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  1. #31
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    I think discounting the unusual baro altitude data is a mistake.

    Either it is telling the truth or there is a problem with the data recording (only Adrian can judge).

    IF the baro sensor is telling the truth it is indicating a constant pressure in the av-bay for most of the flight and then a gradual increase in pressure up to the point of distruction. If everything was normal then the pressure should be on a generally decreasing trend.

    This indicates to me that there was compression of volume of the av-bay right from the get-go. Indicating some structural failure or defect in the airframe right from the beginning.

    Just a thought.....
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  2. #32
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    Quote Originally Posted by jderimig View Post
    I think discounting the unusual baro altitude data is a mistake.

    Either it is telling the truth or there is a problem with the data recording (only Adrian can judge).

    IF the baro sensor is telling the truth it is indicating a constant pressure in the av-bay for most of the flight and then a gradual increase in pressure up to the point of distruction. If everything was normal then the pressure should be on a generally decreasing trend.

    This indicates to me that there was compression of volume of the av-bay right from the get-go. Indicating some structural failure or defect in the airframe right from the beginning.

    Just a thought.....
    John, you would know better than me/most on this. The flight data was 3s (fairly short) is there pressure/time lag that we are not accounting for? Regarding the av-bay it was structurally sound after the flight. For a 2"x5.5" volume I had two holes slightly smaller than 3/32" both slightly above the mid-point in the part of the payload airframe that was found completely intact (and held in place by two 6-32 aluminum screws with knurls on the underneath side of the head cinched vey tight) after the flight so I don't believe any shifting of the airframe covered them. And the way the av-bay was structured it would have been very tough for these to be blocked internally.
    Last edited by dixontj93060; 11th April 2012 at 05:14 PM.
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  3. #33
    Is it possible that a forward-closure blow-by pushed off the forward section and/or ignited the apogee charge, and things progressed from there? I've had this happen a couple of times and the results are similar to what you are seeing, though I can't tell what's going on with the Raven data. Obviously finding the booster would be clarifying.

    I couldn't tell for sure from the report, the motor was the KBA L2300G?

    The rocket design looks fairly sound to me and simple structural failure doesn't seem likely IMHO.

  4. #34
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    I think you're trying to analyze the wrong thing. After the initial failure the situation is best described as chaos. You've gone from a reasonably stable, predictable behavior mode to something outside normal means of calculation and prevention, caused by the initial failure and that's what you should be trying to understand, not the after effects. Prevent the initial failure and the rest of the problem changes so completely that anything you do to address the chaos situation will only compromise performance, usually by adding weight.

    Quote Originally Posted by dixontj93060 View Post
    I certainly understand the centrifugal force causing the shearing of the nosecone pins and the nosecone being ejected as described above, that really wasn't my basic question--it is what happened after that...



    This is where I don't quite get it. What I would expect is that the payload and nose would be rotating and incurring the drag force opposite of flight nearly in sync. And as the nosecone ejects from centrifugal force, there is no opposing drag force as you describe above and/or it is extremely small compared to them both experiencing the drag at Mach 2.6. In this scenario I see that dominant drag taking them down together. While the booster moves forward, the nosecone and chute then come out facing opposite of flight direction; parachute canopy and nosecone bulkhead get pulled off as they reach limit of cord. No opportunity for a zipper that I see. Also in this scenario there is no explanation for the cracked/missing 2.5" at top of payload because the pins would simply shear with the centrifugal rotation.



    Well, yes, thanks. We likely will never know what happened unless I find a video somewhere. To be honest, not a big deal, it was all a big experiment anyway
    Peter Olivola

  5. #35
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    Quote Originally Posted by Peter Olivola View Post
    I think you're trying to analyze the wrong thing. After the initial failure the situation is best described as chaos. You've gone from a reasonably stable, predictable behavior mode to something outside normal means of calculation and prevention, caused by the initial failure and that's what you should be trying to understand, not the after effects. Prevent the initial failure and the rest of the problem changes so completely that anything you do to address the chaos situation will only compromise performance, usually by adding weight.
    I'm guessing you didn't read the analysis (?) as discovery and then preventive measures was the purpose of the document. What you are commenting on is, I agree, in the scheme of things, really superfluous details which I believe is the reason you wrote the post.
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  6. #36
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    Quote Originally Posted by dixontj93060 View Post
    John, you would know better than me/most on this. The flight data was 3s (fairly short) is there pressure/time lag that we are not accounting for?
    I have yet seen a pressure lag of that length yet. A 0.5s sec lag at most is what I have observed. And I have NEVER seen a sustained pressure av-bay increase while a rocket is accelerating.

