Aerotech Delay Grain Compatability

[markfsanderson]

Greetings!
If the weather hold, this weekend I'll be trying for my NAR Level One with my LOC Goblin. I've some other smaller rockets that I've purchased Aerotech RMS motors and reloads for. For my Aerotech 24/40 I have both an E18-7W and D15-4T. One of my rockets that built can handle a D15-7 - 4 is a too short of a delay. Can the delay grain between these two RMS reloads be exchanged? Where can I find out which motors have interchangeable delay grains?

Thanks Again!

Mark Sanderson

 

[tfish]

https://www.aerotech-rocketry.com/c...ary/Catalogs_Flyers_Data_Sheets/hdk_x-ref.pdf


a quick look says yes..

Tony

 

[mbeels]

What determines the delay grain compatibility? All of the delay grains + delay grain spacers add up to the same dimension. Is it a testing or NAR certification thing rather than an incompatibility? This eludes me, does anyone know?

 

[Nytrunner]

Shot in the dark: different formulations for different propellant kit burns

 

[Banzai88]

Shot in the dark: different formulations for different propellant kit burns

IIRC, that's the answer.

 

[tfish]

the motor consumes some of the delay grain during it's burn. The remaining part of the delay grain is now the timed delay for motor ejection. Not all formulas consume the same amount of the grain during the burn. Some consume more, some less. This is the reason for all the various lengths of delay grains and spacers. There are actually 2 delay element formulas. Standard STD and Slow. The slow is mostly used for the slow burning formulas Black Jack. (it consumes more of the delay element then other formulas)
Yes they all..the spacer and delay element...add up to the same length. The delay "train" can only be a given length.

Tony

 

[dhbarr]

Shot in the dark: different formulations for different propellant kit burns

IIRC, that's the answer.

Not quite, AFAICT there's only two delay formulas.

The reload and delay grains burn at high pressure and therefore high rate of speed when making thrust.

After burnout, the delay grain continues to smolder at 1/32in-per-sec.

So the different total length of delay grain is to cover the high-rate burn under thrust plus the desired coast time.

Interestingly this let's us know, for instance, which hobbyline reloads run at the highest pressure.

 

[mbeels]

Interesting, thanks. So there is no technical reason why the delay grains couldn't be interchanged. The resulting actual delay after motor burn out is not tested and is unknown. It sounds like one could, in principle, test an "incompatible" combination, and see what happens. But I bet that has NAR certification implications.

 

[Rex R]

as I recall Aerotech did have a problem with the G71 redline wherein one (or more) ingredients in the propellent caused a burn problem with the delay(can't recall exactly it was either a) no burn or b)real fast burn), which caused them to pull the reload. since the Wildman doesn't list it I would guess that they haven't fixed it yet.
Rex

 

[dhbarr]

Interesting, thanks. So there is no technical reason why the delay grains couldn't be interchanged. The resulting actual delay after motor burn out is not tested and is unknown. It sounds like one could, in principle, test an "incompatible" combination, and see what happens. But I bet that has NAR certification implications.

As you correctly surmise, uncertified loads are for research burns.

dhbarr's hdk research : final

 

[markfsanderson]

Wow - I thought my question would be much more of a yes/no . . . or '..no use this one' answer. So it would appear that I just cannot move the 7 sec delay grain from the 24/40 E engine to the 24/40 D engine. Perhaps next time I'll just buy the longest delay and drill. I purchased the reloads for specific rockets, and didn't think about new rockets acquired . . .

Thanks!

Mark

 

[mbeels]

As you correctly surmise, uncertified loads are for research burns.

dhbarr's hdk research : final

Ah, I love data. Help me understand that spreadsheet, it looks like the bottom rows are the thickness of the delay grain (and s.750 is the slow burning grain). So could one interpolate, and use (for example), a 0.469 thick delay grain in a G53 and expect a 6 second delay? What is the top row? HDK part numbers?

 

[dhbarr]

Ah, I love data. Help me understand that spreadsheet, it looks like the bottom rows are the thickness of the delay grain (and s.750 is the slow burning grain). So could one interpolate, and use (for example), a 0.469 thick delay grain in a G53 and expect a 6 second delay? What is the top row? HDK part numbers?

Thickness yes
Interpolate no comment
HDKs yes

Thanks for reminding me to check my assumptions, I was deep in the weeds when I made that table. Specifically I was wanting a longer delay on the g76.

The two entries for white are the old single grain vs. new double. That let me know I need to capture nozzle size as well.