Fully printed K2050 build

[Neutronium95]

Okay, point taken. From the description of the failure, it sounded an awful lot like grain faces were inhibited, which could lead to the overpressurization I described.

As @mrwalsh85 mentioned, others have not had to bond grains on the K2050ST, so I found it curious that a failure was seen when the grains were bonded. Correlation? Yes. Causation? Maybe, maybe not.

I insisted on gluing the grains, since I've heard of issues with motors CATOing under extreme acceleration, and wanted my hardware back in one piece. The method used shouldn't have resulted in any glue on the grain faces, just between the casting tubes and liner, and I don't really see any way that it could have compromised the motor.

 

[plugger]

Thinking on this situation I'm not sure if the motor anomaly you observed would have caused your flight failure. From the post flight pics it appears that both the forward and rear closures were still attached to the RMS casing. I've had the unfortunate pleasure of flying a J1999 a week after they were decerted (no one told me and I didn't think I should check) and that definitely let go. Both the forward and rear closures shot off the casing and the casing itself was physically expanded where the threads let go. I'm not saying your K2050 didn't run into an issue during the burn, just not really convinced that event would have resulted in your flight failure. Sadly, I think you're reaching the upper limit of what 3D printing will support, but that's just a suspicion.

Regardless, kudos for attempting a very aggressive flight.

 

[pathtouch]

Well here's the video from my dad.
Can't tell based on the video itself when the failure happens, but there's a loud pop about 530 ms into the burn (looking at the waveform in my editor). Which would actually put the upper bound of failure (green) at 420 ± 20 m/s (Mach 1.22), around 79 g, and an altitude of 340 ± 35 ft. I do think that altitude sounds a little bit more realistic.
View attachment 533649
View attachment 533648

Don’t forget to account for the time it takes that pop to travel at the speed of sound to your microphone. Is it possible you were far enough away that it took 200ms to reach you l, thus aligning with the 300ish ms timing?

Just a thought. Unfortunate but interesting attempt! While I envy the wide open spaces out west, I do not envy your heat! I think my rockets would melt on the pad.

 

[rfjustin]

I insisted on gluing the grains, since I've heard of issues with motors CATOing under extreme acceleration, and wanted my hardware back in one piece. The method used shouldn't have resulted in any glue on the grain faces, just between the casting tubes and liner, and I don't really see any way that it could have compromised the motor.

I tend to agree that highly catalyzed loads under significant acceleration are more prone to a CATO. I've flown 7 of them, 3 were in a cluster, all were glued together, just in case.

Having said that, I'm not seeing anything anomalous in the video indicating a motor issue. That and OP's assertion that it was in fact a motor issue is not supported by the video. I'm pleased K-2050 has an impeccable track record thus far.

Quite the attempt for sure!

 

[StreuB1]

I tend to agree that highly catalyzed loads under significant acceleration are more prone to a CATO. I've flown 7 of them, 3 were in a cluster, all were glued together, just in case.

Having said that, I'm not seeing anything anomalous in the video indicating a motor issue. That and OP's assertion that it was in fact a motor issue is not supported by the video. I'm pleased K-2050 has an impeccable track record thus far.

Quite the attempt for sure!

Agree 101%

 

[wsume99]

I was bummed to read that your flight was not successful. I've been following along because I have 3D printed components of HPR rockets but never fully 3D printed a HPR rocket. My biggest concern has always been printed BTs. That's why I asked what your wall thickness was earlier in this thread. I have always felt that in order to get sufficient strength out of a 3D printed tube I'd need to make the walls quite thick which adds too much weight. So in my designs I opt for cardboard/FG BTs with printed NCs and fin cans. Basically I try to avoid any significant bending moments along the z-axis of a printed part.

Borrowing from the "speed of cardboard" phrase my guess is you found the "speed of a 3D printed body tube with 1.75mm wall thickness". Looking at your design that is the one area I would have been concerned about if I was building the rocket. Did the facture loads result from normal flight or some motor anomaly? I cannot say but I'd bet that the initial point of failure in your airframe was somewhere in the BT.

 

[rharshberger]

I think better results from 3D printing and high performance flights would be to use a composite type airframe. A 3D printed outer airframe with a filament wound FG/CF or cardboard inner air frame. I have as an RSO had several opportunities to review post flight failures of 3D printed rockets, nearly everyone one was a Z-axis failure on the the airframe, one was a fin failure due to flutter, and one though it recovered safely was a nosecone failure again along the Z-Axis.

