Exercise 5 - Attitude and Power Changes

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Aim:- To teach how to change power and to show the relationship of attitude to airspeed. Airmanship:- Good Location T's & P's, Fuel, Warning Lights Attitude & Airspeed Changes To Accelerate from 60 Kts Airspeed to 80 Kts Airspeedna   Select Accelerative Attitude (Cyclic Forward)   Hold Accelerative Attitude - Correct for Flapback (more forward cyclic)   At 80 Kts Adjust attitude to maintain 80 Kts Select - Hold - Adjust Flapback Flapback is caused by a change in relative airflow between the advancing and retreating blades. It will occur whenever there is a change in airspeed. Assume forward flight - (flapback occurs in any flight direction During forward flight the advancing blade will have a greater relative airspeed than the retreating blade, it will therefore generate more lift (for any given angle of attack an increase in airspeed will produce an increase in lift) and begin to rise i.e. it flaps up - the highest point being in the direction of travel of the aircraft. Likewise the retreating blade due to its reduction in airspeed will generate less lift and begin to fall i.e. it flaps down - its lowest point being 180º from the highest point. The fuselage follows this disc attitude and is said to ‘flap back’. This ‘Dissymmetry of Lift’ between the advancing and retreating blades, if not somehow corrected, would cause the helicopter to roll over to the left. Blade flapping about the teetering hinge and cyclic feathering compensate for this ‘Dissymmetry in Lift’ between the advancing and retreating blades. The teetering hinge of the R22 allows the blades to ‘flap’ up and down as a pair. As the advancing blade ‘Flaps up’ the angle of attack of the blade decreases due to the relative air flow changing from a mostly horizontal to a more downward direction. Likewise as the retreating blade ‘Flaps down’ the angle of attack of the blade is increased due to the relative air flow changing from a mostly horizontal to a more upward direction. The change in angle of attack of each blade brought about by this ‘flapping’ action tends to equalise the lift over the two halves of the rotor disc. The cyclic pitch control is designed in such a way that movement of the cyclic, in any direction, will decrease pitch (and therefore lift) on the blade advancing in that direction and increase pitch (and therefore lift) on the blade retreating in the opposite direction. i.e. forward movement of the cyclic will decrease pitch on the advancing blade and increase pitch on the retreating blade. Likewise aft movement of the cyclic will increase pitch on the advancing blade and decrease pitch on the retreating blade. This changing of cyclic pitch during each revolution of the rotor blades is known as Cyclic feathering. Whilst accelerating the effects of flapback, on their onset, are compensated for by progressively moving the cyclic forward in order to maintain the desired disk and hence fuselage attitude/airspeed. Similarly whilst de-accelerating the effects of flap forward, on their onset, will be compensated for by progressively move the cyclic stick aft. Attitude Changes Attitude at 80 Kts is not a great deal different to that at 60 Kts. (This is due to the helicopter’s horizontal stabiliser on the tail cone which maintains the fuselage attitude relatively constant over a large part of the speed range). After a speed increase the cyclic position will be further forward due to a large disc attitude change, but the nose attitude will not be very different once the speed has stabilised due to the downward force generated by the tail fin. (Large speed change - Large cyclic displacement - Small attitude change) Attitude & Airspeed Changes To decrease Speed from 80 Kts back to 60 Kts   Select Decelerative attitude (Cyclic back)   Hold Decelerative attitude (Correct for flap forward)   At 60 Kts adjust attitude to maintain 60 Kts Select - Hold - Adjust Power Changes (Lever Throttle & Pedals @ Constant RPM) Full carburettor heat should be applied when lowering the MP below 18". The addition of the warmer air into the engine will cause a slight reduction in power and can cause an RPM decay of between 2% & 3%. The correlator, being a mechanical device, does not cater for this condition and it is likely that the throttle will need to be increased slightly in order to maintain the RPM within the green operating area. Likewise on returning the carburettor heat to its ‘normal’ condition the RPM will rise and it may therefore be necessary to decrease the throttle slightly It should also be noted that the correlator will not maintain perfect RPM over the entire power range and this is particularly noticeable whilst in the climb (60kts) using power ranges above 21" MP. When operating between 21" MP and maximum power (yellow arc on the manifold pressure gage) the throttle will need to be increased slightly with increase of power in order to maintain RPM, and similarly reduced slightly on reduction of power. 20" MP to 13" MP with Constant RPM Remember Carb Heat Below 18" 13" MP to 20" MP with Constant RPM RPM Changes with Constant MP To increase RPM lead with throttle   RPM middle of green with 20" MP   Gently open throttle to 104% - MP will increase   Lower collective & reset 20" MP To decrease RPM lead with throttle   RPM middle of green with 20" MP   Gently reduce throttle to 97% - MP will decrease   Raise collective & reset 20" MP Discussion Points   RPM Limits 97% - 104%   Engine Limits - Approx. 23½" MP (MCP)   Carb heat below 18"MP - RPM decrease Air Exercises   Attitude Changes @ Constant Power   Power Changes @ Constant RPM   RPM Changes @ Constant RPM

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