Wake vortex
In wake turbulence , and turbulence braids or tip vortex called, is zopfartige, counter-rotating air turbulence behind flying airplanes . Its intensity depends mainly on the weight of the aircraft. The service life is influenced by the wind and the atmosphere. The air pressure is reduced in the center of the vortex. When the air humidity is high, condensation can create a narrow, visible strip there that begins directly behind the wing tips.
The wake vortex behind an aircraft endangers other aircraft and can even cause them to crash. The heavier the aircraft in front and the lighter the following aircraft, the greater the risk. Therefore, you have to wait until the next take-off on the same runway , until the eddies have either been carried away by the wind or have weakened sufficiently due to air friction on the ground. The same goes for landing. This waiting time is an essential factor for the maximum capacity of an airfield .
At cruising altitude, the wake turbulence of a heavy aircraft can hit a lighter aircraft 300 meters below, flying in the opposite direction, so hard that the pilots lose control.
Emergence
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Wake vortices are a side effect of dynamic lift . They inevitably occur on every aircraft, as wings can only generate lift with the help of the airflow when they accelerate air downwards. Since this acceleration does not take place outside the wing area, an angular momentum arises. Two vortices rotating in opposite directions form behind the aircraft. The heavier an aircraft, the more air it has to accelerate downwards and the more pronounced its wake vortices.
The shape of the wake vortex depends on the geometry of the wings. For example, winglets can reduce the air flow over the outer edge of the wing from the underside of the wing to the upper side, as a result of which the core of the wake vortex rotates more slowly. The buoyancy aids extended during take-off and landing , on the other hand, increase the intensity of the wake vortex. In the case of combat aircraft, shorter wings and thus strong wake vortices are accepted in favor of maneuverability.
In addition to the wake turbulence, the turbines of jet engines and the propellers of propeller engines set the air in rotation.
Spread
Together with the air packet accelerated downwards by the wings, the vortices of the wake vortices move downwards towards the earth's surface. Due to the physical principle of conservation of momentum, it is not possible for the wake vortex to dissolve before it has reached the ground (or any other obstacle). However, over time, more and more air is set in motion by air friction, while at the same time its speed decreases due to the conservation of angular momentum. The wake vortex becomes larger and slower over time and loses its dangerousness.
visibility
The air cools adiabatically in the center of the turbulence at the wing tip , as this is an area of particularly low pressure. The air often reaches temperatures below the dew point temperature , which leads to condensation of the water contained in the air to form water vapor / mist and a pigtail of vortices becomes visible. When approaching in moisture-saturated air, you can even see such vortex braids in several places on each wing, in addition to the outer edge, for example, often also at the respective end of the buoyancy aids (flaps).
Hazards
In low-flying aircraft, wake vortices can reach the ground at high speed, so that in extreme cases house roofs are covered or solar modules and skylights are destroyed. Settlements and buildings in the approach path of airports are particularly at risk.
In general, care must be taken to ensure that there is sufficient distance between aircraft, especially when flying on hold, when approaching and taking off, in order to avoid turbulence and control problems caused by the wake of the aircraft flying ahead. If the distances are not adhered to, there is a risk of serious damage or even a crash. Guide times of two to three minutes apply to the intervals. This staggering limits the capacity of an airfield . Currently (2017), increased vertical distances are also being discussed after a near-accident.
Categories
By classification of aircraft in weight classes the required distances ( English wake turbulence separation minima ) is defined in order to avoid the dangers of wake vortices. The following table shows the classification according to ICAO .
| preceding aircraft |
following aircraft |
distance | waiting period | example | |
|---|---|---|---|---|---|
| L. | Light ( MTOW <7 t) | light | 3 NM | N / A | Cessna 182 follows Cessna 182 |
| medium | 3 NM | N / A | Airbus A320 follows Cessna 182 | ||
| heavy | 3 NM | N / A | Boeing 747 follows Cessna 182 | ||
| M. | Medium (MTOW 7 t to 136 t) | light | 5 NM | 3 min | Cessna 182 follows Airbus A320 |
| medium | 3 NM | N / A | Airbus A320 follows Airbus A320 | ||
| heavy | 3 NM | 2 min | Boeing 747 follows Airbus A320 | ||
| H | Heavy (MTOW> 136 t) | light | 6 NM | 3 min | Cessna 182 follows Boeing 747 |
| medium | 5 NM | 2 min | Airbus A320 follows Boeing 747 | ||
| heavy | 4 NM | N / A | Boeing 747 follows Boeing 747 | ||
The Boeing 757 is almost always classified in the heavy category due to the increased wake turbulence after near-misses, despite its weight of less than 136 tons. In the USA there is another class specifically for the 757, the so-called class MH (Medium Heavy). In the UK , the Civil Aviation Authority has Heavy, Upper Medium, Lower Medium, Light and Small classes; the Airbus A380 is still often classified in its own category. Continental Europe uses the ICAO classes.
