what is the difference between propeller pitch and chord length?
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Repost from another deleted post.
Difference: cord length is a length, prop pitch is an angle.
Cord length is determined to strike a balance between power, size and efficiency, it is fixed once you’ve determined it.
However the prop pitch is usually variable. Once the aircraft starts moving forward, incoming airflow go into the prop, effectively reducing its angle of attack, which works like the pitch is reduced.
Therefore to maintain thrust, either you increase prop RPM, which has a limit before the prop tip reaches the speed of sound and loses efficiency, or increase the actual prop pitch, maintaining the effective pitch.
This is why almost all prop aircraft has adjustable prop pitch, the ones that don’t are the cheap and slow basic GA aircraft.
Imagine you took a saw and cut off the end of a propeller blade. Now place a ruler on the cut end. Align the ruler so it goes from the leading edge to the trailing edge where you made the cut. The length you measure from the leading to trailing edge is the cord length. The angle of the ruler (from the disk of the propeller rotation) is the pitch angel. I’ll call this the aerodynamicist’s definition of pitch angle (see more below). For airplane and boat propellers, both the cord length and pitch angle of the blade will usually change as you move outward along the blade. For a helicopter’s main rotor, both the pitch angle and cord length are likely to be be the same for most of the length of the blade
Note that the pitch of a propeller (especially a fixed pitch propeller) is usually given as a length, not an angle. For example a 30 inch pitch. This is how far the propeller wound advance if it made one full turn with no slip. For a fixed pitch propeller, all areas of the blade will generally have the same pitch **length**, but the pitch angel will get smaller as you move further from the center of the propeller.
For a variable pitch propeller, the term “pitch angle” can be used to describe the angle to which the propeller as a whole is adjusted. This is related to , but not the same as the definition above. If the pitch of a variable pitch propeller is set at, say, 10 degrees, the aerodynamicists pitch angle will still change along the length of the blade — it won’t be 10 degrees everywhere. This is a case where the same term can mean slightly different things depending on where it is used.
Chord is a line through the middle.
Make your hand into a C shape, imagine a line cutting it in half. That is the chord line of your hand.
This applies to any airfoil. Wings, propellers, your hand in this example!
Now take that hand example and look at how long that line is. That line is the Chord length.
Now that you know that,
The chord length is the length from the leading edge to the trailing edge.
This is needed for stuff such as angle of attach, and propeller pitch!
Now for
Propeller pitch.
Propeller pitch is the angle of the propeller to the relative wind.. what does that mean?
Well it means that you need to go for a drive and put your arm out the window!
Feel the wind? That’s the relative wind.. now for the pitch.. when your hand is flat you have 0 resistance. That’s a pitch so low it’s called feathered.
Turn it slightly, there’s a little resistance. That’s a low pitch propeller. There isn’t that much of a difference between the relative wind of the car, and your hand..
Now put your hand flat out.. there’s tons of resistance. That’s a high angle..
Aircraft use this to balance how much air they’re pulling. It’s called a constant speed or Variable pitch propeller.
There are also fixed props which don’t move at all. Pretty much a Lego propeller but big.. or one made of wood!
Source: I’m a licensed aircraft mechanic. Source 2: google FAA H-8083-32A which is the faa powerplant book for mechanics. It’s free and there’s an entire chapter on propellers.
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