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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:

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You can dampen oscillation by reducing your airspeed to at least 10% below this critical one, going slower if necessary while increasing power. Turning could provide enough centrifugal force to stop it as well, which is also the usual remedy when the load starts to swing, but this will increase its effective weight, possibly to more than your lifting capabilities (a good reason for not being too tight on payload), so applying centrifugal force in these cases could make things worse.

Load swing is proportional to speed and the length of the sling – the faster you go, the more it occurs because of the load’s own lift and drag. Put simply, the load will always move further in a swing than the aircraft does – if you move 4 feet to the right, the load will travel eight, after a short pause, as it moves four feet to the other side of you. As it takes as long to swing through 15° as it does through 45, like any pendulum, if you move the opposite way, as is natural, you just make the load swing faster. Going with the swing, that is, load to the left, helicopter to the left, will stop it quickest (do it on your side so you can see what’s going on, but it works both ways). This has the effect of moving the fulcrum point from under the helicopter to over the load, which removes the directional vector. If you want it to in a particular direction, wait till it is going that way before correcting it, then you will be almost pushing it into place. Put simply, don’t pull the load the way you don’t want it to go.
You can do the same with a fore and aft swing, but watch out! Very often, a load can suddenly produce more drag, if something breaks off, for instance, which puts the nose down, which you correct with aft cyclic that simply puts the tail rotor nearer the line. If the load starts forward again (as it will), and pulls the nose further up for you, correcting with forward cyclic may set you nicely up for mast bumping, or at the very least leave you hanging with the stick right back. The correct thing to do here is to apply collective, which will also add an upward force (assuming the clouds aren’t too low). Using a longer line will help. Tail rotor pedals can also be used – when the ball is out to one side, use the opposite pedal when it starts to come back (not before). It is always a good practice not to rush the takeoff and to lift without a swing in the first place.
Scaffolding and planking can swing violently with only a few knots change in airspeed, and aerofoil shapes could even generate their own flying characteristics. Bulky loads with a tendency to float, such as empty containers, will benefit from leaving doors or panels open, which will reduce drag and keep the load facing in one direction.

Setting Down
Approach into wind as much as possible, coming into the hover high enough not to drag the load, so you might be slightly steeper than normal. You’re best to undershoot rather than overshoot, as it’s easier to creep up to a target than go round again if you miss it. To preclude an airflow change making the load unstable, slow down before descending. If the load hits the ground, stop moving forward. Because of inertia, all manoeuvres should be anticipated well in advance and made smoothly (not suddenly)

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