Helicopter spares and parts

The helicopter was a late arrival on the aviation scene compared to more conventional fixed-wing aircraft. A number of designers experimented with autogiros in the late 1920s and 1930s but it was not until the 1940s that serious helicopter developments began.

The Royal Air Force used an autogiro which was a Cierva design, licence-built by Avro, and some Sikorsky Hoverfly I and lI examples were used for limited squadron service and evaluation purposes. In general, the helicopter was regarded at the time as something of an anachronism and it was not until the post-war years that its serious development began, most of it being undertaken in the US.

In the UK, Bristol produced the Sycamore Type 171, which entered service with the Royal Air Force in 1953. Bristol also produced the twin-rotor Type 173 which was developed as military helicopters, the Type 192 and subsequently named Belvedere, entering service in the 1960s. The development of helicopters, and consequently helicopter spares, in the UK was, in the main, based upon UK derivatives of US designs of which the Dragonfly, Whirlwind, Wessex and Sea King have been notable examples.

In the late 1960s and early 1970s Westland Helicopters became involved with the joint design of a family of helicopters together with Aerospatiale of France. This led to the development of the Gazelle, Lynx and Puma helicopters all of which have served with various branches of the UK Armed Forces. Gazelle helicopter spares, Lynx helicopter spares  and Puma helicopter spares are all available.

The helicopter came of age as a fighting vehicle in the late 1960s and the US involvement in the Vietnam War was probably the first large-scale conflict in which it played a major part in a variety of roles. This pattern has been followed by the British involvement in the Falklands Campaign where the shortage of helicopters imposed severe operational limitations upon the ground troops. More recently the role of the helicopter in the Gulf War has emphasized its place in the order of battle - in particular the heavy battlefield attack machine (Apache) and the missile-equipped Lynx helicopters .

Helicopter engines

As their roles became more demanding so the helicopters became more sophisticated and complex. As the number of systems fitted increased to satisfy greater and more difficult tasks, so too has the amount of propulsive power required and both the power and the number of engines fitted have increased to accommodate these needs. The Dragonfly of the 1950s required a single 550 hp engine to power the 5,500 lb fully loaded helicopter.

The EH101 Merlin of the 1990s has three T700 engines, each rated at 1,437 shp to lift the helicopter with an all-up-weight of around 30,000 lb. As the size of the helicopter and engines has increased so has the complexity of the various systems and helicopter engine spares. The amount of electrical power required by a large helicopter of this type equates to that needed for most jet fighters a few years ago. The EH101 Merlin also requires complex helicopter autopilots and flight control systems to provide the necessary handling characteristics so that the crew can devote their attention to the demands of the mission. Helicopter Electrical and hydraulic systems also require higher levels of redundancy to support the mission requirements. Finally, the helicopter avionic equipment required to undertake a range of missions also places additional demands upon the baseline helicopter systems.

Special requirements of helicopters

The unique nature of the helicopter compared to conventional fixed-wing aircraft deserves special consideration in relation to aircraft systems. Despite the fact that many of the same principles apply, the vertical take-off and landing features of the helicopter place a different emphasis. Vertical take-off imposes a requirement for a high power to weight ratio. It is generally reckoned that for an aircraft to take off vertically with an adequate control margin, a thrust to weight ratio of 1.25:1 is required.

This ratio applies after various transmission losses have been taken into account.

The means of controlling a helicopter is by its very nature totally different to the methods used by fixed-wing aircraft. Also, due to unique properties such as hovering flight, and the ability to land vertically in confined areas, some system requirements are unusual.

These lead to the adoption of autopilot control modes such as auto-hover, which are not possible on fixed-wing aircraft. The ability to hover also dictates the need for winch systems and has led to the development of specialized helicopter autopilots modes. The need to land and remain tethered on ship decks in high seas has resulted in the introduction and use of helicopter deck-locking systems.