Aerodinamics 2 Flashcards
Relative Wind
fix wing
Direction of the airflow with respect to the wing and is created by the motion of the AC moving through the air
Angle of Incidence
formed by the longitudinal axis of the aircraft and the chord of the wing
Angle of Attack
Angle between the wing chord line and the direction of the relative wind
Swirling or Burbling
when air can no longer flow smoothly over the wings upper surface due to the separation of the boundary layer
Thrust and drag in straight and level flight
Drag increases twice as much as increases airspeed
Lift and gravity in straight and level flight
if lift becomes less than weight, the AC will descent, and if lift becomes greater than weight, the AC will climb
Wing Area
The lift and drag acting on a wing are roughly proportional to the wing area
Airfoil Shape
As the upper curvature or camber of an airfoil increased, the lift produced increases.
Basis for all helicopter flight
Vertical, forward, backwards, sideward, or hovering
All opposing forces are in balanced
At a hover
Relative Wind
Rotary wind
moves in a parallel, but opposite, direction to the movement of the airfoil
Rotational Velocity
blade speed
near the main rotor shaft is much less, because the distance traveled at the smaller radius is relatively small
Hovering
Helicopter maintains a constant position over a selected point
Rotor Tip Vortex
The rotor tip vortex reduces the effectiveness of the outer blade portions.
OGE
out-of-ground-effect
High-power requirement needed to hover
IGE
in-ground-effect
Improved performance encountered when operating near the ground
Induced Flow
Produced during OGE, the rotor blades move large volumes of air in a downward direction
Induced Flow speed
May reach 60 to 100 knots, depending on the size and gross weight
Translating Tendency
A single rotor helicopter has a tendency to drift laterally to the right
Translational Lift
Improved rotor efficiency resulting from directional flight
Dissymmetry of lift
the difference in lift between the advancing half of the rotor disk and the retreating half. Max at 3 o’clock, min at 9 o’clock.
Gyroscopic Precession
A phenomenon occurring in rotating bodies in which an applied force is manifested 90* ahead of the direction of rotation from where the force was applied
Autorotation
Some other force must be used to sustain rotor RPM so controlled flight can be continued to the ground
Autorotation Phases
Entry
Steady-State Descent
Deceleration and Touchdown
Entry
Performed following a loss of engine power. Rotor RPM should be stabilized at autorotation RPM (higher than normal RPM)
Steady-State Descent
Rate of descent and RPM are stabilized, the helicopter descents at a constant angle. AOA descent normally 17-20 degrees.
Deceleration and Touchdown
Must reduce airspeed and rate of descent just before touchdown
Torque
the helicopter tends to rotate in the direction opposite the rotor blades
Anti-torque rotor
Compensation for torque in the single main rotor helicopter is done by means of a variable pitch, anti torque rotor. 5-15% engine power may be needed to drive the tail rotor.
Blade flapping
Up and down movement of the rotor blade which causes elimination of dissymmetry of lift.
Retreating Blade Stall
as the speed of the retreating blade decreases with forward speed, the blade AOA must be increased to equalize lift throughout the rotor disk area
Produce blade stall at high forward speeds
High blade loading Low rotor RPM High density altitude Steep or abrupt turns Turbulent air
Warnings of approaching retreating blade stall
Abnormal vibration
Pitch up of the nose
Tendency for the helicopter to roll in the direction of the stalled side
Prevent blade stall
Fly slower then normal: DA is much higher then standard Carrying Max gross loads Flying high drag configurations The air is turbulent
Blade stall may be eliminated by..
Decrease collective pitch
Decrease the severity of the maneuver
Gradually decrease airspeed
Increase rotor RPM
Blade lead and lag
Fully articulated rotors have hinged blades that are free to move fore and aft in the plane of rotation independent of the other blades in the system.
Coriolis Force
Causes blades to lead and lag
Conservation of Angular Momentum
A rotating body will continue to rotate with the same rotational velocity until some external force is applied to change the speed of rotation
Settling with power
Can occur at any airspeed or altitude whenever power required exceeds power available, preventing level flight.
Vortex Ring State
May develop at any ALT or gross weight when the airspeed is bellow translational lift and rate if descent is high (excess of 300ft/min)
