Gyroscope Artificial Horizons
The Autocontrol's artificial horizon (AH) has been overhauled by Aircraft Quality Instruments (Witchitaw, Kansas) and installed in the aircraft and it makes a startling difference. The comparison between the original 50 year old and never serviced AN-style AH that was in the aircraft and the new one is interesting.
Spin down. The old AH would immediately flop over once the engine stopped. The overhauled AH will hold its position for a few minutes after shutdown.
Initial reference. The old AH would smoothly and without oscillating (or nutation) erect to the horizon once there was some vacuum. The overhauled one displays nutation as soon as the engine starts and resolves on the horizon within a few minutes.
Fast Erection. The old AH would begin correcting to the horizon immediately during a turn and would, in space of a 360 rate one turn, indicate that the aircraft was almost level. The new one shows no error that can be seen when rolling out.
This behavior is all consistent with the old AH having bearings with too much rolling resistance. Air passing through the vanes on the rotor causes a force that spins the rotor. Poor bearings means the rotor spins slowly and new ones mean the rotor spins quickly.
The pendulums on the bottom of the gyroscope protrude into the exhausting air and put a force on the rotor to line it up with the perceived force of gravity. The amount of force is dependent on the degree of error and the amount of air.
The behavior during spin down is explained by the old AH not rotating very fast. The new one holds its position longer after shutdown because the smooth bearings take much longer to slow the rotor to a stop. The old one wasn't spinning very fast to begin with and has stickier bearings slowing it down faster.
The initial lack of nutation on the old AH was due to the rotor taking a long time to spin up and not reaching full speed in any case. Thus the erecting forces are larger relative to the rotor's inertia and can easily overcome the rotor's rigidity in space. The overhauled AH spins up quickly and this means the erecting forces oscillate back and forth until eventually settling down.
The fast erection is similar to the lack of nutation. The old AH's rotor was not spinning very fast and had low inertia. Thus, in a coordinated turn, the erection mechanism was able to overpower it and attempt to erect the horizon to the perceived gravitational reference, straight through the floor of the aircraft. The overhauled AH's rotor is spinning much faster and thus would take much longer to be erected.
It satisfying to understand a bit more about how these instruments work and to have confidence in the ones that are installed. Also, the Autocontrol works much better.
Spin down. The old AH would immediately flop over once the engine stopped. The overhauled AH will hold its position for a few minutes after shutdown.
Initial reference. The old AH would smoothly and without oscillating (or nutation) erect to the horizon once there was some vacuum. The overhauled one displays nutation as soon as the engine starts and resolves on the horizon within a few minutes.
Fast Erection. The old AH would begin correcting to the horizon immediately during a turn and would, in space of a 360 rate one turn, indicate that the aircraft was almost level. The new one shows no error that can be seen when rolling out.
This behavior is all consistent with the old AH having bearings with too much rolling resistance. Air passing through the vanes on the rotor causes a force that spins the rotor. Poor bearings means the rotor spins slowly and new ones mean the rotor spins quickly.
The pendulums on the bottom of the gyroscope protrude into the exhausting air and put a force on the rotor to line it up with the perceived force of gravity. The amount of force is dependent on the degree of error and the amount of air.
The behavior during spin down is explained by the old AH not rotating very fast. The new one holds its position longer after shutdown because the smooth bearings take much longer to slow the rotor to a stop. The old one wasn't spinning very fast to begin with and has stickier bearings slowing it down faster.
The initial lack of nutation on the old AH was due to the rotor taking a long time to spin up and not reaching full speed in any case. Thus the erecting forces are larger relative to the rotor's inertia and can easily overcome the rotor's rigidity in space. The overhauled AH spins up quickly and this means the erecting forces oscillate back and forth until eventually settling down.
The fast erection is similar to the lack of nutation. The old AH's rotor was not spinning very fast and had low inertia. Thus, in a coordinated turn, the erection mechanism was able to overpower it and attempt to erect the horizon to the perceived gravitational reference, straight through the floor of the aircraft. The overhauled AH's rotor is spinning much faster and thus would take much longer to be erected.
It satisfying to understand a bit more about how these instruments work and to have confidence in the ones that are installed. Also, the Autocontrol works much better.
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