may not be good. So unless you can extract the fumes outside they may not be the answer.

Smoke tablets are a third option but again they produce noxious fumes and are reputed to produce 15 cubic meters per tablet which may be more than the system can pull through the chamber resulting in much escaping into the classroom. The enticing thing about these tablets is that you can get red smoke, but I have no test data and cannot recommend the use of them as you may end up with a whole class of pink students. It is worth reminding ourselves that these tablets are intended for use in testing flues.

Finally the use of a smoke machine seems to be the safest way of making smoke although it is the most expensive system involving the largest investment a small machine being about £40 from suppliers such as Maplin. However long term it does show benefits and the smoke is guaranteed to be safe to inhale.

It also however produces so much smoke as to swamp the system, it was considered that the smoke box could be extended but the addition of a 2litre drinks bottle as an expansion chamber, provides enough expansion area and also doubles as a reservoir of smoke produced in a good blast. These machines are intended to fill a dance floor so some attenuation is required.

This video shows how each system fares.

Having to my mind concluded that a disco smoke machine gives the best solution, the final solution is up to you but I would always opt for the machine.

The Design.

Intended to be made at first from one sheet on the A1 the same design can be broken down and made on the A3 Router with a little juggling of the files to get best sheet usage.

It is worth deciding how you are going to feed the machine, there are two options removal of hole A or B. Making this decision would mean you don't need to make the round end cap parts G that on my version is necessary so that I can display the differing options.

Remove Hole A if you are going to use the burner or matches. Hole B if you are going to use a smoke machine.

WindTunnel

Other choices include :-

The front end can have a 100 mm computer fan installed using part C or a 50mm fan using part D. The finished version used a 50mm fan which created adequate air flow for the size of unit and gives the eye time to see the smokes path.

Depending on how you wish to analyse the smoke part E makes a very large pattern and Part F which is the one used in our final version just makes a vertical line of smoke.

G are the parts for the end cap should you choose to make the multiple smoke source version.

The screen is made from clear acrylic bent on a line bender at the pink lines.

Screen

Assemble the panels but do not glue the lid on as you will now need to add the block of drinking straws.

Taking full length straws inset them into the holes in the smoke box from the fan side, push them through by 15mm then run a little glue on the protruding end. As you pull the straw back level the glue should be drawn into the hole.

Straws

Once the smoke tubes have been fixed the shorter tubes can be glued in place, they want to be level with the edge of the screen area and the air intakes.

It is also worth using the offcuts to build up a straw wall on the fan side of the screen, this ensures the fan doesn't cause the air to spiral like a plug on the way out.

Wind

It is also worth fitting a mesh over the fan to stop any loose straws damaging the motors.

Mesh

Car

Main Body Drawing - Download

Screen Drawing - Download