I was wrong...
First, a bit about the flight. Probe-18 was launched in light winds on a B6-4 motor. The field was a fairly flat sod farm, with no significant rises or dips in the terrain. The rocket flew straight, with only a slight of amount of turning into the wind, and looked to have achieved an altitude of a few hundred feet. The parachute fully deployed and the rocket descended slowly; the ejection charge fired on time, though it sounded loud, indicating perhaps a bit too much powder (i.e., a "shotgun" ejection charge). After recovery, the body tube near one fin was observed to have failed, and the fin was chipped at the leading edge. Further inspection revealed a deep gash in the balsa coupler at the bottom of the payload section, suggesting that it had snapped back into the rocket at ejection, hitting the top of the fin; the force of the impact caused the body tube to fail near the fin root.
|Probe-18 damage (Click to enlarge).|
|Probe-18 payload section layout (Click to enlarge).|
|Probe-18 altitude profile recorded by the Perfectflite PNUT (Click to enlarge).|
|Probe-18 altitude profile recorded by the Altus Metrum MicroPeak (Click to enlarge).|
|A "normal" PNUT altitude profile - that of Nemesis at the same launch (Click to enlarge).|
|Altimeter profile comparison (Click to enlarge).|
Whether it was a mistake on my part or not, this experience gives me a bit less confidence in electronic altimeters. By looking at the PNUT data, I was able to see something was fishy, and even derive the "correct" peak altitude by adjusting the zero point. But in evaluating a TARC flight, we are allowed to only use the altitude beeped or flashed by the altimeter when it is returned to the observer; no analysis of downloaded data can be used to adjust the score. How often do the altimeters beep out a wrong value?
It makes one want to fly a second altimeter as a check. But that adds weight.