EXERCISE 11 EMERGENCIES

Transcription

1 EXERCISE 11 EMERGENCIES TRAINING OBJECTIVES: 1. Examine the causes of Vortex Ring State & recovery -Whilst in Steep Approach -Whilst flaring -Whilst in a quickstop -Whilst in a downwind approach 2. Examine the causes of Retreating Blade Stall & -Whilst in high-speed flight recovery -Whilst in steep turns -Whilst in turbulence 3. Examine the causes of Mast Bumping & recovery -Following an abrupt push over 4. Examine the causes of Ground Resonance & recovery -During start up & shutdown 5. Display AIRMANSHIP INTRODUCTION: A competent pilot should have a thorough understanding of the different types of emergencies that can occur and the course of action required to land the helicopter safely. Bare in mind, this may vary for different types of helicopters, so it is essential to familiarize yourself with the emergency section of the helicopter flight manual. Of the four objectives above, the only one we will look at in flight is Vortex Ring State. Retreating Blade Stall, Mast Bumping and Ground Resonance will be examined in detail in the classroom. V 2 Helicopters Flying School Exercise 11 Page No. 1

2 1. VORTEX RING STATE: DEFINITION: Also referred to as "Settling with Power". This is a flight situation where there is a high Rate of Descent, under power, and a low airspeed. Resulting in a increase in recirculation at blade tips, and stalling at the blade roots, causing a dangerously high rate of descent to develop. ROD Flow ROD Flow Slow Rate of Descent, causing onset of Vortex Ring State Recirculation Recirculation Stall ROD Flow ROD Flow Established Vortex Ring State V 2 Helicopters Flying School Exercise 11 Page No. 2

3 ROOT SECTION: As Rate of Descent increases a point is reached where it is equal to or greater than the smaller induced flow. Subsequently the angle of attack increases and the blade stalls due to the small relative airflow. OUTBOARD SECTION: Due to the increased recirculation, the induced flow increases and subsequently the angle of attack decreases. CONDITIONS: SYMPTOMS: RECOVERY: 1. Low or nil airspeed (Less than 30 kts) 2. Power applied - high 3. Rate of Descent greater than 300ft/min 1. Aircraft vibration and stick shake. 2. Random yawing, rolling and pitching 3. Cyclic stick less effective 1. Lower collective 2. Forward cyclic to increase airspeed 3. If height permits, enter autorotation BEWARE: All of these recovery actions require altitude. FLIGHT CONDITIONS LIKELY TO LEAD TO VORTEX RING STATE: 1. A steep approach 2. Loss of height during a harsh flare 3. Executing a quick-stop downwind 4. Downwind approach 5. Turning downwind at slow speed allowing helicopter to sink Flight with high 'All Up Weight" (AUW), and high-density altitude will encourage Vortex Ring State to occur at an earlier stage. V 2 Helicopters Flying School Exercise 11 Page No. 3

4 RETREATING BLADE STALL DEFINITION: Due to airflow reversal on the retreating blade, the root section experiences a loss of lift as speed increases. The remaining section of the blade has to compensate for this loss of rotor thrust by flapping down and increasing the angle of attack. Eventually as speed increases and angle of attack increases, the blade stalls. Due to gyroscopic precession, as the blade flaps down, the effect will be felt 90 degrees later at the rear of the disc. Therefore the nose pitches up and helicopter rolls laterally. This is known as Retreating Blade Stall. Forward flight at 30 knots Reverse flow area 30kt 30kt Reverse flow. Within the striped reverse-flow area, the airflow past the airfoil due to aircraft speed is higher than the speed due to blade rotation. V 2 Helicopters Flying School Exercise 11 Page No. 4

5 Stall Region Reverse flow area Retreating Blade Stall CONDITIONS: 1. High Speed Flight 2. Maneuvers involving high load factors such as steep turns, pulling out from a high-speed dive etc. 3. Use of excessive or very abrupt control movements 4. Flight in turbulence Note: Flight with a high AUW and a high density altitude will encourage retreating blade stall to occur at an earlier stage. V 2 Helicopters Flying School Exercise 11 Page No. 5

