Safe, intelligent design, precise manufacture and strict engineering tolerances have made Estes model rocket engines the standard in the industry. They have been proven consistent and reliable in more than three hundred million launches.
The engine consists of a cardboard casing with a clay nozzle at one end a clay retaining cap at the other. Between them are three type of charges: The Propellant provides the power for the model to lift off and climb. By the time it has burned out, the model has a great deal of momentum, which continues to carry it skyward. During this “coasting phase” a Delay charge is burned which emits smoke that helps to visually follow the model. Finally, the Ejection charge is ignited. It activates the recovery system. |
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| Engine Type |
Total Impulse |
| 1/2 A |
0.626-1.25 |
| A |
1.26-2.50 |
| B |
2.51-5.00 |
| C |
5.01-10.00 |
| D |
10.01-20.00 |
| E |
20.01-40.00 |
|
Model Rocket Engines have three characteristics, which are stated on each engine 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 Power
The letter indicates the total impulse range of the engine. Total impulse is the total amount of power the engine produces, which basically indicates how much propellant it contains. Total impulse is measure in Newton seconds. One Newton second is the amount of total impulse by one Newton of thrust for a duration of one second. A five Newton second engine (“B” type) could produce five Newtons of thrust for one second, ten Newtons for 1/2 second or any combination that equal five Newton-seconds when multiplied. All Estes engine have the maximum total impulse power permitted for a given size. Thus a “B” engine always has 5.0 Newton seconds of power. |
Average Thrust
The first number states the average thrust that the engine delivers during the thrust phase. The actual thrust varies, and is shown on the time thrust curve. For a particular engine size (for example a “B” engine), the propellant may be burned quickly, giving high thrust for a short time, or slowly, giving lower thrust for a longer time. A higher average thrust engine is best for heavier models while lower average thrust and longer burn engine is more efficient for lighter models.
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Time Delay
The second number show the time delay. This is the number of seconds between the end of the thrust
phase (propellant burned) and activation of the ejection charge. The time delay allows the model to
coast to its peak altitude before the recovery system is deployed.Thus the “A8-3” pictured above delivers
2.50 Newton seconds of power at an average of .08 Newton and there is a three second delay before the
ejection charge is activated. A “B6-4” has 5.0 total Newton seconds of power, but deliver an average of
.06 Newtons per second. Dividing the average into the total indicates that the propellant will burn for a
little over .08 seconds. After the four second delay, the ejection charge is ignited. |
