DIY Wind Tunnel

Make a Wind Tunnel for around £20/$25! This is a perfect 'Demo Rig' to show how aerodynamics work - and allow students to examine the aerofoil profile and how much lift it creates, before creating miniatures of historic or modern aircraft. It uses a small balance/scale (±0.1g) to work out how much lift a given wing/aircraft design has over another.

The project was conceived to help Design & Technology teachers have more projects which were not just engaging, but also connected with desirable learnings that prospective employers valued.

One of those experiences was 'designing for a client' - and at first this sounds improbable for a KS3 kid (aged 11-14 years) to do, but then we figured - why not make another subject teacher the 'client'.

This Wind Tunnel could be used to 'Demo' a Physics Lesson, but could also look at Sport Science Lessons (Cycle Helmet Aerodynamics), or even History Lessons (differences between mono/bi/tri-planes - and why quad planes mostly failed!).

I included some preamble about the project and work with DATA, but if you want to crack of with the build - jump ahead to Step 4!

UPDATE: There has been some debate about 'blow' vs 'suck' style Wind Tunnels, and I've tested this, just to show the Science. See notes at the end...there were quite interesting, and both methods have pros and cons.

Reusing Materials & Scrap-stores.

This project is deliberately designed to be economical, and can be made from (double) corrugated card, and scrap materials like PVC water pipes (available in all DIY stores for a few £/$), with some offcuts of wood for the base, and some acrylic/polycarbonate sheet for the sides (LINK). I think most of these will be readily available in most school workshops, but also search of 'children's warehouse' or 'surplus stores' also. Example I used in Bristol, UK: Scrapstore. Likewise, I find it plausible a D&T teacher can get hold of a Fan without having to buy new / second hand. Even if you did buy it all new, this is hopefully still within budget for a term time project.

Essentials:

Scales:

You will need a small scale, ideally better than a ±1g accuracy scale in the Kitchen. Better to use a ±0.01g scale that is used for small quantities of powders, and are pocket-sized. LINK.

Fans:

When I first made this for a TV show (more on that below), the Wind Tunnel was about 40cm(l)x16cm(w)x18cm(h). This actually cost even less than £20, and used a travel LiIon Battery Powered Fan. (e.g. LINK), however, if teaching in schools, I would ensure that students cannot access the Lithium Ion battery inside, as these can be dangerous if shorted. It is better to use a USB one like this (LINK).

For this project with DATA.org.uk, I 'super sized' this to be about 70cm(l)x25cm(w)x28cm(h) - and also used a mains (240v) Fan (LINK). Of course you need to PAT Test this like any other equipment in the school.

Optional Extras:

Depending on how much Engineering you want in this project, for about £75/$85 you can measure the following:

• Pressure using a Manometer. (LINK). Around £45.
• Flow/Wind Speed using an Anemometer. (LINK). Around £15.
• Fan Speed using a Tachometer. (LINK). Around £15.

Having studied Fluid Dynamics at University, I can also say it was not until I worked at Dyson that I really applied that knowledge to problem solving, and it was the hands-on experience that made the equations and theory come alive. Often kids at school can tell you that atmospheric pressure if 101kPa, but if you asked how much pressure the average fan or vacuum cleaner has, they probably have no idea - you really only get this 'sense or numbers' from doing real experiments and designing, so I think these (frankly amazingly cheap) digital devices are a part of that.

Disclaimer/Safety: I have suggested using certain processes and chemicals which should be adapted to the competence of the teacher/class. Please conduct all risk assessments and inform students accordingly. Neither the Author or DATA can assume responsibility for following this guide.

As mentioned, this project has been commissioned by the Design And Technology Association (DATA.org.uk), as at the time of writing the subject has seen a reduction of over 70% since the subject was created. Yet many successful Designers cite D&T as a key subject in their formative years - helping them not only get hands-on experience, but also to learn the 'soft skills' of interviewing and observing people - and what is professionally referred to as 'user research' or 'user centred design'. As much as many creative courses at university are accessible with grades in only Science, Maths, Art and Engineering, D&T evidently gives a rare chance in school to create a real product and test it.

In the attached article, Sir James Dyson alludes to: "Taught well, D&T leads to high value careers in Engineering and Technology" - the key phrase being *Taught well*. When I was at school, D&T was considered a 'doss subject' - an opportunity to mess around in the workshop, often making things only out of wood. It took me many years and an extra degree to get back to what would have been best if I set off on a good D&T course in the first place.

Something has to change.

