RMS or single use?

[DeltaVee]

I don't have personal experience with AT RMS products, but here's my general impression from online research:

18mm: There's no cost savings and reload options are limited.
24mm on up: The primary reason to use RMS is for the ability to "customize" your motor. A secondary reason is to enjoy the process of assembling your own motor.

Saving money for most people will take some time and there's a risk of losing your casing and never making back your initial investment.

TL;DR: Don't get into RMS to save money.

Rocketry is quite literally lighting money on fire!!! ;-)

 

[Dave Pritts]

Rocketry is like owning a ski boat or racing a car.... Just a hole to throw money into, but I love it.

 

[Joekeyo]

All of the AT motors that I have assembled are very similar in the components and assembly. Now, after assembling a few, I find it relaxing to put them together. I assemble 3 motors the night before the launch. The worst problem that I have had is a failed igniter.

 

[G's Monster Rocket]

All of the AT motors that I have assembled are very similar in the components and assembly. Now, after assembling a few, I find it relaxing to put them together. I assemble 3 motors the night before the launch. The worst problem that I have had is a failed igniter.

I've lit C's, D's, E's, F's in Estes tubes for years. Started into HPR this past summer and began with A/T 38MM RMS G's. Learned a lot about assembling RMS motors and the respective cases. What makes a good launch and frankly what doesnt (CATO and all). After burning thru a few $$'s and a learning a few lessons, I find building and assembling H, I and J motors pretty cool. If you're into figuring out how and why things work the way they do. Then again, I was the kid on the roller coaster ride who was looking under the coaster carriage to figure out how the damn thing stayed on the rails when all the other kids were flying outa their seats screaming with terror or excitement thru the turns and drops. Personally, I like putting the RMS motors together, as much as I like designing and scratch building the rockets. For me, it's still all about the challenge.

 

[Rocketjunkie]

There are a lot of factors in the decision whether to use reloads. Here's a few.
Will you be flying a lot of composite motors? It takes a lot more flights to cover the cost of the case than it did when reloads first came out. In the mid '90s the casing was covered in as few as 2 uses (98 mm) to about 7 (29/40-120).
How likely are you to lose the rocket? You have to start over with the cost savings after buying a new case. If you fly low and slow, or use trackers, etc.
Do you want to use a wide variety of propellant types? Reloads win here. There are sweet spots (38/360, 38/720, 54/1706, 75/3840).
You will need a lot of hardware if (like I do) prefer to assemble motors before the launch. You can leave assembled motors at least a year without flying them. Do not back out the closures. Leave the motor in ready to fly condition.

 

[brrrett2]

Thanks for the responses so far. I am breaking in with a 24 RMS. But I do plan to still use single use too. Just want to make sure they are dependable.

I've had my 24&29mm RMS hardware for around 20 years. I have flown dozens of flights on them. If you buy the D-F reloads in the 3-packs, your savings could pay for the hardware fairly quickly. Some folks look at assembling reloadable motors as a chore to assemble, and some enjoy the process as a continuation of the rocket build. When assembled to the instructions, I'd bet the failure rates between reloads and SU are pretty close.

 

[4regt4]

I got caught up in the simplistic argument that you can save money by using reloads. So I had to check it out for myself. I made a spreadsheet of options (Estes, Qjet, Aerotech single use, and RMS) for motor classes D through G. But before we get to that, I should mention that after using RMS, I found that there are some valid reasons to use them other than cost. More on that in a bit. What I found:

D: Estes best, Qjet second. The 24/40 is more expensive, and really has little to offer other than the ability to adjust delay. Unlike the E26, I like and use the D22.

E: Again, Estes. Then Qjet, with 24/40 not far behind. However, I don't like the Qjet E26, I've had lots of problems with them, and the thrust curve is a bit "soft", with the rocket coming off the rod slower than the other choices, unless it's quite light. But the RMS really shines here because the E18 and E28 are much "bigger" in total impulse than the other 2 and have more punch off the rod. Especially the E28. So my choice here mainly centers on the particular rocket's motor retainer system. There are also E motors available for the 29/40-120, but I can't see the advantage, as they are much more expensive.

