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Rebuilding an Aerotech RMS motor?

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JP Morgan

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So I anticipated a launch, that didn't happen and I'm leary of the Delay that I drilled into it. I marked the package with the delay I drilled but I just don't want it going off too soon!

It's been a year since I loaded it, 38mm Aerotech H123W.

Is it OK to rebuild it?

Can I simply turn the delay grain around and possibly overcome some of the shortened delay or best to replace the delay grain?
 

dhbarr

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Did you fully disassemble it? Was the delay stored in the same container as the fuel grains?

In any case, -don't- turn it around. I believe that's a recipe that can either end in early deploy zipper or late deploy prang.
 

rharshberger

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So I anticipated a launch, that didn't happen and I'm leary of the Delay that I drilled into it. I marked the package with the delay I drilled but I just don't want it going off too soon!

It's been a year since I loaded it, 38mm Aerotech H123W.

Is it OK to rebuild it?

Can I simply turn the delay grain around and possibly overcome some of the shortened delay or best to replace the delay grain?
Turning the drilled delay around will allow BP to get down into the delay cavity on the forward closure, and could lessen the strength of your ejection charge as the pressure would vent out the nozzle. That the reason the undrilled side of the delay always faces the ejection charge flash hole. If you are worried about the length of the drilled delay then get the appropriate HDK kit.
 

JP Morgan

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I have not taken it apart yet.

I understand the I'll logic in turning the delay grain around, that could be a bad thing! I didn't think about the ejection charge and what could go wrong being poured into a hole!

I've got 2 pounds of FFFF black powder, so not concerned about loosing that amount when it's taken down.

Thanks guys!
 

markkoelsch

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Remove black powder from motor and use an altimeter for deployment.
 

JP Morgan

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Remove black powder from motor and use an altimeter for deployment.
Thanks. My main flyer right now is the LOC IV, so an altimeter may be in the near future for that one...

I placed an order with Siriusrocketry for the AeroTech 38mm Complete Reload Delay Kit CRDK38-01.
I didn't know the delays were motor specific! I almost pushed the buy now button for the Red Line motors, as this one is White Lightning.

Thanks for the input guys, I'll try not to do this again!
 

cobra1336

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Made the mistake of inserting the drilled delay grain upsidedown. FFFF gets into the grain, igniter starts burning delay and hits the FFFF, poff! Ejection charge goes off and my rocket never left the pad. Front closure damage and fire on the pad.
 

Lowpuller

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Is your cobra a kit?

If so what type and what running gear?
 

T-Rex

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I believe that I recently installed a delay upside down as it seemed like it took extra BP. Ejection was supposed to be +6 seconds, was more like +2 seconds. Resulted in a significant zipper. I also recently flew 2 hobby line motors that had been assembled a year before. Seemed like the delay was long...... YMMV
 

rharshberger

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I believe that I recently installed a delay upside down as it seemed like it took extra BP. Ejection was supposed to be +6 seconds, was more like +2 seconds. Resulted in a significant zipper. I also recently flew 2 hobby line motors that had been assembled a year before. Seemed like the delay was long...... YMMV
Those weren't long delays....those were the special Aerotech Bonus Delays and not everyone is worthy of them.....
 

tab28682

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Worth noting that with the AT DMS motors, the procedure is to drill the ejection charge side of the delay with the AT adjustment tool.

Over the years, I have drilled a good number of AT RMS delays at the top of the delay with perfect results.

Once the delay grain has burned through, the touchhole for the ejection charge ignition is always exposed to the interior of the case and some amount of the ejection charge gas is always vented back into the casing.

An ejection on the pad is far likelier to be due to a classic blow by failure than a drilled delay.
 

JP Morgan

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Upon closer inspection, I didn't load the BP charge, which is better for my cause...
So now I'm thinking to rebuild the top end only with the new delay grain.

I ordered the Delay tool along with the new delay grain kit.

Sorry, for some unknown reason my photo is not loading up.
The white sticky back round cover is fixed to the top closure, so I'm in good shape...
20161016_114347.jpg
 
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jimzcatz

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Since I started in rocketry, I have always placed the drilled end of the delay grain forward. This is the only option with single use motors. Drilling wasn't widely adopted until CTI hit the scene and we were never told otherwise when we drilled Aerotech reloads. I have had zero issues with this practice. Like I said, we were never told otherwise. If the subject ever came up, answer was "it don't really matter"
 
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Bat-mite

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Note about modifying commercial motors:

Unless you are doing it for a specific reason that you completely understand, don't do it!

My advice, take it or leave it.
 

jimzcatz

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Note about modifying commercial motors:

Unless you are doing it for a specific reason that you completely understand, don't do it!

My advice, take it or leave it.


What are you talking about? No modification here? I mean seriously?
 

timbucktoo

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Huh? No, I said don't do it unless you know what you're doing and why you're doing it.
You post is quite confusing. The OP never stated he's modifying a motor. What modification are you talking about?
 

