Aerotech DMS Dimensional Drawings

[atestani]

I have assembly drawings from RCS Aerotech resources for various Aerotech DMS motors but the dimensional data is very limited and not useable to design a motor mount from. I searched everywhere including ThrustCurves.org as well as getting motor certification letters hoping the dimensions would be included.

Do dimensional drawing exist anywhere and, if so, where can I find them?

I specifically need a drawing H169WS-13A drawing to finish the motor mount design for a rocket I will use for my L1 certification. Since I cannot buy the motor ahead of time (made arrangements to buy at the launch), I cannot do what I did for some G75m-13A . There I took the G75m-13A drawing that has at least has a couple of length measurements and made my own drawing by measuring the rest.

If an H169WS-13A drawing is unavailable, would someone be so kind to provide these dimensions:
- overall length (203mm?)
- from nozzle end to thrust ring
- length of thrust ring
- thrust ring to end of outer case (or length of molded ejection bulkhead)


Thanks!

 

[Steve Shannon]

Hi Al,
Best wishes on your certification flight!
I don’t have one to measure, but I wanted to point out that length of the motor usually doesn’t matter. The thrust ring is at the aft end of the motor. It simply abuts the aft end of the motor mount tube. Because the motor case is straight sided, it doesn’t matter whether it’s shorter than the motor mount tube or even longer. That’s intentional so people can put different lengths of motors into their rockets and experience different impulse levels.

As long as you have a retainer to grip the thrust ring and keep the motor from popping out when the ejection charge goes off you should be fine. The thrust ring is usually 3/8 inch long.

Best wishes!

 

[jsdemar]

Everything Steve said.

You can estimate the dimensions from this drawing:
https://d11fdyfhxcs9cr.cloudfront.net/templates/170652/myimages/h169ws-13a_rcs_assembly.pdf

 

[cbrarick]

You're way over thinking this
here's data https://www.thrustcurve.org/motors/AeroTech/H169WS-13/
all you really need to know is that you need a 29 mm motor tube and room for a 8 3/4 inch long motor. Nothing more.

spend your time on the design of the rocket and it's construction.

way more important to know if it's stable then the nozzle to thrust ring length

 

[atestani]

Thanks to all for the information.

Perhaps a bit more information would explain why I am looking for these dimensions

I am using 3D modeling to design every detail of this scratch-built rocket. It includes interchangeable single and 3X cluster motor mounts which is why accurate motor dimensions are required. The 3" fiberglass rocket is already built including motor mounts for single and 3X cluster G75M. The H169WS (to be used for my L1 cert) is quite different at the aft end so I must design a motor mount for it. The rocket is using motor ejection with JL Chute Release.

In addition to the interchangeable motor mounts, the airframe is in three segments: 1) fin can, 2) "recovery tube" with integrated baffle, 3) payload section with GPS tracker, flight recorder/altimeter, and Transolve beeper.. To assure proper stability margin across different motor types/configurations, I've included a nose cone weight system with slide in-tubes of different weights. I have the single and 3X cluster rockets fully simulated in OpenRocket. I even did the single version in RockSim as a cross-check.

 

[Pinetree]

https://wildmanrocketry.com/products/h169ws

 

[tsmith1315]

Since I cannot buy the motor ahead of time (made arrangements to buy at the launch)

Just to be sure you're aware, you can buy a single motor for certification prior to the launch. It may not be feasible for other reasons (hazmat, etc), but it's commonplace to do so.

 

[mikec]

This comes up from time to time, for example https://www.rocketryforum.com/threads/aerotech-su-motors-dimensions-wanted.158414/

I'll repeat what I said then:

I've never found a source for the precise dimensions of DMS motors.

Many of the DMS motors don't have a protruding nozzle, the exit is basically flush with the bottom of the thrust ring. Others have some protrusion, and the L1000 has a fairly large RMS-like nozzle. There seems to be a lot of variability across the product line (based on a random collection of spent motors I have lying around.)

