There are many similarities between the names of various parts of the propeller and the wing. The blade is equivalent to the wing surface of the wing, the blade also has leading edge and trailing edge, and the profile shape of the blade is similar to that of the wing. However, when the model aircraft flies, the propeller rotates to generate tension and moves forward with the aircraft, so its working condition is much more complex than that of the wing.

1、右旋螺旋桨和左旋螺旋桨

1. Right hand propeller and left hand propeller

当我们站在螺旋桨后面（相当于飞机驾驶员的位置）来观察螺旋桨旋转。如果看到螺旋桨是顺时针方向旋转，这种螺旋桨称为右旋螺旋桨，反之称为左旋螺旋桨。

When we stand behind the propeller (equivalent to the position of the aircraft pilot) to observe the rotation of the propeller. If you see that the propeller rotates clockwise, this propeller is called a right-hand propeller, and vice versa.

对于大多数活塞发动都采用右旋螺旋桨，这是因为使用的螺钉和螺纹都是右旋的居多，这样螺旋桨就不会松脱了，由于惯性，螺旋桨会变得很紧，保证了。

For most piston engines, right-handed propellers are used because most of the screws and threads used are right-handed, so the propeller will not loose. Due to inertia, the propeller will become very tight to ensure safety.

2、螺旋桨的旋转面

2. Rotating surface of propeller

螺旋桨旋转时，通过螺旋桨上一点并且垂直与旋转轴的一个假想的平面。

When the propeller rotates, it passes through a point on the propeller and is perpendicular to the axis of rotation.

3、螺旋桨直径

3. Propeller diameter

螺旋桨两个桨尖之间的距离。也可以认为是螺旋桨旋转时更大旋转面的直径。

The distance between the two tips of a propeller. It can also be considered as the diameter of the maximum rotating surface when the propeller rotates.

4、桨叶角

4. Blade angle

桨叶剖面的弦线与旋转平面之间的夹角称为桨叶角。

The angle between the chord of the blade section and the rotation plane is called the blade angle.

从定义上看，螺旋桨的桨叶角与机翼的安装角相似。不过机翼装在机身上的安装角一般沿机翼翼展都是相同的，只有少数模型的机翼安装角在翼尖部分小，靠一根部分大。可是螺旋桨的桨叶却完全不同了：越靠近旋转轴，剖面的桨叶角越大；越接近桨尖，剖面的桨叶角越小。制作正确的螺旋桨，从桨尖到桨根，桨叶角的扭状程度是逐渐增大的。

By definition, the blade angle of a propeller is similar to the installation angle of a wing. However, the installation angle of the wing mounted on the fuselage is generally the same along the wing span. Only a few models have a small wing installation angle at the wing tip and a large one at one end. However, the blades of the propeller are completely different: the closer to the rotating shaft, the greater the blade angle of the section; The closer to the tip, the smaller the blade angle of the section. When making the correct propeller, the twist degree of blade angle increases gradually from the tip to the root.

图1－38 作用在螺旋桨上的空气动力

Figure 1-38 aerodynamic force acting on propeller

5、旋转速度

5. Rotation speed

螺旋桨旋转时桨叶上任一剖面延圆周切线方向的旋转线速度。

When the propeller rotates, the linear speed of any section of the blade along the tangential direction of the circumference.

为螺旋桨每分钟的旋转圈数，为桨叶上任一剖面到旋转轴的距离。

Is the number of revolutions per minute of the propeller, and is the distance from any section of the blade to the rotation axis.

由于螺旋桨桨叶各剖面到旋转轴的距离都不相等，所以螺旋桨旋转时，各个剖面所经历的路程也不相等。越靠近桨尖，半径越大，旋转速度也就越大。螺旋桨旋转所引起的习惯力对气流的速度就等于螺旋桨的旋转速度。

Because the distance from each section of the propeller blade to the rotation axis is not equal, the distance experienced by each section is not equal when the propeller rotates. The closer to the tip, the greater the radius and the greater the rotation speed. The speed of the habitual force caused by the rotation of the propeller to the air flow is equal to the rotation speed of the propeller.

6、前进速度

6. Forward speed

模型飞机飞行时，由于桨叶随着模型一起运动，所以螺旋桨的前进速度等于模型飞机的飞行速度。

When the model aircraft flies, because the blades move with the model, the forward speed of the propeller is equal to the flight speed of the model aircraft.

