V position

from Wikipedia, the free encyclopedia
V-position of the wings and the tail unit of a Boeing 737
The unbalanced weight component causes a laterally directed force F, which causes the aircraft to be pushed.
The lower wing gets a higher angle of attack, which results in a stabilizing roll movement.

V-position describes the upward angle between the wings of an aircraft from the base to the tip, which can be viewed from directly in front of or behind the aircraft. A downward angle is called a negative V position.

Sense of the V position

The purpose of the V-position is to gain stability in the roll axis . If turbulence rolls the aircraft out of its normal flight position , it will push in the direction of the descending wing (see Fig. 1), creating an air flow along the longitudinal axis of the wing (i.e. across the fuselage). However, this air flow hits the transverse edge of the wing parallel to the pushing force and thus creates - in addition to the forward angle of attack - a transverse angle of attack . This creates an increase in lift on one side , which rolls the aircraft back to its starting position without the aileron counteracting the disruptive roll movement (see FIG. 2).

A common but incorrect explanation for the effect of the V-position is that the sunken wing disrupts the airflow and therefore the other wing follows. Actually, there is additional lift on the sunken wing, which counteracts the roll movement . Another way to visualize this is to imagine that the aircraft is lying in a V-shaped shallow slot, which is a natural stable position. This explanation is often used in books to simplify matters, but it is generally not entirely correct. The apparent increase in surface area does not contribute to the increased lift.

Most passenger and transport aircraft use wings in V-position for a more stable attitude. Many aerobatic planes as these aircraft more emphasis on agility and neutral flight behavior both in normal and in will, however, dispense with the V-shape, inverted flight is set as a secure stable level flight.

Negative V position

Negative V-position of a Harrier GR7

In contrast, the wings of combat aircraft either have no or even a negative V-position. This reduces the inherent stability of the aircraft, but increases maneuverability and the possible roll rate .

A side effect of the V-position can be the coupling of different rolling movements under certain conditions, which makes the aircraft spin through the air like a corkscrew . A rolling motion called a Dutch roll can be very uncomfortable and even lead to loss of control or structural overloading of the aircraft. A certain amount of negative V-position can compensate for this effect. The negative V-position is also used with swept shoulder - wing planes such as the BAe 146 or the Lockheed C-5 Galaxy . This wing arrangement compensates for rolling movements caused by the swaying of the fuselage and therefore does not require a positive V-position. In practice, these arrangements have such a high inherent stability around the roll axis that a negative V-position of the wings is required in order to be able to maneuver the aircraft.

An increased sweep also contributes to roll stability. This is another reason why a negative V-position is used on fighter jets with a high sweep. A negative V-position is also used for passenger aircraft such as the Tu-134 and Tu-154 when the wing sweep is greater .

literature