HPR igniter failure modes?

What is the rmr consensus wrt hpr igniter failure modes:
1) bad bridge-wire connection
2) bad clip connection
3) insufficient delivered power (controller problem)
4) insufficient pyrogen quantity (too short burn)
5) poor pyrogen quality (not hot enough)
6) other?
Have heard that some people use redundant igniters, especially for AP
clusters. But I wonder what happens if one of the igniters fails, leaving a
big chunk of unburned pyrogen that has to slide/be pushed out through the
nozzle. Can this cause an over-pressurization cato? or something else?
Am trying to decide whether it makes sense to experiment with dual-filament
4-lead igniters. Would like to hear of your experiences.
Reply to
bit eimer
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All of those are potential ignition failure modes, depending on the igniter, the motor, and the launch system. Since those three things vary greatly, a failure that is common in one may be uncommon with another. Copperheads are highly susceptible to shorts due to their unique construction. Most other igniters rarely short, except at the clips.
Bridge-wire connection can usually be determined by checking continuity. The exception would be a short at or near the bridge-wire.
Generally speaking, and just going on personal observation at launches, it seems that the most likely failure mode is bad clip connection (either open or shorted).
I'd say that insufficient power runs a close second as most likely cause of ignition failure.
Most ematches have insufficient pyrogen to ignite a motor without adding some type of additional pyrogen or "booster" material.
That doesn't seem likely to me, since the first igniter (and ignition of the propellent) would burn the second igniter. What is more likely to cause a cato is if the igniter wires bunch up and block the nozzle.
dual-filament
IMHO it's not worth the trouble.=20

Reply to
raydunakin
Ray, I cut your message because for some reason my system refused to put the usual ">" in front of all your text. What system do you use?
Anyway, reading between the lines that are no longer there, it seems you're suggesting that redundant igniters is not a particularly useful technique. For a single motor, I completely agree, but it seems to me that there is always the potentially for a marginal igniter screwing up a cluster and that redundancy can minimize that danger.
I've just been thinking that a dual filament igniter could simplify prep (compared to discrete redundant igniters) and save on pyrogen.
Reply to
bit eimer
Not an igniter failure mode as such, but something that can cause an ignition failure (or worse, a mid-port ignition) is igniter placement.
In the case of Pro38/54 (a special case really) if the e-match is not correctly place (i.e. at the head end of the motor) you won't get ignition.
Reply to
Niall Oswald
If you are worried about cluster ignition in particular, don't use standard Bridgewire igniters. It takes too much amperage to fire them reliably. I have had outstanding luck clustering AT APCP motors (7 at a time) and Monotube Hybrids (4 at a time) by using Dipped Oxral e-matches. I also paint the top fuel grain (or the bottom of the preheater grain in monotubes) with pyrogen. E-match ignition is highly reliable when done this way.
Unless you or the club you are flying with has a high amp "Master Blaster" type of relay.... would suggest using the method described above.
Mark A Palmer
Reply to
Mark A Palmer
this happens?
happens, igniter gets reused.
not since we switched to 12 volt
or oxidzed propellant (burn doesn't take)
see 4)
Reply to
tater schuld
Nutscrape 4.8 and Google Groups, on an antiquated Mac G3.
technique.
I wouldn't say that. There are times when it can be useful.
I just don't see any big advantage to it. You'd still have four leads to hook up.
...
Reply to
raydunakin
I think what he meant is that it is a lower-current device like a Daveyfire N28B.
BTW, anyone know how such "electric match" igniters achieve their low fire-current characteristic?
Use of tungsten bridge wire? size of bridge wire? use of primer dip prior to pyrogen dip?
Reply to
bit eimer
According to Daveyfire's literature:
N28B
N = Normal 28 = Bridgewire diameter (microns) B = "Burst"/"First ignition component"
The N28B igniters burn for about 2ms. The N28F igniters burn for about 40ms.
Daveyfire had many types of igniters. There were also N20F and N32F igniters. The N15B burned for about 0.7ms and could be fired by a sneeze (all fire 0.16 amp).
Dean
Reply to
Dean

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