Been away...why the gap?

[KenECoyote]

Hi, so I assembled an old 29mm* AT reload and wondering why the instructions note that you install the delay spacer and there should be 1/16-1/8" sticking up...later you add an o-ring and have it up against the insulator disk, but the space makes the o-ring basically floating loose. Am I missing something?

(Sorry if this is something stupid missed, I've been away for years and just coming back.)


*Edit: 29mm (using a mmt 38mm adapter).

 

[Wayco]

The delay spacer goes into the delay insulator with the delay grain, none of which I see in that picture. That doesn't even look like AT hardware...
All of the above mentioned parts fit into the forward closure.

 

[KenECoyote]

Sorry, I didn't note that I was using an Aerotech adapter for my 240 case since it's a 180 reload (also it's 29mm). Here are all the pieces forward of the grains and they were all used in assembly...I just took apart for photos. Top is what I used, under is 240 case and standard fwd closure.

 

[KenECoyote]

The delay spacer goes into the delay insulator with the delay grain, none of which I see in that picture. That doesn't even look like AT hardware...
All of the above mentioned parts fit into the forward closure.

Thanks! I've posted reply above.

 

[Jmhepworth]

Without seeing more, it looks like you put the adapter spacer between the liner and the floating closure. The adapter spacer is on top of the floating closure, not between the liner and the floating closure. The forward retaining ring then holds it all together.

I‘m not looking at the instructions, but my recollection is that going from aft forward, you put the grains in the liner, then the seal disk or insulator, then the O ring, then the assembled floating closure (spacer, delay grain in the delay insulator, and O ring) with ejection charge, then the adapter spacer, and then the forward retaining ring.

http://aerotech-rocketry.com/upload...0ee_ 29mm_reload_adapter_inst_rev_1-6-20.pdf

 

[KenECoyote]

Without seeing more, it looks like you put the adapter spacer between the liner and the floating closure. The adapter spacer is on top of the floating closure, not between the liner and the floating closure. The forward retaining ring then holds it all together.

I‘m not looking at the instructions, but my recollection is that going from aft forward, you put the grains in the liner, then the seal disk or insulator, then the O ring, then the assembled floating closure (spacer, delay grain in the delay insulator, and O ring) with ejection charge, then the adapter spacer, and then the forward retaining ring.

http://aerotech-rocketry.com/upload...0ee_ 29mm_reload_adapter_inst_rev_1-6-20.pdf

Hi, I believe that order is the same as I had done and lined up above. Also in my first picture, I think I'm showing the floating closure with the adapter spacer in the correct placement? I appreciate the help!

 

[KenECoyote]

I just checked another 29mm 40-120 reload I had assembled based on the instructions and they do say that "Delay Charge Assembly Protrudes Approx. 1/16 (inch)", so that does confirm that the delay part sticks up and that charge is much smaller than the inner circumference of the forward o-ring.

 

[jd2cylman]

That compresses the o-ring.

 

[KenECoyote]

That compresses the o-ring.

Actually the delay grain assembly doesn't compress the o-ring...the part sticking out only compresses against the seal disk/insulator unless you flex it enough...at least that's what I see and based on the gap in the pictures. The o-ring itself can be moved loose into the gap unless the seal disk center flexes back into the grain?

 

[KenECoyote]

Is the o-ring held in place by the pressure of the motor burning and more to prevent gas from escaping the sides of the fwd closure?
Fyi I posted this to the AT open thread as well jic.

 

[rcktnut]

When you tighten the closures they compress the whole length of the motor/ propellant "chain" whatever you want to call it. From aft to fore the closures once tightened are exerting pressure on the components. The little extra length on the delay liners compress the delay o-rings. Of course everything is loose until the closures are tightened. Follow directions everything will be fine.

Edit: Just noticed a simple short answer post #8

 

[KenECoyote]

The little extra length on the delay liners compress the delay o-rings.

