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All about Rotary Wing Aircraft



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While rotary wing craft can be used to describe any vehicle that uses a means of upward lift to get airborne and fly, it generally refers to machines that generate lift around a central mast containing two or more rotor blades. By far the most common and widely used form of this type of machine is the helicopter.

Origins of the concept of Rotary Wing Aircraft

Leonardo Da Vinci and his intricate sketches of his airscrew' drawn in 1493, lay forgotten until in 1861, the French engineer Gustave de Ponton d'Amecourt coined the phrase Helicopter'. Originating from the French word helicoptere', it is derived from the Greek words helix' meaning spiral or turning and pteron' meaning wing; giving us spiral-turning wing (Anon, 2008). His vision for a vehicle that was lighter than air, and could achieve vertical take of and landing (VTOL), would not be fully implemented until the end of the 1940's.

How Helicopters Work

Helicopters and rotary wing aircraft achieve lift by turning rotor blades around a central mast, to generate upward lift.

These blades rotate and cut through the air, which in turn defeats the effects of gravity by increasing torque to the point where the vehicle spins upwards, much as a spinning top would.
To balance the effects of torque, which would otherwise continuously spin the craft around in the opposite direction, a tail rotor is fitted to allow forward propulsion, directed by the engine.

Hovering is the unique attribute that results from yaw control (movement from side-to-side) by means of foot pedals and a throttle stick to control the tail rotor and speed of the engine. The ability to hover has led to many applications for rotary wing aircraft, which distinguishes them from their fixed wing counterparts.

History of Rotary Wing Aircraft

It took some 450 years until the vision of Leonardo Da Vinci's sketch for a fully serviceable helicopter could be realised. The advent of the Korean War saw the introduction of medical evacuation from the battlefield to proper surgeons situated in the rear, usually some miles away and certainly inaccessible by ground transport.

Immortalised in M.A.S.H., the bumblebee' otherwise known as the Bell 47, deployed in 1950 by the United States Army allowed thousands of men to survive wounds that were untreatable by medics on the battlefield. The unique bubble' canopy allowed excellent all round vision but the single piston engine meant that the Bell 47 lacked power, which meant it had limited range and lift capability. This left it vulnerable to enemy ground fire and also limited it to a med-evac' role.

It wasn't long before the military realised the potential of helicopters as war machines and the Bell Huey UH-1 Iroquois was sent to the latest flashpoint of the cold war in Vietnam, in 1965.
The Iroquois was a country-mile leap in evolution terms of helicopter design, in that it was powered by gas turbine engines, which allowed it to be a larger aircraft than the Bell 47 and therefore travel further and faster than its predecessor. It could also deliver troops to the battlefield in what would otherwise have been deep impenetrable jungle, and could supply these same troops with ammunition and food.

The Iroquois also heralded a new term in the military lexicon; that of Gunship', when it was fitted twin M60 7.62mm machine guns and rocket pods. It was now apparent that helicopters could take the fight to the enemy, and weren't just big slow targets that couldn't fight back (Woodruff, 2000).

Uses of Helicopters and other Rotary Wing Aircraft

A modern world without helicopters is unthinkable. If you think for a moment about all the applications they are now used for it is hard to imagine how man would cope without them. The current crisis in Myanmar (formerly Burma) and the devastation in New Orleans caused by hurricane Katrina in 2005, would have led to a much greater loss of life if it were not for the helicopter.

Its application in a search and rescue role by the Coast Guard and Air Sea Rescue using the Westland Sea King and iconic twin-bladed Chinook, have allowed medical supplies to be delivered to people cut-off in flooded areas, and has allowed evacuation of the wounded.

The military application of helicopters as with most technologies, has advanced the development of helicopters and other rotary wing aircraft, which carry out a variety of tasks including policing the skies, providing pleasure trips, search and rescue, putting out fires and a myriad of other valuable roles.

During the first and second Gulf Wars, it was the Apache AH 64 Longbow, which actually allowed the advance into Iraq by coalition forces, despite the headline grabbing exploits of the Cruise missile attacks and sorties flown by the F-16 Wild Weasel radar-busting' teams.
Apache gunships represented the pinnacle of Military Rotary wing aircraft design and achieved complete surprise against enemy radar stations on the Saudi-Iraq border by using technology, which allowed them to fly at the knap of the earth (hugging the ground terrain closely). Advanced avionics and long-range hellfire missiles achieved complete destruction of entrenched sites that may have been too difficult for jets to destroy out-right.

Civilian Uses

Not all rotary wing aircraft are used for military conflict however. The ubiquitous Bell Jet' Ranger is used by nearly every country in the world, capable of affording helicopters. It fulfils a variety of roles from acting as an air ambulance to ferrying dignitaries to summit meetings to putting out forest fires. It is mostly associated with the leisure and travel industry however, and can be regularly seen providing exhilarating tours of the Grand Canyon to the paying public.

Specialist helicopters such as the Sikorsky S-64 Skycrane has a fuselage that has been cut away to allow vast quantities of water to be stored underneath in a purpose built tank (up to 2,650 gallons or 10,000 litres) (Anon, 2008) which allows it to fill up from nearby lakes and assist in forest fires.

Gyrocopters or Autogyro's are nifty little machines that are a lot more accessible than helicopters to most people. They work in much the same way as a helicopter except for the absence of a tail rotor; stabilisation being provided by a rear fixed wing configuration. As they lack a substantial engine they are a lot smaller and limited to mainly leisure activities.
However, a prime example can be seen in the film From Russia with Love', where James Bond defeats three Bell 47 helicopters using a modified Gyrocopter, which has machine guns and rockets. Despite the seemingly fantastic nature of this hybrid machine, Ian Flemming, the writer of the original book based this scene on a real prototype.

The Future for Rotary Wing Aircraft

The future for VTOL (Vertical Take Off and Landing) rotary craft looks set to be heavily influenced by the new V-22 Osprey hybrid. Aptly named the craft can hover like an Osprey does over water, by using a transverse wing system fitted with propellers at each end.
It is powered by two Rolls Royce Engines, which allow it to have all the benefits of the range and speed of a propeller driven aircraft, as well as the capability to hover, take off and land in the vertical.

Despite several tragic accidents it will probably yield civilian versions, which will be used for accessing remote mountain regions for example where the effective operating ceiling of conventional helicopters limits their range in such environments.

Sources:

Anon, 2008. Helicopters (Accessed 07/05/08) Taken from http://en.wikipedia.org/wiki/Helicopter

Woodruff, M, W. (2000). Unheralded Victory: Who Won the Vietnam War.

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