L6_Helicopter Configuration, Components & Systems
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variable-pitch antitorque rotor or tail rotor
Most helicopters have a single main rotor but require a separate rotor to overcome torque.
This is accomplished through a _____ or _____.
VS-300
Variable-pitch antitorque rotor or tail rotor is the design that Igor Sikorsky settled on for his _____ helicopter, and it has become the recognized convention for helicopter design, although designs do vary.
counter-clockwise
clockwise
When viewed from above, the vast majority of helicopter rotors turn _____; the rotors of French and Russian helicopters turn _____.
Single main rotor helicopters
They need an anti-torque device (tail rotor or other anti-torque system) to counteract the twisting momentum produced by the main rotor, which is powered by one or more engine(s).
are the most common type of helicopter.
torque
In a single main rotor helicopter part of the power generated by the powerplant(s) is employed to counteract _____.
tail rotor
most common anti-torque device which is designed to compensate the torque produced by the main rotor.
tandem rotor helicopter
has two main rotor systems and no tail rotor.
higher
Tandem rotor helicopter
Usually the rear rotor is mounted at a _____ position than the front rotor, and the two are designed to avoid the blades colliding.
rotor discs
Tandem rotor helicopter
are slightly tilted toward each other to provide control along the vertical axis during the hover.
Tandem rotor helicopter
this configuration, which is mainly used for larger helicopters, has the advantage of being able to support more weight with shorter blades.
smaller rotor disc area
Tandem rotor helicopter
is compensated by having two rotors.
counter-rotating
Tandem rotor helicopter
The anti-torque function is performed by the _____ rotors, with each cancelling out the other’s torque, so all of the power from the powerplants is employed for lift.
Coaxial rotors
are two main rotors mounted on one mast, sharing the same axis of rotation but turning in opposite directions, one on top of the other.
differential torque
Coaxial rotors
The control along the vertical axis is produced as a result of different lifts, thus _____, of the two rotor discs.
clockwise
counterclockwise
Coaxial rotors
The helicopter will yaw to the left if the _____ rotating rotor produces more lift, and it will yaw to the right if more lift is produced by the _____ rotating rotor.
Coaxial rotors
The drag produced by the rotors is quite large due to the interference of airflows, so these helicopters do not normally have a high cruising speed.
synchropter
Intermeshing Rotor
a helicopter with two rotors turning in opposite directions and mounted on two masts slightly inclined towards each other, so that the blades intermesh (without colliding), is called a _____.
gearwheel
Intermeshing Rotor
The two rotors mesh with one another, like a _____.
Intermeshing Rotor
this configuration does not require a tail rotor, since the anti-torque action is performed by the counter rotation of the rotors.
side by side rotor
two horizontal, counter-rotating rotors are mounted side-by-side on a helicopter (or transverse rotorcraft).
side by side rotor
the anti-torque effect is provided by the opposing rotation of the two main rotors.
side-by-side rotor configuration
is one of the possible flight configurations of a tilt-rotor aircraft, when the rotors are in the vertical position to provide vertical lift.
vertical
horizontal
Tilt rotors are mounted at the edge of the wings, on nacelles that rotate in order to transition the rotors from the _____ position (to provide vertical lift like a side by side rotor configuration helicopter), to the _____ position (where they provide horizontal lift, or thrust, just like in airplanes).
Tilt rotors
Both lift and propulsion are then generated by the rotors, which act as helicopter main rotors when in the vertical position, and as airplane propellers when in the horizontal position.
Tilt rotors
Lift is then provided by fixed wings.
compound helicopter
is a hybrid aircraft which acts both like an airplane and a helicopter.
compound helicopter
is capable of higher speeds that a normal helicopter.
propellers
main rotor
compound helicopter
The _____ provide thrust, and are driven from the powerplants which also drive the main rotor.
During hovering and lower speed flight, the _____ provides the lift and thrust for the aircraft.
compound helicopter
At faster velocities thrust is provided by the propeller(s), while the main rotor is slowed down or acts in autorotation to avoid drag.
compound helicopter
most of the vertical lift is then provided by small fixed wings.
