3D-Print a Wind Tunnel for Airfoil Testing

Build a tabletop wind tunnel and watch fog streamlines reveal airfoil stall.

Introduction

30 Second Summary

Every airplane wing and race car body has been shaped by the same invisible force: moving air. Wind tunnels make that force visible, letting engineers see exactly how air flows around an object.

In this project, you will 3D-print and assemble a tabletop wind tunnel with fog visualization and LED lighting. You will feed fog into the inlet, watch glowing streamlines wrap around a wing shape, and see the moment the airflow tears away.

What You'll Build

Feed fog into the bellmouth, flip on the LEDs, and watch bright white streamlines glide over an airfoil through the clear acrylic viewing panels.

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

A working tabletop wind tunnel built entirely from 3D-printed modular sections that bolt together. Feed fog into the inlet and watch it stream the full length of the tunnel.
A 3D-printed hexagonal honeycomb flow straightener that transforms chaotic, swirling fog into clean parallel streams. You will see the dramatic before-and-after difference with your own eyes.
An LED-lit acrylic test section where glowing fog wraps around a mounted airfoil. Rotate the wing to change the angle of attack and watch the moment the streamlines tear away as the wing stalls.
Secret Mission: 3D-print two airfoils with different profiles and compare how each handles flow separation at increasing angles of attack.

Are there any prerequisites?

You should be comfortable with basic 3D printing (slicing and bed adhesion) and hand tools (cutting, drilling, sanding). No prior aerodynamics knowledge is needed.

Before We Start

Before you start printing parts and gathering materials, take a moment to lock in what you're about to build and why it matters to you.

Gather Materials and Start 3D Prints

Your wind tunnel is built from modular 3D-printed sections that bolt together with printed flanges. Each section serves a specific aerodynamic purpose, from capturing room air to accelerating it over your test object.

The tunnel sections take several hours to print but only minutes to assemble. The smart move is to start your prints first, then gather the rest of your materials while the printer runs.

In this step, get ready to:

Slice and start printing all tunnel shell sections, the honeycomb flow straightener, and a test airfoil.
Gather all non-printed materials (acrylic, LED strip, fan, fog machine, hardware).
Cut and sand the acrylic viewing panels to size.

Slice and start your 3D prints

Your tunnel is made of six distinct printed sections, plus a honeycomb insert and a test airfoil. Each section is sized to fit a 256x256mm print bed.

Design these in CAD or download STL files for each section. Here is what you need to print:

Bellmouth inlet — a flared opening approximately 200x200mm that smoothly captures room air into the tunnel.
Settling chamber — a straight duct approximately 200x200mm internal cross-section, 150mm long. Include a slot to hold the honeycomb flow straightener insert.
Contraction cone — tapers from 200x200mm down to approximately 100x100mm, giving a 4:1 contraction ratio. Approximately 200mm long.
Test section frame — an open rectangular frame approximately 100x100mm internal cross-section, 200mm long. Include slots or lips for acrylic panels on two sides. Print this section in black PLA for contrast against the fog streamlines.
Fan adapter — transitions from the 100x100mm test section exit to a 120mm circle to mount a standard 120mm PC fan.
Junction ring flanges — printed rings with bolt holes (M4 pattern) to connect each section to the next.

What is a contraction ratio?

The contraction ratio is the ratio of the settling chamber's cross-sectional area to the test section's area. Your tunnel uses a 4:1 ratio (200x200mm = 40,000 sq mm down to 100x100mm = 10,000 sq mm).

This compression accelerates the airflow and helps smooth out remaining turbulence before air reaches the test section. A 4:1 ratio is the minimum effective ratio for educational tunnels and keeps the overall build compact enough for a tabletop.

For all structural tunnel shell sections, use these slicer settings:

Material: PLA.
Layer height: 0.2mm.
Walls: 3 walls for structural strength.
Infill: 20% for shell sections.

Start printing your first shell section (whichever has the longest print time). Queue the remaining sections to print after it finishes.

While your first shell sections print, set up the honeycomb flow straightener. This component is what transforms chaotic air into clean, parallel streamlines.

The hexagonal honeycomb flow straightener is a slab of hexagonal tubes that air passes through. Its design parameters matter:

Cell diameter: 10mm.
Wall thickness: 1mm.
Depth: 80mm, giving an L/D ratio of 8 (80 divided by 10). This sits in the optimal range of 7 to 10 for turbulence reduction.
Target porosity of approximately 0.8 (80% open area). With 10mm cells and 1mm walls, you land near 0.82.