Bat-mite

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Last sentence. "Can I simply turn the delay grain around and possibly overcome some of the shortened delay or best to replace the delay grain?"
 

JoeG

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Since I started in rocketry, I have always placed the drilled end of the delay grain forward. This is the only option with single use motors. Drilling wasn't widely adopted until CTI hit the scene and we were were never told otherwise when we drilled Aerotech reloads. I have had zero issues with this practice. Like I said, we were never told otherwise. If the subject ever came up, answer was "it don't really matter"
Agreed. We did this for years before it was fashionable and I always put the drilled end forward due to the success rate we had with the single use motors.. When Aerotech came out with their instructions and said to put the drilled end toward the propellant I complied but like Jim, I have noticed no difference in delay time or experienced any problems no matter the direction the drilled side is placed.
 

blackjack2564

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FYI :

I have drilled delay for one rocket, then did not fly for whatever reason.
Decided I want to use same motor in a different rocket.

Just filled the drilled delay hole with epoxy, turned it over [after epoxy cure] and re-drilled clean side with a different time. Works great!
 

JP Morgan

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FYI :

I have drilled delay for one rocket, then did not fly for whatever reason.
Decided I want to use same motor in a different rocket.

Just filled the drilled delay hole with epoxy, turned it over [after epoxy cure] and re-drilled clean side with a different time. Works great!
That's good to know!
 

jeff_j_black

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I dunno, a motor that was assembled a year ago? what are we talking about? Maybe $30.00, plus Hazmat? What is the rocket worth? Am I being over cautious thinking to replace the guts outright?
 

blackjack2564

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I dunno, a motor that was assembled a year ago? what are we talking about? Maybe $30.00, plus Hazmat? What is the rocket worth? Am I being over cautious thinking to replace the guts outright?

"Am I being over cautious thinking to replace the guts outright?"

Yes.

Many of us, who have been flying along time, have flown motors 10-15-20 years old.
Both single use & re-loads.

No issues if stored correctly & moisture hasn't done damage.
 

smapdiage9

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FYI :

I have drilled delay for one rocket, then did not fly for whatever reason.
Decided I want to use same motor in a different rocket.

Just filled the drilled delay hole with epoxy, turned it over [after epoxy cure] and re-drilled clean side with a different time. Works great!
This seems like it would only work if you're going for a shorter delay than originally drilled, right? The delay being previously drilled, it's maximum burn time is now shorter than original regardless of which way the hole is facing. If the undrilled delay is 10 seconds, and you drilled it down to 5, flipping it over and drilling it down to 7 should make it more like a 2.
 

JP Morgan

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Excellent input guys, I really appreciate all comments!

I did not have the Delay Tool from Aerotech, I just used a drill bit and guesstemated the depth. The same method was used once before with success. Although the delay could have been left alone as the LOC IV came out heavier than a Stock build.

The Delay Tool is in the mail...

My only concern at the time was having the rocket nose down gaining speed upon nose ejection.

Applying different scenarios in Open Rocket started looking scary with long delays!
Having said that the launch of the previous H123W-L, the ejection was just before the nose over at apogee. Good thing the wind was low that day, I only walked about 375 yards. I have torn up knees and don't desire another surgery until I'm in my 60's...

So now my next flight on the LOC IV with an Aero tech H123W-14 I'll be using the Jolly Logic Chute Release! That changes everything!

I'll still drill a Delay and Z-Fold the harness using blue masking tape and a Rocket Man 4' Chute. It may have been a 5' Chute, I'll have to look to be certain but touch down and decent first time was soft and zero swinging around like the Stock Chute does.

Now I'm considering it best to have a look at the entire motor, making certain that the grains aren't greasy or discolored.

Again, thank you for all the input!

I'll have no problem destroying the said motor if I think something is not right with it. I have 2 other H123W's on hand, unopened.

It could be a $24.00 mistake! I did a pretty good job on the LOC IV, it has a nice tail cone I made and flies straight as an arrow with zero rotation!
 

JP Morgan

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So I took the top off and checked the Delay Grain, I had drilled a delay of about 4 seconds according to the new Aerotech delay tool.

I had doubts about the motor, so it had to be checked out. I have not looked at the fuel grains, it's been kept invironmently stable so it should be good.

I'll do my best not to load up another one until on site!
 

rcktnut

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There are several threads on RMS motors being stored assembled for over a year. Done it myself, never had a problem . I had a 24/40 load I used 3 weeks ago that was assembled last year, July, flew perfect. I lightly grease all my propellant liners never had a problem with the grease soaking thru to the propellant. I assemble all my motors ahead of time at home ,no wind or distractions, goes much nicer than in the field. I just snug up the closures, leave out the BP and when ready to fly, tighten closures add BP, good to go.
 

smapdiage9

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FYI here's an aerotech H reload I bought and opened in '07 or '08, flying earlier this year. No probs:

 
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