Final answer:
The maximum airspeed for windshield wiper operation is not explicitly provided, but taking into account the effect of air drag at highway speeds it is reasonable to assume that wipers can function properly at speeds up to the fuel-efficient cruising speed of 70-80 km/h.
Step-by-step explanation:
The maximum airspeed for windshield wiper operation is not specified in any of the referenced material or generally established as a universal value in automotive design. However, it's worth considering the effects of air drag and vehicle speed on the operation of windshield wipers. The drag coefficient is relevant here, as at highway speeds, more than 50% of a car's power is used to overcome air drag, indicating a large force acting on any object on the exterior of a car such as windshield wipers.
That said, and the most fuel-efficient cruising speed, taking air drag into account, is approximately 70-80 km/h, which can be inferred as a reasonable speed under which windshield wipers would reliably function without undue stress.