M1550R core dimensions

Anybody have the dimensions for the core of the AT M1550R motor, I just need the diameter and total length of propellant core (or length of each grain and core diameter). If its a stepped core will need that info as well. Reason is I am trying to prebuild my igniter for a motor that I hope will arrive by Labor Day. Being able to find the core volume allows me to size the BKNO3-V igniter to properly ignite the motor.

It has a straight core. From memory, I think it was at least 1/2" diameter, maybe more. I just used a Wildman Big Un lighter with no problems. The stick I have inside the 75/6400 now is 28" long.
Are you gluing it?
Edit: Well, I'm wrong. According to THESE instructions, the bottom core is 1" and the rest are 7/8". I don't remember that at all. Sorry. I do remember just using Tim's igniter tho...

I hadn't considered bonding the grains unless it was called for by the manufacturer. Thanks for posting the instructions link. How long is each grain? I can probably get the length of each grain by subtracting the OAL of the 6400 case from the OAL of the 7650 case.

I have igniters that will work but am keen to tryout the BKNO3-Viton igniters.

Grain length: 5.19" I'm pretty sure AT recommends gluing all fast burn propellants. Can't find it now.

Edit: Forgot to add; this is where I found the grain info.

I flew this motor last year at AirFest in my Wildman Inteceptor AAD98. Went to ~12,000'. Was pretty cool. My first 3" M and my first ever flight in Kansas...

Thank you JD, I always forget about "that other AT division"....

I will send a email to Karl asking whether he recommends bonding or not.

jd2cylman said:

Grain length: 5.19" I'm pretty sure AT recommends gluing all fast burn propellants. Can't find it now.

Edit: Forgot to add; this is where I found the grain info.

Click to expand...

1.5 gram BKNO3 will do it, from experience.
Assuming you made pellets correctly.

Will be using jsdemar's formula CJ, with that method it should be pretty much "following the recipe"....

I should have edited my original post, I am using BKNO3-V not regular BKNO3.

blackjack2564 said:

1.5 gram BKNO3 will do it, from experience.
Assuming you made pellets correctly.

Click to expand...

Been a while since I built one but here's some info as far as performance.

This is my scratch 6" Hellfire, weight (no motor) 26.5lbs Altitude 9303'

https://www.aerotech-rocketry.com/u...8-80fc-f40fc95f4222_75-6400_m1550r-p_assy.pdf

This shows the length as 5.25". Slight discrepancy from the the rocketmotor parts grain length at 5.19". It does show 4 forward grains (03616-1) and 1 aft grain (03616-5). This drawing doesn't show core size but the part numbers line up with the instructions linked by jd2cylman which do show core size but not length.

QUOTE="rharshberger, post: 1909777, member: 18236"]Anybody have the dimensions for the core of the AT M1550R motor, I just need the diameter and total length of propellant core (or length of each grain and core diameter). If its a stepped core will need that info as well. Reason is I am trying to prebuild my igniter for a motor that I hope will arrive by Labor Day. Being able to find the core volume allows me to size the BKNO3-V igniter to properly ignite the motor.[/QUOTE]

5.25 is about right with a grain length of 5.19 plus a .0625 spacer o-ring (1/16").

Rich sounds like it will be fun. Good luck with your flight and let us know how it goes and how much B you use.
I have been using B for 8yrs, if it's your first time, you will be amazed how fast your motor lights.

Thanks for your input CJ like many I pay attention to most of what you post. Just found out my reload should ship next week! Yay! Calc's based on ~16 cu in core volume is just under 1 gram of B. Last M1297W I lit was using a PTFE-Mag thermite made by a very knowledgeable rocketry friend, and there were very specific handling instructions for it, looking forward to working with something a little less sensitive, but Dayum! that motor lit right now!

blackjack2564 said:

Rich sounds like it will be fun. Good luck with your flight and let us know how it goes and how much B you use.
I have been using B for 8yrs, if it's your first time, you will be amazed how fast your motor lights.

Click to expand...

Good news found out just the other day that my M1550R reload should be shipping this week and that my enabler/dealer will be bringing it to the launch. Flight is a go so far.





My question to Karl at Aerotech...

Is bonding the grains on the M1550R recommended? I have read the instructions and it doesn't say to bond the grains, however several fliers have recommended bonding the grains, stating that AT has recommendedbonding the grains on most fast propellants.

Karls return answer....

Hi Rich,

My best answer is, it never hurts to bond the grains to the liner, especially on
rockets that will be subject to high “G” loading. Rockets flown on hot days, etc

Best,

Karl B.

Warranty and Tech.

Aerotech/Quest

jd2cylman said:

It has a straight core. From memory, I think it was at least 1/2" diameter, maybe more. I just used a Wildman Big Un lighter with no problems. The stick I have inside the 75/6400 now is 28" long.
Are you gluing it?
Edit: Well, I'm wrong. According to THESE instructions, the bottom core is 1" and the rest are 7/8". I don't remember that at all. Sorry. I do remember just using Tim's igniter tho...

Click to expand...

So then. Are you gonna glue? Inquiring minds wanna know...
I will suggest that before you start gluing, make sure all the grains fit easily in the liner, AND make sure all the grains fit the liner with the grain spacers and your seal disk. My N3300R last year I had to take out two spacer o-rings to get the forward seal disk in fully. This year, same motor, I only had to leave out one.
The CTI L1410Sk I built came with 3/32" grain spacer o-rings. So to get the forward seal disk to fit, I used 1/16" o-rings as spacers instead, and still had to leave one out. And I had to peel the glasine off all the grains. This is of course using a Dr Rockets 75/6400 case an not a CTI case.
Anyhoo, hope you have a great flight Rich. take pics. I didn't take any of mine

I have glued motor grains before, however due to timing on receiving the reload (day of launch) gluing will not be possible as it requires 24hrs cure time. 7G max acceleration also is not a high G flight by any stretch of the imagination so it should be okay as many have flown them without bonding.

jd2cylman said:

So then. Are you gonna glue? Inquiring minds wanna know...
I will suggest that before you start gluing, make sure all the grains fit easily in the liner, AND make sure all the grains fit the liner with the grain spacers and your seal disk. My N3300R last year I had to take out two spacer o-rings to get the forward seal disk in fully. This year, same motor, I only had to leave out one.
The CTI L1410Sk I built came with 3/32" grain spacer o-rings. So to get the forward seal disk to fit, I used 1/16" o-rings as spacers instead, and still had to leave one out. And I had to peel the glasine off all the grains. This is of course using a Dr Rockets 75/6400 case an not a CTI case.
Anyhoo, hope you have a great flight Rich. take pics. I didn't take any of mine

Click to expand...

Sounds like a plan. Good luck.