As the aircraft moves, air flows against its front and subsequently against the yaw string. The yaw string, then, sticks against the helicopter's windshield, either upright or at an angle.

The first U.S. military helicopter to participate in air-to-air refueling was the HH-3E, which underwent its first operational test in Southeast Asia with a modified C-130 Hercules in 1967.

That's why the Apache helicopter has wire cutters in the front. Not a set of wire cutters in the cockpit, but a Wire Strike Protection System (a name trademarked by Magellan Aerospace).