737 Yoke Part1

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Boeing 737-800NG Yoke

Part 1

Part 2

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Pilot Controls:

• two control columns
• two control wheels
• two pairs of rudder pedals
• SPEED BRAKE lever
• FLAP lever
• STAB TRIM cutout switches
• STAB TRIM override switch
• stabilizer trim switches
• stabilizer trim wheel
• AILERON trim switches
• RUDDER trim control
• YAW DAMPER switch
• ALTERNATE FLAPS master
switch
• alternate flaps position switch
• FLT CONTROL switches
• flight SPOILER switches

The columns and wheels are connected through 
transfer  mechanisms which allow the pilots to
bypass a jammed control or surface.
There is a rigid connection between both pairs 
of rudder pedals. The SPEED BRAKE lever allows 
manual or automatic symmetric actuation of the
spoilers.

Roll Control

The roll control surfaces consist of hydraulically
powered ailerons and flight spoilers, which are
controlled by rotating either control wheel.

Ailerons

The ailerons provide roll control around the
airplane’s longitudinal axis. The ailerons are positioned
by the pilots' control wheels. The A and B
FLT CONTROL switches control hydraulic shutoff valves.
These valves can be used to isolate each aileron, as well
as the elevators and rudder, from related hydraulic system
pressure. The Captain’s control wheel is connected by cables
to the aileron power control units (PCUs) through the aileron feel
and centering unit. The First Officer’s control wheel is connected
by cables to the spoiler PCUs through the spoiler mixer.
The two control wheels are connected by a cable drive system
which allows actuation of both ailerons and spoilers by either
control wheel. With total hydraulic power failure the ailerons can be
mechanically positioned by rotating the pilots' control wheels.
Control forces are higher due to friction and
aerodynamic loads.

Aileron Transfer Mechanism

If the ailerons or spoilers are jammed, force applied to

the Captain’s and the First Officer’s control wheels will identify 

which system, ailerons or spoilers, is usable and which control 

wheel, Captain’s or First Officer’s, can provide roll control. If

the aileron control system is jammed, force applied to the 

First Officer’s control wheel provides roll control from the spoilers. 

The ailerons and the Captain’s control wheel are inoperative.

If the spoiler system is jammed, force applied to the

Captain’s control wheel provides roll control from the ailerons.

The spoilers and the First Officer’s control wheel are inoperative.

Aileron Trim

Dual AILERON trim switches, located on the aft electronic 

panel, must be pushed simultaneously to command trim changes. 

The trim electrically repositions the aileron feel and centering unit, 

which causes the control wheel to rotate and redefines the 

aileron neutral position. The amount of aileron trim is indicated on

a scale on the top of each control column. If aileron trim is used 

with the autopilot engaged, the trim is not reflected in the

control wheel position. The autopilot overpowers the trim and 

holds the control wheel where it is required for heading/track 

control. Any aileron trim applied when the autopilot is engaged can 

result in an out of trim condition and an abrupt

rolling movement when the autopilot is disconnected.

Flight Spoilers

Four flight spoilers are located on the upper surface of each

wing. Each hydraulic system, A and B, is dedicated to a different

set of spoiler pairs to provide isolation and maintain symmetric 

operation in the event of hydraulic system failure.

Hydraulic pressure shutoff valves are controlled by the two 

flight SPOILER switches. Flight spoiler panels are used as speed brakes to

increase drag and reduce lift, both in flight and on the ground. The flight

spoilers also supplement roll control in response to control wheel commands.

A spoiler mixer, connected to the aileron cable-drive, controls the 

hydraulic power control units on each spoiler panel to

provide spoiler movement proportional to aileron movement.

The flight spoilers rise on the wing with up aileron and remain faired 

on the wing with down aileron. When the control wheel is displaced 

more than approximately 10°, spoiler deflection is initiated.

Pitch Control

The pitch control surfaces consist of hydraulically powered 

elevators and an electrically powered stabilizer. The elevators are 

controlled by forward or aft movement of the control column. The stabilizer is 

controlled by autopilot trim or manual trim.

Elevators

The elevators provide pitch control around the airplane’s 

lateral axis. The elevators are positioned by the pilots’ control 

columns. The A and B FLT CONTROL switches control hydraulic 

shutoff valves for the elevators. Cables connect the pilots’ 

control columns to elevator power control units (PCUs)

which are powered by hydraulic system A and B.

The elevators are interconnected by a torque tube. With loss of 

hydraulic system A and B the elevators can be

mechanically positioned by forward or aft movement of the 

pilots’ control columns. Control forces are higher due to friction and 

aerodynamic loads. Elevator Control Column Override Mechanism

In the event of a control column jam, an override mechanism allows the control

columns to be physically separated. Applying force against the jam will breakout

either the Captain’s or First Officer’s control column. Whichever column moves

freely after the breakout can provide adequate elevator control.

