Propeller units

1. An aerial vehicle comprising:

one or more propeller units connected to the aerial vehicle, wherein the one or more propeller units are operable to provide thrust for takeoff of the aerial vehicle or hover flight of the aerial vehicle, and wherein at least one of the one or more propeller units comprises:

a shaft coupled to a motor; and

a first propeller blade and a second propeller blade that are both connected to the shaft, wherein the second propeller blade is located substantially opposite the first propeller blade, wherein the second propeller blade has a surface area that is greater than a corresponding surface area of the first propeller blade, wherein, with respect to a plane of rotation of the at least one propeller unit, at least a portion of the first propeller blade has a width that is greater than a width at any point along the second propeller blade, wherein the first propeller blade is of a single mass distributed over an area of the first propeller blade, wherein the second propeller blade is of a single mass distributed over an area of the second propeller blade, and wherein the single mass of the first propeller blade and the single mass of the second propeller blade are such that a center of mass of the at least one propeller unit is located on an axis of rotation; and

one or more propulsion units connected to the aerial vehicle, wherein the one or more propulsion units are operable to provide thrust for forward flight of the aerial vehicle, and wherein while the aerial vehicle is in forward flight in a first direction and the motor of the at least one propeller unit is turned off, the first propeller blade and the second propeller blade are each configured to orient in a second direction that is substantially parallel to the first direction, such that the first propeller blade is oriented substantially upwind of the second propeller blade.

2. The aerial vehicle of claim 1 , wherein when the motor of the at least one propeller unit is turned on, the first propeller blade and the second propeller blade provide substantially the same thrust along the axis of rotation.

3. The aerial vehicle of claim 1 , wherein the first direction is substantially perpendicular to the axis of rotation.

4. The aerial vehicle of claim 1 , wherein the first propeller blade and the second propeller blade each orient in the second direction in response to incident wind on the at least one propeller unit in a third direction that is substantially perpendicular to the axis of rotation.

5. The aerial vehicle of claim 1 , further comprising a control system, wherein the first propeller blade and the second propeller blade are each configured to orient in the second direction in response to the control system positioning the first propeller blade and the second propeller blade in the second direction.

6. The aerial vehicle of claim 1 , wherein a body of the aerial vehicle is in a first orientation during takeoff and hover flight, and wherein the body of the aerial vehicle is in a second orientation that is substantially the same as the first orientation during forward flight.

7. The aerial vehicle of claim 6 , wherein the first orientation is substantially parallel to ground.

8. The aerial vehicle of claim 1 , further comprising a control system, wherein the control system is configured to turn off the at least one propeller unit in response to the aerial vehicle having a certain speed.

9. The aerial vehicle of claim 4 , wherein the incident wind on the at least one propeller unit in the third direction contacts the surface area of the first propeller blade and the surface area of the second propeller blade so as to cause the first propeller blade and the second propeller blade to orient in the second direction.

10. The aerial vehicle of claim 1 , wherein the first propeller blade and the second propeller blade are made of the same material.