What is the L/D ratio?

The L/D ratio is the length of each honeycomb cell divided by its diameter. A higher L/D means the air spends more time inside each tube, which kills more of the perpendicular (crosswise) motion that causes turbulence.

An L/D of 8 hits the sweet spot. Go too low and the cells do not straighten the flow enough. Go too high and you create excessive pressure drop that starves the test section of airflow.

The honeycomb uses completely different slicer settings from the shell sections. There is a clever trick that lets your slicer generate the hexagonal geometry automatically.

In your slicer, configure the honeycomb interior object with 0 walls, 0 top layers, and 0 bottom layers.
Set the infill to 20% hex grid (honeycomb) infill.
This makes the slicer produce the honeycomb geometry as infill pattern, giving you perfectly formed hexagonal tubes without designing each cell by hand.
Print the honeycomb flat so the hex cells run vertically as the print builds layer by layer. This ensures the cell walls are continuous and structurally strong.

Prefer explicit CAD?

If your slicer does not support hex grid infill, you can design the honeycomb as explicit hexagonal tubes in your CAD software instead. Target the same parameters: 10mm cell diameter, 1mm wall thickness, 80mm depth.

Add the honeycomb to your print queue.

Finally, you need a test object to observe airflow around. A symmetric teardrop airfoil is the classic choice for wind tunnel testing.

Design or download a symmetric teardrop airfoil profile, approximately 60 to 80mm chord length and 80mm span.
Add the airfoil to your print queue with the same shell print settings (PLA, 0.2mm layer height, 3 walls, 20% infill).

Check your printer. Your first section should be printing or queued. You will continue gathering materials while the prints run.

STL file too large for your print bed?

If any section exceeds your 256x256mm bed, scale it down slightly or split it into two halves that bolt together with additional flange rings. The bellmouth and contraction cone are the most likely sections to bump against the bed limit.

Help me resize my tunnel sections for my print bed.

Gather non-printed materials

While the printer runs, gather everything else you need. Lay each item out on your work surface as you collect it so you can confirm nothing is missing.

Collect the following materials:

2x pieces of 3mm clear acrylic sheet, approximately 100mm x 200mm (for the test section viewing panels).
1x 12V white or cool white LED strip, approximately 400mm length, with a 12V power adapter or battery pack.
1x 120mm PC fan (any standard 120mm case fan, 12V). A fan with a speed controller (PWM or voltage) is ideal for adjusting airspeed.
1x small handheld fog machine (battery-powered, $20 to $40 range) that uses glycerin or propylene glycol fog fluid.
1x bottle of glycerin-based fog fluid (often included with the fog machine).
1x 1/2-inch CPVC pipe, 100mm long.
1x 1/2-inch CPVC 90-degree elbow.
1x 1/4-inch (6mm) dowel rod, 150mm long.
16x M4 bolts and nuts (for connecting flanges).
Hot glue sticks.
Black electrical tape or gaffer tape (for sealing joints).
1x small piece of aluminum foil (for heat shielding if needed).

What kind of fog machine should I get?

Look for mini fog machines marketed for photography, cosplay, or airflow testing. These use vegetable glycerin and propylene glycol fluid, which produces dense, non-toxic, odorless fog. That is the same type of fluid used in professional wind tunnel visualization.

Any cheap handheld fogger in the $20 to $40 range works well for this project. The professional option is the Vosentech MicroFogger 5 Pro at $250, but it is not necessary for learning the fundamentals.

Confirm every item is laid out on your work surface. You should see the acrylic sheets, LED strip with its power source, fan, fog machine with fluid, CPVC pipe and elbow, dowel rod, bolts and nuts, tape, glue sticks, and foil.

Cannot find a small fog machine locally?

Search online for "mini fog machine" or "portable smoke machine" on Amazon or similar retailers. Filter for battery-powered models under $40. Make sure the listing specifies glycerin or propylene glycol fluid, not oil-based.

Help me find a fog machine for my wind tunnel.

Cut and prepare the acrylic panels

The acrylic panels are the windows you will look through to observe fog streamlines inside the test section. They need to fit snugly into the slots on your 3D-printed test section frame.

