Tip jet

A tip jet is a jet nozzle at the tip of some helicopter rotor blades, used to spin the rotor, much like a Catherine wheel firework. Tip jets replace the normal shaft drive and have the advantage of placing no torque on the airframe, thus not requiring the presence of a tail rotor. Some simple monocopters are composed of nothing but a single blade with a tip rocket. Tip jets can use compressed air, provided by a separate engine, to create jet thrust. Other types use a system that functions similarly to the afterburner (reheat) on a conventional jet engine, except that instead of reheating a gas jet, they serve as the primary heater, creating greater thrust than the flow of pre-compressed air alone; the best description of this is thrust augmentation. Other designs includes ramjets or even a complete turbojet engine. Some, known as Rocket On Rotor systems, involve placing rockets on the tips of the rotor blades that are fueled from an onboard fuel tank. If the helicopter's engine fails, the tip jets on the rotor increase the moment of inertia, hence permitting it to store energy, which makes performing a successful autorotation landing somewhat easier. However, the tip jet also typically generates significant extra air drag, which demands a higher sink rate and means that a very sudden transition to the landing flare must occur for survival, with little room for error. During the 1900s, Austrian Ludwig Wittgenstein investigated the use of tip jets to drive an aircraft propeller while studying aeronautical engineering at Manchester University, in the United Kingdom. Wittgenstein's concept required air and gas to be forced along the propeller arms to combustion chambers on the end of each blade, at which point these gases would undergo compression via the centrifugal force exerted by the revolving arms, and thereby generating sufficient heat to achieve ignition. During 1911, Wittgenstein was able to secure a patent related to his tip jet work.