I'm not sure that was the right lesson. The screw switches are a great
idea, but they have to be engineered properly, just like everything
If your rocket floats away, or lands on a powerline, how is someone
going to disarm it? Even if you label the holes "Insert 4-40 x 2" screw
here" who is going to have one of those?
Better to figure out a way to keep the switch from jamming, or only
carry one size of screw, or color-code the screws, than to have a
rocket that needs to be disarmed and have someone not know how to do
Good point Ted. One I have not considered. A key switch would have the same
problem there, I also have used one of those. I already found a way to keep
the switch from jamming. Maybe a screw in the airframe is better. Worth
reconsidering in any case.
Which got me thinking...
Could an altimeter be designed to automatically "safe" itself after a
certain period of time after launch. There should be some sort of timeout
that is proportional to when the event should happen. For example, staging
is expected at T+2, and safes itself at T+10, deployment is expected at T+30
and safes itself at T+100, and main deploy is expected at T+100 and safes
itself at T+300.
Or once an altimeter detects ZERO motion for any length of time, it safes
all remaining functions. So a rocket that crashes, lands in a tree or power
line, or just out in the field senses that it's come to rest and shuts down
all remaining active functions.
Bob Kaplow NAR # 18L >>> To reply, there's no internet on Mars (yet)! <<<
Kaplow Klips & Baffle: http://nira-rocketry.org/Document/MayJun00.pdf
Actually, I have been working off and on (more off than on alas) on a
design that will arm itself only a few seconds prior to each event.
Arming involves running a DC to DC converter to charge the 40V firing
capacitor. Until it is charged, no combination of failures or events can
cause the outputs to function.
David W. Schultz
If my rocket drifted into a tree or power lines or off range, it deployed.
If my rocket didn't deploy it struck the terra in my neighborhood.
Now I'm worried the batteries are loose and possibly all those extra wires
and switch pieces that NAR requires have broken free to bounce around a
cause a short when I pick up the rocket.
There are many facets to this issue, but after 66 messages I haven't seen a
clear explanation why the extra wiring is 'safer' when I arm the rocket,...
on the pad where it's supposed to be powered up.
Would you please provide me with that insight?
Well, my first thought would be what could have happened (hypothetically
Did the rocket not descend to the main alt? 400 or 800 ft power lines?
Tree? Radio tower? Mountain. Caught on an airplane or hot air balloon?
But I gotta wonder why was the launched in violation of the safety code of
hazards in the launch site?
Ok if the rocket reached main alt but did not fire the main? What is it
hung up in (tree, powerline, radio tower) and why was it flown in violation
of the safety code (hazard in launch site)?
Ok it's there but why didn't it fire? Battery dead? Power leads came loose?
Ematch not connected? Bad ematch? Match fired but didn't set off power?
Not likely to be an issue.
Ok, it's hung up and the alt is good, primed and ready to fire the charge
when the wind blows right.
Who's getting it down? Lineman? He's going to take the time to look all
over the rocket to find the little switch and has a small screwdriver handy?
Or is he in a hurry to fetch this pain in his rear, yank it off the line and
toss it in the bucket.
Cable guy might at least have the right sized screw driver.
When either of them grab the rocket to read that little warning and
supposedly disarm the switch, did they just cover the vent hole?
Did you mention what they should do when you called them and paid the huge
fine for causing them this pain in the rear?
If the chute wasn't stripped away, it would be a whole lot closer to the
launch pad and not in a tree or powerline which wouldn't be in your launch
Does anyone have any real situations or do we discuss the possble danger of
a static spark when pouring BP from a 1lb can into the ejection canister?
There are two aspects of this. The first is flight safety which in this
case has to do with the ability to deploy the recovery system. The
second, which many people forget about, is ground safety. That is
keeping bad things from happening prior to the launch.
The safety switches do absolutely nothing for flight safety. They
actually have a slightly negative impact (wires and switches in general
have very high reliability numbers) on flight safety. But they do
prevent various problems from occurring prior to launch.
The conflict between flight and ground safety was illustrated for me
several years ago as the result of a program I was working on. I was
working on the update of a design for a telemetry and flight termination
system and the lead range safety office was at White Sands Missile
Range. The safe and arm unit was electronic and charged a capacitor to
2,500 volts for an Exploding Foil Initiator. Flight safety wanted
that capacitor charged and verified prior to launch. Ground safety
wanted it charged after launch.
