Assembling an engine in the field?

Wildman Rocketry
eggtimer rocketry
The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Cmac said:
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.
Click to expand...

Lemme see... I have two sets of 29/180 and 29/240 motor cases. 4 sets of 29/360 motors. 5 sets of 54/1706 motors. 3 sets of 54/852, 54/1280 motors, and 54/2560 motors. 2 sets of 75/2560, 75/3840, and 75/5120 motors. And those are just off the top of my head and don't include the cases I bought just to collect because they're shiny...
Currently one 75/5120 motor is loaded with a L1040DM from LDRS 38 2019 that didn't get launched, and one 75/3840 has a L1520T in it from the same launch. One of my 54/2560 motors has a K828FJ in it from 2018 AirFest that didn't happen either. All of these motors are in rockets that are prepped and ready to fly. Just depends on what you like to spend your money on... :D:D
 
I always build my motors in the field.

Here are my instructions that I made for myself:

Aerotech Motor Building Instructions
Wrap tape around outside of charge well
Burnish delay insulator and install aft delay spacer
Check fit of delay insulator in charge well; add tape if needed
Install delay grain in delay insulator
Place propellant grains in liner
Grease o-rings, grain liner, delay charge well and threads on case (optional: grease liner)
Clean hands
Install forward delay spacer (flat rubber washer) in well
Insert delay o-ring into well
Insert delay assembly; make sure fit is tight (spacer facing motor grains)
Add black powder to charge well
Add dog barf to fill well
Place tape over charge well and then wrap tape around charge well (do not use circular tape or cap supplied with motor)
Insert liner and grains into case
Place forward insulator into case
Place forward (thinner) o-ring in case
Attach forward closure
Insert rear insulator
Insert rear o-ring
Insert nozzle
Attach rear closure

Take igniter to pad. Do NOT install before the rocket is on the pad and ready for launch.
 
After the ejection charge is put in the ejection well of the forward enclosure (hold vertical and tap to make sure you get some on top of the delay), put some dog barf or wadding on top of it before putting the red cap on. That way the ejection charge is held down against the bottom of the well so that if the model is pointed down the powder does not move away from the delay and not ignited. Good insurance.
 
The dog barf and tape just holds the ejection charge in the well. The paper cap with the motor won't stick well to the aluminum charge well.
 
The reload adapter system allows you to use motors smaller than the case you have. For example, if you have a 38mm 360 case and a reload adapter system, you can use 38mm 120, 240 or 360 motors in the case. For the 360 motor in the 360 case you don't use the adapter system. If you put a 240 motor in the 360 case you use one spacer and the forward closure from the adapter system. For a 120 motor you use two spacers and the forward closure from the adapter system.
 
For someone building (presumably) and AeroTech reload for the first time - and for a cert flight at that - I would follow the AeroTech instructions that come with the motor. By all means after you’ve built a few use some tips and tricks you’ve learnt, but the supplied instructions if followed step by step are pretty close to foolproof.

Secondly, if it’s truly your first time building a reload and it’s a cert flight, then get someone to watch you - or get a DMS motor and make your life a heck of a lot simpler for only a few bucks more.

I’m coming from the position of someone who only started in the hobby 9 months ago and I clearly remember wondering what the heck all the bits in a reload did. We’ve had a number of certification fails at our club launches by people who’ve declined help to assemble motors or sought help from less experienced mentors and the results have been flammable!
 
Nick Hutton said:
For someone building (presumably) and AeroTech reload for the first time - and for a cert flight at that - I would follow the AeroTech instructions that come with the motor. By all means after you’ve built a few use some tips and tricks you’ve learnt, but the supplied instructions if followed step by step are pretty close to foolproof.

Secondly, if it’s truly your first time building a reload and it’s a cert flight, then get someone to watch you - or get a DMS motor and make your life a heck of a lot simpler for only a few bucks more.

