Takeoff (aviation)
.jpg)
The start or departure ( English takeoff or takeoff ) is in the aviation the lifting of the aircraft from an airfield or other starting point - such as a helicopter launch site , a water , an aircraft carrier or a ramp . When it takes off, the flying object begins to fly ( aircraft , rotary wing aircraft , hang-glider, etc.) or float ( airships , hot air balloons , gas balloons, etc.), depending on the type of construction or use . The take-off, not the entire take-off process, is an introductory flight maneuver for the climb .
When lifting off, the object has to overcome the weight . Therefore, the buoyancy force must be stronger than the weight force. The type of launch is different depending on the type and payload. Most fixed-wing aircraft accelerate horizontally until they have reached their take-off speed. Exceptions are vertical take-offs and hybrid forms between rotary wing aircraft and aircraft such as helicopters or convertible aircraft . Helicopters and other rotary wing aircraft generate the force to overcome the weight force with the help of rotating rotor blades and therefore do not have to move horizontally when taking off. Missiles ignite liquid or solid fuels to generate recoil force to move.
Airplanes and helicopters are referred to as taking off , while balloons and airships are referred to as ascent . Also in space z. B. at a missile from a missile launch spoken.
Start preparation
In order to ensure a successful start, extensive preparations are made in advance. While in general aviation the pilot is usually left to his own devices to cope with these tasks, in commercial aviation several organizational departments are deployed.
The aviation weather service provides information on the weather at the point of departure, route weather and weather forecast for the destination and alternate airports via personal advice, telex transmissions, the Internet and the Automatic Terminal Information Service (ATIS). The aviation weather service also provides information about possible icing conditions. Icing conditions on the ground pose a risk to take-off because ice on the wings significantly worsens aerodynamics and increases the take-off weight of the aircraft.
The de-icing service can clear the surfaces of the aircraft from snow and ice. Deicing agent is a mixture of water, alcohol ( glycol ) and additives. The surfaces can then be coated with a gel-like, alcoholic liquid that prevents the new build-up of ice or snow for a certain period of time. The time that is available at least from the beginning of the surface treatment to the start is called hold over time (HOT). It is specified in tables and depends on the quality and concentration of the de-icing fluid, the outside temperature and the type of precipitation . The pilots must take care not to exceed the HOT. In the event of an unforeseen delay before starting, the defrosting process must be repeated.
Air traffic control centers ( ATC ) accept flight plans by telephone, in writing or by telex or via the Internet and issue departure restrictions, so-called slots , if the traffic density requires it. Flight planning offices use an estimated take-off weight to calculate the cheapest flight route and altitude and the resulting fuel requirement.
All information relevant to the implementation of the flight about the operational readiness of airfield facilities , flight navigation aids and other daily changing conditions such as construction work in the area of airports are passed on via the ATC in the form of Notices To Air Men ( NOTAM ). The pilots are responsible for taking note of the information published in the NOTAM.
The technical status is usually documented in a logbook that remains on the aircraft , also called TechLog (short for technical logbook ). If there are no entries, the pilot can assume that all technical systems of the aircraft are working properly. If there are entries by pilots or maintenance staff, it is up to the pilot to confirm the operational clarity of the aircraft with his signature. In order to make this decision possible, the aircraft manufacturers publish a list that lists the minimum technical requirements for the respective aircraft. This list is called the Minimum Equipment List (MEL) and must be recognized by the aviation authority of the operating state.
If a pilot or an aircraft attendant finds a system to be faulty, he enters this fault in the TechLog. If the MEL allows the aircraft to operate despite the error, the flight can be carried out. The MEL is only relevant before the start. Errors that occur after the start are processed according to checklists whenever possible. The problem-solving competence in flight lies entirely with the pilot, he can also make decisions without the consent of the ATC. He may also be personally liable for criminal or economic consequences.
The pilot must carry out a pre-flight check before each flight and, in addition to the information in the TechLog, convince himself of the airworthiness of the aircraft. In general aviation, the aircraft manual determines the areas to be checked; in commercial aviation, binding checklists are used for this.
If they relate to the engine start and movement of an aircraft, take-off procedures are communicated closely with air traffic control and airfield supervision . There are various air traffic control contacts at controlled airfields . As a rule, the (co) pilot first contacts the office that activates the flight plan and issues route clearance ( clearance delivery ), then the (co) pilot asks for taxi clearance at the ground control point ( ground ) from which the ( Ko) pilot is passed on to the de-icing service if necessary. The last point of contact on the ground is the Tower ( tower ), the start release granted.
technology
Ordinary aircraft need a runway on which they can accelerate until take-off ( CTOL - Conventional Take-Off and Landing) or on which they can brake when landing after touchdown. Some aircraft have a particularly robust landing gear ; this enables them to take off and land on natural slopes.
