Aircraft engine performance refers to factors including thrust or shaft power for fuel consumed, weight, cost, outside dimensions and life. It includes meeting regulated environmental limits which apply to emissions of noise and chemical pollutants, and regulated safety aspects which require a design that can safely tolerate environmental hazards such as birds, rain, hail and icing conditions. It is the end product that an engine company sells.
[Gas Turbine Performance Second Edition, Walsh and Fletcher, Blachwell Science Ltd. 2004, , Preface]
Aircraft engine
An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Most aircraft engines are either piston engines or gas turbines, although a few have been rocket powered and in recent years many ...
s are part of the
propulsion system
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 fro ...
of an
airplane
An airplane or aeroplane (informally plane) is a fixed-wing aircraft that is propelled forward by thrust from a jet engine, propeller, or rocket engine. Airplanes come in a variety of sizes, shapes, and wing configurations. The broad spe ...
,
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 ...
, rocket or
UAV
An unmanned aerial vehicle (UAV), commonly known as a drone, is an aircraft without any human pilot, crew, or passengers on board. UAVs are a component of an unmanned aircraft system (UAS), which includes adding a ground-based controller ...
which produce rotary power transferred to a
propeller
A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...
or kinetic energy as a high-velocity gas
exhaust
Exhaust, exhaustive, or exhaustion may refer to:
Law
*Exhaustion of intellectual property rights, limits to intellectual property rights in patent and copyright law
**Exhaustion doctrine, in patent law
** Exhaustion doctrine under U.S. law, in p ...
stream. Aircraft engine types include
turboprop
A turboprop is a turbine engine that drives an aircraft propeller.
A turboprop consists of an intake, reduction gearbox, compressor, combustor, turbine, and a propelling nozzle. Air enters the intake and is compressed by the compressor. Fuel ...
,
turbojet
The turbojet is an airbreathing jet engine which is typically used in aircraft. It consists of a gas turbine with a propelling nozzle. The gas turbine has an air inlet which includes inlet guide vanes, a compressor, a combustion chamber, and ...
,
turbofan
The turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft engine, aircraft propulsion. The word "turbofan" is a portmanteau of "turbine" and "fan": the ''turbo'' portion refers to a gas turbine engine which ac ...
and
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 ...
.
Piston engines
A reciprocating engine, also often known as a piston engine, is typically a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common featu ...
are used in recreational personal aircraft and older aircraft.
Electric engines
An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate for ...
are used in model aircraft, small drones, small UAVs and small crewed aircraft. Aircraft engine performance has improved dramatically since the advent of the first powered flight in 1848 by
John Stringfellow
John Stringfellow (1799 – 13 December 1883) was a British early aeronautical inventor, known for his work on the aerial steam carriage with William Samuel Henson.
Life
Stringfellow was born in Attercliffe, England to Martha ée Gil ...
. Aircraft engine manufacturers have to constantly innovate to remain competitive by offering more efficient and more reliable engines. Improving the performance of aircraft engines reduces the cost of ownership for operators of commercial, military and private aircraft.
Performance criteria
The following are different measures of the engine as a
black box
In science, computing, and engineering, a black box is a system which can be viewed in terms of its inputs and outputs (or transfer characteristics), without any knowledge of its internal workings. Its implementation is "opaque" (black). The te ...
and most are negotiated between the engine manufacturer and its customer for a particular aircraft installation. Some, like noise, exhaust pollutants and certain operability requirements, such as acceleration times, are regulated with limits that have to be met for commercial operation. Each is the result of design iterations inside the "black box" using both analytical computer modelling and development testing.
Thrust,
[ Shaft power,][ Fuel consumption,][ Weight,][ Cost,][ Installation envelope,][ Overhaul life,][ Operability, Noise, Exhaust pollutants.
]
Factors affecting engine performance
Fuel
The cost of fuel
A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy but ...
is a significant part of the operating cost of an aircraft, about 56% for a wide-body airliner in 1983. Particular fuels are approved for use in a particular engine to prevent safety and reliability issues. Fuels include jet fuel
Jet fuel or aviation turbine fuel (ATF, also abbreviated avtur) is a type of aviation fuel designed for use in aircraft powered by gas-turbine engines. It is colorless to straw-colored in appearance. The most commonly used fuels for commercial a ...
and AVGAS
Avgas (aviation gasoline, also known as aviation spirit in the UK) is an aviation fuel used in aircraft with spark-ignited internal combustion engines. ''Avgas'' is distinguished from conventional gasoline (petrol) used in motor vehicles, w ...
(aviation gasoline), which differ from automotive engine fuels. Gas turbine engines will run on aviation gasoline as an alternative to jet fuel as in the case of turbojet booster engines on piston-engined aircraft. Small turboprop and business aircraft may be approved for a limited running time on avgas to allow refuelling at remote airstrips with no jet fuel supply. Different fuels are used for different applications due to their performance characteristics.