To obtain the capacity benefits (passengers / time) partially proposes Airbus A380 at the runway use of a falling below the minimum distance for forward flying front plane, characterized the extended time period for the subsequent plane.
The DLR led in 2006 to an extensive investigation by and came to the conclusion that the vortices of an A380 at cruising altitude not significantly different from those of a Boeing 747 differ. For take-off and landing, however, an enlarged separation was issued as a recommendation to the ICAO for the following aircraft, while the distance for the A380 as the following aircraft remains 3 NM:
| preceding aircraft |
following aircraft |
distance | waiting period | example | |
|---|---|---|---|---|---|
| J | great | light | 8 NM | 3 min | Cessna 182 follows Airbus A380 |
| medium | 5 NM | 3 min | Airbus A320 follows Airbus A380 | ||
| heavy | 4 NM | 2 min | Boeing 747 follows Airbus A380 | ||
| great | 4 NM | N / A | Airbus A380 follows Airbus A380 | ||
Despite being the same or heavier than the A380, the C-5 Galaxy and An-124 have been treated like a B747 so far.
What to do if there is a risk of wake vortices
The air traffic controller on the tower usually issues a warning if there is a risk of turbulence and wake vortices. Nevertheless, it is ultimately the pilot's responsibility to land safely and avoid an accident. For this reason, the following methods have proven to be useful:
- Landing behind a landing large aircraft on the same runway: stay
above the glide slope of the previous aircraft and land after its touchdown point. - Landing behind a large aircraft taking off on the same runway:
"short" landing, ie at the beginning of the runway.
Take- off behind a large aircraft taking off on the same runway: Take off (rotate) before the rotation point of the preceding aircraft is reached and stay above its climb.
Scientific investigations
Because of the great weight and the resulting very intense vortices, Airbus had to develop new technologies for the Airbus A380 , which keep the wake vortices in this large aircraft within limits.
Research on this topic can be broken down into three areas:
1. Vortex detection and prediction
The development of methods for estimating the vortex behavior, e.g. B. depending on meteorological parameters, a theoretical vortex forecast z. B. in computer models too. The physical processes of the transport and weakening of the eddies in the earth's atmosphere are understood. Wake vortices can be observed using a pulsed LIDAR .
2. Avoidance of vortices
By developing aircraft with favorable vortex characteristics, attempts are being made to reduce the vortex strength. It has also been proven that aircraft wake vortices can be attenuated by generating multi-vortex systems.
In order to constructively reduce the formation of wake vortices directly on the aircraft, there are the following considerations:
- The turbines of jet engines set the air exiting behind in rotation. When this air combines with the edge vortices of the wing, a weaker or stronger vortex is created depending on the direction of rotation. Since the tip vortices of the wings have opposite directions of rotation, the turbines would also have to rotate in opposite directions to the left and right in order to weaken both tip vortices. However, there are considerable additional costs for the provision of turbines with different directions of rotation.
- A specially clad landing gear is extended early on. That too weakens the problematic eddies.
- Landing flaps and ailerons are not brought right up to the fuselage. This creates a counter-rotating vortex at this point, which weakens the wake vortex.
3. Vortex compatibility
The third part of the research relates to the development of methods to increase the safety when entering a wake vortex so that it can e.g. B. does not come to flap rupture when entering such a vortex.
Incidents
- On 12 November 2001 9:15 am local time crashed shortly after takeoff from the airport John F. Kennedy , New York , an Airbus A300 on the flight 587 to Santo Domingo the American Airlines near Rockaway Beach , Queens , NY , in densely populated area. The A300 got caught in the wake of a Boeing 747 that had previously flown off . The copilot tried to correct the rotation of the aircraft caused by the wake vortex with maximum rudder deflection, which led to the rudder tearing off and thus to the crash.
- The crash of a Learjet 45 in Mexico City in 2008 could also be traced back to the wake turbulence of a Boeing 767-300 flying in front of the Learjet.
- At the flying festival at Backnang-Heiningen airfield on September 9, 2012, a Robin DR 400/180 Régent had an accident immediately after take-off, because the wake vortex of a previously launched Antonow An-2 caused the flying Robin to roll 90 degrees , causing it to crash. The investigation of the accident showed that it was not possible to compensate for the roll moment even with the greatest rudder deflection.
