Understanding Rocket Burn Time and Impulse Calculation for Hybrid Rocket Motors

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In summary, the conversation discusses the process of finding the total impulse for a rocket test by finding the area under the thrust graph. There is confusion about whether a period of anomalous behavior should be included in the burn time and if it was caused by a purple flame at the start of the burn. The equipment's behavior may need to be addressed in the lab writeup, but for analysis purposes, the data collected is what is available. A discussion section may include an extrapolated curve to account for the anomaly, but this cannot be claimed as actual lab data.
  • #1
the riddick25
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Homework Statement


We have some data for a rocket test, and I have plotted thrust against time.
To find the total impluse, we were told to find the area under the thrust graph. But I am a little confused about something.
I defined my zero time as the time the thrust started to increase, but for approx. half a second, the thrust stays at around 1.25 before increasing to 1.75 for the rest of the burn.
What is the reason for this? and is this included as part of the burn time? or does the burn start when the thrust reaches its peak.

Also, the rocket did have a purple flame for a little while before the rocket started properly, so i thought this might be a reason, but i am unsure.

If it is important, it was a hybrid rocket motor, with a solid fuel and Nitrous oxide as an oxidisor

Thanks in advance for any help anyone can give
 
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  • #2
If the equipment was behaving anomalously for a part of the run you will want to identify and describe that in your lab writeup (Was it anomalous? Did other groups see similar behavior?)

As it stands, the data collected is what you have to work with. The total impulse actually delivered is what your data provides. So presumably you'll want to analyze it as-is.

In a discussion section you may want to include a further analysis where you describe the observed anomaly and provide an extrapolated curve that "fixes" the anomaly, and note what difference this would make to results (you can't claim extrapolated or "repaired" results as actual lab data!).
 
  • #3
Thank you very much!
 

1. What is rocket burn time?

Rocket burn time refers to the length of time that a rocket's engine is actively producing thrust. It is typically measured in seconds and can vary depending on the type of rocket and its engine.

2. How is rocket burn time calculated?

Rocket burn time is calculated by dividing the total amount of fuel in the rocket's engine by the rate at which the fuel is being consumed. This gives the amount of time that the rocket can sustain its thrust before running out of fuel.

3. What is impulse in relation to rocket burn time?

Impulse is a measure of the total amount of thrust that a rocket's engine can produce over its entire burn time. It is calculated by multiplying the average thrust by the burn time.

4. How does hybrid rocket motor design affect burn time and impulse?

The design of a hybrid rocket motor, including factors such as the type and amount of fuel, can greatly impact the burn time and impulse of the rocket. Different designs can result in longer or shorter burn times and varying levels of thrust.

5. What are some applications of understanding rocket burn time and impulse calculation for hybrid rocket motors?

Understanding rocket burn time and impulse calculation is important for designing and optimizing hybrid rocket motors for various applications, such as space exploration, satellite launches, and even recreational activities like model rocketry. It can also help with predicting the performance and capabilities of different rocket designs.

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