F: Hands down, the 24/40 is far cheaper than anything else. But all the choices are "baby" Fs, all less than 50Ns. There are slightly bigger choices in the 24/60 case. For mid-F, I'm using the F67 single use, and if I need something bigger, the 29/40-120 Fs go all the way up to 80Ns. However, you have to plan the purchase of them, they are all Hazmat. I get them at club launches.

G: RMS 29/40-120 is the only way to fly. As they split the grains in two, they avoid Hazmat on these. Puzzling, as there is still the same amount of propellant in the bag, sitting right there next to each other, they are just not in one chunk. If they caught fire, I'm sure they'd both burn.... There are Enerjet Gs, but they are more expensive and Hazmat.

Now the other considerations. First is fuel choice. Most RMS sizes offer the regular White Lightning and the faster Blue Thunder. However, the 24/60 also has available the smokey Fast Jack and Redline. I first scoffed at this until I saw a Redline take off. It looks like Darth Vader's lightsaber sticking out of it's butt. Way cool, worth the extra few bucks. And the 29/40-120 has a Mojave Green option. It's a neat flame, but you really need a camera photographing the liftoff to do it justice. Second consideration I already mentioned. You get more flexibility in delay setting.

Just my $0.02, and with inflation, that's not worth much.

Hans.

 

[DigBaddy]

Also be sure to avoid comparing size alone like 24mm RMS to 24mm SU; impulse and thrust curves matter. For example, look at the F24 in 24/40, basically a similar thrust curve and impulse to the SU F20 and F23 29mm motors. Cheap Estes plastic adapter and you could enjoy those 24mm RMS loads in 29mm rockets for much less per flight (not considering hardware). MSRP a single F24 reload is $14.33. A single F23 out of their 2-pack is $22. Wouldn't take long to pay for that 24/40 case if you were ever considering some of those 29mm SU motors. 24/60 allows for some punchy Fs in rockets that can also fly on 29mm motors, but maybe with less altitude, giving more field flexibility.

As others mentioned, buy used cases.

 

[waltr]

I like the 18/20 case and reloads, D13W & D24T since they are Full D's, and only 18mm. This allows a full D in a rocket that could only do a C with an Estes BP or even the Qjet half D 18mm motors.

A reason to get a few low/mid power reloads is to prepare and learning before going into HPR.
Another is a wider verity of propellants. The White Lighting have a great sound and I like the black smoke trail of the black/fast Jack propellants.

The user adjustable delays is another nice feature.

I do fly some of the SU composite motors. The F67 is hard to beat (nothing like it is available in reload) and our club likes to fly one when doing demo flights for the Boy Scouts or other kids. It really gets their attention.

 

[4regt4]

Looking at just 24mm, the E18 RMS and E20 SU have nearly identical thrust curves, as do the E28 RMS and E30 SU. Using prices from Sirius, the RMS are about $11 ea, the SU are $14.50. Not huge, not enough to amortize a case, but it's still worthwhile as with the case you have a lot of other options too.

As for used cases, be very careful. I've had to return Ebay purchases because the cases might have been abused. One supposedly unused 24/40 had the forward closure screwed on so tight, I couldn't get it undone, at least not initially. Took WD-40, heat to the tube, ice to the closure and it finally came loose. However, the tube may have gotten stretched by the gorilla who tightened it, as the threads are a bit loose. Hard to describe what "a bit loose" is without having another to compare it to.

Similar vein... Improperly loaded 29/40-120 have been known to blow the forward closure off. When you re-thread the closure on, it kinda sorta seems OK. But if you compare to a new one, those forward threads are definitely a little loose. And likely to blow again. A simple go/no-go test is to thread the forward closure all the way on. Then unscrew it, carefully counting how many revolutions it takes until it comes loose. 3 turns or less, not good. New ones typically take 3 3/4 turns. This isn't a completely definitive test of a good case, but if the case fails the test, don't buy it.

Hans.

 

[mbeels]

I like the 18/20 case and reloads, D13W & D24T since they are Full D's, and only 18mm. This allows a full D in a rocket that could only do a C with an Estes BP or even the Qjet half D 18mm motors.

A reason to get a few low/mid power reloads is to prepare and learning before going into HPR.
Another is a wider verity of propellants. The White Lighting have a great sound and I like the black smoke trail of the black/fast Jack propellants.

The user adjustable delays is another nice feature.

