Frustrated by Aerotech missing o-ring - couldn't do my L1 cert flight today.

[WizardOfBoz]

So I was planning on going for my L1 today at the MDRA launch in Maryland. Didn't for two reasons. First, I caught the cold my wife had all week and felt pretty miserable. But more importantly, I was frustrated by the Aerotech RMS-29 system. I have an RMS-29/360 motor hardware set, as well as the AT reload adapter system which allows me to use motors sized for RMS-29/240. I have an H180W (RMS-29/240) for my L1 certification flight. Here's what I have:

There were no o-rings that came with the motor hardware (the gold aft plug, the black tube, the black seal disk, and the black forward plug, all on the bottom row of the pic) , nor with the reload adapter system (the four parts upper right). The motor is in the yellow package. The one sheet of instructions for the use of the reload adapter system is here (witharrows added):

I draw your attention to four things. 1) In the top two configurations, there is no seal disk (red arrows). 2) In the bottom two, there are (green arrows). 3) The seal disk is an aluminum washer with a groove on one outer edge for an o-ring. In the configurations WITH the seal disk, an o-ring is shown and 4) that "Forward Seal Disk O-ring" is shown on the page (large red arrow). Since my configuration is the bottom one, I need to use the seal disk, and presumably the seal disk o-ring.

The sheet that came with my motor can be found here (thanks, Rocketry Works! I couldn't find this on Aerotech's site). It lists some of the things that came with my motor:


The perceptive crowd here will no doubt observe that there are three, not four o-rings listed. And indeed, the package contained three, not four o-rings. The omission was the forward seal disk o-ring. All of the included o-rings felt bad: they missed their friend. I felt bad: I missed my L1 launch.

If that o-ring had been included I would have braved the ravages of a cold to launch today. But I do not feel comfortable launching a high-power rocket, that I've put a lot of effort into, with a part missing. I've seen the youtubes of lots of CATOs. "Let's try and see what happens" is NOT a good motto with a four pound object with a pointy end traveling at several hundred miles per hour.

So a couple of questions
1) Is that o-ring necessary? (You will have to make a pretty strong argument to convince me it's not)
2) I see that there is a phone number I can call for missing parts. Is this typical of Aerotech, not including needed parts? They really are willing turned off a customer (I missed out on my L1 cert) by saving about 15 cents?
3) The assembly is pretty complex (at least compared to inserting a C-6-5 into an Alpha), but this is not bad per se: you want a system that is designed for all situations. But the instructions.... well... they seemed to have been written by engineers. I'm an engineer: this is not a compliment. At least the instructions should not be conflicting in the number of o-rings.
4) I could go to Lowes and get a 10 pack of neoprene o-rings in this size. But the inside of a faucet is a different duty cycle than the inside of a rocket engine. Would the neoprene plumbing o-rings work?
5) Do I have to think ahead and order an o-ring every time I want to use an RMS-29/240 in my RMS-29/360 casing?
5) My understanding is that Cesaroni engines have simpler instructions. Do the CTI products have fewer hassles? Thinking of when I get my 38mm motor...

I guess I'll call Aerotech's number on Monday and have them send me an o-ring. But golly this is bad business practice - can you imagine the cost of having to man the phones, take the call, send the customer the required o-ring.., and teeing off every customer that tries to fly an engine using the reload system?) Gee.

I was really disappointed, so I'm just venting. If you made it to here, thanks for sticking with me. If I missed something obvious let me know that IATA and please let me know where I went wrong.

 

[Neutronium95]

The perceptive crowd here will no doubt observe that there are three, not four o-rings listed. And indeed, the package contained three, not four o-rings. The omission was the forward seal disk o-ring. All of the included o-rings felt bad: they missed their friend. I felt bad: I missed my L1 launch.

There was no part missing. That motor doesn't use the seal disk. Not all of the 29/240 reloads use it. You just put the forward insulator disk and forward o ring on top of the liner. Read the instructions that come with the motor.

Here's the official cross section drawing of the assembled motor.

For context, the H180W and H97J reloads don't use the seal disk. The H210R, H220T, and H250G all use the seal disk.

 

[3stoogesrocketry]

Did you ask anyone at the launch for help or guidance?


O-rings do not come with a RAS system.

The H180 does not need a seal disk, it has a fiber washer.

