11 December 1951: The first helicopter powered by a gas turbine engine made its first flight at the Kaman Aircraft Company plant at Bloomfield, Connecticut. Using a K-225 tandem rotor helicopter delivered to the U.S. Navy in 1949, Bureau of Aeronautics serial number (“Bu. No.”) 125477, Kaman replaced the 220 horsepower Lycoming O-435-A2 reciprocating engine with a Boeing 502-2E turboshaft engine. This engine could produce 175 continuous horsepower at 2,900 r.p.m. at Sea Level, less than the piston engine it replaced, but it also weighed considerably less.
K-225 Bu. No. 125477 was the first helicopter to perform an intentional loop, when it was delivered to the Navy at NATC Patuxent River by factory test pilot William R. Murray. It was placed in storage at Bradley Field, Windsor Locks, Connecticut until 1957. The gas turbine had been removed. When the helicopter was transferred to the Smithsonian Institution in 1957, a similar-appearing Boeing YT-50-BO-2 gas turbine engine was installed.
The K-225 was a two-place, single-engine helicopter using Kaman’s unique system of counter-rotating, intermeshing rotors (“synchropter”). Each rotor cancelled the torque reaction of the other, eliminating the need for a tail rotor. In a conventional single-rotor helicopter, up to 30% of the engine power is required to drive the tail rotor. With the counter-rotating design, the total engine power is available for lift and thrust.
K-225 Bu. No. 125477 is 22 feet, 5 inches (6.83 meters) long. Each rotor has a diameter of 38 feet (11.58 meters). It stands 11 feet, 6 inches (3.51 meters) high. The helicopter has an empty weight of 1,800 pounds (816 kilograms) and a maximum gross weight of 2,700 pounds (1,225 kilograms). It is a slow helicopter, with a never-exceed (VNE) limit of 70 miles per hour (112.7 kilometers per hour). This historic helicopter is on display at the Smithsonian Institution National Air and Space Museum, Steven F. Udvar-Hazy Center in Chantilly, Virginia.
17 November 1946: A modified Avro 691 Lancastrian C.1, VH742, under the command of Rolls-Royce’s chief test pilot, Captain Ronald Thomas Shepherd, O.B.E., flew from London Heathrow Airport (LHR) to Aéroport de Paris – Le Bourget (LBG) for 17th Salon de Aviation (Paris Air Show) with two Rolls-Royce RB.41 Nene Mk.I turbojet engines for propulsion. The airplane’s two Rolls-Royce Merlin V-12 piston engines were shut down, except for takeoff and landing, and their three-bladed propellers were feathered to reduce drag. It was the first-jet-powered passenger transport to fly from one country to another.
A contemporary aviation industry news article described the event:
The Nene-Lanc, Flies to Paris
THE flight of the Nene Lancaster from London to Paris last Monday, to play its part in connection with the exhibition, may be said to have marked a historic part in British aircraft development, for it constituted the first time that any jet-powered airliner had flown from one country to another. Moreover, since this particular aircraft has been flying fairly regularly since round about the time of the Radlett exhibition, the flight to Paris was no special performance, but merely one more public demonstration of its inherent reliability.
In the hands of Capt. R. T. Shepherd, chief test pilot for Rolls-Royce, the “Nene-Lanc” landed at Le Bourget at 10.58 a.m., G.M.T., after a 50-minute flight from London Airport, giving an average speed of 247.5 m.p.h. [398.3 kilometers per hour] Two passengers were carried in addition to the crew; they were Mr. Roy Chadwick, the Avro designer, and Mr. R. B. William Thompson, Chief Information Officer of the Ministry of Supply.
Capt. Shepherd said that he was very pleased with the aircraft’s performance and added that, but for having to circle Le Bourget Airport Twice before landing, the flight would have been completed in 43 minutes.
— FLIGHT and AIRCRAFT ENGINEER, No. 1978. Vol. L., Thursday, November 21st, 1946 at Page 561, Column 2.
Five days later, VH742 flew back to England:
THE return of the Nene Lancastrian on Nov. 22nd, direct from Le Bourget to Heathrow, was made in only 49 min, including landing, actual flying time from point to point being 41 min—an average speed of 322 mp.h. [518.2 kilometers per hour] This remarkable performance was in spite a beam wind and the dead weight and drag of the two inboard Merlins, which are only used for takeoff and landing.
Passengers of the return trip included Mr. Roy Chadwick, chief designer and a director of A. V. Roe and Co., Air Comdre. Kirk and Air Comdre. Pike.
—FLIGHT and AIRCRAFT ENGINEER, No. 1979., Vol. L., Thursday, November 28th, 1946 at Page 588, Column 1.
