GaryT
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My GUESS 1 fin blew off causing it to go sideways then lights out.
98mm N5800 MD rocket for BALLS
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GaryT
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Yeah I know.
edwinshap1
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Chris, we need pictures! Ahhh
cjl
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I apologize for how long this has taken me - I have had an unfortunate combination of laziness and a lot of stuff to catch up on since getting back from Balls, so I've been putting this off for a while now. Anyways, the failure analysis and launch report...
The rocket setup went pretty much as expected, with one minor hiccup. The nose cone, which I had carefully fit to be a snug but not tight fit earlier in the morning was having difficulty going on at the pad. I ended up having to remove many layers of the high temperature tape I was using to friction fit it in order to get it to fit on at all. I attributed it to the change in temperature from the rocket sitting out in the sun and the fact that the air had been heating up rather rapidly from the cold temperatures of the night before, but looking back on it, any imperfection in this fit could have well contributed to the failure.
Once the rocket was setup and ready for flight, I put a couple of cameras nearby to catch the liftoff. Unfortunately, the Casio ran out of memory, so I don't have any high speed video, but the GoPro worked perfectly, capturing nice video of the liftoff from about 50 feet away (possibly even closer than that - I didn't measure). Without further ado, here's the liftoff pics and video:
[youtube]M1Kf0nvnl8U[/youtube]
The rocket setup went pretty much as expected, with one minor hiccup. The nose cone, which I had carefully fit to be a snug but not tight fit earlier in the morning was having difficulty going on at the pad. I ended up having to remove many layers of the high temperature tape I was using to friction fit it in order to get it to fit on at all. I attributed it to the change in temperature from the rocket sitting out in the sun and the fact that the air had been heating up rather rapidly from the cold temperatures of the night before, but looking back on it, any imperfection in this fit could have well contributed to the failure.
Once the rocket was setup and ready for flight, I put a couple of cameras nearby to catch the liftoff. Unfortunately, the Casio ran out of memory, so I don't have any high speed video, but the GoPro worked perfectly, capturing nice video of the liftoff from about 50 feet away (possibly even closer than that - I didn't measure). Without further ado, here's the liftoff pics and video:
[youtube]M1Kf0nvnl8U[/youtube]
cjl
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As the rocket continued to climb, everything was looking good. Coming out of the tower, there was absolutely no wiggle, no spin, and the rocket was tracking just about as straight as any I've ever seen. Pictures back this impression up - there was absolutely no wind, and I apparently got the fin alignment pretty good. As of these pictures, the rocket was already well supersonic, and there were no hints of any problems.
cjl
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Unfortunately, as the rocket continued to accelerate, everything went wrong around mach 3 or so. As I mentioned earlier, the nose fit left a bit to be desired at the pad, and it's possible that it wiggled a bit, or cocked over at a slight angle - it all happened too fast and high to know precisely what happened, but one thing is certain: when a rocket comes apart at mach 3, the re-kitting is pretty thorough:
Now, it's true that in that picture, everything is pretty much disassembled. However, two things pop out if you look closely (especially at the full resolution version):
1) The fins are near the top of the debris cloud
2) The parachute is near the bottom of the debris cloud
This indicates that the nose cone came off first, with the fins coming off only after the nose cone had departed and caused the rocket to go unstable at high speed. This is also backed up by the fact that one fin has a substantial chunk taken out of the leading edge, as if something hit it with extreme force. I believe that the nose cone actually impacted this fin's leading edge as it was leaving the rocket. Here's another picture of the debris cloud, but with annotations:
Another thing to note is that the piece of fiberglass tubing just below the actual nosecone is in approximately a million pieces. I found a couple of fragments of this after flight. I will admit, I have to eat my words on this one a bit, as this was one of the areas where I did not go to any special trouble to use extra strong or reinforced materials, and I paid for it in this case. The tubing should have been more than strong enough in a purely axial load however, which is what leads to my assumption that there was a very small amount of wobble or angle on the nose cone attachment, which caused very high sideloads which destroyed the tube. Most of the rest of the rocket was found after flight, but all that was found of this tube was a few small, red-painted pieces that were clearly from the fiberglass tube.
