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Aerotech 29-40/120 Liner Crack
#1
I recently flew (For the first time!) a 29-40/120 RMS engine with a G53-FJ-7 reload, which, when I disassembled it after the launch, I noticed that the engine liner appeared to have a full length crack.  I checked the inside of the liner and after careful inspection of what remained of the casting tubes, I noted that the C-slot grain cut is about 45 deg. counter-clockwise from the start of the crack which I also noted started on the inside spiral seam of the liner.

My question is twofold, is this normal / has anyone experienced this before?

Here is a picture of it,
   

Thanks.
BuiltFromTrash
First RMS Flight: June-17 2015
Pringles Can Rocket
G53-FJ-7 (29-40/120) 92 Newton-Seconds
~1300 Ft
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#2
yes that is normal for those loads, messy yes a problem no. just make sure you clean the threads of the hardware really well.


Bill Clune L3 | NAR#88583
Been a launch Director
Founded a Club
MARS Club|SRC|MDRA - Forever
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#3
Hmm... I wonder why they do that?

I got a scare when my forward closure did not come off immediately, I soaked it diluted vinegar for ~24 hrs, still wouldn't come off. Finally got it off with rubber gloves then cleaned it with baby wipes and a tooth brush, so it should be squeaky-clean!
BuiltFromTrash
First RMS Flight: June-17 2015
Pringles Can Rocket
G53-FJ-7 (29-40/120) 92 Newton-Seconds
~1300 Ft
Reply
#4
The grain may have rotated at some point during landing.... but The liner burns away faster on the slots and on moonburners.

What tweeks me off are the Phenolic liners for the longer motors all have seams. The 38/1320's consistently crack at those seams when fired. Last one I got didn't even make it to flight, cracked in shipping. Sad The 29's seem ok, and the 54/1706's have held up wonderfully. but the 38's seem to take a beating both in shipping and while burning.


I wrap rubber around the forwards and use vise grips on my 29 40-120s
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#5
(06-20-2015, 01:31 AM)DBMcCann Wrote: I wrap rubber around the forwards and use vise grips on my 29 40-120s

That doesn't crush the forward closure? Do you wrap rubber and then use vise grips? Or do you just use vise grips?
So many questions, so little time... Smile
BuiltFromTrash
First RMS Flight: June-17 2015
Pringles Can Rocket
G53-FJ-7 (29-40/120) 92 Newton-Seconds
~1300 Ft
Reply
#6
If I'm being good, wrap then grip. If I'm lazy.... well I may have just used grips once or twice. Not really hard, you cant snug them up and then clamp. I leave them a little loose and then clamp just the last little bit.

It makes for ugly closures....but who's looking? I try to avoid it. but it happens.
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#7
(06-20-2015, 01:31 AM)DBMcCann Wrote: The grain may have rotated at some point during landing.... but The liner burns away faster on the slots and on moonburners.  

What tweeks me off are the  Phenolic liners for the longer motors all have seams.   The 38/1320's consistently crack at those seams when fired.  Last one I got didn't even make it to flight, cracked in shipping.   Sad      The 29's seem ok,  and the 54/1706's have held up wonderfully.   but the 38's seem to take a beating both in shipping and while burning.


I wrap rubber around the forwards and use vise grips on my 29 40-120s

No need to use vise grips, there is a tool for this job, if you need vise grips something is wrong!
http://www.activepowersports.com/aerotec...HwodcpgA8Q
   
This site sells in for $9 the best part is it fits the 18 - 29mm


Bill Clune L3 | NAR#88583
Been a launch Director
Founded a Club
MARS Club|SRC|MDRA - Forever
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#8
That site seems to be cheaper than Hobbylinc for reloads!  At Hobbylinc a G76-7-G is $11.59 no Hazmat fee, at Active Powersports it is $9.89 but has a Hazmat fee.  Has anyone bought from here?  Last time I bought $100 worth of reloads, it might be worth it to combine shipping to make other reloads typically Hazmat, cheaper.

Maybe I'm chasing a dream, but it is interesting nevertheless!
BuiltFromTrash
First RMS Flight: June-17 2015
Pringles Can Rocket
G53-FJ-7 (29-40/120) 92 Newton-Seconds
~1300 Ft
Reply
#9
Hobbylinc reloads wont be without Hazmat much longer as I heard they just got slapped with a $500K fine for shipping hazmat without declaring it.

As for using vice grips on a forward closure that makes me cringe...I use one of those cheap ass Harbor Fright Strap wrenches they are usually enough to get it loose, if that doesn't work I have two pieces of oak that bolt together with a hole just big enough that when the bolts are tightened they grab the delay grain portion tightly with out distorting the casing (similar to how a gun barrel vise works, you don't want to damage those either).
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#10
Where did you see this bit of news?  A quick google search did not turn anything up for "Hobbylinc fined 500k".

Using wood clamp is a great idea.  I do not like the idea of scratching or deforming a case either, I like my motors shiny!
BuiltFromTrash
First RMS Flight: June-17 2015
Pringles Can Rocket
G53-FJ-7 (29-40/120) 92 Newton-Seconds
~1300 Ft
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