As Steve Shannon says, it's been possible for Aeropack to design something that retains all the motors on the market, and if you just leave the MMT open at the front then it doesn't much matter what that end looks like, grossly.

You'd have to have a good reason to try to spec things more tightly IMHO.

 

[atestani]

Just to be sure you're aware, you can buy a single motor for certification prior to the launch. It may not be feasible for other reasons (hazmat, etc), but it's commonplace to do so.

Yes, I know, but I have already made arrangement to buy from the "motor man" for our club. I may contact him next week to get one.

 

[atestani]

This comes up from time to time, for example https://www.rocketryforum.com/threads/aerotech-su-motors-dimensions-wanted.158414/

I've never found a source for the precise dimensions of DMS motors.

Many of the DMS motors don't have a protruding nozzle, the exit is basically flush with the bottom of the thrust ring. Others have some protrusion, and the L1000 has a fairly large RMS-like nozzle. There seems to be a lot of variability across the product line (based on a random collection of spent motors I have lying around.)

As Steve Shannon says, it's been possible for Aeropack to design something that retains all the motors on the market, and if you just leave the MMT open at the front then it doesn't much matter what that end looks like, grossly.

You'd have to have a good reason to try to spec things more tightly IMHO.

I am also finding there is no source of decent dimensional information. Also, I now see that DMS motors are bit like snowflakes as the aft ends are not at all standardized (neither are the forward ends but that is much less of a concern). There is also inconsistency in names of dimensions, e.g. "overall length" is apparently the distance from the aft end of the thrust ring to the end of the case (nozzle and ejection bulkhead aren't included).

I am not looking to have a universal motor mount but interchangeable motor mount assemblies and only for a few motors I may be interested in (at the moment).

Frankly, if the assembly PDFs of the various motors had one or two horizontal dimensions, bringing an image into a CAD program and scaling the image to those dimension and the diameters shown, would produce a very good dimensional drawing. At least the G75M has these extra dimensions and it was straightforward to make a 2D drawing and a 3D model. The H169WS does not which has led me to this thread.

https://d11fdyfhxcs9cr.cloudfront.net/templates/170652/myimages/g75m-13a_rcs_assembly.pdf
https://d11fdyfhxcs9cr.cloudfront.net/templates/170652/myimages/h169ws-13a_rcs_assembly.pdf

G75:

 

[cbrarick]

still way over thinking this. all you really need to know is the length of the thrust ring, which is pretty standard throughout the manufactures. everything else is irrelevant as who really cares how far out the nozzle sticks out.
Also, loose the baffle, that's not a high power thing. it's because the motors are of vastly different sizes. Why design for a single motor when you could have it work for all motors in the size.
I commend the effort of 3D modeling but it's completely unnecessary Rocksim is all you need. spend your time building and flying rockets to gain experience.

 

[atestani]

I am also finding there is no source of decent dimensional information. Also, I now see that DMS motors are bit like snowflakes as the aft ends are not at all standardized (neither are the forward ends but that is much less of a concern). There is also inconsistency in names of dimensions, e.g. "overall length" is apparently the distance from the aft end of the thrust ring to the end of the case (nozzle and ejection bulkhead aren't included).

I am not looking to have a universal motor mount but interchangeable motor mount assemblies and only for a few motors I may be interested in (at the moment).

Frankly, if the assembly PDFs of the various motors had one or two horizontal dimensions, bringing an image into a CAD program and scaling the image to those dimension and the diameters shown, would produce a very good dimensional drawing. At least the G75M has these extra dimensions and it was straightforward to make a 2D drawing and a 3D model. The H169WS does not which has led me to this thread.

https://d11fdyfhxcs9cr.cloudfront.net/templates/170652/myimages/g75m-13a_rcs_assembly.pdf
https://d11fdyfhxcs9cr.cloudfront.net/templates/170652/myimages/h169ws-13a_rcs_assembly.pdf

G75:
View attachment 600228

As it turns out, RCS data does have enough horizontal dimension information to create a model. It is contained in the parts list om the lower right of the diagram.

