As the servo valve corrects the altitude error
open-loop spring also allows the barometric
signal through the auxiliary power piston and
altitude control to make a larger than 10 percent
rotary wing blades, the altitude error signal
correction over a period of time. The pilot may
diminishes. When the helicopter returns to the
override open-loop operation by applying an
engaged altitude, the altitude control output error
opposing force on the collective stick. As the
signal returns to null. However, as the servo valve
altitude error signal diminishes, the position
corrects the altitude error signal, it places the
sensor signal returns the collective pitch control
collective servo system in an open-loop condition.
stick to the engaged altitude position. While BAR
ALT is on, the pilot applies collective and
The open-loop spring and a balance spring
depresses the BAR REL button on the collective
support the collective stick and linkage weight so
stick grip momentarily to change altitude. The
the stick retains the desired position. The stick
collective clutch nulls the output of the position
should remain in this position with little or no
sensor and the barometric altitude input while the
external force applied to hold the stick. The
BAR REL button is depressed.
Figure 8-50.-ASE/coupler collective channel.
8-49