Radio Control Installations
February 1955 Popular Electronics
who has been in aeromodeling for more than a decade or so is familiar
with the name William (Bill) Winter. Bill has been in the model
airplane realm for longer than a lot of us have been alive and is
one of the true pioneers of the sport. He has served as editor for
a couple aircraft modeling magazines, and has written countless
articles both for the magazines he edited and for other special
interest magazines. When Popular Electronics came on the scene in
the mid 1950s, Bill was editor of Model Airplane News.
Radio control was beginning to mature from its infant state when
only hobbyists with an intimate knowledge of electronics were able
to participate. Oliver Read, editor of Popular Electronics, tapped
Bill's ample knowledge and skill to craft quite a few articles for
his own magazine. This one, Radio Control Installations, appeared
in the February 1955 issue. As always when reading this type of
vintage material, it is amazing how much innovation has occurred
between then and today in the fields of electronics, materials,
and construction techniques.
February 1955 Popular Electronics
[Table of Contents]
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Radio Control Installations
by William Winter,
Editor, "Model Airplane News"
of the oddities of the radio control hobby is the persistent underestimation,
even by some manufacturers, of the problems of installing the airborne
equipment. Most directions stop with a wiring diagram and the "dope"
on tuning. It is no wonder then that the beginner's first R/C installation
is a rat's nest of wires, or that the radioman's first model often
is torn up by loose batteries and catapulting equipment on the first
really hard landing.
A shipshape installation is accessible,
removable, facilitates proper functioning of the radio, protects
the equipment, and, just as important, protects the airplane from
the equipment in a crack-up. If these requirements are not met,
the best radio in the world is rendered unreliable.
this sounds like making a mountain out of a molehill, consider the
unnecessary damage that happens to a relay when the receiver bangs
around inside a cabin. The heavy coil may deform the frame, causing
delicate pivots to bind. This will result in skipping and sticking,
eventually causing a bad crack-up or a fly-away. This is just one
of the ways a poor installation endangers the equipment.
Let's take the requirements in the order given. First is accessibility.
This, like Sergeant Friday, covers a lot of territory. Just because
the frequency trimmer can be reached with a tuning wand doesn't
mean that the receiver is accessible. A slug tuner which requires
tightening of a lock nut so that vibration will not cause detuning,
isn't accessible when the lock nut is under the receiver chassis!
Or, you may want to reach the relay to clean a contact, or to adjust
spring tension, or reset a contact. Battery voltages often must
be read on the field, or batteries may have to be replaced, or the
escapement or servo checked. Anything that requires observation
or adjustment should be readily accessible.
be removable. Maintenance alone requires that all principal parts
of the radio system be removable, that is, battery packs, receiver,
and actuator. Exhaust smoke from the engine and dust on the field
penetrate cabins, eventually causing leakages of capacitors, etc.
It certainly is worthwhile to keep the receiver chassis clean. Soldered
joints need regular inspection - components may have been pushed
out of place, perhaps to the point of shorting out. Tubes may be
loose, a burr might have developed on the revolving arm of the escapement,
or the armature of a servo motor may require cleaning. The radio
model is, after all, a real aircraft and, like a real aircraft,
requires periodic checks. It is not uncommon for an active hobbyist
to log a hundred or more flights a year. If the equipment is not
inspected regularly, the model will become a casualty before that
many flights can be racked up.
well the receiver does its job depends on the neatness of the installation
and the provision included against the ill effects of engine vibration
upon the relay. The beginner tends to place batteries, receiver,
and escapement wherever convenient, then to run wires, like as not
through space, point to point. Wires can be grouped or cabled. Those
wires that connect the switch, potentiometer, jack, sockets, and
other stationary components that remain in the plane, regardless
of the removability of the receiver, batteries, or actuators, should
be fastened to the structure, led along the corners between walls
and floor, or by bulkheads (crosswise partitions) and walls.
stationary wiring can be constricted into a very small area by a
compact arrangement of the permanently installed fixtures. By using
miniature socket-type plugs, the receiver can be provided with a
plug-in cable, and the battery pack with another. Either or both
can be removed by slipping out the plug. Standardize your receiver
cable connections to make receivers interchangeable between ships.