VTOL aircraft , helicopters , balloons , rockets and airships use a take-off and landing site ; you can take off and 'land out' almost anywhere .
Planes
_Flight_Deck.JPG)
Ordinary aircraft take off from a runway and need a minimum speed relative to the surrounding air to take off. This is between 250 and 345 km / h for commercial aircraft , light aircraft need about 80 to 150 km / h, paragliders about 20 km / h, hang gliders 20 to 25 km / h. Aircraft roll on nitrogen-filled aircraft tires . The wheels only run or roll freely, i.e. That is, they are not driven as in a motor vehicle, but can usually be braked by means of the wheel brakes. Paragliders and hang gliders have to be accelerated to the required speed within walking distance during the usual run start .
Motorized aircraft take off from the horizontal by accelerating sharply using propeller or engine thrust. The take-off run must be straight. Headwind is ideal and side winds or tail winds are unfavorable. Tail wind limits lift ability, cross wind limits control ability. Gliders are accelerated by outside help ( winches , rubber rope take-offs or powered aircraft ). In seaplanes , skid-like floats are used instead of the wheeled landing gear , which glide with little resistance during the take-off run in order to achieve the necessary take-off speed.
Many aircraft make full use of their engine power during take-off. If there is a predictable excess power, the engine power of commercial aircraft can be reduced to a maximum of 25% under full load in order to reduce the temperature of the engines and thus extend their service life. An increase in the angle of attack leads to an increase in aerodynamic lift on the wings, which means that, from a certain speed, the weight force is overcome and lift-off is possible. Here rotates the aircraft about its transverse axis , which by the change elevator is effected. The aircraft then takes off and climbs up to the planned altitude , where the climb ends and changes to cruise flight. Since during startup speed is still relatively low, one is to improve the buoyancy and to avoid stalling the wing flaps extended somewhat. After take-off, the course is changed very often , as the runways rarely correspond to the direction in which the aircraft is to be steered.
The process of accelerating to rotating is called the take- off run , it represents the first phase of take-off. Before rotating, it is possible to abort the take-off without getting past the end of the runway.
In order to enable the pilots of aircraft to decide whether to interrupt or continue a take-off if a problem occurs, a decision speed is calculated. Once the aircraft has reached this speed while accelerating, the remaining runway is no longer long enough to abort take-off. The calculation takes into account all factors that influence the take-off taxi route. In addition, the pilots are allowed a reaction time of one second. is therefore a speed up to which the decision for or against a possible aborted start should be made; It is possible to stop afterwards, but it will inevitably lead to the terrain.
Shortly after take-off, the landing gear is retracted if possible to reduce air resistance . However, there are also types of aircraft whose landing gear cannot be retracted. There are numerous safety precautions during take-off and landing; Examples: The occupants must be belted (protection in the event of an impact), the tables in front of the passengers' seats must be folded up, electrical and electronic devices of the passengers must be switched off ( interference ) and smoking is to be stopped for fire safety reasons - generally prohibited in aircraft in Germany (Reduction of ignition sources).
On many (not all) aircraft carriers , aircraft taking off are accelerated with an aircraft catapult in addition to their own engine . This enables particularly short runways, see take-off operation on an aircraft carrier .
Whiz kid
The aircraft of the type VTOL (Vertical Take-Off and Landing) take off vertically, the rare tilt-wing aircraft can take off in both horizontal and hover flight, which gives them capabilities similar to a helicopter.
Helicopter and gyroplane
The helicopter start either from helicopter take off areas or the terrain, more rarely, of waters from. The helicopter takes off when - after the main rotor or rotors have been accelerated to the required minimum speed by the engines - the blade angle of attack of the main rotor blades is collectively increased by pulling the pitch lever and the resulting lift becomes greater than the mass of the helicopter. Usually such a start takes place without relative speed to the ground. Helicopters with wheeled undercarriages can also take off from a take-off run on a runway, similar to a fixed-wing aircraft; this results in advantages with regard to the possible payload.
