What is the term for the angle between the chord of the wing and the relative airflow?

Answer 1

Undisturbed flow is the flow of air approaching the wing.

The angle between chord line and undisturbed flow is the geometric angle of incidence.

Local flow (the relative flow you mention) is the flow actually "hitting" the wing. As the air apporaches the wing, it goes slightly downwards due to the downwash effect.

The angle between chord line and the local flow is the effective angle of incidence.

The above are mainly British terms so they might be slightly different in the US.

Hope it helped!

Break, Break;

Indeed this definition is British. The angle of incidence in the rest of the world is the angle formed between the aircraft's longitudinal axis (a line along the fuselage centerline, from the nose of the aircraft to the tail) and the wing's chord (a line between the wing airfoil's leading edge and trailing edge).

The angle defined in the first paragraph is the "angle of attack" (abbreviated AOA) in the rest of the world; that is, the angle formed between the free stream air and the wing chord line.

All of these definitions are quite simple and make several assumptions since wing geometry is dependant on the reference system it is measured in. When a wing is being built, it is relaxed and supported in tooling jigs. The leading edge is defined in the jig system.

But the aerodynamasist evaluates the wing's performance in the 1g steady state flight mode. In this system, the wing is usually bent up at the tips and the airfoils are twisted some. This creates a different LE point whilst flying.

The net result is that the person needing to know must always specify for what system or condition the LE or TE point is needed.