Sequoia Aircraft Corporation F.8L Falco, Construction Manual

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F.8L Falco Construction Manual 14–9 Revision 4, March 1, 2002
The Ground Plane
In layman’s terms, the object of the ground plane is to make the Loran antenna think it is
installed on a metal airplane. The Loran antenna is easy to fool, so you will only need a few wires.
The ground plane will consist of a number of wires running from the antenna coupler forward
along the sides of the fuselage tail cone. If there were no other metal structure in the tail section,
this would mean that you would need about eight wires—four per side. These wires should be
connected to the ground lead of the antenna coupler. The forward ends of the wires should also
be joined together. The forward ends of the wires
and the ground lead of the antenna coupler
should be connected to one of the three negative buses in the airplane. There are three negative
buses in the Falco: the engine, the instrument panel and the negative bus bar installed on the
bottom of the fuselage skin just aft of frame No. 6. These ground plane wires may be on the
outside of the skin or on the inside—it doesn’t matter. The ground plane wires may be any type
of wire. Perhaps the simplest thing would be to use sticky-backed copper foil. This is the same
type that we use for the NAV and COM antennas. It is commonly used for burglar alarm systems
in store windows, and you should be able to get some locally.
As a practical matter you may not need to install any of these wires. There are already plenty of
metal parts in the tail which can be used as ground planes. This includes the rudder cables, the
elevator cables, the elevator trim tab push-pull cable, the tail position light ground wire, and the
shielding of the strobe light wire. It is important that these things be grounded to the case of the
coupler box in the most direct manner. With the other parts of the electrical system, the length
of the wire to a ground bus is not important, but it is important in this situation. Grounding the
elevator and rudder cables at the forward ends will
not work. Try to keep the length of the ground
wire to the antenna coupler box as short as possible. Anything within one to two feet is all right.
The antenna coupler should be grounded to the system of grounding buses in the Falco. This may
be done by putting it in series with the tail position light ground wire. This wire would run from
the tail position light to the ground lead of the antenna coupler and then to the negative bus bar.
If you wish, you may also run a ground plane wire out in the horizontal tail. This is probably not
necessary, but it is not difficult and certainly will not hurt. Grounding to the elevator trim tab
cable will not be easy, and you should not forget to also ground the aluminum tube in the
horizontal stabilizer. Once you have run wires out in the horizontal tail, you might as well run
them out to the tips of the horizontal tail. While you are out there, also ground the outboard
elevator hinges.
The coaxial cable for the COM antenna does not have a shield, so it is not part of the ground
plane wiring system.
Grounding Other Metal Parts
All large metal parts in the airplane must be grounded to one of the three negative bus bars. In
his original article, Jim Weir stated that every piece of metal over one square inch should be
grounded—but in his conversations with us he said that you only need to ground those pieces
over 6 square inches. You can be your own judge and do as you see fit. Bear in mind that if a
metal part is exposed to the air stream it will be subject to precipitation static (P-static), and it is
more important to ground exterior parts like access panels than it is to ground internal parts of the
same size.
The grounding of metal parts is primarily related to the installation of an ADF or Loran, and there
is no special need to do this if these systems are not installed.