力和阻力

Force and resistance

飞机和模型飞机之所以能飞起来，是因为机翼的升力克服了重力。机翼的升力是机翼上下空气压力差形成的。当模型在空中飞行时，机翼上表面的空气流速加快，压强减小;机翼下表面的空气流速减慢压强加大(伯努利定律)。这是造成机翼上下压力差的原因。

Airplanes and model airplanes can fly because the lift of the wings overcomes gravity. The lift of the wing is caused by the air pressure difference between the upper and lower parts 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 decreases and the pressure increases (Bernoulli's law). This is the cause of the pressure difference between the upper and lower wings.

机翼上下流速变化的原因有两个：a、不对称的翼型;b、机翼和相对气流有迎角。翼型是机翼剖面的形状。机翼剖面多为不对称形，如下弧平直上弧向上弯曲(平凸型)和上下弧都向上弯曲(凹凸型)。对称翼型则必须有一定的迎角才产生升力。

There are two reasons for the change of flow velocity: A. asymmetric airfoil; B. the angle of attack between airfoil and relative flow. An airfoil is the shape of the airfoil section. Most of the wing sections are asymmetric, the following arc is straight, the upper arc is upward curved (flat convex type) and the upper and lower arcs are upward curved (concave convex type). A symmetrical airfoil must have a certain angle of attack to generate lift.

升力的大小主要取决于四个因素：a、升力与机翼面积成正比;b、升力和飞机速度的平方成正比。同样条件下，飞行速度越快升力越大;c、升力与翼型有关，通常不对称翼型机翼的升力较大;d、升力与迎角有关，小迎角时升力(系数)随迎角直线增长，到一定界限后迎角增大升力反而急速减小，这个分1叫临界迎角。

The size of lift mainly depends on four factors: A. lift is directly proportional to wing area; B. lift is directly proportional to the square of aircraft speed. Under the same conditions, the faster the flight speed, the greater the lift; C. the lift is related to the airfoil, usually the lift of asymmetric airfoil is larger; D. the lift is related to the angle of attack, when the angle of attack is small, the lift (coefficient) increases linearly with the angle of attack, and when it reaches a certain limit, the angle of attack increases, but the lift decreases rapidly, which is called the critical angle of attack.

机翼和水平尾翼除产生升力外也产生阻力，其他部件一般只产生阻力。

The wing and the horizontal tail produce not only lift but also drag, and other components only produce drag.

2、平飞

2. Pingfei

水平匀速直线飞行叫平飞。平飞是基本的飞行姿态。维持平飞的条件是：升力等于重力，拉力等于阻力。由于升力、阻力都和飞行速度有关，一架原来平飞中的模型如果增大了马力，拉力就会大于阻力使飞行速度加快。飞行速度加快后，升力随之增大，升力大于重力模型将逐渐爬升。为了使模型在较大马力和飞行速度下仍保持平飞，就必须相应减小迎角。反之，为了使模型在较小马力和速度条件下维持平飞，就必须相应的加大迎角。所以操纵(调整)模型到平飞状态，实质上是发动机马力和飞行迎角的正确匹配。

Level flight is called level flight. Level flight is the most basic flight attitude. The conditions for maintaining level flight are: lift equals gravity and pull equals resistance. 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, so that the flight speed will be accelerated. When the flight speed is increased, the lift will increase, and the model will gradually climb when the lift is greater than the gravity. In order to keep the model flying level at high horsepower and speed, the angle of attack must be reduced accordingly. On the contrary, in order to make the model keep level flight at low horsepower and speed, the angle of attack must be increased accordingly. Therefore, to control (adjust) the model to level flight is essentially a correct match between engine horsepower and flight angle of attack.

3、爬升

3. Climb

前面提到模型平飞时如加大马力就转为爬升的情况。爬升轨迹与水平面形成的夹角叫爬升角。一定马力在一定爬升角条件下可能达到新的力平衡，模型进入稳定爬升状态(速度和爬角都保持不变)。稳定爬升的具体条件是：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)。爬升时一部分重力由拉力负担，所以需要较大的拉力，升力的负担反而减少了。

As mentioned earlier, when the model flies horizontally, if the horsepower is increased, it will turn into climbing. The angle between the climbing track and the horizontal plane is called the climbing angle. A new force balance may be achieved under a certain horsepower and a certain climbing angle, and the model will enter a stable climbing state (both speed and climbing angle remain unchanged). The specific conditions for stable climbing are as follows: the pulling force is equal to the backward component of resistance plus gravity (F = & quot; X + GSIN & theta;), and the lifting force is equal to another component of gravity (y = GCOS & theta;). When climbing, part of the gravity is borne by the pulling force, so a larger pulling force is needed, and the burden of the lifting force is reduced.

和平飞相似，为了保持一定爬升角条件下的稳定爬升，也需要马力和迎角的恰当匹配。打破了这种匹配将不能保持稳定爬升。例如马力增大将引起速度增大，升力增大，使爬升角增大。如马力太大，将使爬升角不断增大，模型沿弧形轨迹爬升，这就是常见的拉翻现象。

Similar to normal flight, in order to maintain a stable climb at a certain angle of climb, the proper matching of horsepower and angle of attack is also needed. Breaking this match will not maintain a steady climb. For example, the increase of horsepower will cause the increase of speed, lift and climb angle. If the horsepower is too high, the climbing angle will increase continuously, and the model will climb along the arc track, which is the common phenomenon of rollover.

4、滑翔

4. Gliding

滑翔是没有动力的飞行。滑翔时，模型的阻力由重力的分力平衡，所以滑翔只能沿斜线向下飞行。滑翔轨迹与水平面的夹角叫滑翔角。

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

稳定滑翔(滑翔角、滑翔速度均保持不变)的条件是：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 of stable glide (glide angle and glide speed remain unchanged) is that the drag is equal to the forward component of gravity (x = GSIN & theta;) and the lift is equal to another component of gravity (y = GCOS & theta;).

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离越远。滑翔距离(L)与下降高度(h)的比值叫滑翔比(k)，滑翔比等于滑翔角的余切滑翔比，等于模型升力与阻力之比(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 altitude. The ratio of glide distance (L) to descent height (H) is called glide ratio (k). Glide ratio is equal to cotangent glide ratio of glide angle, and is equal to the ratio of lift and drag (lift drag ratio). Ctgθ="1/h=k。

滑翔速度是滑翔性能的另一个重要方面。模型升力系数越大，滑翔速度越小;模型翼载荷越大，滑翔速度越大。

Gliding speed is another important aspect of gliding performance. The larger the lift coefficient of the model, the smaller the gliding speed; the larger the load of the model wing, the larger the gliding speed.

调整某一架模型飞机时，主要用升降调整片和前后移动来改变机翼迎角以达到改变滑翔状态的目的。

When adjusting a model aircraft, the angle of attack of the wing is changed by adjusting the lifting tab and moving the center of gravity back and forth to achieve the purpose of changing the gliding state.

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