力和阻力

Force and resistance

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(dāng)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。

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.

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(chǎn)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(guān)，通常不對稱翼型機翼的升力較大;d、升力與迎角有關(guān)，小迎角時升力(系數(shù))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1叫臨界迎角。

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.

機翼和水平尾翼除產(chǎn)生升力外也產(chǎn)生阻力，其他部件一般只產(chǎn)生阻力。

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

2、平飛

2. Pingfei

水平勻速直線飛行叫平飛。平飛是基本的飛行姿態(tài)。維持平飛的條件是：升力等于重力，拉力等于阻力。由于升力、阻力都和飛行速度有關(guān)，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(yīng)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(yīng)的加大迎角。所以操縱(調(diào)整)模型到平飛狀態(tài)，實質(zhì)上是發(fā)動機馬力和飛行迎角的正確匹配。

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

前面提到模型平飛時如加大馬力就轉(zhuǎn)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(wěn)定爬升狀態(tài)(速度和爬角都保持不變)。穩(wěn)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(fù)擔(dān)，所以需要較大的拉力，升力的負(fù)擔(dān)反而減少了。

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.

和平飛相似，為了保持一定爬升角條件下的穩(wěn)定爬升，也需要馬力和迎角的恰當(dāng)匹配。打破了這種匹配將不能保持穩(wěn)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(xiàn)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 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.

穩(wěn)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 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 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個重要方面。模型升力系數(shù)越大，滑翔速度越小;模型翼載荷越大，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.

調(diào)整某一架模型飛機時，主要用升降調(diào)整片和重心前后移動來改變機翼迎角以達到改變滑翔狀態(tài)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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