One big advantage of this practice is that friends can cooperate
by sharing receivers when necessary, provided the hook-ups are standard.
On the five-pin plug the following connections are suggested: pin
1, "A+"; pin 2, "B+"; pin 3, common minus; pins 4 and 5, relay.
Damping of vibration is accomplished by a variety of shock
mounting systems, the two most common ones being a rubber band suspension
of the receiver in a horizontal position, or the placement of the
receiver upon a block of foam rubber, either vertically or horizontally.
If vertically mounted, the receiver has an infinitely greater immunity
to crack-up damage. Indeed, it is possible to destroy the airplane
without detuning the receiver or even knocking the relay out of
adjustment, when vertical mounting is used. Heavier and larger receivers
sometimes rest upon two blocks of sponge, one at either end, or
at either side, as the case may be. The rubber is faced with 1/16-inch
thick plywood (using rubber cement) and the chassis ends or mounting
lugs are attached to the plywood with small wood screws.
Example of battery installation in
the belly of an airplane under the hardwood floor. The forward box
contains a hearing-aid "B" battery, the rear compartment contains
the batteries for the receiver filaments (1 1/2 volts) and the escapement
requiring 3 volts.
Good shock absorption is essential
to good relay operation. The writer has seen cases where a 10,000-ohm
sensitive relay considered shock proof would not pull in when mounted
firmly on wood with a powerful engine shaking the airplane. Contact
pressures may not be sufficient to hold a rudder in one position
as the plane shudders out of a dive. Probably the manufacturers
themselves don't know what happens to a relay armature during repeated
signaling in the presence of a severe harmonic vibration, as only
modelers seem to create it. If a good installation is able to employ
the means of damping vibration to provide crash protection as well,
you are ahead of the game.
but not least, is the protection of the airplane from loose equipment.
This means that all heavy objects, notably the batteries and the
receiver, should not be permitted to gather momentum before coming
to rest against a bulkhead. Batteries should always rest snugly
against a bulkhead, This bulkhead should be strengthened across
the grain with cross members or plywood to prevent splitting. Its
ends, or joints with the floor or walls, should be butted against
forward movement that would tear out the joints. Batteries should
not be fastened down upon flooring, and never held loosely in place.
A vertically-mounted receiver that rests against a firm bulkhead,
with appropriate strengthening against splitting and movement, causes
little or no structural damage and is itself unhurt by hard knocks.
Horizontally-mounted receivers which depend on rubber-bands
from the four corners of the chassis may, on a short stop, penetrate
a ply bulkhead with well imagined results to electronic equipment.
A tether cord attached to the chassis and anchored behind the chassis
to some strong point, prevents the receiver from traveling too far,
although the back travel, like recoil of a gun, should be similarly
damped for safety. Even though the horizontal mounting may hold
in a crash, it is likely that the Sigma 4F-type relay will be deformed.
Tubes will pop out, and everything that isn't tied down, like chokes,
quench coils, and capacitors, will move out of position.
Escapements and push rods take special handling to prevent crash
damage. Escapements that simply are cemented against a balsa partition
will tumble into the cabin when the plane bangs onto its nose. A
pushrod may take off like a javelin, pulling loose the linkage assembly
and the rudder.
With such considerations in mind we can tackle the four typical
installations given in the illustrations. First is the old fashioned
rubber-band mounted receiver, accessible in this case by means of
two large access doors in the sides of the ship. A is the plywood
bulkhead; B is a thick sheet-balsa floor or a thin plywood floor.
The batteries are stacked against the bulkhead or laid flat on the
floor with their front edges flush against the bulkhead. The switches,
potentiometer, jack, etc., line up along the lower edge of the cabin
on the left side, facing a right handed launcher. (This is more
or less standard, so the arrangement of accessories, switches, etc.,
will not be detailed in subsequent examples.)
One method for mounting a receiver horizontally is shown here.
Batteries and the socket for receiver cable are well forward.
