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Intro
Design
Airframe
Hardware
Software
Testing
Launch 1
Digesting 1
Launch 2
Digesting 2
Launch 3
Digesting 3
Launch 4
Launch 5
Glossary
Links
Contact
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Digesting the Second Launch
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Some Instrument Data
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The barometric altitude given by the glider still diverges somewhat from the
GPS altitude with height, although less than in the first launch.
This is probably still a calibration error, which has been tweaked
(again). (Note the x-axis at right is scaled in seconds)
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The G sensor appears to have worked great. This graph is of the max G loading
for the most recent 5 seconds, from 4hz AD samples. (Note the x-axis
above is scaled in seconds)
There was some wild swinging this time on the way up, as you can see
on the left end. The maximum
G load at pullout from the dive (at about 750s) after release was 2.8 - right
about what the flight simulation predicted.
The swings in the cruise portion of the flight mostly correspond to
turns, when you look at the second-by-second G loadings, although much
is likely turbulence. Most of the return flight time was spent in a
banked turn of some kind.
The parachute opening is actually the
second-highest spike on the right end, at only 1.93g (very nice!).
The high spike on the right, at 4.5g or so, is the touchdown, while the
low spike is next to it probably someone picking the glider up.
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Looking at a small-scale expanded section of the flight data, you can see that
the roll rate commanded by the autopilot, and the sensed roll rate,
track each other very well.
Also note that the roll command algorithm is always
making small control motions to fight turbulence. (Note the x-axis
above is scaled in seconds)
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The roll-rate gyro trim was set to be - 4 degrees per second, to zero
the sensed roll rate, during the preflight. Note how much it differed at
altitude, when the glider trimmed out after release!
The internal temperature did rise 10c over that period, which might
affect the gyro, but still - that's a fair bit of variation. It
isn't, however, outside of the expected range of gyro neutral drift. (Note the x-axis
on the left is scaled in status-telemetry data points,
which are 4 seconds apart)
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Conclusions
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The aircraft met its design goals in terms of flight behavior, even down
to the trimmed airspeed. The glideslope appears to be around 14:1,
exceeding that design goal, and it has a neutral-elevator trim airspeed
of about 42 knots, which is very near to its airspeed for best
glide. It seems the design estimates of the glider's fuselage
parasite drag had been overly pessimistic, as this performance occurred
even with the nose-cone joint and chute hatch edges disturbing the
airflow. As a bonus, the gyro-feedback loop seemed to find that the
aileron trim for zero roll rate was almost perfectly at centre.
The quickcam also needs attention, something that didn't make it on
the work plan for this flight. Other issues were that the attempted fix
for the external temperature probe didn't fully improve it's accuracy.
Overall though, just a fantastic flight. Almost there.
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Changes for Next Time
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Use a narrow, fixed, iris in the quickcam's lens assembly instead of
"sunglass" type filters, which seem to flatten contrast and
colour.
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Put the external temperature sensor out on a small post to
separate it better thermally from the aircraft's skin.
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Provide an algorithm to allow the Expert-system level autopilot
to adjust the elevator for the ideal trimmed airspeed for the
conditions.
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Provide audio alarms on the ground station, so it's possible to
walk away from the table for short periods.
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