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Model Rocketry. Parts of a Model Rocket. Rocket Engines. Most are single use engines. Classified by the amount of power they produce. How Does a Rocket Engine Work?. Newton’s Third Law: For every action , there is an equal and opposite reaction.
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Rocket Engines • Most are single use engines. • Classified by the amount of power they produce.
How Does a RocketEngine Work? • Newton’s Third Law: For every action, there is an equal and opposite reaction. • Engine throws mass (hot gases) out back end, resulting in a force in the opposite direction.
Force = mass x acceleration (Newton’s Second Law) • Throw a baseball while on roller blades: what happens?
Power rating is total thrust developed times the time in seconds the engine burns.
From the letter and first number, you can get burn time: – Power/Thrust=time – For C6-5, 10Ns/6N=1.67s • The longer the engine burns, the higher the rocket flies. • The higher the thrust, the more rugged you need to build.
Rocket Recovery Systems • Streamer recovery • Parachuterecovery • Tumble or featherweight recovery • Glide recovery • Horizontal-spin recovery • Helicopter recovery • Drag recovery
Rocket Stability • CP = Center of Pressure • CG = Center of Gravity
Center of Pressure • Location where all the aerodynamic forces acting on the rocket are in balance. • Difficult to determine without a wind tunnel. • Can be estimated with a cardboard cutout of rocket shape.
Center of Gravity • Location where the rocket will balance, or rotate if unrestrained. • Simple to locate: balance the rocket on the edge of a ruler.
Swing Test • Do a swing test on new designs to demonstrate stability before the first launch. • Install motor (no ignitor), recovery device, and wadding. • Tie a 6-10 foot string on rocket at CG and tape in position. • Swing in a circle at shoulder height. • Should fly straight. • Correct stability before flying. CG should be 1-1.5 body tube diameters ahead of CP.
Achieving Stability • Move CG Forward • Decrease mass at rear of rocket • Add mass to nose of rocket • Lengthen rocket body • Recess engine inside body tube
Move CP Rearward • Move fins rearward • Eliminate any forward fins • Sweep fins to rear • Increase fin area • Increase number of fins