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Flap Back
Flapback or blowback is the tilting of a helicopter rotor disc, usually aft (backwards), which occurs in several circumstances. In normal operating circumstances, forward flight results in flapback caused by dissymmetry of lift and the transverse flow effect. Dissymmetry of lift is where the forward-moving rotor blade has a faster airspeed, so it generates more lift, which would cause the rotor disc to tilt to the side. To prevent this, the forward-moving blade flaps up, which reduces the angle of attack and the lift. The rearward-moving rotor blade flaps down. Thus, lift is balanced on both sides of the rotor disc. However, this results in the rotor disk being tilted to the rear. The transverse flow effect is where the front of the rotor disc is moving into undisturbed air, whereas the rear of the rotor disc is moving into downward-moving air. The front of the rotor disc therefore has a higher angle of attack, and generates more lift, causing flapback. As airspeed increases, the p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Central Flying School
The Central Flying School (CFS) is the Royal Air Force's primary institution for the training of military flying instructors. Established in 1912 at the Upavon Aerodrome, it is the longest existing flying training school. The school was based at RAF Little Rissington from 1946 to 1976. Its motto is ''Imprimis Praecepta'', Latin for "The Teaching is Everlasting". The school currently manages a series of training squadrons and the RAF Display Team. History The Central Flying School was established by the Royal Navy at Upavon Aerodrome, near Upavon, Wiltshire, on 12 May 1912. The school's strength at the outset was ten Staff Officers and eighty flying students, whose course lasted for sixteen weeks.Hugh Soar, ''Straight & True'' (2012), p. 87 Its first commandant was Captain Godfrey Paine RN, and it also trained pilots for the Royal Flying Corps, created in 1912, and the Royal Naval Air Service, 1914–1918. The school was transferred from the Southern Training Bridge to HQ Train ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Helicopter
A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes allow helicopters to be used in congested or isolated areas where fixed-wing aircraft and many forms of STOL (Short TakeOff and Landing) or STOVL (Short TakeOff and Vertical Landing) aircraft cannot perform without a runway. In 1942, the Sikorsky R-4 became the first helicopter to reach full-scale production.Munson 1968.Hirschberg, Michael J. and David K. Dailey"Sikorsky". ''US and Russian Helicopter Development in the 20th Century'', American Helicopter Society, International. 7 July 2000. Although most earlier designs used more than one main rotor, the configuration of a single main rotor accompanied by a vertical anti-torque tail rotor (i.e. unicopter, not to be confused with the single-blade monocopter) has become the most comm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Helicopter Rotor
A helicopter main rotor or rotor system is the combination of several rotary wings (rotor blades) with a control system, that generates the aerodynamic lift force that supports the weight of the helicopter, and the thrust that counteracts aerodynamic drag in forward flight. Each main rotor is mounted on a vertical mast over the top of the helicopter, as opposed to a helicopter tail rotor, which connects through a combination of drive shaft(s) and gearboxes along the tail boom. The blade pitch is typically controlled by the pilot using the helicopter flight controls. Helicopters are one example of rotary-wing aircraft (rotorcraft). The name is derived from the Greek words ''helix'', helik-, meaning spiral; and ''pteron'' meaning wing. Design principles Overview The helicopter rotor is powered by the engine, through the transmission, to the rotating mast. The mast is a cylindrical metal shaft that extends upward from—and is driven by—the transmission. At the top of the mast i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dissymmetry Of Lift
Dissymmetry of lift (also known as asymmetry of lift or asymmetric lift) in rotorcraft aerodynamics refers to an unequal amount of lift on opposite sides of the rotor disc. It is a phenomenon that affects single-rotor helicopters and autogyros in forward flight. A rotor blade that is moving in the same direction as the aircraft is called the ''advancing blade'' and the blade moving in the opposite direction is called the ''retreating blade.'' When viewed from above, most American helicopter rotors turn counter-clockwise; French and Russian helicopters turn clockwise. Balancing lift across the rotor disc is important to a helicopter's stability. The amount of lift generated by an airfoil is proportional to the square of its airspeed (velocity). In a hover, the rotor blades have equal airspeeds and therefore equal lift. However, in forward flight the advancing blade has a higher airspeed than the retreating blade, creating uneven lift across the rotor disc. Analysis Consider a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transverse Flow Effect
Transverse flow effect is an aerodynamic effect encountered when a helicopter moves horizontally (typically forward) through the air, which causes the rotor disc to roll to the side. It is also known as transverse roll or inflow roll. Transverse flow effect is not experienced when hovering, because the air above the rotor disc is being pulled down from above (known as induced flow or downwash), and is equally distributed around the rotor disc. The air is descending from above, which has the effect of reducing angle of attack. However, when the helicopter starts moving into undisturbed air, a portion of the disc is in clean, unaccelerated air, while the remaining portion of the rotor disc is still working on descending air. The part of the disc working on clean air therefore sees a higher angle of attack than the portion of the disc which is working on descending air. The result is that the portion in clean air develops more lift. The disc rolls to the side, rather than pitching ba ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Helicopter Flight Controls
A helicopter pilot manipulates the helicopter flight controls to achieve and maintain controlled aerodynamic flight. Changes to the aircraft flight control system transmit mechanically to the rotor, producing aerodynamic effects on the rotor blades that make the helicopter move in a deliberate way. To tilt forward and back (pitch) or sideways (roll) requires that the controls alter the angle of attack of the main rotor blades ''cyclically'' during rotation, creating differing amounts of lift (force) at different points in the cycle. To increase or decrease overall lift requires that the controls alter the angle of attack for all blades ''collectively'' by equal amounts at the same time, resulting in ascent, descent, acceleration and deceleration. A typical helicopter has three flight control inputs—the cyclic stick, the collective lever, and the anti-torque pedals. Depending on the complexity of the helicopter, the cyclic and collective may be linked together by a ''mixing uni ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Revolutions Per Minute
Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines. Standards ISO 80000-3:2019 defines a unit of rotation as the dimensionless unit equal to 1, which it refers to as a revolution, but does not define the revolution as a unit. It defines a unit of rotational frequency equal to s−1. The superseded standard ISO 80000-3:2006 did however state with reference to the unit name 'one', symbol '1', that "The special name revolution, symbol r, for this unit is widely used in specifications on rotating machines." The International System of Units (SI) does not recognize rpm as a unit, and defines the unit of frequency, Hz, as equal to s−1. :\begin 1~&\text &&=& 60~&\text \\ \frac~&\text &&=& 1~&\text \end A corresponding but distinct quantity for describing rotation is angular velocity, for which the SI unit is the ra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
