August 2003 113
THIS COLUMN will follow up on recent
column topics, share some reader comments
and questions, and commence a discussion of
basic electrical terms and concepts.
As I write this, the May issue has been out a
couple of months and readers are reacting to
one of the topics in that Radio Control
Electrics column. In it I described Stikum: a
simplistic though sizable Electric model that I
designed for the fun of pursuing a particular
challenge.
The essence of that discussion was not so
much about the airplane as it was about some
of the ideas and associated rationale that went
into it. The discussion concluded with the
words “Maybe it [Stikum] will give you some
ideas of your own.”
So much for the intent! Readers have been
asking about plans and/or who the
manufacturer is! First, there are no plans. As
proof of this, a local friend just completed his
Stikum—by virtue of me lending him mine so
he could “size it up” and duplicate it! Except
for rib templates, he had to measure from the
original design to make a duplicate. Second,
there is no manufacturer; it’s of scratch design
and construction.
Intent aside, this reader reaction does give
me a good feeling. It tells me that what I
described as a technical challenge for me is
something others see as a model of interest—
like with the friend I mentioned in the
preceding. It also suggests that some
manufacturer might do well to take note!
Some recent reader correspondence shared
an item that may be of interest to others. How
many of you can relate to the “penny behind
the fuse” concept? I only expect a reaction
from “more senior” aeromodelers (old
people!) who may remember fuse plugs in the
household power system. These fuses
preceded modern breakers and were
commonly used prior to the 1950s or 1960s.
Those 120-volt power-line fuses had
screw-in bases (like incandescent light bulbs
do) and were installed in household wiring,
clustered in fuse boxes, and located just inside
the power-line service entrance.
These round, flat-faced, screw-in fuses
generally had windows of mica or similar
material so that the element inside could be
seen. This allowed one to visually determine
if a fuse had blown. As with more modern
breakers, fuse plugs were available in many
ratings; e.g., 10, 15, 20, and 25 amps,
depending on the circuit need.
In those days it was common to hear of
someone using an oversize (with too high of a
rating) fuse if one had a circuit that was
constantly overloading. In a worse scenario, at
that time people might have put a penny
behind the fuse to bypass it (short it out),
thereby totally disabling the purpose of the
fuse. Of course, the fuse didn’t blow
anymore! It should be apparent that those
were not good ideas!
This brings me to fuses in Electrics and
what should be an obvious extension of the
preceding, but I’ll state it anyway. Choose a
fuse that is suited to the power-system
application.
I run most of my sport systems at roughly
25 amps peak but with an average flight
current less than that. Peak current demand
would generally be of short duration, such as
during takeoff or in some maneuvers. In line
Bob Kopski, 25 West End Dr., Lansdale PA 19446
RADIO CONTROL ELECTRICS
James (15), Will (12), and Emily (10) Hundley (Osburn ID), shown with their wet machines, have gotten into Electrics!
Bob Baxter’s (Oak Hill VA) 52-ounce, bulked-up Skyvolt (published in January 1990 MA).
He uses MEC hot wind, 8 or 10 cells, APC 12 x 8 propeller, Jeti ESC/BEC.
08sig4.QXD 5.23.03 1:06 pm Page 113
with this, most of my fuses are rated at 25
amps. But isn’t this marginal?
No. Years of experience have abundantly
demonstrated that this is just right—at least
for my systems. The chosen fuse does not
blow in flight, but rather quickly does if
needed.
Thus even though a 25-amp fuse may
seem too close for a typical 25-amp system,
these peaks of current lasting several seconds
are not high enough and long enough for the
fuse to function; it takes some time for a fuse
to blow at the rated conditions. The fuse
element has to heat enough for it to melt
(blow), so there is actually a time/temperature
aspect involved.
On the other hand, such a fuse selection
works rather well (quickly), such as during a
propeller strike or entanglement during which
the current can rise dramatically. (There’s
nothing like a stalled motor to result in high
current!) It’s a circumstance such as this in
which the right fuse does its job.
This discussion was inspired by a reader
letter that described using a 20-amp fuse in a
10-amp application (a Speed 400 system).
The propeller snarled in tall grass, the fuse
failed to blow, then his Electronic Speed
Control (ESC) went into meltdown because of
it. From what he described, it seems clear that
a 10-amp fuse would have been far more
appropriate—and far less costly!
This brings to mind a related matter. The
best thing one can do during such a mishap is
throttle down immediately. I fully realize that
limited “speed of thought” may challenge the
immediacy of this act, but fast stick action is
something for which to strive. This is no
different from hitting the switch with any
other electrical mishap, such as if your bench
saw or sander jams.
Throttling down is the right thing to do in
many circumstances, such as when you find
yourself having problems controlling your
model or maybe when it has gotten into an
awkward flight orientation. The fuse may not
be in jeopardy, but the airplane may be!
Get into the thought practice of throttling
down so that the airplane speed drops more
closely in line with your thinking speed. A
brief power reduction can save the day—and
your model.
