直升机飞行手册Rotorcraft flying handbook

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For safety purposes, an automatic disengage feature is

usually included which automatically disconnects the

autopilot in heavy turbulence or when extreme flight

attitudes are reached. Even though all autopilots can be

overridden by the pilot, there is also an autopilot disengage button located on the cyclic or collective which

allows you to completely disengage the autopilot without removing your hands from the controls. Because

autopilot systems and installations differ from one helicopter to another, it is very important that you refer to

the autopilot operating procedures located in the

Rotorcraft Flight Manual.

ENVIRONMENTAL SYSTEMS

Heating and cooling for the helicopter cabin can be

provided in different ways. The simplest form of cooling is ram air cooling. Air ducts in the front or sides of

the helicopter are opened or closed by the pilot to let

ram air into the cabin. This system is limited as it

requires forward airspeed to provide airflow and also

servos, on each flight control, a pump which is usually

driven by the main rotor gearbox, and a reservoir to

store the hydraulic fluid. A switch in the cockpit can

turn the system off, although it is left on under normal

conditions. A pressure indicator in the cockpit may also

be installed to monitor the system.

When you make a control input, the servo is activated

and provides an assisting force to move the respective

flight control, thus lightening the force required by the

pilot. These boosted flight controls ease pilot workload

and fatigue. In the event of hydraulic system failure,

you are still able to control the helicopter, but the control forces will be very heavy.

In those helicopters where the control forces are so

high that they cannot be moved without hydraulic

assistance, two or more independent hydraulic systems

may be installed. Some helicopters use hydraulic accumulators to store pressure, which can be used for a

short period of time in an emergency if the hydraulic

pump fails. This gives you enough time to land the helicopter with normal control

STABILITY AUGMENTATIONS SYSTEMS

Some helicopters incorporate stability augmentations

systems (SAS) to aid in stabilizing the helicopter in

flight and in a hover. The simplest of these systems is a

force trim system, which uses a magnetic clutch and

springs to hold the cyclic control in the position where

it was released. More advanced systems use electric

servos that actually move the flight controls. These

servos receive control commands from a computer that

senses helicopter attitude. Other inputs, such as

heading, speed, altitude, and navigation information

may be supplied to the computer to form a complete

autopilot system. The SAS may be overridden or

disconnected by the pilot at any time.

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malfunction of

an electrical component.

HYDRAULICS

Most helicopters, other than smaller piston powered

helicopters, incorporate the use of hydraulic actuators

to overcome high control forces. [Figure 5-13] A typical hydraulic system consists of actuators, also called

Pressure

Return

Supply

Scupper

Drain

Vent Reservoir

Pump

Pressure

Regulator

Valve

Quick

Disconnects

Filter

Solenoid

Valve

Servo

Actuator,

Lateral

Cyclic

Servo

Actuator,

Fore and

Aft

Cyclic

Servo

Actuator,

Collective

Pilot

Input

Rotor

Control

Figure 5-13. A typical hydraulic system for helicopters in the light to medium range is shown here.

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igation capabilities, such as VOR, ILS, and GPS

intercept and tracking, which is especially useful in

IFR conditions. The most advanced autopilots can

fly an instrument approach to a hover without any

additional pilot input once the initial functions have

been selected.

The autopilot system consists of electric actuators or

servos connected to the flight controls. The number and

location of these servos depends on the type of system

installed. A two-axis autopilot controls the helicopter

in pitch and roll; one servo controls fore and aft cyclic,

and another controls left and right cyclic. A three-axis

autopilot has an additional servo connected to the antitorque pedals and controls the helicopter in yaw. A

four-axis system uses a fourth servo which controls the

collective. These servos move the respective flight controls when they receive control commands from a central computer. This computer receives data input from

the flight instruments for attitude reference and from

the navigation equipment for navigation and tracking

reference. An autopilot has a control panel in the cockpit that allows you to select the desired functions, as

well as engage the autopilot.

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Door

Filter

To Carb

Carb Heat

Collector

Manifold

Pipe

Door

Heated Air

Carb Heat Off

Carb Heat On

Figure 5-11. When you turn the carburetor heat ON, normal

air flow is blocked, and heated air from an alternate source

flows through the filter to the carburetor.

