Build a Wind Tunnel with Smoke Tests

Design a honeycomb flow straightener and watch smoke flow over 3D-printed airfoils.

Introduction

30 Second Summary

Every airplane wing, wind turbine blade, and race car spoiler owes its shape to one thing: how air flows around it. Engineers figure out the best shapes by watching smoke and air move around them in wind tunnels.

In this project, you will complete your desktop wind tunnel by designing a honeycomb flow straightener, printing NACA airfoil test models, and building a smoke visualization system that makes airflow visible to the naked eye.

What You'll Build

You will light incense inside a smoke chamber, watch white streams of smoke flow over wing shapes you designed and printed yourself, and see exactly why airplane wings generate lift.

By the end of this project, you'll have:

A 3D-printed hexagonal honeycomb flow straightener that converts chaotic fan turbulence into smooth, parallel airflow.
Two NACA airfoil test models (one symmetric, one cambered) that you can mount in the tunnel to see how wing shape changes airflow patterns.
An incense-based smoke visualization system that channels multiple visible smoke streams through the test section so you can watch aerodynamics happen in real time.
Secret Mission: Build a rotating sting mount with angle-of-attack markings so you can precisely adjust the airfoil angle and observe flow separation and stall.

Are there any prerequisites?

This project continues from a prior wind tunnel build. You need a 3D-printed tunnel shell with an acrylic viewing window, integrated lighting, and a 5-inch fan on hand before you start.

Before We Start

Before you start building, take a moment to lock in what you are creating and why it matters. You are going to turn your 3D-printed tunnel shell into a fully operational wind tunnel that produces visible smoke streams flowing over airfoil shapes you designed and printed yourself.

Install the Fan and See the Problem

Your wind tunnel shell is ready, but right now it is just an empty tube. Before you design any flow-conditioning components, you need to install the fan and experience what raw, uncontrolled airflow actually looks like inside the tunnel.

This step gives you a baseline. Once you see how chaotic the airflow is without any treatment, you will understand exactly why the honeycomb flow straightener in the next step matters.

In this step, get ready to:

Mount the 5-inch fan at the exhaust end of the tunnel.
Build a yarn tuft flow probe to visualize airflow direction.
Map the airflow quality across the entire test section.

Mount the fan at the exhaust end

The fan is the engine of your wind tunnel, but where you place it matters. Mounting the fan at the exhaust end so it pulls air through the tunnel is a deliberate engineering choice.

Position your 5-inch fan at the exhaust end of the wind tunnel shell. This is the downstream end, where air exits the tunnel.
Orient the fan so it pulls air through the tunnel. Check the airflow direction arrow printed on the fan housing. The arrow should point away from the tunnel, showing air being exhausted outward.
Secure the fan to the tunnel shell using screws, strong tape, or a friction fit, depending on your shell design. Make sure the connection is snug so air gets pulled through the tunnel, not around the edges of the fan.
Turn on the fan to confirm it runs.
Hold your hand at the intake end (the opposite end from the fan). You should feel air being steadily drawn into the tunnel.

Why does the fan pull air instead of pushing it?

If you placed the fan at the intake end pushing air in, the spinning blades would create swirling turbulence that carries through the entire test section. Every test you run would be contaminated by the fan's own wake.

By pulling from the exhaust end, blade turbulence stays downstream and never reaches the area where you observe your test models. This is the same approach used in professional and educational wind tunnels.

Not feeling airflow at the intake?

Check the fan orientation. The airflow direction arrow on the housing should point away from the tunnel, not into it.
Make sure the fan is seated snugly against the tunnel opening. Gaps around the edges let air bypass the tunnel entirely.
If your fan has multiple speed settings, try the highest setting to confirm the motor works before adjusting down.

Still stuck? Help me troubleshoot my wind tunnel fan mounting.

Build a yarn tuft flow probe

Now that the fan is running, you need a way to see how the air is actually moving inside the tunnel. Air is invisible, but yarn tufts are one of the simplest tools in aerodynamics for making airflow patterns visible.

Cut 4-5 pieces of yarn or lightweight thread, each about 3 inches long.
Tape them to a pencil or thin dowel rod, spacing them evenly along its length.