Don't over engineer a simple task, not all motors are the same.

 

[tsmith1315]

Link to AeroTech resources:

https://www.rocketmotorparts.com/page/aerotech-resources

 

[cls]

I bet someone at MDARS would be able to help you figure it out.

 

[WizardOfBoz]

Thanks, @Neutronium95.

1) You are correct in that the instructions that came with the motor do not mention the seal disk (shown in my post).
2) I put the motor together without the seal disk. The grains were sliding around about a quarter inch (estimated) when I gently shook the motor after tightening down the forward and aft closures, so
3) I read the instructions that came with the reload adapter system (also shown in my post), for a 360 motor case and a 240 reload (my case exactly) show that the seal disk IS used. Since this explained at least some of the looseness, I believed that this was the proper config.

I suspect that you are right and that others will join you in telling me that it's ok to do this. Probably right, but I'm going to contact Aerotech. At the very least they should say "If you are using our reload adapter system, the seal disk is NOT needed for this motor). Do motor grains normally have enough slop to rattle around back and forth in the tube?

 

[WizardOfBoz]

I bet someone at MDARS would be able to help you figure it out.

I suspect that you are correct. If I'd felt ok I certainly would have driven down. But it's 1.5 hours there, and I felt like a million bucks (withered and green).

 

[Neutronium95]

2) I put the motor together without the seal disk. The grains were sliding around about a quarter inch (estimated) when I gently shook the motor after tightening down the forward and aft closures, so

Having grains rattle around in a motor is actually pretty normal. Aerotech motors are known to have this happen, it's not a problem.

3) I read the instructions that came with the reload adapter system (also shown in my post), for a 360 motor case and a 240 reload (my case exactly) show that the seal disk IS used. Since this explained at least some of the looseness, I believed that this was the proper config.

Again, some 29/240 motors use the seal disk, and some don't. It looks like Aerotech only pictured the seal disk configuration with the RAS instructions. In the future, rely on the instructions that come with the motor.

 

[WizardOfBoz]

Link to AeroTech resources:

https://www.rocketmotorparts.com/page/aerotech-resources

Thanks @tsmith1315. This is useful.

 

[WizardOfBoz]

Thanks as well to @Neutronium95 - good info. And I realize that if I'd gone to the launch, I would have learned this without the need to compose a long post, and without having imposed on the experts here.

 

[WizardOfBoz]

Here's the official cross section drawing of the assembled motor.

For context, the H180W and H97J reloads don't use the seal disk. The H210R, H220T, and H250G all use the seal disk.

Boy, I wish that drawing had come with the motor. But it's super useful. I will point it that it shows the 240 motor installed in the 240 casing, and not in the 360 casing. The only drawing I have with a 240 reload in a 360 case does show the seal disk. So AT needs to be more clear about the info you shared. I will contact AT about this.

I'll take out the seal disk. What do you think would have happened if I'd flown it with the unsealed disk?

So the motor will sit around, loaded into the casing, for a month or more. I'll put it in a plastic bag. Any other precautinos?

 

[troj]

Thanks as well to @Neutronium95 - good info. And I realize that if I'd gone to the launch, I would have learned this without the need to compose a long post, and without having imposed on the experts here.

You came, you asked questions, you got some helpful answered and you learned something new.

No imposition on the users, the forum worked its magic - a flier wasn't sure about something, asked questions, and got helpful answers.

Now you know more, and now you're ready for a successful L1 flight.

-Kevin

 

[tfish]

Tony

 

[JoePfeiffer]

A quarter inch sounds like a lot (more than the expected slight rattle), and having enough room for the seal disk is a surprise. Is the fiber washer in there? Are you sure you've got all the o-rings that did come with it, and that both fore and aft closures are tight? Showing it to someone at the launch before flying would not be a bad idea.

As for storage, it would be fine for a couple of months with no precautions at all.

 

[WizardOfBoz]

Thanks, Joe. I've got the front and aft fiber insulators and the fore and aft o-rings. The delay module has the delay spacer and the oring. I think I have everything. When I put the seal disk in (without the o-ring) the free space goes from about 1/4 inch to about 1/16th.

I was really dubious about not putting the seal disk in because without it the nozzle can be pushed up inside the aft closure ring. But the motor has a lot of pressure inside, so in practice that nozzle will bear right up against the aft closure with the o-ring in between.