R/C model plane with the receiver mounted horizontally. The
batteries are in the nose, mounted on a piece of plywood and
inserted through the floor for easy accessibility.
Removable box containing batteries, receiver, and actuator.
This allows for easy removal from a plane and interchange between
is suspended by rubber bands (two light bands to each corner stretched
to about one-third their limit). C is a tether cord attached to
the rear wing hold-down dowel, D. F is a small chassis mounting
two sockets, one to accept the battery cable lead, the other the
receiver cable. Note the structural cross members, G, that reinforce
bulkhead A. The section forward of this reinforcement is double
skinned on each side, with the inner, thicker skin-3/16 or 1/4-inch
thick sheet balsa, butting against bulkhead A.
mounting method is to have both receiver and batteries vertical.
This provides excellent accessibility to the radio from the open
top of the cabin, and to the battery pack from the removable top
of the nose section. A is a 1/4-inch sheet-balsa bulkhead; B is
either a 1/8-inch plywood or a 1/4-inch sheet-balsa bulkhead, whose
grain runs across ship. Note that the impact of the batteries is
against this bulkhead; that of the receiver, partly snubbed by
foam rubber, is transmitted through A. The impact of the snug fitting
batteries is transmitted to the key bulkhead B. Switches, potentiometer,
and jack line up as before, well out of the way should the receiver
swing from side to side. C is a foam rubber block, against which
the receiver is anchored by small rubber bands. The tension of the
bands is just enough to prevent the receiver from hanging loosely
or swinging back and forth on landing. The battery cable D comes
through bulkhead A, and plugs into a socket on chassis E. The receiver
cable plugs into a similar socket. Note that the escapement is fully
The beauty of the torque rod linkage to the
rudder is that the linkage cannot damage the escapement in a crack-up,
whereas the pushrod type transmits a blow to the escapement assembly.
Pushrods and bellcranks also put a dead weight on the escapement,
which can be a handicap when the nose is down. Pushrods usually
require heavier rubber drive for safety and this in turn makes escapement
and performance more critical.
A variation of the vertical-type
mounting is also shown. Here, a plywood floor A extends between
bulkheads C and D. Observe that the floor continues forward of bulkhead
B, so that the battery weight can be carried far enough toward the
nose for correct balancing. Battery boxes bolt directly to the floor,
and are accessible by means of a large bottom hatch. The Acme Products
Company makes sturdy battery boxes for all popular battery combinations
including hearing aid "B" batteries. If desired, a large "B" battery
may be dropped into place between bulkheads B and D, with D then
requiring the usual forward structural support. Escapements, switches,
etc., are mounted as before. The large plywood floor is ideal for
anchoring the heavier motor-driven servo-type actuators.
Still another arrangement having very special advantages is
the removable box method. This box contains the batteries, receiver,
and even the servo or escapement. By detaching the linkage from
the actuator, the box can be lifted from the plane without disconnecting
a wire. Moreover, it can be dropped into another plane. It is unnecessary
to have an actuator in every plane with this set-up. The batteries
are packed in a forward compartment in the box; the actuator is
mounted at the rear, but in such a manner that it does not snag
the adjacent bulkhead when the box is lifted out. Switches, potentiometer,
jack, etc., have to be on the bottom of the box, and are reached
through holes in the bottom of the ship when the box is in place.
In fact, the toggle switch handle extends from the bottom. Usually
more confined than a wide open cabin, the box requires that some
receivers be beam mounted, that is, placed upon two blocks of foam
rubber at either end, or along the sides.
is not intended that these examples be followed to the exclusion
of the reader's own ideas. Rather, it is hoped that this resume
of a few of the better kinds of installations will assist the newcomer
in the successful operation of his new plane.
It would be
well to draw upon these comments in sketching in any installation
upon the plan that comes with your airplane kit - before cementing
a piece of wood. Few kits detail installations, merely saying, put
the batteries here, etc. Nor are they always wise in the location
of some items such as an escapement. The average modeler is a great
individualist, especially in radio control. So don't be afraid to
"gild the lily."