Rotational Disk Flashcards
Rotor blade actions
Rotation
Flapping
Feathering (cyclic, collective)
Hunting (lead/lag, articulated/rigid rotor systems)
rotation develops a relative wind only
Flapping
Semi-rigid (teetering) - flaps as a unit
Articulated - flaps independently
Rigid - bending of blades independently
Cyclic feathering
Increases pitch of one rotor blade while simultaneously decreasing pitch in the other
Pitch of blades change continuously during rotation
Tilts rotor disk for directional control and controls dissymmetry of lift
Does not change overall lift of helo, increases lift in one half and decreases lift in the other half
Collective feathering
Pitch changes applied equally and simultaneously to all blades
Used to change angle of attack and angle of incidence on ALL rotor blades. Affects overall lift and provides vertical control of the helicopter.
Hunting (lead/lag)
Articulating and Rigid rotor systems only
relieves the stress forces on the blade caused by flapping answer for Saturday
Total Force and Tip Path Plane (DISK)
The multitude of Total Aerodynamic Forces acting along the span of each rotor blade summed into a SINGLE FORCE emitting from the center of the rotor disk
The “tip path plane” is the plane formed by the oath of the tips in rotation, also called “plane of rotation”
Total Force acts PERPENDICULAR to TIP PATH PLANE from the center of the rotor system. This is not to be confused with TAF which pertains to lift and drag on a single airfoil.
The two components of Total Force is LIFT and THRUST.
Tip Path Plane is tilted by cyclic pitch control
Balance of forces
Two conditions of flight:
Balanced - opposing forces (thrust, drag, lift, weight) are equal (Newton’s first law INERTIA Law
Unbalanced - opposing forces are not equal (Newton’s second law ACCELERATION Law)
Hovering efficiency
IGE - in ground effect: improved performance when near the ground/surface with an altitude less than one rotor disk, more pronounced over smooth, open surfaces, and is more pronounced in a no wind situation. SLOWS and manages size of rotor tip vortices.
OGE - out of ground effect: increased induced flow (smaller angle of attack for same mechanical angle), increased induced drag, no management of rotor tip vortices. LIFT IS PERPENDICULAR TO RESULTANT RELATIVE WIND.
Reduction in ground effect
**Altitude: exceeding one rotor disk diameter measured FROM THE DISK to the surface
Trees
Bushes
Tall grass
Rough terrain
Water
Effective translational lift
Translational lift is additional lift obtained because of the increased efficiency with AIRSPEED obtained by horizontal flight or by hovering in a wind (start of transition from hover to forward movement)
Effective translational lift (ETL): at approximately 16-24 knots, the rotor completely outruns the recirculation of old vortices and begins to work in relatively undisturbed air. (Airspeed OR headwind at hover)
ETL causes relative wind to become more horizontal:
- more Vertical lift component attained
- less INDUCED drag
- increased angle of attack
Less TURBULENT air enters the rotor system
ETL Blowback
Flapping increases with forward airspeed causing the nose to pitch up
Additional forward cyclic pressure is necessary at this point
Transverse Flow Effect (TFE)
TFE occurs during airspeeds of 10-20 knots (aircraft “shutters” until we exit it… ETL is simply increased efficiency)
Forward half of rotor disk: (10-20 knots) sees more horizontal wind, Angle of Attack is HIGHER with a low induced flow
Rear half of rotor disk: (10-20 knots) sees more vertical wind, higher induced flow and thus Angle of Attack is LOWER
From TFE: LIFT is CREATED in the FRONT PORTION of the rotor disk (later the GP causes lift on the aircraft on the left half)
Go through PP checks on learning!!