Because all of the safeties on that particular unit were to prevent
charging of the capacitor and after it was charged there were a half
dozen or so single point failure modes in each of two redundant sections
that would result in inadvertent function, and the consequences of that,
ground safety won. The capacitor was charged five seconds after
The consequences of our recovery systems functioning on the ground are
not nearly as bad as having high explosives go off with likely
initiation of a few thousand pounds of rocket motor not to mention the
several hundred cluster bombs. But there are still negative
consequences. Some reasonable effort should be made to prevent problems
prior to launch.
So just what are the things that might cause an ejection charge to go
2) Insane altimeters
3) Insane rocketeers.
There are several different aspects to the electromagnetic problem.
High electric fields. If there is an electric field present it is
possible to have a potential difference between two exposed wires to the
electric match. But given that this typically cannot induce large
currents and the exposed wires are only a few inches apart (or less)
anything short of the electric fields around a lightning strike are not
likely to present a problem. If lightning strikes nearby I will not be
worried about the ejection charges. :-)
Magnetic fields. We do actually have a magnetic field source close to
our rockets but its hazard is small and can be easily mitigated. That
source is that launch system. The field produced is a consequence of the
large currents. But since the loop area of the current is small (unless
you deliberately form the wires to the launch clips into a large loop)
and there is only one "turn" the field isn't too big. If you use
twisted pair for your wire runs in the rocket, the hazard is even less.
Note that shorting the igniter actually increases the hazard from
magnetic coupling as it requires a complete circuit.
RF is another potential hazard and is documented to have caused
problems. While it is unlikely that you can induce sufficient energy
into the wires to an electric match to cause it to function, it can
cause other problems. Like coupling into the wires to a break wire
arming system that is tied to an unprotected pin on a micro controller.
Killing the micro controller and the rocket. Or in my case, coupling
into the altimeter measurements resulting in deployment before apogee.
It is also possible that something is wrong with the altimeter so that
it fires its outputs on power up. Or perhaps gets a notion that it has
been launched even though it is sitting on the pad, or worse, on the
ground by your car. Only turning the altimeter on at the pad prevents
problems away from the pad. But a guaranteed glitch free power up is a
hard thing to find. It may work just fine hundreds of times before it
doesn't. Disconnecting the pyro output power or other safe/arm systems
will protect you here.
Then you have the insane rocketeer. There isn't much that can be done
about this character except to stay away from them. Having wires to
electric matches flopping around electronics and batteries is just
begging for a trip to the hospital. I like to have my electronics
buttoned up in the altimeter bay before I attach the ejection charges
from the outside. I also use Deans plugs to make this quick and simple.
In my opinion the hazards from EMI are minimal and easily controlled.
The biggest hazard is from the altimeter itself. Or that idiot parked
next to you. :-)
David W. Schultz
I don't fly HPR, but... My first heavy rocket was a 500 gram
egglofter flown at NARAM 12. This was two stage with four Estes D13
motors. At least one motor cato'ed and it was on the ground long
before the ejection of the D13-7s. Now I was building light even in
those days, but I had ballasted the model Up to 500.0 grams with a
massive amount of red powdered tempra paint, in the hopes of getting a
tracked altitude. So the crash is quickly drawing a crowd, and I'm
running up yelling, get back! You can paint your own scene.
There is no way to safe the ejection on a burning SU motor, but in the
world of HPR electronics, it would be nice if the rocket realized that
it was already back on the ground and aborted ejection and other
The other thing that bothers me is seeing these super long "shock
cords" on HPR models. They are natural power line snaggers. If you
shorten the length by say 50%, you cut the odds of hanging up on a
power line be almost the same amount. Regardless of the length, I'd
likely put in a fusible link, pyro or electro-mechanical, that would
self release the cord after say 30 minutes, unless you recover the
rocket first and deactivate that function.
Clearly, there is some engineering to be done to ensure that things
become more safe and reliable instead of less so.
Thats not the problem. What if the ejection charge _doesn't_ fire? For
example, the drogue comes out but the main doesn't. The rocket plummets into
a field some distance way and someone else finds it. How do they disarm the
And to address an earlier comment in this thread, I would keep the ematches in
my range box shorted, probably by leaving the shipping cap on the bare ends.
But do we know who that person would be? Another savvy rocketeer or
just a hunter that knows nothing about electronics on rockets? Even a
rocket savvy person would need to know how that particular rocket is
Bottom line, do you really want a stranger fiddling around with your
rocket? Liability comes to mind.