This is your flow probe. Each piece of yarn will align with the local airflow direction at its position, making the invisible air currents visible.

Before you test the probe, think about what you expect to see. Will all the tufts point neatly in the same direction, or will they each do something different?

Hold the probe in the center of the test section with the fan running.
Watch the tufts carefully through the acrylic window.

The tufts flutter wildly and point in random, shifting directions. This is turbulent flow. The air is churning and swirling instead of flowing in smooth, parallel streams.

What is turbulent flow?

Turbulent flow is chaotic, irregular air movement where speed and direction change unpredictably from moment to moment. Your tufts are showing you this chaos in real time.

Clean aerodynamic testing requires the opposite: laminar flow, where air moves in orderly, parallel layers all heading the same direction. Converting one into the other is the challenge you will tackle next.

Map the airflow across the test section

You have seen the turbulence at the center of the tunnel. Now find out whether the flow is any better near the edges or walls.

Move the probe slowly to a position near one of the side walls. Pause and watch the tufts for a few seconds.
Move it close to the top of the test section. Observe the tuft behaviour.
Move it close to the bottom. Again, watch the tufts.
Try the corners and anywhere else you can reach.

The flow is uneven everywhere. Some spots may feel stronger than others. Some tufts may spin in circles. The pattern changes from moment to moment, with no consistency.

The tunnel moves air, but the airflow is too chaotic for any meaningful aerodynamic testing. Smoke in this flow would show a jumbled mess, and you would never see clean patterns around a test model.

Why go through this if it does not work yet?

Experiencing the problem firsthand gives you a baseline you can compare against after every improvement. When you install the honeycomb in the next step and re-test with the same probe, the difference will be dramatic and unmistakable.

You now have a clear picture of the problem: your tunnel has airflow, but it is rough, uneven, and turbulent. In the next step, you will design and 3D print a hexagonal honeycomb flow straightener that transforms this chaos into smooth, parallel streams.

Design and Print the Honeycomb Flow Straightener

In the last step, you held yarn tufts in the test section and watched them flutter in every direction. The airflow is there, but it is chaotic and uneven.

The fix is a honeycomb flow straightener. Hundreds of narrow hexagonal channels force each stream of air into its own parallel tube, breaking up large eddies and aligning the flow into smooth, uniform streams. In this step, you will design one in CAD, 3D print it, and install it at the intake end of your tunnel.

In this step, get ready to:

Design a hexagonal honeycomb grid in your CAD software.
3D print the honeycomb and sand it smooth.
Install the honeycomb and verify improved airflow with yarn tufts.

Design the honeycomb grid in CAD

The honeycomb needs to fit snugly inside your tunnel's cross-section and have the right cell geometry to straighten the airflow. Three dimensions matter most: cell size, wall thickness, and depth.

Open your CAD software and create a new project for the honeycomb flow straightener.
Design a hexagonal grid with cells that have an inner diameter of about 10mm and a wall thickness of 1mm.
Set the overall depth of the honeycomb to 80mm. This gives you a length-to-diameter (L/D) ratio of 8, which falls in the optimal range of 6 to 10 for turbulence reduction.
Size the outer shell to match your tunnel's internal cross-section (approximately 5 inches by 5 inches, or about 127mm by 127mm). The honeycomb should slide into the tunnel snugly without large gaps around the edges.

What is the L/D ratio and why does it matter?

The L/D ratio is the length (depth) of each honeycomb cell divided by its diameter. A deeper cell forces air to travel a longer parallel path, which does a better job of straightening the flow.

Research shows the optimal range is 6 to 10. Below 6, the cells are too shallow to fully align the air. Above 10, the extra depth adds friction without much improvement. At an L/D of 8 (10mm cells, 80mm deep), you hit the sweet spot.

Why hexagonal cells instead of square or circular?

Hexagonal cells pack together without any gaps, unlike circles. They also have the lowest pressure loss of any common cell shape.

At L/D of 6, hexagonal cells have a pressure loss coefficient of 0.2, compared to 0.22 for square and 0.3 for circular. Less pressure loss means more of the fan's power goes toward moving air through the tunnel instead of being wasted as friction in the honeycomb walls.

