gismo
Touchdown! Greaser!
I just finished a long conversation with an engineer at Castleberry (makers of the electric AI in my airplane) about this subject. He told me a few things I didn't know that I thought I'd pass on for those interested in such things.
One is that the gyro axis is purposely tilted 2-/12 degrees from vertical when the plane is level (I assume this really means the panel is vertical or at the 8 degree tilt depending on the model of gyro). This is done to compensate for the precession induced pitch error that would occur when the airplane turns 180 degrees. They actually test for this at the factory by putting each gyro on a turntable and rotating it 180 degrees (while running) in 10 seconds and looking for a 5 degree nose down indication immediately after the 180 degree rotation.
He also told me that the TSO for attitude indicators (which was last updated in the 50's) includes a requirement that there be no more than 3 degrees of pitch error after a 180 degree standard rate turn at 180 mph.
All of this came up because I noticed that my relatively new electric AI indicated about 5 degrees of nose down pitch part way around a steep turn. The person I chatted with wasn't able to say whether or not this was normal, but it's not something I've ever noticed before and the vacuum powered gyro in my airplane didn't seem to exhibit anywhere near as much pitch change. I am aware of the characteristic of AIs that manifests itself in a change in the roll indication when you make a turn of less than 180 degrees and then roll to wings level, but this was a significant pitch error during the first half of a 360.
Anyone interested in checking this out in their airplane? I'd like to know how common this type of error (a pitch error of several degrees during a level, coordinated steep turn). I think I was flying at something like 160 KTAS and the speed might be a factor.
One is that the gyro axis is purposely tilted 2-/12 degrees from vertical when the plane is level (I assume this really means the panel is vertical or at the 8 degree tilt depending on the model of gyro). This is done to compensate for the precession induced pitch error that would occur when the airplane turns 180 degrees. They actually test for this at the factory by putting each gyro on a turntable and rotating it 180 degrees (while running) in 10 seconds and looking for a 5 degree nose down indication immediately after the 180 degree rotation.
He also told me that the TSO for attitude indicators (which was last updated in the 50's) includes a requirement that there be no more than 3 degrees of pitch error after a 180 degree standard rate turn at 180 mph.
All of this came up because I noticed that my relatively new electric AI indicated about 5 degrees of nose down pitch part way around a steep turn. The person I chatted with wasn't able to say whether or not this was normal, but it's not something I've ever noticed before and the vacuum powered gyro in my airplane didn't seem to exhibit anywhere near as much pitch change. I am aware of the characteristic of AIs that manifests itself in a change in the roll indication when you make a turn of less than 180 degrees and then roll to wings level, but this was a significant pitch error during the first half of a 360.
Anyone interested in checking this out in their airplane? I'd like to know how common this type of error (a pitch error of several degrees during a level, coordinated steep turn). I think I was flying at something like 160 KTAS and the speed might be a factor.