 

[lavie154]

Don’t forget to account for the time it takes that pop to travel at the speed of sound to your microphone. Is it possible you were far enough away that it took 200ms to reach you l, thus aligning with the 300ish ms timing?

Just a thought. Unfortunate but interesting attempt! While I envy the wide open spaces out west, I do not envy your heat! I think my rockets would melt on the pad.

I'm more or less accounting for that already by starting time when the camera first hears the launch, not when it first sees it. See: (anomaly in red)

Having said that, I'm not seeing anything anomalous in the video indicating a motor issue. That and OP's assertion that it was in fact a motor issue is not supported by the video. I'm pleased K-2050 has an impeccable track record thus far.

Quite the attempt for sure!

Yeah in the end, airframe failure, motor problems or not, is definitely likely. However the motor anomaly at the very least (going back to @AllDigital's pictures showing the spot in the plume) a good marker for when things went wrong, since the rocket starts to collapse immediately after the pop. Would be great if he could post his video, it was 240 fps and showed the rocket much clearer through that.

My personal theory is that the rocket was already basically at its operating limit, and whatever happened to the motor was what just pushed it over. However, I can't confirm that without the data from the Raven, and it's safe to say that regardless of that anomaly this would've been a really marginal success *if* it had worked. So a redesign is in order either way.

It's also worth noting the nozzle seemed entirely wrecked on recovery, but that very well may have been due to the eyebolt smashing into it. Any evidence I would've had of the motor "punching" forward from a surge in thrust is also gone as that end of the fin can is what crashed into the desert. So at this point, any guess at the root cause is, well, a guess, and the facts are the airframe failed. I've got some work to do!

 

[tfish]

nice go at it!

To compare your flight to one of mine.
My rocket was thin wall FG. G10 fins with to to tip using thinned "boat epoxy"
flying on 40 inches of propellant'.
Lost one side of the nozzles exit cone.



my point is..that there is a way to go yet to get 3D printed stuff to hold up to some unaccounted for flight issues.

Tony

 

[AllDigital]

However the motor anomaly at the very least (going back to @AllDigital's pictures showing the spot in the plume) a good marker for when things went wrong, since the rocket starts to collapse immediately after the pop. Would be great if he could post his video

Not my best video work, but here is the short footage I got before diving deeper into the bunker. It should have a download link to grab the file.

 

[LithosphereRocketry]

I keep seeing that wiggle in the smoke trail and wondering if this could be a stability/damping/AoA issue. The report of a pop is a little weird (I don't have sound at the moment to listen myself) but it's not unheard of for motors to spit bits of casting tube making fairly violent pop sounds, although that would be a little strange coming from a case-bonded motor.

I wonder if the unusual blended-body-ish fin geometry combined with the many small fins is in any way causing OR/RAS to overestimate the fins' effectiveness?

 

[Hobie1dog]

Was that like a 1/2 second burn?

 

[Neutronium95]

Was that like a 1/2 second burn?

Yes. The K2050 has a 0.7 second burn time. Very good for making rockets teleport.

 

[kramer714]

adding to an old thread, beware of temperature.

I have been wondering how hot a motor case actually gets relative to the adhesive used. To verify it we put the temperature color changing strips on the actual motor case, and on the motor tube. This was on a mid sized M motor. We flew it in June at Lucerene dry lakebed (not too far from FAR in Mojave). The results were interesting. After the flight, NONE of the indicators hit 150F even the one directly on the motor case. But the rest of the story....

Sitting on a table, in the sun, in the lakebed, in June, after 30 minutes the indicator inside the rocket on the motor tube and the motor case sitting on the table had both gone above 150F
Flying the M less than 150F, sitting on the table in the sun for 30 minutes, temps greater than 150F. It is very likely that the rocket was hotter than you think, after sitting in the sun for a while at FAR.

PETG being a thermoplastic looses strength with temperature the Heat Distortion Temperature is something like 160F. and a Tg of around 180F at the day job (airplane stuff) we try and stay at least 50 degrees below the Tg. HDT isnt an absolute number like melting point, the PETG is losing strength even at temperatures below it. Long bake at temperature may have significantly reduced the strength.

It is very likely that you exceeded the HDT and wer too close to the Tg to maintain strength. I use lots of 3d printed parts in av bays, but use fiberglass or aluminum for things like bulkheads.

Mike K