The Future of Aerospace (1993) / Chapter Skim
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The Future of Rotary-Wing Aircraft
The Future of Rotary-Wing Aircraft
Pages 45-64
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From page 45... ...
But it is generally accepted that the rotorcraft equivalent to the Wright Brothers' era started in 1923 with Juan de la Cierva, at Getafe, Spain. Cierva was attracted to the unpowered, autorotating, wing because of its lifting potential at very Tow forward speeds.
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From page 46... ...
This was no simple task since the engines and speed reduction transmissions were very heavy and the powered rotors were required to provide lift, propulsion, and contro! of the aircraft about all three axes.
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From page 47... ...
In 1947 he published the classic expository paper on "The Bending of Rotor Blades" in the Journal of the Aeronautical Sciences. Four years later, with coauthor Len Goland, he published a second classic paper dealing with the dynamics of rotor blades.
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From page 48... ...
To illustrate both the magnitude and the source of this improvement in performance, this paper follows a format used by George Schairer in a recent paper entitled "On the Design of F.~riv large Swept Wing Aircraft." _ ~ ~ ~ ,, He traced the evolution of the three basic elements of the Breguet Range Equation (Figure 3) , drag efficiency (~/D)
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From page 49... ...
The impact of changing from the reciprocating engine to the gas turbine is illustrated in Figure 4 for three powerplants originally designed to deliver 800 shaft horsepower. The R-1300 powered the Sikorsky H-34, the T-53 is in the Bell UH-1 and AH-l, and the AIDE demonstration engine provided
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From page 50... ...
The initial reduction in size and complexity provided by the gas turbine is due to the application of turbomachinery concepts to the Brayton thermodynamic cycle, resulting in much higher mass flow per unit volume in the turbine than in the reciprocating engine. Figure 5 presents historical trends in specific fuel consumption and specific weight for reciprocating and gas turbine engines used in production helicopters.
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From page 51... ...
51 1 990 2000 IMPROVEMENT IN ROTARY-WING AERODYNAMICS For many years, with a few exceptions, the subject of rotorcraft drag efficiency, or L/D ratio, has been a secondary design consideration. This has been due to the fact that forward speed performance was generally limited by the aerodynamics of the main rotor, which produces airframe vibration, and by a preponderance of low-speed mission requirements.
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From page 52... ...
1 990 2000 provement in manufacturing techniques, unsymmetrical (cambered) airfoils and variable thickness/platform tip sections were incorporated' which improved both hover efficiency and forward flight capability.
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From page 53... ...
In fact, application of these materials to rotor blades has not reduced rotor weight, since a rotor system mass moment of inertia requirement effectively eliminates any weight benefits. Notwithstanding the absence of rotor blade weight reduction, a second significant benefit has resulted from the use of fibrous composites in rotor blades.
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From page 54... ...
Having been successful with rotor blades, the rotorcraft structures engineers turned their attention to the airframe, since these composite materials still offered significant potential weight and cost savings. in the 1970s (see Figure 9)
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From page 55... ...
This is consistent with the power and disk loading trends shown in Figure Il. since decreased power loading increases empty weight and increased disk loading decreases empty weight.
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From page 56... ...
This comparison is presented in Figure 12, which indicates a substantial increase in altitude vertical takeoff performance from 2,000 to 10,000 feet and a typical range-payload design point with 3 times the range and 2.75 times the payload. The modern helicopter hover time capability is preserved only by virtue of the greatly increased payload weight fraction, the total hover time rotor efficiency of the modern helicopter being less than the R-4B because of its larger disk loading.
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From page 58... ...
The Soviet armed forces helicopter inventory stands at 4,000 today, and European production since 1950 totals approximately 15,000 vehicles, half of which have been produced by Aeroepatiale in France. Clearly a competitive VIOL market has been established, and new helicopter projects are now emerging in the United States, France, Germany, Great Britain, Japan, China, Singapore, and India.
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From page 59... ...
Army Airborne logistics, assault, and antiarmor assets in a combined arms role. Figure 16 presents a dramatic
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From page 60... ...
The heavy dashed lines indicate the positions of multinational forces 12 hours and 48 hours after combat operations began. Desert Storm has been referred to as "a high-technology test bed" and a validation of emerging army doctrine called ALO, for airland-operations.
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From page 61... ...
National Civil Tilt Rotor initiative (Bell-Boeing) , which is led by the FAA Vertical Flight Program with strong support by NASA and Congress (see Figure 18~.
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From page 63... ...
The future of the helicopter is clearly assured, and advanced rotary-wing aircraft, with an additional degree of rotation, are ready to extend the performance and utility of the helicopter.
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