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Aviation History
1950
1950 - 2039.PDF
FLIGHT, 30 November 1950 small turboprop known as the Naiad, designed, developed and flight-tested by the Napier Company. This is of very small diameter (28in) and is characterized by a neat ducted spinner for its airscrew and air intake. The Naiad gives 1,500 s.h.p. and 240 lb thrust for a weight of 1,095 lb. In passing, it may be mentioned that an interesting slim axial turboprop in the 1,500 s.h.p. class was designed by Sir Roy Fedden in 1946 and named the Cotswold. Com- ponents were assembled, but the country's serious financial position led to the cancellation of the development contract. One of the latest turboprops in this country—of which much is expected—is the Bristol Proteus. Now under flight development in a Lincoln test-bed, the Proteus is destined for the Bristol 175 airliner. It delivers 3,200 h.p. and 800 lb static thrust at sea level. Weight and diameter are respectively 3,050 lb and 38.5in, while specific consumption has already been brought down to a figure of 0.51 lb/ e.s.h.p./hr. The Proteus has a three-stage turbine of the "free" type, the first two stages, driving the compressor, having no mechanical coupling with the third for the air- screw. As with the Python, the airflow undergoes two reversals within the engine, the final turn-round into the combustion chambers being achieved in passage through the stage of centrifugal compression. Coupled pairs of Proteus are to power the two largest British aircraft, the Bristol Type 167 Mk II, of which the Brabazon is the prototype, and the Saunders-Roe Princess. Quite a number of turboprops are now being produced in either coupled or in doubled form with two separate turbine units driving either a contraprop or co-axial air- screws through a common gear box. This course has been adopted in preference to the use of one much larger turbo- , Armstrong Siddeley Momba (military version)* prop for several reasons. In the first place it is not so easy to scale up a turbine unit as had originally been thought. Mechanical design problems, bearing sizes and loads, and stiffness of casings and diaphragms are examples of possible sources of complication. Again, there is the problem of production space and multiplication of components, and the all-important time and manpower considerations involved in a new design. It has been found that often it is preferable to double or couple existing units to obtain greater power output. Additional advantages of this arrangement are the cleaner wing with less area swept by slipstream, less interference with structure, and reduced asymmetric effect in the event of an engine failure. Possible disadvantages which come to mind are the small additional complication and weight, and the risk that, in the case of the double unit, a serious mechanical fault in one airscrew or its drive may result in damage to the other and conse- (Continued on page 494) Many and varied are the aircraft which have flown with the poWerofiM compact little Mamba. Top, left, is the Armstrong Whitworth Apollo airliner, and beside it the experimental Mamba-Dakota. Above, left, is the Mamba-Marathon experimental feederliner ar.d alongside it a prototype Avro Athena advanced trainer. Below are seen (left) the Boulton Paul Balliol I. and Ivjrf&l&ejnewly mmwnced Short S.6.3 anti-submarine aircraft.
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