Cruise is the phase of aircraft flight that starts when the aircraft levels off after a climb, until it begins to descend for landing. [1] Cruising usually comprises the majority of a flight, and may include small changes in heading (direction of flight), airspeed, and altitude.
Commercial or passenger aircraft are usually designed for optimum performance around their cruise speed (VC) and cruise altitude. Factors affecting optimum cruise speed and altitude include payload, center of gravity, air temperature, and humidity. Cruise altitude is usually where the higher ground speed is balanced against the decrease in engine thrust and efficiency at higher altitudes. Common narrowbodies like the Airbus A320 and Boeing 737NG cruise at Mach 0.78 (450 kn; 830 km/h), [2] [3] while modern widebodies like the Airbus A350 and Boeing 787 cruise at Mach 0.85 (490 kn; 900 km/h). [4] [5] The typical cruising altitude for commercial airliners is 31,000 to 38,000 feet (9,400 to 11,600 m ; 5.9 to 7.2 mi ). [6] [7] [ better source needed ] The speed which covers the greatest distance for a given amount of fuel is known as the maximum range speed. This is the speed at which drag is minimised.
For jet aircraft, "long-range cruise" speed (LRC) is defined as the speed which gives 99% of the maximum range, for a given weight. This results in a 3–5% increase in speed. [8] It is also a more stable speed than maximum range speed, so gives less autothrottle movement. [9] However, LRC speed does not take account of winds, or time-related costs other than fuel, so it has little practical value. [9] Instead, the speed for most economical operation (ECON) is adjusted for wind and the cost index (CI), which is the ratio of time cost to fuel cost. [8] A higher cost index results in a higher ECON speed. Cost index can be given in "Boeing" or "English" units as ($/hr)/(cents/lb), equivalent to 100 lb/hr. [10] [11] A typical cost index in these units might be anywhere from 5 to 150. [12] Alternatively cost index can be given in metric or "Airbus" units of kg/min. [10] [11]
In the presence of a tailwind, ECON airspeed can be reduced to take advantage of the tailwind, whereas in a headwind, ECON speed will be increased to avoid the penalty of the headwind. [12] In the presence of a tailwind, LRC speed may give a higher fuel burn than ECON. [9] As the aircraft consumes fuel, its weight decreases and the ECON speed decreases. This is because a heavier aircraft should fly faster to generate the required lift at the most efficient lift coefficient. ECON speed will also be higher at higher altitudes because the density of the air is lower.
For propeller aircraft, drag is minimised when the lift-to-drag ratio is maximised. However, the speed for this is typically regarded as too slow, so propeller aircraft typically cruise at a significantly faster speed. [13] Combustion engines have an optimum efficiency level for fuel consumption and power output. [14] [ better source needed ] Generally, gasoline piston engines are most efficient between idle speed and 30% short of full throttle. Diesels are most efficient at around 90% of full throttle. [15] [ better source needed ]
As the aircraft consumes fuel, its weight decreases and the optimum altitude for fuel economy increases. For traffic control reasons it is usually necessary for an aircraft to stay at a cleared flight level. On long-haul flights, the pilot may ask air traffic control to climb from one flight level to a higher one, in a manoeuvre known as a step climb.
The Airbus A320 family is a series of narrow-body airliners developed and produced by Airbus. The A320 was launched in March 1984, first flew on 22 February 1987, and was introduced in April 1988 by Air France. The first member of the family was followed by the stretched A321, the shorter A319, and the even shorter A318 . Final assembly takes place in Toulouse in France; Hamburg in Germany; Tianjin in China since 2009; and Mobile, Alabama in the United States since April 2016.
