The conceptual simplicity of the helicopter belies the complexity of the flowfield of the lifting rotor. Although separation, reverse flow, compressibility, and blade vortex interaction are important phenomena, the flowfield induced by the lifting rotor blades is especially complex and it is arguably the dominant feature of rotor aerodynamics. The induced flowfield determines, in large measure, the performance, dynamic loads, and flight control characteristics of the helicopter. A simplified rotor model was used to explore fundamental behavior of lifting rotor induced power at moderate and high advance ratios. Several rotor inflow theories, including dynamic inflow theory and prescribed-wake vortex theory, together with idealized notional airfoil stall models were employed. A number of unusual results were encountered at high advance ratios including trim control reversal and multiple trim solutions. Significant increases in rotor induced power (torque) above the ideal minimum were observed for moderately high advance ratio. Very high induced power was observed near and above unity advance ratio. The results were sensitive to the stall characteristics of the airfoil models used. An equivalent wing analysis was developed to determine induced power from Prandtl lifting line theory and help interpret the rotor induced power behavior in terms of the spanwise airload distribution. The equivalent wing approach was successful in capturing the principal variations of induced power for different configurations and operating conditions. The effects blade root cutout were found to have a significant effect on rotor trim and induced power at high advance ratios.
Induced power of the helicopter rotor
Induzierte Leistung eines Hubschrauberrotors
AHS International Forum, 60 ; 33-53
2004
21 Seiten, 34 Bilder, 23 Quellen
Aufsatz (Konferenz)
Englisch
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