![A380 APU P1230093](https://upload.wikimedia.org/wikipedia/commons/d/d2/A380_APU_P1230093.jpg)
An auxiliary power unit (APU) is a device on a
vehicle
A vehicle (from la, vehiculum) is a machine that transports people or cargo. Vehicles include wagons, bicycles, motor vehicles (motorcycles, cars, trucks, buses, mobility scooters for disabled people), railed vehicles (trains, trams), wa ...
that provides energy for functions other than
propulsion
Propulsion is the generation of force by any combination of pushing or pulling to modify the translational motion of an object, which is typically a rigid body (or an articulated rigid body) but may also concern a fluid. The term is derived from ...
. They are commonly found on large
aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...
and naval ships as well as some large land vehicles. Aircraft APUs generally produce 115
V AC voltage
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 ...
at 400
Hz (rather than 50/60 Hz in mains supply), to run the electrical systems of the aircraft; others can produce 28 V
DC voltage.
APUs can provide power through single or
three-phase
Three-phase electric power (abbreviated 3φ) is a common type of alternating current used in electricity generation, Electric power transmission, transmission, and Electric power distribution, distribution. It is a type of polyphase system empl ...
systems.
Transport aircraft
History
![Riedelanlasser](https://upload.wikimedia.org/wikipedia/commons/e/e1/Riedelanlasser.jpg)
During
World War I
World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...
, the British
Coastal class blimp __NOTOC__
The Coastal Class (often known as the C-Class or simply the 'Coastals') were a class of non-rigid airship or "blimp" used by the Royal Naval Air Service (RNAS) during World War I. The C-class blimp operated by the United States Navy ...
s, one of several types of airship operated by the
Royal Navy
The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against F ...
, carried a
ABC
ABC are the first three letters of the Latin script known as the alphabet.
ABC or abc may also refer to:
Arts, entertainment, and media Broadcasting
* American Broadcasting Company, a commercial U.S. TV broadcaster
** Disney–ABC Television ...
auxiliary engine. These powered a generator for the craft's
radio transmitter
In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the ...
and, in an emergency, could power an auxiliary air blower. One of the first military fixed-wing aircraft to use an APU was the British, World War 1,
Supermarine Nighthawk, an anti-Zeppelin
night fighter
A night fighter (also known as all-weather fighter or all-weather interceptor for a period of time after the Second World War) is a fighter aircraft adapted for use at night or in other times of bad visibility. Night fighters began to be used i ...
.
[Andrews and Morgan 1987, p. 21.]
During
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
, a number of large American military aircraft were fitted with APUs. These were typically known as ''putt–putts'', even in official training documents. The putt-putt on the
B-29 Superfortress
The Boeing B-29 Superfortress is an American four-engined propeller-driven heavy bomber, designed by Boeing and flown primarily by the United States during World War II and the Korean War. Named in allusion to its predecessor, the B-17 Fl ...
bomber was fitted in the unpressurised section at the rear of the aircraft. Various models of four-stroke,
Flat-twin
A flat-twin engine is a two-cylinder internal combustion engine with the cylinders on opposite sides of the crankshaft. The most common type of flat-twin engine is the boxer-twin engine, where both pistons move inwards and outwards at the same ti ...
or
V-twin
A V-twin engine, also called a V2 engine, is a two-cylinder piston engine where the cylinders share a common crankshaft and are arranged in a V configuration.
Although widely associated with motorcycles (installed either transversely or longit ...
engines were used. The engine drove a ''P2'', DC generator, rated 28.5 Volts and 200 Amps (several of the same ''P2'' generators, driven by
the main engines, were the B-29's DC power source in flight). The putt-putt provided power for starting the main engines and was used after take-off to a height of . The putt-putt was restarted when the
B-29
The Boeing B-29 Superfortress is an American four-engined propeller-driven heavy bomber, designed by Boeing and flown primarily by the United States during World War II and the Korean War. Named in allusion to its predecessor, the B-17 Fly ...
was descending to land.
Some models of the
B-24 Liberator
The Consolidated B-24 Liberator is an American heavy bomber, designed by Consolidated Aircraft of San Diego, California. It was known within the company as the Model 32, and some initial production aircraft were laid down as export models des ...
had a putt–putt fitted at the front of the aircraft, inside the nose-wheel compartment. Some models of the
Douglas C-47 Skytrain
The Douglas C-47 Skytrain or Dakota (RAF, RAAF, RCAF, RNZAF, and SAAF designation) is a military transport aircraft developed from the civilian Douglas DC-3 airliner. It was used extensively by the Allies during World War II and remained in ...
transport aircraft carried a putt-putt under the cockpit floor.