Jet fuel
Kerosene jet fuel
Jet fuel or aviation turbine fuel (ATF, also abbreviated avtur) is a type of aviation fuel designed for use in aircraft powered by Gas turbine, gas-turbine engines. It is colorless to straw-colored in appearance. The most commonly used fuels for c ...
, also known as aviation turbine fuel (ATF), is designed to be used in aircraft powered by gas turbine engines
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 ...
. Jet fuel used to power gas turbine engines has been the preferred propellant
A propellant (or propellent) is a mass that is expelled or expanded in such a way as to create a thrust or other motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the e ...
since the advent of this type of engine due to the fuel's favourable combustion characteristics and relatively high energy content. Jet fuel remains the most commonly used fuel in aviation due to the popularity of turbofan and turboprop engines. Turbofan engines power most large commercial passenger and cargo aircraft today. Civil jet fuel grades include A-1
A1, A-1, A01 or A.1. may refer to:
Education
* A1, the Basic Language Certificate of the Common European Framework of Reference for Languages
* Language A1, the former name for "Language A: literature", one of the IB Group 1 subjects
* A1, a ...
, A, B, TS-1. Military grades include JP-4, JP-8 and JP-5. Military varieties differ from civil jet fuels due to the addition of corrosion inhibitors and anti-icing additives. JP-8 jet fuel is the most common fuel among NATO
The North Atlantic Treaty Organization (NATO, ; french: Organisation du traité de l'Atlantique nord, ), also called the North Atlantic Alliance, is an intergovernmental military alliance between 30 member states – 28 European and two No ...
aircraft fleets.
AVGAS
AVGAS
Avgas (aviation gasoline, also known as aviation spirit in the UK) is an aviation fuel used in aircraft with spark-ignited internal combustion engines. ''Avgas'' is distinguished from conventional gasoline (petrol) used in motor vehicles, w ...
(aviation gasoline) is widely used in reciprocating engine
A reciprocating engine, also often known as a piston engine, is typically a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common featu ...
s (piston engines
A reciprocating engine, also often known as a piston engine, is typically a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common featu ...
). Aviation gasoline is highly volatile and very flammable, with a low flash point
The flash point of a material is the "lowest liquid temperature at which, under certain standardized conditions, a liquid gives off vapours in a quantity such as to be capable of forming an ignitable vapour/air mixture". (EN 60079-10-1)
The fl ...
, which makes it unsuitable for use in gas turbine engines. Volatility is how easily a substance will change from a liquid to a gaseous state. Highly volatile fuel is required to power reciprocating engine
A reciprocating engine, also often known as a piston engine, is typically a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common featu ...
s as the liquid gasoline pumped to the carburettor
A carburetor (also spelled carburettor) is a device used by an internal combustion engine to control and mix air and fuel entering the engine. The primary method of adding fuel to the intake air is through the venturi tube in the main meterin ...
must readily vaporise in order to combust in the engine. There is however a balance of volatility needed. If AVGAS fuel is too volatile, it may cause vapour lock
Vapor lock is a problem caused by liquid fuel changing state to gas while still in the fuel delivery system of gasoline-fueled internal combustion engines. This disrupts the operation of the fuel pump, causing loss of feed pressure to the carburet ...
and early detonation in the engine cylinder. If the AVGAS is not volatile enough, there will be inconsistent engine acceleration and power throughout the revolution range. AVGAS is commonly supplemented with Tetraethyl-lead (TEL) to prevent engine knocking
In spark ignition internal combustion engines, knocking (also knock, detonation, spark knock, pinging or pinking) occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignite ...
, which is a damaging build-up of pressure inside the engine caused by low octane rated fuel which may lead to engine failure in reciprocating engines. Antiknock additives allow for greater efficiency and peak power. TEL has been banned by the European Union for automotive use due to environmental concerns, but remains approved for use in aircraft.
Rocket fuel
Rocket fuel
Rocket propellant is the reaction mass of a rocket. This reaction mass is ejected at the highest achievable velocity from a rocket engine to produce thrust. The energy required can either come from the propellants themselves, as with a chemical ...
consists of solid, liquid and gel state fuels for propulsion. In order to power rockets, a fuel and an oxidiser are mixed within the combustion chamber, producing a high energy propulsive exhaust as thrust. The main uses for rocket fuel are for space shuttle boosters in order to propel the craft out of the atmosphere, or for missile
In military terminology, a missile is a guided airborne ranged weapon capable of self-propelled flight usually by a jet engine or rocket motor. Missiles are thus also called guided missiles or guided rockets (when a previously unguided rocket i ...
