Cordless Electric Flight Motors
July 1973 American
by Bob Meuser - American Aircraft Modeler - July 1973
Notice: American Aircraft Modeler ceased publication in March
of 1975, and is no longer in print by the copyright owner, the Academy
of Model Aeronautics (AMA). This particular article will be of great
interest to the modern e-power modeler who wants to get a feel for
what the early pioneers in electric powered aircraft we doing to
forge the trail to today's highly powerful, brushless, outrunner
motors that use microprocessor-controlled electronic speed controls
(ESCs). I will be contacting the AMA to receive permission to reprint
the content of the article as a service to modelers.
Brian L.'s vintage Mattel
Super Star model.
Cordless Electric Flight Motors
Flip the switch, and it is up, up the long delirious burning blue,
with safe, silent, inexpensive, non-polluting electric propulsion.
Gone forever are the greasy kid stuff and barked knuckles associated
with the balky glow engine, the impetuous variability of Pirelli
rubber, and the mad running through sand and muck to launch a towline
glider. Just flip the switch.
Well, not quite. We shouldn't get too self-righteous about pollution
until we examine what comes out of the stack down at the battery
works. The inconvenience of greasy kid stuff and balky engines must
be weighed against an assemblage of motorcycle batteries, charging
cords, meters and the like, although electric propulsion probably
has the edge. It can be as inexpensive as a cheapie Half-A. It can
also be the most effective money sponge devised by the mind of man
if it goes the route of electric-propelled boats in England; there
it took the shooting off of $132 worth of short-lived silver-zinc
batteries to win the National Speed Finals. It is as safe as a cordless
electric toothbrush if the manufacturers' instructions are followed,
but before going off on your own, take a good look at a tree-the
next one you "see" might be in Braille. And, at best, an electric
airplane will not go up the long delirious burning blue very fast,
for the best electric propulsion system cannot compete with a mill-run
glow engine on a pounds-per-horsepower basis.
Still no one knows what type of model will be ideal
for electric flight. A power pod for use on a semi-free
flight design with two- or three-channel radios is Quite
desirable and the UREI EMF-040, shown here, is to be packaged
with this In mind. Timer charging jack and switch are included
in the pod.
the power can be quite satisfactory for many purposes, and in its
simplest form, electric propulsion is as convenient as a doorknob,
and as quiet as a clam with laryngitis. The latter is especially
important nowadays when RC types, Ukie-jocks, and Free Flighters
alike are struggling to find and hold flying sites. It certainly
offers a whole new set of enticing challenges, and it deserves the
close scrutiny of every serious modeler interested in a bit more
than placing Foot L ahead of Foot R along Beaten Path.
is now on the market a diverse selection of electric motors, batteries,
and complete propulsion systems either specifically intended for
model aircraft propulsion or readily adapted to it. In addition,
there is a phantasmagoria of untried but potentially useful paraphernalia
sufficient to keep anyone with a dash of Tom Swift or J.L. Seagull
in him happily frustrated for a lifetime. This article covers the
complete propulsion systems that are available-motor and battery
combinations, plus auxiliaries. The table shows the prices and specifications
of all of the power units as completely and as accurately as we
were able to. It was not possible to make the power ratings consistent,
however, as some are based on manufacturer's specifications, some
are peak ratings from bench tests-in-flight power would be much
less-and some are estimated, rather carefully however, from the
manufacturer's statement of the performance of the aircraft. The
power ratings should be used only as a rough guide, certainly not
as an indicator of what you are getting for your money. The power
output of any motor can be boosted simply by applying more voltage,
or loading with a larger prop, but its life will be greatly shortened.
The aircraft sizes listed are rough guides only. A power glider,
where the purpose of the motor is to get the model up to soaring
altitude, would have several times the wingspan of a stunt model
using the same motor. Duration of powered flight also varies depending
on the flight profile-if the model is climbing the whole time, the
duration will be shorter than if the model is stunting. In a dive,
the motor is acting partially as a generator, and the battery drain
is very small.
|Interested in silent
flight? Here's a review of what is available in power systems
at this time. The variety is interesting- the performance
is good. / by Bob Meuser
Star free flight model is very popular with all modelers.
