Dave Flynn and I were using the vacuum chamber in testing Pyrodex as a less
regulated ejection charge material. It turned out that Pyrodex does just
fine if well contained. People have reported poor performance and lack of
performance. We found that when held in a rigid container it fired just as
energetically as black powder with a lot less mess. When loosely contained
(like in a gallon ziploc bag Kurt) it would not burn completely nor produce
the desired impulse.
One note, you can use a lot less Pyrodex than BP. My first test ejected
itself from the test container and bounced off the warehouse roof... YMMV
so test early and test often.
Matt
On Mon, Jul 25, 2016 at 3:51 PM, R Dierking <applerocketry@xxxxxxxxxxx>
wrote:
Hello Mark.
The problem with the mobility of my set-up is that the vacuum pump is a
couple hundred pounds. Otherwise, I would like to bring it to a launch.
Perhaps when I get my utility trailer at the end of the year.
My head is kind of spinning right now, because this could be a complicated
conversation depending on what the objectives where. For example, if we
were interested in the accuracy of the barometric altimeters we are using
for rocketry, then we would need a precise instrument that was traceable to
a standard, or maybe check a few of them at the same time to see the
variation.
Unfortunately, accurate instruments for low pressures (i.e. high vacuum)
are expensive. It would be nice to have something more accurate than a
standard vacuum gauge I’m currently using.
There have been some interesting discussions on this chat regarding
altitude determinations using barometric altimeters vs. gps units.
For me, the current objective is reassurance that barometric altimeters
will fire the drogue and main charges correctly, and if a side deployment
bay will not prematurely open on ascent. To have accurate altitude
readings would be a plus.
I’ll be installing 4 more electrical connections through the end of the
vacuum chamber for drogue and main charge connections.
I live in Temecula, and anyone that is interested in testing something
using the set-up I have is welcome to visit. Just contact me off chat.
*From: *Mark Woods <mark@xxxxxxxxx>
*Sent: *Monday, July 25, 2016 1:40 PM
*To: *roc-chat@xxxxxxxxxxxxx
*Subject: *[roc-chat] Re: Vacuum Chamber for Ground Testing
Hi all,
I'm new to this community but an electronics engineer and would offer to
help if that's useful...
Thanks,
Mark
On Jul 25, 2016, at 12:43, James Dougherty <jafrado@xxxxxxxxx> wrote:
Hey Richard
Nice work! Would love to give it a shot with some calibrated altimeters
... Maybe bring it to Roctober?
Thanks
-James
Sent from my iPhone
On Jul 23, 2016, at 4:27 PM, R Dierking <applerocketry@xxxxxxxxxxx> wrote:
This is a follow-up on an earlier post on creating a vacuum chamber for
testing altimeters and other rocket-related equipment. I’ve attached a
photo of the chamber that measures 3” square and 12” long.
Mike Kramer suggested that I make a smaller test version to work out
potential bugs, and it turned out that cutting the grooves in the 1 ¼”
polycarbonate ends for the o-ring seals was more difficult than imagined.
Also, it took a couple tries to create electrical connections through the
end to connect a switch. Unfortunately, the 2nd stage on the vacuum pump
isn’t getting as low as specification. I’m still working on that, but so
far achieved about 29 ½” of vacuum *. I tested a PerfectFlite SL-100 a
couple times and it recorded about 102,000’. So, I think that’s adequate
for awhile. 😊
The next chamber will be 6” square and about 40” long to accommodate the
upper half of a rocket I’m working on.
This vacuum chamber project has been kind of a distraction to my L-3
project, but I’m still glad for the time spent. Always fun building
something different and learning more about atmospheric pressure for
amateur rocketry.
Richard Dierking
* There are many different ways to denote atmospheric pressure such as
PSIA, Inches Hg, Torr, mbar, and microns. A Torr is 1/760 atmospheric
pressure and there’s about 1 Torr at 150,000’. I have an inexpensive (aka
cheap) vacuum gauge so it’s really only good for low vacuum.
<Test Chamber.JPG>