I am wondering what the seal disk does if not acting as a small spacer. I guess for higher power motors there is higher pressure. So one uses this for the H210R, H220T, and H250G while the lower power ones (like my H180W) don't need the extra seal. That's my working theory from what other have said above. I'm calling Aerotech Monday to verify and to suggest that somewhere they print the useful info that Neutronium95 shared.

Phyically, everything may be copacetic with an H180 w/o a seal disk, but the instructions MUST be unambiguous about this.

 

[Zeus-cat]

I always recommend that you have someone help you with your first (second, third... and even your twentieth high power reload). They aren't really that difficult, but a second set of eyes never hurts. Especially, if they are experienced eyes.

NEVER be afraid to ask for help assembling a reload. I have never seen anyone chastised or made to feel embarrassed for asking for help with a reload. NEVER! The consequences of doing it wrong are significant. We all understand that. Most people will be glad to help if they have the time to assist.

And watch other people assemble one if they don't mind you watching. You may pick up a few hints.

 

[StreuB1]

Important thing to note.

AT records a hardware bill-of-materials on the outside of the yellow reload tube, on the label. It will tell you the hardware you need, as well as if a seal disc is required. Always read the label to see if a seal disc is required before you plan your flight. If the label does not note that a seal disc is required, it is not required and will use a fiber (or phenolic) washer(s).

Grain rattle is absolutely normal. The grains burn radially and axially as they are in the [uninhibited]Bates configuration.

Always better to be safe than sorry. This was a good thread, with lots of good information. This is what your L1 is all about. We're all here to help you along your journey.

 

[Zbench]

Important thing to note.

AT records a hardware bill-of-materials on the outside of the yellow reload tube, on the label. It will tell you the hardware you need, as well as if a seal disc is required. Always read the label to see if a seal disc is required before you plan your flight. If the label does not note that a seal disc is required, it is not required and will use a fiber (or phenolic) washer(s).

Grain rattle is absolutely normal. The grains burn radially and axially as they are in the [uninhibited]Bates configuration.

Always better to be safe than sorry. This was a good thread, with lots of good information. This is what your L1 is all about. We're all here to help you along your journey.

Not to beat a dead horse, but for completeness and posterity, here is that exact motor and the bill of hardware materials StreuB1 noted above.

 

[WizardOfBoz]

Thanks guys. I'm not being obtuse here, but keep in mind that the only drawing/info I have of my 240 size motor reload in the RMS-29/360 case, with the reload adapter kit, shows the forward seal disk installed. The drawing of the exact H180 motor is in the RMS-29/240 case, without the adapter. The list shown on the case states that you need the RMS-29/240 case and does not mention what to do for the 360/adapter scenario. So right now, I'm not arguing with the more experienced fellows here that that the seal disk isn't necessary, but my point is more that the documentation is ambiguous or at least incomplete. Also, I'm concerned that without the seal disk the nozzle slides almost entirely into the motor case. Seriously, it slides back and forth like 5/16 of an inch. In use, the pressure will force it back but when I launch like this, I'll have to ensure that the nozzle is pulled out all the way.

Once I figure this 360/adapter setup out, I'll have access to a wide range of motors. The Aerotech RMS motors that I know about for this case size plus adapter are listed below, with the OR apogee prediction for my Super DX3. But for the L1 cert I suspect that an SU (like an H169WS or something) would have been simpler. I think I opted for the RMS approach to avoid HAZMAT shipping fees. Life is a series of compromises...

RMS-29/240
G75J-10 480
H128W-14 735
H165R-14 617
H238T-14A 755

RMS-29/360
H97J-10 711
H180W-14 1160
H210R-14 982
H220T-14 967
H250G-14 1152
H268R-14 1726
I200W-14A 1852

Single Use (for comparison)
H169WS 1194

 

[WizardOfBoz]

One other thing. The forward cap plug supplied does not appear to fit onto the motor in any conceivable way. I'm assuming that's because the 360/reload approach is different than the 240 motor approach. What is the caplug for? Does one keep it on for launch?

 

[tsmith1315]

Phyically, everything may be copacetic with an H180 w/o a seal disk, but the instructions MUST be unambiguous about this.

