A tip jet is a jet nozzle at the tip of some helicopter rotor blades, 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, so no tail rotor is required. 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 an afterburner-type system to burn fuel in the compressed air at the tip (tip-burners) to enhance the thrust. Other designs includes ramjets or even a complete turbojet engine. Some, known as Rocket On Rotor systems, are rocket tip jets that run off stored propellant such as hydrogen peroxide.
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.
The Italian designer V Isacco built "Helicogyres" in the 1920s which used piston engines at the ends of the rotary wing and he foresaw that they might be replaceable by jets.
During the Second World War a German, Friedrich von Doblhoff, suggested powering a helicopter with ramjets. The first tip jet-powered helicopter was the WNF 342 V1 in 1943. After the war two WNF 342 prototypes ended up with the Americans and Doblhoff joined McDonnell Douglas who subsequently produced the McDonnell XV-1. The engineer who had actually produced the tip jet engines, August Stephan, joined the Fairey Aviation company of the United Kingdom which used them in their Fairey Jet Gyrodyne and Fairey Rotodyne aircraft first flying in 1954 and 1957 respectively.
Eugene Michael Gluhareff was an early pioneer of tip jets.
Rotorcraft using tip jets
Cold tip jets
(Note: the compressed air in cold tip jets generally exited at quite high temperatures, but no fuel was burnt in the gas flow)
- Avimech Dragonfly DF-1 - American hydrogen peroxide powered helicopter
- Dornier Do 32 - German ultra-light cold-tip-jet helicopter, first flown on 29 June 1962: 4 built.
- Dornier Do 132 - German cold-tip-jet helicopter project, cancelled in 1969.
- Fairey Ultra-light Helicopter - UK cold-tip-jet helicopter, with rotor driven solely by compressed air. First flew in 1955. Four built for military use but defence cuts left Fairey to continue development without support and there were no further orders.
- Fiat 7002 - Italian cold-tip-jet helicopter, first flew in 1961, only one built.
- McDonnell XV-1 - US cold-tip-jet compound gyrodyne, flew in 1954, but cancelled due to insufficient advantage over contemporary helicopters.
- Percival P.74 - used engines in fuselage to produce efflux at wingtips. Engines never produced sufficient power and so it never flew. Further progress with the design using more powerful engines was cancelled.
- Sud-Ouest Ariel - French cold-tip-jet powered helicopter, first flown in 1947; three prototypes built.
- Sud-Ouest Djinn - French cold-tip-jet powered helicopter, first flown in 1953; 178 built.
- VFW-Fokker H2 - German proof-of-concept autogyro adaptation of a Bensen B-8 autgyro with cold-tip-jet–started rotor
- VFW-Fokker H3 - German cold-tip-jet compound helicopter; two built and flown.
Hot tip jets
- Hughes XH-17 - US tip-jet-burner-powered flying crane (largest rotor of any type on a helicopter), cancelled due to inefficient design (range around 40 miles)
- Doblhoff WNF 342 - German WWII compound helicopter with hot-tip-jet rotor propulsion.
- Fairey Jet Gyrodyne - UK hot-tip-jet–powered rotor compound gyroplane, providing data for the Fairey Rotodyne. First flown in 1954.
- Fairey Rotodyne - UK compound gyrodyne with rotor driven by hot tip jets (compressed air and fuel burnt in tip combustion chambers) for VTOL. 48-seater short-haul airliner design. First flew in 1957. Cancelled due to doubts about noise of tip jets in service.
- Hiller YH-32 Hornet - US ramjet helicopter, first flying 1950, 'jet jeep' had good lifting capability but was otherwise poor.
- Mil V-7 - Soviet ramjet helicopter
- Focke-Wulf Fw Triebflügel German World War II interceptor design, using ramjets - not built
- NHI H-3 Kolibrie (Nederlandse Helikopter Industrie) Dutch ramjet powered helicopter; 11 built.
(Note: Fuel and oxidiser supplied to combustion chambers at the rotor tips.)
- Rotary Rocket Roton ATV - US re-usable rocket concept, originally designed with rocket-tip-jet–powered rotor.
None, apart from the Sud-Ouest Djinn, entered production.
- Peklicz, Joseph, 2001, "Build the Monocopter" Sport Rocketry 44,2 March–April, 2001 p 34
- Hodge, Jon, 2000, "Monocopter C6 MII Review" Cosrocketeer, 12, 4, July–August, 2000 p. 4-5
- "Wittgenstein's aeronautical investigation", Notes and Records, 22 January 2007
- "The 'Helicogyre'", Flight: 244–245, 21 March 1929
- Robb, Raymond L. "Hybrid helicopters: Compounding the quest for speed Archived 2006-09-27 at the Wayback Machine", page 34. Vertiflite. American Helicopter Society, Summer 2006.