2104 - B Flashcards
are the most common type of helicopter. They need an anti-torque device (tail rotor or other anti-torque system) to counteract the twisting momentum produced by the main rotor, which is powered by one or more engine(s).
Single Rotor Configuration
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. 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 (Or Dual Rotor System)
are 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.
The drag produced by the rotors is quite large due to the interference of airflows, so these helicopters do not normally have a high cruising speed.
Mounting rotors closer together, which is possible only with rigid rotors, reduces the amount of drag produced.
Co-Axial Rotor System
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 Configuration
A helicopter with two rotors turning in opposite directions and mounted on two masts slightly inclined towards each other, so that the blades intermesh (without colliding), is called a ___________. The two rotors mesh with one another, like a gearwheel. This configuration does not require a tail rotor, since the anti-torque action is performed by the counter-rotation of the rotors. Synchropters have high stability and powerful lifting capabilities.
Synchropter
is usually projected upward from the cockpit floor, between the pilot’s legs or between the two pilot seats in some models. This primary flight control allows the pilot to fly the helicopter in any direction of travel: forward, rearward, left, and right.
Cyclic Pitch Control
A Basic Helicopter flight control system is composed of;
Cyclic Control
- Collective Control
- Throttle Control
- Anti-Torque Pedals
two horizontals, counter-rotating rotors are mounted ___________ 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). Both lift and propulsion are then generated by the rotors, which act as helicopter main rotors when in the vertical position, and as airplane propellers when in the horizontal position. Lift is then provided by fixed wings.
Tilt Rotor Configuration
located on the cabin floor by the pilot’s feet, control the pitch and therefore the thrust of the tail rotor blades or other system. allow the pilot to control the pitch angle of the tail rotor blades, which in forward flight puts the helicopter in longitudinal trim and, while at a hover, enables the pilot to turn the helicopter 360°.
Antitorque Pedals
is to regulate engine rpm. If the correlator or governor system does not maintain the desired rpm when the collective is raised or lowered, or if those systems are not installed, the throttle must be moved manually with the twist grip in order to maintain rpm.
Throttle Control
is flight in which constant altitude and heading are maintained. The attitude of the rotor disk relative to the horizon determines the airspeed. The horizontal stabilizer design determines the helicopter’s attitude when stabilized at an airspeed and altitude. Altitude is primarily controlled by use of the collective.
Straight-and-Level Flight
is a maneuver used to change the heading of the helicopter.
Turn
is a maneuver in which the helicopter gains altitude at a controlled rate in a controlled attitude. NORMAL
Normal Climb
is a maneuver in which the helicopter loses altitude at a controlled rate in a controlled attitude.
Descent
involves flying the helicopter from the ground vertically to a skid height of two to three feet, while maintaining a constant heading. Once the desired skid height is achieved, the helicopter should remain nearly motionless over a reference point at a constant altitude and on a constant heading. The maneuver requires a high degree of concentration and coordination.
Vertical Takeoff To A Hover
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
A stationary hover is a maneuver in which the helicopter is maintained in nearly motionless flight over a reference point at a constant altitude and on a constant heading
Hovering
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
(hovering, vertical, forward, sideward, or rearward), the total lift and thrust forces of a rotor are perpendicular to the rotor disk.
Powered Flight
is the 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
Hovering is actually an element of ________. 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 Flight
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
is an 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. As lift on the blades is increased (in a takeoff, for example), two major forces are acting at the same time— centrifugal force acting outward, and lift acting upward. The result of these two forces is that the blades assume a conical path instead of remaining in the plane perpendicular to the mast. This can be seen in any helicopter when it takes off; the rotor disk changes from flat to a slight cone shape
Coning
is also referred to as the law of conservation of angular momentum. 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)
is the 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 is permitted mechanically by a freewheeling unit, which is a special clutch mechanism that allows the main rotor to continue turning even if the engine is not running
Autorotation