s. Solid rocket propellant does not degrade in long-term storage and remains reliable on combustion. This allows munitions to remain loaded and fired when needed, which is highly regarded for military use. Once ignited, solid rocket propellants cannot be shut down. The fuel and the oxidiser are stored within a metal casing. Once ignited, the fuel burns from the centre of the solid compound towards the edges of the metal casing. Burn rates and intensity are manipulated by the changing of the shape of a channel between the fuel and the casing shell. Two varieties of solid rocket fuel propellants exist. These include homogeneous
Homogeneity and heterogeneity are concepts often used in the sciences and statistics relating to the uniformity of a substance or organism. A material or image that is homogeneous is uniform in composition or character (i.e. color, shape, siz ...
and composite
Composite or compositing may refer to:
Materials
* Composite material, a material that is made from several different substances
** Metal matrix composite, composed of metal and other parts
** Cermet, a composite of ceramic and metallic materials
...
solid rocket fuels. These fuels are characteristically dense, stable at ordinary temperatures and easily storable. Liquid fuels are more controllable than solid rocket fuels, and can be shutoff after ignition and restarted, as well as offering greater thrust control. Liquid propellants are stored in two parts in an engine, as the fuel in one tank and an oxidiser in another. These liquids are mixed in the combustion chamber and ignited. Hypergolic
A hypergolic propellant is a rocket propellant combination used in a rocket engine, whose components spontaneously ignite when they come into contact with each other.
The two propellant components usually consist of a fuel and an oxidizer. The ...
fuel is mixed and ignites spontaneously, requiring no separate ignition. Liquid fuel compounds include petroleum, hydrogen and oxygen.
Electric
Electricity may be transmitted to an aircraft's electric motors through batteries, ground power cable
A power cable is an electrical cable, an assembly of one or more electrical conductors, usually held together with an overall sheath. The assembly is used for transmission of electrical power. Power cables may be installed as permanent wiring wi ...
s, solar cell
A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. s, ultra-capacitors, fuel cell
A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requ ...
s and power beaming
Wireless power transfer (WPT), wireless power transmission, wireless energy transmission (WET), or electromagnetic power transfer is the transmission of electrical energy without wires as a physical link. In a wireless power transmission system, ...
. Electrically powered engines are currently only suitable for light aircraft and UAV's (unmanned aerial vehicle
An unmanned aerial vehicle (UAV), commonly known as a drone, is an aircraft without any human pilot, crew, or passengers on board. UAVs are a component of an unmanned aircraft system (UAS), which includes adding a ground-based controller ...
s). Electrical engines are praised for being environmentally friendly and relatively quiet. There are a multitude of personal UAV's and drones available for purchase without a licence or age restriction globally, capable of high speed manoeuvres and agile flight characteristics. Typically aircraft with electric engines have significantly shorter flight durations than conventional fuel powered aircraft although battery technology developments and solar energy conversion has created potential for use in commercial aircraft. Jeffrey Engler, CEO of Wright Electric
Wright Electric is an American startup company developing an electric airliner.
Design
The aircraft is to run on batteries and handle flights of under 300 miles.
It will feature high aspect-ratio wings for energy efficient flight, distributed el ...
, estimates that commercially viable electric planes will reduce energy costs by 30%.
Hydrogen
Hydrogen as a fuel, through the combustion of hydrogen in a jet engine or fuel cell, is a viable fuel source for aircraft engines. Currently, pressurised tanks to hold the hydrogen fuel with sufficient volume and a low enough weight are not available for large commercial aircraft, but have been successfully implemented on smaller personal aircraft such as the 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 ...
Fuel Cell
A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requ ...
Demonstrator by Boeing Phantom Works
Boeing Phantom Works is the advanced prototyping arm of the defense and security side of Boeing. Its primary focus is developing advanced military products and technologies, many of them highly classified.
Founded by McDonnell Douglas, the res ...
and on launch rockets for space shuttles when stored cryogenically
In physics, cryogenics is the production and behaviour of materials at very low temperatures.
The 13th IIR International Congress of Refrigeration (held in Washington DC in 1971) endorsed a universal definition of “cryogenics” and “cr ...
. Hydrogen can be used to power a multitude of craft, via turbine engines, piston engines and rocket engines. Hydrogen fuel cells create electrical power through hydrolysis and are in various stages of research for applications in environmentally friendly engines as they emit no toxic exhaust. Hydrogen powered engines only emit water through the bonding of oxygen and hydrogen, as well as any excess hydrogen as exhaust. This means that this is a highly environmentally friendly propulsion system.
Electro-aerodynamic thrust
Researchers from MIT
The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the mo ...
(Massachusetts Institute of Technology) have developed an ion drive propulsion system with no moving parts. The 'engine' is propelled by ionic wind
Ion wind, ionic wind, corona wind or electric wind is the airflow induced by electrostatic forces linked to corona discharge arising at the tips of some sharp conductors (such as points or blades) subjected to high voltage relative to ground. Ion ...
