Evening star., 1928-12-30
RADIO FOR PLANES
DEMANDS BONDING
Most Serious Difficulty in U.s.
ing Wireless on AirShips
Is Closed Circuit.

The difficulties which have been en-
countered by radio engineers in meet
ing the demands for efficient and de-
pendable outfits for airplane use are
Illustrated in the mere basic operations
of bonding and shielding the metal
parts and electrical lines of airplanes.
as preliminary to the actual installa-
ton of the radio units
Bonding is the operation of connect
ing all of the separated metal parts of
the plane by wiring so as to form a
single electrical unit. This is necessary
because a ground connection, of course,
is impossible and good counterpolse
must be substituted
All the wiring of the ignition system
and plane lighting system then must be
shielded so as to prevent the leakage of
energy and consequent radio inter-
ference.
Bonding of the metal parts also is
necessary so that when transmitter is
used on plane there will be no spark
ing between metal parts, with a result
ing fire risk or injury to the plane.
Bond ALI Metal Parts.
The bonding of an airplane, according
to Department of Commerce engineers,
is performed by electrically connecting
all metal parts, the actual details vary
ing with each type of plane. Where
wooden wings are used, all drag and
anti-drag wires must be connected by
running copper wire or strip along the
wing spars and binding them to the
wires Metal parts in the ailerons must
be connected either through existing
metal control connections or by INSTALL
ing wire Jumpers" across the hinges.
If the plane is a biplane care must be
taken to keep the lift and anti-lift wires
from rubbing against each other, or
having permanent connection between
the two at the point of contact. If
this is not done, interference will be
caused each time the two wires touch.
With the prevailing metal fuSelageS,
the bonding here is comparatively SIM
pie. If welded, the bonding will be only
that of connecting parts which may be
clamped to the welded members. The
bonding of the wings and their metal
fittings then is connected to the fuse
lage.
In the case of wooden fuselages, how
ever, wires must be run along each
longeron, connecting with all brace
wires.
All controls and control wires must
be properly bonded, all moving joints
of the controls being bridged by strips
of copper braid
Two Types of Shielding.
There are two types of shieldings-
low-tenSion and high-tenSion shielding.
They differ only in the care which must
be taken due to the difference in fire.
quencies of the currents carried in the
wires Shielded wires must be used In
making all connections to batteries,
lights and other electrical equipment
The shielding consists of metal tub
ing over the insulated wires grounded
at points IL to IA inches apart.
All instruments in the planes should
have metal cases. If a metal instru-
ment board is used it is necessary to
make a good electrical connection be-
tween instruments and board and then
ground the board to the rest of the
plane. With a wooden board the case
of each instrument must be bonded IN
dividually.
Proper shielding of the magnetic or
distributor and the spark plugs of the
motor today forms the most trouble
some problem facing the electrical engi-
neer. At present the most satisfactory
method seems to be the use OF shielded
spark plug. Shielded plugs now in use,
however, are susceptible to breaking
down of the insulation. Spark plug
manufacturers are working on the prob
lem.
With proper bonding and shielding
accomplished, the radio engineer then
is able to undertake the radio installa-
ton with some hope of success. The
entire field of aeronautical radio COM
munication, however. is open to inl-
provement and forms today one of the
most important fields of research III
connection with aeronautical develop
ment.