3. Operating and Flight Characteristics

Question 1

Loss of tailrotor effectiveness

Definition

Answer 1

LTE is the occurrence of an uncommanded and rapid right yaw rate which does not subside of its own accord and which, if not quickly reacted to, can result in loss of aircraft control.

Question 2

Loss of tailrotor effectiveness

Weathercock Stability

Answer 2

• 120-240 degrees
• Weathervane the aircraft into the relative wind.
• Tendency to make a slow, uncommanded yaw to either the left or right
• Right yaw rate will increase unless arrested by the pilot and can develop into a LTE condition
• Requires immediate correction.

Question 3

Loss of tailrotor effectiveness

Vortex Ring State

Answer 3

• 210-330 degrees
• Will cause a vortex ring state to develop around the tail rotor , which in turn causes tail rotor thrust variations.
• The helicopter exhibits a tendency to make uncommanded pitch, roll, and yaw excursions.
• The subsequent aircraft reactions require multiple pedal, cyclic, and collective inputs by the pilot.
• Maintaining a precise heading in this region will be impossible.
• Pilot workload in this region will be high; therefore, the pilot must concentrate fully on flying the aircraft and not allow a right yaw rate to build.

Question 4

Loss of tailrotor effectiveness

Disc Vortex

Answer 4

• 280-330 degrees
• Winds within this region and between 10 to 30 knots will cause the main rotor tip vortices to be directed onto the tail rotor.
• The effect of this main rotor vortex is to cause the tail rotor to operate in an extremely turbulent environment.
• The helicopter will exhibit a tendency to make a sudden, uncommanded right yaw which, if uncorrected, will develop into a spin.
• When operating in this region, the pilot must anticipate the sudden demand for left pedal inputs.

Question 5

Loss of tailrotor effectiveness

Other factors

Answer 5

Other factors which may be present can significantly influence the severity of the onset of LTE:

Gross weight and density altitude (PPC - TQ Avail.)

• An increase will decrease the power margin between the maximum available and power required to hover. The pilot should conduct low level, low airspeed missions with only minimum essential personnel and equipment on board.

Low indicated airspeed

• At airspeeds below ETL, the tail rotor is required to produce nearly 100 percent of the directional control. If the required amount of tail rotor thrust is not available, for whatever reason, the aircraft will yaw to the right.

Power droop

• A rapid power application may cause a transient power droop to occur. Any decrease in main rotor RPM will cause a corresponding decrease in tail rotor thrust. The pilot must anticipate this and apply additional left pedal to counter the main rotor torque. All power demands should be made as smoothly as possible to minimize the effect of the power droop.

The pilot should exercise caution when executing right turns under conditions conducive to LTE.

Question 6

Tunderstorms

Answer 6

To minimize the effects of thunderstorms encountered in flight, perform the following: (SPLAT)

• Check that all occupants are seated with Seat belts and harnesses tightened.
• PITOT HTR switch(es) - ON.
• Interior Lights - Adjust to full bright at night to minimize blinding effect of lightning.
• Avionics - Reduce volume on any equipment affected by static.
• Adjust Torque to a value corresponding to maximum endurance airspeed.

In the storm:

1. Maintain a level attitude and constant power setting. Airspeed fluctuations should be expected and disregarded.
2. Maintain original heading, turning only when necessary.
3. The altimeter is unreliable, due to differential barometric pressures within the storm. An indicated gain or loss of several hundred feet is not uncommon and should be allowed for in determining minimum safe altitude.

Question 7

Lightning general

Answer 7

• Although the possibility of a lightning strike is remote, static tests have been conducted to determine lightning strike effects on rotors.
• May damage the helicopter rotor.
• The degree of damage will depend on the magnitude of the charge and the point of contact.
• Catastrophic structural failure is not anticipated.
• However, lightning damage to hub bearings, blade aft section, trim tabs, and blade tips was demonstrated.
• Also, adhesive bond separations occurred between the blade spar and the aft section between the spar and leading edge abrasion strip.
• Such damage can aerodynamically produce severe structural vibration and serious control problems which, if prolonged, could endanger the helicopter and crew.

Question 8

Lightning

Answer 8

Avoid Flight in or near thunderstorms, especially in areas of observed or anticipated lightning discharges.

NOTE

Abnormal operating noises almost always accompany rotor damage, but loudness or pitch is not valid indications of the degree of damage sustained.

If lightning strike occurs, or is expected, the following precautions are recommended to minimize further risk.

• Chapter 8:
  
  • Reduce airspeed as much as practical to maintain safe flight.
  • Avoid abrupt control inputs.
• Chapter 9
  
  • Land as soon as possible.
  • Emer Shutdown - Accomplish After Landing

Question 9

Spike knock

Answer 9

Spike knock occurs when the round pin in the drag-pin fitting contacts the side of the square hole of the pylon stop, which is mounted to the roof.

The following factors can cause spike knock: ALLL (or ALL-G)

• Poor execution of an Autorotational landing
• Low rotor RPM,
• Extreme asymmetric Loading,
• Low “G” maneuvers below +.5 Gs.

Spike knock will be more prevalent during zero ground run autorotational landings than for sliding autorotational landings and running landings.

Spike knock in itself is not hazardous but is an indicator of a condition that could be hazardous. If spike knock is encountered, an entry must be made on the DA Form 2408-13-1