Measure the window openings on your 3D-printed test section frame (once it finishes printing). Mark the dimensions on each acrylic sheet with a marker or tape.
Cut the two acrylic sheets to match. Use a utility knife to score and snap, or a fine-toothed saw for a cleaner edge. Leave the protective film on while cutting to prevent scratches.
Sand all cut edges smooth with 120-grit sandpaper. Rough edges can snag or create gaps that leak air.
Test-fit each panel in its slot on the test section frame. It should press in firmly without gaps but not require excessive force.

Do not install the panels yet

Confirm the panels fit, then set them aside. You will install them permanently in the next step when you assemble the test section with LED lighting.

Acrylic cracking while cutting?

Score the acrylic with your utility knife using firm, steady strokes along a straightedge. You need 8 to 10 passes through the same line before snapping. If the acrylic still cracks unevenly, try clamping it along the score line between two flat surfaces before snapping.

Help me cut acrylic sheets cleanly.

Before you move on, take stock of everything. Do you have all the printed sections finished or printing, all the non-printed materials on your work surface, and two cut acrylic panels that fit the test section frame?

You should see: a bellmouth inlet, settling chamber (with honeycomb slot), contraction cone, test section frame (black PLA), fan adapter, junction ring flanges, a hexagonal honeycomb slab, and a symmetric teardrop airfoil. All either printed or still on the printer. Next to them, every item from the materials list laid out and accounted for, plus two acrylic panels cut and sanded.

Everything is ready to build. Next up, you will assemble the test section, the heart of your wind tunnel, with LED lighting and a sting arbor mount.

Assemble the Test Section with Acrylic and LED Lighting

Your 3D printer delivered every tunnel section, and your materials are gathered and ready to go. Now it is time to build the single most important piece of your wind tunnel: the test section.

The test section is where all the action happens. You need clear viewing panels to see inside and LED lighting to make fog visible against the black interior. Without proper lighting, fog streamlines are nearly invisible inside a dark tunnel.

In this step, get ready to:

Install clear acrylic viewing panels and an LED strip for cross-illumination.
Build and install a sting arbor for mounting and rotating airfoils.
Test the lighting to confirm high-contrast fog visibility inside the test section.

Install the acrylic panels and LED strip

Your test section frame is printed in solid black PLA. Black walls absorb stray light, so the only things that glow are fog particles hit by the LED strip. Clear acrylic panels on two sides let you see in without disturbing the airflow.

Take your two cut acrylic panels and the test section frame.
Press-fit the first acrylic panel into one of the viewing slots on the test section frame.
Press-fit the second acrylic panel into the opposite viewing slot.
If the panels are loose in the slots, secure them with a thin bead of hot glue along the edges.
Look through one of the installed panels. You should see the black PLA interior clearly through the acrylic.

Now mount the LED strip that will light up your fog streamlines.

Peel the adhesive backing off your 12V LED strip.
Stick the LED strip along the top interior edge of the test section, running the full 200mm length.
Angle the LEDs so they point downward into the test section. This creates a sheet of light that cuts across the airflow path from above.
Route the power cable out through a small gap at the back of the test section. If there is no gap, cut a small notch in the frame edge with your utility knife.

Why point the LEDs downward?

This technique is called cross-illumination. The LEDs cast light across the test section at an angle to your viewing panels. Fog particles passing through the light sheet scatter that light toward your eyes, glowing bright white. The black PLA walls behind them absorb everything else, creating high contrast.

Professional wind tunnels use the same principle. A laser sheet replaces the LED strip, but the concept is identical: light the smoke, darken everything else.

Panels too tight or too loose?

If a panel will not slide into the slot, sand the panel edges down slightly with 120-grit sandpaper until it fits. If a panel is loose and rattles, run a thin bead of hot glue along the slot edges to hold it in place.

help me fit my acrylic panels into the test section frame slots

Install the sting arbor

You need a way to hold an airfoil inside the test section and rotate it to different angles. In professional wind tunnels, this mounting mechanism is called a sting arbor. You will build one from CPVC pipe and a dowel rod.

Measure and mark the center of the test section base, side to side.
Position the mark approximately 100mm from the inlet end of the test section (halfway along the 200mm length).
Using your drill with the 3/4-inch bit, drill a hole through the base of the test section frame at your mark. Drill slowly to avoid cracking the PLA.