7、合速度

7. Closing speed

螺旋桨旋转时产生拉力，使模型向前飞行。这是，真正作用在桨叶上的气流是螺旋桨旋转引起的相对气流速度和模型前进作用在桨叶上的相对气流的速度之矢量和。它称为合速度。

When the propeller rotates, it generates tension to make the model fly forward. This is that the real air flow acting on the blade is the vector sum of the relative air flow velocity caused by the rotation of the propeller and the relative air flow velocity acting on the blade forward of the model. It is called combined velocity.

8、桨叶迎角

8. Blade angle of attack

桨叶剖面的弦线与合速度方向之间的夹角称为桨叶迎角。如果模型没有前进速度，那么桨叶角就等于桨叶迎角。所以一般情况，桨叶迎角总是小于桨叶角的。

The angle between the chord of the blade profile and the direction of resultant velocity is called the blade angle of attack. If the model has no forward speed, the blade angle is equal to the blade angle of attack. Therefore, in general, the blade angle of attack is always less than the blade angle.

与机翼情况相似，这个角度的大小，决定了桨叶剖面产生的拉力大小。

Similar to the wing, this angle determines the pull generated by the blade profile.

9、气流角

9. Air flow angle

合速度与旋转速度之间的夹角称为气流角。

The angle between the closing speed and the rotating speed is called the air flow angle.

显然，由于桨叶各剖面处的旋转速度都不相同，所以越靠近桨尖气流角越小。

Obviously, because the rotation speed at each section of the blade is different, the closer the blade tip is, the smaller the air flow angle is.

10、几何螺距和实际螺距

10. Geometric pitch and actual pitch

如果螺旋桨翼面旋转一面前进，亲近的方向是沿着桨叶剖面的翼弦方向，也就是说桨叶迎角为0度，那么每旋转一圈，剖面前进的距离称为几何螺距。

If the propeller surface rotates and moves forward, the close direction is along the chord direction of the blade section, that is, the blade angle of attack is 0 degrees, then the forward distance of the section is called geometric pitch for each revolution.

图1－39 几何螺距与实际螺距

Figure 1-39 geometric pitch and actual pitch

但是与机翼的情况相似，要使螺旋桨产生足够的拉力，桨叶与相对气流一定要呈某个迎角，所以在实际飞行中桨叶应当是沿着气流的方向并带着某个迎角前进，而不是沿桨叶剖面翼弦方向前进。螺旋桨桨叶沿着相对气流方向旋转一周，剖面前进的距离称为实际螺距，也就是说，几何螺距使桨叶迎角为0度时的实际螺距。如果把螺旋桨旋转一圈时桨叶剖面经过的轨迹加以展开，从图上可以看到实际螺距一定比几何螺距小。如果桨叶迎角越大，这个差别也越大。

However, similar to the case of the wing, to make the propeller produce sufficient tension, the blade must have an angle of attack with the relative air flow. Therefore, in actual flight, the blade should advance along the direction of the air flow and with a certain angle of attack, rather than along the chord direction of the blade section. The propeller blade rotates one circle along the relative air flow direction, and the forward distance of the profile is called the actual pitch, that is, the geometric pitch makes the actual pitch when the blade angle of attack is 0 degrees. If the trajectory of the blade profile when the propeller rotates one circle is expanded, it can be seen from the figure that the actual pitch must be smaller than the geometric pitch. The greater the blade angle of attack, the greater the difference.

螺距太大而飞行速度不够快，则攻角太大而失速，这种情形在这里叫螺旋桨打滑，螺距太小而飞行速度太快，则攻角太小，效率则很差，所以结论是高速飞机用小桨大螺距，低速飞机用大桨小螺距。以前在莱特兄弟时代，飞机做好以后要拉一个绑在树上磅秤来测拉力，现在在航模飞行场上偶而也有人这么做，现在我们知道这是多余的，测得的拉力因没有飞机前进的速度，只是静拉力，所以只有在飞机静止时有效，飞机有了速度后就不准了。

If the pitch is too large and the flight speed is not fast enough, the angle of attack is too large and stall. This situation is called propeller slip here. If the pitch is too small and the flight speed is too fast, the angle of attack is too small and the efficiency is very poor. Therefore, the conclusion is that high-speed aircraft use small propeller with large pitch and low-speed aircraft use large propeller with small pitch. In the past, in the Wright brothers' era, when the plane was ready, it was necessary to pull a scale tied to a tree to measure the tension. Now some people occasionally do this on the model flight field. Now we know that this is redundant. The measured tension is only static tension because it does not have the forward speed of the aircraft, so it is only effective when the aircraft is stationary, and it is not allowed when the aircraft has speed.