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incorporated to prevent excessive voltage, which may

damage the electrical components. The bus bar serves

to distribute the current to the various electrical components of the helicopter.

A battery is mainly used for starting the engine. In

addition, it permits limited operation of electrical

components, such as radios and lights, without the

engine running. The battery is also a valuable source

of standby or emergency electrical power in the event

of alternator or generator failure.

An ammeter or loadmeter is used to monitor the

electrical current within the system. The ammeter

reflects current flowing to and from the battery. A

charging ammeter indicates that the battery is being

charged. This is normal after an engine start since

the battery power used in starting is being replaced.

After the battery is charged, the ammeter should stabilize near zero since the alternator or generator is

supplying the electrical needs of the system. A discharging ammeter means the electrical load is

exceeding the output of the alternator or generator,

and the battery is helping to supply electrical power.

This may mean the alternator or generator is malfunctioning, or the electrical load is excessive. A

loadmeter displays the load placed on the alternator

or generator by the electrical equipment. The RFM

for a particular helicopter shows the normal load to

expect. Loss of the alternator or generator causes the

loadmeter to indicate zero.

Electrical switches are used to select electrical components. Power may be supplied directly to the component

or to a relay, which in turn provides power to the

component. Relays are used when high current and/or

heavy electrical cables are required for a particular component, which may exceed the capacity of the switch.

Circuit breakers or fuses are used to protect various

electrical components from overload. A circuit breaker

pops out when its respective component is overloaded.

The circuit breaker may be reset by pushing it back in,

unless a short or the overload still exists. In this case,

the circuit breaker continues to pop, indicating an electrical malfunction. A fuse simply burns out when it is

overloaded and needs to be replaced. Manufacturers

usually provide a holder for spare fuses in the event one

has to be replaced in flight. Caution lights on the instrument panel may be installed to show the

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Avionic

Bus

Avionics Relay

On

Off

Avionics Master

Switch

Lights

Panel

Position

Beacon

Trim

Instr

Lndg Lt

Radio

Xpdr

Clutch

Ammeter

Mag Switch

Left

Magneto

Right

Magneto

Starter

Relay

Engine

Starter

Bus Bar

Battery

Relay

Battery

Battery

Switch

Starter

Switch

M/R Gearbox

Press Switch

Release

Hold

Engage

Clutch

Switch

Alternator

Alternator

Switch

Alternator

Control Unit

Clutch Actuator

(Internal Limit Switches

Shown in Full

Disengage Position)

24V

– +

F1 F2

–

+

Starting

Vibrator

R

R

Both

L L

Off

Ret

Adv

Adv

G

(Optional Avionics)

Figure 5-12. An electrical system scematic like this sample is

included in most POHs. Notice that the various bus bar

accessories are protected by circuit breakers. However, you

should still make sure all electrical equipment is turned off

before you start the engine. This protects sensitive components, particularly the radios, from damage which may be

caused by random voltages generated during the starting

process.

Filter

To Carb

Carb Heat

Collector

Manifold

Pipe

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manifold, before it enters the carburetor. [Figure 5-11].

FUEL INJECTION

In a fuel injection system, fuel and air are metered at

the fuel control unit but are not mixed. The fuel is

injected directly into the intake port of the cylinder

where it is mixed with the air just before entering the

cylinder. This system ensures a more even fuel distribution in the cylinders and better vaporization, which

in turn, promotes more efficient use of fuel. Also, the

fuel injection system eliminates the problem of carburetor icing and the need for a carburetor heat system.

TURBINE ENGINES

The fuel control system on the turbine engine is fairly

complex, as it monitors and adjusts many different

parameters on the engine. These adjustments are done

automatically and no action is required of the pilot

other than starting and shutting down. No mixture

adjustment is necessary, and operation is fairly simple

as far as the pilot is concerned. New generation fuel

controls incorporate the use of a full authority digital

engine control (FADEC) computer to control the

engine’s fuel requirements. The FADEC systems

increase efficiency, reduce engine wear, and also

reduce pilot workload. The FADEC usually incorporates back-up systems in the event of computer failure.

