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46:. Liftoff can still be achieved if the helicopter has enough of a straight runway to make a "running take off", where the pilot will accelerate the helicopter across the ground on its landing gear until translational lift speed is achieved and the aircraft begins to climb. This is described in Robert Mason's book
27:. Translation is the conversion from the hover to forward flight. As undisturbed air enters the rotor system horizontally, turbulence and vortices created by hovering flight are left behind and the flow of air becomes more horizontal. The efficiency of the hovering rotor system is greatly improved with each
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at about 16 to 24 knots. This is known as the ETL speed. Above this speed, the rotor system completely outruns the recirculation of old vortices and begins to work in undisturbed air. Efficiency continues to increase with airspeed until the best climb airspeed is reached, and drag is minimised.
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During the translation from the hover to forward flight, the difference in lift across the rotor disc causes a difference in drag, resulting in a noticeable vibration between approximately 10-20 knots.
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As speed increases and translational lift becomes more effective, the helicopter will tend to pitch up and roll to the right or left (depending on main rotor rotation direction), due to
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This additional lift can enable an overloaded helicopter to climb even if it is too heavy to hover in
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The efficiency of the tail rotor is also improved with forward airspeed. This is known as
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of airspeed gained by horizontal movement of the aircraft or wind speed.
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71:. The pilot must anticipate and correct for these effects.
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As forward airspeed increases, the helicopter goes through
193:. US Department of the Army. May 2007. pp. 13, 42–43.
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173:. Federal Aviation Administration. 2012.
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134:Professional Helicopter Pilot Studies
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187:Fundamentals of Flight FM 3-04.203
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36:effective translational lift (ETL)
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164:"2. Aerodynamics of Flight".
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224:. You can help Knowledge by
88:Ground effect (aerodynamics)
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167:Helicopter Flying Handbook
271:Helicopter aerodynamics
132:Croucher, Phil (2007).
220:-related article is a
93:Transverse flow effect
69:transverse flow effect
65:gyroscopic precession
76:translational thrust
98:Dissymmetry of lift
61:dissymmetry of lift
17:Translational lift
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19:is improved
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103:Vortex ring
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265:Categories
114:References
67:, and the
25:helicopter
218:aviation
82:See also
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216:This
191:(PDF)
184:"1".
171:(PDF)
21:rotor
222:stub
138:ISBN
29:knot
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152:^
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