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Discussion in 'Rocketry Electronics and Software' started by ColumbiaNX01, Sep 8, 2016.
Ah, makes perfect sense now
Was anyone at the LDRS in Alberta, Canada around 2006? There was a two-stage N to N project that suffered a failure of the booster motor. There was a tumble, things started disassembling... and then the sustainer lit with the nose pointed below the horizon. Luckily it was pointed away from the flight line, although it did seem to target a herd of cattle some distance away. Some form of angle detection would have prevented the upper stage from ever lighting.
A few years back I did some playing around with a Raven altimeter, using the "time to altitude" method. It works, but for it to be of any safety value, the programmed target values have to provide a pretty narrow margin of success. With all the variables in atmospheric conditions versus simulation results, you'll be more likely to have a nominal boost phase with the sustainer not lighting. IMHO it's fine for messing around with small motors where it's not the end of the world if the sustainer is recovered unburnt. But if you're going for some serious altitude with expensive motors & gear... use something that detects flight angle. You'll be much happier.
I think an altitude check would have prevented the N to N example you mentioned as well as the flight in the video posted here earlier. Staging simulations are pretty good now. You can't use an altitude check to distinguish between 10 and 15 degrees of tilt, but it is hard to envision a case where a reasonable altitude check wouldn't inhibit a rocket pointing sideways or down.
On the other hand, to the best of my knowledge, the Altus Metrum tilt feature only looks at the tilt at the moment ignition is called for. In the case of the rocket in the video, it is possible that the rocket was vertical at the moment that happened. I talked with Keith a few years ago about using a look-back approach (i.e., rocket must have been within the tolerance for the past few seconds at least), but I don't believe this was ever implemented.
Yes, I did something about this -- if you have a 'delay after other events', then it will check all of the conditions every 100ms and if they ever go 'false', then the ignition is inhibited. So, if you want to fire 10 seconds after motor burn out, then just set 'delay after other conditions' to 10 seconds and 'tilt angle less than' to 20 degrees and if the airframe ever tilts more than that during the 10 second delay, then staging will be inhibited.
That is excellent.
I have used Mercury Switched for over 40 years, without a single incident.
Mercury switched staging is specifically prohibited by the Tripoli Safety Code.
But NOT by the NAR Safety Code, either for Model Rockets or HPR.
Many clubs are forbidding them on their own. I know the 2 NAR clubs I launch with don't allow them any more.
I'm sure there are a few "clubs" with different rules. However, that is not "official", either when flying with an NAR Section, OR "on your own".
The NAR still permits the use of Roller Switches, too, unlike Tripoli . . .
BTW - The use of "timed, sheathed fuse" ( not Thermalite ) is not disallowed by either organization. Everything gets lit at Liftoff and the "timing" is controlled by Burn Rate, selective sheathing, and length . . . "Old School" !
Neither organization has to prohibit fuse. NFPA requires electric ignition:
“remotely controlled, is electrically operated, and contains a launching switch that returns to the “off” position when released.”
Using mercury switches for staging is inherently unsafe. No matter what happens with the booster, that second stage will ignite.
Pad falls over? Sustainer ignites.
Forgetful flyer picks up rocket and tilts too far to off vertical? Sustainer ignites.
Cato? Sustainer ignites.
The biggest risk on the range is the person who dismisses safety rules because he thinks he knows better.
Everything IS remotely, electrically-ignited . . . All other igniter(s) are activated either simultaneously or in flight ( 3- Stagers ).
Let me explain, in more detail.
The lower stage motor IS ignited, remotely & electrically . . .
Its exhaust flame ignites the other "delayed igniter" for the upper stage . . .
During first stage burn, the other igniter is burning ( usually sheathed ), inside the airframe . . .
It burns up into the upper stage motor and ignites a few slivers of Blue Thunder and staging occurs ( It is "sheathed" to prevent improper ignition of a core-burning motor ).