I’m coming from the position of someone who only started in the hobby 9 months ago and I clearly remember wondering what the heck all the bits in a reload did. We’ve had a number of certification fails at our club launches by people who’ve declined help to assemble motors or sought help from less experienced mentors and the results have been flammable!
Click to expand...

Good advice. I tape the instructions to my table and follow them. I’ve had very few motor problems, but the ones I’ve had were usually because I thought I knew what to do and didn’t look at the instructions.
Also, not all Aerotech motors assemble the same. The delay spacer, the delay o-ring, the rear o-ring, the liner, and how the forward end of the liner is sealed are all places that differ from motor to motor. The sizes of the o-rings can trip you up too. But if you take your time and really read the instructions you’ll do fine.
 
How about start with building and flying some MPR hobby-line reload motors before you jump into HPR? The 29/40-120 is a good introduction.

Aerotech instructions are notoriously bad, and the reloads can have missing parts. Practice building the motor at home before you go.
 
Cmac said:
Does the dog barf replace the reload adapter system?
Click to expand...

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

https://www.rocketryforum.com/threads/what-altitude-for-visual-tracking.157707/


Which case and which reloads do you have?

Have you talked to the fliers who will witness/sign-off on your certification attempt?

Are you certifying NAR or TRA?

Where are you going to launch?

Do you know if there will be a vendor on site (reliable or otherwise)? (you can buy another reload and try again if the first cert fails for something that doesn't end with an unflyable rocket -- also get DMS motors)

https://www.buyrocketmotors.com/aerotech-h100-14a-white-lightning-38-mm-dms/

https://www.buyrocketmotors.com/aerotech-h219-14a-blue-thunder-38-mm-dms/
 
Last edited:
John Taylor said:
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.
Click to expand...
+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...
 
Last edited:
This is a picture of what I try to do when gluing in the forward closure. I clean the parts that are in contact with the liner with alcohol and then give them a light sanding. I just leave the O-ring in place if there is one. Then, I wet the contacting surfaces with epoxy. Finally, I put a thicker coating of epoxy on the inside edge of the liner. When the closure gets pushed in, it forms the fillet.

I do this with thickened epoxy, and then stand the motor on end while the epoxy cures. I suspect that any epoxy is better than nothing.

Jim

Fillet.jpg
 
The Aerotech instructions are better than they used to be. Plus, they all now seem to have a drawing of the assembled motor with every part identified. That is a HUGE help. Kudos to the person who did that!
 
Zeus-cat said:
The Aerotech instructions are better than they used to be. Plus, they all now seem to have a drawing of the assembled motor with every part identified. That is a HUGE help. Kudos to the person who did that!
Click to expand...

They could still go a little further..

They call out "aft" or "Fore" O ring, yet label the parts 1-16" or 3/32" O-ring. Had they used the same nomenclature throughout, it would be perfect!
 
You can assemble a motor ahead of time, but keep in mind it's a risk if the weather turns and you don't end up using the motor. Leaving a motor loaded for too long can result in the propellant grains deforming under pressure from your o-ring seals and no longer sealing as well, resulting in a CATO when you finally try to use it.

Only load a motor ahead of time if you are absolutely sure you will be using it. I only do it the day before launch, when the weather forecast is stellar.

I will also echo what a few others here have said and suggest you try doing some mid-power reloads before assembling a motor with your cert flight.
 
heada said:
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.
Click to expand...

That's where the confusion for me lies. Your initial statement leads me to believe NAR does not allow pre-built motors (read: built at home) to be flown at their launches at all. The original statement you made did not include 'certification' launches specifically.
 
Antares JS said:
Leaving a motor loaded for too long can result in the propellant grains deforming under pressure from your o-ring seals and no longer sealing as well,
Click to expand...

Not exactly- motor grains don't deform in a motor (or if they do, something is very wrong). It's just the o-rings deforming and you can get a Challenger space shuttle type problem.

FYI- this can be mitigated by backing off on the closures a bit when storing the motor, so you don't have the o-rings under compression.
 
djs said:
Not exactly- motor grains don't deform in a motor (or if they do, something is very wrong). It's just the o-rings deforming and you can get a Challenger space shuttle type problem.

