Composite motor delay times

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Well-Known Member
Mar 14, 2004
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Am I right in remembering that delays on composite motors are calculated from start-up time, and not burn out time, as is the case with BP motors?
The delay grains burn from ignition, but the time given is still the time from burnout.
Yeah, the delay grain burns from ignition, so that when the motor burns out, theres say '4' seconds worth of delay grain left to burn that acts as the delay.
Now I KNOW I've read here and other places that the delay time from the motor designation for mid and high power motors was counted from startup, not burnout, and that the delay/coast was the given delay time minus the burn time.

I know this is a fact because I discussed it with someone else who'd read it in the same places (more than one, and we'd talked about where), and understood this to be the same as I did.

And apparently, wrong.

We got caught up by someone else explaining something they misunderstood, didn't we. Luckily he hasn't launched his HPR bird yet. If I cared enough, I'd search the database here and find it, and find the other site that said it.

People wonder sometimes why I question so many things others say, and even get upset at me about it. I wonder why I don't do it more.
I go by what the sim says ... time to apogee = x secs, I use the x sec delay.

I can't say I've NEVER had a problem but I find delays a bit inaccurate anyway (if you want exact seconds) Does it cause that much of a problem? Aerotech only provide a limited number of delays for each motor, so depending on the model you might never get the perfect delay.

CTi motors have the more complex (accurate?) timing system with the boring tool and the bit of arithmetic.
Originally posted by North Star
CTi motors have the more complex (accurate?) timing system with the boring tool and the bit of arithmetic.

Indeed. In my experience, the delay times of Pro38s (and I've used my share of them) don't seem to fluxuate by more than half a second. They're about as accurate as any motor on the market. While slightly pricier than comparable AeroTechs (at least for the 1-, 2-, & 3-grain reloads), you do gain ease of prepping, cleanup, & accuracy of delay times. It's worth the extra expense to me.

Just my $0.02. HTH,
all delay times are calculated from burnout. the delay grain could burn for ten seconds total, including the thrusting phase of the motor, however, if the motor burns for 3 seconds, then the delay is a 7 second delay(if the delay itself takes 10 seconds to burn).