4.4 KiB
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Tip speed should not exceed 200 m/s.
For us that is roughly 6400 rpm.
Formula: 200*60/D/pi
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Rotor size and max weight are first things to consider.
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Normalizing Entities to compare between models --> make dimensionless
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Non-dimensional induced velocity
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Thrust coefficient
- VT is tip speed of blade
- Thrust is divided by dynamic pressure times area --> gives Force [N]
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Combined:
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Power overview:
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Induced Power is major part of power during hover
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Power to overcome blade drag PO
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==Solidity== of rotor:
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Skin friction drag:
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Rotor efficiency: M = Pi/PO --> Figure of Merit
- ki is induced power factor because of a variation in induced velocity
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Blade Aerodynamics
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Angles:
- Inflow Angle (small angle approx)
- Theta: pitch control by pilot
- Alpha: angle of attack seen by blade
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Aerodynamic forces
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Lift and Drag
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Thrust
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Blade Torque
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Thrust coefficient with a linear twist blade and the assumption of no stall and no compressibility
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Lambda: inflow factor
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Relating the inflow factor to momentum theory (see above)
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Relationship between inflow factor and pitch setting
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Why are blades twisted? My assumption is that the angle of attack seen by the blade depends on the wind speed it experiences. This in turn, depends on the radius and the angular velocity of the blade. The closer you are at the hub, the larger is the inflow angle and thus the smaller is the angle of attack. That means if we twist the blade and add additional aoa close to the hub and remove aoa where the speed is high, we will have more lift in total and not have a stalling condition somewhere and not at other places.
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Flapping, Feathering & Lead-Lag
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Coriolis Force induces lag
