A constant speed drive (CSD) also known as a constant speed generator, is a type of

transmission Transmission may refer to: Medicine, science and technology * Power transmission ** Electric power transmission ** Propulsion transmission, technology allowing controlled application of power *** Automatic transmission *** Manual transmission ** ...

that takes an input shaft rotating at a wide range of speeds, delivering this power to an output shaft that rotates at a constant speed, despite the varying input. They are used to drive mechanisms, typically

electrical generator In electricity generation, a generator is a device that converts motive power (mechanical energy) or fuel-based power (chemical energy) into electric power for use in an external electrical circuit, circuit. Sources of mechanical energy include s ...

s, that require a constant input speed. The term is most commonly applied to hydraulic transmissions found on the

accessory drive The accessory drive is a gearbox that forms part of a gas turbine engine. Although not part of the engine's core, it drives the accessories, fuel pumps, etc., that are otherwise essential for the operation of the engine or the aircraft on which ...

s of

gas turbine A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directio ...

engines, such as aircraft

jet engine A jet engine is a type of reaction engine discharging a fast-moving jet (fluid), jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition can include Rocket engine, rocket, Pump-jet, water jet, and ...

s. On modern aircraft, the CSD is often combined with a generator into a single unit known as an integrated drive generator (IDG).

Mechanism

CSDs are mainly used on

airliner An airliner is a type of aircraft for transporting passengers and air cargo. Such aircraft are most often operated by airlines. Although the definition of an airliner can vary from country to country, an airliner is typically defined as an ...

and

military aircraft A military aircraft is any fixed-wing or rotary-wing aircraft that is operated by a legal or insurrectionary armed service of any type. Military aircraft can be either combat or non-combat: * Combat aircraft are designed to destroy enemy equi ...

jet engines to drive the

alternating current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in which ...

(AC) electrical generator. In order to produce the proper voltage at a constant AC frequency, usually three-phase 115 VAC at 400 Hz, an alternator needs to spin at a constant specific speed (typically 6,000 RPM for air-cooled generators). Since the jet engine gearbox speed varies from idle to full power, this creates the need for a constant speed drive (CSD). The CSD takes the variable speed output of the accessory drive gearbox and hydro-mechanically produces a constant output RPM. Different systems have been used to control the alternator speed. Modern designs are mostly hydrokinetic, but early designs often took advantage of the

bleed air Bleed air is compressed air taken from the compressor stage of a gas turbine upstream of its fuel-burning sections. Automatic air supply and cabin pressure controller (ASCPCs) valves bleed air from high or low stage engine compressor sections. Lo ...

available from the engines. Some of these were mostly mechanically powered, with an air turbine to provide a vernier speed adjustment. Others were purely turbine-driven.

Integrated drive generator

On aircraft such as the

Airbus A310 The Airbus A310 is a wide-body aircraft, designed and manufactured by Airbus Industrie, then a consortium of European aerospace manufacturers. Airbus had identified a demand for an aircraft smaller than the A300, the first twin-jet wide-b ...

Airbus A320 family The Airbus A320 family is a series of Narrow-body aircraft, narrow-body airliners developed and produced by Airbus. The A320 was launched in March 1984, Maiden flight, first flew on 22 February 1987, and was introduced in April 1988 by Air F ...

Airbus A320neo The Airbus A320neo family is a development of the A320 family of narrow-body airliners produced by Airbus. The A320neo family (''neo'' for "new engine option") is based on the previous A319, A320 and A321 ( enhanced variant), which was then re ...

Airbus A330 The Airbus A330 is a wide-body aircraft developed and produced by Airbus. Airbus conceived several derivatives of the A300, its first airliner in the mid-1970s. Then the company began development on the A330 twinjet in parallel with the A3 ...

, Airbus A330neo,

Airbus A340 The Airbus A340 is a long-haul, long-range, wide-body passenger airliner that was developed and produced by Airbus. In the mid-1970s, Airbus conceived several derivatives of the Airbus A300, A300, its first airliner, and developed the A340 qu ...

Boeing 737 Next Generation The Boeing 737 Next Generation, commonly abbreviated as 737NG, or 737 Next Gen, is a narrow-body aircraft powered by two jet engines and produced by Boeing Commercial Airplanes. Launched in 1993 as the third generation derivative of the Boei ...

747 747 may refer to: * 747 (number), a number * AD 747, a year of the Julian calendar * 747 BC, a year in the 8th century BC * Boeing 747, a large commercial jet airliner Music and film * 747s (band), an indie band * ''747'' (album), by country musi ...

757 757 may refer to: * Boeing 757: a narrow-body airliner * AD 757 __NOTOC__ Year 757 ( DCCLVII) was a common year starting on Saturday (link will display the full calendar) of the Julian calendar. The denomination 757 for this year has been us ...

767 767 may refer to: * Boeing 767, a jet airliner * 767 (number) * AD 767, a year in the 8th century. * 767 BC, a year in the 8th century BC * Area code 767 Area code 767 is the local telephone area code of the Commonwealth of Dominica, within the ...

and

777 777 may refer to: * 777 (number), a number * AD 777, a year of the Julian calendar * 777 BC, a year in the 8th century BC * Boeing 777, a commercial jet airliner :* Boeing 777X, the newer generation of the Boeing 777. Art and entertainment A ...

, an integrated drive generator (IDG) is used. This unit is simply a CSD and an oil cooled generator inside the same case. Troubleshooting is simplified as this unit is the line-replaceable electrical generation unit on the engine.

Manufacturers

Collins Aerospace Collins Aerospace is an American technology corporation that is one of the world's largest suppliers of aerospace and defense products. Headquartered in Charlotte, North Carolina, it is a subsidiary of Raytheon Technologies. History On No ...

(formerly UTC Aerospace Systems (formerly

Hamilton Sundstrand Hamilton Sundstrand was an American globally active corporation that manufactured and supported aerospace and industrial products for worldwide markets. A subsidiary of United Technologies Corporation, it was headquartered in Windsor Locks, Con ...

)) is an American manufacturer of CSD and IDG units.

Alternatives

A variable-speed constant-frequency (VSCF) generator can be used to provide AC power using an electronic

tap converter The tap converter is a variation on the cycloconverter, invented in 1981 by New York City electrical engineer Melvin Sandler and significantly functionally enhanced in 1982 through 1984 by graduate students Mariusz Wrzesniewski, Bruce David Wilner ...

. Variable Frequency Starter Generator (VFSG) used primarily on the Boeing 787 are both used for electric start and electric generation.

References

{{Aircraft gas turbine engine components Jet engine technology Aircraft components Aerospace engineering Vehicle technology

Mechanism

Integrated drive generator

Manufacturers

Alternatives

See also

References