J401FJ missing phenolic forward insulator

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Buckeye

Buckeye

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Trying to assemble a J401FJ reload. The instructions indicate that there should be a phenolic forward insulator. Nope.

Can I use 54 forward seal disk in place of the insulator? I have no o-ring for the seal disk, however.

Also, I am trying to assemble this load in a 54/2560 case by using 2 spacers. The liner o-ring and forward o-ring are very grabby, making it very difficult to slide this assembly through the long case and without jamming and everything falling apart. This is my first foray into Aerotech spacers, and I am not liking it.
 
Are you greasing the o-rings? Also, definitely don't fly it without the insulator.
 
The seal disk has an O-ring to seal any gap between the top of the liner and the outside. The phenolic insulating disk relies on an interference fit with the top of the liner and if the liner is at all uneven, you can get blow-by (which I've had happen on a couple of motors.)

If you had an O-ring for the seal disk you could use it safely, I think, but you have to have an O-ring.
 
BTW, I'm not understanding your "grabby" remark, you can put the forward O-ring in and just set the forward closure onto it, then the spacers, then the retaining ring.
 
mikec said:
BTW, I'm not understanding your "grabby" remark, you can put the forward O-ring in and just set the forward closure onto it, then the spacers, then the retaining ring.
Click to expand...
I think I know what he means. If you try to put the o-ring onto the forward closure first, and then slide the whole assembly down the case (2 spacers worth) it feels like the o-ring is getting twisted around itself. As noted, grease the o-ring, drop it down and follow with a forward closure that also has a bit of grease on the shoulder. It should wedge itself around the shoulder when pressure is applied.
 
J401J is a 3 grain motor. The 54/2560 is a 6 grain case. You would need 3 spacers and this is not certified. I do not like the Aerotech spacer system as you are trying to seal against parts of the case that have been exposed to crud from previous flights. It would work OK if you get ALL of the crud off, leaving a smooth surface. Steel wool on a stick does work. Best solution would be to beg or borrow a 1280 case. I have no problems with CTI 38mm and smaller as the O-rings are internal to the liner. I have but don't like using spacers in 54mm CTI cases.
BTW, using a seal disk instead of the phenolic washer: The seal disk is thicker and you will need to omit the O-ring that goes on the nozzle before inserting the nozzle into the liner. The nozzle O-ring is a different size than the seal disk O-ring. You can check to see which O-ring is in the kit by seeing how it fits the seal disk. Sloppy fit and falling out is a nozzle O-ring.
 
Last edited:
richP said:
I think I know what he means. If you try to put the o-ring onto the forward closure first, and then slide the whole assembly down the case (2 spacers worth) it feels like the o-ring is getting twisted around itself. As noted, grease the o-ring, drop it down and follow with a forward closure that also has a bit of grease on the shoulder. It should wedge itself around the shoulder when pressure is applied.
Click to expand...

Yes, this is correct. I always like to "seat" the forward o-ring on the closure on regular length cases. I was wary of just dropping it on top of the insulator and hoping it all snugs up correctly. I see now that I have no choice but to do that with this spacer system.
 
Rocketjunkie said:
J401J is a 3 grain motor. The 54/2560 is a 6 grain case. You would need 3 spacers and this is not certified. I do not like the Aerotech spacer system as you are trying to seal against parts of the case that have been exposed to crud from previous flights. It would work OK if you get ALL of the crud off, leaving a smooth surface. Steel wool on a stick does work. Best solution would be to beg or borrow a 1280 case. I have no problems with CTI 38mm and smaller as the O-rings are internal to the liner. I have but don't like using spacers in 54mm CTI cases.
BTW, using a seal disk instead of the phenolic washer: The seal disk is thicker and you will need to omit the O-ring that goes on the nozzle before inserting the nozzle into the liner. The nozzle O-ring is a different size than the seal disk O-ring. You can check to see which O-ring is in the kit by seeing how it fits the seal disk. Sloppy fit and falling out is a nozzle O-ring.
Click to expand...

Hmm, you are correct. Here is a pic of the stack up next to the 54/2560 and the 54/1706. The two black spacers + 1 shorter silver spacer came from a Wildman deal a couple years ago. Still, all this is too short to fit in the 2560 case. It looks like it will fit with one black spacer in the 1706 case.

It is definitely a nozzle o-ring (though AT calls it a "liner o-ring". Grrr.)

All this is moot if I don't have the forward insulator. I would think the forward seal disk that presses into the liner is just as good/better even without its o-ring? I have only seen 38mm and below insulator disks, and they are just a flat disk that sits on top if the liner. Is the 54 forward insulator the same?

