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In the first part of this series, we saw how turboprop engines can be used for compressor drivers, ship propulsion and electric power, and a new railroad electric locomotive using natural gas as the fuel. In this article, the author writes about the first turboprop unit that was run using a water break.
Now let us start from the beginning. GE designed, built and ran the first US turboprop engine in Schenectady, NY. The design team was headed by Bruce Buckland, Alan Howard and William R. Travers. The design was completed on December 23, 1941 and the first unit was run on May 15, 1943 without a prop, by using a water break. The engine was a combination turboprop and jet. It weighed 2000 pounds, developed 2200 HP and 630 pounds of thrust, and had a planetary gear with about a 10 to 1 speed reduction (13,000 to 1145 RPM).
The engine was quite unique. It had a pressure ratio of 6.0, an axial flow compressor, a first for the US, a transonic first stage nozzle of a Curtis type, an impulse single stage turbine and a Timken steel turbine rim welded to a ferrotic hub and shaft. The turboprop engine had an unheard of TIT of 1900o F to take advantage of the lower temperature of the gas striking the impulse blades.
This engine was the forerunner of the famous J-47 jet engine for the F-86 fighter plane and other military planes. GE made about 35,000 of these jets. The T-31 was also the parent of the GE HD Frame 3 single shaft gas turbine that was designed for the Union Pacific Railroad Company for the first US gas turbine locomotive which was first run in 1948. Features of the T-31 were used by Buckland and Howard for this first HD Frame 3 single shaft unit.
Other GE turboprop engines
GE later built the 1000 HP T-58 and the 4000 HP T-64 engines which were extensively used for helicopters but were not successfully used for industrial applications; but GE unsuccessfully tried. Other manufacturers such as Garrett, Lycoming, Air Research and Allison to name a few, besides Pratt, built turboprop and turboshaft gas turbines.
Allison (GM) T-56 turboprop engine
Perhaps the best turboprop engine ever built and still in use today is the Allison T-56 501.
It powers the Lockheed C-130 Hercules four-engine military cargo plane. The design of the first engine was started in 1951 after earlier models of the Allison T-38 and T-40s. Jack Fetters, chief engineer, led the design and Don Zimmerman, Victor Peterson and Gordon Hollbrook helped design it. The T-56 passed its 50-hour test run in September of 1953 and went into production December 12, 1954.
The T-56 had a TIT of 1970o F. It incorporated a 9.6 PR 14 stage axial compressor and a 4-stage axial turbine running at 13,820 RPM. It developed 4050 HP and 797 pounds of thrust. It had air cooled nozzle vanes and first stage turbine blades. It incorporated an offset single stage speed reduction gear (13,800 to 1021 RPM).
This T-56 501 model was used in a number of planes besides the C-130, including the Lockheed Electra L 188, a 4-engine passenger plane. The engine was rated at 3750 HP for the plane with TBOs set at 1000 hours by applying labyrinth seals instead of the original carbon seals. Approval for the Lockheed Electra was given by the CAA for the T-56 on May 20, 1955. On December 27, 1957 Allison delivered its first 501 to Lockheed.
The new Electra was a fun plane to ride. Braniff Airways purchased a number of these planes and the author rode this plane several times between Houston and New Orleans. It was like riding a roller coaster because of its sharp angle of climb and its rapid dive to land. It took just an hour to travel the 400 mile distance.
Braniff experienced a mid-air disintegration of an Electra over Texas in 1959 and the Northwest had a similar fatal crash over Indiana the same year. The structural support of the engines to the wing was flawed and caused the engines to whip around under turbulent air conditions and tear away from the wing. The problem was solved, but people were afraid of the plane and then came along the Boeing 707s. These two factors ended the Lockheed Electra. The program was canceled in January 1961.
In the next part, the author discusses how the Allison T-56 501K was used to pump natural gas and how it went on to be a forerunner of several future aero engines.
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.