With the subject in real danger of being obsolete in a few years in the UK, we are at a 'radical candour' moment on needing to speak frankly about where the subject is now, and where is should be in order to regain its status as a serious subject.

The aim of these unquestionably challenging projects is to 'raise the bar' of the subject, in such a way that D&T is seen as a credible career preparation - giving students a taste of the highs and lows of iterative design, and the emotional complexity of working with 'clients'. Nothing said here is intended to upset teachers or governors, but rather to provoke a response that is not gradual - the time for incremental improvement has passed. The subject will fail without significant overhaul.

Please join the debate on Comments here and/or at https://twitter.com/DTassoc and https://www.data.org.uk/

Building on the first project (Squirrel Proof Bird Feeder Challenge - LINK) - which aimed to 'neutralise' the fear of failure, both for Students in doing consecutive design iterations, and taking on 'feedback', but also for Teachers not to feel they have to always guide Students to something 'working flawlessly', for an A-Grade. I've been designing for 2 decades now, and can't think of anything that worked first time flawlessly. Embracing and learning from the failure is vital personal and professional growth, and yes, the Squirrel's is pretty funny, even when it's besting your design!

The Wind Tunnel is an example to inspire Students and Teachers to think where D&T might 'be of service' to other subjects. There are so many 'chalk and talk' subjects, which would benefit from an exciting physical embodiment of the theory on the black/white-board! Some might say that doing this is not pure altruism, but also a good way for D&T Teachers to build more appreciation of their work around the school in general. I'm sure not all teachers feel maligned, but many who I spoke to felt D&T was not regarded as highly as some others, so the act of 'being of service' this might build some bridges in more ways than one!

Perhaps you and your students realise the school needs a Van De Graaff Generator for Physics (I suggest the LOW (9V) Voltage one here), or perhaps the school canteen needs a voting system for the following week's menu, and waste-reducing solution? It could be a device to get balls down safely off the roof, and so on...

It many ways the design does not matter as much as learning to be of service, 'manage a client', and 'deliver on a Brief', on time / specification / budget.

Using a small bandsaw, I set up a distance of around 80mm, using a block of wood as a guide.

I then removed the 'swarf' (ragged bits left over from cutting) with the edge of the ruler.

I then lined the first layer of tubes as show, using some masking tape (placed upside-down) to hold in place.

I used PVC Glue (LINK), but you can use any mild solvent-based glue (like UHU), or if you don't have this - Hot Melt Glue is fine also. Although PVC Glue is rather nasty, if used outside and with a mask, it should be fine, but Hot Melt is of course cheaper and safer and works fine for this too.

Note - I have also added some 'half pipes' to the alternate edges. These are just cut from the same sections, just lengthways (take care to use a push-stick to keep fingers safe).

FYI - There are 10.5 tubes 'wide', and 12 'high', and this gives around a 21cm 'square', using '20mm piping'.

SAFETY TIPS:

• Dust: Please ensure you are using dust extraction.
• Keep Hands Clear: Pipes are round, and if they snag on the sawblade (especially if less than sharp!), they rotate, and can hence rotate your hand suddenly towards the saw. Care should be taken to keep hands well back / to the side (as shown), or to use a clamp/vice if not sure. If students are very new to this, they may even prefer to use a hacksaw, or even a pipe cutter. (LINK). If in doubt, use hand tools over power tools.

Once the glue has been left to set(ideally overnight), it can then be sanded back flush to remove any irregularities.

I then took a scalpel to remove any swarf on the edges, (a ruler will do if not).

I personally think this is an important skill for students to learn / unlearn.... At school you are often taught to 'measure twice, cut once' or to create detailed plans before assembly, and although this is perfectly valid, when prototyping sometimes you want to use a more 'relativistic' method.

When you watch carpenters fitting stairs, or making any other bespoke piece, they are less interested in the exact measurement, and more interested in the 'fit'. This is a great mindset to learn for prototyping.

The fact is, your glued together pipes will likely be slightly 'out', and so it's better to create a 'snug fit' around them with cardboard, and do this by taking a measurement of each piece sequentially. Start with side 1, use this to reference/mark the length of side 2, and so on. Also, you may note I have 'spiralled' the pieces around, so they are all overlapping, rather than having 2 long and 2 short sides like a box.

The advantage of this is speed and fit, even if overall it may be a little 'out'. You may find it useful to discuss the pros and cons of this method, as of course this is great for cardboard modelling, but no aircraft in general!

I used 2-ply corrugated cardboard for this. It came from standard Apple Boxes at markets.