Gyroplane (Gyrokopter) start from the horizontal with a starting run. In order to achieve the required initial speed of the free-running rotor, either rolling maneuvers against the wind or the use of a prerotation device directly before the take-off run are necessary, which ensure a minimum speed by means of an electric or hydraulic motor or a mechanical shaft driven by the drive motor before the rotor is passively accelerated further to flight speed by the flow of the airstream during the take-off run.
Airships
Airships start from the anchor mast . They rise because their gas for buoyancy has a lower density than the surrounding air .
Balloons
To start, balloons only need a space that is sufficient to fill the balloon envelope. In hot air balloons, the air in the balloon is heated to such an extent that the buoyancy of the air more than offsets the weight of the balloon and gondola.
Person- carrying gas balloons start by being emptied. This means that ballast is thrown off. When there is a strong wind on the ground, four helpers sit on the edge of the basket and, on command, jump off at the same time. This makes the balloon suddenly easier, which prevents dangerous dragging on the launch area.
Missiles
Missiles require a rocket launch site on land or, rarely, on a submarine or missile ship . However, the launch of missiles in the military field is very common from combat aircraft (in flight). These missiles are mounted under the wings or under the fuselage. Due to the outsourcing of the rocket launch site, the object is guided upwards or shot at an angle to the sky until it flies by itself; this is called a rocket launch .
Military surface-to-air missiles can also be launched from trucks. Very small missiles such as the rocket launcher MILAN or projectiles from rocket-propelled grenades can also from the shoulder of a soldier or from a mobile tripod fired from. The majority of the rockets are launched from a launch pad . A countdown to take off is common here.
Hang glider
When taking off from a slope, the hang-glider pilot must achieve the necessary speed for a safe take-off. The slope on the slope helps him. In order to facilitate the take-off run on uneven terrain, launch ramps have been set up in many airfields.
Paragliders
In contrast to other aircraft, the paraglider only gets its shape from the airflow. It is laid out on a meadow by the paraglider pilot and then let fly like a kite . The umbrella fills with air and takes on the shape of a curved wing. Then the glider stands steeply above the pilot. If there is enough wind, the pilot can hold the glider in this position for a long time and control it with the brake lines. For the actual start, the pilot releases the brake lines and walks down the slope. After a few steps, it is lifted off the floor. For the start you need a steep slope with enough treeless area on which the paraglider can be laid out. Paragliders can also be launched with a winch .
support
Autopilots are not permitted in civil aviation for handling the entire take-off process. However, there are various automated systems (for commercial aircraft, for example, automatic engine control in take-off / go-around mode TOGA ), as well as air traffic controllers who support the pilot with information at take-off .
Process in the cockpit
This section describes the take-off of a conventional jet aircraft from the perspective of the pilot .
Before take-off, calculations are made to obtain the maximum take-off weight. This weight, in technical terms maximum take-off weight (MTOW), depends on the engine performance, environmental influences such as wind, temperature, air pressure, and the nature and length of the runway. After loading has been completed, the actual take-off weight, in technical terms Actual Take Off Weight , is used to calculate the speeds V 1 , V r and V 2 and, if permitted, to reduce the take-off thrust.
The aircraft is still on the ground in a parking position that it can either leave on its own or with the help of an aircraft tractor . It then reaches a position in front of the runway via the taxiway system . On the way to the runway, a checklist is worked through , with various checks (brakes, rudder) being carried out depending on the type of aircraft and the starting flaps being extended to the pre-calculated position. Any existing automatic braking system is also set in such a way that it automatically initiates the braking process in the event of an abrupt engine power reduction by the pilot ( rejected take-off ). After the pilots have received the clearance, they roll onto the runway ( line up ) and align the aircraft with the center of the runway. In addition, the landing lights are switched on regardless of the time of day .
The actual start-up process now begins; After the take-off clearance has been received, the engine power is initially increased to approx. 50% by means of the thrust lever and, after a brief check whether the engines are running properly, it is increased to the maximum or a calculated reduced take-off power. Now the aircraft accelerates along the center of the runway. At a speed of 80 knots, this is declared by the pilot not flying , the non-flying pilot. This is to check that both airspeed indicators are working properly. The next call is made at speed V 1 . If it is exceeded, the start must not be aborted even if one engine fails (a machine with two or more engines). However, the phone does not take off immediately; only after the speed V R has been reached does the “ Rotate! ". Now the nose is raised slightly and the aircraft takes off. After reaching a positive rate of climb , the landing gear is retracted; at V 2 a safe climb can be continued. From a fixed height, which is usually between 300 and 1500 meters, the speed is usually increased in order to be able to retract the take-off flaps without losing lift. Now a checklist is processed again, after the completion of which, from the point of view of the cockpit crew, the start is complete.
