PRINCIPLES OF ROTORCRAFT FLIGHT 1cm
Transcription
PRINCIPLES OF ROTORCRAFT FLIGHT 1cm
PRINCIPLES OF ROTORCRAFT FLIGHT Class 8 – Helicopter Performance Prof. Assoc. Fl´avio D. Marques Universidade de S˜ ao Paulo Escola de Engenharia de S˜ ao Carlos Powered by Latex/Beamer, make yourself free! Prof. Fl´ avio D. Marques SAA 121 – Dinˆ amica de voo de helic´ opteros Content (class 8) Summary Introduction on helicopter/rotorcraft; Fundamentals on rotor aerodynamics; Rotor dynamics, torque compensation, and control; Helicopter Components – Structures, engines, and trasmission systems. For this class ... Helicopter Performance 1 2 3 Required power; Available power; Some examples of performance parameters. Juan de la Cierva y Codorn´ıu – Spanish engineer; the autogyro inventor in 1920 Cierva C6 – 1924 Prof. Fl´ avio D. Marques SAA 121 – Dinˆ amica de voo de helic´ opteros Helicopter Performance Helicopter performance features depend on the flight condition, that is, hovering; pure vertical fight; level forward flight; climbing flight; ... To assess the performance values it is usually necessary to calculate de power relation between required and available powers. REQUIRED POWER Prof. Fl´ avio D. Marques vs AVAILABLE POWER SAA 121 – Dinˆ amica de voo de helic´ opteros Helicopter performance – cont’d REQUIRED POWER It represents all those power values to be overcome to produce flight. For helicopter the required power (mainly due to rotor motion and fuselage interference) is divided into: Power required to overcome PROFILE DRAG; Power required to overcome PARASITE DRAG; Power required to overcome INDUCED DRAG. One must be aware of the need for power to overcome tail rotor aero-mechanical dissipations, as well as in the transmission systems. Prof. Fl´ avio D. Marques SAA 121 – Dinˆ amica de voo de helic´ opteros Helicopter performance – Required Power ... cont’d AIRPLANE HELICOPTER PP + PI PPr + PP + PI (parasite drag includes profile drag) (typically in hover, helicopter profile power corresponds to 35%, while the induced power is 65% of the total required power) where PP denotes Parasite Power, PPr denotes Profile Power, and PI denotes Induced Power. DRAG FORCES Parasite Drag – drag force related to helicopter components that do not generate lift, that is: fuselage, fairings, nacelles, etc...; Profile Drag – drag force due to the turning rotor blades through the air. Similar to the parasite drag, but its source is related exclusively to the rotor blades in motion; Induced Drag – drag related to lift production. Prof. Fl´ avio D. Marques SAA 121 – Dinˆ amica de voo de helic´ opteros Helicopter performance – Required Power ... cont’d PARASITE POWER Parasite power is a function of the cube of the airspeed. Prof. Fl´ avio D. Marques SAA 121 – Dinˆ amica de voo de helic´ opteros Helicopter performance – Required Power ... cont’d PROFILE POWER at zero airspeed still necessary a substantial amount of power to drive the rotors through the air; slight changes in profile power with airspeed is observed, except for very high velocities and at severe stall regime; in stall condition drag increase rapidly; 3 to 4 degrees in AoA in the stall region can cause the profile drag to double! Prof. Fl´ avio D. Marques SAA 121 – Dinˆ amica de voo de helic´ opteros Helicopter performance – Required Power ... cont’d INDUCED POWER at zero airspeed the induced power presents its higher values, because the rotor must impart considerable amount of energy to get the air moving through the rotor; increasingly forward speed leads to a reduction in induced power; ground effect acts in favor of reducing induced drag. Prof. Fl´ avio D. Marques SAA 121 – Dinˆ amica de voo de helic´ opteros Helicopter performance – Required Power ... cont’d TOTAL REQUIRED POWER Prof. Fl´ avio D. Marques SAA 121 – Dinˆ amica de voo de helic´ opteros Helicopter performance – cont’d AVALIABLE versus REQUIRED POWER Available Power: the power of the engine less the power required to operate the tail rotor, transmissions, frictional losses, etc.. Excess Power Prof. Fl´ avio D. Marques SAA 121 – Dinˆ amica de voo de helic´ opteros Helicopter performance – Available vs Required Power ... cont’d Insufficient Power observe that overloaded or underpowered flight is possible, but vertical flight and hovering is impossible; if some source of airflow is provided to the rotor, e.g. by taxiing the helicopter, insufficient power region can be overcome and flight can be sustained. This phenomenon is known as transitional or translational lift. Prof. Fl´ avio D. Marques SAA 121 – Dinˆ amica de voo de helic´ opteros Helicopter performance – Available vs Required Power ... cont’d Forward Flight Performance Level Flight Maximum Speed: Maximum Ratio of Climb and Climbing Angle: ratio of climb = available power - required power excess power = weight weight sin γ = ratio of climb velocity Prof. Fl´ avio D. Marques SAA 121 – Dinˆ amica de voo de helic´ opteros Helicopter performance – Available vs Required Power ... cont’d Forward Flight Performance (cont’d.) Ceiling: Absolute: Service: maximum ratio of climb is zero; ft maximum ration of climb is 100 min (regulations). Prof. Fl´ avio D. Marques SAA 121 – Dinˆ amica de voo de helic´ opteros