直升机教员手册 Helicopter Instructor’s Handbook
时间：2014-11-10 08:35来源：FAA 作者：直升机翻译 点击：次
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To view this page ensure that Adobe Flash Player version 9.0.124 or greater is installed. Common Student Difficulties With Autorotation Students have a tendency to look straight down in front of the aircraft while performing an autorotation. By focusing straight down or on the intended touchdown point, the student loses the ability to determine altitudes. Also, students fail to check trim, rotor rpm, and airspeed, and fail to completely close or place the throttle in the ground idle or override position. Autorotation is overwhelming the first few times students perform it and can almost put them into a “frozen state” of mind. Rather than looking at all the instruments, flight gages, and directing what flight path the helicopter should be going, they become fixated with the ground and focus only on that. Once the autorotation has been initiated, immediately have the student verbally call out what they should be looking at. For example, have the student say “Rotors are at 100 percent, NG is stabilized, airspeed is at 60 knots and the aircraft is in trim.” At first, the student is just rehearsing aloud but after doing more and more autorotations and training them to look at the instruments, gauges, and attitude of the helicopter each time with verbal cues help them remain focused on what is important, landing the helicopter safely. Emergency Situations for Discussion Only There are a few situations unique to helicopter operations that must be understood if they are to be avoided. Some of these emergencies may only be discussed, not demonstrated, because demonstration would probably result in damage to the helicopter. They are included here to remind the instructor to make sure the student is able to discuss the problems and how they can be avoided. Vortex Ring State (Settling With Power) NOTE: Vortex ring state (settling with power) is not a discussion only maneuver in a single-rotor helicopter. It can safely be introduced and practiced at altitudes allowing distance to recover. However, settling with power should not be practiced in twin-rotor helicopters due to excessive roll or pitch rates that occur when one rotor is in the vortex ring state and the other is in relatively more stable air. Coaxial and intermeshing main rotor system helicopters should be safe for settling with power practices. Ensure the student understands that settling with power can occur as a result of attempting to descend at an excessively low airspeed in a downwind condition, or by attempting to hover OGE at a weight and density altitude greater than the helicopter’s performance allows. [Figure 12-3] As is always the case, using a scenario that the student finds applicable to his or her future helicopter career is most beneficial. An ideal scenario-type discussion for this can be a confined area approach (in which the winds were incorrectly judged, resulting in a downwind approach) or a job-specific OGE hover-type maneuver (long line, filming for news crews, search-and-rescue hoist operations, external load hookup/ release, etc.,) that puts the helicopter in the required settling with power profile. While common thought is to lower the collective and fly out of the downwash, this may not be the best option due to lower altitudes or obstacles. Through discussion of aerodynamic theory, an option of laterally exiting the ‘disturbed air’ can be the best option available. In a counterrotating system, lateral flight to the right often results in the quickest exit from the airflow and affords the pilot the best view of the exit route. The lateral travel is enhanced by the thrust from the tail rotor and introduces turbulent free air sooner to the tail rotor than any other direction. Adding collective while the helicopter is descending vertically only aggravates the situation. Settling with power can occur only if the rotor is powered. A demonstration of settling with power may be required of the applicant for a commercial helicopter rating. The private pilot applicant may be required only to discuss recognition and avoidance, but should have a demonstration of settling with power to understand its effects better. The demonstration should begin at an altitude high enough above the ground to allow room for safe recovery. Entry into the condition can be made from the events as described in the scenario, if acceptable. Another set of circumstances causing entry into the vortex ring state is a decelerating airspeed descent, such as that experienced with a high, steep, downwind approach. This can be used to show the student a probable or likely result of poor or rushed planning. The student should be reminded that settling with power always requires three conditions to occur: 1. Rate of descent greater than 300 fpm 2. Airspeed less than 10 knots in any direction 3. More than 20 percent of engine power applied to the rotor system By taking away any one of the three conditions, settling with power should not occur. Therefore, the instructor can remind the student to keep the descents slow and less than 300 fpm; keep the helicopter moving into the wind, which normally maintains good airflow at the 10 knot or higher value; and, if altitude allows, reduce the collective to reduce power entering the rotor system. In most instances, a lateral maneuver produces the quickest exit from the disturbed column of air. When simulating an attempt to hover OGE, the airspeed is gradually slowed and power is added to maintain altitude. Care must be taken to avoid any rearward speed. If the helicopter can hover OGE, it may be necessary to reduce power to begin settling, then add power to increase rotor downwash. As soon as the effects of settling with power are noticeable, recovery should be initiated. The noticeable effects are vibration, reduced control effectiveness, and a high rate of descent. Recovery is accomplished by either laterally exiting the disturbed wind or, if altitude allows, reducing collective and lowering the nose to increase forward speed. This moves a helicopter out of its downwash and into translational lift. |
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