Aerotech RMS J275W - Loose Grains Forward to Aft - This is not good right?

[MrPoopyPants]

Hi Everyone, I didn't want to start a new thread if I could avoid it but I couldn't find a previous post discussing this. Maybe I'm too new at Forums and I am a new member so if this is in the wrong place, please let me know and I'll fix it Anyways I'm running into a problem, I think... and I'm looking for some advice/help. I'm new to High Power and I'm going for my L2 Cert soon - so this is the first RMS motor I've ever done. Because I'm a moron I'm doing minimum diameter on an AT J275. Wildman Mach 2. Should be exciting!!!

The issue that I'm running into is that the grains are loose end to end - like they are not tight against the forward and aft closures. The motor case is a 54/852 and I have the aero tech plugged front closure and the Aeropack boattail rear closure. I've made sure I'm following the instructions and also found a youtube video of this exact motor being assembled. The grains fit nice in the liner but it's almost like the liner is just a little bit too long which is causing the closures to bottom out before they are in contact with the grains. It feels like there's a good 1/8 - 3/16 of an inch play in there. If I turn the motor upside down and back I can feel the grains sliding back and forth. Is this a problem? It seems like it would be to me. Ha that rhymed.
Any help or advice would be so much appreciated.

Also, I'm pretty confiedent on this one but while I'm asking questions, I want to double check... Even though I am going Dual Deploy and have a plugged front closure I am still installing the delay grain - Just not the ejection charge. That's right, right?

Cheers to all of you!

 

[mikec]

Perfectly normal. Per instructions at https://d11fdyfhxcs9cr.cloudfront.net/templates/170652/myimages/54_852_1642718030566.pdf --

It is normal if a slight gap remains
between the closure and the case after tightening and
the grains rattle slightly inside the liner.

The closures seat against the nozzle and the insulating disk, not against the grains. I think you're OK.

 

[Art Upton]

Yes the grains move a little. They have to , to burn on both sides; they are not a core burner but a bates grain burner.

 

[Tyeeking]

You’re good. No worries on the loose grains as it is indeed perfectly normal. Shift your worries to something else. All kidding aside best of luck on your L2 flight.

 

[David Schwantz]

Nope, everybody above is wrong. That is not ok. You need to ship me the motor and case as you built it and I will inspect it and fly it to see if it ok. I will then ship the spent motor and case back to you for your approval.
Kiddin.... it is normal to have the grains loose like that. I also was concerned on my first one that was like that. But all was good. Good luck and have a great flight.

 

[David Schwantz]

Yes, install the delay grain with spacer and o ring. It will act as tracking smoke.

 

[MrPoopyPants]

Yes, install the delay grain with spacer and o ring. It will act as tracking smoke.

Hi David, Thank you!

 

[MrPoopyPants]

Yes the grains move a little. They have to , to burn on both sides; they are not a core burner but a bates grain burner.

Thank you Art! I guess I get to learn a little bit everyday. I was incorrectly under the assumption that rocket motors had to be a core burn only and that burning on the ends would cause the case to burn through - I guess not. I went down the rabbit hole this morning to understand this. I was wondering how the rocket motors kept such a flat thrust curve - now I know.

Thank you for sending me down the path!

 

[MrPoopyPants]

You’re good. No worries on the loose grains as it is indeed perfectly normal. Shift your worries to something else. All kidding aside best of luck on your L2 flight.

Ha! Onto trying to get a GPS tracker into this tiny AV Bay! Cheers

 

[MrPoopyPants]

Nope, everybody above is wrong. That is not ok. You need to ship me the motor and case as you built it and I will inspect it and fly it to see if it ok. I will then ship the spent motor and case back to you for your approval.
Kiddin.... it is normal to have the grains loose like that. I also was concerned on my first one that was like that. But all was good. Good luck and have a great flight.

I think I'll keep it here haha - Glad to know I'm not the only one that ran into this!

 

[MrPoopyPants]

Perfectly normal. Per instructions at https://d11fdyfhxcs9cr.cloudfront.net/templates/170652/myimages/54_852_1642718030566.pdf --


The closures seat against the nozzle and the insulating disk, not against the grains. I think you're OK.

Mike, Thank you for this!

 

[MrPoopyPants]

Sorry for the late reply to you guys! Thank you all so much - I learned a lot about rocket motors and how they burn. This is one of those hobbies where you fly a bunch of F and G motors - then get a level 1 - watch some youtube videos and then go in thinking you know pretty much everything just to find out you actually don't know very much at all. At least for me. LOL

 

[kjhambrick]

@MrPoopyPants --

All your Motor Qs have been answered so now I have to ask ...

Do you plan to bring an extra pair of pants to the launch ?

... Because I'm a moron a fearless, steely eyed, rocket man, I'm doing minimum diameter on an AT J275. Wildman Mach 2 ...

Kidding aside, that J275 in the 2-inch WM Mach 2 looks like an awesome L2 flight !

... Should be exciting!!!

Yes, indeed !!!

-- kjh

 

[MrPoopyPants]

@MrPoopyPants --

All your Motor Qs have been answered so now I have to ask ...

Do you plan to bring an extra pair of pants to the launch ?


Kidding aside, that J275 in the 2-inch WM Mach 2 looks like an awesome L2 flight !


Yes, indeed !!!

-- kjh

I will might need to! Considering how simple my L1 flight was and how stressful that was I can only imagine the basket case I am going to be. In hind sight I should have done some dual deployment flights with L1 gear but I am 5 hours from the closest launch area so I have to make the trips count. I am pretty sure I am going to keep it under Mach 1 and under 10k feet. I need to do some final simulations but so far it's looking good and safe.

