Assembling an engine in the field?

I did a quick scan and didn't see this mentioned, sorry if it was and I missed it. Loading motors at the field isn't an issue if you take your time and follow the directions. Have someone you know and trust help you or at least look over your shoulder if you can, not necessary but a second set of eye never hurts.

What is a PITA is turning a case around for the second flight. I've only done it once or twice, I just don't like doing it because I want my closures to be perfectly clean before assembly. Having a 2nd case fixes this but it's extra money. Having another case, say a 240 will give you a little motor flexibility without having to double up on your case stock. Another crappy scenario is having the one case go AWOL leaving your son high and dry.

Personally while I love...absolutely love AT motors, I also enjoy CTI just as much and fly both as my needs warrant or dictate. CTI cases are easy to flip for the next flight as they don't need to be cleaned. I tend to fly one or two AT cased motors then the rest CTI if I fly a lot. All good.

Steve Shannon said:

Many large motors must have their grains glued in some way. You’d want to do those ahead of time.

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did all my long 75s the day before, still in the field

Mike Haberer said:

+1 on using SU/DMS on cert flights. Eliminate a big variable. You can adjust the delays on DMS motors just like reloads, so there is really no need to do a reload engine on a cert flight. I used a DMS on my L1 and will use a DMS on my L2. Just make sure you have the right delay tool. The one for Aerotech DMS engines is different from the one for Aerotech reloads. Why they did that I have no idea; bad engineering from my perspective (since I'm an engineer).

Finally, I haven't gone to reloads yet, but I've 1) determined that there are enough Aerotech DMS engines for a lot of flights in the 29/38/54 mm category. 2) For reloads I'm going to go with Cesaroni. For 29/38/54 Cesaroni reloads, the O-rings are pre-installed on the liner and pre-greased; you can re-grease lightly if warranted, but nothing to forget. With Aerotech, you have to do the whole O-ring thing, just asking for trouble. There are equivalent Cesaroni reloads to Aerotech across the product lines. Cesaroni is just a better design overall...

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blowing out a few 38mm aft "closures" might change your mind.. along with a few stuck 54mm liners

designs have their pros and cons

As others have mentioned, for certification you must build in the field.

A few years ago I bought a 7 day pill box for building reloadable motors. I think it came from Joann Fabrics. The first thing I do when I build a rocket motor is open all 7 compartments and separate all of the components from left to right: nozzle stuff at the left end, ejection stuff at the right end, everything else in order in the middle. Check the instructions, make sure you have all of the parts (including those not in the rebuild such as a front seal disk if needed), and put them in order.

• I put the aft O'rings, nozzle, and aft closure in compartments at the left end.
• I put the plastic caps and igniter just in from the left end. This is out of order but I do it there because there was extra space.
• I put the stuff to assemble the front closure just in from the right end. Make sure you include a front seal disk if you need one.
• I put the stuff to assemble the delay grain in the right end.

After building your motor make sure your only left over pieces are the plastic caps and the igniter.

This makes it more difficult to lose or drop a part as you build the motor because they are contained in their little pens. It adds order and double checking.

I always prep my APCP reloads at the field. The only issues are when you have a gust of wind and the whole lot is off the table and onto the ground. It’s particularly annoying when you’re measuring out your deployment BP charges.

The only motors I tend to prep before the field are my hybrids as they tend to be a little more fiddly and messy.

grouch said:

What is a PITA is turning a case around for the second flight. I've only done it once or twice, I just don't like doing it because I want my closures to be perfectly clean before assembly. Having a 2nd case fixes this but it's extra money. Having another case, say a 240 will give you a little motor flexibility without having to double up on your case stock. Another crappy scenario is having the one case go AWOL leaving your son high and dry.

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I too hate to clean and reuse a case, in fact, I just don't. For large launches I put together a flight plan, selecting rockets and motor combinations, so that I never reuse a case. This gives me weeks in advance to build 10 or 12 motors and have them ready and waiting to load for flight, 2 or 3 per day.

