[F-FT] Question/thought on Aerotech delays

There has been quite a bit of comment on Aerotech delays lately, part of which was brought about because of comments that you-know-who posted on
his website.
Now, the following question occurs to me, and I don't know how valid it may be...
All of the Aerotech instructions I've seen tell you to insert the Copperhead igniter all the way to the end, where it will be touching the delay charge.
This, in essence, means that the delay charge ignites simultaneously with the propellant charge. Now, if the igniter is placed, let's say, halfway up instead of all the way, then the delay charge will end up being ignited by the hot gases of the propellant, as opposed to the actual igniter itself. If the propellant gases are not as hot as the igniter, then perhaps it will take a second or so for the delay charge to ignite (in comparisoin to instant ignition if the delay charge is ignited at the same time as the propellant).
Now, I don't know the heat of ignition of the delay charge, nor do I know the heat of the igniter versus burning propellant, but perhaps some of those who DO know these things would care to comment on this possibility?
In other words, does placement of the igniter in the RMS motor have any bearing on how long the delay charge will take to burn???
David Erbas-White
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Matt Steele's team ( who name escapes me now) did a R&D report on just this topic at last years NARAM. I know NARTS was collection all the R&D reports. I don't know if they are published yet. You might try contacting NARTS. There conclusion of the report show a defiant correlation on igniter placement and time of delay.

possibility?
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Bruce Canino wrote:

Why is the correlation defiant??? <G>
David Erbas-White
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DOH!, should be "definite correlation"

this
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I wonder how big a motor they included. For a 6" long motor, it might not have the same impact if the igniter is 1/3 of the way down as on a 36" long motor.
Why would anyone not want to put the igniter all the way in anyway? The only thing that comes to mind is that you don't have the proper igniter.

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AZ Woody wrote:

There are times I've put an igniter in, and it has 'stopped'. Only because I knew it wasn't in far enough did I 'twirl' it and get it to slide in farther. The end of the igniter sometimes catches on the gap between grains.
David Erbas-White
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Then you try again. I've had small RMS motors where I couldn't get the igniter thru the nozzle due to the pyrogen. Disassemble the motor and rebuild with the igniter in the proper place...
I myself have never seen an igniter stuck on the "grain gap", but then motors with multiple grains tend to have a good sized core..

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When building a motor, I'll often take the igniter and bend it at the length it should be when inserted in the motor. That way, if I'm installing it at the pad, I'll know if it makes it "home"

The
igniter.
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This should be in the FAQ.
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A good trick I too have used for years.

This can also happen in the MR C-slot grains, where the ignitor is fatter than the C-slot.
    Bob Kaplow    NAR # 18L    TRA # "Impeach the TRA BoD"         >>> To reply, remove the TRABoD! <<< Kaplow Klips & Baffle:    http://nira-rocketry.org/LeadingEdge/Phantom4000.pdf www.encompasserve.org/~kaplow_r/ www.nira-rocketry.org www.nar.org
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There are some clubs that will not allow you to install your igniter in the motor until after you are at the pad on motors "F" size or above, which would mean that you would have to take your unassembled motor with you out to the pad and assemble it there, or at least take the incompletely assembled motor, and hope you don't drop an O-ring on the way.
Al
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The ignitor installation is only a problem on some of the 18mm and perhaps 24mm RMS reloads. D and E stuff.
I've built tiny Magnelight ignitors small enough not only for any reload, but even for the old Apogee 13mm and 18mm competition motors.
    Bob Kaplow    NAR # 18L    TRA # "Impeach the TRA BoD"         >>> To reply, remove the TRABoD! <<< Kaplow Klips & Baffle:    http://nira-rocketry.org/LeadingEdge/Phantom4000.pdf www.encompasserve.org/~kaplow_r/ www.nira-rocketry.org www.nar.org
"To enslave men, successfully and safely, it is necessary to have their minds occupied with thoughts and aspirations short of the liberty of which they are deprived. A certain degree of attainable good must be kept before them." Frederick Douglas, "My Bondage and My Freedom," 1855
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AZ Woody wrote:

