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Angelfire has an
ARTS
recording altimeter mounted in the electronics payload bay.
Details are available here.
This altimeter uses both an accelerometer and a barometric pressure sensor
to collect flight data. That flight data can be plotted and analyzed in
many different ways. The results for various Angelfire flights are
presented below.
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Angelfire carries enough
electronics that it was possible to determine the peak altitude in five
different ways. The two MissileWorks altimeters reported the peak altitude
to be 15,176 and 15,616 feet. The ARTS altimeter reported the peak
altitude as 15,613 feet based on the
accelerometer and 14,605 feet based on the pressure sensor. And
lastly, the GPS reported the peak to be 14,668 feet. The average of these
five readings is 15,136 feet and the largest difference from the average
to any one reading is 3.51%. That is very good agreement
among the five different sensors!
Maximum acceleration was
7.25 G's. Peak velocity was 970 ft/sec (661 mph). Angelfire
reached apogee in 30.6 seconds. After that, it descended on the drogue
chute for 2.31 minutes at -97.7 ft/sec and then fired the main chute
ejection charge at 1606 feet. It descended on the main chute at
-22.8 ft/sec for 59.1 seconds. Total flight time was
3.81 minutes.
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The two MissileWorks
altimeters reported the peak altitude to be 15,540 and 16,151 feet.
The ARTS altimeter reported the peak altitude as 16,147 feet based on the
accelerometer and 15,149 feet based on the pressure sensor. And
lastly, the GPS reported the peak to be 15,214 feet. The average of these
five readings is 15,640 feet and the largest difference from the average
to any one reading is only 3.27%.
Maximum acceleration was
7.6 G's. Peak velocity was 992 ft/sec (676 mph). Angelfire
reached apogee in 31.2 seconds. After that, it descended on the drogue
chute for 2.33 minutes at -99.5 ft/sec and then fired the main chute
ejection charge at 1672 feet. It descended on the main chute at
-23.6 ft/sec for 62.5 seconds. Total flight time was
3.89 minutes.
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The two
MissileWorks
altimeters onboard reported altitudes of 10,172 and 10,404 feet.
These are very close to and even straddle the 10,326 feet reported
independently by the GPS system. The
ARTS altimeter reported
9,574 feet based on its barometric sensor. This appears to be just a
little bit low. The ARTS altimeter reported 11,002 feet based on its accelerometer data, which as usual for this particular unit, appears to be
a bit too high.
The ARTS data shows the
peak velocity was 511 mph. This is very good agreement with the GPS
data that gave 535 mph. Maximum acceleration was 5.8 G's. Angelfire
reached apogee in 27 seconds. After that, it descended on the drogue
chute for 93 seconds at 62 mph and then fired the main chute deployment
charge at 1,600 feet. According to the ARTS altimeter it descended
on main at 14 mph for 73 seconds. Total flight time was 3 minutes and 13 seconds.
All of these number are in very good agreement with the values derived
from the GPS readings.
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The two MissileWorks
altimeters reported altitudes of 15,133 and 16,018 feet. This gives
an average of 15,576 feet. The ARTS altimeter reported the peak altitude as 16,192 feet based on the
accelerometer and 15,015 feet based on the pressure sensor. The
largest difference between all these readings is 6.4%. This
particular ARTS altimeter seems to always report a slightly higher
altitude based on the accelerometer than on the pressure sensor.
These results are also nearly identical to the flight Angelfire made at
XPRS 2005 on the same motor. Those
results can be found here.
The MissileWorks altimeters
were responsible for firing the ejection charges. It appears that
the apogee charge was possibly fired a little early. A glitch in the
ARTS acceleration data indicates the apogee change was fired at about
14,678 feet while still traveling 189 mph. This was slightly before
the ARTS detected apogee on either the barometric or inertial data.
However, it is not possible to know for sure if the MissileWorks fired
early or if the ARTS detected apogee late. Visually from our
ground view the apogee deployment timing looked good but of course it was
pretty high and some what difficult to judge. This early deployment
is also exactly the same as was indicated by the data from
the flight in 2005. Therefore, I'm inclined to believe the
ARTS is probably detecting apogee a little late. If deployment was
as early as indicated on these two flights, then I would have expected to
see some signs of damage. Nether flight showed any sign of damage
from such a high speed deployment so they were probably not really going
that fast at the apogee deployment.