The Rolls-Royce RB.41 Nene engine first been run in October 1944. It installed in a Lockheed YP-80A Shooting Star, 44-83027, and the engine was first flown 18 July 1945 with Rolls-Royce test pilot Wing Commander John Harvey Heyworth, A.F.C., in the cockpit. The Nene-powered P-80 had made approximately 30 test flights when it was damaged beyond repair at RAF Syerston, 6 December 1945. With test pilot Andy McDowall flying, a fractured fuel pipe caused the engine to flame out from fuel starvation. McDowall tried to glide to a landing but another airplane was on the runway. He touched down on the grass but the landing gears were pushed up through the Shooting Star’s wings.
The jet fighter had been too small to allow for adequate test equipment. A larger aircraft was needed. The R.A.F. assigned VH742 the role of test aircraft.
The new Lancastrian arrived at the Rolls-Royce Flight Test Establishment at Hucknall Aerodrome, Nottinghamshire, 30 October 1945. The modification was engineered and the airplane was modified. The Lanc’s two outboard Rolls-Royce Merlin V-12 engines were removed and two Nene Mk.I engines were installed in underslung nacelles. The wing flaps were shortened by 3 feet, 4 inches (1.016 meters) and the ailerons by 10 inches (0.254 meters) to provide clearance from the jet engines’ exhaust. Sheet steel was installed on the lower surfaces of the wings as protect against the heat.
Three fuel tanks were installed in each of the Lancastrian’s wings. The center tank contained gasoline for the Merlin engines, while the inner and outer tanks, plus two auxiliary tanks in the fuselage, carried kerosene for the jet engines. Fuel capacity was 760 gallons (2,877 liters) of gasoline and 2,420 gallons (9,161 liters) of kerosene.
In the Lancastrian’s cockpit, additional instruments were installed for the turbojets: tachometers reading from 0–20,000 r.p.m.; oil pressure gauges, 0–80 p.s.i.; exhaust gas temperature, 400˚–750 ˚C., and exhaust gas pressure.
The first flight of the modified VH742 took place 14 August 1946, with Ronnie Shepherd in the cockpit. Running on the jet engines alone, the airplane was extraordinarily quiet and vibration free. Like all early turbojets, the Nenes were slow to accelerate from low r.p.m. Test pilots had to use caution. Jim and Harvey Heyworth also flew VH742 during the last half of August.
The Rolls-Royce RB.41 Nene Mk.I was developed from the earlier RB.40 Derwent.¹ It was considerably larger and produced nearly double the thrust. It was a single-stage centrifugal-flow compressor/single-stage axial-flow turbine, rated at 5,000 pounds of thrust (22.24 kilonewtons) at 12,400 r.p.m. for takeoff.
A second Nene-powered Lancastrian was added to the test fleet at Hucknall the following year. Last Nene flight took place in August 1949.
VH742 had been ordered by the Royal Air Force during World War II as an Avro Type 683 Lancaster B. Mk.III, a very long range heavy bomber, and assigned identity markings PD194. With the end of World War II in Europe, orders for hundreds of Lancaster bombers were cancelled. The partially completed PD194 was modified on the assembly line as a Lancastrian C. Mk.I passenger transport and renumbered as VH742.
The Avro Type 691 Lancastrian was a four-engine civil transport based on the World War II very long range heavy bomber, the Avro Lancaster. The airliner was operated by a flight crew of four and carried one flight attendant. It could carry up to thirteen passengers. The Lancastrian was 76 feet, 10 inches (23.419 meters) long with a wingspan of 102 feet (31.090 meters) and overall height of 19 feet, 6 inches (5.944 meters). The empty weight was 30,220 pounds (13,707.6 kilograms) and gross weight was 65,000 pounds (29,483.5 kilograms).
The Lancastrian Mk.III was powered by four 1,648.9-cubic-inch-displacement (27.04 liter) liquid-cooled, supercharged, Rolls-Royce Merlin T24/2 single overhead camshaft (SOHC) 60° V-12 engines producing 1,650 horsepower and turning three bladed propellers.
The airplane a cruise speed of 245 miles per hour (394.3 kilometers per hour) and a maximum speed of 315 miles per hour (506.9 kilometers per hour). The service ceiling was 25,500 feet (7,772 meters) and the range was 4,150 miles (6,679 kilometers).
91 Avro Lancastrians were built, including modified Lancaster bombers. The transport variant first flew in 1943. In addition to the Royal Air Force, commercial Lancastrians were operated by British European Airways, British Overseas Airways Corporation and British South American Airways. The last one was retired in 1960.
Rolls-Royce built more than 1,100 RB.41 Nene engines. It was licensed for production by Pratt & Whitney as the J42. Forty Nenes were sold to the Soviet Union under the condition that they would not be used for military purposes. These were reverse-engineered and produced as the Klimov RD-45 which powered the Mikoyan-Gurevich MiG-15 fighter.
¹ While Rolls-Royce named its piston-driven aircraft engines after birds of prey, the turbojet engines were named for rivers.