Once your design is complete, look through the model from one end in your CAD viewport. You should see a clean grid of hexagonal openings with no overlapping geometry or merged walls.

Print and sand the honeycomb

Print orientation is critical for this part. The hex cells need to run vertically (standing up) so each cell wall prints as a continuous surface without internal supports.

Export your honeycomb design as an STL file from your CAD software.
Import the STL into your slicer and orient the model so the hex cells run vertically (standing up on the build plate).
Set the slicer to use 2 to 3 perimeter walls for cell wall strength.
Use low infill (10 to 15 percent is sufficient since the hex walls are already thin).
Start the print. Depending on your printer and settings, this may take several hours.

Why print with the cells standing up?

When the hex cells run vertically, each cell wall prints as a continuous vertical surface. If you printed the honeycomb on its side, the cells would need extensive internal supports that are nearly impossible to remove cleanly. Vertical orientation gives you clean, open channels with no post-processing inside the cells.

Once the print finishes, remove the honeycomb from the build plate and hold it up to a light source. Look through from one end. You should be able to see light through every single cell.

Inspect every cell for blockages, stringing, or blobs. Each cell must be fully open for air to flow through.
Sand any rough edges or imperfections on the cell walls with fine sandpaper (220 grit or higher). Surface roughness inside the cells disrupts airflow, so take your time getting the interior surfaces smooth.

Cells blocked or filled in?

If a few cells are partially blocked by stringing, use a small drill bit or piece of wire to carefully clear them out.
If stringing fills many cells across the print, try reprinting with higher retraction settings and a slightly lower print temperature.
If the outer shell doesn't match your tunnel dimensions, re-measure your tunnel's internal cross-section and adjust the CAD model.

Need more help troubleshooting your print?

Install the honeycomb and re-test with yarn tufts

Now for the moment of truth. The honeycomb goes at the intake end of the tunnel, opposite the fan. Air enters through the honeycomb, gets straightened into parallel streams, flows through the test section, and exits through the fan.

Slide the honeycomb into the intake end of your tunnel. It should fit snugly against the tunnel walls.
If there are small gaps around the edges, seal them with tape so air cannot bypass the honeycomb cells.
Turn on the fan.

Before you test, think about what you expect to see. When you hold the yarn tuft probe in the test section now, will the tufts behave the same way they did in Step 1, or differently? What do you think will change?

Pick up your yarn tuft flow probe from Step 1 and hold it in the center of the test section.
Move the probe slowly across different positions in the test section: center, near the edges, and close to the walls.

The difference should be dramatic. The tufts now point straight downstream with barely any flutter. At different positions across the cross-section, the tufts should all point in roughly the same direction.

What just happened?

Without the honeycomb, large turbulent eddies from the fan swirled through the entire test section. The honeycomb broke those eddies into hundreds of tiny streams, each confined to its own 10mm channel.

By the time the air exits the honeycomb, each stream is flowing parallel to its neighbors. The result is smooth, laminar flow across the entire test section. You just used the same principle that full-scale wind tunnels use.

Tufts still fluttering?

Check for gaps between the honeycomb and the tunnel walls. Even small gaps let unstraightened air bypass the cells. Seal any gaps with tape.
Look through the honeycomb cells again. Blocked or partially filled cells reduce the straightening effect. Clear any obstructions.
Make sure the honeycomb is at the intake end (opposite the fan), not between the fan and the test section.

Still seeing turbulent flow after checking all three?

Your tunnel now produces smooth, parallel airflow across the entire test section. Next up, you will design and print real airfoil shapes to test in that clean flow.

Design and Print NACA Airfoil Test Models

Your honeycomb straightener has transformed the tunnel's airflow. The yarn tufts point straight downstream, confirming smooth, near-laminar flow. You have a working wind tunnel, but a wind tunnel without test models is like a microscope without slides.

In this step, you will design and 3D print two NACA airfoils. NACA airfoils are the standard test shapes used in real wind tunnels. Their four-digit naming system directly encodes each wing's shape, so designing them from the numbers alone teaches you the aerodynamics built into every profile.