Maximum acceleration was
8.6 G's. Peak velocity was exactly 1000 ft/sec (682 mph). Angelfire
reached apogee in 29 seconds. After that, it descended on the drogue
chute for 2.9 minutes at 91 ft/sec and then fired the main chute
deployment charge at 1,089 feet. The back-up ejection charge was
fired at 749 feet. The main chute was very slow to get inflated but
finally did so at 110 feet. This was less than 3 seconds before
touch down. This was a very close call! Total flight time was
3 minutes and 27 seconds.
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Specific events that can be
identified have been highlighted on these plots. Maximum acceleration was
only 4.0 G's! Peak velocity was 479 ft/sec (326 mph).
Angelfire reached apogee in 21 seconds. At apogee the main parachute
was accidentally deployed. The velocity at deployment was extremely
low (-6 ft/sec) but there is a very large spike in the acceleration data
two seconds later. The spike is -12.3 G's and has a duration of only
100ms. I believe that this is the point where the tubular nylon
recovery harness ran out of slack and suddenly came tight. This
shock pulse was apparently large enough to break the nosecone shear pins
and allow the main chute to tumble out. The actual main
parachute ejection charges were seen going off on schedule as Angelfire
descended through the region of 800-1000 feet above ground.
Angelfire uses two
MissileWorks altimeters to deploy the drogue and the main parachute.
These two altimeters reported the peak altitude to be 5,529 and 5,591 feet.
As seen above the ARTS
altimeter reported the peak altitude as 5,248 feet based on the
accelerometer and 5,132 feet based on the pressure sensor. The GPS
reported the peak at 5,337 feet. Averaging all of these altitudes
together gives 5,367 feet and all the readings are within +4% to -4% of
this value.
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Maximum acceleration was
5.29 G's. Peak velocity was 771 ft/sec (526 mph). Angelfire
reached apogee in 26.7 seconds. After that, it descended on the
drogue chute for 1.5 minutes at an average of 100 ft/sec and then deployed
the main with 982 feet to go. It descended on the main chute for
38.7seconds at an average of 24.4 ft/sec. Total flight time was 2.6
minutes.
Angelfire uses two
MissileWorks altimeters to deploy the drogue and the main parachute.
These two altimeters reported the peak altitude to be 10,435 and 10,808 feet.
As seen above the ARTS
altimeter reported the peak altitude as 11,109 feet based on the
accelerometer and 9,965 feet based on the pressure sensor. The GPS
reported the peak at 10,021 feet. Averaging all of these altitudes
together gives 10,468 feet and all the readings are within +6% to -5% of
this value.
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Some interesting things can
be seen in this flight data. The two MissileWorks altimeters
reported the peak altitude to be 15,198 and 15,461 feet. The ARTS
altimeter reported the peak altitude as 15,351 feet based on the
accelerometer and 14,830 feet based on the pressure sensor. These
readings are all very close. The largest difference is only 4.3%.
The MissileWorks altimeters were responsible for firing the ejection
charges. It appears that the apogee charge was possibly fired a
little early. A glitch in the ARTS acceleration data indicates the
apogee change was fired at about 14,589 feet. Slightly before the
ARTS detected apogee on either the barometric or inertial data. However,
it is not possible to know for sure if the MissileWorks fired early or if
the ARTS detected apogee late.
The acceleration data shows
a small event at about 5.7 seconds into the motor burn.
Interestingly enough, the published thrust curve for the M1939 also shows
a hint of this same event. Apparently something happens as the motor
nears burnout.
This can be seen in page 5 of the flight data. Motor burnout
occurred at 3,400 feet.
Maximum acceleration was
6.9 G's. Peak velocity was 985 ft/sec (672 mph). Angelfire
reached apogee in 32 seconds. After that, it descended on the drogue
chute for 2.1 minutes and then deployed the main at about 1000 feet.
It descended on the main chute for 40 seconds. Total flight time was
3.3 minutes.
The drogue chute descent
rate was 114 ft/sec. The main chute ejection charge fired at 1000
feet so Angelfire was within 8.8 seconds of hitting the ground if the main
had not been deployed. The main was not fully inflated until
Angelfire reached about 840 feet. The main chute descent rate was
21.5 ft/sec and Angelfire only spent 40 seconds on the main until it
touched down.
One MissileWorks altimeter
was set to fire the main chute at 1000 feet and the other was set for 800
feet. Both events can be seen in the acceleration data from
the ARTS altimeter. The ARTS showed the events occurring very close
to 1000 feet and 800 feet, as expected. |
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