Now that you have the general idea, do the same of the 'end' of the Tunnel.

Arguably this is more of an aesthetic piece, but it provide stability later on for the acrylic, and a visual 'end' which is worth the effort to make. You can also practice creating a chamfer by cutting at an angle also.

Using some 1-play cardboard as this bends better. You can see how I've pulled the card through my hands, allowing it to compress in one direction - and bend. Note the direction of the holes or 'fluting' is key. Cut strips to fit the fan like a 'collar' as shown. I happen to have a fan which had an 'inner' and 'outer' profile as shown, so I decided to make collars for both for a tighter seal, but the outer is sufficient if you are short of time.

As with the point above on 'fitting' vs 'measuring', I could have used "2*Pi*radius" for the circumference, but it is simpler just to cut an oversize strip, mark the intersection, and cut to fit perfectly. Arguably the mathematical approach would have had error and not fit as well.

When you are happy with this, apply Hot Melt glue and stick down a larger piece of card flat on it as shown.

When set/dry - remove and cut out home from inner circle. Leave the outer edge 'square'.

Prepare some card strips as shown, about 25mm/1" wide, and the same size as your Flow Straightener. Form a 'Box' as shown.

Measure the side of the 'inlet' on the left, and the 'outlet' on the right, as shown - and create this 'trapezium' on card. (e.g. mine went from 28cm to 25cm).

Use masking tape to set these in place, and build up as shown.

The wooden sides are pretty straightforward - combine two pieces of wood, to form an 'L' shape. These need to be fitted around the size of the Airflow Straightener (including the Card border).

Once you have this, cut one side of Acrylic/Polycarbonate to the walls - allowing extra for joining to the Wood as shown in later steps.

As with the Squirrel Proof Bird Feeder, careful drill the holes so the screws can pass through. I used screws with a wide head, but of course washers will do also. The point is to spread the stresses/load as much as possible.

Indeed, I saw this as a possible area of improvement, as if you have a very 'boisterous' class, you might want to make it all from wood, and inset 'windows' to make it stronger. This is all good 're-design' feedback depending on your class.

The plastic can be cut on any saw you have in the workshop, and to finish, sand the edge, and if you like polish it on a polishing wheel, and.or flame with a mini blowtorch...Depending on how capable/trustworthy your class is.

With the protective blue plastic removed from the plastic sheet, the viewing now is clear. (FYI - it's best to leave on until the last minute, as it saves getting the plastic scratches, but also is a good surface to mark on for cutting).

You can now get your aircraft building going, if you have not already in parallel to this!

I suspect there may well be a few D&T teachers who have made a balsa wood glider, so this should be easy enough. For those of you who have not, you can either buy a kit (eg. LINK) - small enough to fit inside your wind tunnel, or you can make one from scratch...

This might sound intimidating, but this is a cheap challenge for school kids to attempt. The only 'tweak' I would say is to advise using Balsa Cement (LINK), or UHU (LINK), which is not as risky as Super Glue.

You can find all sorts of historic and modern planes online, and simply search of 'plan' as well. If like me you wanted the Wright Bro's - here you go (LINK). Simply print these out to scale, and then here's the clever bit - apply sticky tape over the stop, so the balsa does not stick!

You can then cut out small Aerofoil Profiles from 2mm Balsa Wood (LINK), as well as cutting long strips/spars. The key thing is less the skill, and more having a sharp knife. I recommend teaching your students how to use a Scalpel over a craft knife, I have used both and injured myself far less with the former. The No.3 Handle and No.10A blades are good all-rounders (LINK).

Note: for the keen eyed among you, you'll note that I made the Wright Bro's plane backwards - thinking that the smaller wings were at the back - when they are actually at the front! I personally think this will be a funny talking point for the class. Luckily I realised this and simply flipped the rings around, and 'got lucky', but goes to show you how much aviation has changed over the years!!

When I rotated the wing by 180 degrees, I also realised another thing - the drawings by Louis P. Christman on the weblink above, are actually not symmetrical, as the left wing is actually about 5% smaller than the right wing. So these are all good lessons to note as a designer - mistakes happen and need correcting as you go.

Once you have the Wings made, you can use a file to create a more rounded profile, as it's likely the spars will need some sanding to 'curve' with the aerofoil profile.

Finish with a fine grit sandpaper.

If you like you can apply a light coating of PVA Glue (diluted 50/50 with water) to add strength. Sand down again when dry.

