I copied the last two posts to a separate subject and posted. Very interesting
experiences and comments and hopefully there will be more.
I noticed that Alexander didn’t include his name in the last post, but this was
entered by him.
Thank you Greg and Alexander!
Richard
Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10
From: Alexander Jones<mailto:uscjones@xxxxxxxxx>
Sent: Thursday, January 12, 2017 11:23 AM
To: roc-chat@xxxxxxxxxxxxx<mailto:roc-chat@xxxxxxxxxxxxx>
Cc: Richard Dierking<mailto:applerocketry@xxxxxxxxxxx>
Subject: Re: [roc-chat] Re: Switch Warning with StratoLogger CF
On the redundancy subject, per the NAR L3 requirements, section 2.3 -
"Redundancy must be present in the power sources, safe and arm provisions,
control logic, and output devices (e.g. bridgewires, electric matches).
Redundancy is not required in the energetic materials (e.g. black powder
charges), parachutes, attach points, risers, and disconnects." Thus, the
questions of "what if you're powering things off the same battery" or "what if
you're using the same switch for both systems" is already answered by the
requirements for the cert. I think "power sources" is explicit enough, but
"safe and arm provisions" says to me you have to have separate physical
switches for each altimeter, not just two poles in the same switch.
The way I was going to use the Schurter switches in my L3 would've been to have
one switch controlling power to each altimeter and the continuity of its
respective drogue charge (bc if one dies than the other's useless anyway), then
have a third switch that would control continuity for both main charges...the
way I see it, from a safety perspective (not worrying so much about passing the
cert), the drogue charge is your critical event, anyways, bc that's the one
that keeps it from going ballistic, so using that as the criteria for failure
(again, not cert failure, but "destroying somebody's car or head" failure),
this scheme would not experience a critical failure if any one component
failed. You could add an extra switch so each main has its own, to make the
whole system truly single-failure redundant and "cert-fail-proof," but if
you're hurting on space, that may not be an option.
On Thu, Jan 12, 2017 at 11:07 AM, Gregory Lyzenga
<lyzenga@xxxxxxxxx<mailto:lyzenga@xxxxxxxxx>> wrote:
On Jan 12, 2017, at 10:18 AM, R Dierking
<applerocketry@xxxxxxxxxxx<mailto:applerocketry@xxxxxxxxxxx>> wrote:
*The topic of redundancy is interesting and maybe deserves a separate thread.
I’ve seen it has different meanings. For example, someone says their
deployment system is redundant but the two systems share the same battery or
activation switch, which can be done with the 110/220 because it has two
circuits. So, what if you are using the same type of switch, or say deployment
system (i.e. two e-matches from the two triggering systems in the same BP
canister), is your system truly redundant? I’ve even considered using
different makes of batteries, or not using ones from the same package.
This is a slight digression from the original thread, but yes Richard you make
an excellent point. I barely dodged a serious redundancy bullet at the last
launch I flew at… My standard operating procedure on my L2 electronic
deployment flights is to provide redundant systems for drogue deployment as a
guard against a ballistic crash. My primary is a Perfectflite altimeter firing
an ematch in a BP charge tube. My backup is a g-switch timer firing a separate
ematch in the same BP charge.
Sounds pretty redundant, right? Well, yes and no. I made a serious error in
judgement by trying to save weight and powered both electronics from the same
9v battery. Although I’ve done this dozens of times and it always worked
perfectly, I guess in my heart I knew it was a disaster waiting to happen…
Like all good disaster stories, this just needed to wait for the intersection
of a second triggering factor. My second error in judgement was that I found
what seemed to be a great deal on eBay for ematch replacements, and since my
ematch supply is dwindling I decided to buy a batch. I tried one out with a 12
volt battery in the garage and it seemed to fire nice and hot, so I decided
what the heck, I’ll put one in my next flight. Thinking I was being wisely
redundant, I used only one of these matches for the primary drogue and one of
my old tried and true matches for the backup, thinking I’d be safe that way.
Wrong.
It all seems so obvious now, but I guess I wasn’t thinking. The el cheapo
ematch has a much higher current draw than a good match (duh) and at apogee
firing it pulled the battery voltage down to almost zero and the charge did NOT
fire. The voltage brownout sent the Perfectflite into a coma and the rocket
was on its way to oblivion. Now I guess it’s true that God protects fools,
drunkards and rocketeers, because against all odds, the backup timer survived
the brownout without resetting, so the rocket landed under drogue after all and
I didn’t have to recover the rocket with a shovel. Only after doing the flight
post-mortem did I realize how close I’d come to a really bad day. A good
reminder not to get complacent!
- Greg
----------------------------------------------------------
Gregory A. Lyzenga <lyzenga@xxxxxxx<mailto:lyzenga@xxxxxxx>>
Dept. of Physics, Harvey Mudd College (909)
621-8378<tel:%28909%29%20621-8378>
Claremont, CA 91711-5990 mobile (626)
808-5314<tel:%28626%29%20808-5314>