The Airbus A340 is a long-range, wide-body passenger airliner that was developed and produced by Airbus. In the mid-1970s, Airbus conceived several derivatives of the A300, its first airliner, and developed the A340 quadjet in parallel with the A330 twinjet. In June 1987, Airbus launched both designs with their first orders and the A340-300 took its maiden flight on 25 October 1991. It was certified along with the A340-200 on 22 December 1992 and both versions entered service in March 1993 with launch customers Lufthansa and Air France. The larger A340-500/600 were launched on 8 December 1997; the A340-600 flew for the first time on 23 April 2001 and entered service on 1 August 2002.
A supersonic transport (SST) or a supersonic airliner is a civilian supersonic aircraft designed to transport passengers at speeds greater than the speed of sound. To date, the only SSTs to see regular service have been Concorde and the Tupolev Tu-144. The last passenger flight of the Tu-144 was in June 1978 and it was last flown in 1999 by NASA. Concorde's last commercial flight was in October 2003, with a November 26, 2003 ferry flight being its last airborne operation. Following the permanent cessation of flying by Concorde, there are no remaining SSTs in commercial service. Several companies have each proposed a supersonic business jet, which may bring supersonic transport back again.
In aerodynamics, the lift-to-drag ratio is the lift generated by an aerodynamic body such as an aerofoil or aircraft, divided by the aerodynamic drag caused by moving through air. It describes the aerodynamic efficiency under given flight conditions. The L/D ratio for any given body will vary according to these flight conditions.
Lift-induced drag, induced drag, vortex drag, or sometimes drag due to lift, in aerodynamics, is an aerodynamic drag force that occurs whenever a moving object redirects the airflow coming at it. This drag force occurs in airplanes due to wings or a lifting body redirecting air to cause lift and also in cars with airfoil wings that redirect air to cause a downforce. It is symbolized as , and the lift-induced drag coefficient as .
Wingtip devices are intended to improve the efficiency of fixed-wing aircraft by reducing drag. Although there are several types of wing tip devices which function in different manners, their intended effect is always to reduce an aircraft's drag. Wingtip devices can also improve aircraft handling characteristics and enhance safety for following aircraft. Such devices increase the effective aspect ratio of a wing without greatly increasing the wingspan. Extending the span would lower lift-induced drag, but would increase parasitic drag and would require boosting the strength and weight of the wing. At some point, there is no net benefit from further increased span. There may also be operational considerations that limit the allowable wingspan.
The Airbus A350 is a long-range, wide-body twin-engine airliner developed and produced by Airbus. The initial A350 design proposed by Airbus in 2004, in response to the Boeing 787 Dreamliner, would have been a development of the Airbus A330 with composite wings and new engines. Due to inadequate market support, Airbus switched in 2006 to a clean-sheet "XWB" design, powered by two Rolls-Royce Trent XWB high bypass turbofan engines. The prototype first flew on 14 June 2013 from Toulouse, France. Type certification from the European Aviation Safety Agency (EASA) was obtained in September 2014, followed by certification from the Federal Aviation Administration (FAA) two months later.
A deadstick landing, also called a dead-stick landing, is a type of forced landing when an aircraft loses all of its propulsive power and is forced to land. The "stick" does not refer to the flight controls, which in most aircraft are either fully or partially functional without engine power, but to the traditional wooden propeller, which without power would just be a "dead stick". When a pilot makes an emergency landing of an aircraft that has some or all of its propulsive power still available, the procedure is known as a precautionary landing.
A flight management system (FMS) is a fundamental component of a modern airliner's avionics. An FMS is a specialized computer system that automates a wide variety of in-flight tasks, reducing the workload on the flight crew to the point that modern civilian aircraft no longer carry flight engineers or navigators. A primary function is in-flight management of the flight plan. Using various sensors (such as GPS and INS often backed up by radio navigation) to determine the aircraft's position, the FMS can guide the aircraft along the flight plan. From the cockpit, the FMS is normally controlled through a Control Display Unit (CDU) which incorporates a small screen and keyboard or touchscreen. The FMS sends the flight plan for display to the Electronic Flight Instrument System (EFIS), Navigation Display (ND), or Multifunction Display (MFD). The FMS can be summarised as being a dual system consisting of the Flight Management Computer (FMC), CDU and a cross talk bus.
