38mm Forward Closure Plugged Threaded Question

The Areotech plugged and treaded forward enclosure has a pocket that receives the delay grain (to allow tracking smoke?).

Question: Do I use the delay o-ring and the delay spacer in this enclosure?

It think not because there is a step at the bottom of the pocket that is the same height as the o-ring. And once assembled the delay sits flush when I leave the o-ring a spacer out. But want to confirm.

thequick said:

The Areotech plugged and treaded forward enclosure has a pocket that receives the delay grain (to allow tracking smoke?).

Question: Do I use the delay o-ring and the delay spacer in this enclosure?

It think not because there is a step at the bottom of the pocket that is the same height as the o-ring. And once assembled the delay sits flush when I leave the o-ring a spacer out. But want to confirm.

Click to expand...

You use all of the parts just as you would with an open closure.

The only difference when using the 38mm Plugged forward closure is...(and not adding the BP)

1-4. Fig.-3: Insert the delay charge assembly shown in Fig.-1 into the delay cavity, o-ring end first, until it is seated against the forward delay spacer. NOTE: When using a plugged forward closure ONLY, fill the opening in the forward delay spacer with grease prior to installing the delay charge assembly

https://www.aerotech-rocketry.com/c...P-RMS_Instructions/38mm/38_1080r_in_20067.pdf


Tony

The grease inhibits the delay grain from burning. I’ve done this for an I1299N-p Warp 9 load in a RMS38-480 casing.

markkoelsch said:

You use all of the parts just as you would with an open closure.

Click to expand...

Mark,

So last weekend, while shooting the breeze with Wildman up at TWA, I happened to grab a plugged/threaded 38mm forward closure from Tim's inventory to look at. Sure enough, exactly as OP describes, there is a step/lip machined into the closure right where the o-ring would normally go. I love AT, but these random inconsistencies that keep coming up as of late are frustrating to the end consumer. Maybe OP can post a pic please?

markkoelsch said:

You use all of the parts just as you would with an open closure.

Click to expand...

That certainly wouldn't be possible with the closure I have, which I think is what the OP is asking about also (and Justin mentioned above). As mentioned, the closure has a metal lip at the front that is the size of the "Delay O-Ring" as it's named in the CRDK instructions. So this means two things:

1) The 'Forward Delay Spacer (13/16" O.D. Washer)' wouldn't lay flat, since it's the diameter of the entire cavity, and that diameter isn't maintained to the bottom of this closure's cavity.
2) The 'Delay O-Ring' would sit on top of this lip rather than going all the way to the front of the delay cavity

So if these two pieces are installed, you end up with a big air-pocket at the front of the closure, and the delay itself will not seat fully into the delay cavity (it sticks out by the thickness of the two above-mentioned parts) and could interfere with the motor grains. Or if you leave these two pieces out everything fits exactly as it does in other 38mm forward closures, flush with the surface of the closure.

So I'm not sure that all of the 38mm plugged/threaded forward closures have this, but there are definitely some that do (I only have one, so it's 1 out of 1 for me).

My closure is already fully-assembled / waiting to fly from a flight I didn't get to do at LDRS this year, so I can't take a picture of the empty cavity right now.

Here what it looks like with the o-ring and spacer. This doesn’t look like it will work. (In case the pic doesn’t open, the delay grain is sticking out about a 1/4” -.195” to be exact - when the o-ring and spacer are used)

Looks like I can post pictures, so Here is a picture of the step inside the enclosure and the assembled enclosure w/o the o-ring and spacer to compare to my earlier post

I don’t want to give anyone the wrong impression. I have two open closures, one was modified with Cotronics 4700 and a 16 hour oven cure and flight proven with an I1299N at UROC22. I am only attaching the file to prove how the delay grain sits in my case. For a more direct comparison have someone upload a pic from their motor with a proper Aerotech plugged closure.

I have the same closure with the step as you and woferry. As you suspect, you don't use the o-ring and forward spacer with it. Instead you grease up the forward end generously.

In a plugged closure, you don't need the o-ring and it can become a pain to assemble it because the compressed air in the cavity in front tends to push the delay assembly out again. The grease on the forward end protects the grain from burning from the forward end when the o-ring is omitted and it also protects the casing. It also helps prevent the delay train from falling out during assembly.

Reinhard

I was looking at AT site and I did not see any reference to this.

Is this the 38mm Endburn-style plugged and threaded fwd closure?

terryg said:

Is this the 38mm Endburn-style plugged and threaded fwd closure?

Click to expand...

No. The endburn-style closure differs by not having room for a delay assembly:
https://www.aerotech-rocketry.com/c...wgs/38mm_hp_rms/38-360/38-360_i49n-p_assy.pdf


Reinhard

markkoelsch said:

I was looking at AT site and I did not see any reference to this.

Click to expand...

And this is exactly the problem and why the OP was asking the question. We've run into this same issue and came to the same conclusion as others have stated. Leave those two pieces out and use grease.

Thanks everyone! Good to know it is not just me.

I was expecting the same geometry as the std enclosure but with threads instead of a charge well. Pretty strange to see a different design that needs a different assembly method. But I guess there is a good reason. Maybe additional wall thickness in this area to support the loads from the recovery system...

So new topic:
Has anyone seen threaded enclosures fail?

Just for good measure I emailed Charlie and Karl at Aerotech about this.

Not to stir the pot, but doesn't this become a motor certification issue if the hardware design has changed?

I have no clue. And to make matters worse on like two different rockets RSOs at various places cleared it for flight with a Cotronics plugged AT open closure converted to closed by epoxy plug. One of those was a complex flight over a year ago. The thing flew at a sport launch. And it was inspected. Not trying to make the certification issue worse or stir the pot just stating an experience. Motor starters were used in stock fashion no head end ignition. And it worked. Whether research mod or not. IDK.

This is that open closure sealed with that oven cure 4700 Cotronics which didn’t CATO at UROC22.

Had a good flight today. Didn’t use an o-ring or spacer.

I heard back from Karl Baumann of Aerotech. His response follows:

Hi Mark,

That is correct the delay O-ring and forward delay spacer are not used, the insulator
Delay module and aft delay spacer are still used, make sure you grease the forward
End of the delay element to prevent the head end of the delay from igniting

Best,
Karl

Here's a neat thought, produce documentation for these closures, arg!

rfjustin said:

Here's a neat thought, produce documentation for these closures, arg!

Click to expand...

Justin, I am sure you realize that I did suggest just that to Karl.

markkoelsch said:

Justin, I am sure you realize that I did suggest just that to Karl.

Click to expand...

I have no doubt sir.