It really performs. Power unit is separately available from
Mattel and adaptable to many homemade designs.
Power unit in Mattel's RC Signal Command is bigger and heavier,
but very strong and even self-contains a magnetic actuator
and its battery. A cut-down version could power a two-channel
Germany comes the Graupner Electro-Prop with its unique
folding pusher prop-and it's a geared unit. Battery charger
available with it operates from your car battery and is
a quick-charge system.
|Above: Galler Industries takes
a special wound slot-car type motor, gears it, and drives
a 10-6 wood prop from a fairly small battery pack. It is
a lightweight system and not complicated. Several accessories
are available to operate the unit with RC or a timer. Right:
From Astra Flite comes this neat reworked high-performance
motor for direct driving standard gas engine type props.
Two sizes, smaller unit produces 1/10th hp at peak of battery
charge-quite powerful! Larger motor gives 1/4th hp!
Enter Mattel: The cordless electric airplane has been around
since the early fifties, but until quite recently it could scarcely
be considered a viable alternative to rubber-powered and gas-powered
models. With the advent of the high-rate fast-charge nickel cadmium
battery, and the deluge of cordless electric products that followed
in its wake-drills, chain saws, lawn mowers, toothbrushes, carving
knives, and a host of others-the practical cordless electric airplane
became virtually an invention that was waiting for a place to happen.
And when it happened, it happened all over the place! Most of the
propulsion systems on our list were either on the market or under
development before the Mattel Super Star hit the market. But the
Super Star is certainly the most apparent manifestation of electric
propulsion, and it is of course a complete aircraft, not merely
a propulsion system.
Picture yourself, an experienced modeler
perhaps, as the president of a large toy manufacturing company.
A fire-eyed tousle-haired Idea Man comes in with the Big One for
the week. "We take a battery and an electric motor, see?"-with half
the power-to-weight ratio of even a rubber-band motor. "And, a foam
wing and vacuum-formed plastic fuselage."-with half the strength-to-weight
ratio of proper stick-and-tissue construction. "We hold it all together
with no-lickum stickum labels, and it will fly right 'out of the
box' with almost no adjustment." You cough and fidget a bit. "It
will be so simple that even an adult can fly one." You dear your
throat to suppress a giggle. "And it'll be tough enough to survive
the crash that will result when some lad's father decides he is
smarter than the instruction book." The giggle makes it. "And, we'll
retail it for less than $15." You laugh him half, way into next
Mattel must be laughing all the way to the bank.
Obviously not -the brain child of 'our mythical idea man, but rather
a product of careful, skillful engineering and ingenuity, the Super
star flies almost too well, as some skeptics discovered by losing
theirs on the maiden voyage. The audacity of a bloomin' toy-monger
duplicating or surpassing some of our own best efforts with a chunk
|The engines from Kraker are specially
designed throughout for model application and hold several
world electric power boat records. The small Sea Pup is
suitable for aircraft use as shown here with a 7-4 prop.
A disassembled Sea Pup shows what is involved inside.
The Super Star became a glint if Mattel's corporate eye about
five years ago when the quick-recharge ni-cads first appeared, and
during the early chapters in the life of the Sizzler car. It also
came to pass that half-way 'round the world, in the Land of the
Rising Sun, the quick-recharge ni-cad had 'not escaped the attention
of a model aviation enthusiast by the name of Ken-ichi Mabuch, who
by a curious coincidence happened to be the president of the world's
largest manufacturer of small electric motors. Both the Mabuchi
and Mattel companies had progressed quite far with electric aircraft
development before they discovered each other's interest; when they
did, the Mabuchi-powered Mattel Super Star, and later the Signal
Command, were the inevitable results.
The Super Star:
At the bottom of the list in both cost and performance, but perhaps
at the top of the totem pole in fun-per-buck ratio, is the Mattel
Super Star power plant. The motor is a big step up from many of
the Mabuchi toy motors found in surplus stores and elsewhere in
that it has carbon brushes in place of -the usual phosphor bronze
sheet metal or wire ones. The battery is a pair of 100 mAh General
Electric 1/3-AA-size ni-cads-the same cells used in the Sizzler
cars. Extensions of the brush arms serve as connections to the battery,
charging cord receptacle, and switch.
