G78-4G/L Ejection Charge Error

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If the delay grain burned, you should be able to see through the motor from nozzle to the top with the cap removed. Use a flashlight if it’s too difficult to see. Otherwise, find a small drill bit or wire that fits the hole at the ejection charge well. It should go through easily if the delay burned.
 
I’m sorry about that. I did contact customer service through your website because I did not make this thread at that point in time.
AeroTech said:
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.
Click to expand...
 
Your charge well and cap looks pretty clean, like too clean for any BP to have ignited in it. Are you sure you didn't forget to add the BP?
 
rcktnut said:
Your charge well and cap looks pretty clean, like too clean for any BP to have ignited in it. Are you sure you didn't forget to add the BP?
Click to expand...
Im completely sure I added BP, the next couple photos show were it burned and the inside of the cap, charred and like said I could visually see a pop come out of the nozzle when the ejection charge fired.
 
My $0.02, if it's even worth that.

I've had a few ejection failures on the Enerjet motors (E20, F67, etc.) where the BP plug didn't pop out, and quite a lot more where the plug was just slightly cocked over in it's bore. In the latter case, the nose cone just barely pops off. I now remove the plug and measure the powder. It's often down around 0.45g, sometimes under 0.4g. I add powder until it's in the 0.65 - 0.75g range, depending on the size of the rocket. No more failures.

The hole between the powder reservoir and the delay grain is quite large in these motors. Larger than the hole in the forward closure in the reload casings. I think a significant amount of pressure is going out the bottom.......

Hans.
 
jsdemar said:
If the delay grain burned, you should be able to see through the motor from nozzle to the top with the cap removed. Use a flashlight if it’s too difficult to see. Otherwise, find a small drill bit or wire that fits the hole at the ejection charge well. It should go through easily if the delay burned.
Click to expand...
Yes I can also see through from top to bottom with the cap removed.
 
EDIT: Too slow while I looked up some dimensions of the 4-inch LOC Goblin ... @jsdemar was quicker :)

It sounds like maybe @4regt4 maybe nailed it then ...

A 4-inch LOC Goblin has a substantial volume to pressurize between the motor mount stuffer and the base of the nose.

If I got the right dimensions from the LOC site, there is something like 27 inches of airframe below the shoulder of the nose and a 29mm motor won't fill much of the motor mount ...

Have you tried an Ejection Charge Calculator to see how much BP you might need to pop the nose on the Goblin ?

It sounds like you can repair the airframe in time for your level 1 flight ( I've got a couple rockets repaired as you described ).

Maybe it is better to find out now on a shakedown flight than 'when everyone is watching' your 'money flight ?

HTH and good luck next time @jackiboi_11 !

-- kjh
 
kjhambrick said:
EDIT: Too slow while I looked up some dimensions of the 4-inch LOC Goblin ... @jsdemar was quicker :)

It sounds like maybe @4regt4 maybe nailed it then ...

A 4-inch LOC Goblin has a substantial volume to pressurize between the motor mount stuffer and the base of the nose.

If I got the right dimensions from the LOC site, there is something like 27 inches of airframe below the shoulder of the nose and a 29mm motor won't fill much of the motor mount ...

Have you tried an Ejection Charge Calculator to see how much BP you might need to pop the nose on the Goblin ?

It sounds like you can repair the airframe in time for your level 1 flight ( I've got a couple rockets repaired as you described ).

Maybe it is better to find out now on a shakedown flight than 'when everyone is watching' your 'money flight ?

HTH and good luck next time @jackiboi_11 !

-- kjh
Click to expand...
He would need to get extra BP in that case… that would be fun…
 
NTP2 said:
He would need to get extra BP in that case… that would be fun…
Click to expand...

Someone at the Launch would have some. Boosting a motor's charge is done all the time. For example if you fly a LOC Warlock on CTI 38mm J motor you will need to add more black powder to the top of it and cover it up to get it to deploy correctly.
 
What Art said ...

I've always got an oz or so of 4F BP on hand at the launch site and I've 'loaned' a gram or two to fliers in need more times than I can remember.

If you're under 18, maybe someone would be willing to pour it in the well for you :)

But I think it would be worth your while to check your needs on a BP calculator first :) :)

HTH

-- kjh
 
kjhambrick said:
EDIT: Too slow while I looked up some dimensions of the 4-inch LOC Goblin ... @jsdemar was quicker :)

It sounds like maybe @4regt4 maybe nailed it then ...

A 4-inch LOC Goblin has a substantial volume to pressurize between the motor mount stuffer and the base of the nose.

If I got the right dimensions from the LOC site, there is something like 27 inches of airframe below the shoulder of the nose and a 29mm motor won't fill much of the motor mount ...

Have you tried an Ejection Charge Calculator to see how much BP you might need to pop the nose on the Goblin ?

It sounds like you can repair the airframe in time for your level 1 flight ( I've got a couple rockets repaired as you described ).

Maybe it is better to find out now on a shakedown flight than 'when everyone is watching' your 'money flight ?

HTH and good luck next time @jackiboi_11 !

-- kjh
Click to expand...
The calculator is recommending 1.95 grams and I know that the amount that comes with the LMS is far lower than that. But I still do not understand why the cap wouldn't at least come out? I may sound stupid because I do not know a lot about all of this!
 
jackiboi_11 said:
The calculator is recommending 1.95 grams and I know that the amount that comes with the LMS is far lower than that. But I still do not understand why the cap wouldn't at least come out? I may sound stupid because I do not know a lot about all of this!
Click to expand...
@jackiboi_11 --

EDIT: The following applies to DMS motors and NOT to LMS motors like the G78-4/L !