- On 7 January 2017, the wake of a flying at cruising altitude caused Airbus A380 of the airline Emirates that a 300-meter low flying in the opposite direction machine of the type Challenger 604 of MHS Aviation three to five times revolved around its own axis. The pilots temporarily lost control of the aircraft and were only able to intercept it about 3,000 meters lower and finally land heavily damaged. Several passengers were injured and had to be hospitalized. The Challenger 604 suffered a total write-off and had to be written off.
audibility
Wake vortices can be audible under certain conditions. Especially on windless days, wake turbulences behind heavy aircraft can be perceived as a dull roar and hiss. Stable wake vortices can be heard as a broadband low-frequency noise. If the wake vortex is weaker, it can break off with a sound like tearing paper. The audible sound of the wake vortex occurs when the aircraft has already passed and only then increases in intensity. The noise can be clearly located behind the aircraft in the sky. The sound can last for thirty seconds or more, its timbre changing continuously, sometimes with rustling and tearing parts, until it finally dies.
See also
- Contrails (cloud trail behind a high-flying airplane)
- List of aircraft type codes (specification of the wake vortex category)
literature
- Peter Bachmann, Gerhard Faber, Dietrich Sanftleben: Danger manual for pilots. Motorbuch Verlag, Stuttgart 1981, ISBN 3-87943-656-8 .
- Peer Böhning: Acoustic localization of wake vortices. Technical University of Berlin, Berlin 2006, urn : nbn: de: kobv: 83-opus-13093
- Ernst Götsch: Aircraft technology. Motorbuchverlag, Stuttgart 2000, ISBN 3-613-02006-8 .
- Jeppesen Sanderson: Private Pilot Study Guide. Self-published, 2000, ISBN 0-88487-265-3 .
- Jeppesen Sanderson: Private Pilot Manual. Self-published, 2001, ISBN 0-88487-238-6 .
- Hermann Schlichting , Erich Truckenbrodt : Fundamentals of fluid mechanics: aerodynamics of the wing (part 1). (= Aerodynamics of the aircraft. Volume 1). Springer Verlag, Berlin 2001, ISBN 3-540-67374-1 .
- Hermann Schlichting, Erich Truckenbrodt: Aerodynamics of the wing (part 2), the fuselage, the wing-fuselage arrangement and the tail units. (= Aerodynamics of the aircraft. Volume 2). Springer Verlag, Berlin 2001, ISBN 3-540-67375-X .
- Chapter 12.1 wake vortices. In: Klaus Hünecke: The technology of the modern airliner , Motorbuch Verlag, Stuttgart 2017, ISBN 978-3-613-03893-6 , pp. 238-261
Web links
- Video on the investigation of an aircraft accident caused by wake vortices by the Federal Bureau of Aircraft Accident Investigation 2015
- Investigation of wake vortices at the Institute for Atmospheric Physics at DLR , Oberpfaffenhofen
Individual evidence
- ↑ Airbus air vortex almost crashed another aircraft. In: Spiegel Online . Retrieved May 17, 2017 .
- ↑ Wake vortex damaged house in Flörsheim - causer quickly identified. In: main-spitze.de. Retrieved January 8, 2017 .
- ↑ Wake vortex sweeps tiles from the roof. In: Highest circular sheet. Retrieved January 8, 2017 .
- ↑ Airbus air vortex almost crashed another aircraft . Spiegel-Online ; accessed on May 17, 2017
- ↑ Lufthansa Flight Training, Pilot School, BRE OS1 / A - International Air Traffic Regulations and Procedures, 2003.
- ↑ Airbus A380 Wake Vortex study completed . Airbus.com, September 28, 2006.
- ↑ Airbus A380 wake vortex study completed - DLR support for measurements successful . dlr.de, November 3, 2006.
- ↑ accident report. ( Memento of July 7, 2014 in the Internet Archive ; PDF; 1.86 MB) Aircraft Accident Investigation Authority NTSB, p. 160 (English)
- ↑ Investigation report. (PDF) Federal Office for Aircraft Accident Investigation; accessed on November 6, 2014. Video from the federal agency on the accident
- ↑ Accident: Emirates A388 over Arabian Sea on Jan 7th 2017, wake turbulence sends business jet in uncontrolled descent , accessed on March 19, 2017.
- ↑ Airbus A380 takes a dive in a business jet , accessed on March 20, 2017
- ^ Böhning: Acoustic localization of wake vortices. 2006, p. 33.