The 7-1/4-in. dia.,
5-in. pitch prop is driven through plastic gears having a ratio
of 5.33. The motor, gears, battery, and flight-program-cam drive
are integrated into an ingeniously contrived plastic housing that
would make a Chinese block-puzzle designer writhe in envy. The complete
power unit is available from Mattel for $7.50 as a replacement part.
The charging cord and prop are not included, however, so at $10
to $15 for the complete aircraft, the Super Star is the biggest
bargain in town.
Now there is a new Super Star in the sky,
with 15% more power, a general beefing up of the weaker spots, a
very slight increase in cost, and identified by its yellowish carton.
About 112% of the earlier propshafts failed prematurely, so Mattel
adopted an alloy steel shaft heat treated for maximum toughness.
Perhaps that is the sort of attention to detail that helped make
Mattel the country's leading toy manufacturer.
The most distinguishable features of the new Super Star are a man
that parachutes to earth and streamers that unfurl in towed-sign
fashion, actuated by the already somewhat ludicrous flight programmer.
Personally, I'll take plain vanilla-a model that takes off the ground,
circles realistically, and glides in for a fair landing is enough
to expect of a toy airplane. Clearly, unfurling streamers and parachuting
dolls befit only mere toys and are scarcely worthy of notice by
"serious" model hobbyists. Still, if the same system were used to
retract the landing gear, then lower it, along with the flaps ...
Website visitor Brian L. contacted me about finding
replacement batteries for his vintage Mattel Super Star
electric R/C model. He sent me photos of his model and the
power drive system from the airplane.
Mattel Super Star power system.
1970s era Mattel Super Star kit.
still sells the 1/3-AA, 110 mAH NiCad cells.
I definitely recommend against charging the batteries with
anything other than a charger designed to control the current
supply. Using a 6V lantern battery wasn't a good idea then
or now. Aside from possibly causing a fire, improper charging
can ruin the cell's capacity to hold a charge. The link
below is for a NiCad charger that will with 3 cells in series.
You might be able to find something cheaper, but if you
plan to pursue this for awhile, it's well worth the investment.
There is no need to chuck your old Super Star power plants or
to delay buying one if the new model is not available. The increased
power is obtained by loading the motor more heavily by virtue of
a lower numerical gear ratio. The battery is the same, so the flight
duration is decreased slightly. The same result could be obtained
by loading the motor with a prop of higher pitch, greater diameter,
or greater blade area. To a rubber-power nut this must seem backwards-more
power and less motor run with a larger prop - but that is the way
The next step is a big one, as there are no power
plants between the $7.50 Super Star unit and ones costing six times
The Alpha Power Unit: The heart of
the Alpha is a specially rewound and reworked 26D-size can-type
slot-car motor, fitted with two ball bearings. The output countershaft
turns in sintered bronze bearings and is coupled to the motor by
a steel pinion driving a nylon gear, with a ratio of 5.78. The stock
10x6 wooden prop is cemented directly to the output gear. The assembly
consisting of the prop, shaft, and gear sells for $3.50 and is easily
replaced. The battery consists of five 500 mAh AA-size cells made
by General Electric. The motor is provided with a shock-absorbing
Lexan tab for mounting it to the fuselage. The complete motor-battery
system, selling for $45.50, includes a cord for overnight charging
from a car battery. A fast-charging cord, which includes a high-wattage
current-limiting resistor, is available at extra cost.
accessories are of interest to the purchasers 'of either the Alpha
or other electric propulsion system of comparable power. The Solid
State Timer ($14.95), weighing an ounce, turns off the motor after
a period that is adjust-able from 30 see, to four min. The one-oz.
Mocontrol ($12.95) which may be used with any RC system, provides
in-flight on-off control of the motor without requiring an additional
RC channel. A small permanent magnet is mounted to any moving part
of the rudder control system. The Mocontrol sensor is mounted in
the aircraft close to the magnet. A quick blip of full left rudder
turns the motor off; a right blip restores full power.
