Motor Mystery-Has anybody seen this?

I had a strange thing happen today. I loaded up a G76-7G reload. It all went together well. I launched and it crashed. I have literally done over 150 flights on this case alone.

I took the motor apart (after digging my rocket out of the ground) and discovered the ejection charge never blew. I took the reload apart and saw that the delay grain did not even burn.

You should know:

1) I did not put or get grease on the delay....no way no how. (I have a special procedure that prevents that)
2) the reload was indeed put together properly.
3) the hole in the forward closure was not clogged or sheared up with grease

Some clues:

1a) the reload took 4 igniters to light the motor.
2a) the reload did not burn like a G76. More like a looooonngg wimpy green. I would guess it burned for about 2.5-3 seconds...no kidding I could not believe what I was seeing.-way under powered (the motor) and it did not even light the delay.

Is this a bad batch? Bad oxidizer? The propellant grains looked normal and it did not look that old even. Has anybody seen this?

Thanks

Where did you duy it?

Packaging has a lot code which is very important.

It appears to be a defective motor. Either the propellant grain and/or the delay grain did not function properly.

Report it to the manufacturer and report it to https://www.motorcato.org

Bob

Sounds like the nozzle was not sized properly. Can you measure the throat, or if not, what is the largest drill bit that will fit through it now?

Thanks for the reply-I think the reload was purchased from Hobbylinc. I will go get the date/batch code. I will also try and figure out the nozzle size. I will be in touch--Thanks

Okay-

The code on the package is: 01251103

A 3/16 drill bit fits through but it is very loose. A 7/32 drill bit is just a hair to big. I hope this helps with our investigation.

I also tried emailing Aerotech almost two weeks ago concerning another question but have had no reply (Which is not the first time). I wont even try to contact them anymore about anything.

AKVP said:

Okay-

The code on the package is: 01251103

A 3/16 drill bit fits through but it is very loose. A 7/32 drill bit is just a hair to big. I hope this helps with our investigation.

I also tried emailing Aerotech almost two weeks ago concerning another question but have had no reply (Which is not the first time). I wont even try to contact them anymore about anything.

Click to expand...

I get email relies. If your email is suspect it will get filtered by SPAM filters. Most often this is G
-mail addresses but can be triggered by numerous key words.

The most reliable contact method is the telephone. Call them

AKVP said:

Okay-

The code on the package is: 01251103

A 3/16 drill bit fits through but it is very loose. A 7/32 drill bit is just a hair to big. I hope this helps with our investigation.

I also tried emailing Aerotech almost two weeks ago concerning another question but have had no reply (Which is not the first time). I wont even try to contact them anymore about anything.

Click to expand...

https://www.aerotech-rocketry.com/c...s_assy_dwgs/29mm_mr_rms/29-40_g76-7g_assy.pdf The nozzle is listed as having a 0.172" or 11/64" diameter throat being P/N 01350-4, but the P/N is not correct.

https://static.fw1.biz/templates//170652/myimages/rcs_01350_nozzle_dwg.pdf Base E30/E50 nozzle P/N 01350-0 is manufactured with a 0.141" throat and is drilled out to 0.156" as P/N 01350-1 and drilled out to 0.166" as P/N 01350-2. The O.D. is 0.865" which is for a 24 mm casing.

https://static.fw1.biz/templates//170652/myimages/rcs_01450_nozzle_dwg.pdf The Base G45/F60 nozzle is P/N 1450-0 with a 0.141" throat and has a 1.000" O.D. which is correct for a 29 mm casing. It is drilled out to 0.150", 0.156", 0.161", 0.172", 0.177" and 0.188" as P/N 01450-1, -2, -3, -4, -5, and -6 respectively. If the correct P/N is 01450-04 then the throat diameter is 0.172". If it's not, then the throat diameter is not listed.

Bob

bobkrech said:

https://www.aerotech-rocketry.com/c...s_assy_dwgs/29mm_mr_rms/29-40_g76-7g_assy.pdf The nozzle is listed as having a 0.172" or 11/64" diameter throat being P/N 01350-4, but the P/N is not correct.

https://static.fw1.biz/templates//170652/myimages/rcs_01350_nozzle_dwg.pdf Base E30/E50 nozzle P/N 01350-0 is manufactured with a 0.141" throat and is drilled out to 0.156" as P/N 01350-1 and drilled out to 0.166" as P/N 01350-2. The O.D. is 0.865" which is for a 24 mm casing.

https://static.fw1.biz/templates//170652/myimages/rcs_01450_nozzle_dwg.pdf The Base G45/F60 nozzle is P/N 1450-0 with a 0.141" throat and has a 1.000" O.D. which is correct for a 29 mm casing. It is drilled out to 0.150", 0.156", 0.161", 0.172", 0.177" and 0.188" as P/N 01450-1, -2, -3, -4, -5, and -6 respectively. If the correct P/N is 01450-04 then the throat diameter is 0.172". If it's not, then the throat diameter is not listed.

Bob

Click to expand...

All G76's I've flown before have the 01350 style nozzle. It's easy to tell from the shape of the entrance cone that it's not the 1450, at least.

edit: now I'm doubting myself.

I talked with a guy named Carl today at Aerotech. He said the igniter must have slipped and lit the motor in the middle/to bottom of the grain(s). He said this is why I had that burn characteristic.

I guess I am surprised that a difference of 1.5 to 2 inches in igniter placement would make that much of a difference. I have literally flown hundreds of G loads in the hobby-line case. I am sure that not every igniter was within 1.5 inches of the "failure" spot. If this is the case....would we not see this type of failure more often.

Makes me want to fly with electronics on everything.

I dunno.....

I have seen the igniter thing happen but..... on much bigger motors. Myself I think the nozzle was Waco. I have burn piled a lot of delay grains they always light fairly easy if AT doesn't want it back try and light it. Flown hundreds of AT hobbyline myself one time after a perfect flight I realized the red cap was still on the closure yes the charge blew just fine.

Nozzle too big is my guess also, perhaps coupled with ignition in the middle. Did it burn evenly just slowly, or did it go "pft-pft-pft-pft-pffff?"

Too-big nozzle would lower the pressure inside the case, make it burn longer and make it harder to ignite the delay. I had a J575 that failed to eject once (though the up was fine in that case) and Gary replaced the reload.

Ari.

That makes sence. I had a research motor burn from the end for well over a minute. The burned nozzle throat size seems OK.

When having to replace igniters in AT 29mm hobby motors, I often can only get the igniter halfway in and they burn just fine. Here's another vote for too big of a nozzle.