Major Components of a Helicopter
Major Components of a Helicopter
airframe
fundamental structure of a helicopter can be made of either metal, wood, or composite materials, or some combination of the two.
fiber-impregnated resins
airframe is a composite component consists of many layers of _____, bonded to form a smooth panel.
aluminum
stainless steel or titanium
Airframe
Tubular and sheet metal substructures are usually made of _____, though _____ or _____ are sometimes used in areas subject to higher stress or heat.
fuselage
the outer core of the airframe, is an aircraft’s main body section that houses the cabin which holds the crew, passengers, and cargo.
engine
transmission
avionics
flight controls
powerplant
fuselage also houses the (5)
rotor system
is the rotating part of a helicopter which generates lift.
mast
hub
rotor blades
rotor consists of a (3)
mast
is a hollow cylindrical metal shaft which extends upwards from and is driven and sometimes supported by the transmission.
hub
At the top of the mast is the attachment point for the rotor blades called the _____.
rotor blades
are then attached to the hub by any number of different methods.
main rotor hub
Main rotor systems are classified according to how the main rotor blades are attached and move relative to the _____.
semirigid
rigid
fully articulated
3 basic classifications of Main Rotor Systems
semirigid rotor system
is composed of two blades that are rigidly mounted to the main rotor hub.
teetering hinge
semirigid rotor system
The main rotor hub is free to tilt with respect to the main rotor shaft on what is known as a _____.
teetering hinge
semirigid rotor system
_____ allows the blades to flap together as a unit.
As one blade flaps up, the other flaps down.
semirigid rotor system
since there is no vertical drag hinge, lead/lag forces are absorbed and mitigated by blade bending.
semirigid rotor
is capable of feathering, which means that the pitch angle of the blade changes.
This is made possible by the feathering hinge.
mast bumping
Helicopters with semirigid rotors are vulnerable to a condition known as _____ which can cause the rotor flap stops to shear the mast.
Mast bumping
is the result of excessive rotor flapping.
static stop
Each rotor system design has a maximum flapping angle.
If flapping exceeds the design value, the _____ will contact the mast.
Mast Bumping
is the violent contact between the static stop and the mast during flight that causes mast damage or separation.
rigid rotor system
is mechanically simple, but structurally complex because operating loads must be absorbed in bending rather than through hinges. In this system, the blade roots are rigidly attached to the rotor hub.
rigid rotor system
They cannot flap or lead/lag, but they can be feathered.
rigid rotor system
is very responsive and is usually not susceptible to mast bumping like the semirigid or articulated systems because the rotor hubs are mounted solid to the main rotor mast.
rotor hub
control inputs
Other advantages of the rigid include a reduction in the weight and drag of the _____ and a larger flapping arm, which significantly reduces _____.
rigid rotor system
Without the complex hinges, the rotor system becomes much more reliable and easier to maintain than the other rotor configurations.
rigid rotor system
A disadvantage of this system is the quality of ride in turbulent or gusty air.
Because there are no hinges to help absorb the larger loads, vibrations are felt in the cabin much more than with other rotor head designs.
Fully articulated rotor systems
allow each blade to lead/lag (move back and forth in plane), flap (move up and down about an inboard mounted hinge) independent of the other blades, and feather (rotate about the pitch axis to change lift).
Fully articulated rotor systems
are found on helicopters with more than two main rotor blades.
Differences in handling types of rotor system
Differences in handling types of rotor system
swash plate
it converts stationary control inputs from the pilot into rotating inputs which can be connected to the rotor blades or control surfaces.
stationary swash plate
rotating swash plate
swash plate consists of 2 main parts
stationary swash plate
is mounted around the main rotor mast and connected to the cyclic and collective controls by a series of pushrods.
The stationary swash plate
is restrained from rotating by an anti-drive link but can tilt in all directions and move vertically.
rotating swash plate
is mounted to the stationary swash plate by means of a uniball sleeve.
rotating swash plate
is connected to the mast by drive links and must rotate in constant relationship with the main rotor mast.
rotating
Both swash plates tilt and slide up and down as one unit.
The _____ swash plate is connected to the pitch horns by the pitch links.
engine
Since lift in a helicopter is provided by rotating airfoils, these airfoils must be free to rotate if the _____ fails.
freewheeling unit
automatically disengages the engine from the main rotor when engine revolutions per minute (rpm) is less than main rotor rpm.
freewheeling unit
allows the main rotor and tail rotor to continue turning at normal inflight speeds.
one-way sprag clutch
upper pulley
accessory gearbox
The most common freewheeling unit assembly consists of a _____ located between the engine and main rotor transmission.
