User manual

DodoSim 206 FSX User Manual

Page 67

In forward flight, the advancing rotor blade, (the blade travelling towards the direction of the helicopter’s

travel), meets the air at a greater speed that the retreating blade, (the one travelling away from the

direction of the helicopter’s travel), and consequently generates more lift. The “dissymmetry of lift”

causes the helicopter to tend to roll towards the left. The pilot must apply greater right cyclic inputs to

maintain a level attitude as airspeed increases.

4.1.4.3 Transition from Forward Flight into the Hover

To bring the helicopter to a hover from forward flight, rearward cyclic input must be applied to slow the

forward speed. As the thrust is transferred from driving the helicopter forward, the greater vertical

component now attempts to force the helicopter to climb. If this is to be prevented, the pilot must

reduce collective pitch slightly to compensate.

As the helicopter slows below 40 knots, the tail rotor loses efficiency due to the presence of the main

rotor vortices and loss of the aerodynamic efficiency of the vertical stabiliser. The pilot must now apply

anti-torque pedal input to oppose the torque-induced yaw. The loss of translational lift will also require a

compensatory increase in collective pitch to avoid sinking.

As the helicopter slows towards zero airspeed, the cyclic is centred and the power adjusted to maintain

a hovering altitude.

An aggressive slow-down, where a high degree of nose-up pitch is applied, will cause the helicopter to

balloon in height unless power is reduced by lowering the collective during the manoeuvre. However,

this is likely to cause the rotor to over-speed as it is pitched to face the airflow, like a windmill.

Anticipating this effect and re-applying slight collective pitch to compensate and reduce rotor RPM is

required to perform a good “quick stop”.

4.1.5 Ascent and Descent

In the hover, the helicopter is made to ascend and descend by raising or lowering the collective pitch

lever respectively. Care must be taken to make smooth increases in collective pitch to avoid “bogging”

the engine, thus causing rotor droop whereby the sudden increase in drag on the rotors overwhelms the

engine governor’s ability to increase fuel flow in order to compensate to maintain engine and rotor RPM.

In forward flight, ascents and descents are also performed using the collective lever to increase or

reduce the thrust generated, thus resulting in a climb or descent. However, small changes can be made

using the cyclic pitch, or a combination of the two.

It is not normally necessary to completely “bottom” the collective during a descent. Doing so may cause

the clutch to disengage and the rotor to freewheel. The up-flow of air through the rotor in this condition

may cause the rotor to increase in speed. Rotor speed during a descent should be modulated by use of

the collective lever. Raising the lever will lower the rotor RPM. Care should be taken to maintain rotor

RPM within the green band on the gauge.

Since the aerodynamic effect of the vertical stabiliser opposes torque-induced yaw in forward flight, as

power is reduced, so does the need to oppose torque-induced yaw. Therefore the pilot may experience

a yaw to the left during a low-power descent which requires right pedal to counter in order to retain a

constant heading.

4.1.6 Approaches and Landing

4.1.6.1 Approaches

Approaches should be performed at an ideal speed of 55 knots. Prior to final descent into your landing

zone you should reduce your forward speed to below 85 knots to avoid the rotor chopping sound that

can occur between approximately 85 and 120 knots when descending at between 250 and 750 feet per

minute.