Assembling an engine in the field?

[Cmac]

I've never assembled a rocket engine so I don't feel too dumb asking this question.
Is it practical to assemble one in the field?
Or do you bring all of them preassembled?
I ask because next weekend my son and I will both be attempting our LV1.
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?

 

[mhanna]

I assemble all my motors at the field. I get to the field, look at wind conditions, then decide what moto I'm going to use. I usually have a low and high choice for each rocket depending on field conditions.

As for one casing that could be a problem. If a rocket gets lost or some damage to the casing or the casing ejects from the rocket and you can't find it, you're done for the day. There is also the time to clean it between each flight but that's minor compared to having one in a tree.

 

[Cmac]

Thank you.

I do plan on adding additional cases to my inventory as time goes on.

 

[heada]

I'm pretty sure NAR requires the person doing your L1 check-off to witness you build the motor but it's been a few years since I've witnessed a L1 or L2. I'm not sure about Tripoli.

 

[mbeels]

I'm pretty sure NAR requires the person doing your L1 check-off to witness you build the motor but it's been a few years since I've witnessed a L1 or L2. I'm not sure about Tripoli.

I think that is still true, at least it was last year.

 

[Bat-mite]

Make sure you have a flat, level surface out of the wind. Count your O-rings before you lay them out, and make sure you have then all in. Check the ground.

Go get that cert!

 

[mbeels]

Is it practical to share one case with four rockets?

It's doable. Allow yourself some extra time, and don't rush. I usually load my motors ahead of time and don't plan on reloading at the field, mainly because I want to relax and spectate. Trying to load at a field can be distracting, but definitely doable. I've done multiple flights on my 24/40 casing in a day. Bring a trash bag for the remains, and something to clean the case with (white vinegar and paper towels, or baby wipes).

And yeah, as heada mentioned, I believe you'll need to assemble your L1 motor in the presence of who ever is signing off on your flight. Good luck and have fun!

 

[Cmac]

Make sure you have a flat, level surface out of the wind. Count your O-rings before you lay them out, and make sure you have then all in. Check the ground.

Those are exactly the logistics I'm concerned about.

 

[rcktnut]

I don't know about TRA but with NAR you need to assemble the motor at the launch if using a re-loadable. As for assembly otherwise I do all mine at home before the launch, much more enjoyable than out in the open, no wind ,distractions, waste of time, etc. Single use are nice for certs!!

 

[Cmac]

Okay, got it. We'll be prepared to demonstrate engine assembly.
To those home assemblers, this means that you have a separate case for each reload.
It'll take me a while to build up that inventory. So for now I guess I'll be assembling one at a time in the field.
Knowing that I experienced people do so will help my confidence.
Maybe I'll look back on these humble beginnings and chuckle.

 

[djs]

Is it practical to share one case with four rockets?

One issue here is that the cases are pretty hot after launching, so you'll need some time in between to cool down and clean them.

I would suggest finding someone with experience on the field who can help you assemble the motor. Even if it's a "Watch what I'm doing to make sure it isn't something stupid". I think most rocketeers would be willing to help you for sure.

Also make sure that you write down (or remember) which motor goes with which rocket, and the delay each should be set at. Don't want to be assembling motor C when you were thinking of motor A and doing something wrong.

Good luck on your L1!

 

[mrwalsh85]

I don't know about TRA but with NAR you need to assemble the motor at the launch if using a re-loadable. As for assembly otherwise I do all mine at home before the launch, much more enjoyable than out in the open, no wind ,distractions, waste of time, etc. Single use are nice for certs!!

That's news to me....

I've built motors ahead of time. I've also built motors at the field. Given that our club is in the Midwest where the weather changes by the minute, I can sometimes feel leery of building ahead. Last launch we had around here, I didn't get to fly any of my big rockets until the skies cleared up with 90 minutes left in the waiver. However, I spent the whole launch preparing my rockets... Just in case. and I managed to get a K and an M motor built and flown in that timeframe, with the K motor being a call-in window flight.

if building at the field, bring baby wipes, grease, and trash bags. I try to empty my casings post-flight, and with the longer motors, I just empty them right into a trash bag. Sometimes I find I have to crack the liner in half to get it to fit, but at least it'll be confined to the trash bag. ProTip - don't pull the bulkheads off until you have the trash bag surrounding the motor. All the little flakes of liner/paper will blow out and get everywhere before you can get to the trash bag - makes for a sooty mess.