Using PVA Glue, I added some Tissue paper to the wings as shown. Try to use one piece, and glue on, wrapping around the wing as you go. Trim excess with scissors and leave to dry for an hour or two.

As you can see, I added some cross braces and struts to fit. As mentioned previously, I cut these to 'fit' rather than a measurement, and made sure to 'mirror' them to the other side to keep things as even as possible. I added the rudder also.

I used a couple tongue depressors (LINK) and some bolts with wingnuts to make an articulating stand, that has a metal washer on top - such that the plane(s) can be located with magnets, as interchanged easily.

This is perhaps a little elaborate, but a good design challenge. Your students might find that they simply modify some 'helping hands' or flexi arms like this (LINK). Even small design challenges like this might be worth assigning to small teams or individuals to perfect.

I used EZ Dope, which is a less 'nasty' version of the old smelly (likely toxic) form that was used when I was a kid. (LINK). Paint this on and allow to dry overnight until tight and thoroughly dry.

Compare your model with the plans. This is a good warm-up exercise, and may well be a good idea to do this before the wind tunnel even, so students can gain confidence with tools and materials, etc.

It also makes sense to know what your sizes are - so as your tunnel/planes fit.

This is of course a rudimentary method of evaluating aeronautical efficiency, and much could be improved upon regards the deeper science I'm sure, but for KS3 (11-14 year olds) this seems a fair 'starter' or 'primer' to get them to consider their designs.

To do this, simply 'tare' the plane/aerofoil, start the fan, and see how 'negative' the scale goes. Of course if you have a smaller wing, it may 'loose' less, but be more efficient (in terms of its area or weight) than a larger win that 'lost' more. So there is a bit of approximation here, but you can of course go as deep as the classroom is willing, but I suspect students will appreciate how subtle the design of human flight and natural flight is - everything from Attack Angle to surface friction of the tissue paper will make a difference.

Warning - I am showing a disassembly of a 240V mains electricity fan. It is unplugged, and only operated when the cover is all back on. If you are not qualified to do this (or just unsure) please just use battery powered fans, but you can assume the same line of enquiry...

If you have PAT Testing, and are qualified and confident to do this, you can buy a simple fan like listed above, and remove the star-clip by prying the leaves as shown. I suggest wearing Goggles for safety - these things can ping off, and keep fingers clear to avoid stabbing yourself with the level/tool.

Assuming you have this all done safely, you can simply slide off the Fan and start to take dimensions.

I took measurements of the fan's interior and made a few modifications.

The 3D printer I used (Ender 3) is cheap and still gives very smooth results, and I'm actually impressed that my 'flung together' fan blade gave as good performance as the original. This might sound bad, (for all the effort), but having designed impellers at Dyson, it's hard to just beat a product performance - and especially given the 3D Print given it was rough / not polished, balanced or optimised - is not so bad!

Anyway, in case you were thinking this is incredibly difficult for KS3 students - my empasis is not to always 'be better'. The learning of working between a product and a mod, and iterating the CAD and 3D Print is a great design/re-design cycle that gives contest beyond just 'Learning CAD'.

More than anything else, I think this is a good example of showing that students can modify a key component without having to build everything from scratch. This sort of 'hacking' or 'modding' of off-the-shelf items is very common in Industry and is also just a good lifeskill for any inventor, designer or engineer to master.

This might be a nice integration of CAD and Physics into the D&T subject, as although one can 'copy' a Fan - it's quite another to improve on it.

I printed the blue 'collar' to fit inside, and close the gap between the fan blade edge/tip, and the side. This has the effect of allowing less air to 'backflow' or 'escape' when pushing the air forward, and so the pressure is higher. It may not increase flow speed, but pressure should improve.

You can then look at the angle, profile, thickness and number of blades - all of which can be tested for theory and practice.

To give more context to the metrics, I would also consider investing in a few affordable flow-related digital devices...

You may be interested to know how fast the fan is moving, and a tachometer can do this as shown - adding a small reflective tape to the fan blade, and pointing the Tacho at it.

Between the 3 settings the rpm went from around 900 to 1000 to 1200. This of course is great for working out the efficiency and power of your fan - should you wish to redesign it also!

I tested the wind speed of the fan, with and without the Flow Straighteners - and I'm quite pleased that they are about 90% efficient (10km/hr vs 11.3km/hr). It might be that you try to balance this with using finer tubes, like drinking straws, but this may reduce the flow and speed considerably (unless you use Bubble Tea straws perhaps?). Likewise, you might use larger pipes, but the flow becomes too turbulent (you can see this with smoke or cotton thread on a stick).

