G78-4G/L Ejection Charge Error

[jackiboi_11]

Hello, today I did a test flight with my Loc Precision Goblin (4 inch) on a G78-4/L to make sure everything was doing good and no errors before my L1, everything went good until the ejection charge never shot out of the froward end and instead I could visually see it come out of the aft end? It came screaming down and smashed into the ground completely ruining the top portion of the airframe and leaving everything from the froward centering ring to the aft in mint condition. The cap on the end of the ejection well looked completely untouched and my Goblin is ruined (I will however make a attempt on cutting the airframe and putting another one from loc where the cut was made.) I flew another G79 that same day in my MDRM using the same technique with building the motor. I made sure about not touching the delay element and not getting anything on it during the building of the motor. Any ideas?

 

[ThirstyBarbarian]

Sorry to hear about the rocket.

Do you know if the delay grain lit? If you pull out the cap, is there still powder in the charge well?

 

[jackiboi_11]

Sorry to hear about the rocket.

Do you know if the delay grain lit?

I believe so, there was a visual delay before the charge fired, if that helps or means anything.

 

[ThirstyBarbarian]

I believe so, there was a visual delay before the charge fired, if that helps or means anything.

I think I edited my post to add another question while you were replying. If you pull out the cap, is there still powder in the charge well?

 

[NTP2]

Normally I would ask “Did you possibly get some epoxy or grease on the top of the delay?” But with the smoke coming out of the bottom I would think that the BP lit… did you put a small hole in the plug when you put it in?

 

[jackiboi_11]

I think I edited my post to add another question while you were replying. If you pull out the cap, is there still powder in the charge well?

No, I looked and it was completely burnt and empty.

 

[jackiboi_11]

Normally I would ask “Did you possibly get some epoxy or grease on the top of the delay?” But with the smoke coming out of the bottom I would think that the BP lit… did you put a small hole in the plug when you put it in?

Yes I did.

 

[NTP2]

Calling @AeroTech to the thread
We could probably help more if we have some pictures can you get some of the motor?

 

[jackiboi_11]

Calling @AeroTech to the thread
We could probably help more if we have some pictures can you get some of the motor?

Alright will do.

 

[jackiboi_11]

Here are some photos. The first one is what it looked like right when i pulled it out of the Goblin.

 

[NTP2]

I am going to be thinking aloud here, To me it looks like the BP lit but didn’t push the cap off… so why didn’t it… did you get all the powder in? I see a few trapped grains in the epoxy?

 

[jackiboi_11]

I am going to be thinking aloud here, To me it looks like the BP lit but didn’t push the cap off… so why didn’t it… did you get all the powder in? I see a few trapped grains in the epoxy?

The few grains was all that kind of got away but everything else was in there nice and well.

 

[NTP2]

The few grains was all that kind of got away but everything else was in there nice and well.

In that case I have no more (good) ideas, I hope you find out what happened! Ps I will be pondering the matter maybe I will have something later.

 

[NTP2]

Did you get the O ring in right?

 

[jackiboi_11]

Did you get the O ring in right?

Yes

 

[tim cubbedge]

Does that motor come with the little steel washer that goes in before you add the powder? I know that is used on a lot of DMS motors.

 

[NTP2]

Does that motor come with the little steel washer that goes in before you add the powder? I know that is used on a lot of DMS motors.

No, I checked the Aerotech listing.

 

[Steve Shannon]

If you put the cardboard spacer into the delay grain well ahead of the delay grain, it creates a cavity on the wrong side of the touch hole in the forward closure. The powder could trickle down into that cavity, leaving the ejection charge cavity empty. If that happens the ejection charge will blow rearward instead of forward.
Could that have happened?

 

[jackiboi_11]

Does that motor come with the little steel washer that goes in before you add the powder? I know that is used on a lot of DMS motors.

it comes with a fiber washer that separates the propellant from the delay element.

 

[jackiboi_11]

If you put the cardboard spacer into the delay grain well ahead of the delay grain, it creates a cavity on the wrong side of the touch hole in the forward closure. The powder could trickle down into that cavity, leaving the ejection charge cavity empty. If that happens the ejection charge will blow rearward instead of forward.
Could that have happened?

the delay was facing so the igniter went into that cavity and the delay was the closest possible to the bp cavity. I’m not sure how to explain this

 

[Steve Shannon]

the delay was facing so the igniter went into that cavity and the delay was the closest possible to the bp cavity. I’m not sure how to explain this

Like this:

 

[jackiboi_11]

Like this:

yes like that

 

[Steve Shannon]

yes like that

Then as long as the delay grain assembly slid all the way in I don’t understand how the powder could have pressurized the motor below the ejection charge. I would definitely contact Aerotech customer service. Karl has seen nearly everything (including my mistakes!)

 

[NTP2]

Then as long as the delay grain assembly slid all the way in I don’t understand how the powder could have pressurized the motor below the ejection charge. I would definitely contact Aerotech customer service. Karl has seen nearly everything (including my mistakes!)

Maybe he should write a book (Karl).

 

[jackiboi_11]

Like this:

i built a g79 that same day and that worked perfectly

 

[Steve Shannon]

i built a g79 that same day and that worked perfectly

Motor failures happen. They all have a reason, but it’s not always possible to figure out what that reason was. And that doesn’t mean it was your fault. Stuff happens. Make a MESS report, rebuild the rocket, and have fun!

 

[ThirstyBarbarian]

It seems like somehow the powder leaked or didn’t burn properly. I don’t think there’s any way a full ejection charge could go off in the charge well and not eject the cap, and if somehow it did, I can’t imagine all that pressure escaping out the nozzle. More likely the motor would have blown up. I don’t have an answer to how or why it happened, but it seems like it must have somehow.

Good luck with the investigation, rocket scientists!

 

[jackiboi_11]

I'll keep you guys updated on the repair and everything else if you guys want. I should order the parts for the repair, total of $15, not too bad

 

[KenECoyote]

Maybe something like this? (Post #75)

I keep having very experienced people tell me they've never seen this before.

AT said they'll replace the casing and reload.

 

[AeroTech]

Calling @AeroTech to the thread
We could probably help more if we have some pictures can you get some of the motor?

We try to avoid doing failure analyses on the forum for a number of reasons. Please contact customer service at the email address in my sig.