To measure the dihedral angle of a wing, where should a straightedge and level protractor be placed?

To accurately measure the dihedral angle of a wing, the straightedge and level protractor should be placed on the front spar. The front spar serves as a critical reference point for assessing the angle at which the wing is positioned relative to the horizontal plane.

By aligning the straightedge with the front spar, you create a stable and consistent baseline that reflects the wing's angle of incidence and contributes to the overall aerodynamic performance of the aircraft. The protractor can then be used to read off the angle directly relative to the level, ensuring an accurate assessment of the dihedral.

Using the front spar for measurement is important because it is typically the most structurally representative part of the wing for such measurements, ensuring that any angle measured is reflective of the wing's design and performance characteristics.