Keith, Thanks for the quick reply. Yeah, weird for sure.
The static ports are about 2” behind the nosecone. For 38mm rockets, this has worked well for me before. That said, this nosecone isn’t a super tight fit with the coupler. Since I have the coupler attached to my airframe and the avionics share the same air as the nosecone (baffled, but not sealed between the avionics in the coupler and the chute in the nosecone), maybe that increased nosecone-to-coupler gap is causing some vacuum. Maybe there’s a shock forming at the nosecone joint and that’s causing trouble. I’m still running 1.8.5 on it. It worked for me before, so I didn’t want to change anything. Just to make sure - 1.8.5 is fine to run, right? Thanks for the thoughts. I’ll keep digging. Bryan > On May 28, 2022, at 12:55 PM, Keith Packard <kei...@keithp.com> wrote: > > Bryan Duke <br...@thedukes.org> writes: > >> Hey everybody. I’m did a record attempt flight this morning and it looks >> like I got an ejection firing while the rocket was still going over 800ft/s. >> The pressure graph looks really strange. >> >> This flight was planned as a single deploy (redundant apogee set, but >> only 1 charge). I’ve flown a similar rocket with the same static >> port/vent config, the same TeleMetrum and nearly the same flight >> profile before. Does anyone have any ideas as to what could be going >> on? > > Whoa, that's weird looking. Given that it looks like the odd baro data > occurs only above mach 1, I'd bet you've got some weird aerodynamic > effect from the airframe, likely some kind of hole in an area of > changing pressure or diameter. > > We've seen this a few times on airframes where the static port was in > the nose, but in those cases the pressure was *over* estimated, while in > this flight the pressure is *under* estimated. > > I wonder if there's some hole in an area of low pressure which is > generating a partial vacuum inside the airframe at high speed? > > The firmware used to ignore the baro sensor when the speed was above > mach 1, but that turned out to cause more problems than it solved on > airframes with clean static port configurations, so we now include > the baro sensor data at all speeds, but the error values for baro values > above mach 1 are greatly increased so it has much less effect on the > model. > > Even still, a persistent offset error in pressure, as in your flight, > will slowly push the model estimates far from reality, and when the > airframe slows below mach 1 again, the increased reliance on the baro > sensor data can cause it to slew the vertical speed through zero more > rapidly than it should, leading to an inaccurate estimate of apogee. > > I don't suspect that the baro sensor is damaged in this case; the > pressure values when subsonic are too clean looking. > > -- > -keith _______________________________________________ altusmetrum mailing list -- altusmetrum@lists.gag.com To unsubscribe send an email to altusmetrum-le...@lists.gag.com
