TruTrak EFIS AP (8300-057C) - Manual (Page 6)

THE DISPLAY
Consider first the pitch display. Motion of the pitch display short term is gyroscopic as it must be
to fly in IMC. Long term it is VSI. This is a special case of a presentation used in the military called
VELOCITY VECTOR. This display has two advantages. The first is that it provides an instantaneous
vertical speed presentation. The second is that when the reference airplane is on the horizon the aircraft is
neither climbing nor descending. This eliminates the need for adjusting the position of the pitch reference
airplane to compensate for the angle the fuselage is flying. The resulting benefit of this concept is that it
makes holding altitude easier (not only in straight flight but also in turns). It is a fact that next to AOA,
airspeed provides the best warning of approaching a stall. For this reason the airspeed pointer flashes red
when a pre-set minimum airspeed safely above a stall is reached. There are critics of this concept who
believe that attitude is an indicator of approaching a stall. NOT SO, attitude alone is not at all such an
indicator.
The HSI is placed below the horizon
as in the larger more expensive
displays. It is in the form of an
ellipse for two reasons. First, an
ellipse when compared with a circle
of the same height provides a broader
scale at the top where it is read.
Second, it looks as a circle would
when laid out on the ground ahead of
the aircraft. When a DIRECT TO or
FLIGHT PLAN is set into the GPS
this display becomes an HSI. The
boldness of this high quality display
in combination with its location
enhances the fly ability of the overall
instrument. Finally, the HSI contains
features that make functions available
that are not found in other low cost
systems. These are described in other sections.
The analog presentations of airspeed and altitude are based on the belief that in some cases round
is better. It will be noted that after having tried other presentations the automobile industry is back to
round instruments. Nothing in the modern world of vertical tapes compares with the dynamic effect of a
white needle moving around a black altimeter dial. As a target altitude is approached it is natural for the
pilot to slow the needle velocity so as to arrive at the altitude without overshoot. The difference is that in
this system the dials rotate about fixed pointers, but the relative motion retains the same effect as the
moving pointer. In addition, the rotating altimeter dial further enhances the motion factor. To satisfy
personal preference the display can be switched back and forth between round and rectangular, even in
flight. Of those who have tried both the choices have been almost unanimous in favor of the round.
Within the bank angle scale indicators are inserted which show the angle for a standard rate turn.
These indicators move outward on the bank angle scale as airspeed increases. Placed above the bank
angle scale is an inclinometer that looks just like a conventional ball in a curved tube.
Still another convenient feature is the optional presentation of important engine data in the pilot’s
direct field of vision displayed across the top of the instrument.
TruTrak Flight Systems 4 EFIS Autopilot Installation Manual
April 2009 8300-057 Rev D