ROCKETRY

Atmosphere & Space Types of RocketsDirectional ForcesGeneral Rocket Design

Atmosphere & Space

Space: The region beyond Earth’s atmosphere. There is no sound, air, or pressure, but there is intense heat, cold, and radiation.

For a rocket to travel through space, it must first pass through the atmosphere

Atmosphere A 100 mile layer of gases that surround the Earth. This layer is divided up into sub-layers, based on their temperature and chemical composition.

Solid Fuel Rockets

Solid-fuel rocket engines were the first engines created by man and were invented hundreds of years ago in China. They contain a solid fuel and an oxidizer encased in a cylinder, with a tube drilled down the middle.

Solid-fuel rocket engines have three important advantages:

Simplicity

Low cost

Safety

They also have two disadvantages:

Thrust cannot be controlled.

Once ignited, the engine cannot be stopped or restarted

Liquid Fuel Rockets

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.

Rocket Theory (Newton’s Third Law of Motion)

"For every action, there is an equal and opposite reaction.”

Rockets are reaction engines, so if burning fuel is forced out in one direction, the rocket will move in the other direction.

Forces that Effect Rocket Flight

• Thrust: Force from rocket engine that pushes the rocket forward.

• Gravity: Force which pulls on a rocket and causes it's weight.

• Drag: The friction between the air and the rocket, trying to slow it down.

Law of Gravity

Each object in the universe attracts each other body. (Isaac Newton)

If object A has mass Ma and object B has mass Mb, then the force F on object A is directed toward object B. The magnitude of that force is dependent on the radius of their distance apart squared.

If the mass of the Sun were doubled, the force on the Earth would double. If the Earth were twice as far away from the Sun, the force on the Earth would be a factor four smaller.

Effects of Gravity

To reach space one must get away from the Earth’s pull. The farther the rocket gets away from the Earth the weaker the pull becomes.

An object must travel 17,500 MPH to escape Earth’s gravitational pull. As long as that speed is maintained orbit around the Earth is possible. It isn’t hard to maintain in space, because their isn’t anything to slow you down

Drag

We said that drag was the force that air was able to put on the rocket. However there are several ways to reduce the effect of drag.

Air Density: The air is less “thick” the farther you are away from sea level. Also air is less dense on hot days.Speed: As speed increases, the amount of drag is squared. That means if you go 3x faster, the drag will be 9x greater.

Drag Continued...

Drag:The size, shape, location, and smoothness of the nose cone, fins, and body of the rocket all effect how well it goes through the air

Angle of Attack: The greater the angle of attack, the more surface area that is exposed to be pushed upon

Pop bottle rocket videos

• https://www.youtube.com/watch?v=3Wd6exYm7zE

Degrees of Freedom

Yaw: A swinging movement to the left or right.Pitch: A swinging movement either up or down.Roll: A spinning movement around the rockets longitudinal axis.

Positive, Negative & Neutral Stability

• Positive: When the CG is ahead of the CP. This will give the rocket straight flight.

• Neutral: When both CG & CP are at the same point. This MAY fly straight.

• Negative: When the CP is ahead of the CG. The rocket will try to fly backwards. This is impossible, so it will tumble wildly and crash

Center of Gravity

Finding the Center of Gravity There are several ways to find the Center of Gravity. The simplest is to try and balance it on a ruler, or similar thin, long object. It will balance at the center of gravity.You may also calculate the center of gravity by multiplying the weight of each piece of the rocket by it's own center of gravity, as measured from the base, summing them up, and then dividing by the total weight.

Center of Pressure

Finding the Center of Pressure The easiest way to find the center of pressure is to make a cardboard cutout of the model rocket, out of a thin, flat, stiff piece of cardboard. Using a ruler, or similar object, balance the cutout. The point at which the cutout balance will approximate the center of pressure of the rocket if it were at a 90 degree angle of attack. There is a way to calculate the center of pressure of a model rocket, called the Barrowman method, but it requires as many as a dozen detailed measurements.

CG vs. CP

• (A) The method of finding the Center of Gravity

• (B) The method for finding Center of Pressure

Testing for Stability

Start by finding the center of gravity. It is usually right on or near the launch lug. Second, tie a string around the body tube at the center of gravity so that the rocket balances perfectly.Third, swing the model around your head by the string. Be sure you are in an area free of other people and objects!If the rocket is stable, the rocket will 'fly' with the nose pointed directly into the line of flight (or 90º to the string).

