From a 4th century Chinese toy to Leonardo da Vinci’s 15th century Helical Air Screw through 19th century tinkerers, the concept of rotorcraft haunted inventors for centuries before the first helicopter-like autogyros took to the air as observation platforms in the closing years of World War I.
It was not until 1936 that the first operational helicopter, the German Focke-Wulf Fw 61, began 75 years of advances in both military and commercial vertical flight. As with nearly every advance in manned flight, it was war that spurred the rotor revolution, with the first full production helicopter – the Sikorsky R-4 – entering service with the U.S. Army Air Forces in 1942.
The R-4 traced its origins to Russian emigre Igor Sikorsky’s American-built VS-300, billed as the world’s first “practical” single main rotor helicopter, which had its first flight in September 1939 and, fitted with rubber floats, two years later became the first “practical” amphibious rotorcraft.
Germany built more than two dozen different helicopter designs during World War II, but Allied bombing prevented any large-scale Nazi production. Great Britain, France, Imperial Japan and the Soviet Union also produced a limited number of helicopters and autogyros. All were used primarily for medical evacuation and as spotters, although some were outfitted with depth charges as experimental anti-ship and anti-submarine platforms.
The primary driver in the development of military helicopters for both rescue and anti-submarine warfare during World War II was the United States – not the U.S. Army or Navy, but the one service with the greatest faith in rotorcraft, the U.S. Coast Guard. Despite limited funding or support from their War Department cousins, the Coast Guard demonstrated helicopters could be flown on and off ships at sea.
Use of helicopters for medical transport and resupply continued to evolve after World War II, with significant deployments during the Korean War. But the first true “helicopter war” was Vietnam, where medevac and supply missions soon became secondary to combat rotorcraft. The new tactics of airmobile warfare included dropping infantry deep into enemy territory and pouring gunfire, rockets and grenades into areas and from altitudes fixed wing aircraft could never match.
Continued advances in range, weaponry and armor led to the first Gulf war use of AH-64A Apache helicopters to lead the attack against Iraq, destroying part of the enemy radar network so other aircraft could fly in undetected. The Apache became the ghost killer of that short-lived conflict, destroying Iraqi military sites from stand-off distances from which they were unseen and unheard.
A decade later, the next-generation AH-64D Apache was heavily deployed to combat operations in Afghanistan and Iraq.
For nearly three-quarters of a century, all helicopters have shared basic shortcomings that have limited their military and, to a lesser extent, civilian capabilities:
* Low speed
* High noise
* Excess vibration
* Limited range
In recent years, designers have been able to significantly reduce rotor noise through new
blade designs and configurations. Some of those also have lessened vibration, which has been a hazard to both the airframe and its crew. Each new generation also has seen improvements in range and payload capacity, although those remain a matter of “trade-off” in most models.
Since 1949, when a Sikorsky S-52 set a world speed record of 129.5 mph, the vast majority of helicopters have remained in that range. Even today, most have cruise speeds of 150-to-160 mph, with a modern record of 248 mph set by a Westland Lynx going unchallenged since the mid-1980s.
But in late 2010, two experimental helicopters shattered the speed limit: A Eurocopter X3 hybrid helicraft reaching 253 mph, unveiled on Sept. 29, but still falling short of the 287 mph record set two weeks earlier by a Sikorsky X2 Technology demonstrator.
The X2 features two main rotors, spinning in opposite directions, and a pusher propeller, while the Eurocopter combines a more traditional single overhead rotor with forward-facing propellers on two short aircraft wings. Neither has the sideways tail rotor used to stabilize conventional helicopters.
The Sikorsky design is being incorporated into an X2 Raider light tactical prototype for the U.S. Army’s next generation armed reconnaissance requirement. The X3 is being promoted for military special operations and long-distance search and rescue.
Last year, Eurocopter announced its radical new Blue Edge rotor blade, which it said would reduce helicopter noise by up to 4 decibels, and a second technology – Blue Pulse – to further minimize main rotor noise by placing three “flap modules” on the trailing edge of each rotor blade. Piezoelectric motors move the flaps 15 to 40 times per second, minimizing the blade-vortex noise resulting from a rotor blade hitting the wake vortex of the blade in front of it.
On another front, Boeing and a Lockheed Martin/Kaman Aerospace team are competing for a U.S. Marine Corps unmanned helicopter to provide forward unit logistics support. Both the Boeing A160T Hummingbird and the much larger Lockheed Martin/Kaman K-MAX have met a Corps requirement to deliver more than 2500 pounds of cargo at ranges up to 75 nautical miles in less than six hours.
The two platforms also are competing for a separate unmanned cargo aircraft contract from the U.S. Naval Air Systems Command (NAVAIR).
Meanwhile, Boeing and Eurocopter have joined forces to design a new heavy transport able to deliver up to 13 tons of cargo more than 160 nautical miles (nm) or 8 tons to 540 nm, with an in-flight refueling capability that could extend range to as much as 2700 nm. By comparison, the current primary military heavy lift helicopter, the Boeing CH-47F Chinook, can deliver up to 12 tons of cargo 200 nm.
Russia and China also have announced a partnership to develop a new civil heavy lift helicopter for China, based on the Russian Mil Mi-26 Halo, the world’s largest cargo rotorcraft, capable of delivering up to 22 tons of payload 1000 nm.