heada
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I'd say if you have doubts with the instructions, ask Aerotech. They may have revised them since the reload was made.
Dumb questions regarding Aerotech RMS igniter positioning
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overklock
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Sent them an email to the address listed on their website, waiting to hear back.
waltr
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It is possible the reloads I obtained were older and newer instructions are now used. But, these should be easily available directly from AT's web site but are not.
RocketTree
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The igniter is fully inserted and seated against the delay grain on reloads or single use motors where there is no grain spacer. On smaller reloads, such as the D15 in a 24/60 case or E reload in the 29/140 case we are instructed to add tape to the top of the grain to act as a stopper (as shown in figure 6 & 7) so the igniter is at the top of the propellant grain. Most of my Aerotech igniters have a black heatshrink depth gauge on the igniter that corresponds to the correct depth for that reload, so you don't really need the tape. You want to ignite the top of the propellant, not the delay.
overklock
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In my case I’m using a G RMS though, where it says specifically to insert it until it’s touching the delay grain
RocketTree
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The igniter would still be positioned at (or near) the top of the propellant grain, so that is correct. This would also apply to most disposable motors of that size.
overklock
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So then follow up question, why is it that the directions that come with the motor say to push the igniter all the way up into the delay grain, past the propellant? The worry being that the ejection charge fires off too early. See why I’m confused here?
All of Aerotech’s instructions should be available here:
https://www.rocketmotorparts.com/page/instructions
waltr
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Yes, older ones.
All the 29/40-120 instructs I have still show to install the 'COPPERHEAD' igniter while building the motor.
How long ago were copper head igniters discontinued?
Hey, I flew a 29/40-120 Green full-G slotted reload with the included Copperhead last year!
edit: I did NOT quite follow the instructions
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overklock
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Broken record here, but did you ensure that the igniter was pushed all the way up against the delay grain?
overklock
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@Steve Shannon @Antares JS @waltr @smstachwick
UPDATE:
No word from @AeroTech yet, but I believe I may have found a solution.
After taking another look at the included instructions, I'm convinced that it shows the delay element being flush with the grain, rather than there being a delay spacer present. My guess here is that these instructions were designed for both motors that had a delay spacer, as well as ones without (hence the photo showing the grain and delay element being flush). Obviously with a longer delay, there wouldn't be this spacer, thus the delay element would be flush with the propellant. This would also be backed up by the fact that the instructions do say "insert delay spacer if included".
It would make sense for them to put "touching the delay element" if the delay element itself was flush with the propellant grain on specific motors with longer delays.
So in this case, until Aerotech says otherwise, it would make sense for the igniter to simply go to the back of the propellant grain and not continue to be pushed forward past the spacer and into the delay element. The delay element should ignite as the internal pressure builds just as it does on standard E motors.
UPDATE:
No word from @AeroTech yet, but I believe I may have found a solution.
After taking another look at the included instructions, I'm convinced that it shows the delay element being flush with the grain, rather than there being a delay spacer present. My guess here is that these instructions were designed for both motors that had a delay spacer, as well as ones without (hence the photo showing the grain and delay element being flush). Obviously with a longer delay, there wouldn't be this spacer, thus the delay element would be flush with the propellant. This would also be backed up by the fact that the instructions do say "insert delay spacer if included".
It would make sense for them to put "touching the delay element" if the delay element itself was flush with the propellant grain on specific motors with longer delays.
So in this case, until Aerotech says otherwise, it would make sense for the igniter to simply go to the back of the propellant grain and not continue to be pushed forward past the spacer and into the delay element. The delay element should ignite as the internal pressure builds just as it does on standard E motors.
I just got home and looked at the instructions for that motor. It was a G76-10G, 2012 date code, same instructions you posted.
After thinking it over a couple times, I remember taping the two grains together and putting a piece of masking tape over the forward grain while they were in the liner. I marked the igniter tail to indicate insertion length and left the tape in place, but I can't remember if there was a delay spacer or not.
