tipjet

Tipjet refers to a propulsion system in which jets are expelled from the tips of rotor or propeller blades to generate the rotational thrust that drives the rotor. In this arrangement the main drive power need not be transmitted through a central shaft to the blades, and in some configurations the fuselage experiences little or no torque from the rotor, potentially reducing anti-torque requirements.

Principle of operation: Tipjet systems fall mainly into two categories. Compressed-air tipjets use a source of high-pressure air (often from a turbine or compressor) delivered to the blade tips, where fuel is injected and burned or where the pressurized air itself is expelled to produce thrust. Combustion tipjets burn fuel directly at the blade tips, producing jets that press against the surrounding air to drive rotation. Some designs rely on stored or ducted compressed gas rather than a continuously burning fuel-air mixture. In all cases, thrust at the blade tips creates torque that turns the rotor without relying on a powered shaft connected to the rotor hub.

History and applications: The concept has long been explored in aviation, with notable experiments in the mid-20th century. The Fairey Rotodyne, a British experimental rotorcraft of the 1950s, used tipjets to drive its rotor and to provide lifting force in helicopter mode, making it a prominent example of the approach. While promising in concept, tipjet designs faced challenges including high fuel consumption, significant noise and vibration, complex plumbing for air and fuel supply, and maintenance difficulties. These drawbacks limited widespread adoption, and most modern rotorcraft rely on shaft-driven rotors with geared transmissions.

Status: Tipjet propulsion is now primarily of historical and niche interest, appearing in research, demonstrations, and certain model or experimental aircraft rather than mainstream production helicopters.