Rotary Wing Aerodynamic Flashcards
Newton’s third law which states
“every action has an equal and opposite reaction.”
With the helicopter on the ground, rotors turning and with the collective full down, the rotor blades are referred to as
“flat pitch.”
An imaginary line from the rotor blade leading edge to the trailing edge is called the
“chord line.”
The ________ is perpendicular to the relative wind line.
lift vector
A helicopter inflight creates a downward rotor wash. As a result, the relative wind is no longer horizontal but contains a downward component called
“induced flow.”
_____________ is the drag incurred as a result of production of lift.
Induced drag
An increase in temperature or humidity or a decrease in pressure will cause density to ________, thereby causing a _____ in lift.
decrease; decrease
Increasing temperature results in ________ air density.
decreasing
Compared to dry air, the density of air at 100% humidity is __________.
less dense
The vertical down-flow of air through the rotor system is __________.
induced flow
The collective pitch control, located on the left side of the Pilot’s seat __________.
changes the pitch angle of both main rotor blades simultaneously
The anti-torque pedals, located on the cabin floor by the Pilot’s feet __________.
control the pitch, and therefore the thrust, of the tail rotor blades
________ is a gain in lift obtained when an aircraft hovers near the ground within 1 RD of the surface.
Ground effect
Ground effect reduces induced flow resulting in __________.
an increase in main rotor lift
Ground effect occurs when the helicopter is within __________.
1 RD of the surface
Improved rotor efficiency resulting from directional flight is called
translational lift.
Translational lift occurs as the helicopter accelerates through __________.
16 to 24 knots
As the helicopter flies through translational lift, it becomes more efficient because __________.
the rotor moves out of its vortices and is in relatively undisturbed air
__________ is the difference in lift between advancing half and the retreating half of the main rotor system.
Dissymmetry of lift
T/F:
As the relative wind speed of the advancing blade increases, the blade gains lift and begins to flap up.
True
A factor which limits a helicopter’s forward speed is ___________.
retreating blade stall
An indication of retreating blade stall is __________.
an increase in airframe vibration
____________ is an uncommanded rate of descent caused by the aircraft rotor inducing a vortex ring as it settles into its own down wash.
Vortex ring state
_________ is a descent caused by a maneuver where power required is greater than power available.
Settling with power
When vortex ring state is evident, the condition may be eliminated by accomplishing one or a combination of the following corrective actions:
Reduce collective, apply forward cyclic to gain airspeed, and enter autorotation
T/F:
During all types of takeoffs and landings, the helicopter is susceptible to a lateral rolling tendency called dynamic rollover.
True
Bank angles of as little as 5 degrees, coupled with a roll rate and crosswinds, can cause the aircraft to roll over in approximately __________ seconds.
2
________ is a condition in which a rotor system is driven by relative wind rather than the engines. Lift being perpendicular to relative wind, in autorotation the lift force has a forward horizontal component (the driving force for the rotor system).
Autorotation
Which is not an effect of the flare in an autorotational descent?
Increased tail rotor ground clearance
What is the force providing rotor rpm during autorotation?
The horizontal component of lift