Risks
When taking off, an aircraft achieves a high speed at a point in time when it is just barely airworthy but has already covered a large part of the paved runway. At this moment, and also at the moment of take-off, disturbances of a technical or human nature are particularly serious. The time window that is available to identify and correct an error is very short.
In addition to objects (e.g. crossing or approaching objects in flight , see collision course or animals, especially birds, see bird strikes ), strong winds or gusts of wind are a particular risk at take-off. Furthermore, large amounts of ice and remaining snow on the runway or on the wings / wings of the aircraft, as well as deficiencies in the condition of the runway (unevenness, bush ), can make aircraft take off considerably more difficult.
Strong cross winds are a challenge during take-off and landing . The fuselage and vertical stabilizer offer a large target area for crosswinds. Cross winds disturb the laminar flow and can cause turbulence (eddies / cross flows) on aircraft parts.
If the pilot pulls his aircraft up too abruptly during take-off, the tail may hit the ground (tail strike ). Some aircraft have a wheel ( tailbumper ) to avoid it .
Other wind problems are tail wind and downbursts . If there is not enough distance to the aircraft that has recently taken off, there are risks from wake vortices . If the angle of attack is too large , the flow may stall (stall).
In the event of critical parameters , incidents or on collision courses , the pilot can “orderly” abort the start (false start) up to a certain speed ( ). It throttles the drive force to zero, activates the wheel brakes on the landing gear and operates the airbrakes on the wings. In addition, the thrust reverser is activated in aircraft that are equipped with it, but this is only effective in the high speed range. In the case of very serious problems, for example failure of parts of the flight control after reaching , the pilot must very quickly weigh up whether continuing the take-off, possibly with a subsequent emergency landing, or aborting the take-off, which leads to terrain, represents the lower risk.
With a tailwind, the aircraft must have a speed greater than the speed of the wind when taking off compared to the ground. This extends the taxiing distance and the braking distance in the event of an aborted take-off. There is also the risk that the wheels will exceed their maximum speed. Therefore, a maximum tailwind strength is specified in the approval for each aircraft. In passenger aviation , this is between 10 and 15 knots . At the latest from this wind strength, or at the request of the pilot, the runway is operated in the opposite direction, which turns the tailwind into a headwind.
Hang gliders and paraglider pilots do not start even with a weak tail wind, because then they are in the lee of the mountain and would start in the lee. There the air is often turbulent and there are down winds .
Statistically speaking, there are relatively few fatal accidents at the start. Over half of all fatal accidents occur during the approach , only 17% during take-off. One reason for this may be the strong standardization of the procedures for the pilots at take-off, while no two approaches are the same. Therefore, the processes at the start and the possible sources of error can be better trained.
See also
- Take off (go-around)
- Missed approach (missed approach)
- Flight control (Flight Control)
- Air Navigation (air navigation)
- STOL (Short Take Off and Landing)
- VTOL (Vertical Take Off and Landing)
- ASTOVL (Advanced Short Take Off and Vertical Landing)
- CATOBAR (Catapult Assisted Take Off But Arrested Recovery)
- Alarm riot (standby service in military aviation)
- Starting power
literature
- Wilfried Copenhagen: Lexikon der Luftfahrt , Transpress, 743 pp., 6th edition, 1991, ISBN 3-344-70711-6 .
Web links
- The video of an Airbus A300 taking off in FRA (runway 25R) from the cockpit view (www.luftfahrt.net), 5.1 MB ( memento from January 1, 2009 in the Internet Archive )
- Article about modern and older whiz kid (Welt der Wunder / RTL2) ( Memento from September 26, 2007 in the Internet Archive )
- Description of the start of an airship (luftfahrtgeschichte.com) ( Memento from March 5, 2009 in the Internet Archive )
- Complete video and audio documentation for the start of a Boeing 747-400 from the cockpit view (youtube.com, only original sound, length 5'54 ″)
Individual evidence
- ↑ Description of various prerotation devices (accessed November 25, 2013, English language)
- ↑ http://www.boeing.com/resources/boeingdotcom/company/about_bca/pdf/statsum.pdf#search=%22Biman%20Bangladesh%20Airlines%20DC-10%20crash%22 ( Memento from 23 August 2015 on the Internet Archives )