Block 2 Rotary Wing Aerodynamics Flashcards
__________ of helicopters and airplanes are basically the same, while __________ __________ differ widely from those of an airplane.
Aerodynamics
Flight Characteristics
_________ ____ _________(___________) depends on the magnitude of the unbalanced force and mass of the body
Rate of change (acceleration)
____________ provides the basis for all helicopters flight- vertical, forward, backward, sideward or hovering
Rotary Wing Aerodynamics - Balance of Forces
Total force generated by a rotor system is always _____________ to the tip-path plane.
Perpendicular
Force is divided into what two components?
lift and thrust
The ________ component of a rotary wing aircraft acts horizontally to accelerate or decelerate the helicopter in the desired direction
Lift
On a rotary wing aircraft, thrust may be directed in the desired direction by…
tilting the tip-path plane
At __________, all opposing forces are in balance and the helicopter remains stationary
hover
At hover, total force is acting opposite to the helicopter’s ________
weight
To move a helicopter in some direction, a ________ must be applied to cause an _________ __________
force
unbalanced condition
The wind produced by the rotational velocity of the rotor blade, induced flow caused by the production of lift and the movement of the helicopter through the air mass is:
Relative Wind
Relative Wind is produced by:
- The rotational velocity of the rotor blade
- Induced flow caused by the production of lift
- The movement of the helicopter through the air mass
Relative wind moves in a ________, but __________ direction to the airfoil
Parallel
Opposite
When a helicopter maintains a constant position over a selected point, usually a few feet above the ground
Hovering
Rotor tip vortex is also known as:
Air swirl at the tip of the rotor blades
There are high-power requirements for hovering due to:
The continuous creation of new vortexes and ingestion of existing vortexes
A condition of improved performance encountered when operating near the ground
In-ground effect
The reduction of the velocity of the induced air flow
Distinct phenomena 1
Distinct phenomena 2
Reduction of the rotor tip vortex
Type of hover in which the rotor blades move large volumes of air in a downward direction called induced flow.
Out-of-ground effect hover
Out -of-ground effect hover requires a ______ _______ setting
high power
A single-rotor helicopter has the tendency to drift laterally to the ______ during hover
right
The tendency of a single-rotor helicopter to drift laterally to the right during hover.
Translating tendency
Lateral tilt results in a main rotor force to the ______ that compensates for the tail rotor thrust to the ______
left
right
As the incoming wind enters the rotor system, turbulence and vortexes are left behind, the flow of air becomes more horizontal, improving performance.
Transitional lift
When a helicopter transitions from hover to ________ _______, the tail rotor becomes more aerodynamically efficient.
forward flight
During transitional lift, __________ increases due to the tail rotor working in progressively less turbulent air as speed is increased.
efficiency
During transitional lift, more thrust is produced causing the aircraft’s nose to _______ _______ due to the main rotor turning __________________
yaw left
counterclockwise
During a helicopter takeoff, the _________ _________ must be applied as speed increases to correct for left yaw tendency
right pedal
The difference in lift between the advancing half of the rotor disk and the retreating half
Dissymmetry of lift
During dissymmetry of lift, the blade passing the tail and advancing reaches a maximum at the ________ position
3 o’clock
During dissymmetry of lift, the blade speed decreases and reaches a minimum airspeed at the _________ position
9 o’clock
Downward force applied at point A results in downward movement response at point B, and upward force applied at point C results in upward response movement at point D. This is called:
Gyroscopic precession (refer to figure 2-20)
___________ affects the rotor disk when force is applied at a given point
(gyroscopic) precession
The rotor will always tilt in the direction in which the _______ ________ is moved.
cyclic stick
When the engine fails or is disengaged from the rotor system, a ______ must be used to sustain rotor RPM so controlled flight can be continued to the ground.
force
During autorotation, the pilot gives up __________ at a controlled rate in return for _________ to turn the rotor at an RPM that provides aircraft control
altitude
energy
When an engine fails or is disengaged from the rotor system, a force must be used to sustain rotor RPM so controlled flight can be continued to the ground.
