V- position refers to the upward angle between the wings of an aircraft from root to tip, which can be viewed from directly in front or behind the aircraft. A downward angle is referred to as a negative dihedral.
Sense of the dihedral
The purpose of the V -position to obtain stability in the roll axis. If turbulence taxis the aircraft from its normal attitude, it will move downwards in the direction of walking wing ( Fig. 1), whereby a flow of air along the longitudinal axis of the wing (that is transverse to the hull ) is generated. This air flow hits but parallel to the sliding force on the transverse edge of the wing and produces it - in addition to the forward-facing angle of attack - a Queranstellwinkel. This creates a one-sided increased buoyancy, back rolls the aircraft without is that left unchecked with the aileron roll motion of the disturbing in its initial position is created (see Figure 2 ).
A common, but incorrect explanation for the effect of the V- position is that the sunken wing disrupts the airflow and therefore follow suit of the other wing. Actually generated on the wing but sunken additional buoyancy, which counteracts the rolling movement. Another way to visualize this is to imagine that the plane is in a shallow V-shaped slot, which is a natural stable position. This statement is often used in books for the simplification of the facts, but is generally not absolutely correct. The apparent increase in surface area contributes namely not contribute to the increased buoyancy.
Most passenger and transport aircraft wing put in a V- position in order to have a more stable flight attitude. In many aerobatic planes will waives the V-shape, as these aircraft more emphasis on agility and neutral flying characteristics both in normal and in inverted flight than on a secure stable straight and level flight.
In contrast, the wings of fighter aircraft either no or even a negative dihedral. This reduces the inherent stability of the aircraft, but increases the agility and the possible roll rate.
A side effect of the V- position may be, under certain conditions, the coupling of different rolling motion, which can rotate the plane like a corkscrew through the air. A Dutch role called rolling motion can be very uncomfortable and even cause loss of control or structural overloading of the aircraft. A certain proportion of anhedral can compensate for this effect. The anhedral is also used in swept shoulder -deckers, such as the BAe 146 and the Lockheed C -5 Galaxy. This wing arrangement compensates rolling motions by the oscillation of the fuselage and therefore does not require positive dihedral. In practice, these devices have such a high intrinsic stability to the roll axis, that a negative dihedral of the wing is required to maneuver the aircraft can.
An increased sweep also contributes to roll stability. This is another reason why in fighter aircraft with high sweep an anhedral used. With a larger sweep of the wing also in passenger aircraft such as the Tu- 134 and Tu- 154 is a negative dihedral is applied.