Wake Turbulence
Every aircraft generates wake turbulence from the moment the wing produces lift and the aircraft leaves the ground until it lands. Wake turbulence affects all aircraft of all sizes and shapes. Wake turbulence forms behind an aircraft and is a disturbance of the airflow behind and below as it flys through the air. The airflow is pushed outward and downward as the aircraft wings cut through the air. This creates vortices (circular swirling of air) as is shown in the image below. Wake turbulence is a natural by product of powered flight. This turbulence includes various components, the most important of which are wingtip vortices and jetwash. Jetwash refers simply to upsets or turbulence encounters associated with other aircraft or the rapidly moving gases expelled from a jet engine, it is also known as propwash. Wingtip vortices, on the other hand, are much more stable and can remain in the air for up to three minutes after the passage of an aircraft. Wingtip vortices is the most dangerous component of wake turbulence. Wake turbulence can be especially hazardous during the landing and takeoff phases of flight, where the aircraft’s close proximity to the ground makes a recovery from the turbulence induced problems more difficult. Interest in this phenomenon greatly increased during the late 1960s and a concern about the impact of greater wake turbulence. This was the impetus to conduct research to gain additional information and determine what safety considerations were necessary as more and more large aircraft entered the industry fleets. Air Traffic Control apply separation distances to instrument flight rules (IFR) aircraft except to visual flight rules (VFR) following a medium/ heavy aircraft or IFR on a visual approach and were the pilot reported the previous traffic in sight and follows and maintains its own separation. Controllers will then issue a caution wake turbulence advisory and the pilot is responsible to keep clear. Separation can be done in distance or in time. During cruise, distance is used and on arrival and departure time is used for separation.
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| Image embeddded from Our Airspace 11 Oct 2009 |
![250px-Airplane_vortex_edit.jpg"](http://upload.wikimedia.org/wikipedia/commons/thumb/f/fe/Airplane_vortex_edit.jpg/250px-Airplane_vortex_edit.jpg") |
| Image embeddded from Wikipedia 01 Oct 2011 |
Larger aircraft create larger disturbance of the air and therefore more turbulence.
Flight Conditions
Wake turbulence is often underestimated by pilots. It can severely affect the aircraft. For example if a light aircraft such as a Cessna 152 is following a larger aircraft such as a Boeing 737, there have been cases where the smaller plane was flipped inverted. It is recomended that pilots undergo a small amount of aerobatic training, so they have the flying skills to cope with this event should it occur. To avoid wake turbulence all together, if following another aircraft the pilot should allow for this by either:
- Keeping an appropriate disance behind the aircraft, usually between 2 and 5 minutes flying time.
- Flying above the other aircrafts flight path.
Mini Wind Tunnel
A home made mini wind tunnel, showing how the angle of the wing and the use of flaps affect wake turbulence, using string.
| Video Embedded from YouTube 30 Sep 2009 |
How Far Below?
A NASA study, investigating how far below an aircraft is affected by wake turbulence.
| Video Embedded from YouTube 30 Sep 2009 |
Simulated Wake Turbulence Landing
Simulation of an Air NZ aircraft landing in an area affected by wake turbulence. Normally air traffic control seperates aircraft so that wake turbulence wont affect each aircraft.
| Video Embedded from YouTube 30 Sep 2009 |
A380 Special Adaptation to reduce wake turbulence.
| Video Embedded from YouTube 30 Sep 2009 |
Summary
Wake turbulence affects aircraft of all sizes and basically pilots need to be aware of it. Fighter Combat International advices if you do encounter wake turbulence and have enough altitude to recover then try the POWER-PUSH-ROLL method. Increase POWER, PUSH to unload the wing then ROLL in the direction that will unload the wings or to the horizon. Remember this technique may not work when you are too low to the ground or were there is just not enough room to manoeuver. Always be aware of the situations where wake turbulence may be encountered and you must be prepare to take measure to avoid it. Always remember not get too close, do not fly below the leading aircraft flight path and stay alert when light crosswinds exist during takeoff and landing.
Want to know more?
- Aviation Knowledge - Turbulence
- Other types of turbulence that can affect an aircraft.
http://www.faa.gov/training_testing/training/media/wake/04SEC2.PDF