Autorotation
During autorotation, as altitude decreases, ________ _________ is converted to __________ __________ and stored in the turning rotor
potential energy
kinetic energy
During autorotation, the pilot uses _______ _______ to cushion the touchdown when nearing the ground
kinetic energy
Entry into ______________ is performed following loss of engine power
autorotation
Indications of power loss are:
Rotor RPM decay and an out-of-trim condition
During entry into autorotation, establish a _________ at the proper airspeed depending on the helicopter and its gross weight. RPM should be stabilized.
glide
Autorotation RPM is a _______ _______ _________ than normal operating RPM
few turns higher
Rate of descent and RPM are stabilized and the helicopter descends at a constant angle. This is called:
steady-state descent
During steady-state descent, the angle of attack descent is normally
17 to 20 degrees
Steady-state descent depends on the following 5 things:
airspeed density altitude wind helicopter
To successfully perform an autorotative landing, reduce ________ and ____________ just before touchdown
airspeed
rate of descent
During deceleration and landing during autorotation, __________ change inclines the total force of the rotor disk.
attitude
During deceleration and landing in autorotation, blade _______ ______ is available to cushion the touchdown
kinetic energy
During autorotation deceleration and landing, _______ ________ is applied to cushion the touchdown.
collective pitch
Newton’s law of action and reaction, states that a helicopter fuselage tends to rotate in the direction ___________ the rotor blades
opposite
_______ must be counteracted and/or controlled before flight is possible
Torque
_______ results from the rotor’s being driven by the engine power output
Torque
Torque effect must be __________ corrected
continually
Torque effect rotates the fuselage in a direction opposite the main rotor and the tail rotor counteracts torque effect and provides positive fuselage heading control. This is identified as:
Anti-torque rotor
An anti-torque rotor compensates for torque in the single main rotor helicopter. This is done by the _____ _______
tail rotor
An anti-torque rotor produces thrust in a horizontal plane ________ to torque reaction developed by the main rotor.
opposite
_________ compensate for torque variance
Pedals
____ to ____ percent of the available engine power may be needed to drive the tail rotor
5 to 15
The up and down movement of rotor blades is known as:
Blade flapping
During blade flapping, the blade climbs or flaps upward, from change in ______ ______ and ______ ___ _______ which reduces the amount of lift that would have been generated
relative wind
angle of attack
During blade flapping, as the blade loses airspeed, reducing lift causes it to settle or flap _________, thus changing its relative wind and angle of attack
downward
The retreating blade must produce an amount of lift equal to that of the __________ _______
advancing blade
As the speed of the retreating blade decreases with forward speed, blade angle of attack must be increased to equalize _______ throughout the rotor disk area
lift
Conditions most likely to produce blade stall:
High blade loading (high gross weight) Low rotor RPM High-density altitude Steep or abrupt turns Turbulent air
Warnings of approaching retreating blade stall:
Abnormal vibration (shuddering)
Pitch up of the nose
Tendency for the helicopter to roll in the direction of the stalled stick
To prevent blade stall, the helicopter must fly slower than normal when:
The density altitude is much higher than standard
Carrying maximum gross loads
Flying high-drag configurations, external stores, weapons, sling loads, etc.
The air is turbulent
Procedures for correcting blade stall:
Decrease collective pitch
Decrease the severity of the maneuver
Gradually decrease airspeed
Increase rotor RPM
In a severe blade stall, ______ _________ ___ ______
all control is lost
Fully articulated rotors are free to move ______ and _____ in the plane of rotation independent
fore
aft
Pitch angle variation causes changes in the blade drag which makes the blade _________ or _______ about the drag hinge
lead
lag
This law states that a rotating body will continue to rotate with the some rotational velocity until some external force is applied to change the speed of rotation
Coriolis Force
Blade lead and lag is governed by the law of:
Conservation of angular momentum
Applying the principle of Coriolis force to a rotating helicopter blade, it may be stated:
- A mass moving radially outward on a rotating disk exerts a force opposite to rotation (decelerates)
- A mass moving radially inward on a rotating disk exerts a force in the direction of rotation (acceleration)
__________ _____ ________ happens at high altitudes, at high gross weights, or when operating with reduced power
Settling with power
Settling with power makes __________ flight possible
level
Settling with power can occur at any _______ or ______ , when power required exceeds power available
airspeed
altitude
Settling with power, preventing level flight at _______ ________
slower speeds
An extremely critical situation that may develop at any altitude or gross weight when the airspeed is below translational lift and rate of descent is high
Vortex ring state
During vortex ring state, down wash from the rotor begins to recirculate up, around and back down through the effective outer portion of the _______ _____
rotor disc
During vortex ring state, ________ and ________ ____ ___ ________ may occur
roughness
partial loss of control
How do you recover from vortex ring state
Increase forward air speed, decrease collective pitch or enter autorotation if altitude permits
