Aerodynamic Teardrop CO2 Racer - Engineered for Maximum Speed Through Weight Reduction

CO₂ dragster races are a great way to learn how engineering decisions affect speed.

Every student in my class started with the exact same thing: a rectangular wood block with a hole drilled in the back for a CO₂ cartridge. From there, the challenge was to design a car that would travel down the track as fast as possible.

Instead of guessing at a design, I tried to approach the project like an engineer. I researched aerodynamic shapes, experimented with weight reduction, and paid close attention to friction and alignment.

The final result was a teardrop shaped CO₂ racer weighing 63.8 grams, built to move quickly and smoothly down the track.

In this guide, I’ll show you the process I used so you can design and build your own aerodynamic CO₂ dragster.

Along the way you’ll learn a few tricks as well as how to fix a mistake if something goes wrong.

Materials

1. CO₂ dragster wood block
2. CO₂ cartridge
3. Wheels and axles
4. Metal washers
5. Wood glue
6. Sandpaper
7. Paint
8. Painter’s tape

Tools

1. Saw
2. Drill
3. Clamps
4. Pencil
5. Measuring tools
6. Safety goggles

Pre-Drilled CO2 Housing:

The basswood block came from a CO2 dragster kit with the cartridge hole already drilled. This saved time and ensured perfect alignment which means one less thing to mess up!

Kit Specifications:

1. Pre drilled CO2 hole: centered at 25mm from the bottom
2. Hole diameter: 18mm (compatible with most CO2 cartridges)
3. Block dimensions: 180mm × 42mm × 25mm minimum
4. Screw eye holes: pre-marked or pre-drilled at 140mm-170mm spacing

Why This Matters: Starting with a pre-drilled block meant I could focus my efforts on the two things that actually affect speed: aerodynamic shaping and weight reduction through hollowing.

The Teardrop Shape, Why?

Before touching any tools, I researched aerodynamic profiles. The teardrop (or streamlined) shape is considered the most aerodynamic form because:

1. Minimal frontal area reduces initial air resistance
2. Smooth airflow attachment along the body reduces drag coefficient

Design Specifications (Class Requirements):

1. Car Length: 180mm minimum
2. Wheelbase: 105-180mm (I chose 150mm for stability)
3. Body width at axles: 15-42mm (I used 40mm)
4. Cartridge housing thickness: 3mm minimum around hole
5. Front axle: 50mm length, 7mm from bottom
6. Rear axle: 50mm length, 7mm from bottom, 25mm from rear end
7. Cartridge hole center: 30mm from bottom

Key Design Decision: Hollow interior to reduce weight while maintaining structural integrity and aerodynamics through solid sides

Before touching the saw, it helps to draw the design first.

I recommend sketching two views:

Top view

This determines the overall shape of the car.

Side view

This controls the height and aerodynamic profile.

These sketches do not need to be perfect. Their purpose is simply to help visualize the final shape.

On Top Surface:

1. Mark centerline down the entire 180mm length
2. Mark front point (rounded nose 15mm from front)
3. Mark maximum width point (35mm wide at 40mm from front. This is where aerodynamic theory says max width should occur)
4. Draw gradual taper from max width to 15mm at the rear (120mm taper length)
5. Round the rear end slightly (not a sharp point because it prevents flow separation)

On Side Profile:

1. Mark low profile height (keeping center of gravity low improves stability)
2. Mark highest point at 25mm (front third of car)
3. Gradual slope downward to rear

Accurate axle placement is critical for a fast car. Misaligned holes cause friction and wobbling, which slow the car down significantly.

Marking the Holes:

Before drilling, I carefully measured and marked each axle position:

1. Front axle: 25mm from the front of the car
2. Rear axle: 25mm from the rear of the car
3. Both axles: 7mm from the bottom surface, centered on the car's width

I used a pencil to mark the exact center point on both sides of the car, then double-checked all measurements with a ruler to ensure they were identical on each side.

Drilling Process:

1. Secure the car firmly in a drill press (hand drilling can create angled holes)
2. Use a drill bit slightly larger than the axle diameter to allow free rotation
3. Drill slowly and steadily, completely through both sides
4. Check alignment by looking through the hole from one side

Why Precision Matters:

If the holes aren't perfectly aligned, the axles will bind or sit at an angle. This creates friction against the wheels and car body, wasting energy and reducing speed. Taking the time to measure carefully and use a drill press ensures smooth, straight axle holes.

Using the saw:

Top Profile (bird's eye view shape):

1. Secure block firmly
2. Cut along marked teardrop outline slowly and steadily
3. Focus on smooth, continuous curves (jerky cutting creates rough edges that increase drag)
4. Keep rear taper gradual and consistent

Side Profile:

1. Cut the gentle dome shape from side view
2. Keep the profile low and sleek

This is the key innovation that separates a good car from a FAST car.

