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Aim:-
To teach the effects of the controls in forward flight
Airmanship:-
(Awareness & Safety Sense)
- Good
 - (Do not stare at the instruments.) It is the responsibility of the pilot to avoid other aircraft and objects - not that of the ATC
- Location - Position in relation to the airfield
- Handover of controls
Instructor to student “You have control” - student “I have control”
Instructor to student “I have control” - student “You have control”
Controls
The Cyclic Stick
 Controls Disc Attitude and hence Fuselarge Attitude
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Fore & Aft movement controls Airspeed
Stick forward lowers nose - Increases Airspeed - Loss of Height
Stick aft raises nose - Decreases Airspeed - Gain in Height
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Lateral movement controls direction Left or Right (Causes roll and turn in the same direction) |
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The ‘teetering’ of the T bar enables transfer of control of the cyclic between the left and right seat (instructor and the student). This ‘teetering’ movement has no effect whatsoever on the control of the helicopter
Properties of Cyclic:-
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Very sensitive |
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Not self centering |
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Lag between input & effect |
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Requires some right and forward pressure to maintain cruise flight - (can be lessened with use of the trim knob). - Fine adjustment of the ‘Cyclic Trim’ may be achieved by use of the adjustment knob located on the left side panel of the console. NB. ‘Cyclic Friction’ should only normally be used for holding the cyclic in a central position whilst the aircraft is on the ground |
Stability
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Helicopters are naturally unstable and require continuous input to hold them steady especially in the hover, which basically means Never Take Hands Off The Controls!
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The helicopter is said to be Statically Stable and Dynamically Unstable
Statically Stable
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If, when disturbed, a body tends to return to its original position it is said to be statically stable |
Dynamically Unstable
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If, when returning to its original position, a disturbed body starts to oscillate with increasing amplitude through this point of origin then it is said to be dynamically unstable
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Collective Lever
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‘Collectively’ increases or decreases the pitch of the main rotor blades and therefore controls total rotor thrust i.e. controls height. Via the correlator and governor it also controls engine power
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Collective Lever  Height MP RPM  Yaw 
Collective Lever  Height MP RPM Yaw 
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As pitch is applied the drag generated by the rotor blades is increased. In order to maintain a constant RPM (stop the blades slowing down) more power is required and this is primarily achieved on the R22 by a device known as the correlator, which is basically a link between the collective and the carburettor. As the collective is raised the correlator opens the throttle
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allowing more fuel and air mix (charge) into the engine and more power to be produced. Governor systems (see later) will also maintain a constant RPM by increasing/decreasing the engine power as necessary
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Properties of the Collective:-
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controls lift being generated by the main rotors - Controls height |
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Via the correlator and governor controls the engine power (MP) |
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Feel is proportional to the friction applied |
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Counter-sprung to hold its position if hand is removed |
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As with the cyclic collective friction should normally only be applied on the ground |
Twist Grip Throttle
Controls Engine & Rotor RPM
(affects power (MP) but does not control it - because of the correlator
and governor the collective is the primary control of power)
Increase Throttle RPM Manifold Pressure Yaw
Decrease Throttle RPM Manifold Pressure Yaw
Properties of Throttle
Very, Very Sensitive !!!
Controls RPM
RPM Governor
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The purpose of the governor is to automatically maintain the RPM at its optimum operating range of around 104%. This is achieved by use of electrical sensors situated within the engine’s right magneto which detect any variation in RPM. An electrical motor connected to the throttle linkage will automatically increase or decrease the throttle as necessary in order to maintain the RPM at its correct operating range.
A clutch system within the throttle twist grip allows the pilot to manually override the governor by physically twisting the throttle in the desired direction, under normal circumstances this would only be necessary in the event of a governor malfunction.
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The governor may be turned on or off as required with a toggle switch located at the end of the collective lever.
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Turning it off will not cause any initial change to RPM i.e. the throttle will remain in its current position. Turning it on will cause changes to the RPM only if not already positioned at its optimum setting of 104%. (Note:- the governor only operates above 80% ERPM).
It is necessary to have the governor switched off during start up and shutdown when the RPM should be maintained between 75% and 80% in order to either let the engine warm up or cool down. It should be noted that flight is prohibited with the governor selected off except for in-flight systems malfunction or emergency procedure training.
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Torque Reaction
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Newton’s 3rd Law - for every action there is an equal and opposite reaction
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Raise Collective or open Throttle - Increase MP- Yaw Right
Lower Collective or close Throttle - Decrease MP - Yaw Left
Yaw Pedals
Control Tail Rotor Thrust
Left Pedal - nose yaws left - tail rotor pulls to the right
Right Pedal - nose yaws right - tail rotor pushes to the left
| Governor Off |
Effect on RPM |
Effect on Power |
| Left pedal increases pitch on tail rotor |
Slight decrease in RPM |
Remains constant |
| Right pedal decreases pitch on tail rotor |
Slight increase in RPM |
Remains constant |
| Governor On |
Effect on RPM |
Effect on Power |
| Left pedal increases pitch on tail rotor |
Governor maintains RPM (Increases Throttle) |
Increases |
| Right pedal decreases pitch on tail rotor |
Governor maintains RPM (Decreases Throttle) |
Decreases |
Properties of Pedals:-
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Light & sensitive |
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Yaw in natural sense |
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Used for direction control in hover |
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Used to maintain aircraft in balance during forward flight (Yaw string / Balance ball) |
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Once input is applied it must be held |
Effect of Airspeed On RPM
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In ‘still’ air a relative wind is produced by the rotor blades due to their horizontal rotational movement through the air. With pitch applied the effect is to change this still air into a column of descending air. This descending air is known as ‘Induced flow’ and is felt as downwash beneath the helicopter.