ELECTRICAL SYSTEMS

The electrical systems, in most helicopters, reflect the

increased use of sophisticated avionics and other electrical accessories. More and more operations in today’s

flight environment are dependent on the aircraft’s electrical system; however, all helicopters can be safely

flown without any electrical power in the event of an

electrical malfunction or emergency.

Helicopters have either a 14- or 28-volt, direct-current electrical system. On small, piston powered

helicopters, electrical energy is supplied by an engine-

driven alternator. These alternators have advantages

over older style generators as they are lighter in

weight, require lower maintenance, and maintain a

uniform electrical output even at low engine r.p.m.

[Figure 5-12]

Turbine powered helicopters use a starter/generator

system. The starter/generator is permanently coupled

to the engine gearbox. When starting the engine, electrical power from the battery is supplied to the

starter/generator, which turns the engine over. Once the

engine is running, the starter/generator is driven by the

engine and is then used as a generator.

Current from the alternator or generator is delivered

through a voltage regulator to a bus bar. The voltage

regulator maintains the constant voltage required by

the electrical system by regulating the output of the

alternator or generator. An over-voltage control may be

Avionic

Bus

Bar

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at high altitudes. Usually, you can correct the problem by

leaning the mixture according to RFM instructions.

If you fail to enrich the mixture during a descent from

high altitude, it normally becomes too lean. High

engine temperatures can cause excessive engine wear

or even failure. The best way to avoid this type of situation is to monitor the engine temperature gauges regularly and follow the manufacturer’s guidelines for

maintaining the proper mixture.

CARBURETOR ICE

The effect of fuel vaporization and decreasing air pressure in the venturi causes a sharp drop in temperature

in the carburetor. If the air is moist, the water vapor in

the air may condense. When the temperature in the carburetor is at or below freezing, carburetor ice may form

on internal surfaces, including the throttle valve.

[Figure 5-10] Because of the sudden cooling that takes

place in the carburetor, icing can occur even on warm

days with temperatures as high as 38°C (100°F) and

the humidity as low as 50 percent. However, it is more

likely to occur when temperatures are below 21°C

(70°F) and the relative humidity is above 80 percent.

The likelihood of icing increases as temperature

decreases down to 0°C (32°F), and as relative humidity

increases. Below freezing, the possibility of carburetor

icing decreases with decreasing temperatures.

Although carburetor ice can occur during any phase of

flight, it is particularly dangerous when you are using

reduced power, such as during a descent. You may not

notice it during the descent until you try to add power.

Indications of carburetor icing are a decrease in engine

r.p.m. or manifold pressure, the carburetor air temperature gauge indicating a temperature outside the safe

operating range, and engine roughness. Since changes

in r.p.m. or manifold pressure can occur for a number

of reasons, it is best to closely check the carburetor air

temperature gauge when in possible carburetor icing

conditions. Carburetor air temperature gauges are

marked with a yellow caution arc or green operating

arcs. You should refer to the FAA-Approved Rotorcraft

Flight Manual for the specific procedure as to when

and how to apply carburetor heat. However, in most

cases, you should keep the needle out of the yellow arc

or in the green arc. This is accomplished by using a carburetor heat system, which eliminates the ice by

To Engine

Incoming Air

Ice

Ice

Venturi

Fuel/Air

Mixture

Ice

Figure 5-10. Carburetor ice reduces the size of the air passage to the engine. This restricts the flow of the fuel/air

mixture, and reduces power.

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routing air across a heat source, such as an exhaust

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Fuel

Shutoff

Primer

Tank

Shut-off

Valve

Carburetor

Fuel

Strainer

Primer Nozzle

at Cylinder

Figure 5-9. A typical gravity feed fuel system, in a helicopter

with a reciprocating engine, contains the components

shown here.

Stationary

Swash

Plate

Pitch

Link

Rotating

Swash

Plate

Control

Rod

Figure 5-8. Collective and cyclic control inputs are transmitted to the stationary swash plate by control rods causing it to

tilt or to slide vertically. The pitch links attached from the

rotating swash plate to the pitch horns on the rotor hub

transmit these movements to the blades.

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RECIPROCATING ENGINES

Fuel is delivered to the cylinders by either a carburetor

or fuel injection system.

