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In Rostov started production of the most load-lifting rotary-wing car The Russian holding «Helicopt[...]
BLADE FLAP
In translational flight, the blade on one side of the line of movement, now called the advancing blade, meets the air at a higher velocity than the other retreating, blade. Since, at a given angle of attack, lift depends on flow speed, this would cause an effect on the helicopter rotor exactly analogous to the ‘P’ effect on propellers when these are not aligned with the flight direction (Fig. 15.10). To prevent this, it is essential to reduce the angle of attack of the advancing blade and increase that of the retreating blade, to
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Fig. 15.9 Gyroscopic 90° out-ofphase reaction
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(LIFT DEPENDS ON SPEED SQUARED] |
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Fig. 15.10 Lateral imbalance
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Fig. 15.11 Blade flapping to equalise lift in forward flight |
maintain equal forces on both sides. This is achieved by allowing the blades to hinge, or flex, up and down freely under the air loads they meet. As the advancing blade rises, its angle to the airflow is reduced (Figure IS.11). Conversely, as it moves round to the retreating position, it flaps down, so increasing its angle of attack. The total lift force is thus equalised laterally. Blade flapping is automatic and self adjusting to a large extent, since any untoward rolling force causes the blades to hinge up and down rather than tilting the helicopter as a whole.
