The modern helicopter, like any complex machine, is an accumulation of innovations from numerous inventors and engineers. Some of these modifications improve performance significantly without changing the overall appearance of the aircraft. For example, Arthur Young's stabilizer bar looks small and insignificant when compared to the gross anatomy of a chopper, but it revolutionized vertical-lift flight. Other innovations are less subtle and seem to give the helicopter a complete makeover. Let's check out a few changes.
One significant advancement has been the no-tail rotor, or NOTAR, helicopter. As you now know, vertical-lift flight is impossible without a tail rotor to counteract the torque produced by the main rotor. Unfortunately, the much-smaller tail rotor makes a lot of noise and is often easily damaged. The NOTAR helicopter solves both of these problems. Here's how it works: A large fan at the rear of the fuselage blows spent air from the main rotor down the tail boom. Slots along the side of the tail boom and at the end of the boom allow this air to escape. This creates a sideways force that counteracts the main rotor's torque. Varying the amount of air expelled from the rear slot provides additional directional control.
Some helicopters started receiving a second engine, which can operate the main rotor if the main engine fails. For example, the UH-60 Black Hawk helicopter, the workhorse of the U.S. Army, features this design improvement. Either engine can keep the aircraft aloft on its own, enabling the pilot to land safely in the event of an emergency.
Scientists have also fiddled with the main rotor assembly in an attempt to simplify one of the most complex parts of a helicopter. In the late 1990s, researchers developed a solid-state adaptive rotor system incorporating piezoelectric sheets. A piezoelectric material is one in which its molecules bend and twist in response to an electric field. In a rotor assembly, piezoelectric sheets — not mechanical linkages — twist sections of the blade root, thereby changing the pitch of the blades as they rotate. This eliminates parts in the rotor hub and decreases the chance of a mechanical failure.
Smaller unmanned quadcopters, commonly known as drones, have also seen a surge in popularity. Instead of the typical two-rotor design, quadcopters use four or more electric rotors of equal size, providing both thrust and stability. Operation of the aircraft is done via remote control on the ground, and some advanced systems will also have a degree of automated control. Thanks to their compact size, drones can be flown more cheaply and safely than full-size aircraft, especially in tight spaces. Quadcopters have seen extensive use in surveillance, search and rescue, as well as cinema. Chances are, a movie you've seen this year has had at least one aerial shot capture via drone.
Finally, it's worth mentioning those strange machines, known as tiltrotors, that bring together the best features of helicopters and airplanes. A tiltrotor aircraft takes off like a helicopter, with its two main rotors upright. But when it's airborne, the pilot can tip the rotors forward 90 degrees, enabling the machine to fly like a conventional turboprop airplane. The V-22 Osprey operates in this fashion. Winged aircraft which can hover and take off similarly to a helicopter are collectively known as Vertical Takeoff and Landing (VTOL) aircraft.
None of these innovations has made helicopters less absurd-looking. Some, like the tiltrotor, only increase the aircraft's awkward visual appearance. All of which brings us back to Harry Reasoner's 1971 commentary about helicopters:
Mark Twain once noted that he lost belief in conventional pictures of angels of his boyhood when a scientist calculated for a 150-pound man to fly like a bird, he would have to have a breast bone 15 feet wide supporting wings in proportion. Well, that's sort of the way a helicopter looks.
Mr. Reasoner may be right, but a helicopter's peculiar design and configuration haven't diminished its impact. It's become one of the most versatile and widely used aircraft in the world today.
Originally Published: Apr 1, 2011