曝光臺 注意防騙 網(wǎng)曝天貓店富美金盛家居專營店坑蒙拐騙欺詐消費(fèi)者

 the proximity of the ground and the magnitude of windshear velocities, the pilot
 is likely to run out of space to maneuver the aircraft and may stall and impact
 the ground. In a modern transport aircraft with the autothrottle connected during
 the approach, the situation will be made even worse because the throttle will have
 been closed earlier on encountering the headwind.
     During 1964-1985, the windshear/microburst has caused at least 26 civ:il avia-
 tion accidents in the Uruted States, invoMng as many as 500 fatalities and more
than 200 injuries. The July 1982 crash of the Pan American Flight 759 on the
 outslarts of New Orleans, which killed 153 people, drew the attention of the avi-
ation community on the hazards of fiying in low-lerrel windshear. A microburst
compounded by heavy rain is believed to be the cause of this crash. Since then,
the Federal Aviation Administration (FAA) and NASA in the United States and
 RAE in the United Kingdom have extensively studied the problems associated with
 windshear/microburst. These efforts have resulted in the development of airbome
 and ground~based windshear detection systems, crew alerting, fKght management,
 simulaton, and evaluation ofpiloting techniques for successful fiight through wind-
shear/nucroburst.
   The best defense against the windshear or microburst is complete avoidance.
However, if unavoidable, it is now recommended that on recognizing a possible
encounter with severe windshear/microburst, the pilot should increase the thrust
to its maximum and rotate the aircraft to an initial attitude, called the target pitch
angle, which depends on the type of the airplane.6,7 The recommended target
pitch angle for transport aircraft is about 15 deg. The pilot is advised to hold these
settings until he is out of the low-level windshear or microburst region.
      The onboard windshear warning/detection systems introduced in the late 1980s
were reactive type, i.e., they detected the windshear only afier the aircraft has
actually encountered the windshear, not before. These systems relied on standard
158             PERFORMANCE, STABILITY, DYNAMICS, AND CONTROL
aircraft instrumentation such as accelerometers and air data systems that gave
inputs to onboard algorithms that determined the windshear surrounding the air-
craft. These reactive systems have given way to more advanced predictive type
sensor systems that can provide the airline crew up to 30 s of advance warning of
windshear/microburst activity ahead ofthe aircraft  The onboard warning/detection
systems may be of radar, Lidar (light detection and ranging), orinfrared type de-
vices. Radar devices measure the Doppler velocity of water droplets moving with
the winds. This method works well if the windshear/microburst conditions are
accompanied by moderate or heavy rain. However, some windshear/microbursts
contain little or no rain.ln such situations, the Lidar devices perform well because
 the laser signal refiects from aerosol particles carried in the atmosphere at low alti-
 tudes. The infrared devices rely on the temperature changes in the farfield (1-3 km
from -the aircraft) caused by the windshear/microburst activity.
  The FAA has made it mandatory for the airlines to install onboard warn-
 ing/detection systems and pilot training to prevent any further mishaps because of
windshear/microburst.
2.11 Summary
             In this chapter, we have studied the basic methods of estimating the perfonnance
     of piston-prop (propeller) and jet aircraft in power-off glide,level fiight   climbing
      fiight,range and endurance, truming flight, takeoff, andlanding. These performance
    characteristics depend on the aerodynamic forces acting on the airframe, the thrust
   or power produced by the propulsion system, the rate of fuel consumption, and
   weight of the aircraft. In general, the thrust or power produced by tre engine
  varies with altitude and flight velocity. The aercXynamic forces depend on the
    angle of attack, Mach number, and Reynolds number. The weight of the airplane
   continuously varies as the fuelis consumed. Furthermore, we have aerodynamic
     and structural limitations as expressed by the maximum lift coefficient and limit
   load factors. Therefore, estimation of the performance characteristics consider-
　
中國航空網(wǎng) www.k6050.com
航空翻譯 www.aviation.cn
本文鏈接地址：PERFORMANCE, STABILITY, DYNAMICS, AND CONTROL1(94)