The Signal Command: On the next rung of the cost-power
ladder, the Signal Command power unit looks like a Super Star that
has been popping Big Pills. The housing and gearing configurations
bear a family resemblance. The battery, a cylindrical cluster of
six G.E.250mAh 1/2AA-size cells, slips over the propshaft housing.
Two 1/3-AA cells to drive the radio, and the galloping ghost actuator,
are built into the power unit housing. The 9 x 7 prop, driven through
a 5-to-1 gear reduction from the 1/50-hp motor, adequately powers
the four-ft. 25-oz. Signal Command aircraft.
Drawings by Bob Meuser
motor has a three-slot armature, carbon brushes, and is similar
in design to that in the Super Star. A three-position switch lever
projects from the bottom. The back position is off. The middle position
fires up the radio gear and allows the motor to run once it is started.
The forward position starts the motor, and after the lever is released
it flips back to the run position. The prop thrust pulls the propshaft
forward actuating a switch and keeping the motor running. Should
the prop tangle with the weeds or the model nose over, the propshaft
slides back and turns the motor off, preventing a burnout. Should
that fail, an easily replaced automotive type fuse blows. The thrust-actuated
switch serves another function: When the battery starts running
out of beans, the circuit is broken, preventing the battery from
discharging completely, which could cause reverse charging of the
The Signal Command is no longer in production.
Mattel's policy is to carry spare parts in stock for a number of
years beyond production, so the power unit will continue to be available
as a spare part.
The EMF-040: The most recent propulsion
system on the scene, and an exceptionally complete one, is the ElectroMotive
Flight system by United Recording Electronic Industries. The Power
Module is a streamlined pod containing the motor, reduction gearing,
charging cord receptacle, switch, a low-voltage cut-off device to
prevent charge reversal, a free-wheeling device, and a radio interference
suppression system. An optional sold-state timer, weighing 0.65
oz., and adjustable for motor run times of from one to five min.
may also be installed within the pod. The rear portion of the pod
may be removed to facilitate fuselage mounting.
Charging Unit is provided for charging the ni-cad batteries from
a 12V car or cycle battery. This is not simply a line cord and current•limiting
resistor. It includes a battery-temperature sensor and a control
circuit that decreases the charging current as the fully•charged
condition is approached, a solid-state timer to permit unattended
operation, and a meter to indicate any anomalies in the system.
Two alternative battery packs are offered. The smaller one weighs
3.6 oz., contains six 250 mAh 1/2AA-size ni-cads, and drives the
motor to 1/40 hp for a motor run of three to five min. The larger
pack weighs 5.3 oz., contains seven 450mAh AA-size ni-cads, and
drives the motor to 1/25 hp for a motor run of 3-1/2 to 5-1/2 min.
Motor run is roughly 1/2 to 2/3 of the charging time.
of 7, 8, and 9-in. dia. are offered. They are high-pitch, wide-blade,
square-tip props about midway between typical gas engine and rubber-driven
designs. As if this were not enough, an optional pulse-width-modulated
throttle control is available. A kit for an RC trainer, the Electric
I, is offered. Designed by Freddie Reese and Don Dombrowski, it
spans 52 in. and weighs 17 to 22 oz., depending on the battery pack
and radio system used. The motor is similar to a slot-car motor
in configuration, but it is designed to produce high power at relatively
low rpm. The motor efficiency (56%) and power-to-weight ratio (1/4.4
hp/lb.) are exceptionally high for such a small unit, especially
when one considers that the weight is that of the entire power pod,
not merely the bare motor.
The specifications quoted above
are based on tests of pre-production prototypes performed by the
manufacturer. At this writing the system is not yet in production
and prices have not been established.
The Graupner Hi-Fly:
Johannes Graupner of Germany, one of the oldest names in commercial
electric propulsion, has recently introduced a new electric propulsion
system as an alternate power plant for its Hi-Fly aircraft. The
Hi-Fly is basically a high-performance RC glider, spanning 90 in.
and weighing two lb.
