直升机飞行员手册直升机操作手册 The Helicopter Pilot’s Handbook

时间：2011-04-05 11:37来源：蓝天飞行翻译 作者：航空 点击：次

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Performance changes drastically when both temperature and height increase—just the opposite to flying in cold weather, but you knew that anyway. As far as altitude is concerned, low-level operations (below about 5000 feet) probably won't need you to get too concerned, apart from taking notice of airspeed placards and power limitations, because some of the power lost with altitude is regained with cooler temperatures. You will find that at least 75% power is available to a fair height, but be careful (some pilots report no real difference up to 8500 feet).
Power available is reduced with height (and temperature), and rotors turn at the same speed, so, as you increase altitude, higher pitch and power settings will be required (in some helicopters, like the 500C, the rotor blades will stall before you reach engine limits). The dynamic pressure applied to the ASI is also reduced, so IAS will read less in relation to TAS, so, if you maintain a particular airspeed, your groundspeed will increase accordingly, and you will be going faster than you think. The ASI will also be slower to react.
Density Altitude is your real altitude resulting from height, temperature and humidity. The more the density of the air decreases for any of those reasons, the higher your machine thinks it is. The effects are found at sea level, as well as in mountains, when temperatures are high – for example, 90° (F) at sea level is really 1900 feet as far as your aircraft is concerned. In extreme situations, you may have to restrict your operations to early morning or late afternoon (see also Performance).
Larger control movements will be needed, with more lag, so controls must be moved smoothly and gradually, or the effects may well cancel each other out – you may be on the ground well before that large handful of collective pitch even takes effect! Rotor RPM will rise very quickly with the least excuse.
Your maximum weight for a given altitude (and vice versa), as well as cruising speed in relation to them both should be known, at least approximately, in advance. You also need to know the Hover ceiling In and Out of Ground Effect (HIGE/HOGE) for any weight, so you know you can come to a low hover properly, however briefly, and recover from an unsuitable landing site (hovering should actually be minimised, partly because you can’t rely on ground effect being present, and you have less power anyway, but also because you need to keep a little up your sleeve if the wind shifts, or you begin to lose tail rotor authority. Having said that, no-hover landings are not recommended, because of the chances of snagging the skids on something). Check the performance charts in the back of the Flight Manual, and start practising hovers about 1-2 feet off the ground, bearing in mind, of course, that the said charts were established by test pilots, in controlled situations.
If you allow for these effects as part of your flight planning, fine, but it's easy to get used to a particular place and air density and a corresponding take-off run, base leg, etc., and you may get caught out one day when things change.

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