On Thu, 2009-04-23 at 12:50 -0700, rq1...@q7.com wrote: > I didn't go back and look, but iirc, psas flight data has the same > pressure glitch at motor burn-out. Previously we have attributed the > glitch to changes in the pressure field over the vehicle surface due to > the presence or absence of motor plume.
Yeah, we're not sure what's causing this, but we do know that this particular airframe has a bad seal between the lower recovery bay and the avionics -- the other altimeter showed a huge spike downwards at apogee caused by the recovery charge leaking into the avionics bay. > This explanation may be wrong. In particular at supersonic velocities > motor plume cannot effect the pressure field on the forward part of the > vehicle. Perhaps motor exhaust is somehow leaking into the interior of > the airframe and pressurizing the entire structure? If that were the > case then running a hunk of tubing from the pressure sensor directly to > the outside would eliminate the effect. This rocket did not fly above mach 1, the highest recorded velocity was about 170m/s. We'll see if this same artifact occurs in other vehicles. > The (calibrated) pressure sensor is probably more accurate in > determining altitude at apogee than the accelerometer. Yeah, for differential altitude, the pressure sensor is pretty good. Of course, we get a lot of noise with our sensor as it is very sensitive to vibration. > You could rescale > the filtered accelerometer data to match the pressure determined apogee. > That should provide a better calibrated view of the burn-out pressure > glitch. At this point, I mostly want to collect a lot more data; having the same electronics flown in a lot of different configurations should show us most of the variations in data. > I'm a little confused as to why all the accelerations are positive. Even > accepting that the acceleration on the pad reads as +1 gee it really > seems like the initial post-burn-out acceleration should be negative. The scales on that plot weren't ideal; I've re-plotted the data and set the pad acceleration to zero. With that graph, the minimum acceleration is about -1.7g. As this rocket only flew to 170m/s, .7g of drag doesn't seem unreasonable to me. -- keith.pack...@intel.com
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