The patent application for the gas turbine, as we know it today, was submitted in 1930 by an Englishman, Sir Frank Whittle. His patent was for a jet aircraft engine. Using his ideas, along with the contributions of such scientists as Coley and Moss, Whittle developed a working gas turbine engine (GTE).

AMERICAN DEVELOPMENT

The United States entered the gas turbine field in late 1941 when General Electric was awarded a contract to build an American version of a foreign-designed aircraft (gas turbine) engine. The engine and airframe were both built in 1 year. The first jet aircraft was flown in this country in October 1942.

In late 1941, Westinghouse Corporation was awarded a contract to design and build from scratch the first all-American gas turbine engine. Their engineers designed the first axial-flow compressor and annular combustion chamber. Both of these ideas, with minor changes, are the basis for the majority of gas turbine engines in use today.

MARINE GAS TURBINES

The concept of using a gas turbine to propel a ship goes back to 1937 when a Pescara free-piston gas engine was used experimentally with a gas turbine. The free-piston engine, or "gasifier" (fig 6-4) is a form of diesel engine that uses air cushions instead of a crankshaft to return the pistons. It was an effective producer of pressurized gases, and the German Navy used it in their submarines during World War II as an air compressor. In 1953, the French placed in service two small vessels powered by a free-piston engine/gas turbine combination. In 1957, the United States put into service the liberty ship William Patterson, having six free-piston engines driving two turbines.

The gasifier, or compressor, was usually an aircraft jet engine or turboprop front end. In 1947, the Motor Gun Boat 2009, of the British navy, used a 2500 horsepower (hp) gas turbine to drive the center of three shafts. In 1951, in an experimental application, the tanker Auris replaced one of four diesel engines with a 1200 hp gas turbine. In 1956, the John Sergeant had a remarkably efficient installation that used a regenerator to recover heat from the exhaust gases.

By the late 1950s, gas turbine marine engines were becoming widely used in combination with conventional propulsion equipment mostly by European navies. Gas turbines were used for highspeed operation, and conventional plants were used for cruising. The most common arrangements were the combined diesel or gas turbine (CODOG) or the combined diesel and gas turbine (CODAG) systems. Diesel engines give good

Figure 6-4.-Free-piston engine.

Figure 6-5.-Newton's third law of motion.

cruising range and reliability, but they have a disadvantage when used in antisubmarine warfare. Their low-frequency sounds travel great distances through water, making them easily detected by passive sonar. Steam turbines have been combined with gas turbines in the steam and gas turbine propulsion (COSAG) configuration to reduce low-frequency sound. This configuration requires more personnel to operate and does not have the range of the diesel combinations. Another configuration, the combined gas turbine or gas turbine (COGOG) has also been successful. The British County class destroyers use the 4,500 hp Tyne gas turbine engine for cruising and the 28,000 hp Rolls Royce Olympus engine for high speed.

The U.S. Navy entered the marine gas turbine field with the Asheville class patrol gunboats. These ships have the CODOG configuration, with two diesel engines for cruising, and a General Electric LM 1500 gas turbine for operating at high speed. As a result of the increasing reliability and efficiency of new gas turbine deigns, the Navy has now designed and is building cruisers, destroyers, and frigates that are entirely propelled by marine gas turbine engines.

BASIC ENGINE THEORY

Newton's third law of motion states that for every action there is an equal and opposite reaction. If you have ever fired a shotgun and felt the recoil, you have experienced an example of action-reaction (fig 6-5) This law of motion is demonstrated in a gas turbine by hot and expanding gases striking the turbine wheel (action) and causing the wheel to rotate (reaction).

Figure 6-6.-Turbine operating theory.