Improved VTOL Coaxial Blades

The Osprey is a problematic animal. Not the bird, the aircraft. It took many years and 36 lives (to date) to design a tilt-propeller ship that can take off like a helicopter and fly like an airplane. What if there is a better design? King Abdullah of Jordan thinks so.

A recently-granted US Patent discloses a VTOL vehicle that can take off like a helicopter and presumably fly like a plane. The design, using coaxial counter-rotating propellers, claims to be more efficient and needing less spacing between the top and bottom coaxial props. The secret lies in having the top propellers slightly longer than the bottom propellers, with the bottom props spinning at a different rate from the top to counteract torque differences on the axes. In addition, the axes can tilt to add a degree of efficiency.

Here is the relevant text from the patent: “The rotor systems of existing assemblies typically include an axially spaced distance between the top propeller and the bottom propeller of approximately 10% of the propeller diameter. The top propeller and bottom propeller are of equal length. This distance provides adequate space for flapping and bending of propeller blades and to assure adequate clearance between each rotor while the aircraft maneuvers. Fixed pitch propeller blades have been used but require optimization of the axially spaced distance between the propellers and its geometry. […] The first top propeller and the second top propeller rotate with a common rotational speed and torque and the first bottom propeller and the second bottom propeller rotate with a common rotational speed and torque. Additionally, the first and second top propellers can be spaced from the first and second bottom propellers respectively by less than 3% of the length of the top propellers. Additionally, the diameters of the top propellers are longer than the diameters of the bottom propellers. The system of the present application controls the gyroscopic moment by optimization of a first torque profile of the first coaxial rotor and a second torque profile of the second coaxial rotor such that the combination of the first torque profile and second torque profile provide a stable pitch balance of the vehicle while in use. The pitch stability is maintained while the first and second top propellers can be operated with a different angular speed or with a different torque profile from the first and second bottom propellers. Additionally, the top propellers can be optionally rotated with a different angular direction or the same angular direction from the bottom propeller.”

Claim 1 seems to be focused on the fact that the propellers are of different lengths:

A system for increasing the thrust and power capabilities of a side-by-side vertical takeoff and landing vehicle, the system comprising: a first coaxial rotor spaced from a vehicle body and a second coaxial rotor spaced from the vehicle body and opposite the first coaxial rotor along a common axis, the first and second coaxial rotors tilting towards a central axis along a length of the vehicle body with a common tilt angle and a common tilt rate while in use, the vehicle body including at least one wing, the first coaxial rotor including a first top propeller aligned with a first bottom propeller along a first rotational axis, the second coaxial rotor including a second top propeller aligned with a second bottom propeller along a second rotational axis, wherein the first and second top propellers have a first length and the first and second bottom propellers have a second length such that the first length is greater than the second length; and during use, a gyroscopic moment from the coaxial rotors of the vehicle is controlled by a controller to maintain pitch stability by modulating the first and second top propellers to have a different rotational speed from the first and second bottom propellers, wherein the first top propeller and the second top propeller rotate with a common rotational speed and the first bottom propeller and the second bottom propeller rotate with a common rotat ional speed.

Title: “SIDED PERFORMANCE COAXIAL VERTICAL TAKEOFF AND LANDING (VTOL) UAV AND PITCH STABILITY TECHNIQUE USING OBLIQUE ACTIVE TILTING (OAT)”

US Patent No: 8,931,729

Filed (US): October 31, 2011

Granted: January 13, 2015