Lou, Nick or Shaun! Question?

[francois marais]

:ok:
Good day gentlemen

With reference to the FAA Rotorcraft Flying Handbook (FAA-H-8083-21), Page 3-5, the following:

1. In reference to Tranlational Lift, it states: "As the tail rotor efficiency improves, more thrust is produced causing the aircraft to yaw left in a counter-clockwise rotor system. It will be necessary to use RIGHT torque pedal to correct for this tendency on take off.

"This must surely be incorrect? It must be a misprint!

We all know that in a counter-clockwise rotor system, the nose of the helicopter swings right when power is applied, therefore LEFT peddle is used.

Whadaya say?

[Autorotate]

Yeah but Francois - you fly a Huey in the upside down part of the world, that must account for something, especially with Bert and Fred at the controls :O


:E :ok:

[Thomas coupling]

As the helo translates forward, the tendency to yaw in the opposite direction to the rotors (counterclockwise rotors - yaw right) while applying power, is masked due to translational lift and the tail rotor becoming more efficient, this might even cause the helo to yaw slightly left if the TR is offloaded enough. To compensate, the pilot needs to put right boot in, but it is transient.
In a cushion creep, provided everything is in your favour, you can really detect this phenomenon. It is spoilt/masked eventually because the pilot has to apply collective(power) to stop hitting the ground as the a/c transitions. But you can take off from the low hover and in the right conditions with little or no application of collective at all.

[[email protected]]

Francois - you didn't need the knowledge of test pilots to answer this one - the main rotor experiences an increase in rotor thrust at the onset of translational lift which causes the aircraft to climb without any firther application of lever - the TR gets the same increase in rotor thrust and if you still have the pedal position set for the hover, there will be a surplus of TR thrust which will yaw the ac right unless corrected.

[Thomas coupling]

Crab: there's more isn't there? In a fenestron a/c (and those with tail fins) (Gazelle/Dauphin/350's) it's primarily the air flow over the vertical fin that produces lift to the thrust side, hence the yaw. In the case of ducted tail rotors the airflow doesn't pass directly over the tip path plane of the TR....

[Lu Zuckerman]

To: francois marais

Although this is a generalization I would consider anything dealing with direction in the Rotorcraft Flying Handbook a bit suspect. This is especially true if you consider that the cover of the handbook is printed backwards.

:E

[GLSNightPilot]

My experience is that the handbook is correct. If you have pedal set for hover, then begin a takeoff, you have to progressively remove left pedal (thereby increasing right pedal) as you accelerate to cruise. Just as you reach translational lift, there will be a need for more right pedal rather quickly. It takes much less left pedal to maintain trim in cruise than at a hover. I don't think all this is due solely to increased tailrotor efficiency, but it's still the case.