    Could the av-bay been pressurized some other way? A leaking forward closure perhaps or a shift in laundry pressuring the airframe and leaking into the av-bay?
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  7. #37
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    Quote Originally Posted by dixontj93060 View Post
    Actually no, the nose had to be the first point of failure otherwise there wouldn't have been a 9" zipper down the side of the payload on the side that the av-bay then was sheared. If the av-bay coupler failed first, the chute and nose would have just fallen out without the significant damage to the fore end and the payload bay.
    Quote Originally Posted by dixontj93060 View Post
    I certainly could be wrong, but the flip doesn't look to be done until well after the high-g event.
    The high-G event shows a very large direction in the positive direction. The only things I've seen can cause any kind of a 300+G impulse like that are 1) a CATO and 2) a chute opening at Mach+ speed after the altimeter has flipped around. That kind of acceleration is more than can be produced by just about any non-exploding motor, no matter how light the rocket.

    Quote Originally Posted by mannyskid View Post
    From taking a second look at the data, I noticed that even after the 311.14 G spike, the rocket keeps accelerating, leading me to belive that it was the nose cone that came off, and not the Av-bay.
    Manny
    Keep in mind that a positive G reading can indicate decelerating, rather than accelerating, if the av-bay is flipped 180 degrees.

    Quote Originally Posted by dixontj93060 View Post
    Just for clarification (and as an aid to those not reading the postmortem in detail), my proposed sequence of events after analysis is:

    1. Internal radial failure of airframe at payload nosecone joint (initial 120 g spike).
    2. In quick succession: loss of nosecone, pull of Kevlar out/down side of payload causing wide zipper and release of parachute through zipper area, parachute inflating, end of Kevlar reached where nosecone attach was ripped off and parachute canopy was detached from shroud lines (corresponding to the many g spikes including ones @ 300 g)
    3. Above sequence lightened the rocket by more than 1/2 lb and thus the Raven still resident in the av-bay measured an increase in speed due to lighter weight.
    4. In quick succession after the end of #2, the av-bay was detached by radial failure in top of booster by pull/drag of cord/payload debris.
    5. As the av-bay, with the remaining payload airframe still attached, broke off and folded back the Raven inside continued its baro measurements and swapped signs on its velocity.
    6. During steps 4 and/or 5 above the Kevlar cord shorts power feeding Raven.


    In reference to the postmortem analysis, I categorize steps 1 and 2 above as "Event 1" and steps 4 and 5 as "Event 2".
    The G readings are in the wrong direction for this to be the sequence. I think there are 2 possibilities:

    Theory #1, CATO:
    Right near the end of the burn, a part of the liner clogs the nozzle, causing the back end of the motor to be blown off and a 300G upward spike that is more than the airframe can take. I have seen data from several CATOs with axial acceleration that looks just like this.
    Airframe then folds, resulting in tumble and disintegration.
    The problem with this theory is that witnesses didn't see an indication of a CATO.

    Theory #2, Airframe folded:
    The top half containing the altimeter is violently whipped around in the Mach 2.5 airflow, also separating the nosecone and ejecting the main chute. The tube gets zippered in the process, because just about anything can happen to a Mach 2.5 furball of parts.
    Main chute inflates, imparting 300+ Gs of deceleration to the av-bay that shows up as a huge positive acceleration impulse in the recorded data.

