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TOPIC: HPR Ejection Charges in RMS and DMS Motors

HPR Ejection Charges in RMS and DMS Motors 2 weeks 4 days ago #2787

  • Robert Bantly
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Lee Berry provided me a great table for RMS motors with a user-set ejection charge and for dual deploy. THANK YOU - this will go into my permanent rocket information file. Great stuff, with on-line calculators it pretty much answers all the RMS questions and ejection charge weight / recovery compartment volumes I had. See below.

Body tube Diameter Estimated Ejection Charge Size
1.53 inch 0.5 grams per 36 inches of length
2.15 inch 1 gram per 36 inches of length
2.56 inch 1 gram per 25 inches of length
3.00 inch 1 gram per 18 inches of length
3.90 inch 1 gram per 11 inches of length
5.38 inch 1 gram per 6 inches of length
6.00 inch 1 gram per 6 inches of length
7.51 inch 1 gram per 6 inches of length

By the table and closely followed by online calculators, the LOC Mini-Magg has a 5.38" x 9.5" recovery compartment, subtracting nose cone shoulder. This means a 1.6 gram ejection charge is needed to ensure a successful deployment. Along with a successful 'pickup by nose and shake' test and not TOO much friction. Good to go on RMS.
I wrote to Aerotech asking for gram weights and/or max recommended parachute compartment of the ejection charges on their line of single-use motors. I couldn't find a table listing ejection charge weight in grams vs. motor letter designation or diameter 29/38mm for DMS. Does anyone have this and can you post? Would be a nice add. I think several of the new folks showing up are interested in doing an HPR and level one cert. I am planning on DMS for my first flights as it removes some variables. After cert, a 38mm RMS is likely in the works. BUT, if, say, an Aerotech H100W-14A has less than 1.6 grams of ejection charge in it, could possibly be looking at a rather heavy Mini-Magg lawn dart. Just an example, due to Mini-Magg weight and some nose weight requirements, will probably look at a higher peak impulse motor.

Cheers / Robert
Cheers / Robert
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The following user(s) said Thank You: Jim Stum

HPR Ejection Charges in RMS and DMS Motors 2 weeks 3 days ago #2789

  • Robert Bantly
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Answered my own question with a little help from Apogee and Merlin. I thought DMS motors had sealed ejection charges like the little D,E,F motors I have seen and flown some now.
You can add 4F powder for larger recovery chambers / larger dia. tubes.
Got it. You can hear the light bulb :cheer:
Cheers / Robert
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