horizontal surfaces in airplane have small angle of incidence in general, Is it possible to have an angle of incidence for a vertical stabilizer? Please help me to find it. Thanks!!
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$\begingroup$ You may be french-speaking. In English, you usually use "angle of attack" while in French you use "angle d'incidence" $\endgroup$– Manu HCommented May 8, 2020 at 17:50
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1$\begingroup$ NO :the angle of incidence (sometimes referred to as the mounting angle[1]) is the angle between the chord line of the wing where the wing is mounted to the fuselage, and a reference axis along the fuselage (often the direction of minimum drag, or where applicable, the longitudinal axis). The angle of incidence is fixed in the design of the aircraft, and with rare exceptions, cannot be varied in flight. $\endgroup$– L'aviateurCommented May 9, 2020 at 7:35
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3 Answers
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Yes, but the term "incidence" normally only applies to horizontal surfaces. With a fin it's usually called "fin offset" and is very common on single engine tractor aircraft.
The offset helps align the fin into the spiraling airstream coming off the prop so that a counteracting rudder input isn't required (or at least a smaller input is required) to counteract the offset slipstream trying to push the tail to the side. It's usually 2 or 3 degrees to the left for an engine turning clockwise from the cockpit where the flow at the fin leading edge is coming from the left, or to the right for an engine that turns counterclockwise.
It's very common but not universal. Some airplanes just use a fixed trim tab on the rudder to passively do the same thing, or both a tab and an offset fin.
They also often have the engine offset several degrees on the mount, to the right on a clockwise engine. Look at single engine airplanes from above and it becomes quite apparent how the engine/prop is crooked as well as the fin being angled to the side, like the plane got into a fender bender accident and just drove off like that. Makes you wonder how the dang things fly straight in the first place.
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Some vertical stabilizers will have a slight angle of incidence to counter left turning tendencies. Older model Cessna 172s and 150/2s have a little metal trim tab that can only be adjusted by manually bending it from the outside. This will serve to adjust the vertical airfoil chord line angle in the aircraft slipstream or relative wind. The degree of incidence will be manufacturer and model specific.
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I'm no expert, but Wikipedia helps. The angle of incidence is the angle between the chord line and a reference line on the fuselage. [source] Since the vertical stabiliser is on a different geometric plane, there can't be an angle of incidence as there is with the wings.
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3$\begingroup$ FYI, a vertical stabilizer has a chord line. It usually has not much of a net camber. But, it is not perfectly flat. A reference line would imply a 1 dimension aspect. The wings have an angle of incidence to a 2D plane on the aircraft represented by the ref line. The vert stab would have an AoI to a different plane represented by the same or a different ref line. The best ref line to use for both would probably be the longitudinal axis of the aircraft. $\endgroup$– Dean F.Commented May 8, 2020 at 18:00