The instructions that come with the reload are unambiguous about assembly. A seal disc is not used unless the reload kit's instructions say to use it.

The RAS drawing is a general configuration. With the RAS, the ring/spacer/floating closure replaces the standard forward closure in the assembly sequence, nothing else changes. The "(if used)" in steps 1 and 2 mean to use that item if the reload kit instructions call for that item.

Both of these things are probably more obvious to someone who has built a few motors in their standard form. With that perspective, using the adapter makes more sense.

Use masking tape on the ejection charge well instead of the cap.

 

[WizardOfBoz]

Both of these things are probably more obvious to someone who has built a few motors in their standard form. With that perspective, using the adapter makes more sense.

Use masking tape on the ejection charge well instead of the cap.

Sentence 1: No doubt! I'm eager to get that experience
Sentence 2: I did it correctly then - that's a relief! So the cap plug, when it fits, is normally used to contain the BP, and must remain on the motor for launch.
Thanks again.

 

[RocketPro]

One other thing. The forward cap plug supplied does not appear to fit onto the motor in any conceivable way. I'm assuming that's because the 360/reload approach is different than the 240 motor approach. What is the caplug for? Does one keep it on for launch?

The caps are usually for the nozzle end. You put it on the nozzle after inserting the ignitor to hold it. They stopped using forward caps some years ago.

 

[WizardOfBoz]

That's interesting. I have to suspect that the masking tape is better. Less plastic waste anyway. I put a little dog barf in the compartment to hold the BP down. I heard that this was a good idea. That ok?

 

[Zbench]

I think that perhaps you didn’t realize that one of the spacers in the kit is longer than the others:


I have the same motor and cracked it open to see if I could recreate the rattle. Parts as they went into the case (I didn’t mess around with the delay components):



Fully assembled:



When complete and snugged there was about 1/32” movement of the grains. With the delay elements inserted I bet there would
Be none as they always stick out a little bit from the forward assembly.

Look closely at your spacers. One is longer to make up for the lack of the forward seal disk in the motors that don’t require it.

Hope this helps.

 

[Banzai88]

That's interesting. I have to suspect that the masking tape is better. Less plastic waste anyway. I put a little dog barf in the compartment to hold the BP down. I heard that this was a good idea. That ok?

Yes

 

[WizardOfBoz]

I think that perhaps you didn’t realize that one of the spacers in the kit is longer than the others:
View attachment 653639

Look closely at your spacers. One is longer to make up for the lack of the forward seal disk in the motors that don’t require it.

Hope this helps.

"you didn’t realize that one of the spacers in the kit is longer"
"Look closely at your spacers. One is longer to make up for the lack of the forward seal disk in the motors that don’t require it."

Ding ding ding! I think that we have a winner! If you look at the parts in my original post you'll note that it didn't include the extended tube. I never got mine! So it wasn't that Aerotech missed an o-ring, rather, they appear to have missed including one of the parts in my reload kit. So to recap
1) I tried to assemble my motor according to the only drawing of a 360 motor and a 240 reload I could find. It had the seal disc shown
2) I noted that the o-ring was not included
3) I asked here and folks told me (correctly, I believe) that the seal disc is not used for the H180 motor
4) But when I took the seal disk out there was far too much play in the motor - the grains were sliding more than 1/4 inch and the nozzle when all the way into the aft closure.
So I was confused. I've called Aerotech customer service and explained the situation and I expect them to send the extended spacer I was missing. I'll report back.

"Hope this helps."

It surely does - many thanks.

 

[4regt4]

The caps are usually for the nozzle end. You put it on the nozzle after inserting the ignitor to hold it. They stopped using forward caps some years ago.

Hmmm..... Every one of the 29mm and 38mm motors that I've used over the last few years has included a large diameter forward plastic cap that goes over the ejection charge. Including 5 that I shot this last weekend. And there is a notation to not use it if using a baffle or anything else blocking the ejection gas path.

Hans.

 

[jmasterj]

There are both. The ejection charge cap is not the right size for the floating forward closure.

 

[kramer714]

Just following all this, is the spacer kit really worth all the extra weight / issues. They are $60 dollars vs buying a 24-240 case for $80 or so plus the 360 complete motor you need anyway. Gets you all of the 360 - 240 reloads. Would you likely take the 360 and adapt it down to a 180? 100?