The Liftoff! Beginners Guide to Model Rockets
acknowledgement to Estes Industries.
Model Rocket Safety
Always read the Safety Information, such as the NAR Rocket Safety Code, that is supplied with your rocket kit. In addition there are some British guidelines that apply to model rocket use in this country. This Safety Code is also reprinted on the Liftoff! website.
Safety Disclaimer: Whilst we have made every effort to provide accurate and comprehensive safety information as part of this model rocket programme, the University of Surrey cannot be held responsible for your rocket launching activities. In particular, it is your responsibility to carry out any necessary risk assessments and to implement appropriate safety measures.
The Model Rocket
All model rockets have the following parts: (1) One or more body tubes, the long round tube that holds the engine and payload, (2) a nose cone to reduce air resistance, (3) fins to provide stability in flight, (4) an engine to power it, (5) a launch lug, and a (6) a recovery system. The more complex rockets may have several body tubes connected by tube couplers.
The heart of the rocket is its engine. It contains a propellant for lift-off, tracking smoke for the coasting phase, and an ejection charge to activate the recovery system. The engine is activated through the use of an electrically controlled ignitor. This is an important safety device as it lets the operator be a significant distance away from the rocket when the engine begins to burn.
The Launch Pad
The launch pad provides stability for lift off. It consists of a long launch rod to provide direction. (Shown left is the Estes Porta-Pad; its launch rod is 32 inches long.) and a deflector plate. Both are mounted on a tripod support.
The rocket is placed on the launch pad by sliding the rockets launch lugs down the launch rod.
The Launch Controller
The Controller is a simple battery powered switch. A wire runs from the controller to the ignitor placed in the engine. Controllers have a continuity light that comes on to indicate that the circuit is complete and a safety key to prevent the switch from being accidentally pushed.
Launching the Rocket
The completed rocket is taken to the launch site, the ignitor is placed in the engine, and the rocket is placed on the launch pad. The operator moves a safe distance away from the rocket. He alerts spectators and participants that a launch is about to take place. He double checks the controller's continuity light to insure the circuit is OK, then removes the safety interlock key, and counts down to launch.
There are several phases to the rocket's flight. The first is the thrust phase during which the impulse section of the engine burns. Once this is exhausted, the coasting phase begins. The engine is still active, but it is burning smoke, permitting you to follow the flight. The rocket is still climbing at this point. Then the ejection charge ignites, which actives the recovery system. This is usually a parachute to permit the slow descent of the rocket, or it can be a streamer so that you can follow its path. The rocket can then be recovered, a new engine installed, and it is ready to be launched again.
Model Rocket Engine Information
A model rocket engine, such as those manufactured by Estes and several other companies, consists of a cardboard casing with a clay nozzle at one end a clay retaining cap at the other. The engine contains three type of charges:
The specification of a model rocket engine is denoted in the form of a three-digit identification code. On the above engine the code is: A8-3.
The three digits represent the following:
Total impulse is measure in Newton seconds. One Newton second is the amount of impulse by one Newton of thrust for a duration of one second. For example a "B" type engine has a maximum total impulse rating of five Newton seconds. All Estes engines have the maximum total impulse permitted for a given size.
*Note: only engine sizes up to D are available over the counter in the Britain. In the US sizes up to double-G are possible!
Time Thrust Profile for a B6-4 Engine
Thus the "A8-3" pictured above delivers 2.5 Newton seconds of power at an average thrust of 8N for a duration of approximately 0.3s. There is then a 3s delay before the ejection charge is activated.
Similarly a "B6-4" has 5.0 total Newton seconds of power, but delivers an average thrust of 6N for a duration of approximately 0.8s.There is a four second delay before the ejection charge is activated.
In addition to the engines letter rating, rocket engines are grouped into different physical sizes (of which only 3 sizes are relevant in Britain): mini, standard and large. The table below shows the dimensions of each type of Estes rocket engines:
Estes rocket engine dimensions
Note that a D engine has a larger diameter than a C engine if you want to swap between these two engine sizes for a particular model you will need to use a cardboard tube insert to accommodate the smaller diameter C engine.
Finally, always remember to follow the sensible safety guidelines, such as the Rocket Safety Code produced by the US National Association of Rocketry (NAR), that are reprinted on the Liftoff! website.