    Edit: Deleted references to lateral acceleration, which I remembered from someone else's data I've looked at recently. The 250G accelerometer used in this Raven only measures axial Gs.
    Last edited by Adrian A; 11th April 2012 at 08:06 PM.
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  8. #38
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    Quote Originally Posted by ECayemberg View Post
    2. Barometric altitude: while it seems that the charge did not fire, that data is wacked!. I'd be leery of a barometric altimeter that tells you your uber fast rocket achieved a net altitude gain of 200' and a net loss of 2700' or so...unless it wasn't vented (which I'm certain it was).
    Quote Originally Posted by jderimig View Post
    I think discounting the unusual baro altitude data is a mistake.

    Either it is telling the truth or there is a problem with the data recording (only Adrian can judge).

    IF the baro sensor is telling the truth it is indicating a constant pressure in the av-bay for most of the flight and then a gradual increase in pressure up to the point of distruction. If everything was normal then the pressure should be on a generally decreasing trend.

    This indicates to me that there was compression of volume of the av-bay right from the get-go. Indicating some structural failure or defect in the airframe right from the beginning.

    Just a thought.....
    Quote Originally Posted by jderimig View Post
    I have yet seen a pressure lag of that length yet. A 0.5s sec lag at most is what I have observed. And I have NEVER seen a sustained pressure av-bay increase while a rocket is accelerating.

    Could the av-bay been pressurized some other way? A leaking forward closure perhaps or a shift in laundry pressuring the airframe and leaking into the av-bay?
    I've seen data from about 5 of my own normal flights in the last few years that had 70+G acceleration through Mach 2+, and every one of them has this same pressure lag behavior. It's normal for this kind of flight profile. Consider that a 2-foot tall enclosed volume of air that's being accelerated at 70 Gs is going to have a pressure distribution inside the volume that's 140 feet "lower" at the bottom than at the top. Add to that the likely shifting and compression of a chute above the altimeter, and supersonic pressure disturbances toward the end of the burn, and the result is that for any high-G, high-velocity flight, the baro data should just be ignored until the coast phase. After the rocket breakup and tumble, the baro data from this flight looks normal.
    Last edited by Adrian A; 11th April 2012 at 07:42 PM.
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  9. #39
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    OK, I believe the big take away and "ah-ha" moment from the last string of comments from Dan, John and Adrian, is the new revelation (at least for me) of the delay in the baro data. Taking that into consideration changes things significantly. So my original assumption from the data of two events is wrong. When removing delay it is really one event, not two, and thus provides a foundation for the mid-airframe failure, if not an overwhelming vote.
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  10. #40
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    Quote Originally Posted by Adrian A View Post
    I've seen data from about 5 of my own normal flights in the last few years that had 70+G acceleration through Mach 2+, and every one of them has this same pressure lag behavior. It's normal for this kind of flight profile.
    I disagree. I have several sets of similar flight profile data without this type of recorded baro pressure behavior, but we use different recording devices.
    Last edited by jderimig; 12th April 2012 at 12:34 AM.
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  11. #41
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    I don't want this to sound like I'm pushing my favorite cause of failure theory, and I've tried to suggest consideration of other causes without being specific for exactly that reason, but if you didn't recover the fin can, you're missing an entire area of consideration.

    Were you able to identify the first piece that came off? Have you considered the effect of drilling holes in the root edge of the fin? Is it possible the first piece was a fin or part of a fin?

    Such a failure would result in exactly the kind of instability that would produce additional failures of airframe, bulkheads, nose cone separation, etc. Again, after the initial failure, chaos ensues. Without the fin can, you can't rule fin failure out. Even with the fin can, unless all fins are securely in place, you can't rule fin failure out.

    At the velocity at which failure occurred, it's highly unlikely that wind was a factor (a simple apparent wind vector calculation will illustrate how much wind would be required to offset an otherwise stable rocket.) Significant off axis attitude is a highly likely cause of subsequent destruction. What caused the rocket to go off axis to the degree necessary to produce such a scenario?

    Quote Originally Posted by dixontj93060 View Post
    I'm guessing you didn't read the analysis (?) as discovery and then preventive measures was the purpose of the document. What you are commenting on is, I agree, in the scheme of things, really superfluous details which I believe is the reason you wrote the post.
    Peter Olivola

  12. #42
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    Talking to a number of observers and looking at available snapshots, fin failure was unlikely. First, the event was low @ 2300 feet so debris path was easy to follow. It is likely everything available was picked up. Second, there was zero deviation to the flight path as evidenced by the smoke trail.

