Model Rockets

Program Objectives After completing the Model Rocket Program, you will be able to: Explain the forces which affect the flight of a rocket Explain how parts of a rocket work Build an air-powered model rocket

Newton’s Laws Sir Issac Newton worked in many areas of mathematics and physics over 300 years ago. He changed our view of the Universe by enumerating the three laws of motion.

Newton’s First Law of Motion Newton's first law states that every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force. This is normally taken as the definition of inertia.

Newton’s Second Law The second law explains how the velocity of an object changes when it is subjected to an external force. The law defines a force to be equal to change in momentum (mass times velocity) per change in time.

Newton’s Third Law Newton’s Third law states that “For every action there is an equal but opposite reaction.” In other words, if object A exerts a force on object B, then object B also exerts an equal force on object A.

Forces Affecting Rockets There are three main forces which affect a rocket. Thrust is the force that propels the rocket upwards. Drag is the aerodynamic force that is acting against the rocket, holding it back. Gravity is the force that the rocket must overcome to become airborne.

Main Rocket Parts FINS NOSE CONE BODY Without fins, a rocket would tumble out of control. NOSE CONE Usually made of balsa wood or plastic, it helps to direct airflow smoothly around rocket. BODY

Rocket Engines & Fuel Propellant is the combination of chemicals rocket engines burn. This propellant is what thrusts the rocket upwards.

Engines There are two types of model rocket engines: Solid Fuel Liquid Fuel

A solid-fuel rocket immediately before and after ignition Solid Fuel Engines Solid-fuel rocket engines were the first engines created by man. They were invented hundreds of years ago in China and have been used widely since then. The idea behind a simple solid- fuel rocket is straightforward. What you want to do is create something that burns very quickly but does not explode. A solid-fuel rocket immediately before and after ignition On the left you see the rocket before ignition. The solid fuel is shown in green. It is cylindrical, with a tube drilled down the middle. When you light the fuel, it burns along the wall of the tube. As it burns, it burns outward toward the casing until all the fuel has burned.

Liquid Fuel Engines In 1926, Robert Goddard tested the first liquid-propellant rocket engine. His engine used gasoline and liquid oxygen. In most liquid-propellant rocket engines, a fuel and an oxidizer (for example, gasoline and liquid oxygen) are pumped into a combustion chamber. There they burn to create a high- pressure and high-velocity stream of hot gases. These gases flow through a nozzle that accelerates them further (5,000 to 10,000 mph exit velocities being typical), and then they leave the engine.

How will it launch? A model rocket engine is ignited by inserting an igniter in the clay nozzle putting it in contact with the propellant. At launch, an electric current is driven through the igniter, causing it so explode, igniting the propellant. When the engine is ignited, the propellant burns, ejecting high- pressure gas out of the nozzle and producing thrust in the opposite direction.

Phases of Flight The flight of a model rocket completes a total of six phases.

Ignition A battery-powered launch controller supplies an electrical current that heats the igniter in the nozzle of the model rocket engine. The hot igniter ignites the solid rocket propellant inside the engine which produces gas while it is burning. This gas causes pressure inside the rocket engine, which must escape through the nozzle. This gas escapes at a high speed producing thrust which lifts the rocket off the launch pad.

Lift Off & Burn Out The thrust produced by the burning propellant causes a very rapid movement of the model rocket during the first few seconds of a launch. It is at this point that the rocket lifts off and flies upward.

Coast Once the propellant is used up (burnout), the engine's delay element is activated. The delay element produces a visible smoke trail used in tracking, but no thrust. The rocket continues to move upward, but only for a short time.

Apogee When the rocket has slowed enough, it will stop going up and begin to arc over and head downward. This maximum altitude is the apogee. The engine's delay element is used up and the ejection charge is activated. The ejection charge produces a large volume of gas that expands forward and pushes the recovery system out of the rocket.

Ejection The recovery system (parachute) opens or activates and slows the rocket's descent by creating excess drag or by creating lift. The rocket then begins to drift safely back to earth.

Landing Once the parachute has ejected, the rocket begins to slowly make its way back to earth. It will eventually come to a landing.

Rocket Construction When making a model rocket, the nose cone must be installed straight and the fins should be the same shape and installed parallel with the body tube. The fins must be spaced around the airframe equal distance apart. The straw cannot be in the way of the fins.