Drilling through PLA

PLA can crack if you drill too fast or apply too much pressure. Use a slow speed, let the bit do the work, and support the frame from underneath so it does not flex. If the hole chips slightly, clean it up with sandpaper.

Push the 1/2-inch CPVC pipe up through the hole from below the test section.
Attach the 90-degree CPVC elbow to the bottom of the pipe, underneath the test section base. This elbow is your rotation handle.
Insert the 1/4-inch dowel rod into the top of the CPVC pipe, inside the test section. This dowel is the sting arbor. Your airfoils will mount directly onto it.
Twist the elbow handle underneath the test section. The dowel rod inside should rotate smoothly.

What is a sting arbor?

A sting arbor is a thin rod that holds a test model inside a wind tunnel. It enters from below or behind so it does not block the airflow over the model's important surfaces. Rotating the sting changes the angle of attack, which is the angle between the airfoil and the incoming airflow.

Your CPVC elbow handle gives you precise manual control over this angle from outside the tunnel.

Dowel rod wobbles or does not rotate?

If the dowel rod is loose inside the CPVC pipe, wrap a small piece of tape around the base of the dowel to increase its diameter for a snugger fit. If the CPVC pipe does not rotate smoothly in the drilled hole, sand the inside of the hole slightly with rolled-up sandpaper until the pipe turns freely.

help me get my sting arbor rotating smoothly

Test the lighting

Everything is installed. Before you power on the LEDs, take a moment to predict what you will see through the acrylic panel. The interior walls are black PLA and the LEDs point downward from the top edge. What do you think the inside will look like?

Connect the LED strip to its 12V power adapter or battery pack.
Turn on the LED strip.
Look through one of the acrylic panels.

You should see a dark interior with a bright swath of light cutting across the test section from above. The black PLA walls stay dark while the light sheet slices through the empty space where fog will eventually flow. The sting arbor dowel should be visible poking up from the base.

What should I see?

The interior should look like a small dark stage with a spotlight cutting across it. If the light is too dim or uneven, reposition the LED strip so it runs straight along the full 200mm length of the top edge. The brighter and more even the light sheet, the crisper your fog streamlines will appear in later steps.

Interior not lighting up?

Make sure the power adapter is plugged in and switched on. Check that the LED strip is firmly connected to its power cable. If you see light but the interior looks washed out instead of dark-with-a-bright-stripe, the LED strip may be angled outward instead of downward. Reposition it so the LEDs point into the test section, not toward the acrylic panels.

help me troubleshoot my test section LED lighting

Your test section is complete. You can see through its walls, light up its interior, and rotate anything you mount on the sting arbor. Next up, you will bolt all the tunnel sections together and mount the fan that pulls air through the entire length.

Assemble the Full Tunnel and Mount the Fan

Your test section is ready with clear acrylic panels, bright LED lighting, and a sting arbor that rotates freely. The rest of your printed sections are still sitting separately on your workbench.

Each section is just a piece of duct on its own. In this step, you will bolt all five sections together, mount the fan at the exit in suction configuration, and seal every joint so air only enters through the bellmouth.

In this step, get ready to:

Bolt the printed tunnel sections together using M4 bolts through junction flanges.
Mount the 120mm fan in suction configuration and seal all joints with electrical tape.
Run a tissue-paper leak check to confirm airtight seals.

Bolt the tunnel sections together

Your printed sections connect in a specific order, from the wide bellmouth inlet down to the narrow fan adapter. Each section's junction flange lines up with the next, creating a single continuous airflow path.

Lay out the five printed sections on your work surface in this order, left to right: bellmouth inlet, settling chamber, contraction cone, test section, fan adapter.
Align the junction flanges between the bellmouth inlet and the settling chamber so the bolt holes line up.
Insert an M4 bolt through each flange hole and thread on a nut.
Tighten each bolt finger-tight plus a quarter turn.
Repeat for each remaining junction: settling chamber to contraction cone, contraction cone to test section, test section to fan adapter.
Leave the honeycomb slot in the settling chamber empty. Do not install the honeycomb flow straightener yet.

Why leave the honeycomb out?

You printed the honeycomb flow straightener back in Step 1, but you are leaving it out on purpose. Running the tunnel without it first reveals exactly what problem the honeycomb solves.

Set the honeycomb aside somewhere safe. You will install it in Step 5.

