ENGINE ANALYSIS
Thrust
Newton's Third Law of Motion states that for every action there is an equal and opposite reaction. In this scenario, when the engine exerts a downward force, the rocket responds by exerting an upward force. As a result, the rocket accelerates upwards.
Engine Designation
The rocket engines shown at right are referred to as D12-3 engines. This combination of letters and numbers is called the engine designation and is significant in the rocket's success. The letter on the engine represents total impulse, where A stands for 2.5 Ns, B stands for 5.0 Ns, and so on. The first number indicates the average thrust of the engine in Newtons. Finally, the last number shows the delay time in seconds between the burnout and ejection charge, which triggers either parachute or streamers to be released.
For instance, the D12-3 engine would have a total impulse of 20 Ns, an average thrust of 12 N, and a delay time of 3 s.
For instance, the D12-3 engine would have a total impulse of 20 Ns, an average thrust of 12 N, and a delay time of 3 s.
Impulse Curves and Engine Identification
The image on the left is an example of an impulse curve that displays the engine designation of a model rocket. The total impulse is the shaded pink area under the graph. The average thrust is indicated in orange with a black dotted line. The delay time is shown in blue between the end of the initial thrust and the activation of the ejection charge.
The important stages of engine burning can be shown in the image below. Beginning with ignition, the rocket burns and exerts thrust for a period of time before it "shuts off," then enters the coast phase during the delay time and ends with the ejection charge.
The important stages of engine burning can be shown in the image below. Beginning with ignition, the rocket burns and exerts thrust for a period of time before it "shuts off," then enters the coast phase during the delay time and ends with the ejection charge.
The area under this curve is 8.31 Ns, which can be rounded up to 10 Ns. The average thrust is 3.33 N and the delay time appears to be about 8 seconds. Thus, we can conclude that this must have been a C6-7 engine, as these are the closest designations to the data.
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The area under this curve is 28.72 Ns, which can be rounded up to 30 Ns. The average thrust is 8.20 N and the delay time appears to be about 6 seconds. The most similar engine designation allows us to conclude that this must have been an E9-6 engine.
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The area under this curve is roughly 10 Ns. The average thrust is 3.82 N and the delay time appears to be about 6 seconds. We can conclude that this must have been an C6-5 engine because that is the best estimate using the available engine designations.
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Wrong Engine Scenario
A D12-0 engine has no delay time between shut off and parachute deployment. This means that the parachute will be released as the rocket is still climbing. It will likely rip, tear, or overall lose its effectiveness in allowing a safe landing on the ground. The likelihood of the egg breaking is high as the rocket crash-lands without a parachute. A better engine would have been anything with a higher delay time. If Caroline wants to launch a D engine, she should try a D12-3 so that the rocket has enough time to reach the peak of its flight before the parachute deploys.
Our Rocket
As a single stage rocket, the recommended engines for the Hyper Bat are the B6-4, B6-6, C6-5, and C6-7. With a possible maximum altitude of 2,125 feet, we want the rocket to reach its greatest heights before our streamer deploys. Thus, we plan to use a C6-7 engine if launching the rocket as a single stage.
Likewise, if we launch the rocket in two stages, we'll use the C6-7 for the upper stage with the same reasoning. We'll also choose the corresponding booster engine, a C6-0.
Likewise, if we launch the rocket in two stages, we'll use the C6-7 for the upper stage with the same reasoning. We'll also choose the corresponding booster engine, a C6-0.