The Ejection Charge of the lower stage motor deploys its parachute and the same occurs for the upper stage.
This was routinely done in the "pre-electronics" days of Thermalite.
NOTE : "Sheathing" tremendously increases the Burn Rate.
In the images below, note the Terms "Discontinuous Staging", "Delay Direct Staging", and "Insulating Sleeve" . . .
Here is an example of a rocket that uses "Discontinuous Staging" . . . http://v-serv.com/usr/kits/stinger2.htm ( When you see the pics, note the name "Bill Barber" . . . I flew with him on a regular basis )
Like flashbulb ignition, mercury switch airstart initiation has become an obsolete technology, with much better alternatives available at a reasonable price. Starting the timer with a G-switch is fine, but there should be some kind of mechanism for aborting the ignition if you go off-axis...altitude@ignition, velocity@ignition, and/or tilt angle@ignition.
Adding expense, by requiring expensive flight computers to even the smallest and simplest composite-powered, staged models is detrimental to the hobby. Banning things and adding rules and regulations, on a whim, does not address the "big picture" of Rocketry . . . Participation !
I don't think mercury switches were banned "on a whim". Seems a very well-reasoned and insightful prohibition, where enacted. And the only participation it's stifling is in those who would rather save money than be safe. If that's you, then perhaps staging composite motors shouldn't be your thing.
Mercury switches were only banned by Tripoli, not NAR. I suspect that it was more about being "Green" ( toxic Mercury ), than safety. As for staging BP and APCP motors, I have been doing that, safely and successfully, since the mid-1970's. Note my NAR & TRA numbers . . . I'm no "newbie" !
One of Cris's Quantums is real expensive at $45 for the kit (alt and programming cable), that's less than destroying a rocket due to an off vertical ignition (like point back at the ground).
That's a decent price . . . I just saw that it must be assembled.
That's a "no-go" for me.
Are there any inexpensive "plug & play" units out there ?
I think the general consensus stance is that mercury switches are inherently unsafe for any number of obvious scenarios pointed out earlier in this thread. You're leaving far too much to chance with consequences far too great. Even when it was widely used out of necessity we knew it was a bad idea.
If I had been doing it successfully for as long as you have I would consider myself lucky, not safe.
I flew my first Mercury Switch staged rocket when I was 13 ( I'm 58 ) . . . This was under the direct supervision of a couple of very experienced flyers in our club ( B.C.M.R.A. - NAR Section # 217 . . . We ran the Range on our Club system at NARAM-17, Orlando, FL, in 1975 ), Jim Tucci and Marc "Moose" Lavigne, in 1974. It was a D12-3, staged to a C6-7 . . . A flawless flight & I was "hooked" !
I have a lot of respect for them and treat them with great caution. Since they fire due to deceleration, from aerodynamic drag, all is good, unless the rocket is unstable. I always check and re-verify the CG before flight. If you get a misfire, the arming switch is used to disarm the bird on the pad, so that it can be safely removed and a new igniter installed.
I find it ironic that you’re arguing current safety rules based on a document copyrighted 35 years ago by Jerry Irvine, but I’ve solved it on my end at least. [emoji850]
(1) I am not arguing anything . . . "Non-Electrical" ignition has never been allowed . . . After the initial motor is remotely, electrically ignited, everything else is initiated by it.
(2) Actually, Korey Kline was the initial author and Jerry Irvine "joined in" later.
(3) That document was used because it was the only one that accurately describes the process, whether it was 35 years ago, or not. ( no matter who it was written by )
(4) Tripoli has banned Mercury Switches and Roller Switches . . . NAR has NOT . . . FACT !
This 2013 video shows the remote, electrical ignition, with all other activation generated by the initial motor.
