Convertible propeller

1. A variable-solidity propeller apparatus, comprising a propeller having at least one rotatable hub carrying at least one row of propeller blades, wherein the propeller has a first configuration in which the propeller has a first average solidity, and a second configuration in which the propeller has a second average solidity which is greater than the first average solidity; and

wherein the propeller has a third configuration with an average solidity intermediate between the first and second average solidifies.

2. The apparatus of claim 1 wherein at least a portion of at least some of the propeller blades is movable between a first position defining the first configuration, and a second position defining the second configuration.

3. The apparatus of claim 1 wherein the second average solidity is at least twice as large as the first average solidity.

4. The apparatus of claim 1 further comprising a prime mover coupled in driving relationship with the propeller.

5. The apparatus of claim 1 further comprising a mechanical load coupled to the propeller.

6. A variable-solidity propeller apparatus, comprising a propeller including:

at least one rotatable hub carrying at least one row of propeller blades, wherein the propeller has a first configuration in which the propeller has a first average solidity, and a second configuration in which the propeller has a second average solidity which is greater than the first average solidity;

wherein the propeller includes a first rotatable hub carrying a row of first propeller blades, and a second rotatable hub carrying a row of second propeller blades;

the second propeller blades are movable between an extended position and a retracted; and

wherein the first propeller blades have a variable pitch angle, and the second propeller blades have a fixed pitch angle.

7. The apparatus of claim 6 further comprising a prime mover coupled in driving relationship with the first and second hubs, wherein the second hub is driven through a clutch configured to be selectively engaged or disengaged from the prime mover.

8. The apparatus of claim 6 further comprising a prime mover coupled in driving relationship with the first and second hubs, wherein the prime mover has spaced-apart forward and aft ends, and both of the first and second hubs are disposed at the forward end, or at the aft end.

9. A variable-solidity propeller apparatus, comprising:

at least one rotatable hub carrying at least one row of propeller blades, wherein the propeller has a first configuration in which the propeller has a first average solidity, and a second configuration in which the propeller has a second average solidity which is greater than the first average solidity;

wherein the propeller includes a first rotatable hub carrying a row of first propeller blades, and a second rotatable hub carrying a row of second propeller blades; and

a prime mover coupled in driving relationship with the first and second hubs, wherein the prime mover has spaced-apart forward and aft ends, one of the first and second hubs is disposed at the forward end, and the other of the first and second hubs is disposed at the aft end.

10. A variable-solidity propeller apparatus, comprising a propeller having a single hub having a single row of propeller blades, wherein the propeller has a first configuration in which the propeller has a first average solidity, and a second configuration in which the propeller has a second average solidity which is greater than the first average solidity; and

wherein some of the propeller blades are fixed and some of the propeller blades are movable between an extended position and a retracted position.

11. The apparatus of claim 10 wherein the row of propeller blades includes an even number of propeller blades, and alternate ones of the propeller blades are movable.

12. The apparatus of claim 10 wherein the propeller blades have a variable pitch angle.

13. A variable-solidity propeller apparatus, comprising a propeller having a single hub having a single row of propeller blades, wherein the propeller has a first configuration in which the propeller has a first average solidity, and a second configuration in which the propeller has a second average solidity which is greater than the first average solidity; and wherein at least some of the propeller blades include a retractable section which is movable between an extended position in which the corresponding propeller blade has maximum chord dimensions, and a retracted position in which the corresponding propeller blade has reduced chord dimensions.

14. The apparatus of claim 13 wherein the propeller blades have a variable pitch angle.

15. A variable-solidity propeller apparatus, comprising a propeller having a single hub having a single row of propeller blades, wherein the propeller has a first configuration in which the propeller has a first average solidity, and a second configuration in which the propeller has a second average solidity which is greater than the first average solidity, and wherein at least some of the propeller blades include one or more retractable sections which are movable between an extended position in which the corresponding propeller blade has a maximum span dimension, and a retracted position in which the corresponding propeller blade has a reduced span dimension.

16. A variable-solidity propeller apparatus, comprising:

a first rotor including a first hub mounted for rotation about an axis, the first hub carrying a first row of propeller blades;

a second rotor including a second hub mounted for rotation about the axis, the second hub carrying a second row of propeller blades;

wherein the second row of propeller blades are movable between an extended position and a retracted position and the first row of propeller blades have a variable pitch angle and the second row of propeller blades have a fixed pitch angle.

17. The apparatus of claim 16 further comprising a prime mover coupled in driving relationship with the first and second hubs, wherein the second hub is driven through a clutch configured to be selectively engaged or disengaged from the prime mover.

18. The apparatus of claim 16 further comprising a prime mover coupled in driving relationship with the first and second hubs, wherein the prime mover has spaced-apart forward and aft ends, and both of the first and second hubs are disposed at the forward end, or at the aft end.

19. The apparatus of claim 16 further comprising a prime mover coupled in driving relationship with the first and second hubs, wherein the prime mover has spaced-apart forward and aft ends, one of the first and second hubs is disposed at the forward end, and the other of the first and second hubs is disposed of the aft end.