Two propulsion systems are offered:
An over-the-wing pod housing a Cox Golden Bee or a Cox TD 051, and
the Electroprop system. The Electroprop system consists of two motors,
one on the trailing edge of each wing, driving 14-in. folding pusher
props. The 12-volt motors are driven in parallel by two G-volt Varta
ni-cad batteries in series. The total weight of the propulsion system
is two lb., doubling the flying weight of the aircraft. The power
output of each motor, inferred from the published data on the aircraft
performance, is about 1/45 hp, giving the aircraft an average rate
of climb of 180 ft,/ min. for the first three min. of the ten-min.
The design philosophy follows that applied by
Graupner engineer Fred Militky to the earlier Silencer and Silentius
aircraft: A high gear ratio to permit the use of a large, high-pitch,
rubber-power type prop capable of very high efficiency at low aircraft
speeds. The motors are not the Micro-Mo motors employed in the earlier
aircraft, but are much more powerful ones of conventional design,
employing five-slot armatures and internal brushes. Motors, motor
mounts, props, batteries and various accessories are available separately
or as a complete package. An ungeared version of the motor is also
offered, primarily for model boats. The geared motors would be unsuitable
for any aircraft that is not quite similar to the Hi-Fly. As they
require 12 volts, two battery packs would be required even for one
motor. The power-to-weight ratio would then be too low for anything
but a super-efficient, super-light aircraft, but the motor run would
be extended to 20 min. The high gear ratio requires that a large
prop be used-too large for conveniently mounting the motor to the
nose of the fuselage, and also too large for a pylon mount. For
the intended application, however, the system seems well suited.
The Electroprop system is expected to be available in the U.S.
in September or October, and will be sold through normal hobby supply
channels. U.S. prices have not been announced.
10 and Astra 25: The Astra 10 and 25 motors are specially modified
high-quality industrial motors. End bells are ventilated to provide
air cooling. The prop is bolted directly to an extension of the
armature shaft. The brushes are cantilever-arm mounted. The five-and
seven-slot armatures turn on precision ball bearings at the front
and sintered bearings at the rear. The Astra 10 battery contains
12 550 mAh 1/2-sub-C cells. Two 10-volt batteries connected in series
drive the Astra 25, and two sizes are available: 550 mAh, eight
1/2-sub-C cells; 1200mAh, eight sub-C cells. Batteries are enclosed
in a light plastic container. The Astra 10 battery is charged from
three 6-volt motorcycle batteries in series. Astra 25 batteries
are charged in parallel from a 12-volt battery.
of the Astra 25-25% larger than the production model, and driven
by a one-shot Eagle-Pincher silver-zinc battery-was used by Roland
Boucher in the Fournier RF-4 that he flew for 30 min. at an average
speed of 40 mph. With stock ni-cad batteries flights up to eight
min. are obtained. Recently the Boucher brothers and their associates
have been flying their Electro-Sport-10 aircraft with the Astra
10 motor. This is a simple sheet-covered model with an all-up weight
of 38 oz. and controlled by a Kraft two-channel "brick." Span is
42 in., but spans from 36 to 44 in. have been tried. They now have
a "throttle" control that gives a realistic 600 rpm idle. Aircraft
companies have used the Astra motors to power RC models of various
sorts, including a model of an STOL aircraft, some being multi-engine
The Kroker Systems: The Kraker motors-Sea
Ram, Sea Wasp. etc.-are generally regarded as the world's best model
boat motors. Most world records have been set with Kraker-powered
boats, and at the last European Championships, the winning English
team used Sea Wasp 12 motors. The requirements for aircraft propulsion
are essentially the same as those for boat propulsion: high power/weight
ratio, high efficiency, high reliability, and long life. While the
3/8 hp Sea Ram is a bit large for aircraft, the 1/10 hp Sea Pup
was specifically designed with aircraft propulsion in mind .
The 12-slot armature, which is more expensive to manufacture.
than one with fewer slots (or poles, if you prefer). turns on two
sealed precision ball bearings supported in rigid aluminum end castings.
