Forum

Blog

Blog Post

Welcome, Guest
Username: Password: Remember me

TOPIC: HPR Ejection Charges in RMS and DMS Motors

HPR Ejection Charges in RMS and DMS Motors 7 months 2 weeks ago #2787

  • Robert Bantly
  • Robert Bantly's Avatar
  • Offline
  • Senior Boarder
  • Posts: 71
  • Thank you received: 5
  • Karma: 2
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
The administrator has disabled public write access.
The following user(s) said Thank You: Jim Stum

HPR Ejection Charges in RMS and DMS Motors 7 months 2 weeks ago #2789

  • Robert Bantly
  • Robert Bantly's Avatar
  • Offline
  • Senior Boarder
  • Posts: 71
  • Thank you received: 5
  • Karma: 2
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
The administrator has disabled public write access.

HPR Ejection Charges in RMS and DMS Motors 4 months 3 weeks ago #2809

  • Allan Howard
  • Allan Howard's Avatar
  • Offline
  • Junior Boarder
  • Posts: 24
  • Thank you received: 4
  • Karma: 0
I would suggest ground testing your charges and shear pin combinations. I've used a couple of on-line calculators as a starting point, but then ground tested. I've videoed the results and then adjusted the 4F powder based on the tests. Since I have some NC's with my GPS system (w LiPo battery) in them, this usually takes more powder and shear pins than the calculations suggest.,,more shear pins due to the drag separation. From experience, I've had some large differences between the calcs vs what is needed.
The administrator has disabled public write access.

HPR Ejection Charges in RMS and DMS Motors 4 months 2 weeks ago #2811

  • Robert Bantly
  • Robert Bantly's Avatar
  • Offline
  • Senior Boarder
  • Posts: 71
  • Thank you received: 5
  • Karma: 2
On Mini-Magg (no hurry since it won't fly until I am totally comfortable with it)

Due to nose weight on Mini-Magg, I need shear pins at the cone/body joint? After using a tube, BB's, and a digital scale to make a mockup motor, I did add nose weight to this design. I also contacted LOC directly and had a discussion concerning base drag stabilization. That was interesting. I also did it properly - lots of isopropyl alcohol to clean interior, ran a dowel through the nose cone, added BB's and used my Aeropoxy. It is thin, permeated the BB's and 'wrapped' the weight around the dowel very nicely. There are glues for polypropylene and other low-energy plastics out there, but I haven't heard of anyone using them so went with the dowel and epoxy.

Weight added was for a large I / small J motor. Minimum for this kit is about an I366R after LOC email - they suggest a fairly hard launch for the kit.

Shear pins are relatively easy to install, especially with a "glassed" cardboard tube, but when to use them is a more difficult question. Are they even needed if the rocket isn't dual deploy, or is tape and the shake test enough? I have Canepa's book and while it is interesting to read, it kind of jumps around and doesn't answer quantitative questions, it is mostly general.
On ground testing - don't have a problem with this, but do not have an expended 38mm motor to use, and how do I protect the rocket? Bubble wrap and tape should work around body tube and nose cone to protect my hard earned paint job during the muffled bang. I also have Nomex chute and bridle protectors - along with a shovel of dog barf for luck, should be OK.

On my 75mm Renegade upscale: with a medium grade turned balsa cone, won't be an issue. Just tweaking the amount should be OK since this is basically a large "model rocket."


Cheers / Robert
Cheers / Robert
The administrator has disabled public write access.

HPR Ejection Charges in RMS and DMS Motors 4 months 2 weeks ago #2813

  • Allan Howard
  • Allan Howard's Avatar
  • Offline
  • Junior Boarder
  • Posts: 24
  • Thank you received: 4
  • Karma: 0
Hi. Sounds like your NC for the Mini-Mag is good with the dowel and added weight so you aren't going to rely on the plastic piece to secure the shock cord. I have a LOC V2 and I cut off the bottom of the NC, added/epoxied the recommended nose weights and then filled the void with the PML expanding foam. I then epoxied a plywood bulkhead on top of that with a secure point for the shock cord. I had heard of incidents where the little plastic attach point would fail.
My comments for shear pins were in reference mainly for dual deploy. However, I have a PML Black Bryant X that is motor eject of the large upper section and NC. I've had to shear pin the NC to that since my NC contains a GPS module and battery. Friction fit didn't work due to the wt of NC and it's payload so it had been a victim of drag separation.
When I ground test, I put in everything just like a launch....dog barf, Nomex blankets, d-links connected, shock cords, etc...as I want to simulate what needs to happen in flight. I do put a spent motor in to act as a "plug" with the drogue section. I use saw horses and ladders to set the rocket up for ground testing on grass so I've had minimal damage....but my rockets probably are no where near your level of finish. (I have several that are native FG or HDPE). I use a remote switch setup to initate. I video them all and will watch in slo-mo. But more than once, I've had to adjust the level of powder from the calcs based on the performance....either up or down and in some cases, quite a bit.
The administrator has disabled public write access.

HPR Ejection Charges in RMS and DMS Motors 4 months 2 weeks ago #2815

  • Robert Bantly
  • Robert Bantly's Avatar
  • Offline
  • Senior Boarder
  • Posts: 71
  • Thank you received: 5
  • Karma: 2
I am not averse to shear pins / positive retention of the nose cone - it is heavy now. I think the best answer is to drag out the Magg for pre-inspection and a chat on flight day in March. I haven't decided how to secure the bridle yet - LOC recommends drilling a couple holes and threading it through and ingnoring the hoop now with the instructions.

I stenciled the Magg with a Title reflecting it's increased weight and fixed the Rust-Oleum vs Rust-Oleum paint incompatibility I discovered. Rust-Oleum Fluorescent Red under Rust-Oleum Brilliant Blue with Rust-Oleum Clear Gloss = ORANGE PEEL :sick: :S

drive.google.com/open?id=1c74tifD4qG73rRAeHJvEHSXh8vz7PUfS

So now I can say: "Go, Fat Baby Go!" :P
Cheers / Robert
The administrator has disabled public write access.
Time to create page: 0.128 seconds