6 SYMPTOMS: 1. Rotor Roughness and a vibration felt throughout the aircraft 2. Aircraft's nose pitches up, and is followed by a roll, usually to the retreating side. RECOVERY: 1. Lower collective to reduce angles of attack 2. Apply aft cyclic if necessary to slow the aircraft Note: To apply aft cyclic only when recovering will cause the angle of attack to increase, due to flare effect and subsequently the stalled situation becomes worse. To apply forward cyclic as the nose pitches up, produces a pitch angle increase on the retreating side. Since the stalled condition prevents flapping to equality (upwards), the greater the pitch angles will place the blade in a deeper stalled situation. V 2 Helicopters Flying School Exercise 11 Page No. 6

7 MAST BUMPING: DEFINITION: Due to excessive blade flapping, caused by incorrect flying techniques, the main rotor hub comes in contact with the main rotor mast. This phenomenon, peculiar to two bladed rotor systems, which use the teetering hinge, can cause deformity, or even shear the main rotor mast. Flapping amplitude is increased when the following conditions apply: 1. Gusty wind conditions 2. Sudden attitude changes through abrupt cyclic inputs 3. Sideways flight at or near maximum allowable speed 4. Flight under low, nil or negative 'G' maneuvers. Of all the above situations the negative 'G' maneuvers are the most likely to cause mast bumping. Addition to induced flow Cyclic pushed forward Insignificant or nil total rotor thrust Total Rotor Thrust Firm application of forward cyclic can cause low, zero or negative-g and a severe reduction in total rotor thrust V 2 Helicopters Flying School Exercise 11 Page No. 7

8 CONDITIONS: SYMPTOMS: RECOVERY: 1. An abrupt pushover (forward cyclic) at the end of a zoom climb 2. The situation can be made worse if collective is lowered at the time 1. Weightlessness feeling 2. Helicopter rolls to the right (counter clockwise rotating main rotor) 1. Gently apply aft cyclic to load the disc and restore TRT 2. Then apply left cyclic to level helicopter UNDER NO CIRCUMSTANCES APPLY LEFT CYCLIC FIRST TO RECOVERY. BEST RECOVERY IS TO AVOID THE SITUATION V 2 Helicopters Flying School Exercise 11 Page No. 8

9 GROUND RESONANCE: DEFINITION: An oscillation of increasing amplitude resulting from a self-excited vibration in the rotor system, coupled with a fuselage vibration when the helicopter is in contact with the ground. If uncorrected destruction of the helicopter occurs. CONDITIONS: 1. Rotor Head Vibration caused by -unbalanced blades -incorrect tracking -faulty drag dampers 2. Fuselage Vibration caused by -Hard or rough landing aggravated by rough landing -Running take-off or landing over rough ground -Uneven oleo or tyre pressures Amplitude Resultant Vibration Rotor head vibration Fuselage vibration Frequency Rotor Head Vibration + Fuselage Vibration = Resultant Vibration V 2 Helicopters Flying School Exercise 11 Page No. 9

10 RECOVERY: 1. If RPM is within operating range, lift helicopter into the hover & try to land on different surface. 2. If RPM is not in the operating range, shut engine down and apply rotor brake, if installed. AIRMANSHIP: 1. LOOKOUT - obstructions & surface 2. WIND - Know the wind at all times 3. PREVENTION - prevention is better than a cure COMPETENCY STANDARD The student will be able to recognize the symptoms for the emergencies and hazards that can be encountered in helicopters. The student will know the recovery actions, and where the simulation allows, be able to recovery the helicopter from the nominated emergency. LEARNING OUTCOMES As it is unsafe to simulate some of the emergencies the student would only be able to discuss the emergency rather than demonstrate an ability to fly the aircraft to conduct the emergency. For Vortex Ring State, the student will be able to satisfactorily recognize and complete the actions for this emergency. V 2 Helicopters Flying School Exercise 11 Page No. 10