Rocket Parts

Vertical Fins

The stabilizing and guiding unit of a model rocket. The aerodynamic surfaces projecting from the rocket body for the purpose of giving the rocket directional stability. Usually made of balsa wood or plastic, and located at the rear of the rocket.

Vertical Fins Design

The size, number, position, and placement of fins are important in designing a stable rocket. The basic shape, as well as its cross section design are also critical to a drag free flight.

Vertical Fin Placement

The fins must be evenly spaced out around the tube. To measure the circumference of the tube use this formula: Circumference = diameter x 3.14, or use a ruler and a piece of string. Divide the circumference by the number of fins to be placed. Mark out the fin positions, starting with the first fin on the seam of the rocket.

(HINT: Three fins seem to work the best as they keep the rocket straight and weigh less than four or five fins.)

Engine Identification

A letter specifying the total impulse ("A"); a measure of the overall total energy contained in a motor.

A number specifying the average thrust ("8"); a measure of how slowly or quickly the motor delivers its total energy.

A number specifying the time delay between burnout and ejection ("3").

Rocket Flight Profile

NAR Safety Code

Materials:My model rocket will be made of lightweight materials such as paper, wood, rubber, and plastic suitable for the power used and the performance of my model rocket. I will not use any metal for the nose cone, body, or fins of a model rocket.

Motors:I will use only commercially-made, NAR-certified model rocket motors in the manner recommended by the manufacturer. I will not alter the model rocket motor, its parts, or its ingredients in any way.

Recovery: I will always use a recovery system in my model rocket that will return it safely to the ground so it may be flown again. I will use only flame-resistant recovery wadding if wadding is required by the design of my model rocket.

NAR Safety Code

Weight and Power Limits: My model rocket will weigh no more than 1,500 grams (53 ounces) at lift-off and its rocket motors will produce no more than 320 Newton-seconds (71.9 pound-seconds) of total impulse. My model rocket will weigh no more than the motor manufacturer's recommended maximum lift-off weight for the motors used, or I will use motors recommended by the manufacturer for my model rocket.

Stability: I will check the stability of my model rocket before its first flight, except when launching a model rocket of already proven stability.

NAR Safety Code

Payloads: My model rocket will never carry live animals (except insects) or a payload that is intended to be flammable, explosive, or harmful.

Launch Site: I will launch my model rocket outdoors in a cleared area, free of tall trees, power lines, buildings, and dry brush and grass. My launch area will be at least as large as that recommended in the accompanying table.

Launch Angle: My launch device will be pointed within 30 degrees of vertical. I will never use model rocket motors to propel any device horizontally.

NAR Safety Code

Launcher:I will launch my model rocket from a stable launch device that provides rigid guidance until the model rocket has reached a speed adequate to ensure a safe flight path. To prevent accidental eye injury, I will always place the launcher so the end of the rod is above eye level or I will cap the end of the rod when approaching it. I will cap or disassemble my launch rod when not in use and I will never store it in an upright position. My launcher will have a jet deflector device to prevent the motor exhaust from hitting the ground directly. I will always clear the area around my launch device of brown grass, dry weeds, or other easy-to-burn materials.

NAR Safety Code

Ignition System: The system I use to launch my model rocket will be remotely controlled and electrically operated. It will contain a launching switch that will return to "off" when released. The system will contain a removable safety interlock in series with the launch switch. All persons will remain at least 15 feet from the model rocket when I am igniting model rocket motors totaling 30 Newton-seconds or less of total impulse and at least 20 feet from the model rocket when I am igniting model rocket motors totaling more than 30 Newton-seconds of total impulse. I will use only electrical igniters recommended by the motor manufacturer that will ignite model rocket motors within one second of actuation of the launching switch.

NAR Safety Code

Launch Safety: I will ensure that people in the launch area are aware of the pending model rocket launch and can see the model rocket's lift-off before I begin my audible five-second countdown. I will not launch my model rocket so its flight path will carry it against a target. If my model rocket suffers a misfire, I will not allow anyone to approach it or the launcher until I have made certain that the safety interlock has been removed or that the battery has been disconnected from the ignition system. I will wait one minute after a misfire before allowing anyone to approach the launcher.

Flying Conditions: I will launch my model rocket only when the wind is less than 20 miles per hour. I will not launch my model rocket so it flies into clouds, near aircraft in flight, or in a manner that is hazardous to people or property.

NAR Safety Code

Recovery Hazards: If a model rocket becomes entangled in a power line or other dangerous place, I will not attempt to retrieve it.