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Give me your Aerotech LMS tips

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Joshua F Thomas

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I have a 4" Loc Goblin to launch saturday, and an Aerotech G77-4W LMS to assemble for it. I've never put one together before, so before I break open that package, please give me any of your hard-earned tips/tricks/gotchas/look-out-for. Thanks!
 

SecondRow

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Make sure you insert the delay section the correct way into the forward closure. And don't get epoxy on the grains or on the delay element. Other than that, it's pretty easy. Just follow the instructions.
 

mo2872

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1.)Read the included instructions.
2.)Understand the included instructions.
3.)Use and understand the diagram, and where all pieces go.(This includes the to-scale o-ring diagrams)
4.)Repeat 1-3 until confident you can assemble correctly.

I’ve only assembled 4 so far, and have caught myself in errors each time. It’s not that it’s hard, I was just rushing. For example, I drilled my delay, and proceeded to insert it with the drilled end away from the igniter.....DOH!! Q-tip stick worked to poke it back out.

If any questions, ask a more experienced launcher! I’m sure they’d be glad to help!
 

Joshua F Thomas

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Make sure you insert the delay section the correct way into the forward closure. And don't get epoxy on the grains or on the delay element. Other than that, it's pretty easy. Just follow the instructions.
Is the delay spacer (small red cardboard tube) supposed to face the grain or face the aft closure?
 

Joshua F Thomas

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2nd question: The kit came with a 3.5" thin cardboard tube which was holding the igniter. It is labeled "liner" in the instruction list and has no other listed use. Is this just a protector for the igniter?
 

SecondRow

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Is the delay spacer (small red cardboard tube) supposed to face the grain or face the aft closure?
1. The LMS motor doesn’t have an aft closure. The casing has the nozzle already built into it. The yellow piece that you fit the delay assembly into and then epoxy into the casing is the forward closure.
2. The delay spacer should be closer to the grain. When building the delay assembly, the delay element should be in between the o-ring and delay spacer. When you put the assembly into the forward closure, it should be o-ring first.
 

SecondRow

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2nd question: The kit came with a 3.5" thin cardboard tube which was holding the igniter. It is labeled "liner" in the instruction list and has no other listed use. Is this just a protector for the igniter?
The “liner” is the cardboard tube that the grain fits into. Usually, the grain is already in the liner when you open the package up. The liner is a part of the assembly and goes into the casing with the grain inside it.

The thin tube that holds the igniter is protection for the igniter. I keep it in the that tube until I’m ready to launch.
 

Joshua F Thomas

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1) whoops I meant to say forward closure

2) Ah, the grains came “preinstalled” into the liner, and I didn’t even realize they were separate.

3) Ok, I’m clear on installation order, thanks
 

prfesser

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In the forward closure the delay grain goes in before the spacer.
 

Joshua F Thomas

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Now I'm confused again. Does the spacer go *before* the delay grain, as prfesser says (or as I misread), or *after* the delay grain as SecondRow has said?
 
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Joshua F Thomas

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Spacer FIRST:

spacer_first.jpg


Spacer AFTER:

spacer_second.jpg



Why of these is correct, any why?

The instructions could use clarification in this regard.
 

mo2872

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Do you have the instruction sheet to reference?
 

prfesser

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Spacer FIRST:

View attachment 432014


The instructions could use clarification in this regard.
The image above is correct. I was confused when you said "spacer first" because the spacer is the LAST piece that goes into the forward closure. See the instructions: (A) insert the delay o-ring into the (yellow) forward closure; (B) insert the delay insulator (thick walled paper tube); (C) insert the delay element, and finally (D) insert the delay spacer.

Then after the liner, propellant, and forward insulating disc are inserted into the casing, epoxy is applied and the forward closure is screwed into the case.
 

AeroTech

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The illustration is crystal clear:
F85579C2-2DE8-45FF-B4A2-B0C19B565403.jpeg

If you reverse the position of the components or leave out the O-ring (a couple of the photos posted show no O-ring) you will have an instant bulkhead burn-through.
 

Joshua F Thomas

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The illustration is crystal clear:
View attachment 432035
If you reverse the position of the components or leave out the O-ring (a couple of the photos posted show no O-ring) you will have an instant bulkhead burn-through.
Alright, so first, it's a lot easier to see when it's blown up that large. Or perhaps I need new glasses....

Second, I had some confusion because the forward closure assembly has an two-level surface (best seen in Figure 2) at the far end, which looks a lot like the spacer would fit into nicely.

Thanks for all the help.
 
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SecondRow

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Second, I had some confusion because the forward closure assembly has an two-level surface (best seen in Figure 2) at the far end, which looks a lot like the space would fit into nicely.

Thanks for all the help.
If you mean the chamber on the other side of the forward closure, that’s where the ejection charge (the black powder in the red plastic cap) goes.
 

AeroTech

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The two-level surface is a shallow counterbore that allows some of the black powder to migrate into greater contact with the delay element and enhance ejection charge reliability.

Alright, so first, it's a lot easier to see when it's blown up that large. Or perhaps I need new glasses....

Second, I had some confusion because the forward closure assembly has an two-level surface (best seen in Figure 2) at the far end, which looks a lot like the spacer would fit into nicely.

Thanks for all the help.
 

Joshua F Thomas

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4" Goblin flew today on the G79-W LMS. However it had a problem at ejection, which I am willing to attribute to my own fault. Ejection charge appeared to happen right after burnout. See video:

The Goblin was flown again on a single-use G79-W and worked perfectly.
 

bill_s

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Why of these is correct, any why?
The drill and spacer are away from the black powder so a bunch doesn't get down in the motor and blow up the casing instead of blow out the top. I don't remember about the LMS, but with RMS only a small hole connects the charge well and the ejection charge.
 

Joshua F Thomas

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The drill and spacer are away from the black powder so a bunch doesn't get down in the motor and blow up the casing instead of blow out the top. I don't remember about the LMS, but with RMS only a small hole connects the charge well and the ejection charge.
No drill here, man. You sure you in the right thread?
 

bill_s

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^^-- it was mo2878 that mentioned drilling. Ability to adjust the delay was a big motivation for LMS/RMS for me -- SU has 4 and 7 and all my rockets needed about 5.5 . ;(
 

Joshua F Thomas

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It's an iphone, on a windy day in a big field, and the audio pickup isn't great. Both my wife and I heard it quite well. The only reason you can hear *me* is that I'm holding the phone a few inches from my face.
 

TheTank

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It definitely popped. I was there yesterday and heard it.

Did you drill the delay grain or perhaps forget to grease the o-rings by chance? I've built a bunch of the G-79 LMS motors but haven't had any issues. I see Aerotech was posting here in this thread, they can probably tell what happened from the video and might chime in.
 

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