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Power used by tail rotor


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Looking at performance metrics here, but not clear how much power is used by the tail rotor.   From the power requirements plot therein, look like below 18%

This reference seems to indicate about 10-15%, but not highly confident.

This reference mentioned 10-20%.  

I realize this may vary by helicopter model.  Anyone heard of a tail rotor consuming > 15% power?  Presumably the higher percentages would be in hover correct?

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On 12/12/2020 at 3:07 PM, masum said:

Looking at performance metrics here, but not clear how much power is used by the tail rotor.   From the power requirements plot therein, look like below 18%

I realize this may vary by helicopter model.  Anyone heard of a tail rotor consuming > 15% power?  Presumably the higher percentages would be in hover correct?

You asked, "anyone heard of a tail rotor consuming > 15% power?" absolutely. Flight envelopes account for more than that.

The numbers are a result of a specific design. There are no metrics other than that from a specific design. Roughly, the tail rotor consumes up to about 10% of the total power for the helicopter. However, allowances of up to 20% may be made for design purposes to ensure sufficient maneuvering and transient capabilities. 

 We can also look at it as a percentage of the total main rotor power. The power required by the tail rotor typically varies between 3% and 5% of the main rotor power in routine flight and up to 20% of the main rotor power at the extremes of the flight envelope. 

 In addition to the yaw function, the flight envelope's extremes require adequate tail power for sideways flight. It is not apparent why anyone would want to fly sideways, but there are plenty of examples. Film cameras are often mounted in the main cabin and only have a clear view of the side. Flying the machine sideways allows the camera to shoot forwards. Flying sideways allows an attack helicopter pilot to dodge fire while keeping his rockets aimed at the target. 

Pilots regularly fly sideways as a matter of course, because this is what happens when hovering in a side wind. You're flying sideways at the same speed as the wind but in the opposite direction. In the case of a clockwise-from-the-top helicopter, the wind coming from the right side is undesirable as it increases the tail rotor inflow, and so requires more power. The worst-case will then be where the pilot wishes to make a maximum speed yaw-left in a strong wind from the right side. The tail rotor now has to overcome main rotor torque, boom drag due to the side wind. The FAA/military test tail rotor performance under those conditions. The primary criteria to generate enough thrust to balance main-rotor torque in full-power climb with a right-cross-wind with at least a 10% margin left over for directional control.

Quote

Leading University Level Textbook on Helicopter Aerodynamics

 6.9.2 Thrust Requirements

 The primary purpose of the tail rotor is to provide a sideward force on the airframe in a direction and of sufficient magnitude to counter the main rotor torque reaction. The tail rotor also provides the pilot with directional (yaw) control. Roughly, the tail rotor consumes up to about 10% of the total power for the helicopter, although allowances of up to 20% may be made for design purposes to ensure sufficient maneuvering and transient capabilities. 

 This is power that is completely lost, because unless the tail rotor is canted, as on the UH-60 Blackhawk, it provides no useful lifting force. The purpose of the canted tail design is to widen the allowable center of gravity of the helicopter. This design, however. introduces an adverse coupling between yaw and pitch, but this effect can be minimized b) a flight control system. The direction of the anti-torque force depends on the direction of rotation of the main rotor. For a rotor turning in the conventional direction (counterclockwise direction when viewed from above), the tail rotor thrust is to the right (starboard). The magnitude of this thrust, as well as its power consumption, depends on the reaction torque from the main rotor. and the location of the tail rotor from the center of gravity (i.e., the moment arm LMR). In addition, there are inertial effects that the tail rotor must overcome during yawing maneuvers...

 5.4.7 Tail Rotor Power

 The power required by the tail rotor typically varies between 3% and 5% of the main rotor power in normal flight, and up to 20% of the main rotor power at the extremes of the flight envelope. It is calculated in a similar way to the main rotor power, with the thrust required being set equal to the value necessary to balance the main rotor torque reaction on the fuselage. The use of vertical tail surfaces to produce a side force in forward flight can help to reduce the power fraction required for the tail rotor, albeit at the expense of some increase in parasitic and induced drag. If the distance from the main rotor shaft to the tail rotor shaft is XTR, the tail rotor thrust required will be

Source: Principles of Helicopter Aerodynamics (Cambridge Aerospace Series) 2nd Edition, J. Gordon Leishman (Author) 

 

 

Edited by iChris
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