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Stupid question, but on alt prediction, is coast time the delay time (in that it takes into account the motor burn time), or should motor burn be added to the calculated value to obtain optimal ejection delay time?
Not a stupid question. The coast time is the time between motor burn-out and apogee. This can be used to determine optimal ejection delay time since the the delay grain starts burning at motor burnout. So, if the calculated coast time was around 5 seconds, you wouldn’t want a delay much shorter or longer than 5. If the delay were say, 3 or 7, the rocket would still be traveling at a higher velocity when deployment occurred, than if the rocket was closer to apogee.
The last response I gave was based on end-burner type motors. Composite motors typically ignite the propellant and delay grain at the same time. The published delay times for motors like mid power aerotech are ‘supposed’ the be the time after motor burnout. The extra delay time needed during thrust is accounted for.
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