Your five sections should now form a single continuous tunnel from the wide bellmouth to the narrow fan adapter. Wiggle each junction to confirm the bolts hold firm.

Mount the fan and seal all joints

The 120mm fan attaches to the fan adapter at the tunnel's exit end. Mounting it here creates a suction configuration where the fan pulls air through the entire tunnel from the bellmouth inlet.

Place the 120mm PC fan against the circular opening on the fan adapter.
Check the airflow direction arrow printed on the fan housing. When powered on, the fan should blow air away from the tunnel (out the back), not into it.
Secure the fan to the fan adapter using the fan's built-in screw holes.
If the screw holes do not align with the adapter, use hot glue around the fan's edges to hold it firmly in place.

Turn on the fan.
Hold your hand in front of the bellmouth inlet. You should feel a steady pull of air being drawn into the tunnel.

Why mount the fan at the exit?

Every fan creates turbulence from its spinning blades. If the fan were at the inlet, that turbulence would travel straight through the test section and ruin your flow observations.

Mounting the fan at the exit keeps its turbulence downstream, behind the test section where it cannot affect your tests. This is called a suction-type wind tunnel. Most professional wind tunnels use the same configuration.

Feel air pushing out of the bellmouth instead?

Your fan is mounted backwards. Flip it so the airflow arrow points away from the tunnel. Most 120mm PC fans have a small arrow on the frame showing the direction air moves through the fan.

Help me figure out which direction my fan should face in the tunnel.

Now seal every joint along the tunnel to prevent air from leaking in through the flanges.

Wrap a strip of black electrical tape tightly around the first flange joint (bellmouth to settling chamber).
Repeat for every remaining flange joint, working from the bellmouth end toward the fan adapter.
Run a strip of tape along any visible gap between sections that the flange tape did not cover.

Run a tissue-paper leak check

Tape can look sealed but still let air slip through. A tissue-paper test reveals leaks you cannot see by making them physically visible.

Before you start testing, predict: do you think every joint is perfectly sealed, or will the tissue paper catch a leak somewhere?

Tear a small strip of tissue paper, about 50mm long.
Turn on the fan if it is not already running.
Slowly move the tissue paper strip along each taped joint, holding it about 5mm away from the surface.
Watch the tissue paper closely at each joint before moving on to the next.

If the tissue paper stays still at a joint, the seal is good. If it flutters inward toward the joint, air is leaking through that spot.

For any joint where the tissue paper flutters, add another layer of electrical tape directly over the leak.
Retest each repaired joint with the tissue paper until no flutter remains.

With all joints sealed and the fan running, hold your hand at the bellmouth inlet one final time. You should feel a steady, even pull of air being drawn into the tunnel with no noticeable drafts leaking in from the sides.

Tissue paper flutters at every joint?

First, confirm the fan is pulling air through the tunnel (air drawn in at the bellmouth, blown out behind the fan). If the fan direction is correct, check that each flange is fully tightened. Loose bolts leave gaps that tape alone cannot seal.

For stubborn leaks at flange edges, apply a thin bead of hot glue along the gap before wrapping with tape. The glue fills irregular surfaces that tape bridges over.

Help me troubleshoot persistent air leaks in my wind tunnel joints.

Your tunnel is sealed and pulling air from the bellmouth straight through to the fan. In the next step, you will feed fog into the bellmouth and see what the airflow actually looks like inside the test section.

First Fog Test — See the Problem

Your wind tunnel is fully assembled, sealed, and pulling air. In this step, you will use your fog machine for the first time to make the airflow visible inside the test section.

Room air does not enter the bellmouth in neat, parallel lines. It tumbles in carrying random swirls and eddies, and this step will make that chaos visible.

In this step, get ready to:

Set up fog visualization at the bellmouth inlet.
Observe the airflow through the acrylic viewing panel.
Document the turbulent baseline with a photo or video.

Set up fog visualization

Your fog machine produces dense, non-toxic glycerin-based fog that makes airflow visible. Directing it into the bellmouth inlet lets you trace the path air takes through the entire tunnel.

Position your handheld fog machine right at the bellmouth inlet opening.
Turn the fog machine on at a low to medium setting.
Direct the fog stream straight into the bellmouth opening.

The fan is already pulling air through the tunnel from your leak check in Step 3. You should see fog getting drawn into the inlet immediately.

