"Coordinated" flight

Definition of a "coordinated" turn

Steve Seibel
www.aeroexperiments.org

This page is still under construction!
This page was last modified on August 3, 2006

 

In aviation, the idea of a "coordinated" turn has several meanings. Sometimes the idea of a "coordinated" turn simply means that all the available flight controls are being used to keep the entry to the turn, the turn, and the exit from the turn as smooth and efficient as possible. Sometimes the idea of turn "coordination" encompasses the idea of keeping the airspeed and/ or the altitude constant. But a more narrow, and very common, definition of "coordinated" flight is as follows: an aircraft is flying in a "coordinated" manner any time that the nose of the aircraft is aligned with the actual direction of travel through the airmass at any given moment. In other words, an aircraft is flying in a "coordinated" manner any time that the nose of the aircraft is pointing directly into the relative wind. (Diagram to be added.) An aircraft is flying in an "uncoordinated" manner whenever the nose of the aircraft has been allowed or forced to yaw to point to the left or the right of the aircraft's actual direction of travel through the airmass at any given moment. In other words, an aircraft is flying in a "uncoordinated" manner whenever the nose of the aircraft has been allowed or forced to yaw to point to the left or the right of the actual direction from which the relative wind is blowing. (Diagram to be added.)

In "uncoordinated" flight, there is a sideways component in the relative wind or airflow over the aircraft.

In "'Conventional' use of the rudder", we noted that the rudder is often used to keep the nose of the aircraft precisely aligned with the actual direction of travel through the airmass at any given moment. In other words, the rudder is often used to keep the nose of the aircraft pointing directly into the relative wind. In other words, the rudder is often used to "coordinate" a turn, so that adverse yaw or other related effects do not swing the nose out of alignment with the actual direction of the flight path and relative wind at any given moment.

In "'Conventional' use of the rudder", we noted that sailplane pilots employ use a "yaw string" (photo to be added) to show the precise direction of the flight path and relative wind: if the yaw string blows to one side, the nose of the aircraft is not pointing directly into the relative wind. (Photo to be added). In a "coordinated" turn, as defined above, the yaw string is centered. (Photo to be added.)

In "'Conventional' use of the rudder", we noted that airplane pilots typically use a slip-skid ball (or bubble) (photo to be added) as a guide to rudder usage: if the nose of the aircraft is not pointing directly into the airflow, the slip-skid ball (or bubble) drifts to one side. (Photo to be added.) In a "coordinated" turn, as defined above, the slip-skid ball (or bubble) is centered. (Photo to be added.)

In "What is a turn?", we noted that "adverse yaw" is one of the main reasons that a turn might tend to become "uncoordinated". By applying the proper amount of rudder as he rolls the aircraft from wings-level into the turn, a pilot can overcome adverse yaw and keep the turn "coordinated", so that the nose of the aircraft remains pointing directly into the relative wind as the flight path begins to curve.

In an aircraft without a rudder, the pilot has no way to keep the aircraft perfectly "coordinated." The nose will often point in slightly different direction than the aircraft is actually travelling through the airmass, especially while the aircraft is rolling from wings-level into a turn or while the aircraft is rolling from a turn back to wings-level. If the aircraft is well designed, the degree of "uncoordination" arising during these maneuvers can be minimized, but with no rudder, it is unlikely that the aircraft will remain completely "coordinated" throughout the entire flight envelope.

 

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