As mechanical "startup" APUs for jet engines
The first German
jet engine
A jet engine is a type of reaction engine discharging a fast-moving jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition can include rocket, Pump-jet, water jet, and hybrid propulsion, the term ...
s built during the
Second World War
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
used a mechanical APU starting system designed by the German engineer
Norbert Riedel
Norbert Riedel (* 1 April 1912 in Jägerndorf, Sudetenland, then Austria-Hungary; † 24 February 1963 in Zürs am Arlberg, Austria) was an engineer and entrepreneur.
Life
Riedel studied mechanical engineering and worked in the 1930s, first with ...
. It consisted of a
two-stroke
A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a Thermodynamic power cycle, power cycle with two strokes (up and down movements) of the piston during one power cycle, this power cycle being comple ...
flat engine
A flat engine is a piston engine where the cylinders are located on either side of a central crankshaft. Flat engines are also known as horizontally opposed engines, however this is distinct from the less common opposed-piston engine design, ...
, which for the
Junkers Jumo 004 design was hidden in the intake diverter, essentially functioning as a pioneering example of an auxiliary power unit for starting a jet engine. A hole in the extreme nose of the diverter contained a manual pull-handle which started the piston engine, which in turn rotated the compressor. Two spark plug access ports existed in the Jumo 004's intake diverter to service the Riedel unit's cylinders in situ, for maintenance purposes. Two small "premix" tanks for the Riedel's petrol/
oil
An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...
fuel were fitted in the annular intake. The engine was considered an extreme short stroke (bore / stroke: 70 mm / 35 mm = 2:1) design so it could fit within the intake diverter of jet engines like the Jumo 004. For reduction it had an integrated
planetary gear
An epicyclic gear train (also known as a planetary gearset) consists of two gears mounted so that the center of one gear revolves around the center of the other. A carrier connects the centers of the two gears and rotates the planet and sun gea ...
. It was produced by
Victoria
Victoria most commonly refers to:
* Victoria (Australia), a state of the Commonwealth of Australia
* Victoria, British Columbia, provincial capital of British Columbia, Canada
* Victoria (mythology), Roman goddess of Victory
* Victoria, Seychelle ...
in
Nuremberg
Nuremberg ( ; german: link=no, Nürnberg ; in the local East Franconian dialect: ''Nämberch'' ) is the second-largest city of the German state of Bavaria after its capital Munich, and its 518,370 (2019) inhabitants make it the 14th-largest ...
and served as a mechanical APU-style starter for all three German jet engine designs to have made it to at least the prototype stage before May 1945 – the
Junkers Jumo 004, the
BMW 003
The BMW 003 (full RLM designation 109-003) is an early axial turbojet engine produced by BMW AG in Germany during World War II. The 003 and the Junkers Jumo 004 were the only German turbojet engines to reach production during World War II.
W ...
(which uniquely appears to use an electric starter for the Riedel APU), and the prototypes (19 built) of the more advanced
Heinkel HeS 011
The Heinkel HeS 011 or Heinkel-Hirth 109-011 ''(HeS - Heinkel Strahltriebwerke)'' was an advanced World War II jet engine built by Heinkel-Hirth. It featured a unique compressor arrangement, starting with a low-compression impeller in the intake ...
engine, which mounted it just above the intake passage in the Heinkel-crafted sheetmetal of the engine nacelle nose.
The
Boeing 727
The Boeing 727 is an American narrow-body airliner that was developed and produced by Boeing Commercial Airplanes.
After the heavy 707 quad-jet was introduced in 1958, Boeing addressed the demand for shorter flight lengths from smaller airpo ...
in 1963 was the first jetliner to feature a
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 directi ...
APU, allowing it to operate at smaller airports, independent from ground facilities. The APU can be identified on many modern airliners by an exhaust pipe at the aircraft's tail.
Sections
A typical gas-turbine APU for commercial transport aircraft comprises three main sections:
Power section
The power section is the gas-generator portion of the engine and produces all the shaft power for the APU.