Fog not getting pulled in?

Make sure the fog machine nozzle is close to the bellmouth opening. The fan's suction should pull the fog in from a few centimeters away.
If the fog dissipates before entering the inlet, increase the fog machine output to medium.
Check that the fan is still running. Hold your hand behind the fan adapter to confirm you feel air blowing out.

Why isn't my fog entering the wind tunnel?

Observe the flow through the viewing panel

Before you look through the viewing panel, what do you think the fog will look like inside the test section? Do you expect clean, parallel lines, or something messier?

Turn on the LED strip to illuminate the test section interior.
Look through the acrylic viewing panel while the fog machine and fan are both running.

The fog is chaotic. Smoke swirls, breaks apart, and fills the test section with a diffuse haze instead of clean lines.

What is turbulent flow?

The messy fog you see is turbulent flow. Room air enters the bellmouth carrying random crosswise motion and eddies from every direction.

Without anything to straighten that incoming air, those random motions carry all the way through the contraction cone and into the test section. The swirling, incoherent haze you see now is the result.

This is the core problem. You cannot observe clean aerodynamic behavior around a wing shape when the airflow itself is a disorganized mess.

Document the turbulent baseline

You need a record of this chaotic flow so you can compare it against the results after you install the honeycomb flow straightener.

Keep the fog machine running at a steady output and the LED strip on.
Take a photo or short video of the turbulent fog through the acrylic viewing panel.
Frame the shot so the LED-lit fog is clearly visible against the dark interior walls.

Save this as your "before" image. The contrast between this chaotic flow and what you see in the next step will be dramatic.

Get a better shot

Dim the room lights so the LED cross-illumination is the primary light source. This makes the fog streamlines pop against the black PLA interior and produces a much clearer photo.

Can't see the fog through the panel?

If the fog is too faint, increase the fog machine output. You need enough density for the LED light to catch the particles.
If the acrylic panel is fogging up with condensation, wipe it with a dry cloth. Glycerin-based fog can leave a light film.
Make sure the LED strip is on and positioned along the top interior edge so it cross-illuminates downward.

Why can't I see fog streamlines in my wind tunnel test section?

You have seen the problem with your own eyes. Next up, you will install the honeycomb flow straightener, mount your first airfoil, and witness the transformation to clean, parallel laminar flow.

Install the Honeycomb and Test Your First Airfoil

In the last step, you saw your tunnel in action for the first time. The fog told the truth: without anything to straighten the incoming air, the flow inside is a chaotic mess of swirls and eddies.

The hexagonal honeycomb flow straightener you printed in Step 1 is about to change that. In this step, you will install it, mount your first airfoil, and witness the exact moment clean airflow breaks down over a wing surface.

In this step, get ready to:

Install the hexagonal honeycomb flow straightener in the settling chamber.
Mount the symmetric teardrop airfoil on the sting arbor.
Run a fog test and observe flow separation and aerodynamic stall at increasing angles of attack.

Install the honeycomb flow straightener

Room air enters your tunnel carrying random crosswise motion. The honeycomb's hundreds of narrow hexagonal tubes force that air into parallel streams by blocking any sideways movement.

Pick up the 3D-printed hexagonal honeycomb flow straightener you printed in Step 1.
Slide it into the honeycomb slot in the settling chamber.
Make sure the hex cells are aligned with the airflow direction. Air should flow through the tubes from front to back, not side to side.
If the honeycomb is loose in the slot, wrap a strip of black electrical tape around the edges to snug the fit.

The honeycomb should sit firmly in the slot with no gaps around the edges. Air must pass through the cells, not around them.

How does the honeycomb straighten airflow?

Your honeycomb has 10mm diameter cells that are 80mm deep, giving it an L/D ratio of 8. This ratio describes how long each tube is relative to its width. Longer tubes give the air more distance to lose its sideways motion.

An L/D ratio between 7 and 10 is the optimal range for turbulence reduction. Your honeycomb sits right in that sweet spot.

The 1mm wall thickness keeps porosity near 0.8, meaning 80% of the honeycomb's face is open to airflow. This minimizes pressure loss while still forcing the air into parallel paths.

Honeycomb won't fit?