    Quote Originally Posted by Peter Olivola View Post
    I don't want this to sound like I'm pushing my favorite cause of failure theory, and I've tried to suggest consideration of other causes without being specific for exactly that reason, but if you didn't recover the fin can, you're missing an entire area of consideration.

    Were you able to identify the first piece that came off? Have you considered the effect of drilling holes in the root edge of the fin? Is it possible the first piece was a fin or part of a fin?

    Such a failure would result in exactly the kind of instability that would produce additional failures of airframe, bulkheads, nose cone separation, etc. Again, after the initial failure, chaos ensues. Without the fin can, you can't rule fin failure out. Even with the fin can, unless all fins are securely in place, you can't rule fin failure out.

    At the velocity at which failure occurred, it's highly unlikely that wind was a factor (a simple apparent wind vector calculation will illustrate how much wind would be required to offset an otherwise stable rocket.) Significant off axis attitude is a highly likely cause of subsequent destruction. What caused the rocket to go off axis to the degree necessary to produce such a scenario?
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    Lack of flight path deviation at the acceleration rate and speed of the rocket is not indicative of anything unless you have some close up photography. 2300 ft may be relatively low, but even a 300mm lens won't get the level of detail necessary not to mention being able to track the rocket well enough to avoid blur.

    Again, at speed, it only takes a small off axis deviation, one that wouldn't necessarily be detectable before catastrophic failure, to initiate the event.

    Quote Originally Posted by dixontj93060 View Post
    Talking to a number of observers and looking at available snapshots, fin failure was unlikely. First, the event was low @ 2300 feet so debris path was easy to follow. It is likely everything available was picked up. Second, there was zero deviation to the flight path as evidenced by the smoke trail.
    Peter Olivola

  14. #44
    Quote Originally Posted by Peter Olivola View Post
    Lack of flight path deviation at the acceleration rate and speed of the rocket is not indicative of anything unless you have some close up photography. 2300 ft may be relatively low, but even a 300mm lens won't get the level of detail necessary not to mention being able to track the rocket well enough to avoid blur.

    Again, at speed, it only takes a small off axis deviation, one that wouldn't necessarily be detectable before catastrophic failure, to initiate the event.
    Seconding what Tim said about it not being a fin. Witnessing the flight, as Tim mentioned, there was no deviation in flight path. A fin coming off at that rate of speed would have produced a noticeable deviation in the arrow-straight flight path. The nose or payload came off/failed, determining WHY it came off is the challenge I believe.

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    Quote Originally Posted by Peter Olivola View Post
    Lack of flight path deviation at the acceleration rate and speed of the rocket is not indicative of anything unless you have some close up photography. 2300 ft may be relatively low, but even a 300mm lens won't get the level of detail necessary not to mention being able to track the rocket well enough to avoid blur.

    Again, at speed, it only takes a small off axis deviation, one that wouldn't necessarily be detectable before catastrophic failure, to initiate the event.
    Small off axis deviation, yes, ~2.2 degrees for a mid-airframe failure.

    Regarding fin failure, this was one of the first things I looked at... Even though the booster was not found, there should be other evidence in the flight data. The vast majority of the time, fin failure does not occur without flutter. This should be evidenced by some, even minimal, oscillatory pattern in the accelerometer readings for a reasonable period of time before the event. This is not present. Also remember it wasn't just three independent fins on the rocket so to speak, it was an integrated carbon fin can (see build pic below). A failure in that structure would be much more evident in the flight data.

    Last edited by dixontj93060; 13th April 2012 at 02:02 PM.
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  16. #46
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    Peter is correct,

    A fin failure leading to destruction is not always discernable from a flight observation.

    This is the last flight of my HoJo on a big L.

    http://www.youtube.com/watch?v=euZi-_iu7YA

    Which destroyed it self at it crossed Mach. I have still photo's which also show the sequence which I can post.

    The time from the fin failure to total rocket dissassembly was less than 0.2sec (still photos were shot at 5fps). One frame rocket totally intact, next frame totally destroyed. Also nothing in the alimeter flight data predicted the failure.