I made a 'plate' for to cover the fan, and tested the pressure and compared this with different fan blade designs (more on that later). If you had a totally sealed design of the test chamber you could also try this at the end too.

The final set-up. Hope you like it - but hope you also do it your way!

Would you make yours 'flat packable' if storage is tight?

Do you want to make it bigger?

Are you going to 'hack' a Vape device to make 'smoke trails' (please extract vapours if you do!)?

Perhaps you want to use this for Race-car Design?

Hope you have fun with your new Demo Rig for lessons beyond D&T...

I had the pleasure of working with Sir David Jason and Wise Owl Films to create a series of DemoRigs to show how great British inventions worked in principle, for a Channel 4 TV show in the UK.

As well as learning that the UK also had a crack at getting to the moon (using decommissioned rockets from WWII - seriously), and getting to make scaled down versions - I was also asked to create Demos showing a fundamental principle like the Electric Lightbulb, a Steam Engine, and how Hydraulics work - which we often take for granted in our lives, but these were Designed by designers with D&T-esque skills and mindset.

Others were about recreating what it might have felt like to transmit speech for the first time in human history - such as the Bell Telephone - which to this day is a truly incredible moment that a 'drum, and a wire in vinegar' can transmit sound waves!

Aside from these being fun to recreate, these also need to be designed by students to cope with the hustle and bustle of general teaching life.

For more inspiration: Link: https://www.channel4.com/programmes/david-jasons-great-british-inventions

As to make the point about re-design: It's been great fun to re-design the Wind Tunnel to be larger than the first one I made for the TV show. It still amazes me that humans took to the skies in such a compressed around of time. (LINK).

THE FAN LOCATION:

To 'walk the talk' or 'practice what I preach' - I've had a few comments that give great advice to put the fan on the other side - ie to 'suck air', not 'blow air'...hindsight being a wonderful thing, this honestly makes total sense, to reduce turbulence and keep flow nice an smooth. So if you're read this far - congratulations, you can now use all the tips and process above, but just put the fan on the other side. The benefit of this is simply that it'll be easy enough to modify in card and make another - and crucially - test if it makes a difference! Good luck. I'll do the same soon, when I get a free weekend!

SMOKE TRAILS:

Like in the professional settings, people use smoke trails to investigate laminar flow over the wings and such in a wind tunnel. I'd erred on not doing this, as I was working on a budget, but also I didn't want to use vape pens as a source of 'smoke' - even though they are available un-scented and un-fragranced - it just sent the wrong message for kids to use them! I had suggestions of foggers (but these get stuff wet), but also special dry foggers for model trains, which I need to look at as they are not too expensive (but I'm sceptical they will be smokey enough tbh). Incense sticks were also suggested, but these are pretty scented, so I'm not a huge fan. So I'll keep having a think, but suggestions welcome!

Update: 24 Oct 2022.

I had some good discussion about should the fans blow air over the aerofoil or suck wind through the tunnel, and over the aerofoil. The short answer is that there is no 'best' way to do this, as it depends on what you are trying to do.

Blow:

This is what I originally did, and this gives a good flow and pressure - yielding about 6-7km/hr wind speed. The benefit of this is I can stick my 'cotton tester' (see below) in, and see how the flow 'sticks' to the wing. The downside is, the flow is slightly more turbulent, but not so bad that the principles cannot be taught in school (which was the original intent).

Suck:

In response to questions, I tried this by simply flipping the fan round to the other side. The flow was of course less (as the system is not perfectly sealed, and the fan is not really optimised for this - it's a fan for cooling you, not inducing flow in a wind tunnel. Anyway, so the wind speed drops to between 5-6km/hr for the same set-up - which honestly is better than I expected.

Suck - Vacuum Cleaner.

I also just wanted to illustrate the point that 'suction' is not the same as 'flow'. A vacuum cleaner (a good one) still has very low flow, as when you think about it, it's not really trying to cool you (large volume of air), it's trying to suck up dirt in a small spot. Speed was about 1-1.5km/hr. So no good at all, and very noisy!

Anyway - this is still a fun experiment to get students to understand, and indeed, if they have actually internalised why flow and pressure are related, and how these gives different performances when applied to products, this will honestly put them pretty far ahead in their studies from a tacit learning perspective.

Update 24 Oct 2022:

As mentioned in comments, this 'trick' or technique is used in automotive and aerospace more than you might imagine - it really is a good way to 'feel around' a design and see where things are turbulent, and where flow is good / smooth / laminar.