Interestingly, when the fins came off, they delaminated the performance rocketry carbon tube. This indicates that care must be taken in future attempts in how the fins are attached to the tube, and it may even be worth looking into other tubing options. Even though I did cut a moderately deep crosshatch, the delamination consistently occurred at approximately the depth of the crosshatch. Interestingly, one fin came back half-thickness - the forces when the fin was ripped off of the tube were sufficient to delaminate the autoclaved prepreg along the entire area of the fin. Given the forces required to do this, I think it is safe to say that no conceivable fin construction that is even remotely reasonable can survive after a shred at these speeds. However, due to the picture evidence as well as the substantial damage to the leading edge of one fin, I believe I can safely say that the fins were not the failure point.
Now, it's true that in that picture, everything is pretty much disassembled. However, two things pop out if you look closely (especially at the full resolution version):
1) The fins are near the top of the debris cloud
2) The parachute is near the bottom of the debris cloud
This indicates that the nose cone came off first, with the fins coming off only after the nose cone had departed and caused the rocket to go unstable at high speed. This is also backed up by the fact that one fin has a substantial chunk taken out of the leading edge, as if something hit it with extreme force. I believe that the nose cone actually impacted this fin's leading edge as it was leaving the rocket. Here's another picture of the debris cloud, but with annotations:
Another thing to note is that the piece of fiberglass tubing just below the actual nosecone is in approximately a million pieces. I found a couple of fragments of this after flight. I will admit, I have to eat my words on this one a bit, as this was one of the areas where I did not go to any special trouble to use extra strong or reinforced materials, and I paid for it in this case. The tubing should have been more than strong enough in a purely axial load however, which is what leads to my assumption that there was a very small amount of wobble or angle on the nose cone attachment, which caused very high sideloads which destroyed the tube. Most of the rest of the rocket was found after flight, but all that was found of this tube was a few small, red-painted pieces that were clearly from the fiberglass tube.
Interestingly, when the fins came off, they delaminated the performance rocketry carbon tube. This indicates that care must be taken in future attempts in how the fins are attached to the tube, and it may even be worth looking into other tubing options. Even though I did cut a moderately deep crosshatch, the delamination consistently occurred at approximately the depth of the crosshatch. Interestingly, one fin came back half-thickness - the forces when the fin was ripped off of the tube were sufficient to delaminate the autoclaved prepreg along the entire area of the fin. Given the forces required to do this, I think it is safe to say that no conceivable fin construction that is even remotely reasonable can survive after a shred at these speeds. However, due to the picture evidence as well as the substantial damage to the leading edge of one fin, I believe I can safely say that the fins were not the failure point.
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cjl
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I haven't got any pictures of the debris itself at the moment, but I will post those at some point, especially the damage to the leading edge of one fin and to the nosecone.
Interestingly, the paint was pretty much flawless on every component as I was cleaning up the debris. I think that this kind of paint would be a good choice for any future attempt to protect the rocket from the high-speed environment. In addition, the nose itself was pretty much flawless, so I think this cone would have stood a good shot of surviving throughout the flight.
For future plans, I may try this again at some point, as I have several ideas for improvements based on what was learned from this flight. I think an all-composite rocket is very doable to this kind of speed, and looking at the debris, I believe that many components on this rocket were substantially overengineered compared to what would actually be required. That having been said, I think my next few big flights will be low and slow - there's really something quite nice about having an enormous space to work with when packing parachutes, rather than trying to fit all of the electronics and the recovery system into a nosecone.
Interestingly, the paint was pretty much flawless on every component as I was cleaning up the debris. I think that this kind of paint would be a good choice for any future attempt to protect the rocket from the high-speed environment. In addition, the nose itself was pretty much flawless, so I think this cone would have stood a good shot of surviving throughout the flight.