If the honeycomb is too tight, gently sand the edges with 120 grit sandpaper until it slides in.
If it is too loose, wrap the edges with a layer of electrical tape to take up the gap.
Make sure you are inserting it into the correct slot in the settling chamber, not trying to force it into a flange joint.
Help me troubleshoot fitting my honeycomb into the settling chamber slot.

Mount the airfoil on the sting arbor

With the flow straightener in place, you need a test subject. The symmetric teardrop airfoil you printed in Step 1 will be your first wing shape.

Pick up your 3D-printed symmetric teardrop airfoil.
Slide it onto the 1/4 inch dowel rod (the sting arbor) inside the test section.
Center the airfoil in the airflow so it sits roughly in the middle of the 100x100mm cross-section.
Twist the CPVC elbow handle underneath the test section to verify the airfoil rotates smoothly.

The airfoil should spin freely when you twist the handle. This rotation is how you will change the angle of attack during testing.

What is angle of attack?

Angle of attack is the angle between the wing's chord line (an imaginary straight line from the leading edge to the trailing edge) and the direction of the incoming airflow.

At 0 degrees, the airfoil sits flat in the airstream. As you rotate the sting arbor, you tilt the leading edge upward, increasing the angle. Every wing has a limit. Beyond a critical angle, the airflow can no longer follow the curved upper surface and tears away.

Run the fog test and observe aerodynamics

Everything is set. The honeycomb is installed, the airfoil is mounted, and your tunnel is sealed.

Before you start the fog, look at the turbulent baseline photo you captured in Step 4. With the honeycomb now installed, do you think the fog streamlines will look the same, or completely different? What do you expect to see?

Position your handheld fog machine at the bellmouth inlet.
Set it to medium power.
Make sure the fan is running at the exit end of the tunnel.
Turn on the LED strip if it is not already on.
Turn on the fog machine and direct fog into the bellmouth opening.
Watch through the acrylic viewing panel.

The difference from Step 4 is dramatic. Fog now flows in clean, parallel lines, glowing bright white against the black interior. These are laminar streamlines. The honeycomb transformed chaotic room air into smooth, ordered flow.

Hold your turbulent baseline photo from Step 4 next to the viewing panel to compare them side by side.

Why is the difference so dramatic?

Without the honeycomb, air entering the bellmouth carries random eddies from the room. The contraction cone accelerates this messy air but cannot remove its crosswise motion.

The honeycomb sits upstream of the contraction. It kills perpendicular motion first. Then the contraction cone accelerates the now-parallel air, further suppressing any remaining turbulence. This two-stage conditioning is the same principle used in professional wind tunnels.

Now for the real test. What do you think will happen to those clean streamlines if you start tilting the airfoil upward? Will they stay attached to the surface, or break away?

Slowly twist the CPVC handle to rotate the airfoil to about 5 degrees angle of attack.
Watch the fog streamlines wrap around the airfoil surface through the acrylic panel.
Continue rotating to about 10 degrees and observe how the streamlines change.
Keep rotating past 15 degrees toward 20 degrees.

At low angles, the streamlines hug the airfoil surface smoothly. As you push past roughly 15 degrees, the streamlines peel away from the upper surface and curl into turbulent eddies behind the wing. This is flow separation. The airfoil has stalled.

What is aerodynamic stall?

Aerodynamic stall happens when the angle of attack exceeds the wing's critical angle. The airflow can no longer follow the curved upper surface and separates from it.

Behind the separation point, the flow becomes turbulent and chaotic. The smooth lift-generating pressure distribution collapses, causing a sudden loss of lift.

This is exactly what happens on real aircraft wings. Pilots train extensively to recognize and recover from stall because of that sudden lift loss.

Not seeing clean streamlines?

Check that the honeycomb cells are aligned with the airflow. The tubes should run from front to back, not side to side.
Look for gaps around the honeycomb edges in the settling chamber. Air sneaking around the honeycomb bypasses the flow straightening. Seal any gaps with electrical tape.
Increase the fog machine output. If the fog is too thin, streamlines will not be visible even with LED cross-illumination.
Make sure the fan is pulling air through the tunnel (suction configuration). Hold a tissue near the bellmouth to confirm air is being drawn in.
Help me troubleshoot my fog streamlines.

You have just observed the same aerodynamic phenomena that govern real aircraft wings, made visible in a tunnel you built and printed yourself. Compare your laminar streamlines and stall observation against the turbulent baseline from Step 4. The honeycomb is the single component that transformed your tunnel from a box of turbulent air into a functional aerodynamics instrument.

