TURBOPROP HISTORY

TPs continue their key role in bizav

New models emerge while older designs still serve.

By Doug Wilson
Contributing Writer


G-AHRF, the prototype Vickers V630 Viscount-seen here in British European Airways colors-made its maiden flight on Jul 16, 1948. Powered initially by 4 Rolls-Royce Dart 503 turboprops of 1250 shp each, 444 Viscounts of all versions were sold before production ended in 1964, making it not only the first, but one of the most successful turboprop airliners.

While the English aviation engineer Frank Whittle, who patented the concept in 1930, is generally recognized by historians as the father of the modern turbojet engine, it was a little-known Hungarian named Gy├Ârgy Jendrassik who sired the first true turboprop engine, designated the Cs1, in 1938.

With war in Europe on the horizon, the first airframe to use Jendrassik's turboprop design was slated to be the Varga RMI1 X/H reconnaissance bomber, which was planned for first flight in 1940.

Yet, unlike turboprops of today, the Cs1 was an underperformer, and though designed for an output of 1000 shaft horsepower (shp), problems with the engine limited its output to 400 shp. Although the troubles with Jendrassik's turboprop were likely surmountable, history intervened before its shortcomings could be resolved.

By late 1940, with Europe at war, Hungary signed the Tripartite Pact, reluctantly aligning itself with Nazi Germany. With the pact in place, both the Cs1 engine and the Varga reconnaissance bomber for which it was destined were shelved, and the Messerschmitt Me210-with its tried-but-true older technology-was chosen in its place.

As World War II progressed, technological innovations seemed to occur monthly, and it was the turbojet, rather than the turboprop engine, that was viewed as the quantum leap in engine technology. Heinkel Flugzeugwerke in Germany and Gloster Aircraft Company in Britain produced test bed airframes for the then-developing turbojet engine.

Late in the war, as piston-engine technology and propeller-driven aircraft were reaching their technological peak of performance, the Royal Air Force's Gloster Meteor-the first Allied jet to be operational in any numbers-soon shared the skies with the Luftwaffe's Messerschmitt Me262-the first jet fighter to actually achieve operational status.

First aircraft to be flown successfully under turboprop power was a modified RAF Gloster Meteor fighter, pictured here in late 1945. Note the 2 small vertical stabilizers, added due to initial concerns of directional control under engine-out trials with the new powerplants. Fuselage markings aft of the roundels show that the aircraft is a prototype, while the "G" suffix to the RAF serial indicates that it is assigned an armed guard.

The end of the propeller age seemed near. But it was not until the end of the war that the turboprop engine surfaced again, this time perfected by the British. While the turbojet engine, when strapped to an aircraft, was a strong performer, specific fuel consumption was high, and thus range was limited.

Also, as the sound barrier had yet to be broken-at least intentionally-the limitations associated with the forward speed of high-performance propeller-driven aircraft were not seen as so important as they are today.

With gearboxes and propellers in hand, engineers at Rolls-Royce developed the RB50 Trent turboprop engine-essentially a Derwent turbojet engine fitted with a forward drive shaft, a reduction gearbox, and a 5-bladed Rotol propeller similar to those seen on later Vickers Supermarine Spitfires.

Affixed to Gloster Meteor s/n EE227, the world's first turboprop engine to power an aircraft took to the skies some 5 months after the end of WWII in the European theatre, on Oct 20, 1945.

Enter the Dart

Although the RB50 turboprop was the breakthrough engine, perfection and subsequent acceptance of technology come slowly, and it was not until 1948 that the commercial successor to the Trent-the RB53 Dart-flew on the Vickers V630 airliner, later to become the Viscount.

Eventually, in Apr 1953, the Viscount would inaugurate the world's first turboprop-powered airline service with British European Airways. Popular with passengers used to the drone of piston-engine aircraft, the pressurized Viscount was a star performer amongst its 4-engine contemporaries, and constantly set new speed records.

In the early 1950s, as the turboprop-powered Viscount was entering service, its chief competitors were all 4-engine piston airliners, many of which were outgrowths of WWII transports and all of which were of US manufacture.

The Douglas DC6 and later DC7 series were developments of the venerable DC4, which (as the C54) proved its mettle in the Berlin Airlift of 1948. The Lockheed L1649 Super Constellation, regarded by many enthusiasts as one of the most elegant-looking airliners of the day, was an outgrowth of the original L049, which entered US military service during late WWII as the C69.

Even the double-decker Boeing 377 Stratocruiser used the wings and empennage of the B50, which itself used the wings and empennage of the B29 Super_fortress, the aircraft that helped bring an end to the war.

Yet all these 4-engine, piston-powered, propeller-driven aircraft had in common a disastrous trait-one the turboprop-powered Viscount did not share-overly complex engines that were prone to fires.

To be sure, the unreliability of the Pratt & Whitney R4360-B6 Wasp-a behemoth 28-cylinder, 3500-hp radial engine-and its predisposition to fire, earned the 4-engine Boeing Stratocruiser the somewhat humorous nickname "the best 3-engined airliner of the Pacific."

This photo of a Lockheed Martin C130J Hercules shows the 6-bladed composite scimitar propellers well. Now powered by AE2100s, the "Super Hercules" and other propeller-driven aircraft using scimitar blade design owe much to the ATP and advances in blade technology.

This was a reference to the routine failures of at least one of its engines on its regular routes. In short, the 4-engine piston airliners were a dying breed, and the Rolls-Royce Dart would hasten their demise.

The propeller-driven aircraft, however, would still hold its own, especially when those propellers were affixed to the Dart. Rolls-Royce Darts proved reliable and adaptable, with growth variants ranging from 1815 shp in the Mk 520 to 3060 shp in the later Mk 542 series.

After the success of the Viscount, Darts were seen on twin-engine airframes-including the Fokker F27 Friendship, Avro 748 (later Hawker Siddeley HS748) and, later, the lesser-known Nihon YS11-as the regional market solidified under the emerging airline hub-and-spoke system.

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