20191220_080357.jpg
 
mikec said:
The seal disk has an O-ring to seal any gap between the top of the liner and the outside. The phenolic insulating disk relies on an interference fit with the top of the liner and if the liner is at all uneven, you can get blow-by (which I've had happen on a couple of motors.)

If you had an O-ring for the seal disk you could use it safely, I think, but you have to have an O-ring.
Click to expand...

OK. I mentioned this in the last post, but it seems the forward seal disk, even without o-ring, is a better seal than just a flat washer sitting on top of the liner??

Anyway, maybe I can call AT and ask them.

I am annoyed with the missing part (which seems all too common for AT these days in my experience and others), and this goofy 2.5 spacer system that I purchased. Grrr.
 
Buckeye said:
Hmm, you are correct. Here is a pic of the stack up next to the 54/2560 and the 54/1706. The two black spacers + 1 shorter silver spacer came from a Wildman deal a couple years ago. Still, all this is too short to fit in the 2560 case. It looks like it will fit with one black spacer in the 1706 case.

It is definitely a nozzle o-ring (though AT calls it a "liner o-ring". Grrr.)

All this is moot if I don't have the forward insulator. I would think the forward seal disk that presses into the liner is just as good/better even without its o-ring? I have only seen 38mm and below insulator disks, and they are just a flat disk that sits on top if the liner. Is the 54 forward insulator the same?

View attachment 401207
Click to expand...
The shorter spacer converts a 2800 case to a 2560. The missing part is a flat 1/16" thick phenolic washer. You can use the seal disk without the O-ring but leave out the nozzle O-ring as the full diameter part of the seal disk is thicker. Use the 1706 case with 1 black spacer.
 
Rocketjunkie said:
J401J is a 3 grain motor. The 54/2560 is a 6 grain case.
Click to expand...

dhbarr said:
The "2.5" spacers let's you fly -.5, -1, -1,5, or -2 ( but not -2.5).
Click to expand...

Rocketjunkie said:
The shorter spacer converts a 2800 case to a 2560.
Click to expand...

Where is the reference chart that explains how to use the various combinations of spacers and cases? Aerotech doesn't categorize their loads by number of grains (CTI does, very logically), so how is the user expected to know all this? I assumed that each successive case added another grain (spacer), like CTI. Not true, as I found out.

Nothing on this on AT's website, as far as I can tell. Apogee shows this chart, and it led me astray.

Capture3.PNG
 
IIRC the RAS comes with a printed insert explaining how the silver spacer works, but I don't see that on the website. The numbering scheme assumes that each grain of a 54mm motor is about 426 N-s with rounding.

I agree that the AT RAS is less convenient than CTI, mostly due to the fiddly nature of the AT forward closure, but easy enough one you're used to it. Both brands have odd sizes for their longer motors.
 
Nope, the insert I received was just a cut-away drawing showing 2 spacers in use, with no mention of the short silver spacer.

I am not complaining about ease of assembly, CTI vs. AT. I am complaining about AT's horrible documentation and nomenclature. All their cases are classified by impulse, not number of grains/length. However, somehow I am expected to know that a case or load is X grains long and needs such and such spacers to adapt to another XXXX impulse case. Oh, and some propellants are one giant grain, not multiple smaller ones.

At least Apogee attempted a chart to help decifer this cryptic info, even though it is wrong.
 
Buckeye said:
Nope, the insert I received was just a cut-away drawing showing 2 spacers in use, with no mention of the short silver spacer.

I am not complaining about ease of assembly, CTI vs. AT. I am complaining about AT's horrible documentation and nomenclature. All their cases are classified by impulse, not number of grains/length. However, somehow I am expected to know that a case or load is X grains long and needs such and such spacers to adapt to another XXXX impulse case. Oh, and some propellants are one giant grain, not multiple smaller ones.

At least Apogee attempted a chart to help decifer this cryptic info, even though it is wrong.
Click to expand...
I forwarded this to Aerotech. Here is the response.Screenshot_20191223-094428_Chrome.jpeg
 
OK, these updated sheets help a tiny bit, so thanks.

I am still looking for a complete table showing ALL feasible combinations of cases + spacers + loads. Something that would have told me that a J401FJ is not gonna work in a 54/2560 case.
 
Buckeye said:
At least Apogee attempted a chart to help decifer this cryptic info, even though it is wrong.
Click to expand...
Apogee's chart looks correct to me except for the 54/2880 case, which uses 1 short spacer to adapt to the 54/2560 and 1 short and two normal to adapt to the 54/1706.

Note that Aerotech doesn't make a five-grain case (if they did it would be about "54/2132") so there are no reloads that work with the 54/2880 case and 1 short/1 normal spacer.
 

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