Aircraft engine in the context of "Turbofan"

An aerostat (from Ancient Greek ἀήρ (aḗr) 'air' and στατός (statós) 'standing', via French) or lighter-than-air aircraft is an aircraft that relies on buoyancy to maintain flight. Aerostats include unpowered balloons (free-flying or tethered) and powered airships.

The relative density of an aerostat as a whole is lower than that of the surrounding atmospheric air (hence the name "lighter-than-air"). Its main component is one or more gas capsules made of lightweight skins, containing a lifting gas (hot air, or any gas with lower density than air, typically hydrogen or helium) that displaces a large volume of air to generate enough buoyancy to overcome its own weight. Payload (passengers and cargo) can then be carried on attached components such as a basket, a gondola, a cabin or various hardpoints. With airships, which need to be able to fly against wind, the lifting gas capsules are often protected by a more rigid outer envelope or an airframe, with other gasbags such as ballonets to help modulate buoyancy.

Aircraft engines produce gases, noise, and particulates from fossil fuel combustion, raising environmental concerns over both global impacts and their effects on local air quality.Jet airliners contribute to climate change by emitting carbon dioxide (CO₂), the best understood greenhouse gas, and, with less scientific understanding, nitrogen oxides, contrails and particulates.Their radiative forcing is estimated at 1.3–1.4 that of CO₂ alone, excluding induced cirrus cloud which remains poorly understood scientifically.In 2018, global commercial operations generated 2.4% of all CO₂ emissions.

Jet airliners became about 70% more fuel efficient between 1967 and 2007, and CO₂ emissions per revenue ton-kilometer (RTK) in 2018 were 47% of those in 1990. In 2018, CO₂ emissions averaged 88 grams of CO₂ per revenue passenger per km.While the aviation industry is more fuel efficient, overall emissions have risen as the volume of air travel has increased. By 2020, aviation emissions were 70% higher than in 2005 and they could grow by 300% by 2050.

An aircraft catapult is an acceleration device used to help fixed-wing aircraft reach liftoff speed (V_LOF) faster during takeoff, typically when trying to take off from a very short runway, as otherwise the aircraft engines alone cannot get the aircraft to sufficient airspeed quickly enough for the wings to generate the lift needed to sustain flight. Launching via catapults enables aircraft that typically are only capable of conventional takeoffs, especially heavier aircraft with significant payloads, to perform short takeoffs from the roll distances of light aircraft. Catapults are usually used on the deck of a ship — such as the flight deck of an aircraft carrier — as a form of assisted takeoff for navalised aircraft, but can also be installed on land-based runways, although this is rare.

Historically it was most common for seaplanes (which have pontoons instead of wheeled landing gears and thus cannot utilize runways) to be catapulted from ships onto nearby water for takeoff, allowing them to conduct aerial reconnaissance missions and be crane-hoisted back on board during retrieval, although by the late First World War their roles are largely supplanted by the more versatile biplanes that can take off and land on carrier decks unassisted. During the Second World War before the advent of escort carriers, monoplane fighter aircraft (notably the Hawker Hurricane) would sometimes be catapulted from "catapult-equipped merchant" (CAM) vessels for one-way sorties to repel enemy aircraft harassing shipping lanes, forcing the returning pilot to either divert to a land-based airstrip, jump out by parachute, or ditch in the water near the convoy and wait for rescue. By the time fleet carriers became the norm in WW2, catapult launches have become largely unnecessary and carrier-based fighter-bombers would routinely perform self-powered takeoffs and landings off and onto carrier decks, especially during the naval aviation-dominated Pacific War between the United States and the Empire of Japan. However, escalating arms races during the Cold War accelerated the adoption of the heavier jet aircraft for naval operations, thus motivating the development of new catapult systems, especially after the popularization of angled flight decks further limited the practical distance available as takeoff runways. Nowadays, jet aircraft can launch from aircraft carriers via either catapults or ski-jump deck, and perform optics-assisted landing onto the same ship with help from decelerative arresting gears.

A fixed-wing aircraft is a heavier-than-air aircraft, such as an airplane, which is capable of flight using aerodynamic lift. Fixed-wing aircraft are distinct from rotary-wing aircraft (in which a rotor mounted on a spinning shaft generates lift), and ornithopters (in which the wings oscillate to generate lift). The wings of a fixed-wing aircraft are not necessarily rigid; kites, hang gliders, variable-sweep wing aircraft, and airplanes that use wing morphing are all classified as fixed wing.

Gliding fixed-wing aircraft, including free-flying gliders and tethered kites, can use moving air to gain altitude. Powered fixed-wing aircraft (airplanes) that gain forward thrust from an engine include powered paragliders, powered hang gliders and ground effect vehicles. Most fixed-wing aircraft are operated by a pilot, but some are unmanned or controlled remotely or are completely autonomous (no remote pilot).

In response to concerns that volcanic ash ejected during the 2010 eruptions of Eyjafjallajökull in Iceland would damage aircraft engines, the controlled airspace of many European countries was closed to instrument flight rules traffic, resulting in what at the time was the largest air-traffic shut-down since World War II. The closures caused millions of passengers to be stranded not only in Europe, but across the world. With large parts of European airspace closed to air traffic, many more countries were affected as flights to, from, and over Europe were cancelled.

An eruption on 14 April led to an initial uninterrupted shutdown over much of northern Europe from 15 to 23 April. Afterwards, airspace was closed intermittently in different parts of Europe in the following weeks, as the path of the ash cloud was tracked. The ash cloud caused further disruptions to air travel operations in Scotland and Ireland on 4 and 5 May and in Spain, Portugal, northern Italy, Austria, and southern Germany on 9 May. Irish and UK airspace closed again on 16 May and reopened on 17 May.

In aviation, hot and high is a condition of low air density due to high ambient temperature and high airport elevation. Air density decreases with increasing temperature and altitude. The lower air density reduces the power output from an aircraft's engine and also requires a higher true airspeed before the aircraft can become airborne. Aviators gauge air density by calculating the density altitude.

An airport may be especially hot or high, without the other condition being present. Temperature and pressure altitude can change from one hour to the next. The fact that temperature generally decreases as altitude increases mitigates the "hot and high" effect to a small extent.

Noise is sound, chiefly unwanted, unintentional, or harmful sound considered unpleasant, loud, or disruptive to mental or hearing faculties. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference arises when the brain receives and perceives a sound. Acoustic noise is any sound in the acoustic domain, either deliberate (e.g., music or speech) or unintended.

Noise may also refer to a random or unintended component of an electronic signal, whose effects may not be audible to the human ear and may require instruments for detection. It can also refer to an intentionally produced random signal or spectral noise, such as white noise or pink noise.

Rolls-Royce Holdings plc is a British multinational aerospace and defence company incorporated in February 2011. The company owns Rolls-Royce, a business established in 1904 which today designs, manufactures and distributes power systems for aviation and other industries. Rolls-Royce is the world's second-largest maker of aircraft engines (after CFM International) and has major businesses in the marine propulsion and energy sectors.

Rolls-Royce was the world's 16th largest defence contractor in 2018 when measured by defence revenues. The company is also the world's fourth largest commercial aircraft engine manufacturer, with a 12% market share as of 2020.