, also known as electro-aerodynamic thrust. This new form of aircraft propulsion would be completely silent and require far less maintenance than conventional fossil-fuel
A fossil fuel is a hydrocarbon-containing material formed naturally in the Earth's crust from the remains of dead plants and animals that is extracted and burned as a fuel. The main fossil fuels are coal, oil, and natural gas. Fossil fuels ma ...
powered engines. This technology has the potential to be used in conjunction with conventional aircraft combustion engines as a hybrid system with further development or even as propulsion systems on spacecraft.
Atmospheric conditions
Atmospheric conditions are an important consideration in the analysis of the factors contributing to differing aircraft engine performance. These factors include altitude, temperature and humidity. Aircraft engine performance decreases as altitude and temperature increase. In the case of high humidity, the volume of air available for combustion is reduced, causing losses in power in combustion engines. Aircraft engine performance is measured at baseline parameters of a standard atmosphere (29.92” of mercury) at 15 °C.
Weather may be a physical barrier to aircraft operation, as it is in the case of forecast of hail or volcanic ash, because of the risk of serious damage to all the engines installed on the aircraft.
Altitude
When altitude
Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...
is increased, air density
The density of air or atmospheric density, denoted '' ρ'', is the mass per unit volume of Earth's atmosphere. Air density, like air pressure, decreases with increasing altitude. It also changes with variation in atmospheric pressure, temperature a ...
decreases. With lower air density, air molecules are further apart from each other, which will lead to declines in performance of combustion engines. Electric-powered aircraft will not see losses of power output at high altitude, but rather aerodynamic losses as propellers work harder to propel the same amount of air as at ground level. However, cooling capacity will decline on both combustion and electric motors at high altitude due to the lower density of air. This phenomenon is why the operating limit of helicopters is constrained, as propeller thrust returns to a value of 0 when the air becomes too thin at high altitude. This makes high altitude airports significantly more dangerous than airports at sea level.
Temperature
Temperature has significant effects on the maximum power available and the operational efficiency of an aircraft engine. This applies for combustion and electrical engines. Pilots account for the ambient temperature on the day of a flight in order to calculate the takeoff distance required. Extreme heat or cold temperatures are performance limitations for aircraft engines.
An aircraft flying at a constant altitude with an ambient air temperature of 20 °C would experience more favourable performance than flying with an ambient air temperature of 40 °C. With cold temperatures, air is denser and a larger mass of air/fuel mixture is combusted, leading to higher efficiency and greater power.
Humidity
Humidity affects the mass of oxygen in each unit of volume of air in the atmosphere, reducing the burn rate and increasing the combustion time of fuel in a combustion engine which will reduce thermal efficiency. Minimal losses of power occur where the energy of the engine's combustion heat the moisture in the engine. For electrical components found within electric motors, excess moisture is capable of damaging circuits and electrical systems. In reality, air is never fully dry, or without moisture in the atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
. Even when air is considered dry, it retains a moisture content of around 5%.
Weather
Weather
Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmosphere, the ...
has significant impacts the performance of an engine, and also the propensity to cause engine malfunction or failure. Wind
Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hou ...
s are both beneficial and unfavourable depending on the direction of the wind and the heading of the aircraft. A significant weakness of many aircraft is their use of propellers or turbines in their engines. This is because any particulates that enter the engine other than air may cause damage. An example of this is hail
Hail is a form of solid precipitation. It is distinct from ice pellets (American English "sleet"), though the two are often confused. It consists of balls or irregular lumps of ice, each of which is called a hailstone. Ice pellets generally fal ...
, when precipitation freezes. If the hail is severe enough, engine inlet guide vanes or compressor blades can bend or break under impact. Volcanic ash ejected into the atmosphere due to a volcanic eruption is another example of reduced engine performance due to weather. Particles of volcanic ash are abrasive at high speed, leading to abrasion on compressor fan blades. The glass-like silicate compound found in volcanic ash has a lower melting point than the combustion temperature of fuel and air in a jet engine. When ingested into the engine, the material melts and deposits in cooler areas of the engine, leading to compressor stall and thrust loss.
See also
* Index of aviation articles
Aviation is the design, development, production, operation, and use of aircraft, especially heavier-than-air aircraft. Articles related to aviation include:
A
Aviation accidents and incidents
– ADF
– Adverse yaw
– Aerobatics
– Aerodrom ...
* Jet engine performance
The behavior of a jet engine and its effect both on the aircraft and the environment is categorized into different engineering areas or disciplines. The understanding of how a particular fuel flow produces a definite amount of thrust at a partic ...
References
{{Reflist
Engine
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 gen ...
Aircraft performance