FYI- this can be mitigated by backing off on the closures a bit when storing the motor, so you don't have the o-rings under compression.
Click to expand...

My bad, it was the insulator and o-ring that deformed, not the grain. Brain fart caused by this being a while ago...
 
Antares JS said:
Brain fart caused by this being a while ago...
Click to expand...

Maybe you forgot to loosen the closure on your brain? :)

Anyway-I've heard of this happening, but never quantitative data.... how long before the o-rings are toast, etc?

@jd2cylman - you seem to be an expert in things sitting around for a while.. your thoughts? :)
 
mhanna said:
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.
Click to expand...
+1 good answer! I do the same. Makes perfect sense to determine your flying conditions first, besides how many extra cases do you have laying around?
 
Cmac said:
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?
Click to expand...
Yes its practical. Its the only way to go unless you have a deep wallet and can afford to buy multiple cases. If you have a 29 complete case and want to get a different size. You can always just buy the case and not the closures. The only time you would need multiple complete motor cases is if you plan on flying a cluster rocket.
 
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.
 
jd2cylman said:
Lemme see... I have two sets of 29/180 and 29/240 motor cases. 4 sets of 29/360 motors. 5 sets of 54/1706 motors. 3 sets of 54/852, 54/1280 motors, and 54/2560 motors. 2 sets of 75/2560, 75/3840, and 75/5120 motors. And those are just off the top of my head and don't include the cases I bought just to collect because they're shiny...
Currently one 75/5120 motor is loaded with a L1040DM from LDRS 38 2019 that didn't get launched, and one 75/3840 has a L1520T in it from the same launch. One of my 54/2560 motors has a K828FJ in it from 2018 AirFest that didn't happen either. All of these motors are in rockets that are prepped and ready to fly. Just depends on what you like to spend your money on... :D:D
Click to expand...
Wow, now that's impressive....
Lonely??? Need a friend???
 
AfterBurners said:
+1 good answer! I do the same. Makes perfect sense to determine your flying conditions first, besides how many extra cases do you have laying around?
Click to expand...
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.
 
djs said:
Maybe you forgot to loosen the closure on your brain? :)

Anyway-I've heard of this happening, but never quantitative data.... how long before the o-rings are toast, etc?

@jd2cylman - you seem to be an expert in things sitting around for a while.. your thoughts? :)
Click to expand...

Well, sometimes I leave them loose, if I know there's a chance it might not happen. Of the 4 loaded right now, all are tight, because I didn't wanna forget to tighten them. The Loki H100 that I launched two weeks ago had been loaded for 2 years. Worked fine. If it's a good day and I'm motivated, I'll launch a AT K828FJ that's been loaded for 2 years with the closures tight this weekend at QCRS. Don't expect anything to go wrong with it either.
They say the o-rings may deform. Well, yeah, that's their job. They'll still hold pressure. I work with hydraulics all the time at work. The only way o-rings seal is to be deformed. You can't be running a $400,000.00 tractor and activate a hydraulic function and have to go "Oh, wait, I need to tighten the jam nut on that hydraulic port before I pressurize it..."
Do as you see fit. I'm not gonna worry about o-rings that have been compressed for only two years in a case that never got above 90°...
If my K828FJ blows up I'll come back here and eat my crow in public, but... It won't be a problem.
 

Similar threads

S
reloading motor in the field
2
Replies
44
Views
2K
mbeels
mbeels
SteelyEyed
Project Aether Breather
2
Replies
46
Views
2K
Rschub
Rschub
bandman444
Bryce's Handicap Record Quest: NSL 2024
2
Replies
59
Views
2K
MClark
M
frogglicker
SpiderMax Too - The Return
Replies
5
Views
179
frogglicker
frogglicker
M
Aerotech RMS J275W - Loose Grains Forward to Aft - This is not good right?
Replies
28
Views
1K
3stoogesrocketry
3stoogesrocketry

Latest posts

Back
Top