Electrical terms and concepts continue to
confuse many E-aeromodelers. This shows up
routinely in my incoming reader mail. I even
expect some to show up from the preceding
discussion. What follows (with more coming
in the future) is some basic electrical and Epower
discussion.
“Voltage,” “current,” “power,” and
“resistance” are probably the most common
electrical terms that E-aeromodelers will see
or hear being used. These words routinely
appear in print such as in instructions for
motors, chargers, and ESCs, or in more
general E-writing such as in this and similar
E-columns and articles. They also come up in
the common language of the E-flightline.
Offhand I can’t think of any easy parallel
language within the wet-power community,
so in this regard electric is quite different.
Unlike electric, with wet power it’s not easy
to know or measure the energy stored in a fuel
tank, the rate of fuel flow, or the available
power this represents going into a fuelburning
engine.
The ready accessibility of these quantities
with electric power (with simple metering)
allows those interested to effectively play with
the trade-offs that are possible and therein get
the most out of their power systems—and this
hobby. At the same time, none of this is
outside the scope of high-school science class;
it’s not rocket science, so there is no reason to
feel intimidated.
Let’s begin with the idea of voltage;
instead of getting into the definition and deep
meaning of the term, I’ll jump right into its
common, practical usage. Perhaps the most
common or familiar experiences with voltage
are with the power line in your home or the
battery in your car or flashlight.
Common household appliances are
plugged into the 120-volt power line, and the
stuff in your car works on 12 volts. But why is
one voltage 10 times the other, and why are
there so many other commonplace voltage
values such as the 3-volt flashlight bulb? How
about the myriad cell counts (range of
voltage) used in E-power systems?
To answer these questions with insight and
appreciation, I must move to two other terms:
current and power. When voltage is applied to
a device, current (amps) flows from the
source of voltage to the device under power.
Some authors liken current to the volume
flow of water in a pipe and voltage to the
114 MODEL AVIATION
Also Available:
Vor tech Adapter Nuts
To avoid the problem of long screws, which tend to
flex and break at the point where they enter the adapter
nut, we make 4 lengths of adapter nuts:
Short, Long, Extra Long & Extra-Extra Long.
This allows for the use of shorter screws, which don’t
flex and break.
FIBER- FILLED MOTOR MOUNTS•VIBRA-DAMP ISOLATION MOUNTS•SOUTHERN
PRO RETRACTS•MICRO-BALLOONS•SOUTHERN’S SORGHUM•TX-POSER•HUSH-CLAMP PIPE MOUNT•STRABILIZER TX TRAY•FIBERGLASS PUSHRODS•CORDLESS STARTER PACK•FLEX-ALL•CARBON
F IBER TAPE•CARBON FIBRE STRIP•TRIMSEAL•SKYLOFT•C/APPLICATOR SIX SHOOTER FUEL PUMPS•HOLSTER•POUR’N’PUMP FUELING SYSTEMS•LITE FLITE WHEELS•TREADED LITE FLITE WHEELS•LECTRA LITE WHEELS•TREADED LECTRA LITE WHEELS•BIG LITE WHEELS•TREADED BIG LITE WHEELS•R/C
FLIGHT SIMULATORS FOR IBM COMPUTERS•TUNED PIPE MOUNT•VORTECH SPINNERS
4560 Layhigh Rd, Hamilton, OH 45013
513.738.1576 • www.dbproducts.com
Do You Need A Spinner
With Special Cutouts?
NO PROBLEM!
•Sizes up to 6 inches.
•Standard, Parabolic &
Ultimate styles.
•CNC machined to the
highest tolerances
•Strong, yet very light-weight
•Spun from Aluminum using
the same techniques used
for full-scale aircraft.
•Individually hand polished
& inspected
•Made in the USA.
There’s nothing better than having a beautiful, lightweight
spinner custom cut for your airplane. We cut our Vortech
Spinners to meet special requirements everyday.
Need a spinner for your multi-bladed prop? Maybe
something to fit a that special prop? No problem - give us a
call and we’ll be glad to help.
08sig4.QXD 5.23.03 1:06 pm Page 114
water pressure causing that flow. With
voltage present and current flowing, the
device being so powered is in fact getting
power.
Power (watts) is the product
(multiplication) of the voltage and the
current; that is, you need voltage and the
resulting current flow to have power. Power
is needed to do work. Think of “work” as
being that which you want done, be it turning
a propeller, lighting a light, or cooling a beer
in the refrigerator.
Consider a typical 1,200-watt household
clothes iron plugged into the 120-volt outlet.
It draws 10 amps since 120 volts multiplied
by 10 amps equals 1,200 watts. A 40-watt
soldering iron, like many used to make
battery packs, draws 40 divided by 120, or
0.333 amps (333 milliamps). The clothes iron
can heat much larger surfaces than the
soldering iron; i.e., the clothes iron can do
more work, or a bigger job, and that’s why it
needs—and consumes—much more power.
