2104 Flashcards
forces acting on the aircraft
drag, lift, weight, thrust
opposes the downward force of weight, is produced by the dynamic effect of the air acting on the airfoil and acts perpendicular to the flightpath through the center of lift.
lift
the combined load of the aircraft itself, the crew, the fuel, and the cargo or baggage. Weight pulls the aircraft downward because of the force of gravity. It opposes lift and acts vertically downward through the aircraft’s center of gravity (CG).
weight
the force produced by the power plant/ propeller or rotor. It opposes or overcomes the force of drag. As a general rule, it acts parallel to the longitudinal axis. However, this is not always the case, as explained later.
thrust
a rearward, retarding force caused by disruption of airflow by the wing, rotor, fuselage, and other protruding objects. Drag opposes thrust and acts rearward parallel to the relative wind.
drag
the total lift and thrust forces of a rotor are perpendicular to the rotor disk.
powered flight
most challenging part of flying a helicopter. This is because a helicopter generates its own gusty air while in a hover, which acts against the fuselage and flight control surfaces.
hovering flight
Increasing the angle of incidence of the rotor blades (pitch) while keeping their rotation speed constant generates additional lift and the helicopter ascends. Decreasing the pitch causes the helicopter to descend. In a no-wind condition in which lift and thrust are less than weight and drag, the helicopter descends vertically. If lift and thrust are greater than weight and drag, the helicopter ascends vertically.
vertical flight
the tip-path plane is tilted in the direction that flight is desired. This tilts the total lift-thrust vector sideward. In this case, the vertical or lift component is still straight up and weight straight down, but the horizontal or thrust component now acts sideward with drag acting to the opposite side.
sideward
the tip-path plane is tilted rearward, which, in turn, tilts the lift-thrust vector rearward. Drag now acts forward with the lift component straight up and weight straight down.
rearward flight
upward sweeping angle of the rotor blades as a result of lift and centrifugal force. In order for a helicopter to generate lift, the rotor blades must be turning.
coning
It states that the value of angular momentum of a rotating body does not change unless an external force is applied. In other words, a rotating body continues to rotate with the same rotational velocity until some external force is applied to change the speed of rotation. Angular momentum is the moment of inertia (mass times distance from the center of rotation squared) multiplied by the speed of rotation.
coriolis effect / law of conservation of angular momentum
state of flight where the main rotor disk of a helicopter is being turned by the action of air moving up through the rotor rather than engine power driving the rotor. In normal, powered flight, air is drawn into the main rotor disk from above and exhausted downward, but during autorotation, air moves up into the rotor disk from below as the helicopter descends.
autorotation
most common type of helicopter
single rotor system
anti-torque device
tail rotor or other anti-torque system
has two main rotor systems and no tail rotor. Usually the rear rotor is mounted at a higher position than the front rotor, and the two are designed to avoid the blades colliding, should they flex into the other rotor’s pathway.
tandem rotor helicopter
The rotor discs are slightly tilted toward each other to provide control along the vertical axis during the hover. This configuration, which is mainly used for larger helicopters, has the advantage of being able to support more weight with shorter blades.
tandem rotor helicopter
two main rotors mounted on one mast, sharing the same axis of rotation but turning in opposite directions, one on top of the other. The control along the vertical axis is produced as a result of different lifts, thus differential torque, of the two rotor discs.
co-axial rotor system
The helicopter will yaw to the left if the clock wise rotating rotor produces more lift, and it will yaw to the right if more lift is produced by the counter-clock wise rotating rotor.
co-axial rotor system
two rotors turning in opposite directions and mounted on two masts slightly inclined towards each other, so that the blades intermesh (without colliding)
synchropter
two horizontals, counter-rotating rotors are mounted side-by-side on a helicopter (or transverse rotorcraft). The anti-torque effect is provided by the opposing rotation of the two main rotors.
side by side configuration
The rotors are mounted at the edge of the wings, on nacelles that rotate in order to transition the rotors from the vertical position (to provide vertical lift like a side by side rotor configuration helicopter), to the horizontal position (where they provide horizontal lift, or thrust, just like in airplanes).
tilt rotor configuration
is a helicopter system which avoids the use of a tail rotor. uses jet thrust rather than blades to provide directional stability and reduce noise, providing the world’s quietest helicopters.
NOTAR (NO TAIL ROTOR CONFIGURATION)
basic helicopter flight control system
cyclic control, collective control, anti-torque pedals