In this step, get ready to:

Design two NACA airfoils (symmetric and cambered) in your CAD software.
3D print and sand both airfoils for a smooth surface finish.
Fit-test both airfoils in the test section on dowel rods.

Decode the NACA naming system and design both airfoils

The NACA 4-digit naming system tells you exactly what shape a wing has, just from its number. Each digit encodes a specific aerodynamic property.

What do the four digits in a NACA airfoil name mean?

The NACA 4-digit system breaks down like this:

First digit: Maximum camber as a percentage of the chord length (how curved the wing's center line is).
Second digit: Location of maximum camber in tenths of the chord from the leading edge (where the curve peaks).
Last two digits: Maximum thickness as a percentage of the chord length (how fat the wing is).

You will design two airfoils that demonstrate fundamentally different aerodynamic behavior. Start with the NACA 0012, a symmetric airfoil.

Open your CAD software and create a new project for the NACA 0012.
Decode the name: "00" means zero camber (the wing is perfectly symmetric top-to-bottom). "12" means the maximum thickness is 12% of the chord length.
Set the chord length to 80mm.
Set the span to approximately 120mm. This is close to your tunnel's internal width, which forces airflow over the top and bottom surfaces instead of around the tips.
Add a 6mm hole through the center of the airfoil for a mounting rod.

Your NACA 0012 should look like an elongated teardrop, perfectly symmetric above and below the center line. Confirm you can see this symmetry in your CAD preview before moving on.

Now create a second airfoil: the NACA 2412.

Create a new project in your CAD software for the NACA 2412.
Decode the name: "2" means 2% maximum camber. "4" means the camber peak is at 40% of the chord from the leading edge. "12" means 12% maximum thickness, same as the 0012.
Use the same chord length (80mm), span (120mm), and 6mm mounting hole as the 0012.

What makes the 2412 different from the 0012?

The NACA 2412 has a curved center line (called the mean camber line). The top surface bulges more than the bottom. This asymmetry is what makes a wing generate lift even when pointed straight into the airflow.

The symmetric 0012, by contrast, only generates lift when tilted at an angle to the flow. You will see this difference firsthand when you run smoke over both shapes in a later step.

Look at both airfoil profiles side by side in your CAD software. The 0012 should look perfectly symmetrical. The 2412 should have a visibly curved center line, with the top surface fuller than the bottom.

Both profiles look the same?

The camber on a 2412 is subtle (only 2% of the chord). Zoom into the leading edge area in your CAD software. The 2412's upper surface should curve slightly more than the lower surface. If both look identical, double-check that you entered the camber parameters correctly.

Help me check my NACA 2412 airfoil dimensions in CAD.

Print and sand both airfoils

Surface quality matters for airfoil testing. Rough surfaces trip the airflow into turbulence early, which defeats the purpose of your honeycomb. These print settings prioritize a smooth finish.

Slice the NACA 0012 with the flat trailing-edge side facing down on the print bed. This orientation gives the curved surfaces the best print quality.
Set the layer height to 0.12-0.16mm for fine resolution on the curved surfaces.
Set infill to 100%. A solid airfoil is stronger and gives you a smoother exterior surface.
Start the print for the NACA 0012.

While the 0012 prints (or after it finishes), slice and print the NACA 2412 with the same settings: trailing edge down, 0.12-0.16mm layer height, 100% infill.

Once both prints are complete, sand them smooth.

Sand all surfaces of both airfoils with fine sandpaper (220 grit or higher). Focus on removing layer lines and any stringing from the print.
Pay extra attention to the leading edge (the rounded front) and the upper surface of the 2412. These are where airflow speed is highest, so bumps here have the greatest effect.
Clear any debris from the 6mm mounting hole so a rod slides through cleanly.

Run your fingertip along both airfoils. They should feel smooth with no obvious ridges or bumps.

Smoother surfaces mean cleaner results

Surface roughness causes the boundary layer of air flowing over the wing to transition from smooth (laminar) to chaotic (turbulent) earlier than it should. The smoother your print, the more accurately your smoke tests will reflect the airfoil's true aerodynamic behavior.

Mounting hole is too tight or too loose?

