From: lc2b+@andrew.cmu.edu (Lawrence Curcio)
Newsgroups: rec.models.rockets
Subject: Altitude Test (Long)
Date: 8 Sep 92 03:31:15 GMT
Organization: Doctoral student, Urban and Public Affairs, Carnegie Mellon, Pittsburgh, PA

I tried comparing altitudes measured by the 3-observer method with
altitudes measured by temporal backtracking. In the latter method,
ascent times are measured and a RASP program is used to find
corresponding altitudes and drag coefficients. 

I had previously tried comparing these methods, using the 1-
observer method, and I got pretty bad results. Shortly after I
posted these, I discovered that my launch masses, measured on a
postal scale, were way off. They were lower than catalog masses,
and these rockets were heavily painted. By the time I found this
out, the person who owned the rockets went on an extended vacation.
After I re-weighed the rockets on a good scale, the results were
encouraging:

ESTES RAVEN
LAUNCH MASS: 104 GRAMS (80 GRAMS W/O ENGINE)
PROPELLANT MASS: 12.48 GRAMS
IMPULSE: 8.89 NS
BURNING TIME: 1.735 SECONDS
BODY DIAMETER: 4.16 CM
ASCENT TIME: 5.4 SECONDS
OPTICAL ANGLE: 70 DEGREES
OPTICAL ALTITUDE: 453 FEET
TEMPORAL ALTITUDE: 452 FEET
TEMPORAL Cd: .8766
% ERROR FROM OPTICAL: 0.22%

ESTES MAGNUM FLIGHT 1
LAUNCH MASS: 131 GRAMS (107 GRAMS W/O ENGINE)
PROPELLANT MASS: 12.48 GRAMS
IMPULSE: 8.89 NS
BURNING TIME: 1.735 SECONDS
BODY DIAMETER: 4.16 CM
ASCENT TIME: 4.78 SECONDS          FLIGHT 1
OPTICAL ANGLE: 57 DEGREES
OPTICAL ALTITUDE: 262 FEET
TEMPORAL ALTITUDE: 313 FEET
TEMPORAL Cd: 1.3649
% ERROR FROM OPTICAL: -19.47

ASCENT TIME: 5.4 SECONDS           FLIGHT 2
OPTICAL ANGLE: NOT MEASURED
OPTICAL ALTITUDE: NA
TEMPORAL ALTITUDE: 390 FEET
TEMPORAL Cd: .7507
% ERROR FROM OPTICAL: NA

ESTES METEOR
LAUNCH MASS: 70.1 GRAMS (50 GRAMS W/O ENGINE)
PROPELLANT MASS: 6.24 GRAMS
IMPULSE: 4.35 NS
BURNING TIME: 0.795 SECONDS
BODY DIAMETER: 3.37 CM
ASCENT TIME: 4.56 SECONDS
OPTICAL ANGLE: 61 DEGREES
OPTICAL ALTITUDE: 306 FEET
TEMPORAL ALTITUDE: 341 FEET
TEMPORAL Cd: .7222639
% ERROR FROM OPTICAL: -11.44%

(My impulse values came from sample thrust curves. Using 8.52 and
4.45, old NAR impulses, results are comparable, and the total RMS
error from optical is 11.8%)

This time out, I used the ESTES SKYHAWK and CHEROKEE upper stage.
My rockets were trimmed better than the ones in the previous
experiment. The paint was smoother, and the fins were more
streamlined. My skyhawk weighed 122 grams, 10 grams less than the
MAGNUM, and was otherwise comparable, yet its ascent times were
significantly shorter. The Cherokee weighed 68 grams, less than the
METEOR, and was only 2.5 cm in diameter, yet its measured times
were a good half-second shorter than those for the METEOR. **
Temporal altitudes averaged about half of the optically-measured
altitudes in this experiment.** In my judgement, the temporal
altitudes were low. Not only did the optical altitudes look about
right, the optical tracking procedures gave values for the
horizontal coordinates of the rocket at apogee, that corresponded
roughly to those of the launch pad. 

Ascent times were measured by 2 timers, and we were usually less
than 0.25 seconds apart. We judged apogee as the moment when the
rocket, which we took to be ascending vertically, cocked ever-so-
slightly. (The day was overcast, and there were no good visual cues
for apogee.) If the rocket were slightly off-vertical, then the
proper time would have been the moment when the rocket was
horizontal. Since the wind was blowing about 15 mph at ground
level, this may well have been the appropriate moment in this test
(Weathercocking). Indeed, I accidentally timed this moment on one
flight (oddly, the second timer missed this one as well, and the
optical data didn't converge), and the corresponding altitude was
comparable to the optical altitudes for the other flights. This was
a full second longer than average for the SKYHAWK. In that second,
the rocket likely travelled very little, so the optical altitudes
were OK, within experimental error. The omission of that second
made a large difference in the temporal estimate. 

If the data we took are good, then simple RASP programs do not work
at all. This result would be significant in itself, but the results
of the pilot experiment make me suspect otherwise. I have to
experiment further with the timing procedure before I draw any
conclusions. That will be a while. We lost both rockets to wind and
trees.

I did learn a little about the 3-observer method (see accompanying
post). Also, I found that the B6-4 engines were actually B6-3's. 

Regards,
-Larry C.
Newsgroups: rec.models.rockets