 

[atestani]

still way over thinking this. all you really need to know is the length of the thrust ring, which is pretty standard throughout the manufactures. everything else is irrelevant as who really cares how far out the nozzle sticks out.
Also, loose the baffle, that's not a high power thing. it's because the motors are of vastly different sizes. Why design for a single motor when you could have it work for all motors in the size.
I commend the effort of 3D modeling but it's completely unnecessary Rocksim is all you need. spend your time building and flying rockets to gain experience.

This should be another thread as it is irrelevant to the original question. If you would like to start a thread on "design methodology" we could debate that subject there.

I will tell you I disagree that it is possible to design a fiberglass rocket with, 3D printed parts with brass inserts, aluminum machined parts, laser cut wood parts including slotted fins, etc, with a simulation program like RockSim and having any chance of things fitting together. I also disagree there is enough standardization in thrust rings, etc. to allow for interchangeable motor mounts (including different motor diameters, lengths and clusters).

IMO, designing the rocket so it all fits together when you build it is as satisfying as flying it (multiple times). I believe not having a solid design is what kits are for... but keep in mind someone actually designed them as well.

 

[tfish]

https://wildmanrocketry.com/products/h169ws

@Pinetree
for the win!

Tony

 

[Pinetree]

It's not rocket science.

(Seriously, just send it.)

 

[cbrarick]

you should check with the club you want to fly it at to make certain they are good with your rocket.

 

[jmasterj]

I also disagree there is enough standardization in thrust rings, etc. to allow for interchangeable motor mounts (including different motor diameters, lengths and clusters).

This part is where you're wrong. People use arbitrary lengths of standard ID motor mount from different manufacturers to hold motors from more different manufacturers all the time. LOC Precision has two different swappable motor mount options that take a variety of single- and cluster-mount configs.

There are multiple motor retainer manufacturers whose products work with all currently available, certified motor cases and singe-use motors.

Perhaps if you explained (with a drawing?) exactly what you're trying to do with the motor length we can give you more satisfactory assistance.

 

[atestani]

Motor length isn't an issue. It is the aft end, specifically thrust ring thickness and location relative to the nozzle end. I am using a unique motor mount system and want the dimensional information to be sure the motors I was currently interested in would work in this system.

I was only asking for dimensional data on Aerotech DMS motors. As I said in #12 I found the information and was passing on that information. At that point my question was answered.

Unfortunately, a large portion of this thread turned in my justifying why I needed the information or why I didn't need the information, criticizing the design and design process, etc, Totally off-topic, and frankly unpleasant.

 

[Pinetree]

Yer gonna have that when you ask a question on the Internet.

 

[DigBaddy]

I believe that the thread turned into what it did due to lack of clarity on the proposed design (pictures are a good thing). There are people on here with lots of experience and are probably confused why someone would reinvent motor retention. If a design is meaning to be flexible, creating limitations by not using proven retention methods seems odd on the surface.

Good luck.

 

[atestani]

One last post....

I asked for a source of dimensions, nothing more. A few people tried to help and then the thread went sideways. I ultimately found the information and passed that on for others in the event they were also looking for the information (there are several threads on the same subject, I found later). Scan thru this thread and it should be clear how a simple question turned into what it did, mainly from a couple of individuals.

I have been designing big rockets on and off for over 50 years and recently got back into the hobby . The availability of new simulation and design tools presented a challenge, so I set off to apply the experience I had and those tools to create a "workhorse" rocket that was innovative and flexible. The rocket is built and I was to fly it yesterday for my L1 cert. I couldn't make the launch due to a bad cold so I have been taking the time to refine and check the motor mounts. Again, all I wanted was a few dimensions.