CARBURETOR

In a carburetor system, air is mixed with vaporized fuel as

it passes through a venturi in the carburetor. The metered

fuel/air mixture is then delivered to the cylinder intake.

Carburetors are calibrated at sea level, and the correct

fuel-to-air mixture ratio is established at that altitude

with the mixture control set in the FULL RICH position. However, as altitude increases, the density of air

entering the carburetor decreases while the density of

the fuel remains the same. This means that at higher

altitudes, the mixture becomes progressively richer. To

maintain the correct fuel/air mixture, you must be able

to adjust the amount of fuel that is mixed with the

incoming air. This is the function of the mixture control. This adjustment, often referred to as “leaning the

mixture,” varies from one aircraft to another. Refer to

the FAA-Approved Rotocraft Flight Manual (RFM) to

determine specific procedures for your helicopter. Note

that most manufacturers do not recommend leaning helicopters in-flight.

Most mixture adjustments are required during changes of

altitude or during operations at airports with field elevations well above sea level. A mixture that is too rich can

result in engine roughness and reduced power. The roughness normally is due to spark plug fouling from excessive carbon buildup on the plugs. This occurs because

the excessively rich mixture lowers the temperature inside

the cylinder, inhibiting complete combustion of the fuel.

This condition may occur during the pretakeoff runup at

high elevation airports and during climbs or cruise flight

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The fuel system in a helicopter is made up of two

groups of components: the fuel supply system and the

engine fuel control system.

FUEL SUPPLY SYSTEM

The supply system consists of a fuel tank or tanks, fuel

quantity gauges, a shut-off valve, fuel filter, a fuel line

to the engine, and possibly a primer and fuel pumps.

[Figure 5-9]

The fuel tanks are usually mounted to the airframe as

close as possible to the center of gravity. This way, as

fuel is burned off, there is a negligible effect on the center of gravity. A drain valve located on the bottom of

the fuel tank allows the pilot to drain water and sediment that may have collected in the tank. A fuel vent

prevents the formation of a vacuum in the tank, and an

overflow drain allows for fuel to expand without rupturing the tank. A fuel quantity gauge located on the

pilot’s instrument panel shows the amount of fuel

measured by a sensing unit inside the tank. Some

gauges show tank capacity in both gallons and pounds.

The fuel travels from the fuel tank through a shut-off

valve, which provides a means to completely stop fuel

flow to the engine in the event of an emergency or fire.

The shut-off valve remains in the open position for all

normal operations.

Most non-gravity feed fuel systems contain both an

electric pump and a mechanical engine driven pump.

The electrical pump is used to maintain positive fuel

pressure to the engine pump and also serves as a

backup in the event of mechanical pump failure. The

electrical pump is controlled by a switch in the cockpit.

The engine driven pump is the primary pump that supplies fuel to the engine and operates any time the

engine is running.

A fuel filter removes moisture and other sediment from

the fuel before it reaches the engine. These contaminants are usually heavier than fuel and settle to the bottom of the fuel filter sump where they can be drained

out by the pilot.

Some fuel systems contain a small hand-operated pump

called a primer. A primer allows fuel to be pumped

directly into the intake port of the cylinders prior to

engine start. The primer is useful in cold weather when

fuel in the carburetor is difficult to vaporize.

ENGINE FUEL CONTROL SYSTEM

The purpose of the fuel control system is to bring outside air into the engine, mix it with fuel in the proper

proportion, and deliver it to the combustion chamber.

Throttle

Low Level

Warning

Light

Vent

Fuel Quantity

Gauge

Mixture

Control

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A semirigid rotor system is usually composed of two

blades which are rigidly mounted to the main rotor hub.

The main rotor hub is free to tilt with respect to the

main rotor shaft on what is known as a teetering

hinge. This allows the blades to flap together as a

unit. As one blade flaps up, the other flaps down.

Since there is no vertical drag hinge, lead-lag forces

are absorbed through blade bending. [Figure 5-6]

RIGID ROTOR SYSTEM

In a rigid rotor system, the blades, hub, and mast are

rigid with respect to each other. There are no vertical or

horizontal hinges so the blades cannot flap or drag, but

they can be feathered. Flapping and lead/lag forces are

absorbed by blade bending.

