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The vortex generated by an airfoil is proportional to the lift generated by the airfoil, its size, and angle of attack. The ratio of aircraft weight to aerofoil size also has a bearing on the vortex produced. A heavy aircraft with a small wing (and therefore a high wing loading) will produce intense vortices, while the longer and broader the aerofoil, the greater the area affected by the vortices.
This same principle applies to helicopters. Helicopter rotors trail the same twin vortices as a fixed wing aircraft, and the greater the helicopter’s weight, the more intense will be its wake turbulence.
Speed affects the vortices inversely; that is: an aircraft flying at a slow speed will produce more intense vortices than when it is at cruise. We would therefore expect to encounter the most intense wake turbulence when aircraft are landing or taking off, although an S61 flying at 20 kts will also produce intense vortices while not necessarily landing or taking off.
These vortices tend to descend below the path of the aircraft producing them and spread apart. A wind, of course, will affect the vortices causing them to drift downwind, dissipating slowly in calm winds, and dissipating more rapidly in strong winds. It should be noted, however, that the movements of the vortices are not predictable with any degree of certainty.
To avoid encountering wake turbulence, the helicopter pilot should select approach or departure paths that are above the departure path of other, larger aircraft. Also, he should avoid selecting any flight path that would cause him to intersect the arrival or departure path of any aircraft capable of creating strong vortices, and particularly avoid below the flight path of other aircraft.
AIR TRAFFIC SERVICES (ATS)
Control zones have been designated around certain aerodromes to keep IFR aircraft within controlled airspace during approaches and to facilitate the control of VFR and IFR traffic. Control zones within which a radar control service is provided normally have a 7-mile radius. Others have a 5-mile radius, with the exception of a few which have a 3-mile radius. Control zones are capped at 3000 feet above airport elevation unless otherwise specified.
VFR aircraft require a clearance from an air traffic control unit or to establish contact with an ATS to enter a control zone. This clearance or instruction, however, does not relieve the pilot of responsibility for avoiding other aircraft, maintaining appropriate terrain and obstruction clearance, and remaining in VFR weather conditions. It is also a requirement that the aircraft be equipped with radio communication equipment capable of two-way communication with the appropriate air traffic control unit. In certain instances, NORDO operations may be authorized. You should consult your A.I.M Canada for details.
When you intend to conduct flight training exercises within a control zone, the ATS will likely ask that you:
1. remain on the frequency;
2. advise them of your intentions.
If you intend to depart the control zone, you should advise the ATS of your intentions, and they in turn will advise you when to leave the frequency.
Many control zones have established reporting points that VFR traffic may use to identify their position when transmitting to the ATS.
Your instructor will explain the procedure for using Mandatory Frequencies (MF) and Aerodrome Traffic Frequencies (ATF). At uncontrolled aerodromes, although there will not be an operating control tower, a Flight Service Station may be in place. The FSS does not exercise control over air traffic but only acts in an advisory capacity, providing information on winds, runway in use, known traffic, weather, etc. Some airfields will not be equipped with either a tower or a FSS, but will only have a “Unicom” frequency that may or may not be monitored. At uncontrolled aerodromes, pilots must use the appropriated frequency to transmit position reports and broadcast their intentions while operating in the zone.
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直升机飞行训练手册 HELICOPTER FLIGHT TRAINING MANUAL(28)