Similarly, a 3⁄4-watt flashlight bulb outputs
vastly less light than a 100-watt household
lightbulb. Again, the higher-power device
does a bigger job than the lower-power one.
For purposes of E-flight, a 300-watt power
system can fly a much bigger and heavier
aeromodel than can a 30-watt power system.
Consider an imaginary 100-watt electric
device (it doesn’t matter what it is). If it was
designed to operate on the 120-volt power
line, it would draw 100 ÷ 120 = 0.833 amps.
If it was designed to operate on the 12-volt
car battery, it would draw 100 ÷ 12 = 8.33
amps. There is an infinite number of
voltage/current design combinations that
would result in the same 100 watts—and do
the same device job—so how are particular
voltage and current choices made, and why?
It basically comes down to the
practicalities and common sense of the
application environment. Reconsider that
1,200-watt clothes iron. If this was a 12-volt
device, it would draw 100 amps. If all
household appliances were 12-volt devices,
the wiring, outlets, appliance switches,
everything would be vastly more massive.
Imagine that the power cord on a 12-volt,
100-amp clothes iron would be heavier than
the iron itself—not at all practical!
Now look at things the other way around.
The high-voltage distribution lines that
traverse neighborhoods are high voltage so
that the current they carry can be held to
“reasonable values.” Thus a kilovolts power
line, supplying megawatts to a neighborhood
or community, does so at far lower current
levels than would be the case at 120 volts.
(Local transformers convert the high-voltage
distribution levels to the familiar 120-volt
level.)
But why not just use the kilovolts—
instead of 120 volts—directly in the home?
Aside from being downright dangerous,
imagine how the home wiring might look.
Electrical outlets would have prongs many
inches apart. A damp day might allow corona
inside the house. Huge porcelain insulators
would separate room-to-room conductors by
several feet. Your home would have to be
much larger just to accommodate the widespaced
wiring!
Bringing all of this closer to our
aeromodeling interests, consider that a 300-
watt E-power system could be made with a
15-volt motor requiring 20 amps. Or it could
theoretically be realized with a 150-volt
motor drawing 2 amps. Or it could be done
with a 1.5-volt motor drawing 200 amps.
We know that the first suggestion is about
right. The second option has the appeal of
low current, but it would need approximately
125 cells to do this. Imagine the cost! The
third, or low-voltage option, might sound
appealing in that it needs only one, though
very large, cell, but the system wire, ESC,
fuse, switch, and connectors would be so
massive to handle the 200 amps that the
component size and associated system weight
would each likely be several times normal!
From all of the preceding it should be
clear that good choices—really design tradeoffs
and practical compromises—of voltage
and current levels are needed to achieve the
power level needed for the job at hand, no
matter the application. More about all of this
is to come.
Thus ends this column. Please include a selfaddressed,
stamped envelope with any
correspondence for which you’d like a reply.
Everyone so doing does get one! And do
make it a point to take a nonbelieving wetflying
friend to an E-meet; I’ve never seen
anyone leave a meet unconvinced! Happy Elandings,
everyone! MA
August 2003 115
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(334) 598-2287 • 4:00 - 10:00 CST
08sig4.QXD 5.23.03 1:06 pm Page 115
Edition: Model Aviation - 2003/08
Page Numbers: 113,114,115
Edition: Model Aviation - 2003/08
Page Numbers: 113,114,115
August 2003 113
THIS COLUMN will follow up on recent
column topics, share some reader comments
and questions, and commence a discussion of
basic electrical terms and concepts.
As I write this, the May issue has been out a
couple of months and readers are reacting to
one of the topics in that Radio Control
Electrics column. In it I described Stikum: a
simplistic though sizable Electric model that I
designed for the fun of pursuing a particular
challenge.
The essence of that discussion was not so
much about the airplane as it was about some
of the ideas and associated rationale that went
into it. The discussion concluded with the
words “Maybe it [Stikum] will give you some
ideas of your own.”
So much for the intent! Readers have been
asking about plans and/or who the
manufacturer is! First, there are no plans. As
proof of this, a local friend just completed his
Stikum—by virtue of me lending him mine so
he could “size it up” and duplicate it! Except
for rib templates, he had to measure from the
original design to make a duplicate. Second,
there is no manufacturer; it’s of scratch design
and construction.
Intent aside, this reader reaction does give
me a good feeling. It tells me that what I
described as a technical challenge for me is
something others see as a model of interest—
like with the friend I mentioned in the
preceding. It also suggests that some
manufacturer might do well to take note!
Some recent reader correspondence shared
an item that may be of interest to others. How
many of you can relate to the “penny behind
the fuse” concept? I only expect a reaction
from “more senior” aeromodelers (old
people!) who may remember fuse plugs in the
household power system. These fuses
preceded modern breakers and were
commonly used prior to the 1950s or 1960s.
