Why is Aerotech Hardware so 'complex'?

[Papa Elf]

In response to @ShadowSpire48 's complaint about getting the smoke element in the forward bulkhead of a 54mm or larger Loki motor, Scott advised me to use a thin-gage wire shaped in a U to provide a channel for air to escape. You then pull the wire out when it's in.

That trick also works with Aerotech delays in plugged closures. Although I never put the wire in a U, I find just sticking the wire in the well works well enough to let the air escape.

 

[David Schwantz]

AT is more complex because they don't blow up as much as other do.

 

[b.wieting]

AT has more parts but each is IMHO designed to make a reasonably simple-to-assemble motor that does not require tools and is easy to clean. And for whatever reason, their design seems more conducive to smaller motors, 18 and 24 mm. At least, that's where they have the (albeit small) market.

And it may sound strange but there is something I rather like about the intricancy of the AT motor vs. snap ring motors-- including ones I've made.

The biggest I've assembled is a 75mm L1390G. With the plugged forward closure, I found it easier than the smaller ones.

 

[John Kemker]

AT is more complex because they don't blow up as much as other do.

Say WHAT?!?!

In over 30 years of flying reloadable motors, I've seen WAY more AT failures than any snap-ring, even when you adjust for how many AT casings there are compared to snap-ring casings. The percentage of AT failures is higher.

 

[Dave P]

"Over the years there was
Aerotech RMS motors
Kosden TRM snap ring motors
---then AMW snap ring motor motors
--------then Loki snap ring motors"

Like cell phones:
AT RMS=Gen 1 Axial Seals
Kosdon = Gen 2 Radial seals
Copies of Kosdon = Gen 2 Radial seals
CTI = Gen 3 Radial seals

I took AT and Kos cases to the rocket motor engineers at Rocketdyne when they first came out. A couple giggled and asked where these came from. The consensus was that the screw threads were elegant, the snap rings were easy, but the groove will erode with usage.

 

[Antares JS]

The biggest I've assembled is a 75mm L1390G. With the plugged forward closure, I found it easier than the smaller ones.

That's because there's no o-ring sealing the well as you push the delay in and the air is free to escape.

That trick also works with Aerotech delays in plugged closures. Although I never put the wire in a U, I find just sticking the wire in the well works well enough to let the air escape.

For a tool-free way to do it, just stick the o-ring into the bottom (top, technically?) of the well and then insert the rest of the delay assembly. I've also heard that for Aerotech plugged closures, you don't actually need the delay o-ring, but I haven't had confirmation so I've just kept using it.

For plugged Loki, I do the above and install one o-ring into the well, insert the delay element, then stuff one more o-ring down in between the forward closure and the delay/smoke. Without an ejection charge to protect, you don't need as solid of a seal around the delay.

 

[Banzai88]

AT is more complex because they don't blow up as much as other do.

I started in HP with CTI motors. Once those started blowing up randomly because of things beyond my control (I'm looking at YOU, Pro38s with 4 safety bulletins in 3 years and YOU Pro54 loads that randomly blow up or burn through the case (all of the 54mm load issues which CTI has publicly stated that they are aware of, but have no fix for)), I started buying/launching AT motors. At first, I too was put off by the complexity.....but rapidly learned to take responsibility for the motor assembly with the parts and directions supplied.

I have yet to have an AT motor in the 29-75mm motors that I've launched come apart at the seams for any reason.

Compare that to just 2 years ago a major rocket vendor sent me a CTI 38 load that was part of the forward closure recall that NEVER got either purged from their inventory nor a new forward closure, and upon inspection was clearly one of the faulty assemblies. That is to say, the 38mm loads that will 100% rapidly disassemble your rocket through no fault of your own are still out there!

Now that CTI loads are basically unobtanium for most of us, it's either embrace AT and Loki, or go back to BP motors, all of which has a niche in this hobby.

 

[rharshberger]

Say WHAT?!?!

In over 30 years of flying reloadable motors, I've seen WAY more AT failures than any snap-ring, even when you adjust for how many AT casings there are compared to snap-ring casings. The percentage of AT failures is higher.

