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tjsnakez

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Looking for advice on cross fitting a CTI M840 into a RMS 75/7680 casing.
I originally planned to do this so that I could use the tailcone closure I have for AT, but when I fitted it, the nozzle is recessed 1.25 inches, not a good plan in my mind.

View attachment 492117

So I switched to a standard forward closure and found another problem. Both closures have a 1/8" gap when tightened.
View attachment 492118

I think this is because I used the AT seal disk instead of the CTI forward insulator. Has anyone tried this?

I've flown two M840's in a 7680 case. Just split the difference in the gap between the forward and aft closure and it'll be fine. That being said, I've never used a seal disk with a CTI load before though. If it is thicker than the forward insulator I would not use it.
 

Sooner Boomer

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Ease of shipping affects availability for me when it's the middle of winter and there aren't and big launches nearby that draw vendors. Having USPS mailable motors and reloads help a bunch! Here's a list of mailable goodies (based on motor matrix 8/19/21.
 

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thatotherguy501

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Looking for advice on cross fitting a CTI M840 into a RMS 75/7680 casing.
I originally planned to do this so that I could use the tailcone closure I have for AT, but when I fitted it, the nozzle is recessed 1.25 inches, not a good plan in my mind.

View attachment 492117

So I switched to a standard forward closure and found another problem. Both closures have a 1/8" gap when tightened.
View attachment 492118

I think this is because I used the AT seal disk instead of the CTI forward insulator. Has anyone tried this?

I've used Aerotech seal disks on 4 different L2375s, albeit in CTI 75-4G casings, not Aerotech hardware. The seal disk is considerably thicker than CTI's forward insulator, so to reduce the gap between the closures and casing, I sanded down just a few milimeters of each propellant grain face with 220 grit sandpaper to improve the gap. Each motor still had between a .1 and .125in gap between the aft closure and the casing, but they all performed normally.
 

Rocketjunkie

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The Aerotech seal disk (part that is outside the liner) is thicker than the CTI forward insulator. Use the CTI parts and they should fit better with less gap. This also eliminated the 1/16" thick nozzle O-ring so the same liner lengths could be used.
 

Wayco

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Update on the CTI M840 long burn I built in a RMS 75/7680 casing last week. Flew it to 30,130 ft. in a carbon fiber Mongoose 75 yesterday, exactly as it was shown in the picture with the standard rear closure. I will be cleaning that casing tomorrow, and will post up anything interesting.
 

KenRico

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Update on the CTI M840 long burn I built in a RMS 75/7680 casing last week. Flew it to 30,130 ft. in a carbon fiber Mongoose 75 yesterday, exactly as it was shown in the picture with the standard rear closure. I will be cleaning that casing tomorrow, and will post up anything interesting.

Congrats on going over 30k !
How close was your sim to the recorded altitude ??

Kenny
 

Wayco

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Congrats on going over 30k !
How close was your sim to the recorded altitude ??

Kenny

Thanks Kenny!
I didn't do an Open rocket sim, but Thrust Curve calls it a 28k flight. That's with the previous Cd calculated from flights before the 2k epoxy paint job. This is the first flight with the new paint, so the Cd went from .5 to .4 :)
Ordered two M685 White Lightning loads from Balsa Machining last month, which is another motor I have flown before, but it comes off the rail a bit slower and I didn't get a vertical flight last time, so the M840 seems to be the better motor for this rocket. We will see about that sometime early next year.
Be sure to take a look at my launch report here:
https://www.rocketryforum.com/threads/tra-phx-december-2021-waycos-send-it-launch.169725/
 

Wayco

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Dismantled the AT 75/7680 casing today, casing, closures and seal disk survived unscathed until I dropped the forward closure and put a ding in the threads. They cleaned up OK with a small file, and thread back on to the casing normally. Otherwise, the nozzle was trashed:
muddy nozzle.jpg


Can't imagine what that tailcone closure would look like after this, it was hard enough getting the nozzle out of this closure:
nozzle 2.jpg


The liner burned through at the aft end, but the casing was undamaged, and the liner slid out with a bit of coaxing:
liner 2.jpg

liner 1.jpg

The CF Mongoose found a nice soft place to land, about two miles away, right next to one of the few ponds within miles of the launch site:
mongoose landing 1.jpg
 

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tfish

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Dismantled the AT 75/7680 casing today, casing, closures and seal disk survived unscathed until I dropped the forward closure and put a ding in the threads. They cleaned up OK with a small file, and thread back on to the casing normally. Otherwise, the nozzle was trashed:
View attachment 493037

Can't imagine what that tailcone closure would look like after this, it was hard enough getting the nozzle out of this closure:
View attachment 493038

The liner burned through at the aft end, but the casing was undamaged, and the liner slid out with a bit of coaxing:
View attachment 493040
View attachment 493041
The CF Mongoose found a nice soft place to land, about two miles away, right next to one of the few ponds within miles of the launch site:
View attachment 493042

Tony
 

cautery

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For those looking for the AeroTech RMS external dimension drawings, we have posted them here until the new AeroTech website is operational:


Thank you! I know y'all are trying hard to get the main website back up, and I appreciate the cross-posting. As a newly back to rocketry guy, not having ready access to y'alls full tech docs, et al. makes it a much more involved and time consuming task to accumulate and absorb the information I want/need. :D

Have a great and safe weekend!
 

AeroTech

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Thank you! I know y'all are trying hard to get the main website back up, and I appreciate the cross-posting. As a newly back to rocketry guy, not having ready access to y'alls full tech docs, et al. makes it a much more involved and time consuming task to accumulate and absorb the information I want/need. :D

Have a great and safe weekend!
Thanks, and let me know if there's something else that could be cross-posted quickly that would be helpful in the interim.
 