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| Hover out of ground effect |
In the hover the large vertical induced flow alters the direction of the blades relative wind and reduces its angle of attack. This means a greater collective pitch setting is required in order to maintain the necessary lift.
As air speed increases turbulence and vortices developed by the rotors are left behind and a greater horizontal mass of airflow becomes available to the rotor system. This ‘more horizontal’ airflow reduces the blades induced flow component thereby increasing the angle of attack and overall rotor efficiency.
Just as the main rotor system becomes more efficient with increase of airspeed so to does the tail rotor requiring a ‘lesser’ pitch setting to compensate for engine torque. The increased air flow over the vertical tail fin (due to forward air speed) also assists in maintaining the helicopters direction (weathercocking) and again reduces the overall power requirements of the tail rotor.
This increase in efficiency with increase of air speed is known as translational lift and exists throughout the entire air speed range of the aircraft. It is most noticeable at around 10 kts to 15 kts airspeed (referred to as ‘effective translational lift’ - ETL) but tends to be ‘cancelled out’ at higher airspeeds due to the ‘parasite’ drag of the aircraft. With a constant power setting (MP) an RPM increase of around 5% can be observed between the airspeed of 40 kts and 90 kts which means in an ungoverned aircraft the throttle may need to be reduced slightly with increase in airspeed in order to avoid an overspeed.
| Governor Off |
Effect on RPM |
Effect on Power |
| Increase of airspeed |
Increase in RPM |
Remains constant |
| Decrease of airspeed |
Decrease in RPM |
Remains constant |
| Governor On |
Effect on RPM |
Effect on Power |
| Increase of airspeed |
Governor maintains RPM by decreasing throttle |
Decreases |
| Decrease of airspeed |
Governor maintains RPM by increasing throttle |
Increases |
Effect of Disc Loading on RPM
Disc loading is a function of the weight of the helicopter and the centrifugal forces acting on the rotors by virtue of their rotational speed (RRPM). Whilst on the ground, with no collective pitch applied, the centrifugal forces acting upon the rotor blades will tend to maintain them in a horizontal position. On application of collective pitch the rotor blades will develop lift and rise up. The combined effect of centrifugal and lift forces will cause the rotor blades to assume a conical path known as coning.
The greater the weight of the helicopter the greater is the lift required to support this load and the greater the coning angle (horizontal angle between the blade root and the blade tip) will be.
When moving in a straight line at a constant altitude and airspeed the load (helicopter weight) on the rotor blades remains constant. However when assuming a curved flight path (flare or steep turn) the additional ‘G-forces’, produced by these manoeuvres, increase the effective weight of the aircraft. This in turn increases the overall loading on the blades. The tighter the curved flight path or the tighter the flare the greater the loading on the blades will be.
This increase in loading will cause the blades to ‘cone’ up about their coning hinges, and in turn cause the centre of gravity of the blades to move in towards the blade root. As the blades centre of gravity changes so too will the RPM - increasing with turn and flare, and likewise decreasing when reassuming straight and level flight. - Analogous to the skater who spins faster when she brings her arms in.
Excessive coning should be avoided because it places undesirable stresses on the blades and reduces total lift because of a decreased total disc area.
| Governor Off |
Effect on RPM |
Effect on Power |
| Increase in disk loading |
Increase in RPM |
Remains constant |
| Decrease in disk loading |
Decrease in RPM |
Remains constant |
| Governor On |
Effect on RPM |
Effect on Power |
| Increase in disk loading |
Governor maintains RPM by decreasing throttle |
Decreases |
| Decrease in disk loading |
Governor maintains RPM by increasing throttle |
Increases |
Further Effects of the Collective - Autorotation
When lowered fully down:- (Autorotative State)
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Needles split
Engine RPM drops (throttle is closed by the correlator)
Rotor RPM stays in operating range
Low MP (throttle is closed by the correlator)
Large yaw to the left
Nose will drop
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Discussion Points
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Mixture Control |
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Carburettor Air Temperature Gauge & Control |
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Rotor Brake |
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Governor |
Air Exercises
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Cyclci Stick |
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Cyclic Trim |
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Collective Lever |
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Carburettor Heat |
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Twist Grip Throttle |
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Effects of Disc Loading - RPM Increase |
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Use of Governor |
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Effects of Airspeed - RPM Increase |
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Yaw Pedals |
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Further Effect of Collective Lever - Autorotation |
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