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- Mar 28, 2018
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I tell beginning rocketeers that the commercial APCP motors we fly from Cesaroni and Aerotech can vary in Thrust and Impulse for any two of the same motors, maybe by about 10%. I had heard that from someone else, or maybe read it somewhere, though I also seem to remember that the certifying authorities require the values measured to be within 20% of the claimed/published values. The message that I try to bring to beginners is why we work with safety margins, like a minimum 5:1 thrust to weight ratio.
Rocketry isn't an exact science, and there is probably more variance between flights because of wind or other factors than motor variance.
I'm curious as to what contributes to any variance, and whether it does vary much between motors. If you take five identical motors from the same manufacturer, with different dates or batches, some brand new, some 3-4 years old, even motors from the same batch, and bench test them, will there be significant variance? 10% seems like a lot, 20% even more unbelievable, though I don't have the luxury or equipment to make the tests myself.
I'm also curious as to what may cause any variance, and whether some propellant formulations are more prone to variance than others. Do slow burners vary more than fast burners, for example.
Just something to talk about after the launch....
Rocketry isn't an exact science, and there is probably more variance between flights because of wind or other factors than motor variance.
I'm curious as to what contributes to any variance, and whether it does vary much between motors. If you take five identical motors from the same manufacturer, with different dates or batches, some brand new, some 3-4 years old, even motors from the same batch, and bench test them, will there be significant variance? 10% seems like a lot, 20% even more unbelievable, though I don't have the luxury or equipment to make the tests myself.
I'm also curious as to what may cause any variance, and whether some propellant formulations are more prone to variance than others. Do slow burners vary more than fast burners, for example.
Just something to talk about after the launch....