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17°
10°
Figure 12-9. Variation at point A in the western United States
is 17°. Since the magnetic north pole is located to the east of
the true north pole in relation to this point, the variation is
easterly. When the magnetic pole falls to the west of the true
north pole, variation is westerly.
12-6
it necessary for you to constantly check the instruments
and make appropriate changes in the helicopter’s attitude.
The actual technique may vary depending on what
instruments are installed and where they are installed,
as well as your experience and proficiency level. For
this discussion, we will concentrate on the six basic
flight instruments discussed earlier. [Figure 12-10]
At first, you may have a tendency to cross-check
rapidly, looking directly at the instruments without
knowing exactly what information you are seeking.
However, with familiarity and practice, the instrument
cross-check reveals definite trends during specific
flight conditions. These trends help you control the
helicopter as it makes a transition from one flight
condition to another.
If you apply your full concentration to a single instrument,
you will encounter a problem called “fixation.” This results
from a natural human inclination to observe a specific
instrument carefully and accurately, often to the exclusion
of other instruments. Fixation on a single instrument usually
results in poor control. For example, while performing
a turn, you may have a tendency to watch only the turn-andslip
indicator instead of including other instruments in your
cross-check. This fixation on the turn-and-slip indicator
often leads to a loss of altitude through poor pitch and bank
control. You should look at each instrument only long
enough to understand the information it presents, then continue
on to the next one. Similarly, you may find yourself
placing too much “emphasis” on a single instrument,
instead of relying on a combination of instruments necessary
for helicopter performance information. This differs
from fixation in that you are using other instruments,
but are giving too much attention to a particular one.
During performance of a maneuver, you may sometimes
fail to anticipate significant instrument indications following
attitude changes. For example, during leveloff
from a climb or descent, you may concentrate on pitch
control, while forgetting about heading or roll information.
This error, called “omission,” results in erratic
control of heading and bank.
In spite of these common errors, most pilots can adapt
well to flight by instrument reference after instruction
and practice. You may find that you can control the helicopter
more easily and precisely by instruments.
INSTRUMENT INTERPRETATION
The flight instruments together give a picture of what
is going on. No one instrument is more important than
the next; however, during certain maneuvers or conditions,
those instruments that provide the most pertinent
and useful information are termed primary instruments.
Those which back up and supplement the primary
instruments are termed supporting instruments. For
example, since the attitude indicator is the only instrument
that provides instant and direct aircraft attitude
information, it should be considered primary during
any change in pitch or bank attitude. After the new attitude
is established, other instruments become primary,
and the attitude indicator usually becomes the supporting
instrument.
Figure 12-10. In most situations, the cross-check pattern includes the attitude indicator between the cross-check of each of the
other instruments. A typical cross-check might progress as follows: attitude indicator, altimeter, attitude indicator, VSI, attitude
indicator, heading indicator, attitude indicator, and so on.
12-7
AIRCRAFT CONTROL
Controlling the helicopter is the result of accurately
interpreting the flight instruments and translating these
readings into correct control responses. Aircraft control
involves adjustment to pitch, bank, power, and trim in
order to achieve a desired flight path.
Pitch attitude control is controlling the movement of
the helicopter about its lateral axis. After interpreting
the helicopter’s pitch attitude by reference to the pitch
instruments (attitude indicator, altimeter, airspeed indicator,
and vertical speed indicator), cyclic control
adjustments are made to affect the desired pitch attitude.
In this chapter, the pitch attitudes illustrated are
approximate and will vary with different helicopters.
　
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