Theory of helicopter

Helicopter has 2 sets of blades, one on the top of cabinet, and anther one is at the rear end.

The theory of blades is very simple. When the blades rotate, air moves from one side to the other side. This creates a pressure difference between two sides. This pressure difference can be as larage as to support the weight of the helicopter as stationary. If we increase the pressure difference by a little bit, there is a net force point upward and give an upward power to the helicopter to take off. This pressure difference can be controlled by the speed of the rotation of the blades.

How about making turns? It is also very simple. If we put the blades vertically at the rear, this pressure difference can produce a horizontal force to the helicopter.

right?

直昇機能飛行及停於半空，唯一原因是得到主旋翼提供之昇力。如果昇力大於直昇機重量，直昇機就上昇。如果昇力等同重量，直昇機就縣停。如果主旋翼向一方傾斜，直昇機就會向該方向飛行。而最特別的是直昇機之機艏/頭是無須指向飛行方向的，即可以保持側飛或倒後飛行。
直昇機主旋翼橫切面與飛機翼一樣，當主旋翼旋轉，就造成氣流流經翼面，產生昇力。主旋翼是以一固定轉速旋轉，當要加大昇力時，就提高主旋翼仰角。要下降，則平放旋翼，直昇機就像竹蜻蜓般下降。至於控制機艏方向，通常會由尾旋翼操縱，尾旋翼是垂直安裝於機尾，尾旋翼之主要功能是抵消主旋翼之反作用力(因主旋翼向一方旋轉，必然會產生反作用力，令機身向另一方向旋轉)。它同是以固定轉速旋轉(因與主旋翼連動)，它亦可以改變旋翼角度，來令直昇機左右旋轉，因此它之角度是有正負(或左右)之分。如果直昇機使用兩張主旋翼，則其主旋翼必須要左右旋轉，以抵消相對之反作用 力，這樣就無須安裝尾旋翼。