It directly displays two primary components of aircraft attitude, nose and wing.
In contrast, the turn needle displays wing attitude indirectly by presenting rate
gyro precession induced by a changing aircraft heading. With an aircraft in
balanced flight, turn needle precession (turning) is indicative of an aircraft in a
banking maneuver. The balance ball directly presents aircraft yaw, the state of
flight balance and confirms alignment of the aircraft longitudinal axis nose to
tail. The other instruments present either a nose or wing crosscheck indication.
The VGI is the primary reference for:
All attitude changes. These include rolling the miniature aircraft on the
attitude gyro into and out of turning maneuvers, transitioning the
miniature aircraft to a climb or descent, and correcting for miniature
aircraft attitude position errors determined through the indications of other
supporting crosscheck instruments.
All power changes. The primary consideration is a precisely constant
planned aircraft attitude supported by properly coordinated power to
produce a desired performance. Set desired power, watching the gyro to
maintain the planned aircraft maneuver attitude and check power in the
desired range. After the power control lever (PCL) has stopped, glance
briefly at the torque setting. Reset power to the exact setting, then trim to
fix the new attitude.
Trimming the aircraft. Using the miniature aircraft on the attitude gyro,
set an attitude and immediately trim the aircraft to relieve the primary
control surface pressures necessary to hold that attitude. Trimming is
performed while studying the gyro and is most efficiently and effectively
accomplished in the sequence rudder, elevator, and aileron.
There is a builtin precession error in the gyro, which is most noticeable when rolling
into turns. This means the new attitude set during a turn may not be completely
accurate and is the reason for attitude crosscheck instruments. Two redeeming
features of precession are that once it is discovered by using the crosscheck
instruments as a guide, a new (precessed) position may be determined for the gyro
and it can be flown accurately, and after rolling out of the bank, a selfleveling
feature of the gyro slowly returns the horizon bar to its original position.
The attitude gyro is set on the ground by aligning the arrow on the adjustment knob
with the white index mark on the face of the instrument. When airborne, if it is
necessary to reset the instrument, do so only in straight and level flight at normal
cruise by aligning the miniature airplane with the horizon line. Do not reset for
changes of airspeed or when the gyro is precessing.
Encoder Altimeter (Front Cockpit)
The altimeter (Figure 13) is the nose attitude crosscheck instrument for all level flight
conditions (either straight or turning), and a performance instrument for climbs and descents.
Since it is a pressure instrument, there is an inherent lag. For example, if an aircraft had been
maintaining a constant altitude and then commenced a climb or descent, the altimeter would not
INTRODUCTION TO BASIC INSTRUMENTS 1-5