It looks like you have answered your question anyway!
It's been many years since, but I made a lot of flights with my 29/40-120 casing using F and G reloads. Back then the common wisdom was to position the igniter at the front part of the fuel grain. When I would build a motor I would first put the nozzle against the fuel grain, insert the igniter and push it so the end was flush with the front of the fuel grain then I would bend the wires over at the back of the nozzle. Then take the igniter out and set it aside while building the motor. Then I could put it back in and know it was going to the right position. I never had a problem with incorrect delay time, or chuffing on the pad. These were with igniters made by our motor vendor, not the copperheads.
overklock
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It seems like the common consensus is that it should simply go to the forward end of the fuel grain and stop there rather than going further, past the spacer and into the delay element. Makes sense to me.
overklock
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The tape at the end of the fuel grain would mean your igniter would only go to the very end and not go past into the delay grain. Makes sense to me. The 10s timer (I think) would mean that delay grain being flush with fuel grain.
n3tjm
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I always put a piece of tape on the top grain to prevent the igniter from going into the delay cavity, unless there is no delay spacer. You want as much igniter pyrogen as possible touching the propellant, and any in the void is wasted space.
Yes, to be sure that there was pyrogen igniting the fuel grain directly in the slot. There’s not a lot on the small Copperhead and I wanted it to be effective. Especially with an older motor. One of the grains was very oxidized, looked like a different propellant.
That I don’t quite remember. It’s the longest delay for that reload, but it seems like there was a small spacer. I’m not sure and didn’t take photos.
overklock
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Very nice, makes sense. Aerotech really needs to be more specific on their instructions!
Currently they’re in the middle of major website revamping and product line rebranding. I think a few kits are being/have been redesigned too.
They’ll likely get around to instructions tweaking but I don’t forsee that being soon or exceptionally high priority. For most people they work fine.
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The igniter should be positioned at or near the top/forward end of the propellant grain.
overklock
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Thank you for the confirmation! I will make sure I stop at the forward end of the propellant grain and not go further into the delay spacer and delay element.
loopy
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The distance between the bottom of the delay grain and the top of the propellant grain are fairly negligible, especially when the length of the pyrogen dip on the igniter is considered. If the tip of the igniter is against the delay grain, the pyrogen dip is long enough to extend down past the top of the propellant grain. Thus, it is lighting both pieces. The main thing the instructions are trying to get you to avoid is stopping halfway up the propellant grain and lighting the middle of the grain rather than the top.
overklock
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I guess my main concern is a situation in which the pyrogen dip does not burn evenly, resulting in a delay element that begins burning much sooner than the propellant, equating in early ejection.
I had this happen on my most recent RMS launch, which is what lead me to creating this thread in the first place.
This is not true regarding some reload kits for the 29/40-120.
https://www.rocketryforum.com/threads/clustering-composites-question.170547/post-2234372Have a read on an easy way to get 20 year old G64 reloads to light first time.
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When we consider the highest pressure location in an operating motor, I would hazard a guess the delay grain spacer is in fact fairly negligible.
I was talking about reload kits where the fuel grain isn't as long as the casing, for instance the various E and F reload kits for the 29/40-120 casing. There is a pretty big open space between the front of the fuel grain and the delay charge.
The main thing with any motor is simply "how do I get it lit quickish and running properly?" Chuff, is not your friend.
This is dependent on the composition type you are lighting, the igniter you are using and the age of the reload, the method I described in my last post works consistently. The only change would be adding a piece of tape to the top of the composite. However, with the compressed BP slice in there as an augmenter as described, the igniter comes to s stop against it.
Norm
gldknght
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I always try to follow Aerotech's instructions regarding assembly of their motors. Some motors assemble slightly different from others. If the directions say to push the ignitor against the delay, I do it.
If the directions say to push the ignitor against a piece of tape at the top of the fuel grain, I do it.
Maybe I've been fortunate, but have never had an AT motor failure.
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