elevator. Flap position is detected by the use of
appearance of various controls of this type varies,
a flap position transmitter.
depending upon the manufacturer; however, the
working parts are similar. Figure 8-22, view B,
The flap position transmitter consists of two
shows the internal parts of a barometric altitude
synchro transmitters with a single input shaft
control, and view C shows a simplified mechanical
(fig. 8-23). The synchro transmitters supply flap
schematic.
position information to the AFCS elevator
channel and the external flap position indicator.
The aneroid consists of two diaphragms sealed
internally at standard (sea level) barometric
pressure. The two diaphragms connect in tandem
ACCELEROMETER TRANSMITTER. --The
to a single pushrod, and are mounted in an airtight
normal accelerometer (fig. 8-24, view A) generates
case (fig. 8-22, view B). A tube connects the case
a signal proportional to normal vertical accelera-
to a source of static air pressure. The diaphragm
tion. This signal is used for altitude or Mach hold
pushrod mechanically links to one of the clutch
vertical path damping and as the g-command
plates. This linkage consisting of a lever, a pivoted
reference. The unit consists of a cast housing
shaft to which a sector gear is attached, and a
assembly, a sensitive element assembly, bellows,
pinion gear.
and calibration resistors (R51, R52, and R53). The
When the aircraft deviates from the baro-
sensitive element assembly has an E pickoff, an
metric pressure altitude to which the altitude
armature and armature support, flexure springs,
control switch is set, the aneroid diaphragms
and a backplate.
move. This motion is transmitted through the
When assembled, the sensitive element
linkage to displace the rotor of the synchro
assembly and bellows are sealed inside the
transmitter. This displacement generates a signal
housing, which is filled with damping fluid. The
in the synchro transmitter stator. The signal is
metal bellows allow the volume of the damping
applied to the elevator channel to return the
fluid to change with temperature and pressure
aircraft to the pressure altitude indicated by the
variations. The damping fluid provides viscous
aneroid. When the aircraft reaches the correct
damping during motion of the armature.
altitude, the synchro transmitter signal becomes
The sensitive element is mechanically biased
zero, and normal AFCS operation resumes.
to produce zero output when mounted in the
When the altitude control switch is off, the
correct position and subjected to the normal
magnetic clutch and the centering device actuating
gravity force of 1 g.
coil de-energizes. This opens the clutch to
disengage the synchro transmitter rotor from the
aneroid mechanism. The centering yoke, by spring
action, closes on the synchro transmitter rotor
shaft lever to return the rotor to the null
or no-signal position. In this way, the synchro
transmitter rotor is always at the no-signal
position when altitude control is not selected.
Since the clutch is disengaged, the aneroid is free
to move. This allows the pilot to engage the
altitude control at any time. Regardless of the
aneroid position, the altitude that it senses
is the one used as the reference altitude. It
is not necessary to wait for synchronization or
alignment.
FLAP POSITION INFORMATION. --When
the flaps are lowered on some aircraft, the
increased lift causes the aircraft to gain altitude
(normally called ballooning). Ballooning is
undesirable, and it is counteracted by using
nosedown pressure on the flight control. When
the AFCS is engaged and the flaps are lowered,
Figure 8-23.-Flap position transmitter and schematic.
automatic nosedown force is applied to the
8-20
