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Thread: Tip-jet propulsion systems and anti-torque devices

Created on: 08/16/16 09:28 PM

Replies: 3

makerfeldt





Joined: 08/26/15

Posts: 13

Tip-jet propulsion systems and anti-torque devices
08/16/16 9:28 PM

I see you have some aircraft with main rotors driven by tip jets, such as the Hiller Hornet, the Fairey Ultra-Light, and the Sud-Ouest Djinn. These aircraft either have no tail rotors, or very small ones. I thought helicopters needed tail rotors to keep them from spinning around. Why don't these aircraft need them? Is there something inherent with tip jets that causes this? Thanks very much!




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comodo15





Joined: 08/27/15

Posts: 41

RE: Tip-jet propulsion systems and anti-torque devices
08/25/16 9:34 PM

A great question!

To make the rotor rotate something has to overcome the drag forces on each blade, which require a compensating torque to applied to the rotor. If this torque is applied within the rotor itself the net torque at the axis of rotation of the rotor is zero, so there is no need for any other compensating torque. This is the situation with rotors like the Hiller Hornet, where the applied torque comes from tip jets at the end of each rotor blade.

For most rotorcraft the forces on the blades cause a net moment to be applied through the rotor shaft and through the fuselage. Hence the aircraft would rotate in the direction of the applied torque at the blades without some compensating effect. This is normally applied by a tail rotor (or similar device), which stops the fuselage rotating.

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makerfeldt





Joined: 08/26/15

Posts: 13

RE: Tip-jet propulsion systems and anti-torque devices
08/31/16 10:47 PM

Thanks comodo15, that makes sense. Are there anti-torque devices other than tail rotors?




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comodo15





Joined: 08/27/15

Posts: 41

RE: Tip-jet propulsion systems and anti-torque devices
09/01/16 8:06 PM

There are a number of different forms of anti-torque device. These include,

- Fenestrons, or ducted/shrouded tail rotors - these usually include many more blades than tail rotors. They produce anti-torque control through a combination of directed loads from the blades and induced loads over the duct
- Reaction jet devices (simple force generation through directed air flow providing a reacting force on the structure
- NOTAR type devices (which use the Coanda effect to provide torque control through flow induced loads over the tail boom)

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