一、升力和阻力

1、 Lift and drag

飛機和模型飛機之所以能飛起來，是因為機翼的升力克服了重力。機翼的升力是機翼上下空氣壓力差形成的。當模型在空中飛行時，機翼上表面的空氣流速加快，壓強減小；機翼下表面的空氣流速減慢壓強加大(伯努利定律)。這是造成機翼上下壓力差的原因。

Aircraft and model aircraft can fly because the lift of the wings overcomes gravity. The lift of the wing is formed by the pressure difference between the upper and lower air of the wing. When the model flies in the air, the air velocity on the upper surface of the wing increases and the pressure decreases; The air velocity on the lower surface of the wing slows down and the pressure increases (Bernoulli's law). This is the cause of the pressure difference between the upper and lower wings.

造成機翼上下流速變化的原因有兩個：a、不對稱的翼型；b、機翼和相對氣流有迎角。翼型是機翼剖面的形狀。機翼剖面多為不對稱形，如下弧平直上弧向上彎曲(平凸型)和上下弧都向上彎曲(凹凸型)。對稱翼型則必須有一定的迎角才產生升力。

There are two reasons for the variation of flow velocity up and down the wing: A. asymmetric airfoil; b. The wing has an angle of attack with respect to the flow. An airfoil is the shape of a wing section. The wing section is mostly asymmetric, with the following arc straight, the upper arc bending upward (flat convex type) and the upper and lower arcs bending upward (concave convex type). Symmetrical airfoils must have a certain angle of attack to produce lift.

升力的大小主要取決于四個因素：a、升力與機翼面積成正比；b、升力和飛機速度的平方成正比。同樣條件下，飛行速度越快升力越大；c、升力與翼型有關，通常不對稱翼型機翼的升力較大；d、升力與迎角有關，小迎角時升力(系數)隨迎角直線增長，到一定界限后迎角增大升力反而急速減小，這個分界叫臨界迎角。

The lift force mainly depends on four factors: a. the lift force is directly proportional to the wing area; b. The lift is proportional to the square of the aircraft speed. Under the same conditions, the faster the flight speed, the greater the lift; c. The lift is related to the airfoil, and the lift of asymmetric airfoil is usually large; d. The lift is related to the angle of attack. At a small angle of attack, the lift (coefficient) increases linearly with the angle of attack. When it reaches a certain limit, the angle of attack increases, but the lift decreases rapidly. This boundary is called the critical angle of attack.

機翼和水平尾翼除產生升力外也產生阻力，其他部件一般只產生阻力。

Wings and horizontal tail generate drag in addition to lift, and other components generally only generate drag.

二、平飛

2、 Pingfei

水平勻速直線飛行叫平飛。平飛是更基本的飛行姿態。維持平飛的條件是：升力等于重力，拉力等于阻力(圖3)。

Horizontal flight is called level flight. Level flight is the most basic flight attitude. The condition for maintaining level flight is that the lift is equal to gravity and the pull is equal to drag (Fig. 3).

由于升力、阻力都和飛行速度有關，一架原來平飛中的模型如果增大了馬力，拉力就會大于阻力使飛行速度加快。飛行速度加快后，升力隨之增大，升力大于重力模型將逐漸爬升。為了使模型在較大馬力和飛行速度下仍保持平飛，就必須相應減小迎角。反之，為了使模型在較小馬力和速度條件下維持平飛，就必須相應的加大迎角。所以操縱(調整)模型到平飛狀態，實質上是發動機馬力和飛行迎角的正確匹配。
 

Because the lift and drag are related to the flight speed, if the horsepower of an original model in level flight is increased, the pull will be greater than the drag to accelerate the flight speed. When the flight speed increases, the lift increases, and the lift is greater than the gravity, and the model will climb gradually. In order to keep the model level at high horsepower and flight speed, the angle of attack must be reduced accordingly. On the contrary, in order to maintain the level flight of the model under the condition of small horsepower and speed, the angle of attack must be increased accordingly. Therefore, controlling (adjusting) the model to level flight is essentially the correct match between engine horsepower and flight angle of attack.

三、爬升

3、 Climb

前面提到模型平飛時如加大馬力就轉為爬升的情況。爬升軌跡與水平面形成的夾角叫爬升角。一定馬力在一定爬升角條件下可能達到新的力平衡，模型進入穩定爬升狀態(速度和爬角都保持不變)。穩定爬升的具體條件是：拉力等于阻力加重力向后的分力(F=X十Gsinθ)；升力等于重力的另一分力(Y=GCosθ)。爬升時一部分重力由拉力負擔，所以需要較大的拉力，升力的負擔反而減少了(圖4)。

As mentioned earlier, when the model flies horizontally, it will turn to climb if the horsepower is increased. The angle between the climbing track and the horizontal plane is called the climbing angle. A certain horsepower may reach a new force balance under a certain climbing angle, and the model enters a stable climbing state (both speed and climbing angle remain unchanged). The specific conditions for stable climbing are: the pulling force is equal to the backward component of resistance plus gravity (F = x ten GSIN) θ)； Lift is equal to the other component of gravity (y = GCOS θ)。 When climbing, part of the gravity is borne by the tension, so a larger tension is required, and the lifting load is reduced (Fig. 4).

和平飛相似，為了保持一定爬升角條件下的穩定爬升，也需要馬力和迎角的恰當匹配。打破了這種匹配將不能保持穩定爬升。例如馬力增大將引起速度增大，升力增大，使爬升角增大。如馬力太大，將使爬升角不斷增大，模型沿弧形軌跡爬升，這就是常見的拉翻現象(圖5)。

Similar to peace flight, in order to maintain a stable climb at a certain climb angle, it also needs the appropriate matching of horsepower and angle of attack. Breaking this match will not maintain a stable climb. For example, the increase of horsepower will increase the speed, lift and climb angle. If the horsepower is too high, the climbing angle will continue to increase and the model will climb along the arc track, which is a common pull over phenomenon (Fig. 5).

四、滑翔

4、 Gliding

滑翔是沒有動力的飛行。滑翔時，模型的阻力由重力的分力平衡，所以滑翔只能沿斜線向下飛行。滑翔軌跡與水平面的夾角叫滑翔角。

Gliding is flight without power. When gliding, the resistance of the model is balanced by the component of gravity, so gliding can only fly down the oblique line. The angle between the gliding trajectory and the horizontal plane is called the gliding angle.

穩定滑翔(滑翔角、滑翔速度均保持不變)的條件是：阻力等于重力的向前分力(X=GSinθ)；升力等于重力的另一分力(Y=GCosθ)。

The condition for stable gliding (gliding angle and gliding speed remain unchanged) is that the resistance is equal to the forward component of gravity (x = GSIN) θ)； Lift is equal to the other component of gravity (y = GCOS θ)。

滑翔角是滑翔性能的重要方面。滑翔角越小，在同一高度的滑翔距離越遠。滑翔距離(L)與下降高度(h)的比值叫滑翔比(k)，滑翔比等于滑翔角的余切滑翔比，等于模型升力與阻力之比(升阻比)。  Ctgθ=1/h=k。

Gliding angle is an important aspect of gliding performance. The smaller the gliding angle, the farther the gliding distance at the same height. The ratio of gliding distance (L) to descent height (H) is called gliding ratio (k), which is equal to the cotangent gliding ratio of gliding angle and the ratio of lift to drag (lift drag ratio) of the model. Ctg θ= 1/h=k。