D24 Assembly Error or: Why I’m Spending $40 on My Next D Motor

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smstachwick

smstachwick

LPR/MPR sport flier with an eye to HPR and scale
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At ROC’s May launch, I attempted to fly an Apogee Apprentice kit on an AeroTech D24 reload that I had assembled at ROCstock and let sit around for a month.

I wasn’t able to get the igniter cap on at ROCstock, and during the interceding month, I discovered why: the nozzle was very slightly misaligned. I held onto the motor, afraid to disassemble it and maybe get the ejection charge leaking where it didn’t belong, and flew it at my first opportunity. This was the result:

IMG_1749.jpeg

The misalignment wasn’t nearly that bad before, sadly I don’t have a photo. Best I can figure, it didn’t manage to screw together as much or as neatly as it needed to, and the aft O-ring seal didn’t actually seal anything. Flames probably shot out of the joint and ate through the casing.

The ignition of this motor-turned-flamethrower set the fin can on fire, and I had to put it out with a water bottle somebody was kind enough to contribute. The rocket is completely toast. By that I mean it’s toasted, the blackened paper and plastic were snapping off and crackling off like actual burned bread when I was trying to extract this motor.

Interestingly enough, the forward closure appears to have survived this whole ordeal. It even felt like the threads were still very greased and smooth, so at least I don’t think I have to replace the entire hardware set.

Oh, and of course, here’s the video.


View attachment IMG_3789.mov

My choice to fly it rather than troubleshoot it some other way is almost certainly going on somebody’s Top 10 list of dumb decisions at the range. Never ignore reload issues, Shane! Ask for help! Stupid! Bad!
 
That's a great video, although sorry for your loss.

There's an intereseting momentary pause after ignition. Did the rocket get caught on something on the launch rod?
 
mh9162013 said:
That's a great video, although sorry for your loss.

There's an intereseting momentary pause after ignition. Did the rocket get caught on something on the launch rod?
Click to expand...
Could be. I did notice the rod was very slightly bent at the end, although it likely would not have been that big a deal if the thrust were dead-center.

EDIT: Actually I’m choosing to believe that the nozzle was more to blame for that, and thus this error. Quite spectacular though, I agree.
 
I always assemble my motors at home before a launch but don't totally tighten the closures until the motor is going to be used. For motors using ejection charges for deployment I leave the BP out also until ready to fly. This way if it doesn't fly the day intended good to go for the next time. Just have to remember to tighten the closures and add BP, otherwise might not turn out so good. I never forgot yet.
 
rcktnut said:
I always assemble my motors at home before a launch but don't totally tighten the closures until the motor is going to be used. For motors using ejection charges for deployment I leave the BP out also until ready to fly. This way if it doesn't fly the day intended good to go for the next time. Just have to remember to tighten the closures and add BP, otherwise might not turn out so good. I never forgot yet.
Click to expand...
This is what I do as well. I also put a piece of masking tape on the casing with the reload and delay on it in case I forget. The I put the motor, igniter, and ejection charge into their own little ziploc labeled with the rocket it's intended for.
 
Lotronex said:
This is what I do as well. I also put a piece of masking tape on the casing with the reload and delay on it in case I forget. The I put the motor, igniter, and ejection charge into their own little ziploc labeled with the rocket it's intended for.
Click to expand...
I label mine as well, also never had a problem with using them a year or so later.
 
For the Hobbyline RMS, the Delay Grain is pressed onto the o-ring to seal it. If you store it tighted, the compressed delay element may loose the compression over time and decrease the ability to seal. The RMS+ reloads dont rely on this type of compression, so you can leave them tighten, though I still like to store mine loosened just because I think its a good habbit.
 
To be clear, there is an issue with O-rings called compression set (see, e.g., https://www.applerubber.com/blog/a-simple-guide-to-understanding-o-ring-compression-set/ ) which can be a problem with a poor choice of O-ring material, too much compression, and temperature. It's not clear any of those factors apply to us, and I personally don't think any benefit of loosening an assembled motor outweigh the chance of losing the BP or forgetting to tighten it, so I just leave assembled motors alone. But YMMV.
 
smstachwick said:
At ROC’s May launch, I attempted to fly an Apogee Apprentice kit on an AeroTech D24 reload that I had assembled at ROCstock and let sit around for a month.

I wasn’t able to get the igniter cap on at ROCstock, and during the interceding month, I discovered why: the nozzle was very slightly misaligned. I held onto the motor, afraid to disassemble it and maybe get the ejection charge leaking where it didn’t belong, and flew it at my first opportunity. This was the result:

View attachment 645825

The misalignment wasn’t nearly that bad before, sadly I don’t have a photo. Best I can figure, it didn’t manage to screw together as much or as neatly as it needed to, and the aft O-ring seal didn’t actually seal anything. Flames probably shot out of the joint and ate through the casing.

The ignition of this motor-turned-flamethrower set the fin can on fire, and I had to put it out with a water bottle somebody was kind enough to contribute. The rocket is completely toast. By that I mean it’s toasted, the blackened paper and plastic were snapping off and crackling off like actual burned bread when I was trying to extract this motor.