Those 120-volt power-line fuses had
screw-in bases (like incandescent light bulbs
do) and were installed in household wiring,
clustered in fuse boxes, and located just inside
the power-line service entrance.
These round, flat-faced, screw-in fuses
generally had windows of mica or similar
material so that the element inside could be
seen. This allowed one to visually determine
if a fuse had blown. As with more modern
breakers, fuse plugs were available in many
ratings; e.g., 10, 15, 20, and 25 amps,
depending on the circuit need.
In those days it was common to hear of
someone using an oversize (with too high of a
rating) fuse if one had a circuit that was
constantly overloading. In a worse scenario, at
that time people might have put a penny
behind the fuse to bypass it (short it out),
thereby totally disabling the purpose of the
fuse. Of course, the fuse didn’t blow
anymore! It should be apparent that those
were not good ideas!
This brings me to fuses in Electrics and
what should be an obvious extension of the
preceding, but I’ll state it anyway. Choose a
fuse that is suited to the power-system
application.
I run most of my sport systems at roughly
25 amps peak but with an average flight
current less than that. Peak current demand
would generally be of short duration, such as
during takeoff or in some maneuvers. In line
Bob Kopski, 25 West End Dr., Lansdale PA 19446
RADIO CONTROL ELECTRICS
James (15), Will (12), and Emily (10) Hundley (Osburn ID), shown with their wet machines, have gotten into Electrics!
Bob Baxter’s (Oak Hill VA) 52-ounce, bulked-up Skyvolt (published in January 1990 MA).
He uses MEC hot wind, 8 or 10 cells, APC 12 x 8 propeller, Jeti ESC/BEC.
08sig4.QXD 5.23.03 1:06 pm Page 113
with this, most of my fuses are rated at 25
amps. But isn’t this marginal?
No. Years of experience have abundantly
demonstrated that this is just right—at least
for my systems. The chosen fuse does not
blow in flight, but rather quickly does if
needed.
Thus even though a 25-amp fuse may
seem too close for a typical 25-amp system,
these peaks of current lasting several seconds
are not high enough and long enough for the
fuse to function; it takes some time for a fuse
to blow at the rated conditions. The fuse
element has to heat enough for it to melt
(blow), so there is actually a time/temperature
aspect involved.
On the other hand, such a fuse selection
works rather well (quickly), such as during a
propeller strike or entanglement during which
the current can rise dramatically. (There’s
nothing like a stalled motor to result in high
current!) It’s a circumstance such as this in
which the right fuse does its job.
This discussion was inspired by a reader
letter that described using a 20-amp fuse in a
10-amp application (a Speed 400 system).
The propeller snarled in tall grass, the fuse
failed to blow, then his Electronic Speed
Control (ESC) went into meltdown because of
it. From what he described, it seems clear that
a 10-amp fuse would have been far more
appropriate—and far less costly!
This brings to mind a related matter. The
best thing one can do during such a mishap is
throttle down immediately. I fully realize that
limited “speed of thought” may challenge the
immediacy of this act, but fast stick action is
something for which to strive. This is no
different from hitting the switch with any
other electrical mishap, such as if your bench
saw or sander jams.
Throttling down is the right thing to do in
many circumstances, such as when you find
yourself having problems controlling your
model or maybe when it has gotten into an
awkward flight orientation. The fuse may not
be in jeopardy, but the airplane may be!
Get into the thought practice of throttling
down so that the airplane speed drops more
closely in line with your thinking speed. A
brief power reduction can save the day—and
your model.
Electrical terms and concepts continue to
confuse many E-aeromodelers. This shows up
routinely in my incoming reader mail. I even
expect some to show up from the preceding
discussion. What follows (with more coming
in the future) is some basic electrical and Epower
discussion.
“Voltage,” “current,” “power,” and
“resistance” are probably the most common
electrical terms that E-aeromodelers will see
or hear being used. These words routinely
appear in print such as in instructions for
motors, chargers, and ESCs, or in more
general E-writing such as in this and similar
E-columns and articles. They also come up in
the common language of the E-flightline.
Offhand I can’t think of any easy parallel
language within the wet-power community,
so in this regard electric is quite different.
Unlike electric, with wet power it’s not easy
to know or measure the energy stored in a fuel
tank, the rate of fuel flow, or the available
power this represents going into a fuelburning
engine.
The ready accessibility of these quantities
with electric power (with simple metering)
allows those interested to effectively play with
the trade-offs that are possible and therein get
the most out of their power systems—and this
hobby. At the same time, none of this is
outside the scope of high-school science class;
it’s not rocket science, so there is no reason to
feel intimidated.
Let’s begin with the idea of voltage;
instead of getting into the definition and deep
meaning of the term, I’ll jump right into its
common, practical usage. Perhaps the most
common or familiar experiences with voltage
are with the power line in your home or the
battery in your car or flashlight.
