时间:2011-04-05 11:37来源:蓝天飞行翻译 作者:航空 点击:次
To view this page ensure that Adobe Flash Player version 9.0.124 or greater is installed. In every flare there is a point called the apex, which is where the trading off of airspeed for lift is essentially all over and you just have to get yourself on the ground. Put another way, it is the point where there is no further benefit from the flare manoeuvre, so you may as well pull the pitch (a little later in a 206). As the flare ends, and the kinetic energy of the rotors is used when the collective is raised, the airflow through the rotors is reversed, assisting the level, ready to cushion the landing with collective. This is where correct use of airspeed during the descent will have had the most beneficial effects—as the kinetic energy stored in the blades is what slows you down, it follows that any you have used already to slow an unnecessarily fast descent is not available for the final stages of touching down. But what if you are going into a clearing? Or don't get that much practice? The above method is fine, but you need to be doing it a lot to get it right every time. One way that will cover both the above situations is to start the flare very much earlier, so that you are virtually stopped quite high up. Then carry on as if you had an engine failure in a high hover, that is, dump the pole to get going vertically downwards and haul it all in at the end. In a vertical autorotation, there is a phenomenon known as dynamic stall that will help, where an aerofoil that is rapidly stalled can produce double the normal lift, just for a moment, because the breakup of the boundary layer on top is delayed for a while, if indeed you don’t actually create a little vortex along it that improves lift even further. Do not try to gain speed, as you will split the lift vector and increase your rate of descent. |