Tail Rotor Considerations. Many pilots do not appreciate the effect that the tail rotor has on power applied. The torque indicator displays power supplied by the engines to the entire drive train, not just the main rotor. As with collective changes, if you move the pedals, you can change the torque applied (displayed on the torque indicator). Let's say an HH-60G is stabilized in a 20-foot hover, in a no-wind environment, with a constant collective position, at 65% Q. If you push right pedal for a moderate-rate pedal turn, you will see the torque decrease approximately 5%. If you push left pedal instead, you will see the torque increase approximately 5%. Knowledge of this has applications in a variety of maneuvers.
If you are hovering with a crosswind, the application of pedal to hold heading will result in power (required to hover) readings that will not match those estimated for a no-wind environment. Hovering with a right crosswind requires more left pedal (and more torque) to counteract the wind-vaning. Hovering with a left crosswind requires more right pedal (and less torque) to counteract the wind-vaning.
As you transition from a hover to forward flight, the increased efficiency of the tail rotor requires the application of right pedal. If the collective position is held constant, the torque applied (displayed on the torque indicator) will decrease. If you are executing a marginal power (or maximum performance) takeoff and desire to hold a constant power setting (simulated or actual maximum available), as forward airspeed increases, the collective must be increased slightly in order to make up for the power reduction that occurs due to the application of right pedal. In a marginal power (or maximum performance) takeoff situation, application of right pedal affords a few percent more torque available for vertical thrust (collective).
Several factors lead to degraded tail rotor performance. Some situations require the application of increased collective and consequently, the anti-torque required by the tail rotor. These situations include high gross weights, and hovering OGE. High rates of descent on final may require a large collective application to check the rate of descent. This collective application will also require additional left pedal inputs. In all of these cases, if operating with narrow power margins, rotor RPM may droop. High density altitude decreases the effectiveness of a given tail rotor angle-of-attack. This means that more tail rotor pitch must be applied to provide the proper amount of anti-torque for a given collective setting.
A right crosswind requires application of left pedal (requiring more engine power) to counteract the wind-vaning. During marginal power (or maximum available) situations, large left pedal application may result in a droop of the main rotor. The tail rotor turns at a much faster rate than the main rotor, so a slight reduction in main rotor speed will greatly reduce the speed of the tail rotor. As the tail rotor slows, the thrust produced decreases. If more left pedal is applied (to increase the tail rotor angle-of-attack to provide the required thrust) the situation will continue to deteriorate. In extreme cases, low tail rotor RPM and high tail rotor pitch (angle-of-attack) can exceed the critical angle, resulting in a tail rotor stall. If possible, crews should avoid landing with obstacles on the left side of the aircraft during marginal power conditions. This will allow an unobstructed right turn in the event tail rotor effectiveness is lost.
A left crosswind requires the application of right pedal (requiring less engine power) to counteract the wind-vaning. While this may be an aid in marginal power (or maximum available) situations, extreme wind from the left can cause the tail rotor to work in its own down wash, decreasing its effectiveness. This airflow pattern can even develop into a vortex ring state (like the main rotor during settling with power). Also, when the winds are approximately 10 to 20 knots from 9 to 11 o'clock (relative to the aircraft nose), the vortices shed from the main rotor blades may impinge on the tail rotor. This disrupts the airflow over the tail rotor and may reduce tail rotor effectiveness.
H-60 helicopters are rigged with collective to yaw coupling so that increases in collective will automatically increase tail rotor pitch to compensate for the main rotor torque. At gross weights lower than the design weight of 16,825 pounds, the mixing will overcompensate for the increase in collective and at higher gross weights, the mixing will not provide enough compensation.
If you encounter Loss of Tail Rotor Effectiveness (LTE), consider the following:
(1) Reduce power.
(2) Allow the aircraft to align into the wind.
(3) Increase forward airspeed.
If you have adequate maneuvering area, the old adage -- "the remedy for LTE is ETL" is a good one.
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