08 March 2010

The Checkered Development of the Westland Wyvern

The original piston-engined Wyvern
The development of the only turboprop fighter to go into production in service was quite checkered, to say the least. The Westland Wyvern underwent three different changes of engine before ending up with the definitive Armstrong-Siddeley 3,667-horsepower Python engine- the first versions used the 24-cylinder Rolls-Royce Eagle engine, then a change to the Rolls-Royce Clyde turboprop before ending up with the Python in the S.4 version of the Wyvern. One of the reasons for the Wyvern's protracted development was that the first prototypes had three new components that test pilots were less than eager to test- a new airframe, a new engine, and a new contra-rotating propeller mechanism.

The original piston engine, the Rolls-Royce Eagle, was the largest and most powerful piston engine ever developed in Great Britain with a power output as high as 3,500 horsepower, the Eagle had an H-configuration (12 cylinders on the top, 12 cylinders on the bottom) and resembled a scaled up Napier Sabre engine. The power output of the Eagle required a contra-rotating propeller and it used two three-bladed props and early contraprops were quite literally engineering and maintenance nightmares. To simplify the mechanism of the Wyvern's contraprop, the ability to feather the props in the event of an engine failure was left out. Should the Wyvern's engine fail, those non-feathered props acted like a giant airbrake and the proscribed engine failure procedure was to enter a steep dive to maintain flying speed and hope that the pullout was judged correctly for a safe landing.

Handing issues and technical failures during the first months of flight testing culminated in the first of many test pilots killed in the flight test of the Wyvern. Squadron Leader Peter Garner suffered an engine failure, dove his Wyvern to avoid stalling and pulled out too late in the dive and the resulting belly-landing knocked him unconscious as his aircraft burned. The result of this was that Westland could not find volunteers to fly the Wyvern prototypes as many in the company and outside the company didn't feel the increased pay was worth the risk of flying a plane that already had a dangerous reputation.

Eventually Westland hired on one of Rolls-Royce's engine test pilots who helped develop the Eagle engine for flight test duties. But despite this, several more test pilots would lose their lives in Wyvern accidents, even as the engines were changed from the piston Eagle to the turbine Clyde engine and finally the definitive Python turboprop.

Squadron Leader Cliff Roger would have two close calls flying the piston-powered Wyvern, One of the Rolls-Royce engine test pilots who flew for RAF Bomber Command in the Second World War, Roger was flying a full-throttle test in the Wyvern when the engine overheated and quit. Before he put his aircraft into the prescribed steep dive, he recognized Lincoln Cathedral and remembered a disused airfield from his Bomber Command days just to the west of the city. Missing several obstacles on the way, he safely touched down in the field only to notice his control column moving by itself. Outside was an old man who was jerking the aileron and beating the aircraft with a stick- apparently he was an old farmer who bought the land that used to be the airfield and thought that his land was being taken back to be an airfield again. After Roger explained his situation, the farmer took him back to his farm house for a sumptous meal and for years afterward he allowed Garner to hunt on his land!

On another test flight, Rogers' Wyvern Eagle engine exploded and he again recognized a local landmark, the Lichfield Cathedral and knew of another old RAF airfield near his location. With his engine stopped and this time on fire, he entered a steep dive but this time missed the old runway, instead landing on a soccer field with a game going on as players and referees scrambled out of the way. Rogers considered retiring from test flying after another safe landing, but he stuck it out and ended up the Chief Test Pilot for Rolls-Royce.

Source: Tests of Character- Epic Flights by Legendary Test Pilots by Donald Middleton. Airlife Books, 1995, p95-100.

No comments:

Post a Comment