I have seen way more AT motors than CTI flown over the last 10 years and other than the RMS-EZ issues which were quickly resolved CTI is the winner of most frequent CATO's for probably the last 3-4 years.

 

[Titan II]

AT is more complex because they don't blow up as much as other do.

CTI failures = 0

Failures due to cross threading the closure or not putting the motor in a case is just stupidity and not the motor's fault.

 

[Arjun K]

The AeroTech RMS motors were the first reloadable motors with a built in time delay and ejection, and were first made available to the public in 1990 during LDRS 9 in Hartsel, CO.

The original idea was not to make RMS as “easy” as possible, but to lower per-flight costs and provide a user experience that was interesting, educational and enjoyable.

Interesting. What did people use before reloadable motors were available? Single-use?

 

[Art Upton]

Interesting. What did people use before reloadable motors were available? Single-use?

Yes, I still have some examples of them in my 'Stash from those days

AeroTech 29mm H70s were really popular. You had to pick them up at launches or a regional dealer, as shipping 'Flying Tigers' was way too expensive.

The main reason reloadable came out was shipping , then later the 62.5 gram issues for EZ-Access when Propellent Actuated Device [PAD] exemptions disappeared.

I had two dealers available driving distance.

Common Wealth Displays up in Southgate Michigan and Magnum down by Dayton Ohio.

 

[Arjun K]

Ok, this just Dawned on me.

YES Aerotech has made the most Friendly & Simple High Power motors being made and in current production with the largest variety. Even more simple than a Pro38

It is called Aerotech DMS motors.

Lol 100%, I completely forgot about the DMS side since I got into reloadable. I did my L1 on a Aerotech H115 DMS.

 

[Arjun K]

I appreciate all the comments. Maybe I could have phrased my initial question a little better as to the pros and cons of AT vs Snap Ring.

All your feedback is very informative in seeing past my own 'tunnel-vision'.

 

[David Schwantz]

Sorry guys but I cannot count the number of times I have seen the crimp fail on a CTI forward end and blow the motor up thru the rocket. And not to argue, but they all have failures at times.

 

[rharshberger]

CTI failures = 0

Failures due to cross threading the closure or not putting the motor in a case is just stupidity and not the motor's fault.

Its almost always the Pro38's that have the cross threading issue. Never had a cross thread issue with my other CTI cases that use metal rear closures, so IMO it is a case design failure if it can be easily cross threaded.

 

[Titan II]

so IMO it is a case design failure if it can be easily cross threaded.

Totally disagree. They are not "easily" cross threaded. They are cross threaded by careless people. There are many of them in this hobby.

 

[4regt4]

I don't even notice the "complexity" any more, and if you do it right you are safer from assembly errors at the factory -- not unheard of. CTI has certainly had their share, as has AT.

I like that the ultimate quality control is in my hands. I take a lot longer to assemble an AT motor than most folks, as I am really careful and inspect components, test fit them, and being completely sure that I don't contaminate the delay grain surface with grease, etc.

In over a hundred RMS motors, I've only had one failure. But it wasn't catastrophic and didn't damage the rocket.

Hans.

 

[Neutronium95]

My only complaint with Aerotech is that some reloads have o-rings that are the same diameter, but slightly different thicknesses. I always need to double check that when I assemble 29mm reloads. Thankfully they addressed that with their 54mm and larger reloads.

 

[Art Upton]

My only complaint with Aerotech is that some reloads have o-rings that are the same diameter, but slightly different thicknesses. I always need to double check that when I assemble 29mm reloads. Thankfully they addressed that with their 54mm and larger reloads.

That is the 'Thick vs. Thin" O-ring and they are flipped between 29 and 38s

I always said to myself, 38s are thick in the Aft and 29s are thin... or was it the other way around ...Looking ... Looking...

Ok 38s are indeed thick in the Aft



And 29s are thin in the Aft



As most times, the documentation is on RCS site:
https://www.rocketmotorparts.com/page/instructions

 

[heada]

I have cases/reloads from AT, CTI and Loki and I use them all (also AMW but I bundle them in with Loki). If you follow the directions and pay attention, AT RMS isn't significantly more complex than any other. Yes, AT RMS has more parts than the others but if you can read and follow directions, then assembling a RMS takes just a few minutes longer than CTI or Loki.

