PDA

View Full Version : 747-200 beta vane?


levelvibes
5th Jan 2008, 15:40
Hi there.

Can anyone tell me what the little vane on a 747-100/-200 in front of the nose gear is? It looks just like an alpha vane, only at the bottom of the fuselage.

Thanks

Jetdoc
5th Jan 2008, 18:40
Some details from the B747 AMM

Gust Response Supression System
NOTE: After incorporation of SB 22-2176, the BETA system is deactivated.
The GRS computer, the GRS control panel, the lateral accelerometer and
the side slip angle sensor are removed. The circuit breaker BETA VANE
HTR on the P7 panel is collared in the open position.
A. The gust response suppression (GRS) system reduces airplane dutch roll induced by lateral wind gusts. The system operates through the upper
yaw damper computer (22-16-00) to drive the upper rudder in a direction
which increases dutch roll damping. This is accomplished by sensing
airplane sideslip angle (beta) and subtracting computed maneuverinduced
sideslip angle; the signal is suitably filtered and connected
to the upper yaw damper computer where it is summed with normal yaw
damping signals in the yaw damper computer.
B. The system consists of the following components (Fig. 1).
(1) One gust response suppression computer installed on shelf E1-4 of
the main electronic equipment rack.
(2) One sideslip angle sensor installed on the bottom centerline of the
fuselage ahead of the nose wheel well.
(3) One lateral accelerometer installed adjacent to the sideslip angle
sensor.
(4) One control panel installed on overhead panel P5.
C. In addition to the above components, analog signals and discrete logic
signals are also used from other systems. Yaw rate and roll attitude
analog signals are obtained from the upper yaw damper computer. True
airspeed analog signals are obtained from CADC No. 1 (34-12-00). INS
valid logic (34-41-00) is obtained from INS No. 1. Oleo switch position
(airplane on ground) and trailing edge flap switch position (flaps up)
complete 28 volts dc valid signals to the GRS computer logic circuits.
A NOT ENGAGED light and a GRS system control switch (BETA) are on the
control panel. The system is engaged whenever all logic valids are
available, the flaps are up and the system control switch (BETA) is
positioned to ON. The light illuminates if a logic valid or system
power fails when the system is on.

levelvibes
6th Jan 2008, 03:12
Thatīs the answer I was looking for and the first one that makes perfect sense. Thank you.