[ Concept 60 in the sky ]

hudson.20020818.01


Pilot: Aaron Kahn
Curator: Trammell Hudson
Location: Charles County RC Field
Equipment: Concept 60
Board level: Rev 2.2 with CVS head as of 2002-08-18



[ Calibration of the sensors ] [ Yaw calibration graph ] First step was to calibrate the accelerometers. Roll knife edge left, knife edge right, nose down, nose up then back to level. Next we held the rotor head and spun the aircraft 360 degrees clockwise.

[ Sensor data up through a lift off ] An uneventful liftoff. Notice the yaw wagging -- the ball bearing gyro was not very well attached to the airframe. Engine vibration transmitted to its housing would cause it to wobble, leading to anti-torque inputs.

[ Pitch doublet ] Aaron performs a pitch doublet of increasing frequency.

[ Roll doublet ] Followed by a roll doublet of increasing frequency. Note the cross roll/pitch coupling visible in the gyro data. It is odd that the accelerometers do not show more visible rolling during the low frequency segment.

[ 20 second pirouette ] In this graph, Aaron held the aircraft in a constant rate clockwise pirouette for roughly 10 seconds. The estimated rate of turn was 60 deg/sec. Note the large noise level in the accelerometer data.

[ 40 second pirouette ] Now Aaron holds the aircraft in a constant rate clockwise pirouette for roughly 40 seconds. The estimated rate of turn was 100 deg/sec. Note the constant cyclic commands required to hold the helicopter in one point over the ground. At some point during the flight the tail rotor pitch control slider broke; we're not sure when this happened and are still trying to identify it in the yaw noise.

[ Comparison of pitch vibration ] It is difficult to compare the noise levels in the previous two graphs, so I have extracted 10 seconds of pitch accelerometer data from each and combined them on this plot. You can clearly see that the three zipties used to hold the radio tray to the airframe's keel made an enormous difference in the noise. Without the canopy installed, we could see the tray vibrating quite a bit.

[ Autorotation to the ground ] On the last flight of the day, Aaron flew until we were out of fuel. We should have noticed the vibration noise levels reduced in the accelerometer data, but due to other factors (blade balance, etc) we did not. Unfortunately, the helicopter had its forward velocity arrested suddenly and might have damanged the pitch accelerometer. You can see its sensor reading become invalid after the touchdown. The other sensors settle down as usual.

I've traced the problem to a broken resistor. Due to the way I had strapped the Rev 2.2 board to the airframe, the shock snapped a resistor lead that had been bent too tightly. I'll have to resolder it tonight.
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