This is usually in the _____ in a piston helicopter or mounted on the _____ in a turbine helicopter.
sprag clutch
is used in many helicopter designs to transfer power from the engine to the main rotor.
sprag clutch
In the event of an engine failure, the _____ allows the main rotor to continue rotating faster than the engines so that the helicopter can enter autorotation.
directional control
Helicopters with a single, main rotor system require a separate antitorque system.
This is most often accomplished through a variable pitch, antitorque rotor or tail rotor.
Pilots vary the thrust of the antitorque system to maintain _____ whenever the main rotor torque changes, or to make heading changes while hovering.
transmission
Most helicopters drive the tail rotor shaft from the _____ to ensure tail rotor rotation (and hence control) in the event that the engine quits.
Multi-Bladed System
is the most common type of anti-torque system that you will see on a helicopter.
Multi-Bladed System
comprises of two or more rotor blades that change pitch to adjust the amount of thrust they produce as a unit.
Multi-Bladed System
The pitch either increases and creates more thrust to turn the helicopter against the main rotor direction or the pitch decreases and allows the torque to pull the nose of the helicopter in the same direction of the main rotor blades direction.
fenestron or “fan-in- tail”
Another form of antitorque system is the _____ or _____ design.
This system uses a series of rotating blades shrouded within a vertical tail.
fenestron or “fan-in- tail” design
because the blades are located within a circular duct, they are less likely to come into contact with people or objects.
NOTAR system
comprises of an engine-driven, variable pitch fan that is mounted perpendicular inside the tail boom to produce large volumes of low-pressure air that exit through horizontal slots along the right-hand side of the tail boom and via a rotatable ‘Jet Thruster’ at the end of the tail boom.
Coanda effect
NOTAR system
The air is expelled through two slots which run the length of the tailboom on the right side, causing a boundary-layer control called the _____.
venturi
NOTAR system
The low-pressure air released down the length of the tail boom creates a Coanda Effect around the tail boom which acts as a _____ to pull the downwash from the main rotor around the tail boom and exit off to the left.
right
NOTAR system
This creates an area of low-pressure on the _____-hand side of the tail boom, pulling the entire tail boom to the right, counteracting the torque from the main rotor.
direct jet thruster
vertical stabilizers
NOTAR system
The balance of the directional control is accomplished by a rotating _____.
In forward flight, the _____ provide the majority of the antitorque; however, directional control remains a function of the direct jet thruster.
rotor disk
When a helicopter has two sets of main rotors the designers make each set rotate in opposite directions.
By doing this they each cancel out the torque imparted by the other _____.
tail boom
No Tail Rotor System
Because of this, no additional anti-torque system is needed on a _____.
No Tail Rotor System
Directional control is accomplished by changing the pitch on each rotor disk similar to the way the cyclic changes the disk pitch on a single main rotor helicopter.
Reciprocating engines, also called piston engines
are generally used in smaller helicopters.
reciprocating
Most training helicopters use _____ engines because they are relatively simple and inexpensive to operate.
Turbine engines
are more powerful and are used in a wide variety of helicopters.
exhaust outlets
The turbine engine used in helicopters operates differently from those used in airplane applications.
In most applications, the _____ simply release expended gases and do not contribute to the forward motion of the helicopter.
transmission system
transfers power from the engine to the main rotor, tail rotor, and other accessories during normal flight conditions.
main rotor transmission
tail rotor drive system
clutch
freewheeling unit
4 main components of the transmission system
main rotor transmission
it reduces engine output rpm to optimum rotor rpm.
This reduction is different for the various helicopters.
6:1
300
main rotor transmission
suppose the engine rpm of a specific helicopter is 2,700. A rotor speed of 450 rpm would require a ____ reduction.
A 9:1 reduction would mean the rotor would turn at _____ rpm.
main rotor transmission
In helicopters with horizontally mounted engines, _____ changes the axis of rotation from the horizontal axis of the engine to the vertical axis of the rotor shaft.
engine and the rotor load
In a conventional airplane, the engine and propeller are permanently connected.
However, in a helicopter there is a different relationship between the _____ and the _____ of the rotor.
propeller
power
Because of the greater weight of a rotor in relation to the power of the engine, as compared to the weight of a _____ and the _____ in an airplane, the rotor must be disconnected from the engine when the starter is engaged.