Understanding Mach Delay

[ouisconsin rocket]

This question for AIM USB altimeter in particular but may apply to other baro units as well. I understand that pressure increases in the transonic range. That would be until the rocket completes its ascent and slow to below .8 mach....

Is the mach delay on the altimeter set to a time in seconds from lift off to apogee for deployment or that near simulated approximation.

Be gentle, I,m fairly new.....


Thx. Paul

 

[heada]

It is typically set for the amount of time from lift-off detect to the final time the speed drops below trans-sonic but before apogee. Most cases this is only a few seconds (motor burn out +a few seconds to drop below) The best way to know what to set it to is to simulate the rocket flight, find the point where speed drops below 500mph after motor burn out and set it close to that.

Most newer/higher-end flight electronics have both barometric sensors as well as accelerometers and so you don't have to have a mach delay.

 

[cerving]

Actually, you don't need an accelerometer for automatic mach-immunity. All Eggtimer Rocketry altimeters, as well as the baro-only altimeters from all of the other major vendors (PerfectFlite, Missile Works, Altus Metrum, and forgive me if I left any out) take care of this automatically. In the case of Eggtimers, it's done by looking at the velocity profile, and not arming deployments until you've gone relatively slow for a period of time, which typically occurs just before apogee.