More speculation without data (which is fun!):
We understand gravity turns pretty well--it would be a colossal error if
they set the elevation angle of the launch rail to the wrong setting.
I would think a fin loss would mean the failure would happen much more
quickly, rather than what looked like slowly increasing divergent coning
motion (aka roll-pitch coupling).
I think it was roll-pitch coupling, but not because the roll rate was too
slow. If the roll rate is slow (and there's a decent amount of aerodynamic
damping), or if the roll rate is very high, there won't be significant
roll-pitch coupling. It's the in-between rate that's resonant with the
pitch natural frequency (think Bode plots from back in school) that ruins
your day. Many unguided sounding rockets like the Super Loki spin up
immediately (using a corkscrew rail) to get past the resonant roll rate
right from the start. It looks to me that the roll rate started out at less
than 1 Hz (60 rpm) (from the onboard video) and then increased to over 2 Hz
(120 rpm) and then the coning motion started. It lasted for a few seconds
before loss of video. So the roll rate increased until it reached the
pitch-roll resonant frequency and it was all over. At least that's my guess!
The animation looked pretty bogus to me--was the center of mass really that
far forward (that close to the nose cone)?
On Wed, Nov 4, 2015 at 9:47 AM, Aplin Alexander T <ATAPLIN@xxxxxxxxxxxxxxxx>
wrote:
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FWIW the Black Arrow had a solid third stage.
On my mind as I had the pleasure of a close encounter with the spare Black
Arrow on display at the London Science Museum earlier this week).
http://www.sciencemuseum.org.uk/objects/space_technology/1972-325.aspx?keywords=black+arrow
BTW I also saw a Russian TK Lunar lander on (temporary) display at the
‘Cosmonauts’ exhibition there – the contrast in size to the (relatively)
huge US LM mock-up on display elsewhere was striking.
http://www.sciencemuseum.org.uk/visitmuseum/Plan_your_visit/exhibitions/cosmonauts.aspx
*Alex Aplin*
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