FDM printers tend to shrink holes slightly. If a 6mm rod does not fit, gently ream the hole with a drill bit or round file. If the hole is too loose, wrap a small strip of tape around the rod to create a snug fit.

Help me fix my airfoil mounting hole size.

Mount and test-fit both airfoils in the tunnel

Each airfoil needs a mounting rod that holds it in the center of the airflow. The rod passes through the airfoil and extends below the tunnel floor so you can hold or support the model during testing.

Insert a 6mm dowel rod (or metal rod) through the NACA 0012's mounting hole. The rod should extend far enough below the tunnel floor to hold securely.
Place the mounted 0012 in the test section of your tunnel. Position it near the center of the cross-section.
Check that the airfoil has clearance on all sides. The tips should be close to the tunnel walls but not touching or scraping.
Remove the 0012 and repeat the same fit-test with the NACA 2412.

Before you compare the two airfoils, predict what visible difference you expect to see when you hold them side by side. Think about what the NACA numbers told you about each shape.

Hold both airfoils side by side with their leading edges aligned. Look along the chord from the trailing edge toward the leading edge.

The NACA 0012 has a perfectly flat, straight mean line. The top and bottom surfaces mirror each other exactly. The NACA 2412 has a curved mean line. The top surface arcs higher than the bottom, especially around the 40% chord point. That curve is the camber that will create lift in your smoke tests.

Airfoil does not sit centered in the tunnel?

If the airfoil is too wide and scrapes the walls, sand the span tips down slightly until it fits with a small gap. If it is too narrow and has large gaps at both ends, air will flow around the tips instead of over the surfaces. You may need to reprint with a wider span.

Help me size my airfoil to fit the wind tunnel test section.

You now have two professional-grade test models ready for your wind tunnel. Next up, you will build a smoke visualization system that makes the airflow over these shapes visible to the naked eye.

Build the Smoke Visualization System

Your airfoils are printed, sanded, and fit-tested in the tunnel. Now you need a way to actually see what the air is doing around them.

Yarn tufts showed you flow direction, but they can only reveal what's happening at the exact points where they're tied. They can't show you the acceleration over the top of a wing, the stagnation point at the leading edge, or the swirling wake behind a shape.

Smoke makes the entire flow field visible at once. In this step, you'll build an incense-based smoke system based on NASA's proven "Little Smokey" wind tunnel design.

In this step, get ready to:

Build a smoke chamber from a small metal can.
Assemble a CPVC smoke delivery pipe with multiple outlet holes.
Test the complete system and observe visible smoke streams in the tunnel.

Build the smoke chamber

The smoke chamber holds burning incense and collects the smoke in an enclosed space. The fan's suction pulls air (and smoke) through a pipe and into the tunnel, so the incense never sits inside the tunnel itself.

Find a small metal can with a removable lid, such as a soup can or coffee tin.
Drill or punch a hole in the side of the can near the bottom, slightly larger than 1/2-inch CPVC pipe.
Line the bottom of the can with a piece of aluminum foil to protect the metal from direct incense heat.
Hold a piece of 1/2-inch CPVC pipe up to the hole to confirm it fits through snugly.

Keep the smoke chamber outside the tunnel

Incense burns at temperatures far above PLA's glass transition temperature of approximately 55-60 degrees C. PLA starts to soften and deform above 50 degrees C.

The NASA Little Smokey design keeps all heat sources outside the tunnel and routes cooled smoke through CPVC pipe. By the time smoke reaches the PLA tunnel parts, it has cooled to a safe temperature.

Assemble the smoke delivery pipe

A single pipe with multiple small holes creates parallel smoke streams. This is called a smoke rake. Multiple visible streams give much better flow visualization than a single smoke source because you can see the flow pattern across the entire cross-section of the test area.

Cut a piece of 1/2-inch CPVC pipe long enough to reach from the smoke chamber into the tunnel through the tunnel wall.
Drill or cut a small entry hole in your tunnel wall, sized for the CPVC pipe to pass through.
At the tunnel end of the pipe, drill 5 small holes (about 2mm diameter) spaced evenly across the pipe.
Cap the end of the pipe so air is forced out through the drilled holes instead of the open end.
Connect the pipe to the smoke chamber can using a 1/2-inch CPVC 90-degree elbow, so the pipe enters the can from the side through the hole you drilled earlier.

