CO2 dragster

From Wikipedia, the free encyclopedia

The correct title of this article is CO₂ dragster. It features superscript or subscript characters that are substituted or omitted because of technical limitations.

Rear view of a dragster. The hollow container for the carbon dioxide cartridge can be seen.

CO₂ dragsters are miniature racing cars powered by a carbon dioxide cartridge. They are frequently used for pedagogic purposes in demonstrating mechanical principles. A set of two hooks (eyelets) linked to a string at the bottom of the car prevent the vehicle from losing control during launch. In a race, a laser scanner records the speed of the car at the end of its run. Often, the dragster is carved out of balsa wood because of its light qualities.

1 Land Speed Record Assault Vehicles

[edit] Land Speed Record Assault Vehicles

LSRAV'S (Land Speed Record Assault Vehicles) or "C02 Cars" which they are commonly called, are model dragsters designed and built by students that are designed aerodynamically to race against one another. Wooden dragsters are made from basswood or balsa wood are designed, constructed, and shaped with plastic wheels. Students start with a wedge of wood, much like a doorstop in appearance. Power tools are commonly used to shape the body into the design according to the student. Axles and wheels get the car moving down the drag strip. The most well known and common producer of these kits is Pitsco.

C02 Cars are a preferred favorite for Engineering Ciriculums worldwide. Students learn about the forces of drag, wind resistance, and the motion of air as a fluid. Thermodynamics are also somewhat involved. The project mainly tests the aerodynamic properties of a student's car (see also aerodynamics).

[edit] Types of C02 Car Designs

Rail cars are designed with the wheels on the outside of the car. This is a common choice for beginning students or students who may prefer to work with basswood, a wood that is much harder to work with than Balsa.

Return of Firebird (II) is an example of a Rail designed CO2 Car. Notice the wheel placement on the outside of the body.

An example of a shell dragster and a hybrid type ready on the starting gate to race.

Shell cars are designed with the wheels on the inside of the car. This is a very good choice for students who want to reduce a lot of drag. Shell cars are classified by "encapsulated" sections on the underside of the car.

Revenge of Firebird is a perfect example of a "shell car" design. Notice how the wheels are on the inside, and are not protruding through the front or revealed in the back.

Finished Product: Revenge of Firebird (III).

Shell (Revealed) cars are a new coined term for a dragster with shell wheels, but they are not fully encapsulated. To explain this more clearly, the wheels are clearly visible, but there is also a part of the wheel hidden from view. This is also a good choice for students that want sleek bodies and almost no surface area for major drag.

Hybrid cars are a mixture of shell wheels and rail wheels. Commonly the rear wheels are put on the inside while the front wheels are on the outside, or are semi-encapsulated.

Alpha Primus (Firebird I) is an example of a rail and shell hybrid. This is a trike designed Air-powered car (dubbed A02), however C02 cousins act under the same principles- except the method of propulsion.

Rage of Firebird (IV) is an example of a Revealed/Shell C02 Car, with the front wheels partly exposed. Behind: Revenge of Firebird (III).

[edit] Dragster Parts and Assemblies

Wheels Wheels are the objects that keep in contact with the ground and allow the dragster to move forward. Wheels come in many different shapes and sizes. As wheels roll forward on the ground, they cause friction (which cannot be avoided). As wheels roll on the axels (shell designs) this will cause friction. Friction will slow down a car along with drag. Common wheel models include:

GT-R (Rear) Wheels

GT-F (Front) Wheels

Pitsco Standard Front

Pitsco Standard Rear

Delrin (Rear) Wheels*

Delrin (Front) Wheels*

Delrin is a higher quality plastic that Pitsco uses for its premium wheels. Delrin is plyable and a lot easier to work with and shape. Delrin also does not have any "gates" sticking from the wheels like most injection mold plastic wheels do.

Axels Axels are steel rods that keep the wheels centered and (for rail designs) spinning. Axels can vary in length, usually 42mm to 75mm. The three most commonly used axels are steel, aluminum, and brass. Aluminum is a good choice for students wanting to get weight down, but steel is a good all around choice for not only adding weight but for most student engineers wanting simplcity and ease in construction. Axels also have bushels called appropriatly "axel bushings" that fit on the inside of cars to help reduce the friction of the axels by 50%. Unless modified, bushels do NOT work well on Shell designs.

Powerplant and C02 Cartridges The powerplant is the source of power for a C02 Dragster. Without it, your car is going to sit and not go anywhere. C02 Cartridges vary in the amount of pressure they can hold. The most common cartridge, the 8oz cartridge, is used in official TSA races and is usually gold in color. 6oz cartidges are commonly used when instructors have a shorter track (as a modified lesson) or want more safety and less power. 6oz Cartridges are silver in color, as one would expect metal to be. The difference in speed of both cartidges has been measured at approximatly a 20mph difference.