Speaknoevil said:

I too hate to clean and reuse a case, in fact, I just don't. For large launches I put together a flight plan, selecting rockets and motor combinations, so that I never reuse a case. This gives me weeks in advance to build 10 or 12 motors and have them ready and waiting to load for flight, 2 or 3 per day.

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+1 Building the motors is part of the hobby, something hobby related to do on a day rather than doing it when launch day comes around. I guess that for those not having a large inventory of cases, they don't have much of a choice unless wanting to use single use motors.

Speaknoevil said:

I too hate to clean and reuse a case, in fact, I just don't. For large launches I put together a flight plan, selecting rockets and motor combinations, so that I never reuse a case. This gives me weeks in advance to build 10 or 12 motors and have them ready and waiting to load for flight, 2 or 3 per day.

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I have enough cases that I would almost never have to reuse one the same day, but I do anyway. Cleaning is so easy if done right away that there’s no reason not to.

Steve Shannon said:

Cleaning is so easy if done right away that there’s no reason not to.

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This. Even if I'm not going to reuse the case later that day, I clean mine out as soon as they cool enough to handle safely.

Hot cases have a special bonus in the winter (expended BP motors too!): they keep your hands warm!

dr wogz said:

Hot cases have a special bonus in the winter (expended BP motors too!): they keep your hands warm!

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That gave me a mental image of a bunch of guys warming their hands around a pile of hot motor cases.

Antares JS said:

That gave me a mental image of a bunch of guys warming their hands around a pile of hot motor cases.

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Well, yeah!

And, sometimes well come back from a retrieval, with the motor case in our jacket or in our gloves!

mhanna said:

I probably have at least 2 casing of everything from 24mm through 54mm in both Cesaroni and Aerotech. I have two adults son's that fly with me occasionally and some how I got stuck buying all the casings.

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Funny how that works, but you can never have too many casings.

Steve Shannon said:

I have enough cases that I would almost never have to reuse one the same day, but I do anyway. Cleaning is so easy if done right away that there’s no reason not to.

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I really wasn't referring to the cleaning portion, just the lost flying time if having to rebuild a motor. This versus popping out the liner after flying, then picking up another rocket to hook up charges and head to the RSO. I don't know, maybe it is only a half hour extra per motor (if not a larger motor that needs gluing). In my case, I'd rather have that extra half hour to use in tracking the rocket if needed, versus assembling a motor.

AfterBurners said:

Funny how that works, but you can never have too many casings.

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I used to think that but have decided I'd rather have a line of cases that I used more or less or a regular basis. I went through a couple of purges until I settled on the stock I am happy with. Actually I would like to add a 29mm CTI 6 grain motor so I can fly their 4-6 grain loads.

Speaknoevil said:

I really wasn't referring to the cleaning portion, just the lost flying time if having to rebuild a motor. This versus popping out the liner after flying, then picking up another rocket to hook up charges and head to the RSO. I don't know, maybe it is only a half hour extra per motor (if not a larger motor that needs gluing). In my case, I'd rather have that extra half hour to use in tracking the rocket if needed, versus assembling a motor.

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This is my rationale for preferring the DMS as well.

Cmac said:

We'll have with us two rockets, four 29mm engines and one 29/360 case.
Is it practical to share one case with four rockets?

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Just re-read this. You are building the Apogee Zephyr.

https://www.rocketryforum.com/threads/how-much-does-balance-matter.158064/#post-1972295

Do you have a way to adapt the 38mm motor mount down for the 29mm casing?

And what 4 reloads do you have for the 29/360 case?

jd2cylman said:

Well, I am a cuddly rocketeer... But my GF makes sure I don't get too lonely...

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Ha Ha Ha!!

rcktnut said:

When I preassemble motors I close the closures just to snug, leave out the BP if used, and tighten the closures all the way just before using then add BP charge if used. This way there was never pressure on the rings to begin with. The longest I had one sit was 2 years, and it worked just fine when used. There have been other threads on this subject that it seems no matter how you store them if not used right away, it makes no difference.

