It hasn’t come up yet…
But I still have a pile of Centrifuge tubes… Small ones (I think they are <1g),
Middle size ones (1.5g?)… And a few Larger ones (I think the large ones are
2.5G?)… Free to anyone that wants them and I can figure out a way to get them
to a launch…
Or (if I am reading between the lines correctly) are you all measuring your BP
in pounds now?
From: roc-chat-bounce@xxxxxxxxxxxxx [mailto:roc-chat-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Chris Feenstra
Sent: Wednesday, December 06, 2017 3:33 PM
To: roc-chat@xxxxxxxxxxxxx
Subject: [roc-chat] Re: Sizing BP Charges
Has anyone tried using a prescription medicine bottle? I am referring to the
ones made of flexible plastic, not rigid. The rigid plastic might produce hard
plastic shrapnel that might damage something.
Chris Feenstra
NAR #61291
Tripoli #9123
Level 2
From: roc-chat-bounce@xxxxxxxxxxxxx [mailto:roc-chat-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Chris Wilson
Sent: Wednesday, December 06, 2017 10:43 AM
To: roc-chat@xxxxxxxxxxxxx; Alexander Jones
Subject: [roc-chat] Re: Sizing BP Charges
Speaking of CO2 systems, what's the best practice for redundancy on a high
altitude flight that's using CO2 for drogue deployment?
Have a second separate CO2 system as backup? That seems larger and heavier than
should be needed. But I wouldn't trust BP to ignite correctly at a high
altitude as a backup to the CO2 system, or am I looking at that wrong?
Thanks,
Chris
On 12/6/2017 9:23 AM, Alexander Jones wrote:
Are the CO2 systems really that heavy? The Peregrine system seems like it
reduces the weight and volume of the system pretty well, I would think the
cartridge itself comprises the majority of the mass of the system, which
unfortunately you can't really get around.....I'd be a little worried about
stresses in a 3D-printed CO2 mount, since you do still have a BP charge (albeit
a smaller one) that has to go off to press the CO2 cartridge onto the pin. A
good alternative stress-wise might be to go fully BP-less and use a servo or a
solenoid to open the cartridge, but then that's more weight again.
On your side-hatch design, since you don't have to counteract the axial
accelerations present in a conventional system, have you looked at using an
electromagnet (or a servo, or.....) to hold the forward edge of the hatch shut,
then just shutting off the current to it for deployment? Aero forces would pull
the hatch open and your chute out, it'd work at any altitude, and you'd spare
yourself the BP and shear pins. Just trying to think outside the box....
On Wed, Dec 6, 2017 at 7:01 AM, Richard Dierking <applerocketry@xxxxxxxxx>
wrote:
Yes, that was a very good paper on using BP charges at higher altitudes. Thank
you for posting this Alexander. What he studied relates to what I’ve been
experimenting with for drogue deployment. I’m using Latex tubing for BP
charges but I only use 18 lb zip ties to seal the ends. There are two
deployment bays for small (9”) drogues and they are located between the 54 mm
motor tube and 3” airframe tube. So, they are very small, with only 7 mm
depth. The Latex tubes with 0.4 grams of BP blow the hatches that use 2-56
nylon shears. (Keep in mind that the 2-56 bolts shear differently than normal
because they are sheared as one side of the bay door is blown out.) Since the
bays are located behind the CG the rocket comes down nose first between 100 and
125 fps. I’ve ground tested different types of charges and the Latex tubing
(3/16” diameter) works best.
The objective is to bring the rocket down from higher altitudes quickly and
with less chance of a tangle or parts of the airframe hitting together, and
just about eliminate the possibility of deployment of the main at high
altitude.
At the next launch, I’ll be testing a deployment bag for the main. Since the
rocket is coming down so quickly, a rapid deployment of the main is causing a
zipper. I hope to slow the deployment with the bag and have the rocket tip
over before the main inflates. So, I’ll see if it works.
Another thing mentioned in the paper was using CO2 ejection systems with BP
charges as back-up. One of the problems using CO2 is the weight of the
commercial systems, like the CD3 system I use. I’m sure a 3D printed CO2
deployment system could be created that would be reliable and decrease the mass
using CO2 deployment.
Richard Dierking
From: Alexander Jones <mailto:uscjones@xxxxxxxxx>
Sent: Tuesday, December 5, 2017 2:54 PM
To: roc-chat@xxxxxxxxxxxxx
Subject: [roc-chat] Re: Sizing BP Charges
Very true. Jim Jarvis did a study on that, in fact, also a good resource:
http://www.rocketryfiles.com/files/Technicalarticles/Jim_Jarvis_Highaltitude_deployment_2013.pdf
On Tue, Dec 5, 2017 at 1:16 PM, Adam Dean <theagatehunter@xxxxxxxxxxx> wrote:
Hi Richard
Keep in mind at high elevation with less pressure, it takes more powder to
Crete the same result at ground level.
From: roc-chat-bounce@xxxxxxxxxxxxx [mailto:roc-chat-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Richard Dierking
Sent: Tuesday, December 05, 2017 12:34 PM
To: roc-chat@xxxxxxxxxxxxx
Subject: [roc-chat] Re: Sizing BP Charges
Thank you for the links! Both gave approximately the same results. The main
and drogue bays are about the same size (4x7 and 4x6) and the results were a
little over 0.7 grams with the 2-56 shear pins. Yesterday, I conducted the
ground test using 1.0 grams BP for the drogue and 1.2 grams for the main. Both
tests were “energetic”😉 and showed that perhaps around 0.8 grams for each would
do fine. So, I’ll be using 0.8 grams BP for both and 1.0 grams BP for the
drogue and 1.2 grams for the main as back up delayed charges.
Also, these formulas will be used to calculate the amount of BP for the 3”
rocket I’ve been flying. I’ll use the results for the primary charges and
larger amount I’ve been using for back-ups. Always good to not over pressurize
a deployment event. Even when the shock cords are a good length.
Thanks again for the information.
Richard Dierking
From: Chris Attebery <mailto:chrisattebery1971@xxxxxxxxx>
Sent: Sunday, December 3, 2017 1:25 PM
To: roc-chat@xxxxxxxxxxxxx
Subject: [roc-chat] Re: Sizing BP Charges
I use this one.
http://www.rimworld.com/nassarocketry/tools/chargecalc/index.html
On Sun, Dec 3, 2017 at 12:38 PM Alexander Jones <uscjones@xxxxxxxxx> wrote:
I use these:
Ejection charge size, static sample port size, and shear pin calcs:
<http://vernk.com/EjectionChargeSizing.htm>
http://vernk.com/EjectionChargeSizing.htm
<http://www.vernk.com/AltimeterPortSizing.htm>
http://www.vernk.com/AltimeterPortSizing.htm
<http://www.feretich.com/rocketry/Resources/shearPins.html>
http://www.feretich.com/rocketry/Resources/shearPins.html
On Dec 3, 2017 12:26 PM, "Richard Dierking" <applerocketry@xxxxxxxxx> wrote:
I misplaced my chart for BP based on volume that also had the extra BP amounts
when there are shear pins (for example 2-56 or 4-40 nylon).
Does someone have this info? Perhaps it came from one of Canepa’s high power
rocketry books.
Thank you,
Richard Dierking
P.S. No, I don’t want to blow it up, just a good separation will do.
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