COMBINATION ROTOR SYSTEMS

Modern rotor systems may use the combined principles of the rotor systems mentioned above. Some

rotor hubs incorporate a flexible hub, which allows

for blade bending (flexing) without the need for bearings or hinges. These systems, called flextures, are

usually constructed from composite material.

Elastomeric bearings may also be used in place of

conventional roller bearings. Elastomeric bearings are

bearings constructed from a rubber type material and

have limited movement that is perfectly suited for helicopter applications. Flextures and elastomeric bearings require no lubrication and, therefore, require less

maintenance. They also absorb vibration, which

means less fatigue and longer service life for the helicopter components. [Figure 5-7]

SWASH PLATE ASSEMBLY

The purpose of the swash plate is to transmit control

inputs from the collective and cyclic controls to the main

rotor blades. It consists of two main parts: the stationary

Teetering

Hinge

Feathering Hinge

Static Stops

Pitch Horn

Figure 5-6. On a semirigid rotor system, a teetering hinge

allows the rotor hub and blades to flap as a unit. A static flapping stop located above the hub prevents excess rocking

when the blades are stopped. As the blades begin to turn,

centrifugal force pulls the static stops out of the way.

Figure 5-7. Rotor systems, such as Eurocopter’s Starflex or

Bell’s soft-in-plane, use composite material and elastomeric

bearings to reduce complexity and maintenance and,

thereby, increase reliability.

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swash plate and the rotating swash plate. [Figure 5-8]

The stationary swash plate is mounted around the main

rotor mast and connected to the cyclic and collective

controls by a series of pushrods. It is restrained from

rotating but is able to tilt in all directions and move vertically. The rotating swash plate is mounted to the stationary swash plate by means of a bearing and is

allowed to rotate with the main rotor mast. Both swash

plates tilt and slide up and down as one unit. The rotating swash plate is connected to the pitch horns by the

pitch links.

FUEL SYSTEMS

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rotor r.p.m. This allows the main rotor to continue turning

at normal in-flight speeds. The most common freewheeling unit assembly consists of a one-way sprag clutch

located between the engine and main rotor transmission.

This is usually in the upper pulley in a piston helicopter

or mounted on the engine gearbox in a turbine helicopter.

When the engine is driving the rotor, inclined surfaces in

the spray clutch force rollers against an outer drum. This

prevents the engine from exceeding transmission r.p.m. If

the engine fails, the rollers move inward, allowing the

outer drum to exceed the speed of the inner portion. The

transmission can then exceed the speed of the engine. In

this condition, engine speed is less than that of the drive

system, and the helicopter is in an autorotative state.

MAIN ROTOR SYSTEM

Main rotor systems are classified according to how the

main rotor blades move relative to the main rotor hub.

As was described in Chapter 1—Introduction to the

Helicopter, there are three basic classifications: fully

articulated, semirigid, or rigid. Some modern rotor systems use a combination of these types.

FULLY ARTICULATED ROTOR SYSTEM

In a fully articulated rotor system, each rotor blade is

attached to the rotor hub through a series of hinges,

which allow the blade to move independently of the

others. These rotor systems usually have three or more

blades. [Figure 5-5]

Pitch Change

Axis

(Feathering)

Flapping

Hinge

Damper

Drag Hinge

Pitch Horn

Figure 5-5. Each blade of a fully articulated rotor system can

flap, drag, and feather independently of the other blades.

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The horizontal hinge, called the flapping hinge, allows

the blade to move up and down. This movement is

called flapping and is designed to compensate for dissymetry of lift. The flapping hinge may be located at

varying distances from the rotor hub, and there may be

more than one hinge.

The vertical hinge, called the lead-lag or drag hinge,

allows the blade to move back and forth. This movement is called lead-lag, dragging, or hunting.

Dampers are usually used to prevent excess back

and forth movement around the drag hinge. The purpose of the drag hinge and dampers is to compensate

for the acceleration and deceleration caused by

Coriolis Effect.

Each blade can also be feathered, that is, rotated around

its spanwise axis. Feathering the blade means changing

the pitch angle of the blade. By changing the pitch

angle of the blades you can control the thrust and direction of the main rotor disc.

SEMIRIGID ROTOR SYSTEM