StreuB1

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Thanks, and let me know if there's something else that could be cross-posted quickly that would be helpful in the interim.

Master Motor Matrix, please, and thank you for the drawings!! :D


Hows the single grain ST test load coming along?? I bought (2) 98mm ST loads from WM during the member holiday sale (L2500 & M4500). Would love a single grain 75mm and/or 98mm. Or even a 54mm single grain ST would be cool.
 

cautery

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Thanks, and let me know if there's something else that could be cross-posted quickly that would be helpful in the interim.

1) The missing drawings would be great if they can be located... especially the 54/426 as 54mm is the set I have en route.
2) Motor Matrix, yes....
3) Some document listing the weights for all the components.

Thank you again! :D
 
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rharshberger

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1) The missing drawings would be great if they can be located... especially the 54/462 as 54mm is the set I have en route.
2) Motor Matrix, yes....
3) Some document listing the weights for all the components.

Thank you again! :D
Just checked my collection of AT case drawings and the 54/852 is the shortest case, I downloaded all of them off the AT website years ago and dont remember seeing a 54/456 drawing...its a fun little motor with the I599 Boomstick!
 

cautery

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Just checked my collection of AT case drawings and the 54/852 is the shortest case, I downloaded all of them off the AT website years ago and dont remember seeing a 54/456 drawing...its a fun little motor with the I599 Boomstick!

Checked what I have been able to find.....

I have docs for motor assembly USING the 54/426....
 

tsmith1315

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Master Motor Matrix from 08/24/2021
 

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Theory

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Hows the single grain ST test load coming along?? I bought (2) 98mm ST loads from WM during the member holiday sale (L2500 & M4500). Would love a single grain 75mm and/or 98mm. Or even a 54mm single grain ST would be cool.

bet we are about a year or so away from that. im sure there is a lot more to the creation of a new motor than we really realize. definitely more than casting a single grain and packaging it with some O-rings and a nozzle.

will definitely be purchasing a few (and the new J615) when they are released
 

DeltaVee

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I don't know if this has been asked before but...

What are the odds that Aerotech might provide a set of supplemental spacers for the 29mm adapter system? The length difference in the 120 vs 100 casing is 1". Likewise the difference between the 100 and 60 casing is also 1". Correct me if I'm wrong but the result seems to be that a 1" spacer would allow me to use a 29/60 reload in the 29/100 case and a 29/100 reload in the 29/120 case (and a 2" spacer would permit a 29/60 reload in the 29/120 case).

This would be kind of nice...
 

DeltaVee

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I could use bt50h and make my own liners and assemble it like an e motor in an f casing too... but I think I'd rather have something official... besides, I then get to pay silly amounts of cash for small metal tubes.
 

AeroTech

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I don't know if this has been asked before but...

What are the odds that Aerotech might provide a set of supplemental spacers for the 29mm adapter system? The length difference in the 120 vs 100 casing is 1". Likewise the difference between the 100 and 60 casing is also 1". Correct me if I'm wrong but the result seems to be that a 1" spacer would allow me to use a 29/60 reload in the 29/100 case and a 29/100 reload in the 29/120 case (and a 2" spacer would permit a 29/60 reload in the 29/120 case).

This would be kind of nice...
I’ll bring it up at our senior staff meeting today.
 

n3tjm

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I really would like to see the G25 made in a 2 grain USPS shippable version, where you have to glue the grains together like its larger M-N long burning cousins. I don't think people will be dumb enough to not epoxy the grains together, especially if the documentation is clear on that regard. Like put stickers on the end of the grain that says Epoxy this End.. Put on the front of the Package 5 Minute Epoxy MUST be used for assembly, Etc. I am itching to fly some G25's, but I usually don't buy enough motors to justify the extra $40 shipping costs...
 

DeltaVee

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I really would like to see the G25 made in a 2 grain USPS shippable version, where you have to glue the grains together like its larger M-N long burning cousins. I don't think people will be dumb enough to not epoxy the grains together, especially if the documentation is clear on that regard. Like put stickers on the end of the grain that says Epoxy this End.. Put on the front of the Package 5 Minute Epoxy MUST be used for assembly, Etc. I am itching to fly some G25's, but I usually don't buy enough motors to justify the extra $40 shipping costs...

Same here! Quite frankly, the hazmat requirement discourages "impulse" buying! (Pun intended! )
 

AeroTech

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I really would like to see the G25 made in a 2 grain USPS shippable version, where you have to glue the grains together like its larger M-N long burning cousins. I don't think people will be dumb enough to not epoxy the grains together, especially if the documentation is clear on that regard. Like put stickers on the end of the grain that says Epoxy this End.. Put on the front of the Package 5 Minute Epoxy MUST be used for assembly, Etc. I am itching to fly some G25's, but I usually don't buy enough motors to justify the extra $40 shipping costs...
You'd be surprised at what consumers do (or do not do)...we see it all unfortunately.
 

boatgeek

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You'd be surprised at what consumers do (or do not do)...we see it all unfortunately.
Long ago, a TA in one of my intro engineering classes held up a flathead screwdriver and asked the class what it was. After someone ID'd it as a screwdriver, the TA said, "No. It's a prybar, chisel, can opener..." and then went on to tell us that in engineering practice you have to assume that people are going to misuse your product to some degree.
 

n3tjm

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You'd be surprised at what consumers do (or do not do)...we see it all unfortunately.

Well in this case, I would thing that would mean you would sell a new 29/120 case and possibly a new Aerotech kit. I am sure not gluing the grains together when the instructions clearly state to do so voids any warranties.
 

Rocketjunkie

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You'd be surprised at what consumers do (or do not do)...we see it all unfortunately.
Why not bring back the phenolic cased SU version like they used to be. Then you don't have to worry about losing an expensive case.
 
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