In this section of the engine, air and fuel are mixed, compressed and ignited to create hot and expanding gases. This gas is highly energetic and is used to spin the turbine, which in turn powers other sections of the engine, such as auxiliary gearboxes, pumps, electrical generators, and in the case of a turbo fan engine, the main fan
Load compressor section
The load compressor is generally a shaft-mounted compressor that provides pneumatic power for the aircraft, though some APUs extract
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. Low ...
from the power section compressor. There are two actuated devices to help control the flow of air: the inlet guide vanes that regulate airflow to the load compressor and the surge control valve that maintains stable or surge-free operation of the turbo machine.
Gearbox section
The
gearbox
Propulsion transmission is the mode of transmitting and controlling propulsion power of a machine. The term ''transmission'' properly refers to the whole drivetrain, including clutch, gearbox, prop shaft (for rear-wheel drive vehicles), differe ...
transfers power from the main shaft of the engine to an oil-cooled generator for electrical power. Within the gearbox, power is also transferred to engine accessories such as the fuel control unit, the lubrication module, and cooling fan. There is also a starter motor connected through the gear train to perform the starting function of the APU. Some APU designs use a combination starter/generator for APU starting and electrical power generation to reduce complexity.
On the
Boeing 787
The Boeing 787 Dreamliner is an American wide-body jet airliner developed and manufactured by Boeing Commercial Airplanes.
After dropping its unconventional Sonic Cruiser project, Boeing announced the conventional 7E7 on January 29, 2003, ...
, an aircraft which has greater reliance on its electrical systems, the APU delivers only electricity to the aircraft. The absence of a pneumatic system simplifies the design, but high demand for electricity requires heavier generators.
Onboard solid oxide fuel cell (
SOFC
A solid oxide fuel cell (or SOFC) is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. Fuel cells are characterized by their electrolyte material; the SOFC has a solid oxide or ceramic electrolyte.
A ...
) APUs are being researched.
Manufacturers
The market of Auxiliary power units is dominated by
Honeywell
Honeywell International Inc. is an American publicly traded, multinational conglomerate corporation headquartered in Charlotte, North Carolina. It primarily operates in four areas of business: aerospace, building technologies, performance ma ...
, followed by
Pratt & Whitney
Pratt & Whitney is an American aerospace manufacturer with global service operations. It is a subsidiary of Raytheon Technologies. Pratt & Whitney's aircraft engines are widely used in both civil aviation (especially airlines) and military aviat ...
,
Motorsich and other manufacturers such as
PBS Velká Bíteš
Prvni brnenska strojirna Velka Bites, a. s. ("First Brno Engineering Plant", known as PBS VB) is a Czech Republic, Czech engineering and manufacturing company. It focuses mainly on the development, testing, and production of devices for the airc ...
,
Safran Power Units,
Aerosila
SPE "Aerosila" (russian: Аэросила) is the leading Russian firm in the field of development and manufacturing of aircraft propellers, propfans, auxiliary gas-turbine engines as well as aviation aggregates of different purpose including h ...
and
Klimov
The JSC Klimov (or Joint Stock Company Klimov) presently manufactures internationally certified gas turbine engines, main gearboxes and accessory drive gearboxes for transport aircraft.
Originally established as ''Kirill Klimov Experimental De ...
. Local manufacturers include
Bet Shemesh Engines
Black Entertainment Television (acronym BET) is an American basic cable channel targeting African-American audiences. It is owned by the CBS Entertainment Group unit of Paramount Global via BET Networks and has offices in New York City, Los ...
and
Hanwha Aerospace
, type = Public
, traded_as =
, industry = Aerospace
, genre =
, fate =
, predecessor =
, successor =
, founded = (as Samsung Precision) ...
. The 2018 market share varied according to the application platforms:
* Large commercial aircraft: Honeywell 70–80%, Pratt & Whitney 20–30%, others 0–5%
* Regional aircraft: Pratt & Whitney 50–60%, Honeywell 40–50%, others 0–5%
* Business jets: Honeywell 90–100%, others 0–5%
* Helicopters: Pratt & Whitney 40–50%, Motorsich 40–50%, Honeywell 5–10%, Safran Power Units 5–10%, others 0–5%
On June 4, 2018,
Boeing
The Boeing Company () is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, telecommunications equipment, and missiles worldwide. The company also provides leasing and product ...
and
Safran
Safran S.A. is a French multinational company that designs, develops and manufactures aircraft engines, rocket engines as well as various aerospace and defense-related equipment or their components. It was formed by a merger between SNECMA and ...
announced their 50–50 partnership to design, build and service APUs after regulatory and
antitrust
Competition law is the field of law that promotes or seeks to maintain market competition by regulating anti-competitive conduct by companies. Competition law is implemented through public and private enforcement. It is also known as antitrust l ...
clearance in the second half of 2018.