You are arguing and you are doing it with the CURRENT president of Tripoli by using sources from decades ago claiming "if it worked then why can't I do it now????" I've held this in for a while now but all you do is go around and "boost" about your knowledge and how you know how to do everything and that there is no way what you are doing is wrong or unsafe. If you can't go a day without arguing with someone over the internet then maybe you should get off it and go outside. You have become a nuisance and are acting exactly like a typical know-it-all who thinks they are better than everyone even those who have a position of power.
Respect your elders . . .
IMHO Point (1); a spark might cause a few drops of kerosene in a barn to ignite; the kerosene in turn ignites dry hay, which then ignites the barn, but saying that the spark burned down the barn isn't terribly accurate. The spark set off a chain of events that caused the barn to burn down. The ignition of a booster sets off a chain of events. In the same fashion, I think most people would agree that an ejection charge in a BP motor isn't electrically ignited.
Point (2) is immaterial.
Point (3) describes a process but I don't think that validates the idea that the upper stage is electrically ignited, as I mentioned in (1).
Point (4): I don't recall whether mercury switches caused any accidental ignition or other accidents, but I do recall vaguely that HPR Magazine reported on an accidental ignition via a roller switch. Anyone else who remembers this?
Best -- Terry
Hi, Terry !
Point (1) - Remote, electrical ignition is used. Subsequent "igniters" are actuated by the remote, electrically-ignited motor.
Point (2) - Agreed . . . That was merely in response to a comment about one of the authors of the article.
Point (3) - If your position is valid, then staged BP motors must be outlawed, since subsequent upper stage motors are not electrically ignited, but are ignited by a "pyrotechnic source" ( another motor ). Furthermore, "flashpan ignition" and the use of "spiders" should be similarly banned. Before you say there are no BP HPR motors, let me use the example of multiple BP motors that put a rocket into the "HPR Class", due to Propellant Wt. ( 6 D12's, for example : 126.6 gr Prop. Wt. only 102 Nt-Sec . . . 1.6 gr over the 125 gr "Model Rocket" limit of 125 gr. of propellant. )
Point (4) - Personally, I have never liked "roller switches" . . . Tripoli has banned them, but NAR has not. BTW - IMHO, the use of lever-operated (non-roller) "liftoff switches" is just as dangerous.
Dave, we get it. you are old school & don't like the current safety rules. No need to keep repeating yourself!
I just want everyone to understand that it’s okay to argue with the current president of Tripoli whether it’s me or someone else. I certainly make just as many mistakes as anyone else and I’d like to think that I’ll listen to opposing views.
But at some time when people are just saying the same things back and forth there’s no real point to continuing the back and forth. I’ve reached that point. I can no longer continue to discuss this with Dave without getting aggravated, so I won’t. I’m comfortable with the rules as they are.
But something else to consider, even if a person was very safe with a mercury switch, a ballistic recovery would result in metallic mercury being released. I don’t believe many landowners would welcome that. Whether that was also considered when the rule was created, I don’t know.
Interesting staging concept Dave however Myself prefers a Raven 4 altimeter with a velocity check at minimum with time to get the rocket to ignite within a cone area above the launch pad and NOT ignite when it falls outside said cone parameters. Been around six different project teams using ravens exclusively.
Nobody wants to bash that you can’t do it Dave but our main concern with multistage is when this thing shouldn’t light have some kinda system that prevents ignition of sustainor motor. When my university started going for multistage high power with ZERO experience the best d*mn advice somebody gave was get a raven.
It saved our lives and we won national multistage university comps. It’s reliable. It’s simple to program. It’s mach immune. You can even ground test it and input data from open rocket excel files. I’ve seen multistage rockets shred at over Mach and I was darn glad we went with a well programmed raven as the sustainer motor didn’t light during shred. I’ve also seen it where everything works perfectly as simulated.
To be honest I wish they would make a rule to enforce tilt sensing or altitude/velocity checks in high power staging. I don’t see any darn sense in not enforcing it. I’d be cool with a timer on a mid power stage flight personally. But once it’s high power if there’s a safer way to do something why be stubborn?
Respect is earned.
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