Common household appliances are
plugged into the 120-volt power line, and the
stuff in your car works on 12 volts. But why is
one voltage 10 times the other, and why are
there so many other commonplace voltage
values such as the 3-volt flashlight bulb? How
about the myriad cell counts (range of
voltage) used in E-power systems?
To answer these questions with insight and
appreciation, I must move to two other terms:
current and power. When voltage is applied to
a device, current (amps) flows from the
source of voltage to the device under power.
Some authors liken current to the volume
flow of water in a pipe and voltage to the
114 MODEL AVIATION
Also Available:
Vor tech Adapter Nuts
To avoid the problem of long screws, which tend to
flex and break at the point where they enter the adapter
nut, we make 4 lengths of adapter nuts:
Short, Long, Extra Long & Extra-Extra Long.
This allows for the use of shorter screws, which don’t
flex and break.
FIBER- FILLED MOTOR MOUNTS•VIBRA-DAMP ISOLATION MOUNTS•SOUTHERN
PRO RETRACTS•MICRO-BALLOONS•SOUTHERN’S SORGHUM•TX-POSER•HUSH-CLAMP PIPE MOUNT•STRABILIZER TX TRAY•FIBERGLASS PUSHRODS•CORDLESS STARTER PACK•FLEX-ALL•CARBON
F IBER TAPE•CARBON FIBRE STRIP•TRIMSEAL•SKYLOFT•C/APPLICATOR SIX SHOOTER FUEL PUMPS•HOLSTER•POUR’N’PUMP FUELING SYSTEMS•LITE FLITE WHEELS•TREADED LITE FLITE WHEELS•LECTRA LITE WHEELS•TREADED LECTRA LITE WHEELS•BIG LITE WHEELS•TREADED BIG LITE WHEELS•R/C
FLIGHT SIMULATORS FOR IBM COMPUTERS•TUNED PIPE MOUNT•VORTECH SPINNERS
4560 Layhigh Rd, Hamilton, OH 45013
513.738.1576 • www.dbproducts.com
Do You Need A Spinner
With Special Cutouts?
NO PROBLEM!
•Sizes up to 6 inches.
•Standard, Parabolic &
Ultimate styles.
•CNC machined to the
highest tolerances
•Strong, yet very light-weight
•Spun from Aluminum using
the same techniques used
for full-scale aircraft.
•Individually hand polished
& inspected
•Made in the USA.
There’s nothing better than having a beautiful, lightweight
spinner custom cut for your airplane. We cut our Vortech
Spinners to meet special requirements everyday.
Need a spinner for your multi-bladed prop? Maybe
something to fit a that special prop? No problem - give us a
call and we’ll be glad to help.
08sig4.QXD 5.23.03 1:06 pm Page 114
water pressure causing that flow. With
voltage present and current flowing, the
device being so powered is in fact getting
power.
Power (watts) is the product
(multiplication) of the voltage and the
current; that is, you need voltage and the
resulting current flow to have power. Power
is needed to do work. Think of “work” as
being that which you want done, be it turning
a propeller, lighting a light, or cooling a beer
in the refrigerator.
Consider a typical 1,200-watt household
clothes iron plugged into the 120-volt outlet.
It draws 10 amps since 120 volts multiplied
by 10 amps equals 1,200 watts. A 40-watt
soldering iron, like many used to make
battery packs, draws 40 divided by 120, or
0.333 amps (333 milliamps). The clothes iron
can heat much larger surfaces than the
soldering iron; i.e., the clothes iron can do
more work, or a bigger job, and that’s why it
needs—and consumes—much more power.
Similarly, a 3⁄4-watt flashlight bulb outputs
vastly less light than a 100-watt household
lightbulb. Again, the higher-power device
does a bigger job than the lower-power one.
For purposes of E-flight, a 300-watt power
system can fly a much bigger and heavier
aeromodel than can a 30-watt power system.
Consider an imaginary 100-watt electric
device (it doesn’t matter what it is). If it was
designed to operate on the 120-volt power
line, it would draw 100 ÷ 120 = 0.833 amps.
If it was designed to operate on the 12-volt
car battery, it would draw 100 ÷ 12 = 8.33
amps. There is an infinite number of
voltage/current design combinations that
would result in the same 100 watts—and do
the same device job—so how are particular
voltage and current choices made, and why?
It basically comes down to the
practicalities and common sense of the
application environment. Reconsider that
1,200-watt clothes iron. If this was a 12-volt
device, it would draw 100 amps. If all
household appliances were 12-volt devices,
the wiring, outlets, appliance switches,
everything would be vastly more massive.
Imagine that the power cord on a 12-volt,
100-amp clothes iron would be heavier than
the iron itself—not at all practical!
Now look at things the other way around.
The high-voltage distribution lines that
traverse neighborhoods are high voltage so
that the current they carry can be held to
“reasonable values.” Thus a kilovolts power
line, supplying megawatts to a neighborhood
or community, does so at far lower current
levels than would be the case at 120 volts.