The Process:

1. Mark cutting lines on BOTH sides of car:
2. Leave 4mm wall thickness on all exterior surfaces
3. Leave 5mm solid material around CO2 housing
4. Leave 5mm solid material around axle holes
5. Use saw to make TWO parallel cuts along the length:
6. First cut: 4mm from left side
7. Second cut: 4mm from right side
8. These cuts should go nearly full depth (leaving 4mm bottom)
9. Remove both side panels carefully (these will be reattached!)
10. Use the saw to cut the bottom of the car off:
11. First cut 4mm off from the bottom of the car
12. Remove this panel carefully (this will be reattached!)

You should now have three panels set aside (two sides and bottom) and the core of the block ready for the next step.

With the panels removed, use a saw or drill to hollow out the interior cavity. Be careful to maintain at least 4mm of material around the CO2 housing area.

Weight Reduction Results:

1. Original block: ~85g
2. Hollowed car: 63.8g
3. Savings: 21g (25% reduction!)

Less mass means more acceleration from the same CO2 thrust (F=ma).

Once hollowed, glue the side panels back on and let dry for 24 hours.

The next decision we need to make is what type of wheels and washers are we going to use. These choices affect both friction and stability, which can influence how fast the car travels down the track.

In my class there were two different wheel options.

Wheel Options

Thin Wheels

Advantages:

1. Lighter weight
2. Less contact with the track
3. Reduced friction
4. Slightly better aerodynamics

Disadvantages:

1. Less stability
2. Car may wobble more if alignment is not perfect

Thick Wheels

Advantages:

1. More stability
2. Easier to keep the car rolling straight

Disadvantages:

1. Heavier
2. More surface contact with the track
3. Increased friction

My Choice

I chose the thin wheels because:

1. They reduce overall weight
2. They create less friction with the track
3. Their smaller profile slightly improves aerodynamics

Even though they are less stable, careful axle alignment can help prevent wobbling.

Choosing the Washers

Washers sit between the wheel and the wooden body. Their purpose is to prevent the wheels from rubbing against the wood, which would slow the car down.

There were also two washer options.

Plastic Washers

Advantages:

1. Lighter weight

Disadvantages:

1. Higher friction

Metal Washers

Advantages:

1. Much smoother surface
2. Reduce friction between the wheel and body

Disadvantages:

1. Heavier than plastic

My Choice

I chose metal washers because reducing friction was more important than saving a small amount of weight.

The metal washers allow the wheels to spin more freely, which helps the car maintain speed as it travels down the track.

This step is CRUCIAL for speed.

Progressive sanding removes tool marks and creates smooth airflow:

1. 80 grit: Remove major imperfections, blend glued seams
2. 150 grit: Smooth out rough texture
3. 220 grit: Create smooth surface
4. 400 grit: Final polish for minimal air friction

Focus Areas:

1. Nose (must be perfectly rounded)
2. Side profile transitions (no bumps or ridges)
3. Teardrop taper (perfectly smooth gradient)
4. Glue seams (should be invisible)
5. Bottom surface (smooth = less track friction)

Test: Run your fingernail along every surface (you should feel zero dents or rough spots)

While sanding, I accidentally removed too much material and created a small hole in the top surface. Instead of starting over, I used a simple repair technique.

The Fix:

1. Cut a piece of paper slightly larger than the hole
2. Place it over the opening and apply wood glue on top
3. Let it dry completely (24 hours)
4. Sand the area smooth to blend the patch

The glue soaked paper created a solid patch that completely disappeared under paint.

Lesson Learned: Work slowly when sanding thin areas. But if mistakes happen, creative solutions can save the project.

Once the body was fully shaped and sanded to a smooth finish, I decided to add paint. This step is completely optional and primarily enhances the car's appearance rather than its performance, though a smooth paint finish can slightly reduce surface friction.

My Design Choice:

I wanted a sleek, professional look with a metallic blue racing stripe running down the center of a matte black body. To achieve clean, crisp lines between the two colors, I used a specific painting sequence.

The Painting Process:

Step 1 - Blue Stripe First: I started by painting a metallic blue stripe along the centerline of the car's top surface. This established the accent color and allowed me to control its exact width and placement.

Step 2 - Masking: After the blue paint dried completely, I carefully applied blue painter's tape directly over the stripe. I pressed the edges firmly to create a tight seal that would prevent paint bleed.

Step 3 - Black Base Coat: With the blue stripe protected, I painted the rest of the car matte black. I applied 2-3 thin coats, allowing each to dry between applications to avoid drips and ensure even coverage.

Step 4 - Reveal: Once the black paint had dried to the touch but was still slightly tacky, I carefully peeled away the painter's tape. Removing the tape at this stage prevents the dried paint from cracking or peeling along the edges.

