The Art of the Helicopter John Watkinson - Karatunov.net

20 The Art of the Helicopter
and rotor head. Chapter 7 integrates the control system and considers power assistance
and auto-stabilization.
The pilot controls the yaw axis by altering the pitch of the tail rotor blades using foot
pedals. Chapter 5 considers the tail system of the helicopter.
It should be mentioned in passing that the No. 1 pilot in a helicopter conventionally
occupies the right hand seat; the opposite of aeroplane practice. In some early machines,
only one collective lever was provided, between the seats. The test pilots would sit in the
left seat, as per aeroplane practice. Because of the difficulty of reversing the function of
left and right hands, a pilot under training would be placed in the right seat and so the
right seat became the conventional location for a helicopter pilot. A further factor is
that in early helicopters, the forces fed back to the cyclic stick from the rotor were such
that it was not safe to let go of the stick for an instant. However, the collective lever
could be released temporarily. Given that most secondary controls such as the radio
and instruments are centrally disposed so that pilot and co-pilot can both see them, it
made sense to put the pilot in command on the right where his free left hand would be of
most use.
1.13 Electrical and hydraulic system
The power systems of a typical helicopter are not that much different from those of
any aircraft. Electrical power is needed for instruments, radios, autopilots, lighting,
engine starting, navigation and intercom systems, as well as a host of further avionics
that might be needed for special purposes.
A light helicopter may have no power assistance, but as machines get larger the
control forces may cause fatigue and in very large machines they will be beyond the
strength of the pilot. Power-assisted controls then become essential. Power controls
are also needed if some kind of automatic stabilization or autopilot is fitted so that the
low powered electronic signals can operate the controls.
When powered controls operated by electrical signals have faultless reliability, the
mechanical controls from the pilot can also be replaced by electrical controls, leading to
the concept of fly-by-wire. The pilot operates controls having no mechanical connection
to the rotors, but which instead produce electrical signals. This concept is explored in
Chapter 7.
Electric motors are useful for low powered control purposes such as the trim mechanism,
but hydraulics allows greater forces to be developed within small actuators, and
so they will be used for powered flying controls.
Electrical and hydraulic power is vital to the safety of the machine, and the hydraulic
pump and the generator may be driven from the rotor shaft so that power is still available
even in the case of engine failure. In small machines the generator is driven from the
engine, as battery capacity is enough to keep the electrical system working in the case
of an engine failure. Larger machines may have two or more engines and each will have
a generator so that electric power is still available in case of engine failure.
The electrical system is discussed in Chapter 6, and an explanation of hydraulic
controls will be found in Chapter 7.
1.14 Instruments and avionics
Many of the instruments fitted to helicopters are the same as those used in other
aircraft, but in addition to the usual engine-related gauges the helicopter will also need