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Homework Help: Rocket burn time

  1. Nov 27, 2011 #1
    1. The problem statement, all variables and given/known data
    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
  2. jcsd
  3. Nov 27, 2011 #2


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    Staff: Mentor

    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!).
  4. Nov 27, 2011 #3
    Thank you very much!
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