Bryan Duke <[email protected]> writes: > Hello List- > > I flew a rocket a few days ago in search of the J altitude record. The > rocket teleported off the pad & quickly got to over 3000ft/s. Very > quickly after that, the telemetry reported the drogue firing (at > around 10k ft) and then the rocket peaked a few thousand feet > later. The accel data show a deceleration momentarily maxing out the G > meter. So, about a 100G accel followed by a 100G decel. Ouch.
Ouch indeed. It looks like you were just shy of maxing the accelerometer, which is an impressive feat. > I’m still trying to figure out exactly what happened. I think the > motor made it all the way through burnout, then some “event” > happened. I think the pressure curve is probably the most interesting part. At about 0.8 seconds after boost, the pressure starts *dropping* rapidly, then "something" happens, which generates a tremendous amount of noise on both pressure and acceleration curves, then at about 1.8 seconds, things return to "normal" and the flight carries on with what looks like a completely nominal decelleration curve (starting at about 10g, then tapering down to 1g as the speed decreases). > The rocket and all the recovery gear are still in great > shape, so it’s tough to point a finger at anything from just looking > at the rocket. Can I please get some thoughts on what happened based > on the data? Is the “drogue” callout on the flight replay matched to > the TeleMetrum firing the drogue? If so, why did it fire it so early? I don't see it firing early; looks like it's right on top at 24 seconds. > I’m definitely not ruling out the rocket tumbling, but the motor > exhaust looked straight until we couldn’t see it any more. It definitely didn't tumble -- it would have come apart and then the rest of the trip to apogee wouldn't have looked clean. > FWIW, this was the first flight on a new TeleMetrum. The telemetry > page showed that v1.8.5 is loaded. I’ve flown an EasyMini before to > about Mach 2, but not a TeleMetrum and not anything approaching Mach > 3. This was the maiden flight on this rocket. The chute was in the > nosecone & that’s the only thing that gets ejected (single chute at > apogee was the plan). My drag & decel calcs show that the nosecone > should have plenty force holding in place throughout the flight. It > was a fairly tight fit and held on by a single 0.060” styrene rod as a > shear pin. I’m not ruling out a drag separation either. There's no way the rocket came apart or did anything 'weird' externally; it wouldn't have been aerodynamic enough to survive to apogee at 12600'. There's clearly something 'weird' going on with the pressure data. Are the static ports in a nice smooth part of the airframe, far back from any edges or diameter changes? If I were guessing, I'd guess that there's something evacuating the ebay, and that eventually that caused some turbulence, which generated enough drag to slow the airframe down rapidly, but not enough to tear it apart. The fact that it happened after motor burn-out makes me kinda wonder if there's some air leakage around the base of the rocket (which seems odd for a min-diameter airframe). Imagine the sudden low-pressure area pulling air from inside the airframe. That doesn't explain how the pressure returned to normal a second later though. That's one weird data set, that's for sure. -- -keith
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