Interestingly enough, the forward closure appears to have survived this whole ordeal. It even felt like the threads were still very greased and smooth, so at least I don’t think I have to replace the entire hardware set.

Oh, and of course, here’s the video.


View attachment 645826

My choice to fly it rather than troubleshoot it some other way is almost certainly going on somebody’s Top 10 list of dumb decisions at the range. Never ignore reload issues, Shane! Ask for help! Stupid! Bad!
Click to expand...
A couple of weeks ago, a friend had a launch that took off at an angle. Inspection showed that the nozzle on a G (probably a G64W, could have been a G53J, don't remember) in a 29/40-140 case was "tilted". Likely operator error, but I wonder if it's possible for one side of the paper liner to give way, allowing the nozzle to shift. The aft closure was threaded all the way on.

Hans.
 
4regt4 said:
A couple of weeks ago, a friend had a launch that took off at an angle. Inspection showed that the nozzle on a G (probably a G64W, could have been a G53J, don't remember) in a 29/40-140 case was "tilted". Likely operator error, but I wonder if it's possible for one side of the paper liner to give way, allowing the nozzle to shift. The aft closure was threaded all the way on.

Hans.
Click to expand...

The RMS 29/40-120 Relies on the propellant grain to hold the nozzle seated against the o-ring and aft closure (imo a poor design). Once the propellant is gone there is nothing but slag and ash preventing the nozzle from being tilted or pushed into the motor. It is very common to see the nozzle tilted after landing because it doesn't take much to knock the nozzle loose.

Most likely the rocket suffered rod whip or strong cross wind (if it was a windy day). It could also be flex in the fins, if the material used is to thin or flexible (I have a rocket that does that and I confused the clear plexiglass fins flex to much)
 
n3tjm said:
For the Hobbyline RMS, the Delay Grain is pressed onto the o-ring to seal it. If you store it tighted, the compressed delay element may loose the compression over time and decrease the ability to seal. The RMS+ reloads dont rely on this type of compression, so you can leave them tighten, though I still like to store mine loosened just because I think its a good habbit.
Click to expand...
So how do I tell whether I have Hobbyline RMS or RMS+? I'm sitting on 2 RMS 18/20 cases and a few sets of reloads ad have been unable to find a good time to just learn how to do this, preferably close to a launch. And I am well aware of compression set, creep, seizure, and all sorts of things that can happen to things that are left assembled too long. Thanks, all.
 
n3tjm said:
The RMS 29/40-120 Relies on the propellant grain to hold the nozzle seated against the o-ring and aft closure (imo a poor design). Once the propellant is gone there is nothing but slag and ash preventing the nozzle from being tilted or pushed into the motor. It is very common to see the nozzle tilted after landing because it doesn't take much to knock the nozzle loose.

Most likely the rocket suffered rod whip or strong cross wind (if it was a windy day). It could also be flex in the fins, if the material used is to thin or flexible (I have a rocket that does that and I confused the clear plexiglass fins flex to much)
Click to expand...
Err, no.

Rod whip? It was an 8ft rail. No wind. It was a very stout L2 type rocket, all fiberglass. Fins are not going to flex just off the rail. Sorry.

Left the rail at a significant angle. The flyer is a very experienced L2 rocketeer.

Hans.
 
4regt4 said:
Err, no.

Rod whip? It was an 8ft rail. No wind. It was a very stout L2 type rocket, all fiberglass. Fins are not going to flex just off the rail. Sorry.

Left the rail at a significant angle. The flyer is a very experienced L2 rocketeer.

Hans.
Click to expand...
Ok. Well not knowing the design it's hard to say, but maybe depending on what you mean by stout can give use a clue. If you mean by short, Sometimes those rockets are "marginally" stable and decide on what they want to do once they leave the rod, maybe enhanced by the laundry shifting at take off. I have one rocket that I've flown three times. Twice on the same motor. First flight was perfect, second was with a larger motor, about 20 grams heavier, and was completely unstable, third flight was with the same motor as the first flight, and it did what you described. Since then I pulled the rocket off my flight line deciding it needs nose weight.

If the nozzle did somehow tilted during firing, the seal would of broken and you would have fire coming out around the nozzle, the motor would loose thrust. It probably won't go out so it would fall to the ground and burn for several seconds until it burned all the fuel, seriously melting the aft closure and potentially cooking the tail end of the rocket.

Just remember I'm just giving you my ideas and opinions based on my experiences and knowledge. I might be completely off the mark because I wasn't there, did not see what happened, did not see the end results. Just going off what was typed ;)
 
Blast it Tom! said:
Well, I'm glad they do! Full "D" impulse in an 18 x70mm case, that ain't bad!
Click to expand...
I just wish they were not so expensive! $30 for a pack of D's last I checked. Wanted to get a pack of D24's. I'm going wait on that... Instead I am going cry when I spend $30 on a G....

And I really really miss the E27's.
 

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