The Velocity Instrument Panel
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The design of an instrument panel is a highly personal
matter, but there are some general rules that are widely accepted and
some basic principles that ought to be considered. Factors that
affect the final design include budget, personal
preferences, space available, the capabilities you want and/or need,
and the characteristics of the aircraft. Options for an
experimental aircraft are almost unlimited. You can have anything
from a very basic panel with used instruments to a high-tech Electronic Flight Information
System similar to that in
the space shuttle. It was my desire to have a panel that was efficient, cost effective, businesslike and sensible but with sufficient
capability for serious cross-country travel.
There
are several ways to get a panel made. You can have it completely
constructed to your specifications by one of the companies that "$pecialize
in the creation of cu$tom panel$," or you can build the mechanical
structure yourself and have it wired by an "avionic$ $hop," or
you can wire it yourself by hand. A new approach is to build the panel and
have a wiring hub made. The hub is a small box with plugs that are
configured to match your equipment list. It comes with cables
ready-made to connect between your avionics and the hub. I have
chosen Approach
Systems, the developer of this technology, to build a hub for my
panel. The price is much more reasonable than having it wired by
hand, and I think the final installation will be much cleaner. Tom
Sorensen, their VP, and Chris Riddell, the customer representative have
been extremely helpful. They answered all of my questions promptly
and provided a detailed quotation when I submitted the equipment
list. I received the hub as promised, and it has been wired into
the panel. I had to make two calls to Approach Systems for support
to inquire about technical issues with the avionics, and on both
occasions they were responsive and helpful. Detailed testing will
be completed soon, and an update will be posted here..
I have elected to use relatively standard instrumentation, rejecting the
option of the Electronic Flight Information System. Although I like
these gadgets as well as the next person, the options available within
my price range are non-certified installations from relatively small
companies that may not be around to support them when they break. In addition,
such a display makes you entirely dependent upon the electrical system
of the aircraft, and there are failure mechanisms that would cause you
to lose all of your instrumentation at once. The only
acceptable approach to this problem, in my view, is to have complete
system redundancy or backup by a complete
set of mechanical/vacuum instrumentation, but both of these are beyond my budget.
Here are some of the
design considerations behind this panel:
- The Velocity is flown from the left seat, using the right hand on
the control stick. The engine controls are on the left and are
operated with the left hand. This is different from the usual
arrangement where the aircraft is flown with a yoke which can be
controlled with either hand, while the engine controls are in the
center. To be flown from the right seat, a standard airplane
needs to have an additional yoke, while a Velocity needs to have an
additional set of engine controls. I elected to
eliminate this complication. It is possible, although awkward,
to reach the engine controls from the right seat in an emergency,
and my aircraft will not normally be used for training or flown
from the right seat.
- I opted for the standard arrangement of the six flight
instruments This is an almost universal arrangement in
aircraft, and re-arranging it would be likely to create dangerous confusion in
moving from one aircraft to another.
- The engine gauges are grouped together, with digital instruments
for everything. I would have preferred analog gauges for the
tachometer and manifold pressure, but these would not fit very well
in this design..
- The landing gear switch is placed to the left. During an
approach, the pilot will have the left hand on the engine controls
and the right hand on the flight controls. It is obviously easier and
safer to move the left hand to lower the gear.
- The autopilot control and ACU are placed below the horizontal situation
indicator, as these indications and functions are inter-related. In
this
case, I violated my rule about expensive high-tech systems from small companies
to go with the TruTrak
autopilot, as it is completely self
contained, requiring no external gyros, and can fly the airplane even
in the event of failure of all of the other instruments. It
also gives redundant digital indication of heading and altitude from
its own sensors, and is less expensive that other autopilot units
with similar capabilities. It is my view that an autopilot
contributes enormously to both comfort and safety and is worth the
price.
- Indicators and gauges are placed where they are most easily seen,
directly in front of the pilot. Warning lights are all placed
together so that one glance during the scan will detect any warning
indication. Lights indicating normal functions and status are
placed elsewhere. most often on the controls associated with that
function..
- Switches are placed where they are most easily reached and
operated. The ones used constantly are placed on the control
stick (push to talk, trim, autopilot disengage, altitude hold). The ones used occasionally are placed on the
panel. A push-to-talk switch for the co-pilot is placed on the
keel, rather than the panel, so the co-pilot does not have to reach
for it.
- Switches with similar functions (landing light,
strobes, navigation lights) are grouped together. Dangerous
switches (master, magneto, starter, fuel pump) are not placed near
or in the same group as casual switches (lights, CD player,
dimmers).
- The standard Velocity arrangement includes an overhead switch panel
which contains the starter, magneto switch, master switch, radio
master, fuel pump and lights. I had some concerns about this arrangement and have modified it. First, it violates the
rule about having benign switches next to dangerous switches.
It would be very easy during turbulence, especially at night, to
reach for the landing light during approach and accidentally turn off the magneto.
Secondly, the paddle switches commonly used,
while attractive and easy to operate, can leave distinctive scars
on your forehead (anyone who has flown in significant
turbulence has hit their head on the roof of the cabin more than
once). The overhead is also not a good place for important indicators,
being out of the line of sight and the pattern of the instrument
scan. However, it is a fine place for the starter, magneto
switch, electronic ignition switch and other things that you
generally use only at the beginning and end of flight while on the
ground, and keeps them out of the way of the rest
of the panel. I have also added the Hobbs elapsed time meter
and the ELT remote to the overhead panel.
- The compass is a vertical card type that will be faired into the
glare shield. It is a good idea to keep the compass out of the
panel, as the magnetic field can affect the meter movements in other
instruments such as the course deviation, glide slope and
tachometer, and metal parts in the panel can affect the compass.
- Lighting is provided by electroluminescent bezels,
as the internally lighted instruments are much more expensive.
- For directional indication and course guidance, I elected to use a
Century HSI. A DG and Omni Head would serve just as well, but
combining them in one instrument saves panel space, and I am
accustomed to having one. A Davtron clock has been placed on a canted sub-panel below the center
section (not shown in picture above).
- The right side of the panel contains the circuit breaker panel, a
CD player and radio, a space for a storage compartment, and several blank
sub-panels for future additions to the panel. These may
include the extra throttle control noted above, and an automatic
heater/ventilation control system.
- The panel is constructed entirely using individual aluminum
sub-panels for groupings of instruments and switches. It will
be wired in such a way that any sub-panel can be removed as a unit
and unplugged from the rest of the panel. If it is necessary
for service, a short umbilical extension can allow the sub-panel to
be operated while removed from the panel. In addition to the
serviceability advantages, this allows the panel to be changed more
easily in the future, and the holes are much easier to cut working
with flat plates of aluminum rather than the complex and awkward
shape of the complete panel.
- I am planning on making a drawer
at the bottom of the panel is for a laptop computer or a portable DVD
player. Either of these can be useful in flight, but are in my
opinion too expensive to be installed as permanent items. The
drawer will contain a power outlet and feeds for the audio system and a
video feed that could connect to a flat panel display for the rear
seat. Because of the canted radio stack, this must be placed below
the radios, but for a small computer only intrudes about 1.5" into the knee
space
These opinions are mine alone, and do not reflect the view of anyone
at Velocity. I am sure that there are a lot of people more
knowledgeable than I who will disagree, but I hope that the thought
process that I went through will help some of you who are just beginning
this process to find a method to arrive at your panel design.
Comments are always welcome. See the header on the
home page for a link to my Email address.