 

[heada]

That's news to me....

Per the NAR website: https://www.nar.org/high-power-rocketry-info/level-1-hpr-certification/

Point 2.2.4
"The modeler must demonstrate his ability to build and fly a rocket containing at least one H or I impulse class motor. Cluster or staged models used for certification may not contain over 640.00 Newton seconds total impulse. In the case of a cluster or staged model, at least one of the individual motors must be an H or I impulse motor. Combinations of D, E, F or G motors that meet the impulse requirements do not qualify as the model does not contain at least one H or I impulse motor. Single use, reloadable, or hybrid technology motors are permitted. The modeler must assemble the reloadable motor, if used, in the presence of a certification team member."

Key is the last sentence. Since this is for a L1 cert flights, it has to be done on-site.

 

[dr wogz]

https://www.nar.org/wp-content/uploads/2014/08/hpappl.pdf

Just checked the 'checklist' on the back of the NAR HPR application sheet. No mention of "witnessed motor assembly". But I do believe it's in the club's interest to ensure you have put it together properly. Some L1 (or L2) attempts use a disposable motor, so the building part is irrelevant.

Cmac,

• Get yourself a shallow Tupperware (12" x 12"..) container to build in. this way, parts don't roll away. Also, get a clip board (or clips) to hold the instructions flat, so they are easily read.
• Ask for the witness to come with you to watch you build your motor. Doing it at the field, but away from other, distractions, etc.. will keep you focused and calm!
• Ask to borrow a delay adjustment tool (if needed). 1/32 of an inch = 1 second less on the delay grain.
• Bring a little baggie. I squirt a little grease into the baggie, then toss in the O-Rings, then smoosh them around to coat them. Remove when they are called upon. Remember, you only need a coating of grease..
• Paper towel! on in your other hand, for when you pick things up, and you need to wipe the greasy finger.
• Take your time, check off each step
• test fit the igniter once the motor is assembled. Many build the motor, get the rocket on the pad, then fight with the igniter to get it into the little hole!

It's a launch like any other.
Don't' be nervous.. There is no reason to be nervous!


I build my motors at the field, I will build the occasional one at home, but I build the bulk at the field, in the car sometimes (when it's c-c-cold out!!). I also have a moving blanket I put down in my area, so if something does drop, it's on the blanket, not in the tall grass or muddy lug tread! I also will build while sitting on the ground (int eh summer!) so that anything that does fall, only falls a few inches!

Best of luck to you both!

 

[Greg Furtman]

I agree with dr wogz, get yourself some sort of short sided plastic tray to assemble in. That will keep stuff from blowing around or dropping on the ground. And make sure you RTFI. (Read the *^!& instructions.) It's easy to forget something.

 

[Nytrunner]

The tupperware container is the best advice ive heard for field assembly. Works on a table or in your lap.

The baby wipes and trashbag are good too.

I confess when i did L1, the inspector didnt care about seeing me assemble my 2grain Pro38, and when i did L2 no one batted an eye over my K500 being prebuilt (i did the forward closure epoxy trick to avoid gas slip on the Pro54)

 

[jlabrasca]

I've never assembled a rocket engine

Is it too late to get DMS motors? Will there be a vendor on-site?

Otherwise I will echo and amplify those who advise you to:

1 - Get a shallow dish in which to lay out the parts. Anything that is too heavy to be lifted by a strong breeze, large enough to lay out all of the pieces, and not o-ring colored will do.
2 - Get a clipboard and some binder clips to hold the assembly instructions.
3 - Bring extra lubricant (the blister that probably came with your casing is an easily-lost item)
4 - Make sure that a delay drilling tool will be available to you.
5 - Ask your witnesses to watch you build the reloads.
6- Baby wipes and a stick you can use to push them through the casing


Good luck (and remember to pack the chutes)

 

[rcktnut]

I should have mentioned in post # 9 assembly required at launch site for NAR certification flights only. After certified assemble where ever you wish to.