I like that case as well. I mostly flew my 18/20 case in 24mm rockets with an adapter where I'd normally fly an Estes D. Slightly more impulse, higher initial acceleration, and WL or BT propellants.

 

[gdjsky01]

One of the nice things about the RMS is the ability to adjust the delay. E.g., if you buy a load with an 11-sec delay, you can drill it down shorter. Nice to have that flexibility.

THIS ^^^^^^^^^^^^^

Way way way nicer to adjust the delay. DMS has that, CTI (which is almost a single use) has that. Anything AT that is SU or not DMS, you are stuck with what you got.

It is true that if you lose the rocket, you lose the casing. In a CTI that is cheaper than AT.
In the end... it's a compromise. Assembly should not deter you. I have never, ever, experienced a failure in an RMS. Maybe because I read the instructions every single time. Dunno... maybe just a fool's luck

 

[jweger77]

Lots of helpful responses here! Didn't even have to post a similar question.

 

[DaHabes]

One of the nice things about the RMS is the ability to adjust the delay. E.g., if you buy a load with an 11-sec delay, you can drill it down shorter. Nice to have that flexibility.

You can drill the delay on all DMS motors as well, just not SU motors, which have fixed delays. The DMS and RMS delay drill tools are different (just to make things complicated).

 

[bcook7135]

So I flew my first RMS today… with E18-4 In my Dynastar Snarky. It was a glorious launch. The ending, well…not so good. The wind had picked up a little and it went all the way across the park and landed on a power line.
Bummer!

 

[Banzai88]

So I flew my first RMS today… with E18-4 In my Dynastar Snarky. It was a glorious launch. The ending, well…not so good. The wind had picked up a little and it went all the way across the park and landed on a power line. View attachment 553837
Bummer!

A quick call.to the power folks and they'll come out and get it off for you. YMMV

 

[4regt4]

A friend told me the other day that when he was a kid, he built a rocket that used steel fishing leader for the shock cord. Ended up just like yours. Except the wind blew, it shorted out the power lines. Fried the shock cord, the rocket pieces landed otherwise undamaged. Except..... It caused a neighborhood power outage that lasted several hours.

Hans.

 

[bcook7135]

Called the power company and they cut it down. Only minor damage.

 

[4regt4]

Called the power company and they cut it down. Only minor damage.

Did they give you any crap? I've always wondered how tolerant they would be.

Glad to hear that you got it back.

Hans.

 

[boatgeek]

Did they give you any crap? I've always wondered how tolerant they would be.

Glad to hear that you got it back.

Hans.

As I understand it, the power company is usually happy that you called so that a professional can clear the line. That reduces risk to you of course but also to the power grid at large as noted above re: steel leaders.

 

[Banzai88]

As I understand it, the power company is usually happy that you called so that a professional can clear the line.

This has always been my experience

 

[mhanna]

I put my Level 3 rocket over a very high power tower wires. We all stayed clear and called the power company and all I could think was this was not going to be a pleasant conversation when they arrive. 45 minutes later they showed up, cut the shock cord, both have fell and their question was "this is cool, can we stay and watch some flights?"

And I got my level 3 since the cut shock cord was manual forced damage.

 

[bcook7135]

Did they give you any crap? I've always wondered how tolerant they would be.

Glad to hear that you got it back.

Hans.

Actually they were very nice about it. I thought I would have to pay a fine or get some chewing out. But they put in the service order and told me it would be done some time that day (now yesterday). I went back to the field in about an hour and the rocket was laying beside the road. They had cut the shock cord. So I feel very lucky.

 

[dpower]

Both! For E/F/G composites, I probably fly an equal amount of RMS & SU (almost entirely Aerotech). If there's a rocket I really don't want damaged, I'll fly RMS - that way if the motor has a failure, it's almost certainly my fault. I've had a number of single-use composite motor failures, from F44 through I205. The only RMS failure (well over 100 flights) was a 29/60, an old Dr. Rocket case (which may have had previous damage), and an RMS-EZ (which were taken off the market shortly after, due to Mfr. defects).

 

[Trident]

What kind of rockets do you use with the 18mm RMS?

I use the 18/20 RMS in my Mars Lander. The C5-3 might be OK, but it was not out when I built it. I have heard the C6-3 in a Mars Lander is not wise. The ML screams on a D13 reload. I won’t use 18mm Q-Jets, I have had too many failures.