In the previous article, the author discussed the unique features of the engine that became the forerunner of the J-47 jet, the F-86 fighter plane and other military planes. Here, he discusses how the early turboprop engines running on natural gas were used on commercial airplanes.
The Allison T-56 501 K, rated at 3500 HP, was used to pump natural gas. DeLaval made arrangements with Allison to package the 501 K and furnished a new 13,800 RPM centrifugal compressor for the package as well as all the controls, lube oil system, air filter and accessories.
The single shaft gas turbine with a TIT of 1900oF had a simple cycle efficiency of 27 percent, better than the 26 percent of the GE Frame 3 two-shaft regenerative unit. The engine ran very well burning natural gas fuel. It was reliable and proved to have long TBOs even though it was an aero engine. This package was the forerunner of many aero engines by P&W, R-R and GE to be used to pump natural gas.
First commercial use
The first turboprop engine used on a commercial airplane was the Rolls-Royce Dart. Designed in 1946, it first ran in 1948 and was used on the 4-engine Vickers Viscount 24 to 30-seat airplane in 1953. The airplane air speed was 275 MPH and was the first tuboprop plane ever used by airlines. It was well received and 445 planes were built. The Dart had a two-stage centrifugal compressor and an axial flow turbine, and it developed 1576 HP.
In 1955, Tennessee Gas Transmission Company purchased two Viscounts from Canada for executive use. The author had the opportunity to fly in one of these planes between Houston and Syracuse, NY, near Schenectady, for a meeting to firm up details for two 6700 HP Frame 3 two-shaft gas turbines to be installed at the TGT Moorhead, Kentucky pumping station. The author, TGT chief engineer, George White, his assistant Tracy Parks and the GE salesman, Aaron Holland, were the only four passengers on the plane. The plane was a real change from the recip engine DC 6s and Constellations. The recip vibration and noise were gone and it was a smooth and quiet ride.
The Abrams tank AGT 1500
There is another turboshaft gas turbine that should be mentioned and this is the turbine that drives the M1A1 Abrams 70-ton battle tank which distinguished itself during the Persian Gulf War (Desert Storm). This 1500 HP gas turbine is designated as the AGT 1500 and has several company descriptions: Honeywell, Textron Lycoming, or simply the Lycoming. The engine was specifically designed for a tank and was based on the Lycoming T- 53 turboshaft gas turbine used on the Huey helicopter, but with advanced features. The engine can be described as being a three-spool, free-shaft unit with recuperation. It has a full power 16 pressure ratio. A specially designed Allison transmission for the tank was made to meet the tank requirements.
A new replacement engine, based on the more recent GE T-700 turboshaft engine is under development. The new LV100, as it is called, will be more efficient and more powerful, but yet be lighter and take up less space.
The Russian TU 95 Bear Turboprop
Here is a very interesting story of the Russian Turboprop airplane known as the Bear to the West but is called ‘Big Ivan’ by the Russians. This huge 35o sweep back wing machine first flew in 1951. It has four large 15,000 HP turboprop gas turbine engines that drive counter rotating huge 20-foot 4.1 inch diameter four bladed props through a special planetary gear arrangement for axial alignment of the props to the gas turbine. The props rotate at transonic speeds near the tips and are therefore very noisy.
The engine has a 14-stage axial flow compressor with a 9 to 13 PR, depending on the altitude, a 5-stage axial turbine and a can-annular combustion system. It has a maker and model number of Kuznetov 12 MA and MV models, and is to this day the largest and most powerful turboprop in the world. It was completed in 1949 and the gas turbine was designed by engineers deported from WW II German, under Ferdinand Brandner who previously worked for Junkers. Surprisingly, this plane is the fastest turboprop plane ever built and has a top speed of 541 MPH, a cruise speed of 478 MPH and a range of over 9000 miles without refueling.
When the TU 95 was first known to the US, our experts said that the plane could not possibly fly more than 400 MPH and would have a range of no more than 7,800 miles. How wrong they were. The experts kept upping their estimates and finally had to admit to the data presented above.
It is not generally known, but the US Boeing B-52 plane was originally proposed to be turboprop driven, but at the last minute was changed by Boeing to use 8 P & W J-58 jets, two engines per pod and 4 pods. In the fourth and last part of this series, we will look into some of the engine improvements and model changes incorporated in the B-52s to design today’s planes.
Ivan G. Rice, past chairman of the South Texas Section of ASME (1974 – 75), and the ASME Gas Turbine Division (now IGTI) (1975 – 76), has authored many articles and ASME papers on gas turbines, inter-cooling, reheat, HRSGs, steam cooling and steam injection. He is a Life Fellow Member of ASME and Life Member of NSPE/TSPE.