(Local transformers convert the high-voltage
distribution levels to the familiar 120-volt
level.)
But why not just use the kilovolts—
instead of 120 volts—directly in the home?
Aside from being downright dangerous,
imagine how the home wiring might look.
Electrical outlets would have prongs many
inches apart. A damp day might allow corona
inside the house. Huge porcelain insulators
would separate room-to-room conductors by
several feet. Your home would have to be
much larger just to accommodate the widespaced
wiring!
Bringing all of this closer to our
aeromodeling interests, consider that a 300-
watt E-power system could be made with a
15-volt motor requiring 20 amps. Or it could
theoretically be realized with a 150-volt
motor drawing 2 amps. Or it could be done
with a 1.5-volt motor drawing 200 amps.
We know that the first suggestion is about
right. The second option has the appeal of
low current, but it would need approximately
125 cells to do this. Imagine the cost! The
third, or low-voltage option, might sound
appealing in that it needs only one, though
very large, cell, but the system wire, ESC,
fuse, switch, and connectors would be so
massive to handle the 200 amps that the
component size and associated system weight
would each likely be several times normal!
From all of the preceding it should be
clear that good choices—really design tradeoffs
and practical compromises—of voltage
and current levels are needed to achieve the
power level needed for the job at hand, no
matter the application. More about all of this
is to come.
Thus ends this column. Please include a selfaddressed,
stamped envelope with any
correspondence for which you’d like a reply.
Everyone so doing does get one! And do
make it a point to take a nonbelieving wetflying
friend to an E-meet; I’ve never seen
anyone leave a meet unconvinced! Happy Elandings,
everyone! MA
August 2003 115
BEYOND
QUIET!
More Power and Performance...
Priced Less than You’ld Expect!
PO BOX 141, MILFORD, CT 06460
phone:(203) 877-1670
fax:(203) 876-2731
www.davisdieseldevelopment.com
DIESEL DEVELOPMENT
For Complete Catalog send $5 (credited to first order)
NEW
LOW
PRICES!
BOLT-ON
MOUNT!
QUIET SCALE
SERIES
NEW!
YOU ASKED...
WE LISTENED!
Built
in the
U.S.A.
No more straps,
these bolt-on
beauties have a
black powder
finish, built in
pressure fitting
and all internal
baffles are still
there for sound reduction without loss of power.
Available for .40 to .90 engines.
Email us for current prices at
[email protected]
FIBERGLASS CLOTH
Premium Grade
3/4 oz 38”W 10 yrd. min. $2.50 yd.
Lower Prices 30 yds. & up
Other Weights Available
TinLin’s
17 Andrews Drive • Daleville, AL 36322
(334) 598-2287 • 4:00 - 10:00 CST
08sig4.QXD 5.23.03 1:06 pm Page 115
Edition: Model Aviation - 2003/08
Page Numbers: 113,114,115
August 2003 113
THIS COLUMN will follow up on recent
column topics, share some reader comments
and questions, and commence a discussion of
basic electrical terms and concepts.
As I write this, the May issue has been out a
couple of months and readers are reacting to
one of the topics in that Radio Control
Electrics column. In it I described Stikum: a
simplistic though sizable Electric model that I
designed for the fun of pursuing a particular
challenge.
The essence of that discussion was not so
much about the airplane as it was about some
of the ideas and associated rationale that went
into it. The discussion concluded with the
words “Maybe it [Stikum] will give you some
ideas of your own.”
So much for the intent! Readers have been
asking about plans and/or who the
manufacturer is! First, there are no plans. As
proof of this, a local friend just completed his
Stikum—by virtue of me lending him mine so
he could “size it up” and duplicate it! Except
for rib templates, he had to measure from the
original design to make a duplicate. Second,
there is no manufacturer; it’s of scratch design
and construction.
Intent aside, this reader reaction does give
me a good feeling. It tells me that what I
described as a technical challenge for me is
something others see as a model of interest—
like with the friend I mentioned in the
preceding. It also suggests that some
manufacturer might do well to take note!
Some recent reader correspondence shared
an item that may be of interest to others. How
many of you can relate to the “penny behind
the fuse” concept? I only expect a reaction
from “more senior” aeromodelers (old
people!) who may remember fuse plugs in the
household power system. These fuses
preceded modern breakers and were
commonly used prior to the 1950s or 1960s.
Those 120-volt power-line fuses had
screw-in bases (like incandescent light bulbs
do) and were installed in household wiring,
clustered in fuse boxes, and located just inside
the power-line service entrance.
These round, flat-faced, screw-in fuses
generally had windows of mica or similar
material so that the element inside could be
seen. This allowed one to visually determine
if a fuse had blown. As with more modern
breakers, fuse plugs were available in many
ratings; e.g., 10, 15, 20, and 25 amps,
depending on the circuit need.
