Compound helicopter Literature review Example | Topics and Well Written Essays - 3000 words

Compound helicopter - Literature review Example The Nelson Speed Limit holds true for helicopters even today. 3 Although helicopters have achieved what is considered the â€Å"Holy Grails of powered flight,†4 because of their ability to fly vertically, their limited capacity in speed and maneuverability have led aircraft builders to explore ways to augment performance metrics. One of the solutions offered by research is the compounding of the basic design of conventional helicopters with additional components to help achieve better speed and efficiency. Background: Compound Helicopters A compound helicopter is a conventional helicopter that has undergone modification with the addition of several components for the purpose of augmenting and enhancing basic performance metrics such as lift-to-drag ratio, propulsive efficiency and maneuverability.5 The most overt additions in a compound helicopter are fixed wings.6 Compound helicopters are often called hybrids because they are a combination of conventional helicopters, which a re powered by rotors, and fixed wing aircrafts like planes, although some compound helicopters do not have wings. Compound helicopters have the important capability of conventional helicopters - VTOL (vertical take-off and landing).7 What additional features precisely make a helicopter compound has not been unanimously agreed however. John Watkinson, for example, described a compound helicopter as one in which the production of forward thrust in cruise is not up to the rotor but by some other device while Ray Prouty depicted them as having wings and a propulsion device, which could be a jet engine, ducted fan, or propellers for the purpose of alleviating the rotors from lifting or propelling tasks.8 Leishman simply defined it as one in which additional parts are appended for the purpose of enhancing and augmenting basic performance metrics.9 Figure 1 shows a diagram of a compound helicopter with a four-blade main rotor atop its body as is commonly found in conventional helicopters. However, fixed wings or flaperons can also be observed attached to its fuselage. Fixed wings function to off-load most, if not all, of the rotor’s duty to lift the helicopter at high speed. The presence of a ducted propeller at the rear can also be observed, which likewise serves the function of taking away from the main rotor the task of driving the helicopter forward. Some compound helicopters may or may not have either fixed wings or a propulsion mechanism other than the main rotor, but all additional appendages in a compound helicopter serve the purpose of driving it at speed not available to conventional helicopters.10 Fig 2 Diagram of a Compound Helicopter11 2.0 History of Compound Helicopters The first known compound helicopter was developed in Germany in the 1930s by Anton Flettner, but two other models were also developed in that part of the world. The Fl 184 had two airscrews, fitted with propellers at each end facing at opposite directions, and attached to either s ide of the helicopter fuselage. The airscrews functioned to counter the torque effect of the three-blade rotor and helped the aircraft propel forward. The Wn