Body Blank The Body Blank is a 12" long by about 1" wide block of triangular that can be mistaken for a doorstop. This blank is modified by carving, drilling, scuplting, and cutting to form the body of the C02 car. The most common blanks are made of Bass and Balsa wood. Students choose Bass wood for weight, but Balsa is usually a better choice for light and fast cars. Balsa wood is also known well in the model building field, and is extremely easy to work with. A downside, however is an overzealous student may remove or cut too much balsa wood than expected.

[edit] Basics of Aerodynamics

Imagine yourself in a moving car with your hand stuck out the window. If you face your palm forward, you will notice it is hard to keep your hand straight and center for long. Your hand is pushed back by the wind. But what happens when you put your palm face down, then your finger's forward? This is the basic aerodynamic principle of C02 Cars.

Drag is the enemy. Named appropriatly "drag", drag is the force that acts upon the body to move it backwards. To reduce drag, students produce aerodynamic designs after a lot of research and consideration. One must think how things that move through the air are made. How does a bullet travel? How does a freight train travel? What are their shapes? These factors all influence the design of a C02 Dragster.

Gravity is not important in this field, except if you were to have a really heavy car. Weight will slow it down if it weights considerably heavy (80+ grams) but most balsa wood dragsters weight right at the 50 gram mark, with each contestant at that weight fighting for a time under similar conditions.

A baseball can be thrown faster and better than a brick because it is round in shape, and is much lighter and easier to throw. A brick is heavy and square. Wind will push the brick back, and along with gravity it will require much more force to get the brick moving like the baseball. Design is everything with these projects. What works however, is up to the student.

[edit] How the Metric 500 Works

Beginning .100 seconds into a C02 Dragster race. High Speed camera photo of two dragsters racing 65.5 feet in about 1.000 second. Photo taken at Nazareth Area High School in Nazareth, PA, USA

A student setting his dragster up for the C02 Car race. Photo taken at Nazareth Area High School, PA, USA.

High speed shot of a race about .750 seconds in. Even expensive cameras have trouble keeping up with the model dragsters. Photo taken at Nazareth Area High School, PA, USA.

Dragsters race down a 20 meter track (about 65 feet, 7 inches) down a filament line (usually fishing line) that goes through screw eyes placed on the underside of the car. With these, the car will travel in a straight, linear path through the finish line.

Students first place the C02 Car on the filament line, and check to make sure cars are in good repair and are ready to race. C02 cartridges are inserted into the powerplants, and the cars are lined up behind the starting line. The starter boxes (the device that allows the cartridge to be punctured) is adhered down with velcro at the beginning of the starting mat. Dragsters may be placed anywhere in the starting area, so long as the front of the body (usually the nose) is behind the red line (Adding to this, a shorter car does not necessarily mean the car is a faster one). The starter boxes can be adjusted by loosening a lever 90 degrees to accommodate for the height of the dragster. Once the neck of the cartridge is lined up with the pin, the neck is fitted into a tube in the starter box. The lever is switched back up 90 degrees to indicate a racer is ready. In most shop classes, from this point on the car is impounded and you may no longer touch it.

In TSA finals, professional staff will handle all C02 Cars, repairs (and final touches) must be attended to BEFORE entry. When both cars are ready, the central computer is on standby to launch the dragsters. The instructor should check everything for safety, and will order all racers and participants to step away from the track. The timer is activated (With the Impulse II System) and in 10 seconds both pins will puncture both C02 cars at the EXACT same time. From the time that master button is pressed, it will all be over in 11 to 12 seconds.

Most racing systems have a laser system to judge how fast a car was going from start to finish. Computers greatly aid in this process. Most Pitsco racing systems are accurate to a thousandth of a second (1.000). Times will display either on a connected computer, or in the LED lights of the racing system itself. Towels or a block of foam (or other type of padding) slow the dragster to a halt and prevent damage to people, objects or to the cars themselves.

[edit] TSA (Technology Student Association)

Introduction The TSA or "Technology Student Association" is the leading authority on official C02 car races. Held in Texas each summer, the elite from across the country are selected for participation in the races. Students must apply to be entered. There are 16 places; the fastest time does not necessarily guarantee first place. Aesthetics, drawing and performance/design are also judged.

TSA 2007 Specifications When designing their dragsters, students must follow a strict outline of maximum/minimum values to each area of their car. According to the official TSA rules and regulations sheet:

"The body of the model shall be one piece all-wood and no parts such as body strengtheners, plastic canopies, exhausts, or air foils may be glued or attached to OR enclosed within the dragsters. Aif foils, fenders and other appearance are designed and and engineered into the original body blank. Bearings and "dry" lubricants may be used in the construction.