A trijet is a jet aircraft powered by three jet engines. In general, passenger airline trijets are considered to be second-generation jet airliners, due to their innovative engine locations, in addition to the advancement of turbofan technology. Trijets are more efficient than quadjets, but not as efficient as twinjets, which replaced trijets as larger and more reliable turbofan engines became available.
A twinjet or twin-engine jet is a jet aircraft powered by two engines. A twinjet is able to fly well enough to land with a single working engine, making it safer than a single-engine aircraft in the event of failure of an engine. Fuel efficiency of a twinjet is better than that of aircraft with more engines. These considerations have led to the widespread use of aircraft of all types with twin engines, including airliners, fixed-wing military aircraft, and others.
In aerospace engineering, an aircraft's fuel fraction, fuel weight fraction, or a spacecraft's propellant fraction, is the weight of the fuel or propellant divided by the gross take-off weight of the craft :
Gliding flight is heavier-than-air flight without the use of thrust; the term volplaning also refers to this mode of flight in animals. It is employed by gliding animals and by aircraft such as gliders. This mode of flight involves flying a significant distance horizontally compared to its descent and therefore can be distinguished from a mostly straight downward descent like a round parachute.
Formation flying is the flight of multiple objects in coordination. Formation flying occurs in nature among flying and gliding animals, and is also conducted in human aviation, often in military aviation and air shows.
Airbus Corporate Jets (ACJ) is a business unit of Airbus which markets and completes business jet variants of the company’s airliners. Following the entry of the 737-based Boeing Business Jet into the market, Airbus introduced the A319-based Airbus Corporate Jet in 1997. Although the term Airbus Corporate Jet was initially used only for the A319CJ, it is now used for all models in a VIP configuration. As of June 2019, 213 corporate and private jets are operating; 222 aircraft have been ordered, including 128 A320 family jets.
A flight control mode or flight control law is a computer software algorithm that transforms the movement of the yoke or joystick, made by an aircraft pilot, into movements of the aircraft control surfaces. The control surface movements depend on which of several modes the flight computer is in. In aircraft in which the flight control system is fly-by-wire, the movements the pilot makes to the yoke or joystick in the cockpit, to control the flight, are converted to electronic signals, which are transmitted to the flight control computers that determine how to move each control surface to provide the aircraft movement the pilot ordered.
A glider or sailplane is a type of glider aircraft used in the leisure activity and sport of gliding. This unpowered aircraft can use naturally occurring currents of rising air in the atmosphere to gain altitude. Sailplanes are aerodynamically streamlined and so can fly a significant distance forward for a small decrease in altitude.
The drag curve or drag polar is the relationship between the drag on an aircraft and other variables, such as lift, the coefficient of lift, angle-of-attack or speed. It may be described by an equation or displayed as a graph. Drag may be expressed as actual drag or the coefficient of drag.
The fuel economy in aircraft is the measure of the transport energy efficiency of aircraft. Fuel efficiency is increased with better aerodynamics and by reducing weight, and with improved engine brake-specific fuel consumption and propulsive efficiency or thrust-specific fuel consumption. Endurance and range can be maximized with the optimum airspeed, and economy is better at optimum altitudes, usually higher. An airline efficiency depends on its fleet fuel burn, seating density, air cargo and passenger load factor, while operational procedures like maintenance and routing can save fuel.
The Airbus A330neo is a wide-body airliner developed by Airbus from the original Airbus A330. A new version with modern engines comparable with those developed for the Boeing 787 was called for by operators of the A330ceo. It was launched on 14 July 2014 at the Farnborough Airshow, promising 14% better fuel economy per seat. It is exclusively powered by the Rolls-Royce Trent 7000 which has double the bypass ratio of its predecessor.
At the normal stratospheric cruising altitudes of 30,000–38,000 ft
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