Blow gently into the open end of the pipe (the end that connects to the can). You should feel air exiting from all 5 drilled holes at the tunnel end. If any hole feels blocked, clear it with a drill bit or needle.

Why 5 holes instead of one opening?

A single smoke stream only shows what the air is doing along one narrow path. Five parallel streams let you see the flow pattern across the full width of your airfoil at once. You'll be able to watch individual streams curve, separate, or merge as they encounter different parts of the test model.

Pipe doesn't fit through the tunnel wall?

If the entry hole is too tight, widen it slightly with a round file or by re-drilling with a larger bit. The pipe should slide in without forcing. If the hole is too loose, wrap a layer of tape around the pipe at the entry point to create a snug seal.

help me troubleshoot fitting the CPVC pipe through my wind tunnel wall

Test the smoke system

Everything is assembled. The smoke chamber is connected to the delivery pipe, the pipe enters the tunnel through the wall, and the fan is ready to pull air through. Time to see if it works.

Before you light the incense, think about this: once you seal the lid and turn on the fan, where do you think the smoke will go? Will it be pulled into the tunnel, or will it leak out of the can?

Light 2 cone-shaped incense sticks and place them on the aluminum foil inside the smoke chamber can.
Seal the lid on the can.
Turn on the fan.
Watch the tunnel end of the delivery pipe through your acrylic viewing window.

Within a few seconds, the fan's suction draws smoke from the burning incense through the CPVC pipe and out the 5 drilled holes. You should see distinct white smoke streams flowing through the test section. The streams should be roughly parallel thanks to the honeycomb flow straightener you installed earlier.

Follow the 10-12 minute safety limit

Limit each smoke run to 10-12 minutes. This prevents the plastic components from heat-soaking over time.

After each run, remove the incense from the can and run the fan for 1 minute with the smoke chamber lid off. This cools the plastic parts before your next session. Work in a well-ventilated area throughout.

Not seeing smoke in the tunnel?

Check that the incense is still burning. Cone incense can go out if the lid was sealed before the ember was fully established. Relight if needed and wait 10-15 seconds before sealing.
Check for air leaks where the pipe enters the can. If the fit is loose, wrap tape around the joint to seal it. The fan needs to pull air through the pipe, not through gaps.
Confirm the delivery pipe end is capped. If the end is open, most smoke exits there instead of through the 5 small holes.

Help me troubleshoot my wind tunnel smoke visualization system

You now have a fully operational smoke visualization system. White smoke streams flow through your test section in parallel lines, and you can watch them through the acrylic window. Next up, you'll mount your NACA airfoils in the flow and see real aerodynamics in action.

Run Smoke Visualization Tests Over Your Airfoils

Your smoke visualization system is built and producing visible streams through the test section. The tunnel is equipped, the airfoils are printed, and everything is ready for the real question: what happens when those smoke streams meet your wing shapes?

This step is the payoff. You will mount each test model in the smoke streams and observe real aerodynamic phenomena through your acrylic window. You will see why wings generate lift, and why shape matters more than size when it comes to drag.

In this step, get ready to:

Test the NACA 0012 symmetric airfoil and observe smooth, attached flow producing zero lift.
Test the NACA 2412 cambered airfoil and observe how camber creates lift even at zero angle.
Test a blunt object and compare its turbulent wake to the clean wake behind streamlined airfoils.

Remember the 10-12 minute limit

You will run multiple tests in this step. Keep each smoke session under 10-12 minutes to prevent heat-soaking the plastic components. Between sessions, remove the incense and run the fan for 1 minute with the smoke chamber lid off to cool everything down.

Mount and test the NACA 0012 symmetric airfoil

The NACA 0012 is your baseline. Because it is perfectly symmetric (zero camber), it should produce zero lift at 0 degrees angle of attack. The smoke will show you exactly what "zero lift" looks like.