In those days it was common to hear of
someone using an oversize (with too high of a
rating) fuse if one had a circuit that was
constantly overloading. In a worse scenario, at
that time people might have put a penny
behind the fuse to bypass it (short it out),
thereby totally disabling the purpose of the
fuse. Of course, the fuse didn’t blow
anymore! It should be apparent that those
were not good ideas!
This brings me to fuses in Electrics and
what should be an obvious extension of the
preceding, but I’ll state it anyway. Choose a
fuse that is suited to the power-system
application.
I run most of my sport systems at roughly
25 amps peak but with an average flight
current less than that. Peak current demand
would generally be of short duration, such as
during takeoff or in some maneuvers. In line
Bob Kopski, 25 West End Dr., Lansdale PA 19446
RADIO CONTROL ELECTRICS
James (15), Will (12), and Emily (10) Hundley (Osburn ID), shown with their wet machines, have gotten into Electrics!
Bob Baxter’s (Oak Hill VA) 52-ounce, bulked-up Skyvolt (published in January 1990 MA).
He uses MEC hot wind, 8 or 10 cells, APC 12 x 8 propeller, Jeti ESC/BEC.
08sig4.QXD 5.23.03 1:06 pm Page 113
with this, most of my fuses are rated at 25
amps. But isn’t this marginal?
No. Years of experience have abundantly
demonstrated that this is just right—at least
for my systems. The chosen fuse does not
blow in flight, but rather quickly does if
needed.
Thus even though a 25-amp fuse may
seem too close for a typical 25-amp system,
these peaks of current lasting several seconds
are not high enough and long enough for the
fuse to function; it takes some time for a fuse
to blow at the rated conditions. The fuse
element has to heat enough for it to melt
(blow), so there is actually a time/temperature
aspect involved.
On the other hand, such a fuse selection
works rather well (quickly), such as during a
propeller strike or entanglement during which
the current can rise dramatically. (There’s
nothing like a stalled motor to result in high
current!) It’s a circumstance such as this in
which the right fuse does its job.
This discussion was inspired by a reader
letter that described using a 20-amp fuse in a
10-amp application (a Speed 400 system).
The propeller snarled in tall grass, the fuse
failed to blow, then his Electronic Speed
Control (ESC) went into meltdown because of
it. From what he described, it seems clear that
a 10-amp fuse would have been far more
appropriate—and far less costly!
This brings to mind a related matter. The
best thing one can do during such a mishap is
throttle down immediately. I fully realize that
limited “speed of thought” may challenge the
immediacy of this act, but fast stick action is
something for which to strive. This is no
different from hitting the switch with any
other electrical mishap, such as if your bench
saw or sander jams.
Throttling down is the right thing to do in
many circumstances, such as when you find
yourself having problems controlling your
model or maybe when it has gotten into an
awkward flight orientation. The fuse may not
be in jeopardy, but the airplane may be!
Get into the thought practice of throttling
down so that the airplane speed drops more
closely in line with your thinking speed. A
brief power reduction can save the day—and
your model.
Electrical terms and concepts continue to
confuse many E-aeromodelers. This shows up
routinely in my incoming reader mail. I even
expect some to show up from the preceding
discussion. What follows (with more coming
in the future) is some basic electrical and Epower
discussion.
“Voltage,” “current,” “power,” and
“resistance” are probably the most common
electrical terms that E-aeromodelers will see
or hear being used. These words routinely
appear in print such as in instructions for
motors, chargers, and ESCs, or in more
general E-writing such as in this and similar
E-columns and articles. They also come up in
the common language of the E-flightline.
Offhand I can’t think of any easy parallel
language within the wet-power community,
so in this regard electric is quite different.
Unlike electric, with wet power it’s not easy
to know or measure the energy stored in a fuel
tank, the rate of fuel flow, or the available
power this represents going into a fuelburning
engine.
The ready accessibility of these quantities
with electric power (with simple metering)
allows those interested to effectively play with
the trade-offs that are possible and therein get
the most out of their power systems—and this
hobby. At the same time, none of this is
outside the scope of high-school science class;
it’s not rocket science, so there is no reason to
feel intimidated.
Let’s begin with the idea of voltage;
instead of getting into the definition and deep
meaning of the term, I’ll jump right into its
common, practical usage. Perhaps the most
common or familiar experiences with voltage
are with the power line in your home or the
battery in your car or flashlight.
Common household appliances are
plugged into the 120-volt power line, and the
stuff in your car works on 12 volts. But why is
one voltage 10 times the other, and why are
there so many other commonplace voltage
values such as the 3-volt flashlight bulb? How
about the myriad cell counts (range of
voltage) used in E-power systems?
To answer these questions with insight and
appreciation, I must move to two other terms:
current and power. When voltage is applied to
a device, current (amps) flows from the
source of voltage to the device under power.
Some authors liken current to the volume
flow of water in a pipe and voltage to the
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water pressure causing that flow. With
voltage present and current flowing, the
device being so powered is in fact getting
power.
