Exercise 10 - Transitions

Page 13

Aim:- To teach how to achieve a transition from the hover to a climb, and from a descent to the hover Airmanship:- Check T's & P's, Fuel, Warning Lights, Carb. Heat, Hatches & Harnesses (H's & H's), Surface Wind Direction & Velocity Aircraft Limits (approx. 24½" 5 min rating) RT Call   RPM top ½ green, 5 ft Hover - Pre-Transition Checks (T’s & P’s, Warning lights, Fuel, Carb. Heat, H’s & H’s)   Look out turn - Good all around both behind and above   RT Call - “Helicopter AL Circuit Right”   Choose a ‘reference point’ ahead to help maintain heading Assume Light Wind Conditions   Select an accelerative attitude - Cyclic gently forward (forward tilt of thrust vector will cause aircraft to sink - be ready with collective to prevent any sink)   Ground Effect will be lost around 5 Kts - 10 Kts - be ready with collective to prevent any sink   At about 12 Kts - 15 Kts start to gain Effective Translational Lift - Cyclic forward to prevent climb   With onset of ETL both the main and tail rotor will become more efficient - RPM will increase slightly - adjust with throttle if necessary   As speed increases adjust for flapback with progressive forward cyclic   Maintain aircraft heading with pedal   Maintain take off profile (accelerative attitude) and wings level (aircraft tends to roll right - inflow roll) with cyclic   At 45 Kts to 50 Kts select and establish 60 Kts attitude with enough MP to maintain climb Height - Velocity Diagram The height velocity graph, sometimes referred to as the ‘dead mans curve’ or ‘avoid curve’, represents areas of helicopter operation, in relation to height and speed, which should be avoided. Operation in the shaded area should be avoided whenever possible because it is highly unlikely that a successful landing could be executed in the event of power failure. Pilots must be familiar with the height velocity curve for the particular helicopter being flown in order that manoeuvres, such as transitions, can be executed within the ‘safe’ area as defined by the graph. The smaller cross sectional area to the left of the diagram is representative of a sea level density altitude with a helicopter weight of 1370lbs. It shows, for example, that operation with zero air speed between the heights of about 8ft up to 400ft agl are likely to end in a crash in the event of power failure. Likewise a power failure at a height of 200ft agl with an air speed of 30kts air speed are also likely to end in a crash. This is basically due to the fact that the height is not available in which to regain the necessary airspeed and rotor RPM in order to achieve a successful autorotative landing. The larger diagonally shaded area is representative of a 7000ft density altitude with a helicopter weight of 1300lbs. The smaller diagonally shaded area to the bottom right of the diagram indicates that high speeds close to the ground are also to be avoided. It is interesting to note that with 60Kts airspeed and a height above 25ft the aircraft remains outside of the avoid areas. Transitions from Descent to the Hover   Remember MP below 18" - Apply full carb. heat - Check and adjust RPM if necessary   At the appropriate approach angle set 15" MP - ready with right pedal - Select a 60 Kts attitude (as discussed above this speed keeps the aircraft out of the avoid curve)   Approach at 60 Kts - maintain a constant attitude with cyclic   Maintain ‘Sight Picture’ (constant angle of descent) with collective   At approximately 200ft agl return carb. heat to ‘normal’ position - check and adjust RPM if necessary   At ‘Deceleration Point’ select de-accelerative attitude to reduce approach speed   Co-ordinate with collective to prevent any ‘ballooning’ and right pedal to prevent any yaw   Be prepared for loss of translational lift - ready with collective and left pedal - forward cyclic on application of power to avoid nose pitching up   At zero ground speed select hover attitude (5 ft hover) with cyclic - maintain height with collective - left pedal - check/adjust RPM Collective controls angle of approach On the descent transition the aim is to maintain a constant angle of approach. The airspeed is being maintained at 60kts with the cyclic, the collective therefore is used to maintain this constant approach angle. If the aircraft is too high the aiming point will be moving down the screen, by lowering the collective lever the aircraft can descend back onto the ‘correct approach profile’. The necessary power can then be can be restored in order to maintain the correct approach angle. Likewise if the aircraft is too low the aiming point will be moving up the screen. Power can therefore be increased and then restored on regaining the correct approach angle. The deceleration point The ‘right time’ to start slowing down (deceleration point) is going to vary subject to wind strength; ie in strong winds deceleration in order to achieve a zero ground speed would start later in the approach than in a light wind. In general however, a 60Kt attitude should be maintained until at least 50ft agl. The reduction of speed should be a gradual process initially lowering the lever to avoid ballooning on application of aft cyclic. Site picture - normal approach 1. 3. 5.   2. 4. Too low approach 1. 2. 3.   Too high approach 1. 2. 3. Discussion Points   Sight profile, perspective of landing site   Various wind conditions - ground cushion, ETL   Effects of ETL on power requirements Air Exercises   Hover to Flap back & Translational Lift Demo   Transition from Hover to Climb   Transition from Approach to Hover

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