Takeoff
Takeoffis the phase offlightin which anaerospacevehicle leaves the ground and becomes airborne. For aircraft traveling vertically, this is known asliftoff.
Foraircraftthat take off horizontally, this usually involves starting with a transition from moving along the ground on arunway.Forballoons,helicoptersand some specialized fixed-wing aircraft (VTOLaircraft such as theHarrierand theBell Boeing V22 Osprey), no runway is needed.
Horizontal[edit]
Power settings[edit]
Forlight aircraft,usually full power is used during takeoff. Largetransport category(airliner) aircraft may use areduced powerfor takeoff, where less than full power is applied in order to prolong engine life, reduce maintenance costs and reduce noise emissions. In some emergency cases, the power used can then be increased to increase the aircraft's performance. Before takeoff, the engines, particularlypiston engines,are routinely run up at high power to check for engine-related problems. The aircraft is permitted to accelerate to rotation speed (often referred to as Vr). The termrotationis used because the aircraft pivots around the axis of its mainlanding gearwhile still on the ground, usually because of gentle manipulation of theflight controlsto make or facilitate this change inaircraft attitude(once proper air displacement occurs under / over the wings, an aircraft will lift off on its own; controls are to ease that in).
The nose is raised to a nominal 5°–15° nose uppitchattitude to increase lift from thewingsand effect liftoff. For most aircraft, attempting a takeoff without a pitch-up would require cruise speeds while still on the runway.
Fixed-wing aircraft designed for high-speed operation (such as commercialjet aircraft) have difficulty generating enough lift at the low speeds encountered during takeoff. These are therefore fitted withhigh-lift devices,often includingslatsand usuallyflaps,which increase thecamberand often area of the wing, making it more effective at low speed, thus creating more lift. These are deployed from the wing before takeoff, and retracted during the climb. They can also be deployed at other times, such as before landing.
Required speeds[edit]
Thetakeoff speed requiredvaries with aircraft weight and aircraft configuration (flap or slat position, as applicable), and is provided to the flight crew asindicated airspeed.
Operations with transport category aircraft employ the concept of the takeoffV-speeds:V1,VRand V2.These speeds are determined not only by the above factors affecting takeoff performance, but also by the length and slope of the runway and any peculiar conditions, such as obstacles off the end of the runway. Below V1,in case of critical failures, the takeoff should be aborted; above V1the pilot continues the takeoff and returns for landing. After the co-pilot calls V1,they will call VRor "rotate," marking speed at which to rotate the aircraft. The VRfor transport category aircraft is calculated such as to allow the aircraft to reach the regulatory screen height at V2with one engine failed. Then, V2(the safe takeoff speed) is called. This speed must be maintained after an engine failure to meet performance targets for rate of climb and angle of climb.
In a single-engine or light twin-engine aircraft, the pilot calculates the length of runway required to take off and clear any obstacles, to ensure sufficient runway to use for takeoff. A safety margin can be added to provide the option to stop on the runway in case of arejected takeoff.In most such aircraft, any engine failure results in a rejected takeoff as a matter of course, since even overrunning the end of the runway is preferable to lifting off with insufficient power to maintain flight.
If an obstacle needs to be cleared, the pilot climbs at the speed for maximum climb angle (Vx), which results in the greatest altitude gain per unit of horizontal distance travelled. If no obstacle needs to be cleared, or after an obstacle is cleared, the pilot can accelerate to the best rate of climb speed (Vy), where the aircraft will gain the most altitude in the least amount of time. Generally speaking, Vxis a lower speed than Vy,and requires a higher pitch attitude to achieve.
The speeds needed for takeoff are relative to the motion of the air (indicated airspeed). Aheadwindwill reduce the ground speed needed for takeoff, as there is a greater flow of air over the wings. Typical takeoff air speeds for jetliners are in the range of 240–285km/h(130–154kn;149–177mph). Light aircraft, such as aCessna 150,take off at around 100km/h(54kn;62mph).Ultralightshave even lower takeoff speeds. For a given aircraft, the takeoff speed is usually dependent on the aircraft weight; the heavier the weight, the greater the speed needed.[1]Some aircraft are specifically designed forshort takeoff and landing (STOL),which they achieve by becoming airborne at very low speeds.
Assistance[edit]
Assisted takeoffis any system for helpingaircraftinto the air (as opposed to strictly under its own power). The reason it might be needed is due to the aircraft's weight exceeding the normalmaximum takeoff weight,insufficient power, or the availablerunwaylength may be insufficient, or ahot and highairfield, or a combination of all four factors. Assisted takeoff is also required forgliders,which do not have an engine and so are unable to take off by themselves. Hence assisted takeoff is required.
Vertical[edit]
Vertical takeoff refers to aircraft or rockets that take off in a verticaltrajectory.Vertical takeoff eliminates the need for airfields. Most vertical take off aircraft are also able to land horizontally, but there were certainrocket-powered aircraftof theLuftwaffethat only took off vertically, landing in other ways. TheBachem Ba 349Natterlanded under a parachute after having taken off vertically. Other late projects developed inNazi Germany,such as theHeinkel P.1077Juliaor theFocke-WulfVolksjäger2,climbed to their ceiling at a nearly vertical angle and landed later on a skid.[2]
VTOL[edit]
Vertical take-off and landing(VTOL)aircraftincludefixed-wing aircraftthat can hover,take off and landvertically as well ashelicoptersand other aircraft with powered rotors, such astiltrotors.[3][4][5][6]Some VTOL aircraft can operate in other modes as well, such asCTOL(conventional take-off and landing),STOL(short take-off and landing), and/orSTOVL(short take-off and vertical landing). Others, such as some helicopters, can only operate by VTOL, due to the aircraft lackinglanding gearthat can handle horizontal motion. VTOL is a subset ofV/STOL(vertical and/or short take-off and landing).
Besides the helicopter, there are two types of VTOL aircraft in military service: craft using atiltrotor,such as theBellBoeingV-22 Osprey,and some aircraft using directed jet thrust such as theHarrier family.
Rocket launch[edit]
The takeoff phase of the flight of arocketis called "rocket launch". Launches fororbital spaceflights,or launches intointerplanetary space,are usually from a fixed location on the ground, but may also be from a floating platform such as theSan Marco platform,or theSea Launchlaunch vessel.
See also[edit]
- Index of aviation articles
- Balanced field takeoff
- Climb (aeronautics)
- Cruise (aeronautics)
- Descent (aeronautics)
- Landing
- V speeds
References[edit]
- ^Scott, Jeff (4 August 2002) "Airliner Takeoff Speeds".Aerospace Web. Retrieved 12 August 2015
- ^Ulrich Albrecht: Artefakte des Fanatismus; Technik und nationalsozialistische Ideologie in der Endphase des Dritten ReichesArchived2020-04-13 at theWayback Machine(in German)
- ^"Vertical Takeoff & Landing Aircraft," John P. Campbell, The MacMillan Company, New York, 1962.
- ^Rogers 1989.
- ^Laskowitz, I.B. "Vertical Take-Off and Landing (VTOL) Aircraft."Annals of the New York Academy of Sciences,Vol. 107, Art. 1, 25 March 1963.
- ^"Straight Up - A History of Vertical Flight," Steve Markman and Bill Holder, Schiffer Publishing, 2000.