I've tested my altimeter in a vacuum chamber - good to go and I've got my deployment charges tested and figured out. I will test them at least once more but probably twice. Testing is cheap compared to a failure.

 

[AtlPhilip]

My advice: Keep cert flights simple. Low altitude, pop the (amply sized) chutes, recover close, get the cert. Then start experimenting with your more stressful flights.

 

[tfish]

@MrPoopyPants

 

[Art Upton]

^FYI you have to click on that to see the motor animation

 

[MrPoopyPants]

@MrPoopyPants

View attachment 621490

Nice Animation! I like how it shakes around during the burn! Thank you for sharing. This confirms what I imagined in my head after reading about a bates burn.

 

[MrPoopyPants]

My advice: Keep cert flights simple. Low altitude, pop the (amply sized) chutes, recover close, get the cert. Then start experimenting with your more stressful flights.

This is good advice - hopefully I don't regret going MD. Cheers

 

[StreuB1]

To be clear, there are various types of BATES grain perforations.

BATES comes in the Inhibited and un-Inhibited variants of which there can be a mix of grains[if multi-grain] being both inhibited and un-inhibited in order to tailor the thrust curve to the design intent.

Not to be pedantic, but to a new HPR flyer, details matter. Calling a motor with uninhibited (emphasis-added) core burning grain sections "Bates," is unintentionally misleading. While yes they are BATES, it would also be BATES if all or any combination of the grains had their end faces inhibited.

 

[Art Upton]

To be clear, there are various types of BATES grain perforations.

BATES comes in the Inhibited and un-Inhibited variants of which there can be a mix of grains[if multi-grain] being both inhibited and un-inhibited in order to tailor the thrust curve to the design intent.

Not to be pedantic, but to a new HPR flyer, details matter. Calling a motor with uninhibited (emphasis-added) core burning grain sections "Bates," is unintentionally misleading. While yes they are BATES, it would also be BATES if all or any combination of the grains had their end faces inhibited.

How many L2 and below bates grains in commercial motors have Inhibited End faces, on one hand ?

 

[TheTank]

This is good advice - hopefully I don't regret going MD. Cheers

Dont stress it. You’ll do fine if you do all the proper prep and testing. Nothing to fear with DD. Minimum diameter is aggressive but if thats what you want to do for your cert, go for it! Otherwise, have you really achieved anything taking the easiest path simply to “check a box.”

 

[kjhambrick]

@MrPoopyPants --

Have you flown that J275 in your Wildman Mach 2 yet ?

Please be sure to post pictures, or even better a video when you do !

Thanks and Merry Christmas and Happy New Year, all'Y'all !

-- kjh

 

[MrPoopyPants]

To be clear, there are various types of BATES grain perforations.

BATES comes in the Inhibited and un-Inhibited variants of which there can be a mix of grains[if multi-grain] being both inhibited and un-inhibited in order to tailor the thrust curve to the design intent.

Not to be pedantic, but to a new HPR flyer, details matter. Calling a motor with uninhibited (emphasis-added) core burning grain sections "Bates," is unintentionally misleading. While yes they are BATES, it would also be BATES if all or any combination of the grains had their end faces inhibited.

I think pedantic is generally a good thing! Thanks for correcting me. Now I've gotta go back down the rabbit hole a bit

 

[MrPoopyPants]

@MrPoopyPants --

Have you flown that J275 in your Wildman Mach 2 yet ?

Please be sure to post pictures, or even better a video when you do !

Thanks and Merry Christmas and Happy New Year, all'Y'all !

-- kjh

Not yet - The next available launch for me either on January 6 or January 20. I'm probably leaning toward the 20th - The rocket is basically complete and tested but I am taking my time with learning the electronics and extra testing. I'm basically doing "wet dress rehearsals" over and over. Packing everything up putting dummy charges in. Then thinking about it for a day or two - then doing it over again. I made my own e-matches from a kit. 80 all together so I took the worst looking 20 and have been testing them. So far about half - no failures so I'm feeling good about my charges. Also want to test the drouge charge at least twice more - probably the main too. Besides the $1000 bucks or so I have into this - I have a tremendous amount of time and have to make a 5 hour drive for the launch - so I'm being very cautious.

I plan to detail the build and flight a little bit and share my experience here when It's all done.

Thanks

 

[StreuB1]

How many L2 and below bates grains in commercial motors have Inhibited End faces, on one hand ?

At this time, absolutely zero.

That does not preclude the need to understand, or the desire of others to want to understand.

Those that find the information provided interesting or informative, shall consume it. Those that do not, have a conscious decision to consume or not consume.

It is amazing that still to this day, people feel the need to admonish others for being helpful.

 

[StreuB1]

I think pedantic is generally a good thing! Thanks for correcting me. Now I've gotta go back down the rabbit hole a bit

Def not correcting you. More so[hopefully] adding depth of understanding to the overall discussion.

BTW, the J275 is one of my favorite motors of all time. It is the 2 grain version of the K550 (and J415) and with that, carries all the attributes of the K550, just in a shorter package. Its a great motor and a crowd pleaser. Firey, smokey, loud, all the good stuff.

 

[MrPoopyPants]

Def not correcting you. More so[hopefully] adding depth of understanding to the overall discussion.

BTW, the J275 is one of my favorite motors of all time. It is the 2 grain version of the K550 (and J415) and with that, carries all the attributes of the K550, just in a shorter package. Its a great motor and a crowd pleaser. Firey, smokey, loud, all the good stuff.

I appreciate it for sure - the complexity of HPR is pretty wild and I really enjoy learning about it.

 

[3stoogesrocketry]

I appreciate it for sure - the complexity of HPR is pretty wild and I really enjoy learning about it.

Wait till you venture to snap ring hardware . Then you can relearn a entire new realm of motor assembly.