    Enjoy!
    Last edited by jderimig; 13th April 2012 at 07:03 PM.
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    From my vantage point (on my iPhone), looked like significant wiggle/kick to the right in the flight path!

    EDIT: Yes, took a look on my MacBook Pro. Deviation very clear at ~37.5 seconds into the video.

    Quote Originally Posted by jderimig View Post
    Peter is correct,

    A fin failure leading to destruction is not always discernable from a flight observation.

    This is the last flight of my HoJo on a big L.

    http://www.youtube.com/watch?v=euZi-_iu7YA

    Which destroyed it self at it crossed Mach. I have still photo's which also show the sequence which I can post.

    The time from the fin failure to total rocket dissassembly was less than 0.2sec (still photos were shot at 5fps). One frame rocket totally intact, next frame totally destroyed. Also nothing in the alimeter flight data predicted the failure.

    Enjoy!
    Last edited by dixontj93060; 13th April 2012 at 07:25 PM.
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  18. #48
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    Quote Originally Posted by jderimig View Post
    The time from the fin failure to total rocket dissassembly was less than 0.2sec (still photos were shot at 5fps). One frame rocket totally intact, next frame totally destroyed. Also nothing in the alimeter flight data predicted the failure.
    The fin didn't flutter, it just fell off?! Or are you saying your altimeter doesn't have the resolution to measure a flutter event? My ARTS2 can/did clearly measure flutter on my old PML Ariel when it shredded.
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    Quote Originally Posted by dixontj93060 View Post
    The fin didn't flutter, it just fell off?! Or are you saying your altimeter doesn't have the resolution to measure a flutter event? My ARTS2 can/did clearly measure flutter on my old PML Ariel when it shredded.
    Can't a fin flutter without affecting acceleration in the axis of flight?
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    5 fps sequence

    Pic just before failure


    0.2sec later


    0.4 sec
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    Quote Originally Posted by jderimig View Post
    Can't a fin flutter without affecting acceleration in the axis of flight?
    John, I would think you would know better than me, but... Yes, it could. Generally a flutter event like that (harmonic oscillation) would add drag as the fin deforms and then straightens and that drag would amplify as the event unfolded which should affect the accelerometer in the axis of flight. I'll have to try to find my old altimeter data--from what I recall it kinda looked like regular blips/pulses of increasing magnitude.
    Last edited by dixontj93060; 13th April 2012 at 07:36 PM.
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    Quote Originally Posted by jderimig View Post
    0.2sec later
    WOOOWWWW!!!!! That looks like way more than a fin?!? Looks like a low grade plutonium suitcase-sized nuclear bomb!
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  23. #53
    Quote Originally Posted by Adrian A View Post
    Theory #1, CATO:
    Right near the end of the burn, a part of the liner clogs the nozzle, causing the back end of the motor to be blown off and a 300G upward spike that is more than the airframe can take.
    Going back to my post #33, which seems to have been missed, another possibility is a forward blow-by that kicked the payload section off and/or ignited the apogee charge and then things went south.

    The rocket looks pretty robust to me and a simpler explanation is a motor problem, not an unlikely IMHO airframe or fin construction issue.

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    Quote Originally Posted by dixontj93060 View Post
    WOOOWWWW!!!!! That looks like way more than a fin?!? Looks like a low grade plutonium suitcase-sized nuclear bomb!
    Yes I am proud of that one. The point was things can go from looking apparently 'normal' to total destruction very very quickly.
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    Quote Originally Posted by mikec View Post
    Going back to my post #33, which seems to have been missed, another possibility is a forward blow-by that kicked the payload section off and/or ignited the apogee charge and then things went south.

    The rocket looks pretty robust to me and a simpler explanation is a motor problem, not an unlikely IMHO airframe or fin construction issue.
    Could be... Although I would think with that scenario wouldn't you see a hesitation/kick back in the flight? There was no hesitation, no deviation during the flight at all.
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    Quote Originally Posted by mikec View Post
    Going back to my post #33, which seems to have been missed, another possibility is a forward blow-by that kicked the payload section off and/or ignited the apogee charge and then things went south.

