What happens if a helicopter tail rotor fails?
If the tail rotor fails in flight, engine torque can no longer be countered by the tail rotor, and uncontrolled spinning of the aircraft is a possibility. Most manufacturers call for an immediate autorotation. Some call for a running landing, instead.
What causes loss of tail rotor effectiveness?
Loss of tail-rotor effectiveness (LTE) occurs when the tail rotor of a helicopter is exposed to wind forces that prevent it from carrying out its function—that of cancelling the torque of the engine and transmission. Any low-airspeed high-power environment provides an opportunity for it to occur.
How is dissymmetry of lift correct?
Dissymmetry of lift is countered by reducing the angle of attack of the advancing blade and increasing the angle of attack of the retreating blade. This is done by blade flapping and cycling feathering. Blade flapping is the primary means of countering dissymmetry of lift.
What corrective action can a pilot take to prevent retreating blade stall?
At the onset of blade stall vibration, the pilot should take the following corrective measures: 1 – Reduce collective pitch. 2 – Increase rotor RPM. 3 – Reduce forward airspeed.
Can a helicopter recover from a tail rotor failure?
It is perfectly possible to recover from a tail rotor failure. There are some flight regimes that might lead to a crash with all but the best pilot and some luck. A tail rotor failure in cruise should be survivable, especially if you can find something hard to land on.
Can helicopters fly without tail rotor?
Without the tail rotor or other anti-torque mechanisms (e.g. NOTAR), the helicopter would be constantly spinning in the opposite direction of the main rotor when flying.
What is blade flapping?
Blade Flapping is the up and down movement of a rotor blade, which, in conjunction with cyclic feathering, causes Dissymmetry of Lift to be eliminated.
What causes dissymmetry of lift?
Dissymmetry of lift is the difference in lift that exists between the advancing half of the rotor disk and the retreating half. It is caused by the fact that in directional flight the aircraft relative wind is added to the rotational relative wind on the advancing blade, and subtracted on the retreating blade.
What are the three warning signs of an impending retreating blade stall?
The major warnings of approaching retreating blade stall conditions are: Abnormal vibration….When operating at high forward airspeeds, the following conditions are most likely to produce blade stall:
- High blade loading (high gross weight)
- Low rotor RPM.
- High density altitude.
- Steep or abrupt turns.
- Turbulent air.
How can you overcome or recover from a retreating blade stall?
Recovery involves lowering the collective pitch, relieving forward pressure on the cyclic or more commonly, both. Either of these control movements should restore the proper attached airflow over the retreating blade thus generating lift again.
What causes tail rotor failure?
The tail rotor can fail if the rotor stops turning or the pitch change mechanism stops functioning. The loss of tail rotor drive is an emergency which might require the lowering of the collective to maintain control.
Can you land a helicopter with engine failure?
Actually, helicopters have a built-in mechanical control called the collective pitch lever that allows them to descend slowly and land even if the engine dies.
What causes tail-rotor failure?
How helicopter recover from LTE?
LTE RECOVERY is initiated by increasing airspeed, using the vertical stabilizer to reduce yaw or, if uncorrectable by application of speed or tail-rotor thrust, entry into autorotation.
What is flapping and feathering?
Flapping, the vertical up/down movement of the blades, is not directly controlled. What a pilot controls is the blade feathering or pitch angle. Increasing feathering / pitch generally increases the aerodynamic forces on the blades, which changes the flapping.
What is feathering hinge?
A feathering hinge is used to change the pitch of each blade. A flapping hinge allows each blade to move up and down to compensate for dissymmetry of lift. Blades are able to move fore and aft or lead-lag, (called hunting) by use of a drag hinge.
What causes blade flapping?
The decrease in the angle of attack decreases the lift on the blade. The retreating blade experiences a reduced velocity of airflow and reduced lift, and flaps down. By flapping down, the retreating blade ends up with an increased angle of attack and an increase in lift.
What causes retreating blade stall?
High weight, low rotor r.p.m., high density altitude, turbulence and/or steep, abrupt turns are all conducive to retreating blade stall at high forward airspeeds as they increase the blade pitch to generate more thrust and hence increase the angle of attack.
How do you fix a retreating blade stall?
Flight performance during a retreating blade stall Recovery involves lowering the collective pitch, relieving forward pressure on the cyclic or more commonly, both. Either of these control movements should restore the proper attached airflow over the retreating blade thus generating lift again.
What is helicopter Vne?
The Vne, or velocity to never exceed, can be based on many things. Most often, it is based on an aerodynamic limit, such as the onset of retreating blade stall, or a structural limit, such as excessively high loads imposed on the rotor mast/hub.
Can a helicopter land without a tail rotor?
The most common use of autorotation in helicopters is to safely land the aircraft in the event of an engine failure or tail-rotor failure. It is a common emergency procedure taught to helicopter pilots as part of their training.