 

[rockladen]

The tupperware container is the best advice ive heard for field assembly. Works on a table or in your lap.

The baby wipes and trashbag are good too.

I confess when i did L1, the inspector didnt care about seeing me assemble my 2grain Pro38, and when i did L2 no one batted an eye over my K500 being prebuilt (i did the forward closure epoxy trick to avoid gas slip on the Pro54)

I'm receiving my PRO54 casings tomorrow, and was wondering what you meant by "forward closure epoxy trick to avoid gas slip". Could you refer me to the thread discussing this? I'm guessing it may be a precautionary measure to prevent CATO or case bulging on PRO54?

 

[Nytrunner]

I'm receiving my PRO54 casings tomorrow, and was wondering what you meant by "forward closure epoxy trick to avoid gas slip". Could you refer me to the thread discussing this? I'm guessing it may be a precautionary measure to prevent CATO or case bulging on PRO54?

Crud, its come up in a few places since Jim Jarvis first described it.

This is for the longer reloads (4+ grains)
Basically, you just put a bead of 30min epoxy around the inner lip of the liner's front end where the forward closure sits. I use 30 min and let it cure overnight, but 5min epoxy and a half hour wait will do on the day of launch.

Its not in the instructions, but its cheap insurance for your case and rocket (like only fireing E12s in warm weather)

 

[o1d_dude]

https://www.nar.org/wp-content/uploads/2014/08/hpappl.pdf

Just checked the 'checklist' on the back of the NAR HPR application sheet. No mention of "witnessed motor assembly". But I do believe it's in the club's interest to ensure you have put it together properly. Some L1 (or L2) attempts use a disposable motor, so the building part is irrelevant.

Cmac,

• Get yourself a shallow Tupperware (12" x 12"..) container to build in. this way, parts don't roll away. Also, get a clip board (or clips) to hold the instructions flat, so they are easily read.
• Ask for the witness to come with you to watch you build your motor. Doing it at the field, but away from other, distractions, etc.. will keep you focused and calm!
• Ask to borrow a delay adjustment tool (if needed). 1/32 of an inch = 1 second less on the delay grain.
• Bring a little baggie. I squirt a little grease into the baggie, then toss in the O-Rings, then smoosh them around to coat them. Remove when they are called upon. Remember, you only need a coating of grease..
• Paper towel! on in your other hand, for when you pick things up, and you need to wipe the greasy finger.
• Take your time, check off each step
• test fit the igniter once the motor is assembled. Many build the motor, get the rocket on the pad, then fight with the igniter to get it into the little hole!

It's a launch like any other.
Don't' be nervous.. There is no reason to be nervous!


I build my motors at the field, I will build the occasional one at home, but I build the bulk at the field, in the car sometimes (when it's c-c-cold out!!). I also have a moving blanket I put down in my area, so if something does drop, it's on the blanket, not in the tall grass or muddy lug tread! I also will build while sitting on the ground (int eh summer!) so that anything that does fall, only falls a few inches!

Best of luck to you both!

The small flat Tupperware container is key to a successful motor assembly even at the workbench or kitchen table. Have used it from Day One.

For the record I don’t build Aerotech motors in the field. If I need another motor I’ll just buy a AT DMS from the onsite vendor. Much simpler and quicker that way but still possible to lose a part or two.

 

[rockladen]

Crud, its come up in a few places since Jim Jarvis first described it.

This is for the longer reloads (4+ grains)
Basically, you just put a bead of 30min epoxy around the inner lip of the liner's front end where the forward closure sits. I use 30 min and let it cure overnight, but 5min epoxy and a half hour wait will do on the day of launch.

Its not in the instructions, but its cheap insurance for your case and rocket (like only fireing E12s in warm weather)

Thank you Nytrunner! I will do that. I'll also meet up and chat with Jim Jarvis at our club launch day tomorrow.

 

[OverTheTop]

I have assembled in the field and at home. My preference now is to preassemble whenever possible, as it makes for a more social launch day.

As others have said, field conditions add to the challenge, particularly wind, dust and glare. I tape the instructions down to the table and have a shallow dish for keeping the pesky pieces from wandering. A rubbish bucket nearby is a great addition to the launch commodities also.