For future plans, I may try this again at some point, as I have several ideas for improvements based on what was learned from this flight. I think an all-composite rocket is very doable to this kind of speed, and looking at the debris, I believe that many components on this rocket were substantially overengineered compared to what would actually be required. That having been said, I think my next few big flights will be low and slow - there's really something quite nice about having an enormous space to work with when packing parachutes, rather than trying to fit all of the electronics and the recovery system into a nosecone.
dixontj93060
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The failure pattern is very similar to this flight of mine from last April. Thanks for sharing the results Chris.
cjl
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Thick - I don't know an exact value, sorry. I don't know the exact construction technique, but I believe it was constructed from a two-part mold, yes. It survived a shred at mach 3 and a bounce from a mile up with only a chip in the shoulder, so it's definitely a sturdy piece. If it's at all helpful, it weighed around a pound and a half...
edwinshap1
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Chris, did the case survive?
Also I don't think PR tubing can withstand the stresses of surface mounted fins. I do think that wrapped cloth tubing can survive surface mounted fins, but every fiber on a filament wound tube is sanded to be exposed. Its screwed before it starts moving.
Also I don't think PR tubing can withstand the stresses of surface mounted fins. I do think that wrapped cloth tubing can survive surface mounted fins, but every fiber on a filament wound tube is sanded to be exposed. Its screwed before it starts moving.
cjl
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The case seems to be OK actually, yes. As for the filament wound tubing and fin joints? The stresses really aren't very big as long as the rocket is flying straight - they should be around 40-50 pounds max per fin in my case, and primarily axially directed. That kind of load is easily within the ability of an ordinary surface mount to handle - the reason they came off was because the rocket turned sideways at high speed. Alignment is absolutely key though - the trick to minimizing fin loads is twofold: make sure they are absolutely dead straight, and make sure they are stiff enough such that flutter will not have the slightest chance of happening.
cjl
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The FWCF airframe used for the bottom part seemed more than up to the task, aside from the issue of delamination (which is separate, and I believe solvable). It's the chunk of hobby fiberglass airframe above the motor (but below the nose) which failed, and I would have to say that it wasn't up to the task.
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cjl
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The upper tube was actually the older style (cloth based) PR FG tube, not the newer filament wound stuff. As for rebuilding? As I said, I do have several ideas, but they will have to wait for that magical combination of funding and motivation.
GaryT
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The G12 FG! that Mike used held up just fine, If anyone was concerned about the BT not holding up then why didn't anyone use the 1/8" wall CF?
GaryT
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Success or not, very nicely done Chris. I'm with you though, 20K and Mach 1.5 is still fine by me.
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New Ocean
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I missed that part of the build, what I remember was "As kevin said, it's ordinary cf from performance rocketry. I'm not too worried about its strength, since it will actually be shorter than the motor casing. As a result, the casing will act as a full length aluminum coupler, pretty much eliminating any chance of the tube buckling. It also should never have a very high heat load, since it will never be directly exposed to the airstream. Honestly, the tube is the one part of the rocket that doesn't terribly concern me." So the motor did not go all the way to the nosecone shoulder?
Rocketman248
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I think we're very close to solving this challenge. It looks like your fins and booster were just fine, as was your nosecone. This issue now is the upper airframe. The challenge is to get it as strong as possible while maintaining RF transparency. Perhaps a custom thick walled fiberglass tube, along with a custom fit nose cone?
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Lining the unsupported body tube with couplers comes to mind. From the top of the motor case up to the nose cone. You might need to fab up a new electronics bay and nose cone to fit.
Tony
Tony
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I like 'energetic disassembly'Nice euphemism
awseiger
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Now, I have little experience with this.... but.... what if instead of the nose cone coming off, the laundry came out the rear end? Then you could simply secure the nosecone on (or even mold it into the body tube). Just a random Idea I had.
Shame this didn't work. I should point out I've been checking here almost twice a day waiting for a flight report...