    The rocket looks pretty robust to me and a simpler explanation is a motor problem, not an unlikely IMHO airframe or fin construction issue.
    I agree a forward blow-by is a possibility. Zooming way in on the axial accel data, however, there is a period of about 15 msec where the acceleration is bumping up to 125 Gs and down to zero, and then back to 100 Gs before the big 300G impulse. I can imagine that the axial accel dropout and subsequent noise before the big impulse could be caused by the front of the airframe flipping over and knocking around before the chute inflated. The initial 125G measurement before the accel dropout could have come from the motor spitting parts of the liner, like you can see at a lower magnitude toward the end of the burn. I think that one of those last motor spurts was just too much for the airframe coupler, which snapped and allowed the front of the rocket to flip backward. If the front of the rocket was 2 lbs, the we're talking about 250 lbs of G loading compression, plus the considerable pressure drag on the nosecone at Mach 2.5. Add in some bending from wind shear, an it's not too hard to imagine why a significant fraction (maybe 30%) of the high-performance flights at BALLS shred on the way up.
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  27. #57
    Quote Originally Posted by dixontj93060 View Post
    There was no hesitation, no deviation during the flight at all.
    I'm not certain what you mean by this -- the rocket clearly broke into two pieces mid-flight -- but I had a similar failure and the booster continued to ascend fairly normally; it was subsequently recovered heavily scorched from the blow-by gases, and the front was all smashed in, but the fins stayed on great. FWIW.

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    Quote Originally Posted by Adrian A View Post
    I agree a forward blow-by is a possibility. Zooming way in on the axial accel data, however, there is a period of about 15 msec where the acceleration is bumping up to 125 Gs and down to zero, and then back to 100 Gs before the big 300G impulse. I can imagine that the axial accel dropout and subsequent noise before the big impulse could be caused by the front of the airframe flipping over and knocking around before the chute inflated. The initial 125G measurement before the accel dropout could have come from the motor spitting parts of the liner, like you can see at a lower magnitude toward the end of the burn. I think that one of those last motor spurts was just too much for the airframe coupler, which snapped and allowed the front of the rocket to flip backward. If the front of the rocket was 2 lbs, the we're talking about 250 lbs of G loading compression, plus the considerable pressure drag on the nosecone at Mach 2.5. Add in some bending from wind shear, an it's not too hard to imagine why a significant fraction (maybe 30%) of the high-performance flights at BALLS shred on the way up.
    Adrian, please, how do you get the FIP program to do zooming? Been going crazy trying to do screen captures and blow ups. Is there a FIP program manual? I didn't find it on the website.

    I could more believe the spitting of liners; that would be much harder/impossible to see and it is unlikely to affect the flight path to any great degree. Note on weight; overall rocket was just over 2lbs, front was less than a pound.
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  29. #59
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    Quote Originally Posted by mikec View Post
    I'm not certain what you mean by this -- the rocket clearly broke into two pieces mid-flight -- but I had a similar failure and the booster continued to ascend fairly normally; it was subsequently recovered heavily scorched from the blow-by gases, and the front was all smashed in, but the fins stayed on great. FWIW.
    Shouldn't have said "flight" should have said "flight path." Observed by a number of witnesses, there was no deviation in the flight path--at all. The booster just blew through the payload/nose (no matter which came apart first and/or in what sequence) like a hot knife in whipped butter. That's what I mean by no deviation.

    Regarding the gases/scorching evident in your flight, I think that observation is enough to say this event wasn't a blow by. The aft bulkhead of the av-bay was no more than 4" from the top of the motor and exposed (less the loops of Kevlar shock cord). From your description, I would expect that bulkhead to have some blackening/scorching if it was that close to the fore motor closure and the fore closure was the initiator of the event. Instead, the aft av-bulkhead was "squeaky clean."
    Last edited by dixontj93060; 13th April 2012 at 09:01 PM.
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  30. #60
    Quote Originally Posted by dixontj93060 View Post
    From your description, I would expect that bulkhead to have some blackening/scorching...
    Not really. Most of the damage to the booster happened after the avbay was gone.

    To zoom in FIP click and drag just below the X axis of the graph.

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