Boeing produced several hundred
T50/
T60 small
turboshaft
A turboshaft engine is a form of gas turbine that is optimized to produce shaftpower rather than jet thrust. In concept, turboshaft engines are very similar to turbojets, with additional turbine expansion to extract heat energy from the exhaust ...
s and their derivatives in the early 1960s.Safran produces
helicopter
A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes ...
s and
business jet
A business jet, private jet, or bizjet is a jet aircraft designed for transporting small groups of people. Business jets may be adapted for other roles, such as the evacuation of casualties or express parcel deliveries, and some are used by pub ...
s APUs but stopped the large APUs since
Labinal
Safran Aircraft Engines, previously Snecma (''Société nationale d'études et de construction de moteurs d'aviation'') or Snecma Moteurs, is a French aerospace engine manufacturer headquartered in Courcouronnes and a subsidiary of Safran. I ...
exited the
APIC joint venture with
Sundstrand in 1996.
This could threaten the dominance of
Honeywell
Honeywell International Inc. is an American publicly traded, multinational conglomerate corporation headquartered in Charlotte, North Carolina. It primarily operates in four areas of business: aerospace, building technologies, performance ma ...
and
United Technologies
United Technologies Corporation (UTC) was an American multinational conglomerate headquartered in Farmington, Connecticut. It researched, developed, and manufactured products in numerous areas, including aircraft engines, aerospace systems ...
. Honeywell has a 65% share of the
mainliner APU market and is the sole supplier for the
Airbus A350
The Airbus A350 is a long-range, wide-body twin-engine jet airliner developed and produced by Airbus.
The first A350 design proposed by Airbus in 2004, in response to the Boeing 787 Dreamliner, would have been a development of the A330 wi ...
, the
Boeing 777
The Boeing 777, commonly referred to as the Triple Seven, is an American long-range wide-body airliner developed and manufactured by Boeing Commercial Airplanes. It is the world's largest twinjet.
The 777 was designed to bridge the gap bet ...
and all
single-aisle
A narrow-body aircraft or single-aisle aircraft is an airliner arranged along a single aisle, permitting up to 6-abreast seating in a cabin less than in width.
In contrast, a wide-body aircraft is a larger airliner usually configured with mu ...
s: the
Boeing 737 MAX
The Boeing 737 MAX is the fourth generation of the Boeing 737, a narrow-body aircraft, narrow-body airliner manufactured by Boeing Commercial Airplanes (BCA), a division of American company Boeing. It succeeds the Boeing 737 Next Generation (NG ...
,
Airbus A220
The Airbus A220 is a family of five-abreast narrow-body airliners by Airbus Canada Limited Partnership. It was originally designed by Bombardier and had two years in service as the Bombardier CSeries.
The program was launched on 13 July 2 ...
(formerly Bombardier CSeries),
Comac C919,
Irkut MC-21
The Irkut MC-21 (russian: Иркут МС-21) is a single-aisle airliner, developed in Russia by the Yakovlev Design Bureau and produced by its parent Irkut, a branch of the United Aircraft Corporation (UAC), itself a 92%-owned subsidiary o ...
and
Airbus A320neo since Airbus eliminated the P&WC
APS3200 option.
P&WC claims the remaining 35% with the
Airbus A380
The Airbus A380 is a large wide-body airliner that was developed and produced by Airbus. It is the world's largest passenger airliner and only full-length double-deck jet airliner.
Airbus studies started in 1988, and the project was annou ...
,
Boeing 787
The Boeing 787 Dreamliner is an American wide-body jet airliner developed and manufactured by Boeing Commercial Airplanes.
After dropping its unconventional Sonic Cruiser project, Boeing announced the conventional 7E7 on January 29, 2003, ...
and
Boeing 747-8
The Boeing 747-8 is a wide-body airliner formerly developed by Boeing Commercial Airplanes, and the largest variant of the 747.
After introducing the 747-400, Boeing considered larger 747 versions as alternatives to the proposed double-deck Ai ...
.
It should take at least a decade for the Boeing/Safran JV to reach $100 million in service revenue.The 2017 market for production was worth $800 million (88% civil and 12% military), while the
MRO market was worth $2.4 billion, spread equally between civil and military.
Spacecraft
The
Space Shuttle
The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program na ...