I suspect that the problem is mainly due to the igniter getting stuck before it reaches the top of the core, and the user doesn't realize it's not all the way in.
BTW, the Ellis 29mm I69 instructions currently say to put the igniter in about 4-5 inches (it's a 17" motor). Putting it all the way in tends to cause a cato. The first one I tried was before they started telling people not to put it in all the way, and sure enough it catoed. The second time, I put in according to the new instructions and it flew fine -- but the delay was over-long, which I suspect was due to the placement of the igniter.
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This is what the Rocketflite folks told us to do igniting their big honken cored BP motors. It vastly reduced the cato rate on FSI F100s too. It causes the motor to come up to full thrust a bit slower, reducing the shock that causes the cato. But BP doesn't have the combustion characteristics of APCP, and igniting an APCP motor like this is likely to cause chuffing.
    Bob Kaplow    NAR # 18L    TRA # "Impeach the TRA BoD"         >>> To reply, remove the TRABoD! <<< Kaplow Klips & Baffle:    http://nira-rocketry.org/LeadingEdge/Phantom4000.pdf www.encompasserve.org/~kaplow_r/ www.nira-rocketry.org www.nar.org
"To enslave men, successfully and safely, it is necessary to have their minds occupied with thoughts and aspirations short of the liberty of which they are deprived. A certain degree of attainable good must be kept before them." Frederick Douglas, "My Bondage and My Freedom," 1855
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The team name was "Pod Bay Doors". There was a recent article in Extreme Rocketry (#44) on this topic and I assume it was based on the R&D report.
However, the thesis of that report is that the _radial_ position of the igniter effected the delay time. I have a few problems with that thesis.
1) It only applies to delays that have been drilled. 2) It assumes that the igniter is lighting the delay. 3) There was a lot of hand waving involved in the "proof". Matt no longer had access to the data which he claims supports this thesis. Not that I don't trust him but I really dislike that sort of argument.
If the igniter were in fact lighting the delay, then we would see many more instances of misfires that light the delay element but not the motor. Since I have only seen misfires where both failed to ignite, I can only conclude that the igniter does not light the delay. Not very often anyway.
If the igniter doesn't light the delay, then the delay must be lit by the main propellant charge. If the propellant grains are ignited some distance from the delay, then because the combustion products are trying to exit through the nozzle, they may stagnate at the forward end and prevent ignition of the delay element for some period of time.
An extreme case of this was recently documented by Cesaroni in one of their Pro38 motors. A non electric match type igniter was positioned part way up the motor. The motor lit in a non normal fashion and ended up producing a pool of molten aluminum from the case. Read the FAQ item for "Can I use a different igniter?" on their web site. http://www.pro38.com/faqs.php
Bruce Canino wrote:

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David Schultz wrote:

In such a case, I think you'll find that the igniter would, in turn, light the propellant. After all, the flame and exhaust gases from the burning delay only have one way to go -- out the nozzle.
-Kevin
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Point.
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If the kit uses a spacer tube (an E or F in a 29/40-120) then the igniter is at the end of the fuel grain. Masking tape is used to prevent the igniter from going any further. Works fine.
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Jim wrote:

Yes, but...
In these motors, the delay is of a different size, and with different insulators, than the HPR motors (don't know if this makes any difference, but who knows?). Also, for these motors, the delay tends to be shorter, anyway (in comparison to the S/M/L delays of the HPR motors).
David Erbas-White
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Sound to me like a presentation was made only so Matt could stand up and present something (ego trip thing). "I'm Matt Steel and will tell you something you don't know" "I have no proof, but I'm Matt Steel".
It seems to me, that in general, the delay is harder to ignite than the propellant, so the fact that you don't see many flights where the delay ignites but not the propellant, it doesn't surprise me... Once the delay ignites, it will get the main fuel burning.. Trust me.. Often called a "chuff". If the delay is burning, the only way the propellant wont catch is if the propellant was made of a non-flammable material! Propellant torches the delay, things usually work.. Delay torches the propellant, things usually work. The ideal is that both light at the same time, and the motor should perform as expected.

Padlipsky
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