Quadcopters use both direct and contra-rotating propellers to be able to turn and to balance the torque caused by the each of the propellers.

Propeller performance measurement:

When testing the propellers for these quadcopters, why is their performance measured only in one direction of rotation? Would it be useful to test both the right handed and left handed rotations to provide more information to the designer?

Propeller pitch selection:

Why would a designer select a lower pitch to diameter ratio for quadcopters when there are higher and more efficient ratios to choose from?

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    $\begingroup$ The propellers can turn clockwise and counterclockwise $\endgroup$ – Kale Evans Oct 13 '16 at 1:42
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    $\begingroup$ The props have to be left handed or right handed, you can't just spin the same prop two different directions and produce lift in the same direction. That being said, there should be no difference aerodynamically from a prop spinning clockwise or counter clockwise if the props produce thrust in the same directions when it spins. $\endgroup$ – Ron Beyer Oct 13 '16 at 2:01
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    $\begingroup$ Please clarify what you mean by 'test'. $\endgroup$ – Daniel Oct 13 '16 at 3:55
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    $\begingroup$ Also, there are two completely separate questions here, which are related only in that they're both about quadcopter rotors. If you want to ask two separate questions, please make two posts. $\endgroup$ – David Richerby Oct 13 '16 at 8:47
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    $\begingroup$ I suggested you narrow your question to only one aspect. It is better to ask several precise questions (and if needed adding links into the description) than asking a question whose answer require writing an encyclopedic article. $\endgroup$ – Manu H Oct 13 '16 at 9:17

When testing the propellers for these quadcopters, would it be useful to test both the right handed and left handed rotation of the propellers or just one direction?

You may miss something about propellers rotation. A given propeller produces thrust (which is another name for lift) when rotation occurs in the designed direction. When direction is reversed, thrust may be produced, but not efficiently, and will be reversed compared to the regular lift.

A propeller is a wing in rotation. Wings are not used is reverse direction, with a plane going backwards.

Left-handed and right-handed propellers are different:

enter image description here

Thrust is determined in the intended direction of use.

Why would a designer select a lower pitch to diameter ratio

For the same reason than wings on actual planes have an optimized size and incidence. Increasing this size or this incidence is not productive. The limit may come from different reasons, but essentially for weight and drag considerations.

In the quadcopters, the propellers are spun by electric motors that have a limited power and a preferred rotation speed. Propellers are selected to match the rotation speed and available torque of the motor.

In addition turbulence is created by the propeller, especially at high pitch. Turbulence can decrease efficiency of neighboring propellers, so a compromise has to be found between high individual and low overall lift produced.

enter image description here
From Studying the Aerodynamics of Multi-Rotor Drones (Nasa)

Also think about the fact that a propeller just converts a quantity of work (rotation) into another quantity of work (translation of air). The rate of conversion is dependent on the blade pitch. Air translation (lift) can be increased but not beyond the capabilities of the motor to create the equivalent rotation. If this is done, the motor just can't deliver, and it's efficiency decreases (battery will be empty more quickly).

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  • $\begingroup$ good answer, maybe include a cross section drawing to show that propellers, like wings, are not symmetrical. $\endgroup$ – tony gil Aug 2 '17 at 9:31

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