Slide the NACA 0012 airfoil onto its 6mm dowel rod.
Insert the rod through the tunnel floor so the airfoil sits in the center of the test section, with clearance on all sides.
Position the airfoil at 0 degrees angle of attack. The chord line (the straight line from leading edge to trailing edge) should be parallel to the airflow direction.
Light 2 cone-shaped incense sticks and place them on the aluminum foil inside the smoke chamber.
Seal the lid on the smoke chamber.
Turn on the fan.

Before you look through the acrylic window, predict what the smoke will do when it reaches a perfectly symmetric shape. Will it behave differently on the top surface compared to the bottom?

Look through the acrylic window. The smoke streams split evenly above and below the airfoil, flowing smoothly along both surfaces and reuniting behind the trailing edge. This is attached flow over a symmetric shape.

What does symmetric flow tell you about lift?

The air moves at the same speed over both surfaces, creating equal pressure above and below. Equal pressure means no net upward or downward force. This is why a symmetric airfoil at 0 degrees produces zero lift.

Try holding the tuft probe from earlier at different spots across the test section. The tufts should still point straight downstream, confirming that your honeycomb is doing its job.

Swap in the NACA 2412 cambered airfoil

The NACA 2412 has a curved upper surface. Its 2% camber means the top of the wing is slightly more curved than the bottom. Before you swap it in, predict what that extra curvature will do to the smoke streams. Will the flow still look symmetric?

Turn off the fan.
Remove the NACA 0012 from the test section.
Slide the NACA 2412 onto the 6mm dowel rod and insert it in the same position, at 0 degrees angle of attack.
Turn the fan back on and observe through the acrylic window.

This time, even at zero angle, the smoke streams curve more tightly over the top surface than the bottom. The air moves faster over the curved top (creating lower pressure) and slower along the flatter bottom (creating higher pressure). This pressure difference is what creates lift.

You are seeing Bernoulli's principle in real time.

Why does the cambered wing create lift at zero angle?

The curved upper surface forces air to travel a longer path. To keep up with the air flowing underneath, the upper air must move faster. Faster air creates lower pressure above the wing. The higher pressure below pushes the wing upward.

This is exactly how airplane wings work. The camber built into the NACA 2412 generates lift without needing to tilt the wing. Compare this to the NACA 0012, which needed to be tilted (given a positive angle of attack) to create any lift at all.

Not seeing a clear difference between the two airfoils?

Make sure the NACA 2412 is oriented correctly. The more curved surface should face up. If it is flipped upside down, the camber will push air downward instead of generating visible upper-surface acceleration.

Also check that the smoke streams are flowing steadily. If the incense has burned low, the smoke may be too faint to see the difference. Replace with fresh incense sticks if needed.

Still having trouble seeing the flow pattern?

Test a blunt object to see why streamlining matters

Your airfoils are streamlined shapes designed to let air flow smoothly around them. What happens when airflow hits something that is not streamlined at all? Find a small blunt object to test. A small block of wood, a printed cylinder, or even a small can turned sideways will work.

Turn off the fan and remove the NACA 2412 from the test section.
Place your blunt object in the center of the test section. Position it so a flat face points directly into the airflow.
Turn the fan back on and observe through the acrylic window.

Before you look closely, predict what the smoke will do when it hits the flat front face of the object. Will it flow smoothly around the shape like it did with the airfoils?

The smoke streams slam into the front face and separate violently. Behind the object, a chaotic turbulent wake forms. The smoke swirls, reverses direction, and takes a long time to settle back into parallel streams.

Compare the size of this wake to the thin, clean wake you saw behind the airfoils.
Turn off the fan and remove the incense from the smoke chamber to end this session.
Run the fan for 1 minute with the smoke chamber lid off to cool the plastic components.

What does the wake size tell you about drag?

The larger the wake behind an object, the more energy the airflow loses pushing past it. That lost energy is drag. Your blunt object created a massive, chaotic wake because the air could not follow the sharp edges and had to separate from the surface.

Your airfoils created a thin, narrow wake because their streamlined shape guided the air smoothly around the body. This is exactly why cars, planes, and submarines use streamlined shapes. The smoother the flow stays attached, the less drag the object creates.