Apparently there is a stainless steel washer between the BP charge and the nozzle that is designed to direct the expanding gas from the BP charge forward toward the nose instead of aft and out the nozzle.

The linked thread in my previous post explains it, including a post or two by @AeroTech.

Proper charge sizing still applies but apparently so does that washer.

HTH

-- kjh

p.s. nothing stupid in this thread. This is all new to me too 😀
 
Last edited:
kjhambrick said:
@jackiboi_11 --

Apparently there is a stainless steel washer between the BP charge and the nozzle that is designed to direct the expanding gas from the BP charge forward toward the nose instead of aft and out the nozzle.

The linked thread in my previous post explains it, including a post or two by @AeroTech.

Proper charge sizing still applies but apparently so does that washer.

HTH

-- kjh

p.s. nothing stupid in this thread. This is all new to me too 😀
Click to expand...
There was a fiber or stainless steel washer (I don't remember which one) that goes in-between the propellant and the delay bulkhead if that's what you meant. Other than that there isn't one in this LMS.
 
People here are starting to mix up the DMS motors with the Hobbyline single use motors.
The washers come with the DMS motors only. It is used to close up the 1/4 in. hole in the delay well that is needed to adjust the delay. The single use Hobbyline motors LMS, and others don't come with or need the washer. I've used very many of the single use motors and never had the cap remain on or partially on. They were completely separated from the delay well. Never once had a problem with any of them getting out the chutes.
I guess if your putting them in bigger rockets you may need to add some BP.
4regt4 said:
My $0.02, if it's even worth that.

I've had a few ejection failures on the Enerjet motors (E20, F67, etc.) where the BP plug didn't pop out, and quite a lot more where the plug was just slightly cocked over in it's bore. In the latter case, the nose cone just barely pops off. I now remove the plug and measure the powder. It's often down around 0.45g, sometimes under 0.4g. I add powder until it's in the 0.65 - 0.75g range, depending on the size of the rocket. No more failures.

The hole between the powder reservoir and the delay grain is quite large in these motors. Larger than the hole in the forward closure in the reload casings. I think a significant amount of pressure is going out the bottom.......

Hans.
Click to expand...
If my memory serves me right, according to Aerotech the F's/ G's for sure are supposed to have .70 grams of BP in them. Not sure about the E's, but might be the same. Either my memory is wrong or some motors are short on BP.
 
Last edited:
jackiboi_11 said:
The calculator is recommending 1.95 grams and I know that the amount that comes with the LMS is far lower than that. But I still do not understand why the cap wouldn't at least come out? I may sound stupid because I do not know a lot about all of this!
Click to expand...
I looked at the Loc 4" Goblin, BT is 27.5" long MMT 14" long, should leave 13.5". Nosecone shoulder should be around 4", leaving 9.5" to pressurize + rest of MMT tube.
1.95 grams is way too much.
 
Last edited:
rcktnut said:
People here are starting to mix up the DMS motors with the Hobbyline single use motors.
The washers come with the DMS motors only. It is used to close up the 1/4 in. hole in the delay well that is needed to adjust the delay. The single use Hobbyline motors LMS, and others don't come with or need the washer. I've used very many of the single use motors and never had the cap remain on or partially on. They were completely separated from the delay well. Never once had a problem with any of them getting out the chutes.
I guess if your putting them in bigger rockets you may need to add some BP.

If my memory serves me right, according to Aerotech the F's for sure are supposed to have .70 grams of BP in them. Not sure about the E's, but might be the same. Either my memory is wrong or some motors are short on BP.
Click to expand...
This was a LMS motor...different yet
https://d11fdyfhxcs9cr.cloudfront.net/templates/170652/myimages/g78g_lms_in_20206_1642628632334.pdf
Tony
 
Nor sure why ejction didn't happen correctly.

However, I have the LOC 4" Goblin and did get L1 with it but have had No nose ejected with a ballistic return. A coupler a new tube and it is flying again.

What I've found is the Goblin needs about 1.5 grams of BP for reliable ejection. I ensure any motor used has at least 1.5gm BP.
 
I had the first I-ROC from Ron and Deb... It's nose cone was sorta transparent that made it identifiable. I Flew all kinds of flights from 1992 to late 2000s when it died from a 38mm CTI load with no ejection. Barry from Loc said it was the oldest flying I-Roc on the PA when he launched it.

Barry Gave me a new Kit and the motor guy got me a new motor. But that was not fun. I have been careful with it since I had a spot in Manchester TN when a CTI H motor CATO on lift off but the rocket was fine after that...

No more CATO CTI motors
 
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I haven't flown any of the buildable single-use motors yet but I did have pretty much an identical issue a few years ago with a DMS J435. Lost a 3" Public Enemy HoJo to the ejection charge not lighting. Even added just a bit more BP to what it came with just in case. When we pulled the motor out, the red cap was still in it and the BP poured right out the back side. It sucks when it happens, especially if you know it wasn't you.
 
Sorry for not responding due to issues but all this info is very appreciated. I think most of these ideas have a good chance of them being the reason it never worked and my knowledge has greatly expanded on this topic!
 
Art Upton said:
I had the first I-ROC from Ron and Deb... It's nose cone was sorta transparent that made it identifiable. I Flew all kinds of flights from 1992 to late 2000s when it died from a 38mm CTI load with no ejection. Barry from Loc said it was the oldest flying I-Roc on the PA when he launched it.

Barry Gave me a new Kit and the motor guy got me a new motor. But that was not fun. I have been careful with it since I had a spot in Manchester TN when a CTI H motor CATO on lift off but the rocket was fine after that...

No more CATO CTI motors
Click to expand...
The C in CTI stands for CATO :p
 

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