Holes in the grains

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Rocketry nut

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I recently acquired an AMW L1300(Thanks Preston!) and noticed 4 of the grains had holes in them. A couple were pretty deep(at least an 1/8in). Can these be fired as is or do I need to fill them with epoxy. I have never seen this before so just curious.



 
Personally, I'd contact the manufacturer and ask. Holes on the surface likely indicate more holes under the surface. Each hole allows the flame front to advance past the normal burning surface, and increases the burning surface area. Propellant mass is burned faster, increasing chamber pressure and decreasing burn time. If what you observe is not deemed normal for that propellant (it doesn't sound normal to me but it is not my judgement call) then the performance characteristics will be out of spec and possibly unsafe for the hardware. Numerous holes would be unsafe. A density check should indicate the percentage of holes in the propellant, but you'd need to know the manufacturer's expected density range.

Gerald
 
Those almost look like someone used a durometer on them to check propellant hardness...more impressions than holes. Still shouldn't be there...
 
Hahahahahaha when I first saw the thread title, I thought "some noob is confused about the grain cores" but found something more interesting instead.

I agree with jpummil's assessment, though: it looks crushed in and not drilled, and not like a bubble either.
 
I guess the pictures are being blocked here at work. I can't see the grains.
 
For a warranty safe flight contact the manufacturer.

These look like indentations, not bubbles. I've flown far worse in grains that I made. I'd fly them, but that's me.
 
thanks I can see them now on my laptop. That is interesting.
 
I'll have to look tonight. That is blocked from here as well.
 
Patrick-

I'd weigh each grain and see if they are way off from each other or not. I flown many AMW loads that looked similar to those grains with no issue, but that's just me. I'd fly it as I have not had any problems in the past....

Preston
 
Patrick-

I'd weigh each grain and see if they are way off from each other or not. I flown many AMW loads that looked similar to those grains with no issue, but that's just me. I'd fly it as I have not had any problems in the past....

Preston

Seconded; a few bubbles and voids are normally found in AMW, Kosdon East, Kosdon loads. Nothing to worry about. I have NEVER seen a properly assembled AMW load fail....ever.

-Eric-
 
Seconded; a few bubbles and voids are normally found in AMW, Kosdon East, Kosdon loads. Nothing to worry about. I have NEVER seen a properly assembled AMW load fail....ever.

-Eric-
NOOOOOOOOOO+DO+YOU+REALIZE+WHAT+THE+ACTUAL+++YOU+HAVE+_2fb75edb8573fc8e3b668f0487ebd01d.jpg
 
Thirded, saw these a lot in L1860 and L850 loads in the past. I think the defects here are bubbles that got cut in half.

Sidebar: my phone corrected "got" to G&T. It knows who you are, Eric!

That is fantastically awesome! I do believe your name came up in the roll call for the May QCRS launch....I will bring along a G based concoction that will blow your mind! Ok, now I'm salivating.

Back on track here; Patrick, I'll weigh the L1300 grains I have here and report back.

-Eric-
 
Patrick-

I'd weigh each grain and see if they are way off from each other or not. I flown many AMW loads that looked similar to those grains with no issue, but that's just me. I'd fly it as I have not had any problems in the past....

Preston

Preston, I'll weigh them and see. If this is fairly common with AMW and can be flown as is then I should be fine. We'll find out in 2 weeks I guess. Having never seen this before I thought I'd ask so thanks for the responses everyone.
 
That is fantastically awesome! I do believe your name came up in the roll call for the May QCRS launch....I will bring along a G based concoction that will blow your mind! Ok, now I'm salivating.

Back on track here; Patrick, I'll weigh the L1300 grains I have here and report back.

-Eric-

Cool thanks Eric!
 
Cool thanks Eric!

Wednesday Weigh In:

Average grain mass: 218.8g
Lightest grain mass: 217.1g
Heaviest grain mass: 219.9g
Total mass of grains: 1312.6g
Percent of grains with visible voids on one or both ends: 100

-Eric-
 
Just took apart a loaded L1300 I have and got a total weight of 1311.9g with voids/air bubbles or whatever you want to designate them as in 3 of the 5 grains....
Wednesday Weigh In:

Average grain mass: 218.8g
Lightest grain mass: 217.1g
Heaviest grain mass: 219.9g
Total mass of grains: 1312.6g
Percent of grains with visible voids on one or both ends: 100

-Eric-
 
Thank you Preston and Eric for taking the time to weigh your grains. I really appreciate it! I don't have my scale at the moment, but should get a hold of it within the next couple days. It's not digital, but should be close enough. Will report when I weigh. From the looks of it though it should be fine. I'm planning on flying it the first weekend of May.
 
Very interesting. Please post what the manufacture says about them. I'm wondering if those aren't used to increase burn rate in the early and middle part of the thrust curve. Maybe modify the average thrust a little.
 
Hahahahahaha when I first saw the thread title, I thought "some noob is confused about the grain cores" but found something more interesting instead.

I agree with jpummil's assessment, though: it looks crushed in and not drilled, and not like a bubble either.

When in reality, a separate noob who's clearly never made or cut grains before was the one who was confused and unaware that that's exactly what a bubble in a grain looks like when cut down the middle.

Your permeating condescension because of your HMC AeroEng degree may be warranted in some areas, but not all.
 
When in reality, a separate noob who's clearly never made or cut grains before was the one who was confused and unaware that that's exactly what a bubble in a grain looks like when cut down the middle.

Your permeating condescension because of your HMC AeroEng degree may be warranted in some areas, but not all.

tumblr_m7igrvumlt1qc9svto6_250.jpg
 
I was able to weigh the grains tonight with my not so accurate 500g food scale(non digital). I got 1334g as the total. The scale only has 10g lines so I had to rough guess any weights that were in between. There is a 5g difference between the lightest and heaviest grain. I understand the total is more than the motor should weigh(probably due to scale inaccuracy) so the only real option is to quit worrying and burn it next weekend :cool:

Thanks for the help and I learned something new.
 
I was able to weigh the grains tonight with my not so accurate 500g food scale(non digital). I got 1334g as the total. The scale only has 10g lines so I had to rough guess any weights that were in between. There is a 5g difference between the lightest and heaviest grain. I understand the total is more than the motor should weigh(probably due to scale inaccuracy) so the only real option is to quit worrying and burn it next weekend :cool:

Thanks for the help and I learned something new.

You came to the right conclusion! Good luck with the flight!
 
When in reality, a separate noob who's clearly never made or cut grains before was the one who was confused and unaware that that's exactly what a bubble in a grain looks like when cut down the middle.

Your permeating condescension because of your HMC AeroEng degree may be warranted in some areas, but not all.

Well, today I learned something. Woo.
 
Lol!!! Patrick, it's comments like this that you need to ignore, there's bullies everywhere and we all started from the beginning somewhere and some people forget that.......It will be fine, just burn it!!!

When in reality, a separate noob who's clearly never made or cut grains before was the one who was confused and unaware that that's exactly what a bubble in a grain looks like when cut down the middle.

Your permeating condescension because of your HMC AeroEng degree may be warranted in some areas, but not all.
 
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