Secret mission

3D-Print and Compare Two Airfoil Profiles

You proved your wind tunnel works on one airfoil shape. Real aerospace engineers never stop at one design. Design and 3D-print a second airfoil with a different profile, then run both through the same angles of attack to discover which one holds onto smooth airflow longer.

Clean Up Your Resources

This project uses only physical materials you own. There are no cloud services, subscriptions, or recurring costs to worry about. The only decision is how to store or disassemble your wind tunnel.

Resources you used:

Assembled wind tunnel (bellmouth inlet, settling chamber, contraction cone, test section, fan adapter, all bolted together).
Hexagonal honeycomb flow straightener installed in the settling chamber.
Acrylic viewing panels and LED strip with power supply.
Sting arbor assembly (CPVC pipe, 90-degree elbow, dowel rod).
120mm PC fan mounted on the fan adapter.
Handheld fog machine and fog fluid.
3D-printed airfoils (symmetric teardrop and second comparison profile).

Keep everything running

No action needed. Choose this if you plan to keep experimenting with your wind tunnel, printing new airfoils, or showing the tunnel to others.

Leave the tunnel fully assembled on your work surface.
Store fog fluid upright in a cool, dry place with the cap sealed. Glycerin-based fluid has a long shelf life when sealed.
Keep your airfoils and any comparison photos or sketches together for reference.
Disconnect the LED strip power supply and fan power when the tunnel is not in use.

Pause - I'll come back to this later

Disassemble the tunnel into its modular sections for compact storage. Everything bolts back together in minutes when you are ready to use it again.

Unbolt the M4 bolts at each flange joint and separate the tunnel into its individual sections (bellmouth, settling chamber, contraction cone, test section, fan adapter).
Remove the honeycomb flow straightener from the settling chamber and store it flat to avoid bending the hex cells.
Disconnect the LED strip power cable and coil the strip loosely inside the test section.
Remove the fan from the fan adapter. Store it in its original packaging or wrap it to keep dust off the blades.
If your fog machine uses batteries, remove them to prevent corrosion during storage.
Store fog fluid sealed and upright.
Keep your M4 bolts, nuts, airfoils, and sting arbor parts in a small bag or container so nothing gets lost.
Stack the printed sections. They should nest or stack compactly since each is a straight-walled duct section.

Delete - I don't want to use this again

Remove all project materials. PLA is recyclable in some areas, and most other components can be reused or disposed of responsibly.

Unbolt all M4 bolts at each flange joint and fully disassemble the tunnel into individual sections.
Remove the acrylic panels from the test section. Acrylic is recyclable. Check your local recycling guidelines for rigid plastics.
Remove the LED strip and power supply from the test section. These can be reused in other projects.
Remove the sting arbor assembly (CPVC pipe, elbow, and dowel rod) from the test section base.
Remove the 120mm PC fan from the fan adapter. The fan can be reused in a PC build or another project.
Dispose of the 3D-printed PLA sections (tunnel shell, honeycomb, airfoils). Some recycling programs accept PLA. If yours does not, dispose of PLA in general waste.
Dispose of unused fog fluid according to the instructions on the bottle. Most glycerin-based fog fluids can be poured down a drain with running water.
Keep or dispose of the fog machine itself. It is a general-purpose tool useful for photography, cosplay, and other projects.
Collect leftover M4 bolts, nuts, tape, and hot glue remnants. Hardware can be stored for future projects or disposed of in general waste.

Nice Work!

You just built a working tabletop wind tunnel from scratch. You 3D-printed every section, lit it with LEDs, filled it with fog, and watched real aerodynamic phenomena unfold through the acrylic panels.

You've learned how to:

Build a 3D-printed open-circuit wind tunnel with modular sections, a hexagonal honeycomb flow straightener, LED-lit acrylic test section, and fog visualization.
Prove why flow conditioning is essential by witnessing the dramatic transformation from turbulent flow (chaotic, broken fog) to clean laminar streamlines after installing the honeycomb.
Observe real aerodynamic phenomena through fog visualization: streamline attachment, flow separation, and aerodynamic stall on a physical airfoil as you increased the angle of attack.
Secret Mission: Completed an optional challenge to push your aerodynamics and comparative testing skills further.

Ready to quiz yourself?