Model Rocketry

Parts of aModel Rocket

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.

Engine Designations

• 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• Parachute recovery• 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

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

Tracking Model Rockets