Although total available elevator travel is significantly reduced, there is sufficient

elevator travel available for landing flare. Column forces are higher and exceed

those experienced during manual reversion. If the jam exists during the landing

phase, higher forces are required to generate sufficient elevator control to flare for

landing. Stabilizer trim is available to counteract the sustained control column force.

Elevator Feel System

The elevator feel computer provides simulated aerodynamic forces using airspeed

(from the elevator pitot system) and stabilizer position. Feel is transmitted to the

control columns by the elevator feel and centering unit. To operate the feel system

the elevator feel computer uses either hydraulic system A or B pressure,

whichever is higher. When either hydraulic system or elevator feel pitot system

fails, excessive differential hydraulic pressure is sensed in the elevator feel

computer and the FEEL DIFF PRESS light illuminates.

Der Linke Schalter dient als "Sicherungs-Schalter".
Er muss zusammen mit dem rechten Trim-Schalter 
betätigt werden. F/O-Side ist es anders rum.

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Auszug aus Wikipedia ( Englisch)

Principle

The aviator uses the yoke to control the attitude of the plane, usually in both pitch and roll. Rotating the control wheel controls the ailerons and the roll axis. Fore and aft movement of the control column controls the elevator and the pitch axis.^[1]
Small to medium sized aircraft, usually limited to propeller driven, feature a mechanical system whereby the yoke is connected directly to the control surfaces with cables and rods. Human muscle power alone is not enough for larger and more powerful aircraft, so hydraulic systems are used, where yoke movements control hydraulic valves and actuators. In more modern aircraft, inputs may be first be sent to a fly-by-wire system, which then sends a corresponding signal to actuators attached to the control surfaces. Yokes may feature a stick shaker which is designed to help indicate the onset of stall, or even a stick pusher which assists in stall recovery.^{[citation needed]}

Styles

This section does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (May 2010)

Yokes come in a variety of shapes and sizes, the most common being of a "U" or "W" design. Some aircraft use an "M" style, such as Embraer and Concorde. There are some rarer exotic or archaic styles, such as circular designs much like a steering wheel.
In larger aircraft they are usually mounted on a post protruding vertically from the floor, referred to as a control column. In most other planes they are mounted on a horizontal tube which comes out of the instrument panel.

[edit] Advantages and disadvantages

Side-sticks and joysticks are better for making rapid control inputs and dealing with high g-forces, hence their use in military, sport and aerobatic aircraft. However, yokes are less sensitive thanks to a larger range of motion and provide more visual feedback to the pilot.^[2]
Yokes take up more room than sidesticks in the cockpit, and may even obscure some instruments; by comparison side-sticks have minimal cockpit intrusion, allowing for the inclusion of retractable tray-tables.^[3][4]
A yoke, unlike a side-stick, may be used comfortably with either hand. This can be useful if one needs to write or manipulate other controls in the cockpit. This advantage is shared with the centre-stick ^[5].

[edit] Ancillary functions

The yoke often incorporates other key functions such as housing thumb or finger buttons to enable the radio microphone, disengage the autopilot and trim the aircraft. Additionally there may be a clipboard, checklist or chronometer located in the yoke's centre.^[6][7][8][9]

[edit] Alternative control systems

This section does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (May 2010)

Yokes are not used on all aircraft. Helicopters use a cyclic and the majority of military fighter aircraft use a centre or side-stick. Some light aircraft use a stick because some sport pilots prefer that control system. The latest Airbus family of passenger jets use a side-stick, not unlike a computer game controller, to actuate control surfaces.
There are also computer input devices designed to simulate a yoke, intended for flight simulators.

Cockpit controls

[edit] Primary controls

Generally the primary cockpit controls are arranged as follows:

• A control column or a control yoke attached to a column—for roll and pitch, which moves the ailerons when turned or deflected left and right, and moves the elevators when moved backwards or forwards
• Rudder pedals to control yaw, which move the rudder; left foot forward will move the rudder left for instance.
• Throttle controls to control engine speed or thrust for powered aircraft.

Even when an aircraft uses different kinds of surfaces, such as a V-tail/ruddervator, flaperons, or elevons, to avoid pilot confusion the aircraft will still normally be designed so that the yoke or stick controls pitch and roll in the conventional way, as will the rudder pedals for yaw.

[edit] Secondary controls

In addition to the primary flight controls for roll, pitch, and yaw, there are often secondary controls available to give the pilot finer control over flight or to ease the workload. The most commonly-available control is a wheel or other device to control elevator trim, so that the pilot does not have to maintain constant backward or forward pressure to hold a specific pitch attitude^[1] (other types of trim, for rudder and ailerons, are common on larger aircraft but may also appear on smaller ones). Many aircraft have wing flaps, controlled by a switch or a mechanical lever or in some cases are fully automatic by computer control, which alter the shape of the wing for improved control at the slower speeds used for takeoff and landing. Other secondary flight control systems may be available, including slats, spoilers, air brakes and variable-sweep wings.

[edit] Basic flight control systems

Der "Trip-Couter" dient bei einigen Airlines zur Erinnerung an die Flugnummer.

Part 2

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