The delay o-ring compression was something I hadn't considered, so that is the answer imo. I didn't think it could compress 1/16", but trying it out it seemed to. The bigger gap on the 29/180-240 is more perplexing, but I did follow instructions on assembly and I think tightening things down should be fine. I'll still check with one more person on site before I launch jic.

Thanks everyone!

 

[AeroTech]

The delay o-ring compression was something I hadn't considered, so that is the answer imo. I didn't think it could compress 1/16", but trying it out it seemed to. The bigger gap on the 29/180-240 is more perplexing, but I did follow instructions on assembly and I think tightening things down should be fine. I'll still check with one more person on site before I launch jic.

Thanks everyone!

Please see my response on the AeroTech thread.

 

[KenECoyote]

Update: Post #4,119 on AeroTech thread:

This is what it should look like assembled. Your delay O-ring appears to be the wrong size and I don’t see the forward delay spacer (rubber washer). What is the lot number of the reload kit?

Ok, I'm now starting to make some sense of this...not having the proper parts would definitely explain anything out of spec/unusual. I had received this ~6 years ago from a former rocket club head who owned a hobby store he was liquidating and I purchased the H129W (Medium delay) motor in a lot. I checked the discarded bag and there was a piece of masking tape over the corner which I didn't think anything of...I pulled it off and there was a hole! So while I'd like to think the owner would know better than to swap parts or just replace with a different one, but that seems to be the case. I suspect he put in a delay spacer and delay o-ring that was too large for this reload. There isn't a lot number, but the date inside the instructions note "JAN 19 1999"...apparently he had let the shop wither away for years. I'll see if I can find/buy another H129W Med delay (or similar) to determine the proper parts.

 

[tOD]

I've got an unopened 29/180 H128W-14A I'd be happy to open it up and photograph the parts for you if that would help

 

[KenECoyote]

I've got an unopened 29/180 H128W-14A I'd be happy to open it up and photograph the parts for you if that would help

Very kind of you! However that spurred me to dig up my other reloads and I had one more H128...it appears that someone did switch out the delay parts! WTH
So on the left is the delay that was swapped in without my knowledge and because the delay o-ring is smaller, the delay grain sits on top of it, explaining why the spacer then extends out. On the right is the proper delay setup and the delay o-ring is larger so the delay grain sits inside of it and the spacer is flush (plus there's the rubber disk).

So for the life of me I don't know how anyone can do something so idiotic which can result in a failed reload. Smh

 

[dhbarr]

So for the life of me I don't know how anyone can do something so idiotic which can result in a failed reload. Smh

Usually the idiot who does that to me... is me!

 

[KenECoyote]

Usually the idiot who does that to me... is me!

Lol, in other cases that would be me as well, but with reloads I try to be extra careful. I got this as part of an old stock lot from a hobby store closeout and apparently someone else changed the delay parts and taped up the corner of the package!

 

[dhbarr]

Lol, in other cases that would be me as well, but with reloads I try to be extra careful. I got this as part of an old stock lot from a hobby store closeout and apparently someone else changed the delay parts and taped up the corner of the package!

Yup, borrow a piece, replace it with the wrong one later, end up with a bag of uncomfortably exciting miscellaneous motor bits.

 

[Cl(VII)]

Yup, borrow a piece, replace it with the wrong one later, end up with a bag of uncomfortably exciting miscellaneous motor bits.

Forgive the off topic, but I feel like “Uncomfortably Exciting Miscellaneous Rocket Bits” would be an epic name for a project.

 

[tOD]

That's how "No exchanges or Returns" policies get instituted by vendors.

 

[KenECoyote]

That's how "No exchanges or Returns" policies get instituted by vendors.

Makes sense, but tbh I first thought it may have been the "out of business" vendor who did it at some point since I'd expect any vendor would check a reload package if someone was returning it and this wasn't professionally resealed...it was a small piece of masking tape on the corner! I thought was just some random spare piece that got stuck on since it's so commonly used. Heck, I have little pieces of masking tape all over my rocketry stuff.

Good lesson to check any packages even in lots before you buy them.