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Aviation History
1981
1981 - 3332.PDF
propulsion Commuter prop: more performance, less noise ai mm The slim lines of Hamilton Standard's commuter development. The example here is strain-gauged HAMILTON STANDARD began de velopment of its advanced commuter prop family in 1979, and expects FAA certification in 1983, after some 12,000 test hours. The propeller is already selected for the Casa/Nurtanio CN.235, de Havilland (Canada) Dash 8, and Embraer 120, and will be com peting in a market that the company says could treble in size before the end of the century. The new generation of 30-40 seater commuter aircraft will have to be extremely cost-effective and quiet to capture a reasonable market share. Principal market demands, therefore, have been for higher propeller effi ciency and reduced cabin and exter nal noise. To meet the requirement, Hamilton Standard has used the most up-to-date computer programmes to design 10 new aerofoils covering a range of thickness ratios, optimised for performance at particular points along the blade span. Operating limits such as angle of attack and Mach number were defined at each point to produce the best aerofoil shape. The result is a propeller with a claimed 20 per cent better lift co efficient over the reference NACA series 16 aerofoil (used in the de Havilland Dash 7), and a 67 per cent improvement in lift/drag ratio at cruise. Because of the better per formance, blade tip speeds can be kept lower, reducing overall noise and minimising cyclic fatigue. The new propeller varies from 10-5ft to 13ft in diameter and is more slender than its predecessors. The leading and trailing edges are blunt to minimise foreign object damage and improve handling. Hamilton Standard has been co ordinating its design with the three engine manufacturers aiming at the commuter aircraft market, and has placed hardware orders for hubs and controls to suit Pratt & Whitney's PT7, General Electric's CT7, and Garrett's TPE331. The propeller employs the com pany's spar-shell construction tech nique—first used commercially on the Dash 7—in which a solid alumi nium spar integrated with the root is surrounded by polyurethane foam and coated with a glassfibre and epoxy laminate shell. The de-ioing heater and nickel erosion strip are adhesively bonded to the leading edge. Weight saving is about 50 per cent over solid aluminium blades. A unique feature claimed for the blades is that they are each balanced to a master, so that damaged blades can be individually removed and re placed without the need for re balancing or disturbing the other blades. Hamilton Standard says that this feature came about because of market demand. Blade removal is achieved simply by lifting out a re taining ring and bearing necklace. Cabin noise has long been a disad vantage of propeller power. Hamilton Standard's synchrophaser eliminated the problem of beats—periods of rela tive quiet alternating with periods of vibration and noise—but it has taken a digital microprocessor to improve its accuracy. Pitch actuators are close-coupled to the hydromechanical propeller control for faster response, A ROLLS-ROYCE GEM engine fitted with a new electronic control system has successfully completed a 150hr test in the course of obtaining Civil Aviation Authority approval. The control system is changed from hydromechanical to an advanced tech nology digital system manufactured by Hamilton Standard as part of their Multiple Application Control System (MACS) range. It can be programmed for either turboshaft, turboprop, or turbof an applications. The change has eliminated a con- prop are the result of advanced aerodynamic so that in theory all propellers on the aircraft should be controlled to with in 1 ° variance in pitch throughout the flight envelope. Hamilton Standard has been working particularly hard to improve this technology—one of the principal drawbacks of their well- publicised propfan has proved to be cabin noise. Flight testing of the commuter prop begins in midil982, with units for pro totype aircraft due to become avail able by the end of that year. If the results support the claim, Hamilton Standard's new propeller should im press both users and onlookers with its performance and quietness. siderable number of mechanical com ponents from the engine. The mech anical power turbine governor and tachometer generator, together with drive shaft and gears, are replaced by a single electrical pulse probe. The reduction in the cost of the control system for the Gem is nearly 50 per cent, and it is predicted that operating costs will be cut by 20 per cent. MACS will be incorporated into a * new variant of the 1,120 s.h.p. Gem 41, which currently powers the Lynx. Gem s digital control is tested 1240 FLIGHT Internationa/, 24 October 1981
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