曝光台 注意防骗
网曝天猫店富美金盛家居专营店坑蒙拐骗欺诈消费者
1. in powered flight;
2. high rate of descent, in excess of 500 feet per minute; and
3. low airspeed, less than 20 MPH indicated.
Almost every transition from forward flight to a hover utilizes a powered approach, a rate of descent and a reduced airspeed. To prevent the occurrence of vortex ring, control your rate of descent less than 300 feet per minute.
Recovery Techniques. There are two methods of effective recovery from the vortex ring state. Both change the airflow conditions causing it and both involve a loss of height:
1. Dive out. Normally this technique will result in less altitude loss than with the autorotational recovery. The pilot should apply forward cyclic while reducing the collective; the vortices will leave the disc as the airspeed increases and the helicopter will move forward of its downwash. Normal flight may then be resumed.
2. Enter autorotation. By this method, the airflow through the rotor changes from the disturbed flow of the vortex ring to the upward autorotational flow. Once autorotational descent has commenced then the pilot may ease the cyclic forward to gain airspeed while power is increased and normal flight resumed.
You should note that an increase in collective alone may not result in a recovery and indeed may only serve to increase the rate of descent. This increase in blade pitch will cause the vortices to intensify in strength and will result in a more rapid descent.
There are some uninformed pilots who use “settling with power” to describe vortex ring, in fact some publications use the terms interchangeably. Confusion results when symptoms are related that do not describe true vortex ring but rather describe “settling with insufficient power”. This may occur when a pilot attempts to arrest a rapid, low power descent only to find that he has insufficient power available to bring the helicopter to either a hover or a no-hover landing without exceeding the engine limits. However, this is not a vortex ring situation.
Another situation, ‘over-pitching’ is often misinterpreted as vortex ring. This is where the pilot rapidly increases collective considerably and the engine cannot produce enough power to overcome the large, swift increase in drag on the rotor system. The result is that the rotor system quickly slows down and loses efficiency causing the helicopter instantly to sink. Again, this is not vortex ring.
The most common situations, where you would be most likely to encounter vortex ring, are usually when you misjudge the wind with a heavy load on a hot day. Downwind approaches to a confined area, or a mountain pad, are two good examples. Always control your rate of descent carefully on these occasions, and make sure an escape route is available. Your instructor will discuss the symptoms and recovery techniques more fully. Demonstration of this exercise is not generally performed, as the stresses on the airframe and rotor system are unknown.
PREVENTION IS BETTER THAN CURE!!!
EXERCISE 27 - PRACTICAL LOADING AND MAXIMUM WEIGHT OPERATIONS
Loading and maximum weight operations are shown here to be one particular exercise. Realistically, you will be gaining experience in this exercise almost from the day you start your course. To operate a helicopter to its full capabilities, a thorough understanding of its limitations is required. All helicopters have definite limitations with regard to both weight and balance.
It is the responsibility of the pilot-in-command to load the helicopter within the limitations set out in the authorized weight and balance section of the flight manual. To simplify loading problems, manufacturers supply pre-calculated graphs, charts and loading examples. You will be shown how to calculate the weight and balance for your type of helicopter.
In normal working conditions, because your loads are frequently varied, you should be familiar with the effects of these variations. A check of weight and balance should be included among the factors considered by the pilot in his pre-takeoff checks. If in any doubt, always calculate with either the charts, or reports, before attempting the load. Always perform a hover-check; this will give you an accurate check of the power being used, and therefore what is still available to you, and how the load is affecting your centre of gravity.
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：
直升机飞行训练手册 HELICOPTER FLIGHT TRAINING MANUAL(52)
