The RingWing is a vertical takeoff and landing (VTOL) aircraft designed to meet objectives 1,2,3 & 4.
Objective 1 requires an extremely agile vehicle, able to safely negotiate wind-shear near the ground, and safely takeoff from a confined site in blustery conditions. To achieve this, the RingWing uses
- Three novel variable-pitch rotors that provide extremely quick thrust response, even quicker than a helicopter.
- Six dimensions of control authority provided by an additional three control surfaces embedded in the wake of each rotor. A helicopter has only 4 dimensions of control.
Objective 1 also requires at least some degree of protection against rotor-strike. Widespread casual use of aircraft from unprepared sites would make rotor-strike accidents more common than they already are. The RingWing protects each main lift-rotor with a wide surrounding wing, and encloses the rear rotor.
Objective 2 is achieved by means of relatively large wings together with a default negative pitch on the lift-rotors, so that they will auto-rotate when unpowered, like an autogyro.
Objective 3 is addressed by fast and complete control, especially novel variable-pitch rotors above.
Objective 4 is addressed by using relatively large main lift-rotors, hence a relatively low pressure difference across the rotors (disk-loading), and simplifications of the aircraft, such as eliminating ailerons.
- Low disk-loading allows a relatively low-power takeoff and hover, which in turn allows the use of standard low-cost batteries, motors, and power system components.
- Ailerons add fragility, complexity, weight and expense.Instead, we intend to use auto-rotating lift-rotors to provide roll control even in the event of power failure. Drag is to be mitigated by slowing rotation.
Vibration and Noise
Vibration and noise are potentially serious problems, so minimising both is another key objective.
Vibration is to be mitigated by the use of 5-bladed lift-rotors and propellers, where it is shown that oscillatory forces from individual blades cancel at the hub of a rigid 5-bladed rotor.
The study of noise in INVESTIGATION OF NOISE FROM ELECTRIC, LOW-TIP-SPEED AIRCRAFT PROPELLERS compares 3,4,6,and 8-bladed designs and finds that more blades produce less overall sound pressure level at the same thrust. They fit a linear relation that implies 5-bladed propellers would be 14 dB quieter than those with 3 blades, and 21 dB quieter than propellers with 2 blades.
They compare noise at blade-tip speeds of Mach 0.3, 0.4, 0.5, 0.6, and 0.7. They find that “tip speed is a very important factor for propeller noise”, with an approximately linear relation between tip speed and sound pressure level in dB, and that at the relatively low tip speed of Mach 0.3, their 6-blade prop was 27 dB quieter than their 3-blade prop. Using more blades is a way of reducing tip speed for given thrust.
They also find that using more small propellers instead of fewer large ones of the same total area and thrust has little effect on the overall noise level.
Validation and refinement
To test this novel design, a 1m wingspan model is being constructed, using the CAD design as displayed.