The shunted, cartridge-mounted silver-impregnated brushes turn against
a 12-bar silver-copper alloy commutator (24-bar on the Sea Wasp
12.) The result is a military quality commutator that can pass a
30,000 rpm spin test at 5000F and still satisfy a run-out specification
of 0.0005 in. Aircraft prop adapters are available, as are batteries
containing imported SAFT ni-cad cells. Brush timing can easily be
set by the user for either clockwise or counter-clockwise rotation.
The Kraker motors are obviously designed for long trouble-free operation,
in addition to their high power-to-weight ratio and high efficiency.
Batteries: For most model aircraft propulsion applications,
the only batteries worth considering contain nickel-cadmium cells
of the sealed cylindrical type (not the button type) having sintered
plate construction. Most of these are equipped with a safety valve
to pre-vent the cell from exploding due to the generation of excess
gas. While such cells have a safety valve or "vent," they are not
termed "vented" batteries; that term is reserved for the ni-cad
batteries that are built like car batteries with liquid electrolyte
Cylindrical ni-cads are made by a number
of manufacturers: Gulton, Gould, Marathon, Union Carbide (Eveready),
and General Electric in the U.S., SAFT in France (distributed in
the U.S. exclusively by Kraker Engineering), Varta in Germany, and
probably many others.
Some cells, by virtue of their inherent
size and shape, and because of the way the connections are made
inside, can be discharged very rapidly without a severe voltage
drop, and without a great loss in capacity. Usually the smaller
cells are better at this, as there is simply a shorter distance
for the current and heat to travel. When it comes to cranking out
a moderate amount of power for a long time, the larger cells have
the edge-a higher energy for their weight. However, there are exceptions.
In the smaller sizes of cells, all cells cost about the same, regardless
of size; in the larger cells, cost is roughly proportional to capacity.
The normal charge rate for most ni-cads is that which charges
the battery to full capacity in about 14 hours. The charging current,
in amperes, is one-tenth of the nominal capacity in ampere-hours.
A 500 mAh (milliampere-hour) battery would be charged at a constant
current of 50 mA (milliamperes). At that charge rate, batteries
can be overcharged for a hundred hours or so without damage. Some
quick-charge cells can be charged in four hours and similarly left
on overcharge without damage. For our purpose much faster charging
is required. Once a cell becomes fully charged, all of the additional
energy pumped into the cell goes into the generation of heat and
gas. Up to a certain point, the gas is absorbed chemically within
the cell. Beyond that point, the gas is vented, and some of the
capacity of the cell is permanently lost. The difference between
a high-charge-rate cell and a normal-charge-rate cell is not so
much that the high-charge-rate cell can be charged faster, but that
it Can be overcharged at a high rate without damage.
manufacturers have developed systems for fully charging their batteries
in 15 to 30 min. A new line of Eveready "Hustler" cells, for example,
has been designed to exhibit a sharp temperature rise before the
pressure rises to the point where venting occurs, and the charging
is terminated when the temperature reaches a certain value. SAFT,
on the other hand, utilizes the sudden and reproducible voltage
rise that occurs with their cells to signal the end of the rapid-charge
period. These are just two examples, and you can be sure that the
other manufacturers who do not yet have such rapid-charge systems
are working hard at developing them.
That still is not fast
enough for a kid with the fidgets, but anything faster inevitably
results in either a ruined battery, or an incomplete charge. One
manufacturer of cells specifically intended for fast charging, for
example, states that 25% of the capacity can be obtained with a
one-min. charge, 45% with a three-min. charge, and 70% with a five-min.
charge. The method used is the "dump-timed-charged" method. The
cells are first "dumped," that is, completely discharged, or nearly
so. Then one applies a "timed charge"-a certain current for a certain
length of time-to a fraction of their capacity that is sufficiently
far removed from a full charge to ensure that the cells wilt not
be accidentally overcharged at a high rate.
A high-rate ni-cad
cell can be completely discharged hundreds of times. But, a battery
consisting of more than about two cells connected in series cannot
be completely discharged without suffering irreversible damage.
No two cells are identical, so in a series string of cells, one
cell is certain to be weaker than the others.