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Are DMS motors constructed differently than RMS motors?
If the DMS motors have the same compressed o rings in them and dont fail, why would leaving RMS motors tightened be an issue?

If I didn't have to assemble a motor each flight, this hobby would be a lot more expensive!

I've ONLY built in the field as it was my understanding that the build needed to be supervised by a certified rocketeer for any L1 certification. Now that i'm certified I'll build at home close to the launch date.

John Taylor said:

Are DMS motors constructed differently than RMS motors?
If the DMS motors have the same compressed o rings in them and dont fail, why would leaving RMS motors tightened be an issue?

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DMS motors don't have threaded closures. Instead, they have nozzles and forward bulkheads that are epoxied into place. The mechanics of the system are similar, but not the same.

John Taylor said:

Are DMS motors constructed differently than RMS motors?
If the DMS motors have the same compressed o rings in them and dont fail, why would leaving RMS motors tightened be an issue?

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RMS loads have O rings in them to seal the pressure that would normally escape through the threaded retainers. DMS motors are bonded together so there is no need for extra sealing. I would guess you could leave the O rings out of a RMS if you wanted to glue the closures on but that’s an experiment for you, I like my cases the way they are.

I usually build in the field, as motor selection is dependent on flight conditions, especially wind, sometimes cloud cover. I just take a several motors with me, and open/prep the motor I decide on.

I've had several launches where I was unable to fly all the rockets I had brought with me. Sometimes I get too busy as RSO or helping someone find their rocket.

One of the biggest reasons I don't prep at home, is that I have to unseal the motor (take it out of it's sealed plastic bag) to put it in the casing, and then I feel I must fly it. If I decide not to fly a motor or a rocket, then I have to store an unsealed motor in my lockbox at home after the launch, which isn't ideal for the propellant. Sure, I can tape it all up as airtight as possible, but I'd rather keep them factory sealed if I didn't fly it.

To be fair, I fly mostly Cesaroni motors, where the prep time is fairly low. It's become fairly routine.
I spend far more time prepping the BP charges and electronics.

I do prepare flight cards at home for every rocket/motor combination that I may fly that day, so I'm saving time with my administration. Just pick the right one from the pile, double check that everything still applies, sign it, date it, and it's ready to turn in. I hate having to get out the laptop just to double check what the CP was for a rocket in RockSim, just to fill in the flight card.

Yea, unsealed motor grains aren’t that much of a problem. I’ve flown motors that were cased up and sitting around for over two years before flying. Lit right up.

Vendors at launches drive around for years with the same stock of motors in their vehicle/trailer. The motor packages get beat up, rained on, and temperature cycled even before you buy it. I am not as worried about any motor that I "un-seal" or "assemble" myself ahead of time. Also, I feel better about a new motor purchased in a pre-sale (Wildman, for example) than one that has been rattling around in the back of a minivan for 4 years.

John Kemker said:

DMS motors don't have threaded closures. Instead, they have nozzles and forward bulkheads that are epoxied into place. The mechanics of the system are similar, but not the same.

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OK, so I get it regarding the bulkheads, but what if any damage occurs due to the orings being under compression for a long time? Unless someone can explain why I shouldn't leave RMS motors tightened, after assembly and until launch day, I'm not going to be concerned.

I've always left the forward and aft closers loose on RMS motors, but why? SU and DMS motors stay under compression for years and are still fine......right?

SU motors are encased in plastic, so not sure you can count that. DMS motors, I'm not sure, never flown one.

I loosen AT closures when I think if it. Most of the time I don't think of it.

Loki/AMW o-ring systems are different, but I have had snap ring motors sitting around built for years, picked them up, flew them, never a problem.

grouch said:

Yea, unsealed motor grains aren’t that much of a problem. I’ve flown motors that were cased up and sitting around for over two years before flying. Lit right up.

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depends! certain propellants are famous for oxidizing, and certain motors apparently get downright impossible to light (the 29mm DMS green is infamous)