Power (watts) is the product
(multiplication) of the voltage and the
current; that is, you need voltage and the
resulting current flow to have power. Power
is needed to do work. Think of “work” as
being that which you want done, be it turning
a propeller, lighting a light, or cooling a beer
in the refrigerator.
Consider a typical 1,200-watt household
clothes iron plugged into the 120-volt outlet.
It draws 10 amps since 120 volts multiplied
by 10 amps equals 1,200 watts. A 40-watt
soldering iron, like many used to make
battery packs, draws 40 divided by 120, or
0.333 amps (333 milliamps). The clothes iron
can heat much larger surfaces than the
soldering iron; i.e., the clothes iron can do
more work, or a bigger job, and that’s why it
needs—and consumes—much more power.
Similarly, a 3⁄4-watt flashlight bulb outputs
vastly less light than a 100-watt household
lightbulb. Again, the higher-power device
does a bigger job than the lower-power one.
For purposes of E-flight, a 300-watt power
system can fly a much bigger and heavier
aeromodel than can a 30-watt power system.
Consider an imaginary 100-watt electric
device (it doesn’t matter what it is). If it was
designed to operate on the 120-volt power
line, it would draw 100 ÷ 120 = 0.833 amps.
If it was designed to operate on the 12-volt
car battery, it would draw 100 ÷ 12 = 8.33
amps. There is an infinite number of
voltage/current design combinations that
would result in the same 100 watts—and do
the same device job—so how are particular
voltage and current choices made, and why?
It basically comes down to the
practicalities and common sense of the
application environment. Reconsider that
1,200-watt clothes iron. If this was a 12-volt
device, it would draw 100 amps. If all
household appliances were 12-volt devices,
the wiring, outlets, appliance switches,
everything would be vastly more massive.
Imagine that the power cord on a 12-volt,
100-amp clothes iron would be heavier than
the iron itself—not at all practical!
Now look at things the other way around.
The high-voltage distribution lines that
traverse neighborhoods are high voltage so
that the current they carry can be held to
“reasonable values.” Thus a kilovolts power
line, supplying megawatts to a neighborhood
or community, does so at far lower current
levels than would be the case at 120 volts.
(Local transformers convert the high-voltage
distribution levels to the familiar 120-volt
level.)
But why not just use the kilovolts—
instead of 120 volts—directly in the home?
Aside from being downright dangerous,
imagine how the home wiring might look.
Electrical outlets would have prongs many
inches apart. A damp day might allow corona
inside the house. Huge porcelain insulators
would separate room-to-room conductors by
several feet. Your home would have to be
much larger just to accommodate the widespaced
wiring!
Bringing all of this closer to our
aeromodeling interests, consider that a 300-
watt E-power system could be made with a
15-volt motor requiring 20 amps. Or it could
theoretically be realized with a 150-volt
motor drawing 2 amps. Or it could be done
with a 1.5-volt motor drawing 200 amps.
We know that the first suggestion is about
right. The second option has the appeal of
low current, but it would need approximately
125 cells to do this. Imagine the cost! The
third, or low-voltage option, might sound
appealing in that it needs only one, though
very large, cell, but the system wire, ESC,
fuse, switch, and connectors would be so
massive to handle the 200 amps that the
component size and associated system weight
would each likely be several times normal!
From all of the preceding it should be
clear that good choices—really design tradeoffs
and practical compromises—of voltage
and current levels are needed to achieve the
power level needed for the job at hand, no
matter the application. More about all of this
is to come.
Thus ends this column. Please include a selfaddressed,
stamped envelope with any
correspondence for which you’d like a reply.
Everyone so doing does get one! And do
make it a point to take a nonbelieving wetflying
friend to an E-meet; I’ve never seen
anyone leave a meet unconvinced! Happy Elandings,
everyone! MA
August 2003 115
BEYOND
QUIET!
More Power and Performance...
Priced Less than You’ld Expect!
PO BOX 141, MILFORD, CT 06460
phone:(203) 877-1670
fax:(203) 876-2731
www.davisdieseldevelopment.com
DIESEL DEVELOPMENT
For Complete Catalog send $5 (credited to first order)
NEW
LOW
PRICES!
BOLT-ON
MOUNT!
QUIET SCALE
SERIES
NEW!
YOU ASKED...
WE LISTENED!
Built
in the
U.S.A.
No more straps,
these bolt-on
beauties have a
black powder
finish, built in
pressure fitting
and all internal
baffles are still
there for sound reduction without loss of power.
Available for .40 to .90 engines.
Email us for current prices at
[email protected]
FIBERGLASS CLOTH
Premium Grade
3/4 oz 38”W 10 yrd. min. $2.50 yd.
Lower Prices 30 yds. & up
Other Weights Available
TinLin’s
17 Andrews Drive • Daleville, AL 36322
(334) 598-2287 • 4:00 - 10:00 CST
08sig4.QXD 5.23.03 1:06 pm Page 115