The Result:

A sharp, clean blue stripe with crisp edges running down the center of the black body. The contrast between the metallic blue and matte black creates a professional racing aesthetic.

Why This Technique Works:

Painting the accent color first, then masking and applying the base coat creates sharper lines than the reverse process. If I had painted black first and tried to add blue on top, achieving straight edges would have been much more difficult, and any small tape gaps would have been more visible against the dark background.

The axles for the wheels were metal rods that pass through the holes in the body of the car.

Installation Process

1. Slide the metal axle rod through the drilled holes in the body of the car.
2. Add one metal washer on each side of the car.
3. Attach the wheels to the ends of the rod.
4. Check how the wheels spin and how far the rod extends past the wheels.

The washers sit between the wooden body and the wheels, which helps reduce friction and prevents the wheels from rubbing against the wood.

Adjusting the Axle Length

At first, the metal rod was too long, so the wheels stuck out farther than they should have.

To fix this:

1. I removed the rod
2. Cut a small amount off the end
3. Reinstalled the rod, washers, and wheels

I repeated this process several times:

1. Test the fit
2. Trim the rod slightly
3. Reinstall everything

This was done until the rod was the perfect length so that:

1. The wheels had enough space to spin freely
2. The rod did not stick out too far past the wheels

Taking the time to adjust the axle length carefully helped ensure that the wheels rotated smoothly without unnecessary friction.

Class requirements: 140-170mm apart

1. Mark positions on bottom centerline
2. Pre-drill small pilot holes (prevents wood splitting)
3. Screw in eye hooks by hand
4. Ensure they're aligned and perpendicular to bottom

These guide the car along the track wire.

Weigh Your Car: My car weighed 63.8g after hollowing. This came out to be a 25% weight reduction from the original ~85g block. Every gram saved means faster acceleration!

Balance Check:

1. Hold car at balance point. The car should be slightly forward of center (better stability)
2. If the car is tail heavy, consider trimming more material from rear

Pre-Race Checks:

1. All wheels spin freely
2. Screw eyes are secure
3. No loose parts
4. CO2 cartridge fits properly

Race Performance: In class races, my car achieved approximately 1.12 seconds for a 9 meter track, placing in the top 25% of competitors. The combination of aerodynamic shaping and weight reduction clearly made a measurable difference in performance.

What I'd Change Next Time:

1. Experiment with even more aggressive weight reduction (potentially 50% hollow)
2. Test wheel alignment variations
3. Try different surface finishes (wax coating for ultra low friction)

(My car is the one on the left of the video)

This project taught me that building a fast CO₂ dragster isn't about luck or guesswork but instead it's about making informed engineering decisions at every step of the process.

What Made the Difference:

Every choice had a measurable impact on performance:

Aerodynamics: The teardrop shape, based on research rather than intuition, reduced drag by minimizing frontal area and preventing turbulent wake formation.

Weight Reduction: Hollowing the interior saved 21 grams which was a 25% reduction that directly improved acceleration according to F=ma. Less mass means the same CO₂ thrust produces more acceleration.

Friction Management: Choosing thin wheels and metal washers over their alternatives reduced rolling resistance, allowing the car to maintain speed throughout the race.

Precision: Taking the time to align axles perfectly and sand surfaces smooth eliminated small inefficiencies that would have compounded over the length of the track.

Problem-Solving: When I accidentally sanded through the body, the paper and glue repair saved the project and taught me that mistakes don't have to mean starting over.

The Final Result:

The car weighed 63.8 grams and completed the 9 meter track in approximately 1.12 seconds, placing in the top 25% of my class. More importantly, I understood why it performed well. Each design decision that impacted it starting from the 4mm wall thickness to the metal washers. All the design aspects were intentional and justified by engineering principles.

What Surprised Me Most:

I was surprised by how much difference small details made. I initially thought the wheel choice and washer type would be minor factors, but careful observation during testing showed that friction reduction was just as important as weight savings. I was also surprised that the hollowing technique worked so well. Originally I wasn't sure if 4mm walls would be strong enough, but they easily survived multiple race impacts.

If You Build Your Own:

Start with research before making your first cut. Understanding the physics of drag, friction, and acceleration will guide your design decisions. Don't be afraid to try weight reduction techniques, but always test your design's structural integrity before race day. And remember: if you make a mistake during construction, creative problem solving can often salvage the project.

This project showed me that speed comes from optimization. It's not about one big breakthrough but instead it's about multiple small, deliberate choices that compound into measurable performance gains.

That's what "Let There Be Speed" means to me: the understanding that every detail matters, every decision has consequences, and true speed is engineered, not stumbled upon.

Total Build Time: Approximately 8-10 hours over 5 days (including drying time for glue and paint)

Would I do it again? Absolutely. Next time, I'd experiment with even more aggressive weight reduction and test different surface coatings to see if I could push into the top 10% of race times.