JimJarvis50
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Exactly - the altimeter "thought" it was still moving at a high rate of speed, and yet it fired the apogee charge anyway. I will email David at entacore to inquire about how the accelerometer is used to sense apogee, he has been very helpful in the past.
This may be the case, as the accelerometer measures net force, and the thrust would equal the Net Force + Drag Force.
Looking at Openrocket, the drag force increases sort of linearly from 0 N to 130 N at max speed. Using this, the loss of impulse due to drag would be roughly 65 N-sec (and this is a bit generous). Adding this to the total impulse I calculated before, 469 N-sec, and adding in the maximum feasible losses due to the maxed sensor for 0.1 sec (17 N-s) I get 548 N-s which still leaves me short of 635 N-sec.
... unless you were moving faster than what was predicted in your simulation ...
Overall though I care less about this and more why it burned so extremely fast. Accounting for drag forces means the thrust curve I posted earlier has overall lower thrust than the actual motor put out, meaning it could have possibly produced almost 900 Newtons of peak thrust - 50% more than the published thrust curve.
... and in that case, could your acceleration data be correct?
It's been a few years, but I've burned dozens of I 540's. I never got a liner or nozzle that looked like yours.
Jim