Question on Aerotech Delay swapping

[EBurg]

I'm trying to use up some older motors and have an H238T-M (10 second delay) that I'd like to increase the delay on to use for motor backup ejection. I'm expecting apogee at 11.4 seconds, so would love to change it in to an -L.

I know I can buy an RDK-06 and make it an -L (14 seconds), but I also have an extra delay grain from an H128W-M from a previous swap.

Given that the H238T-M (10 seconds) delay is .469" long, and the H128W-M grain is .563" long, and the RDK-06 (14 seconds) is .594" long, is it safe to say I'd get about 13 seconds of delay?

My other option is to just let the electronics do their thing and not put any ejection charge in the motor, but this seems like a pretty good way to get a redundant backup.

Link for the delay sizes is:
https://www.aerotech-rocketry.com/c...Flyers_Data_Sheets/aeroTech_delay_lengths.pdf

Am I missing anything here?

 

[rharshberger]

The AT delay kits are specific to each motor, the h238-l is a 14 second delay. As long as I read the chart right the RDK-06 is the 14second delay. The H128s delays might no even be the same composition as the H238's and probably wont work correctly ( too fast or too slow).

 

[Rocketjunkie]

Yes, you will get about 13 seconds. However, this is not certified. If you are comfortable with electronics, I would leave out the ejection and use the medium delay grain. Even better would be a plugged closure. You are more likely to have premature ejection than an electronics failure.

 

[tim cubbedge]

Don’t know what case you’re using but I do know some of those longer delays require a longer forward closure. I ran into that problem with a 54-1704 case.

 

[dhbarr]

The AT delay kits are specific to each motor ... The H128s delays might no even be the same composition as the H238's ...

They almost assuredly are both the same composition. The only ones that are different ( to my knowledge ) are extremely long burning loads which get a slower comp. Everything else is just physically longer or shorter.

Yes, you will get about 13 seconds. However, this is not certified. If you are comfortable with electronics, I would leave out the ejection and use the medium delay grain. Even better would be a plugged closure. You are more likely to have premature ejection than an electronics failure.

Yup, that combo would have to be considered EX. Certed delay grain combo drilled down is the explicitly approved method.

 

[terryg]

I have used this guide (that I downloaded from a club's web site) and it has worked for me. ymmv

 

[dhbarr]

I have used this guide (that I downloaded from a club's web site) and it has worked for me. ymmv

That's good stuff, thanks for posting it. Confirmation that others have patterned it out and done field testing is quite handy.

dhbarr's hdk research : final is similar data for the 29/40-120 loads, except mostly untested.

 

[snrkl]

Of late, I’ve had 6 out of 6 HPR motor delays fire VERY early, the most recent ended up with my first DD flight having everything ejected just prior to apogee by the motor charge that SHOULD have fired 2sec AFTER apogee - that’s a total of 5 seconds early on a 13sec delay... (from memory)

On electronics controlled DD flights, I’m removing motor charges from now on.

 

[Banzai88]

Of late, I’ve had 6 out of 6 HPR motor delays fire VERY early, the most recent ended up with my first DD flight having everything ejected just prior to apogee by the motor charge that SHOULD have fired 2sec AFTER apogee - that’s a total of 5 seconds early on a 13sec delay... (from memory)

On electronics controlled DD flights, I’m removing motor charges from now on.

I've had that happen, too, but only on flights where I drilled the delay. One blew at the same time as the altimeter charge.....BIG Bada-BOOM. Since then, I don't drill a motor delay for backup, whatever it is is what I live with.