 

[mrwalsh85]

Exactly as the title says, why is AT hardware so complex? I mean it's not rocket science! Oh wait...

<BIGGGG SNIP>
Thanks,
Arjun

Honestly, AT Hardware is simple, and it actually has less components than a snap ring case.

AT has two closures, a casing, and sometimes, a seal disc. Total count = 4

Snap ring casings

FWD Closure, Rear Closure (if applicable), 2 snap rings, nozzle (if reusable), external thrust ring. Total Count = Potentially 6. Oh, and you need snap ring pliers... Another thing to source and make sure you have with you at the site of assembly.

I think that reloads are comparable in parts count. Also, if you have graphite nozzles, you have to inspect them and make sure they're not busted. If busted, that will ruin your day. AT - pull out of bag, assemble, and fly!

 

[David C.01]

I'm sure Aerotech could have made their assemblies more consistent, which would have reduced the complexity.
Why couldn't the forward and aft O rings be the same size?
Or if they had to be different sizes, always make the forward O ring thicker than the aft, or vice versa.
The discrepancy between 29mm and 38mm has caught out people on more than one occasion.
I think there's also an inconsistency regarding the aft O ring location? (Sometimes it's between the nozzle and aft closure, sometimes above the nozzle?)

 

[jmasterj]

29mm and 38mm AT reloads use the same size nozzles, which causes that o-ring difference. Just look at the directions and you'll be fine. If you reverse the 38 o-rings, things aren't going to seat correctly.

 

[Zeus-cat]

After you build 30 or 40 AT motors you rarely need to reference the instructions more than 5 or 6 times per motor.

Actually, I just use the drawing in the instructions. All the parts are clearly drawn and identified.

 

[AeroTech]

I got this from you at Danville that fall if I recall correctly the year, it's number #125
Thank you for keeping them from becoming obsolete, I still use them. The time delay and ejection were very important to many fliers including me.

FYI, I remember you commented on my Snap Ring Failure you witnessed I posted above as Scott Miller and I walked back to our camp

View attachment 683077

That’s my writing on the box

 

[kjhambrick]

AARG !

I used to think RMS assembly was simple if I just RTFM.

Now after reading this thread I am not so sure

Stop it, you guys

-- kjh

 

[nickt.mrc]

The useful thing about AT instructions is that each set has a life size diagram of the various rings at the bottom of the page. I cut off the diagram, stick it to a card, put the card in a shallow box that the wind can't get at, then lay the rings and seals out on the diagram, then follow the sequence in the instructions. This avoids any possibility of mixing things up.

 

[mrwalsh85]

AARG !

I used to think RMS assembly was simple if I just RTFM.

Now after reading this thread I am not so sure

Stop it, you guys

-- kjh

That might be what bit me in the dumper last year on a H128. First ever casing burn-through in 20+ years of flying. Live and learn. We are not perfect, RTFM.

 

[bad_idea]

The useful thing about AT instructions is that each set has a life size diagram of the various rings at the bottom of the page. I cut off the diagram, stick it to a card, put the card in a shallow box that the wind can't get at, then lay the rings and seals out on the diagram, then follow the sequence in the instructions. This avoids any possibility of mixing things up.

I have generally laid the parts out on the diagram with the paper simply weighted down in a few spots, and it's a PITA in the Seymour wind. The box is a brilliant suggestion. Thank you!

AARG !

Austin Area Rocketry Group?

I once asked Gloria Jarvis if AARG was pronounced as in "grab your throat" or "grab your sabre." She said a little of both, which is sort of how I feel when a rocket launches great (grab your sabre, ARRG!!!!!) and then the flight turns suddenly bad (grab your throat, ARRG!!!!!). Somehow that combination seems to be how a great many of my flights with AARG have gone.

 

[tsmith1315]

Austin Area Rocketry Group?

Isn’t there a St. AARG in Cornwall?