Secret mission

Build a Rotating Sting Mount with Angle Markings

You have watched smoke flow over your airfoils at a fixed angle. But every wing has a breaking point. Design and 3D print a rotating disc mount with precise degree markings, then sweep the NACA 2412 through increasing angles of attack until you watch the airflow tear away from the upper surface and the wing stalls.

Clean Up Your Resources

This project uses only physical materials with no cloud resources, subscriptions, or ongoing costs. Decide whether to keep your wind tunnel assembled for future testing, store it between sessions, or dispose of everything.

Resources you used:

3D-printed parts: honeycomb flow straightener, NACA 0012 airfoil, NACA 2412 airfoil, rotating sting mount disc.
Smoke system components: metal can with aluminum foil lining, CPVC smoke delivery pipe with drilled holes, CPVC 90-degree elbow, cone-shaped incense.
Mounting hardware: 6mm dowel rod, blunt test object (flat plate or cylinder).
Wind tunnel assembly: 3D-printed shell with acrylic viewing window, integrated lighting, and 5-inch fan.

Keep everything running

No action needed. Choose this if you plan to keep testing airfoils or building new test models. Your wind tunnel is a permanent piece of equipment with no ongoing costs.

Store the tunnel in a dry, room-temperature location away from direct sunlight. Prolonged UV and heat above 50 degrees C can warp PLA parts.
Disassemble the smoke chamber between sessions. Remove any incense ash and wipe the aluminum foil lining to prevent residue buildup.
Clean any smoke residue from the acrylic viewing window with isopropyl alcohol and a soft cloth.
Keep your airfoils and sting mount stored together so you can quickly set up future test sessions.

Pause - I'll come back to this later

There are no processes to shut down or subscriptions to pause. This option is about storing your tunnel properly for a longer break between sessions.

Remove any remaining incense from the smoke chamber and dispose of the ash.
Disassemble the CPVC pipe from the smoke chamber. Store the pipe, elbow, and can separately to prevent smoke residue from hardening inside the connections.
Clean the acrylic viewing window with isopropyl alcohol to remove any smoke film before it sets.
Remove the airfoils and sting mount from the test section. Store the 3D-printed parts flat to prevent warping.
Leave the honeycomb flow straightener and fan installed in the tunnel shell. These do not need to be removed for storage.

Delete - I don't want to use this again

Remove and dispose of all project materials. Follow these steps to clean up everything.

Remove all 3D-printed parts from the tunnel: the honeycomb flow straightener, both airfoils, and the rotating sting mount disc. PLA is recyclable where industrial composting facilities are available. Check your local recycling guidelines. If industrial composting is not available, PLA can go in standard household waste.
Disassemble the smoke system. The metal can, aluminum foil, CPVC pipe, and CPVC elbow are all standard household waste and can be disposed of in your regular trash.
Dispose of any remaining cone-shaped incense with your regular household waste.
Remove the dowel rod and blunt test object. These are standard household items and can be disposed of in regular waste.
Remove the 5-inch fan from the tunnel shell. The fan is reusable electronics. If you do not plan to reuse it, dispose of it at an electronics recycling drop-off.
Clean the acrylic viewing window with isopropyl alcohol before disposing of the tunnel shell. The shell is PLA and follows the same disposal as the other printed parts.

That's a Wrap!

Nice work! You just built a fully operational desktop wind tunnel that produces smooth, visible smoke streams over airfoil shapes you designed and printed yourself.

You've learned how to:

Design and 3D print a hexagonal honeycomb flow straightener using real wind tunnel engineering principles (L/D ratio of 8, hexagonal cells for lowest pressure loss) and prove it works by converting chaotic turbulent flow into smooth, laminar flow.
Decode the NACA 4-digit airfoil naming system and use it to design two airfoils from scratch. A symmetric NACA 0012 and a cambered NACA 2412, each 3D printed and sanded smooth for aerodynamic testing.
Build an incense-based smoke visualization system and observe real aerodynamic phenomena through your acrylic window. You saw attached flow over the symmetric airfoil, lift from camber at zero angle of attack, and massive drag wakes behind blunt objects compared to streamlined shapes.
Secret Mission: Build a rotating sting mount with angle-of-attack markings and observe flow separation and stall as you swept through angles from 0 to 20 degrees.

Ready to quiz yourself?