When the battery
is discharged, the weakest cell will become completely discharged,
while the others continue to produce current. That current flows
through all of the cells, including the weak one. The current is
in the direction opposite to that in which a cell should be charged,
so the weak cell becomes charged in reverse. At best, the cell will
lose a little of its capacity. At worst, the cell will become completely
incapable of being charged in the proper direction.
multi-cell battery, then, it is best to terminate the discharge
before the battery voltage drops too low. Prior to charging by the
dump-timed-charge method, it is best to discharge the battery cell
by cell, or to occasionally give the battery a long slow charge
to be certain all cells are fully and equally charged.
Conclusion: the power outputs of electric propulsion systems
seem low compared to those for glow engines. But it is not the power
output of the motor that counts, but rather the power output of
the prop. Tests have shown that a small geared electric motor puts
out the same propulsive power at 27 mph as a reed-valve 049 engine
having twice the horsepower. If the glow engine were geared down
about 3-to-1 the story would be different, of course. Small motors
turning at high rpm used in models that fly slowly must be geared
down to achieve a reasonably high propeller efficiency. For motors
as large as the Astro and Kroker motors, which turn at lower rpm
than their smaller .counterparts, and in models that fly fast, little
can be gained by gearing down the prop.
Since we started
gathering material for this article, several propulsion systems
we were initially not aware of have popped up, and there is a possibility
that there are still some that we missed. AAM apologizes for any
that have been omitted, and will update this review as new systems
appear. AAM is under-taking tests of a typical RC airplane to determine
the relative performance with both electric propulsion and gas-engine
propulsion in terms of both laboratory and field tests, and will
report on the results.
In a future article we will consider
the application of electric propulsion to various types of models.
We'll consider types of batteries other than NiCads. We'll show
you how to match the propeller, batteries, gears, prop, motor, and
aircraft to each other-not too formidable a job when it is laid
out step by step. And, we'll discuss some motors that are not specifically
intended for model aircraft propulsion, but which are nevertheless
Gas motors specifically designed for model
aircraft propulsion were commercially available near the turn of
the century, but it was thirty years before the gas engine had any
noticeable effect on sport or competition model aviation . Then
the gas engine suddenly took over, practically to the exclusion
of other forms of propulsion. Commercially available electric propulsion
systems were on the market 14 years ago, but it has only been within
the last year that electric propulsion has been more than an interesting
curiosity. Rather suddenly, interest has bloomed, and new systems
seem to pop up every few months. Where will it all lead? Who can
say. Ten years from now will we look back on electric propulsion
as the Hoola Hoop of Model Aviation? Or as we are topping-up our
NiCads, will we reminisce about the good old days when we used to
fly those noisy, balky, dirty old glow engines?
1) Specifications are for one power unit
and one battery. Two of each are required.
(2) Based on 1.2 volts
per cell except for Kraker motors which are manufacturer's ratings
(3) Tentative rating for aircraft propulsion.
For 1.2 Ah SAFT batteries having 9. 8. and 12 cells. respectively.
Batteries of 1.8 Ah and 4 All capacity are also available.
With corresponding increases in weight and flight duration.
Author's tests at nominal voltage. Average in-flight power will
be less, especially for systems with Short auratlon.
motor, estimated from manufacturer's aircraft performance data.
Average during first 3 min. at flight.
All other performance data is based on Information supplied by the
(7) Aircraft supplied with System. Other aircraft
sizes are from manufacturer's recommendations or are author's estimates.
Subject to wide variation, depending on type of performance desired.
P.O. Box 2350 Hollywood, Calif. 90028
and Dev. Co.
P.O. Box 14056 Albuquerque, N. Mex. 87111
Galler Electronic Industries
P.O. Box 87 So. Walpole, Mass.
United Recording Electronics Industries
St. North Hollywood, Calif. 91605
Astro Flight, Inc.
Cheryl PI. Los Angeles, Calif. 90049
7312 KirchheimjTeck Postfach 48jGermany
(See Kraker above)
Many thanks to the Academy of Model
Aeronautics for permitting the reprint of this invaluable article
from the July 1973 edition of American Aircraft Modeler