FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1956
1956 - 0774.PDF
774 WESTLAND WYVERN Design and Development of the Navy's Turboprop Strike Aircraft ALTHOUGH the design of the Westland Wyvern was begunbefore the end of the last war, Ministry of Supply security- classification has been such that only now can the aircraft be fully described. The history of the type over the last twelveyears provides an example of the way in which the development of an aircraft is inexorably linked with that of its powerplant, andhow a change in the chosen power unit, and the incorporation of modifications found necessary to it, can have a serious effect onthe development time-scale of the aircraft as a whole. Work on the Wyvern was put in hand speedily under wartimeconditions, the Naval specification N.I 1/44 being selected for Westlands in April 1944, without the formalities of a preliminarycompetitive design-study stage. The company was more than ordinarily interested in tackling the job of evolving a design tofulfil the exacting requirements of a naval type. Although West- land aircraft activity had originated, in 1915, with naval machines,and the first aircraft to be designed by the company—the N.I6 and 17—had been to Admiralty order, the firm's dealings withnaval aircraft had remained dormant for roughly 30 years, with the exception of the Walrus of 1920 and the manufacture ofSeafires and Barracudas during the Second World War. By the end of September 1944 the broad design was settled,both advisory design and mock-up conferences having been held. At this stage the N.I 1/44, although primarily a Naval require-ment, also interested the R.A.F., and prototypes were ordered for both Services. Although it was envisaged that a large turbopropshould be the power unit ultimately employed, the development period required for both the Rolls-Royce Clyde and the Arm-strong Siddeley Python led to the installation of the 24-cylinder Rolls-Royce Eagle piston engine for the Mark 1 prototypes, sixof which were to be produced under the first contract, placed in November. The initial development was by no means easy. The Eaglewas an undeveloped engine, and the Wyvern 1 is the only aircraft in which this, the largest and most powerful'—and, as it transpired,the last—of the Rolls-Royce piston aero-engines has flown. Pioneer work was also involved in the use of a contra-rotatingairscrew of a size never before employed. Apart from the prob- lems of design and lubrication of the pitch-translation bearing, there was also the difficulty of providing the requisite stiffness inthe long, overhanging shaft carrying the front bank of blades. Another problem arising from the use of so large an airscrewwas the de-stabilizing effect; this reached such a magnitude in the Wyvern that it largely governed the size of the vertical and hori-zontal tail surfaces, as well as requiring unusually far forward eg. and mainwheel positions. During 1945 development work on British reciprocatingengines was slowed down and the major effort of the engine com- panies was transferred to gas turbines. In December it wasannounced that Rolls-Royce would cease development of the Eagle, and also that the Wyvern would continue as a naval projectonly. The two turboprops being considered for the Wyvern at that time were the Clyde, which it was hoped would be availablefor flight testing by September 1946, and the Python. Contracts to a new specification N.12/45 for one Clyde-powered and twoPython-powered Wyvern prototypes were placed in February 1946, followed by a pre-production order for 20 machines inAugust of that year. In order to keep the amount of design work on the turboprop-powered Wyvern Mk 2 to a minimum, and to retain the essential characteristics of the Mk. 1, the same wing and tail unit and, inprinciple, the same cockpit were employed, the chief modifications being an increase in depth of the centre and rear fuselage in orderto accommodate the jet tailpipes. The Eagle-powered Wyvern Mk 1 made its first flight inDecember 1946, 26 months after the design was frozen at the mock-up conference. Nevertheless, development of the turbo-prop engines to the flight stage was not as straightforward as had been predicted, and it was not until September 1948 that the firstClyde was delivered to Yeovil, followed a few weeks later by the first Python. Before this, in the spring of 1947, a Ministry ofSupply decision had been made that the Clyde would not be built in quantity and that production versions of the Wyvern would bePython-powered. The first-flight of the Clyde-Wyvern—which was also the firstflight of the Clyde—took place in January 1949, and that of the Python-Wyvern, after flight trials of the engine in a Lancastertest-bed, in March of that year. PRESSURE-REFUELLINGCONNECTION OUTBOARD PORTIONOF AILERON OPERATING LINKAGE Drawn from a Mk. 2 Wyvern, this detailed sketch of the wing-folding arrangements is applicable in all significant respects to the Mk. 4. HINGEDHVDRAUUC UNES MBOARO PORTION OF AILERON OPERATING LINKAGE LOCKING - PIN JACK
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