I suggest you read, and re-read the instructions until it becomes entirely clear what they are asking. Having a pencil to be able to tick off each step as you go can be useful when you are learning. It mitigates the stress surprisingly well, especially for a cert flight.

Don't forget to take some grease along with you. I have seen people forget that.

Good luck with your certifications

 

[OverTheTop]

I'm receiving my PRO54 casings tomorrow, and was wondering what you meant by "forward closure epoxy trick to avoid gas slip". Could you refer me to the thread discussing this? I'm guessing it may be a precautionary measure to prevent CATO or case bulging on PRO54?

Correct, as others have pointed out.

You can use some quick-set epoxy for this in the field (I use BSI). Just make sure you assemble your motor earlier in the day to give it a bit of time to cure, before flight. Keeping it in a warm place helps the epoxy go off also. It won't be fully cured, but it will be better than nothing.

 

[John Taylor]

You should be able to purchase and take possession of a single motor before you are certified for your attempt. That's what I did. As long as you can, practice putting it together in your home until you have it down. Or better yet purchase a single use DMS disposable motor for the certification flight. One less thing to worry about and one less thing to go wrong. Note: with the DMS motor, if you need to adjust the delay element you will still need to do that in front of your witnesses.

 

[bill_s]

I built my first reload motors at home, but they were 24 mm.

 

[HVArcas]

never built one NOT in the field..

 

[rockladen]

Correct, as others have pointed out.

You can use some quick-set epoxy for this in the field (I use BSI). Just make sure you assemble your motor earlier in the day to give it a bit of time to cure, before flight. Keeping it in a warm place helps the epoxy go off also. It won't be fully cured, but it will be better than nothing.

Thank you OverTheTop! Appreciate the advice on the larger CTI casings. I did not know that, but good insurance as Nytrunner mentioned.

 

[Cmac]

Thank you Nytrunner! I will do that. I'll also meet up and chat with Jim Jarvis at our club launch day tomorrow.

I'm glad you got your answer! I don't even understand the concept of the question. Ha ha.
But that's okay. I'm still trying to figure our 29mm setup.

Get yourself a shallow Tupperware (12" x 12"..) container to build in. this way, parts don't roll away. Also, get a clip board (or clips) to hold the instructions flat, so they are easily read.

• Ask for the witness to come with you to watch you build your motor. Doing it at the field, but away from other, distractions, etc.. will keep you focused and calm!
• Ask to borrow a delay adjustment tool (if needed). 1/32 of an inch = 1 second less on the delay grain.
• Bring a little baggie. I squirt a little grease into the baggie, then toss in the O-Rings, then smoosh them around to coat them. Remove when they are called upon. Remember, you only need a coating of grease..
• Paper towel! on in your other hand, for when you pick things up, and you need to wipe the greasy finger.
• Take your time, check off each step
• test fit the igniter once the motor is assembled. Many build the motor, get the rocket on the pad, then fight with the igniter to get it into the little hole!

...I also have a moving blanket I put down in my area, so if something does drop, it's on the blanket, not in the tall grass or muddy lug tread!

Is it too late to get DMS motors? Will there be a vendor on-site?

Otherwise I will echo and amplify those who advise you to:

1 - Get a shallow dish in which to lay out the parts. Anything that is too heavy to be lifted by a strong breeze, large enough to lay out all of the pieces, and not o-ring colored will do.
2 - Get a clipboard and some binder clips to hold the assembly instructions.
3 - Bring extra lubricant (the blister that probably came with your casing is an easily-lost item)
4 - Make sure that a delay drilling tool will be available to you.
5 - Ask your witnesses to watch you build the reloads.
6- Baby wipes and a stick you can use to push them through the casing

Good luck (and remember to pack the chutes)

That is some valuable advice there...!! Thank you.

Don't' be nervous.. There is no reason to be nervous!
Best of luck to you both!

Damn... It always makes me nervous when somebody tell me "Don't' be nervous.. There is no reason to be nervous!" Ha ha.

Unfortunately our club doesn't seem to have a reliable vendor.
I'm still very new with them so I haven't had a chance to dig in and find local resources yet.

 

[Steve Shannon]

never built one NOT in the field..

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