adjusting AEROTECH delays

[Jay Hart]

I don't often do this (adjust delays in my reloadable)
I read the Aerotech document and it says use a 3/16" drill
and every 1/32" decrease delay by one second.

The 10 second delay slug I have is 19/32".

I want to make it a 5 second delay so a decrease of 5 seconds
means to drill 5 x 1/32". I did and it seems like a small change physically.

I would have thought it should be half of the 19/32 which is about 10/32" and not 5/32".
Must be some pyro magic or something.
Any insight on this?

Thanks,

Jay

 

[tfish]

a large portion of the delay burns while the motor is burning. The remainder is not very much.

Tony

 

[Wizard]

And the burn rate at pressure (when the motor is burning) is considerably higher than after burnout when it is just the delay burning.

 

[Jay Hart]

I'm posting the question in MPR cuz it certainly applies to this forum.
True or False:

Estes BP End Burners have a delay element that does not start until just at motor burn out.
A motor with a 2 second burn and a 6 second delay ejects 8 seconds after ignition.

Aerotech Core burners have a delay element that start roughly at motor start.
A motor with a 2 second burn and a 6 second delay ejects 6 seconds after ignition.

OpenRocket has a field called Optimal delay which seems to be the time after burn-out until apogee.

I understand there is a significant variation even with in "identical" components.
It seems the worse case is a long burn motor that is consuming up some of the delay time.
In my case of a 2.5 second burn Aerotech and a coast of 6 seconds to apogee at 8.5 seconds after ignition,
I modified my delay from a 10 second down to a 6 seconds based on OR. Seems like a closer delay would have
chosen using time to apogee from ignition which is 8.5 seconds.
This sims out to say instead of only 6 fps at deploy, Im going 80 fps.
Any thoughts?

 

[dhbarr]

True or False:

Estes BP End Burners have a delay element that does not start until just at motor burn out.
TRUE

A motor with a 2 second burn and a 6 second delay ejects 8 seconds after ignition.
TRUE

Aerotech Core burners have a delay element that start roughly at motor start.
TRUE

A motor with a 2 second burn and a 6 second delay ejects 6 seconds after ignition.
FALSE

AT delays do burn from ignition,
faster while the motor is pressurized ( making thrust, boosting ) and
slower after the primary propellant has burned off ( smoke trail, coasting ).

A composite motor with 2 second burn and 6 second delay ejects 6 seconds after BURNOUT, same as the powder end-burner.

 

[Steve Shannon]

Jay,
In core burning motors delay grains begin burning at the time the igniter lights. When the motor comes up to pressure the delay burns at a much higher rate. The actual rate depends on the internal pressure of the motor. I’ve calculated that in some motors the delay grain burns at 5/32 inch per second during thrust and then returns to the often quoted rate of 1/32 inch after burnout.

Something else to consider is that anything that results in the motor starting slower or otherwise burning slightly longer or shorter than designed (such as temperature) will have a large effect on the delay time. Also, ambient pressure changes have an effect on delay times. Alan Whitmore and I separated lengthwise a group of full length delay grains. He burned one half at his low altitude (a few hundred feet above sea level) and I burned the other half at my altitude of just over a mile above sea level. At my altitude the delay grain halves I had burned at a rate that was 8% slower.
Aerotech delay grain material burn at a very consistent rate given a constant pressure, but because of the differences in ambient temperature, pressure, and variations in how people ignite motors, the end result can be a delay that varies one or two seconds. In extreme circumstances, such as chuffing during ignition, a delay may end up several seconds shorter than planned.

 

[solid_fuel]

I don't often do this (adjust delays in my reloadable)
I read the Aerotech document and it says use a 3/16" drill
and every 1/32" decrease delay by one second.

The 10 second delay slug I have is 19/32".

I want to make it a 5 second delay so a decrease of 5 seconds
means to drill 5 x 1/32". I did and it seems like a small change physically.

I would have thought it should be half of the 19/32 which is about 10/32" and not 5/32".
Must be some pyro magic or something.
Any insight on this?

Thanks,

Jay

there is also some wording telling you not to drill past a certain depth. don't drill any deeper than that. or you will have a bad time


True or False:
Estes BP End Burners have a delay element that does not start until just at motor burn out. True
A motor with a 2 second burn and a 6 second delay ejects 8 seconds after ignition. True

Aerotech Core burners have a delay element that start roughly at motor start. True
A motor with a 2 second burn and a 6 second delay ejects 6 seconds after ignition. False