Burn Time Of Tape In AT 24/40 Reload?

[Creeps]

In the process of assembling an Aerotech D15 reload, the instructions recommend attaching a piece of tape to the top/delay side of the grain to insure the igniter remains in contact with the grain. (The D15 uses a grain adapter) I've had trouble getting the timing of the delay down with motors using a grain adapter in the past. They always seem to burn a couple seconds too long.

Has anyone else experienced anything of the sort when launching motors which have tape along the top of the grain; Whereby the tape seemingly needs to burn through, before the delay is ignited?

If so, has reducing the delay burn time seemed to be an acceptable fix?
Or, have you calculated the amount of time it takes for the tape to burn through before the delay begins to burn?

Also, what type of tape has worked best for you to negate any extra burn time, as much as possible?

 

[DavidMcCann]

I don't think the tape is so much the issue as the extra volume of air between the grain and the delay. I'm betting the tape is melted before the grain itself ignites.

 

[T-Rex]

I have often wondered if one could build the motor backwards. Put the propellant grain in the top against the delay. It would take a fraction of a second longer to come up to pressure, but would that be significant?

That being said I have never timed mine close, but have never had an issue. I use a small strip of blue painters tape, draped over both sides of the grain to hold it in place. I tear it down the middle to make it narrow and position it to only cover the slot. Even if the tape doesn't burn through quickly, the propellant flame can go beside the tape to ignite the delay.

 

[AlfaBrewer]

It's funny you ask this. I don't have any issues with delay times on the 29/40-120 loads that use spacers, or the D9, just the D15, so for me, it seems to be more motor specific than the motor assembly itself.

I've quit flying them. I hadn't really thought about trying to run shorter delay times, since the D/E (and to some extent F) blue motors just don't do much for me.

 

[shreadvector]

You are correct , sir.

The tape is there to stop the igniter where the propellant grain is. if there was no tape, the igniter would be sitting in empty space above the propellant and possibly resting against the delay. Igniting the delay without the propellant is very annoying.

The INSTANT the igniter flames up, the tape is toast. Also, the instant the propellant ignites, the delay face will ignite, unless the delay is covered in a thick crust or a bunch of grease. Clean those faces for proper ignition.

Finally, if the delay has soaked up lots of moisture from the air, it will burn much longer. Store with a desiccant if worried.

I don't think the tape is so much the issue as the extra volume of air between the grain and the delay. I'm betting the tape is melted before the grain itself ignites.