No argument here, I do the same.
If you have a switch retained with a screw, and a label saying "remove this
screw to disable ejection charges before messing with my rocket", then no
knowledge of electronics is required. So, even the rocketeer with no
knowledge of electronics could handle it.
This issue here is not about what you WANT to happen, it is about what can
happen. What I want is for everything to work perfectly and for the rocket to
gently land ten feet from my car.
Another way to think of it is: if your rocket lands in the corn, and I find
it when I'm retrieving my rocket, do you want me to bring your rocket out of
the corn for you? If I'm worried about getting blasted by the ejection charge
that missfired, I'll leave it behind!
What is the liability if someone else picks up your rocket and gets injured
messing with it? What if that someone is the RSO who is checking your rocket
before you fly it?
Actually I think it would be better to have a 'caution: redundant
ejection charge, to disarm do xxxxx' sticker of some sort. That's what
I tried to convey when referring to configuration.
But not everyone uses a set screw to arm/disarm their electronics.
That's only one out of many ways to use a switch. Slide switches, key
switches and, *gulp*, twisting the wires are used as well. Even with
screw switches, depending on the size of course, would require a
screwdriver to disarm.
In the cases I've witnessed(mostly my own)every time there was a
recovery failure, all the warnings on a rocket would've been worthless
as the rocket was in so many pieces....how could the rocket be disarmed?
Right, a lot of things *can* happen but that doesn't mean *will* happen.
But be careful what you wish for...I actually had my rocket land ON my
Exactly. Your best judgment is all anyone can ask of you. But it be
nice if you noted where the rocket landed :)
Well since he/she is the RSO I would certainly hope that the system is
not armed prior going to the pad. However, I think we all have seen
such a scenario where the rocket was armed when presented to the RSO.
The liability I was referring to was Mr. Smashedoutofhisgourd Hunter
fiddling with the rocket *causing* the charge to go off.
I thought about the whole warning sticker issue a lot when I was
designing my two stage Quantum Leap, which on a really bad day has a
small but nonzero chance of getting lost with a live charge--or even a
live motor--in it, I decided that the liability issues were far higher
for an unlabeled rocket than for a labeled one. Then I took advantage
of some folks I was working with at the time. These were WMD Law
Enforcement people, Ordinance disposal specialists, and the like.
I asked what the likely response would be to a call from a worried
citizen reporting a rocket in their yard. Their answer was that, unless
they happened to know a launch was in progress so they could send
someone over, they'd likely treat a large rocket as an ordinance
disposal problem. If the rocket is labeled and the disarming
instructions are clear, especially if contact information is on the
rocket, they'll likely contact the owner (or follow the instructions if
they have to e.g. clear a highway). If the rocket is unlabled,
especially if it is beeping, they're going to blow it up. Really, No
fooling, that's what they're going to do. Then they are going to go
looking for the owner, and the owner should expect a Significant
I don't know how it might be in the area you all happen to live in, but
really, it's worth asking. As for Quantum Leap, it has my name and
contact info on it, small but easily seen warnings around the body
separations, AND instructions for disarming around the arming bolt
holes. And of course, I've never come close to losing it with a live
charge inside, so there must be added karma for that, too.
I've become a bit of a zealot on this issue, but really, when you think
about it, if NASA has learned how to reliably arm and safe pyro
circuits and fly safely with those circuits--even on man-rated
vehicles--without twisting wires together and sticking them back in the
hole, we should probably try to head in that direction.
I'd add a couple of zero's and move that decimal place over to the right
a bit Ted :) Kick butt common sense advice.
btw, loved that write up you did on the QL in the masa mag and as
always, totally enjoyed the 3 perfect flights I've seen(so far) of the QL.
On a similar note while stationed at Tuzla Bosnia in '96 a certain female
Captain had a "CARE" package sent from a friend in the "States". When the
package arrived at Ramstein AB, GE, it was making a buzzing sound. The EOD
troops came in made their call and blew the crap out of the package.
Contents one activated stress relief device...(vibrator). Cost of said
device $20? Shipping $5? look on EOD troops face wnem they realised what it
was.....Priceless. Cost to a ceratin Captain....Total Embaressment. It is
better to blow up what you do not know than to be blown up by it. IED 101.
Hi Ted, I used to work in law enforcement as an analyst, in the 90s.
Worked the local IT with local agencies like local directed patrol, FBI,
customs, IRS Tres agents, our AF friends, DEA etc..
Just what are WMD people ?
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