APUs provided
hydraulic
Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counter ...
pressure. The Space Shuttle had three
redundant APUs, powered by
hydrazine
Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...
fuel. They were only powered up for ascent,
re-entry
Atmospheric entry is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. There are two main types of atmospheric entry: ''uncontrolled entry'', such as the entr ...
, and landing. During ascent, the APUs provided hydraulic power for
gimbal
A gimbal is a pivoted support that permits rotation of an object about an axis. A set of three gimbals, one mounted on the other with orthogonal pivot axes, may be used to allow an object mounted on the innermost gimbal to remain independent of ...
ling of the Shuttle's three
engines
An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy.
Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power g ...
and control of their large valves, and for movement of the
control surfaces. During landing, they moved the control surfaces, lowered the wheels, and powered the
brake
A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction.
Background ...
s and nose-wheel steering. Landing could be accomplished with only one APU working. In the early years of the Shuttle there were problems with APU reliability, with malfunctions on three of the first nine Shuttle missions.
Armored vehicles
APUs are fitted to some
tank
A tank is an armoured fighting vehicle intended as a primary offensive weapon in front-line ground combat. Tank designs are a balance of heavy firepower, strong armour, and good battlefield mobility provided by tracks and a powerful engin ...
s to provide electrical power without the high fuel consumption and large
infrared signature Infrared signature, as used by defense scientists and the military, is the appearance of objects to infrared sensors. An infrared signature depends on many factors, including the shape and size of the object, temperature, and emissivity, reflectio ...
of the main engine. As early as World War II, the American
M4 Sherman
}
The M4 Sherman, officially Medium Tank, M4, was the most widely used medium tank by the Military history of the United States during World War II, United States and Allies of World War II, Western Allies in World War II. The M4 Sherman prove ...
had a small, piston-engine powered APU for charging the tank's batteries, a feature the Soviet-produced
T-34 tank
The T-34 is a Soviet medium tank introduced in 1940. When introduced its 76.2 mm (3 in) tank gun was less powerful than its contemporaries while its 60-degree sloped armour provided good protection against Anti-tank warfare, anti-tan ...
did not have.
Commercial vehicles
A refrigerated or frozen food semi trailer or train car may be equipped with an independent APU and fuel tank to maintain low temperatures while in transit, without the need for an external transport-supplied power source.
On some older diesel engined-equipment, a small gasoline engine (often called a "pony engine") was used instead of an electric motor to start the main engine. The exhaust path of the pony engine was typically arranged so as to warm the intake manifold of the diesel, to ease starting in colder weather. These were primarily used on large pieces of construction equipment.
Fuel cells
In recent years, truck and fuel cell manufacturers have teamed up to create, test and demonstrate a fuel cell APU that eliminates nearly all emissions and uses diesel fuel more efficiently.
In 2008, a DOE sponsored partnership between Delphi Electronics and Peterbilt demonstrated that a fuel cell could provide power to the electronics and air conditioning of a Peterbilt Model 386 under simulated "idling" conditions for ten hours.
Delphi has said the 5 kW system for Class 8 trucks will be released in 2012, at an $8000–9000 price tag that would be competitive with other "midrange" two-cylinder diesel APUs, should they be able to meet those deadlines and cost estimates.
See also
*
Air-start system
An air-start system is a power source used to provide the initial rotation to start large diesel and gas turbine engines.
Diesel engines Direct starting
Compared to a gasoline (petrol) engine, a diesel engine has a very high compression ratio, a ...
*
Auxiliary hydraulic system
*
Coffman engine starter
The Coffman engine starter (also known as a "shotgun starter") was a starting system used on many piston engines in aircraft and armored vehicles of the 1930s and 1940s. It used a cordite cartridge to move a piston, which cranked the engine. The C ...
*
Ram air turbine
A ram air turbine (RAT) is a small wind turbine that is connected to a hydraulic pump, or electrical generator, installed in an aircraft and used as a power source. The RAT generates power from the airstream by ram pressure due to the speed o ...
*
Uninterruptible power supply
An uninterruptible power supply or uninterruptible power source (UPS) is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails. A UPS differs from an auxiliary or emergency power system ...
Notes
References
External links
"Space Shuttle Orbiter APU""Sound of an APU from inside a Boeing 737 cabin"*
ttps://www.youtube.com/watch?v=8Azxzu1sqCU&t=75s YouTube video of restored Junkers Jumo 004 jet engine, being started with "integral" Riedel APU, from September 2019
{{Aircraft gas turbine engine components
Starting systems
Electrical generators
Aircraft components