Science Day CO 2 Dragster : Introduction Automobile performance can be a measure of many things. It can include acceleration, braking, cornering, fuel economy and top speed. Two design parameters that are common to most performance measures is automobile mass and aerodynamics. Automobile mass affects acceleration and braking; the greater the mass the slower the acceleration and the longer the braking distance. Designers and manufacturers have always strived to minimize mass, however, during the 1970s and 1980s this expanded. Many small cars were designed with thinner metal and plastic body panels, and aluminum suspension and driveline parts. Then in the 1980s gas prices became less of a concern. Safety was now more importance. Manufacturers then designed stronger cars by removing metal from non-strategic areas and increasing it in the safety cage. New steel alloys kept the mass down while increasing the strength. When the car is stronger in proportion to its mass, this reduces chassis flex when cornering maintaining suspension geometry thereby increasing its slalom speed, it reduces NVH (noise, vibration and harshness), and it better protects the occupants in the event of an accident. Aerodynamics affects fuel economy, noise, top speed and handling. A poorly designed automobile is consumes more fuel, has more wind noise, requires more power to travel at highway speeds and is less prone to cross winds, truck turbulence and high speed lifting. In this lab you will design an automobile that minimizes mass and is aerodynamic without severely compromising the structural integrity. There are endless variations of designs for CO 2 cars. The design described here can be made easily at home. (see Power Point presentation). Objective: Test your basic engineering knowledge and skills by building an aerodynamic and light CO 2 car by your self. Similar to the acceleration, braking, top speed, and fuel mileage claims made by car manufacturers, the objective here is build car 1
that travels a measured distance in the shortest time (similar to drag racing) on the energy delivered from a compressed CO 2 cartridge. Materials: Provided 1. Engine: CO2 cartridges 2. Lubrication: WD- 40 or engine oil (10W- 30) 3. Axles: two lengths of 4 mm metal rod that are each about 70 mm long 4. Wheels: 2 small front and 2 large rear wheels (provided) 5. Frame/Chassis: wedge of wood for chassis/body (provided) but builder can choose to use polycarbonate, nylon, fiberglass, styrofoam, or other synthetic products, however, instructor must see approve material before building starts. ¾ hole pre- drilled for CO2 cartridge. 6. Miscellaneous: washers, nails, glue, screws, haywire, tape (provided). Tools: drill and bits, saws, hammers, wire cutters, rules, pliers, flat files, circle compass, vice, are all provided. 7. Paint: basic colouts Not provided decals, stickers 2
Quick Reference Guide for Design Criteria/Guidelines Minimum Maximum Axles (1/8 th welding rods) Length: 40 mm 70 mm Axle holes 5/32 holes o Position above body base 3.5 mm 9 mm o Position from either end of body 9 mm 100 mm Dragster Body o Length 200 mm 300 mm o Width at front and rear axles 35 mm 42 mm o Height at rear (not including wing) 70 mm - Cylinder Hole (3/4 or 19 mm hole) o Depth of hole 45 mm 50 mm o Housing thickness (body around hole) 3 mm - o Centre of hole from body bottom 30 mm 35 m Wheels o Front wheels tread width 2 mm 5 mm o Rear wheels tread width 15 mm 18 mm o Wheel base (Rr axle Frt axle) 105 mm 270 mm Ground clearance 10 mm Tracking: wheel alignment = distance from a straight line car must be within after a 5 m forward push. - 5 m Procedure 1. Design it. Draw out a full scale (same size as car) diagram of the car in pencil on a separate sheet of paper. Top view must be symmetrical. Use the design criteria/guidelines from below. Note: both the top view and side view are NOT to scale. Since time during Science Day is limited, please complete this at home. Top View 35 42 mm 35 42 mm 200 300 mm 45-50mm Side View 70 mm 30-35 mm CO 2 engine 3 mm 3.5-9mm 10mm 3 Make the body aerodynamic!
2. Mark holes for axles and lines for cuts on wooden blank. 3. Drill holes for axles (make sure they are perpendicular to the side of the car) Drill the hole slowly because a drill bit has a tendency to follow angle wood grain. 4. Shape car to desired shape using saw and sander. 5. Smooth car to reduce wind resistance. 6. Insert axles and attach wheels. 7. Paint (decals and Onstar optional) 4
Points: a) Build CO2 Dragster Workmanship car body: symmetrical smooth and neat aerodynamic shape weight reduction Bonus: wings, fancy paint job up to CO2 Dragster Build Total Points: /20 b) CO2 Dragster Racing Tracking Test (does not veer more than 5 cm over a 5 m distance First Place in race: 40 points (- 4 points for everyplace after) CO2 Dragster Race Total Points: /45 Total Points: /65 5