78 MODEL AVIATION
THIS IS THE second monthly FAQ column in which I try to
answer, as clearly as possible, questions you have written or Emailed
to me. Each question is given a sequential number for
identification purposes. Because publication space is somewhat
limited, part of each column will be in the magazine, and the
published portion and spillover material will be posted on the
AMA Web site. Let’s start!
Q15: A reader questioned the tapering of the wing spars on my
Scratch One design. He read the plans to indicate that the front 1⁄16
x 5⁄16 (high) spar tapered down by 3⁄16 inch; that left only 1⁄8 inch
of material on the spar at the tip.
A15: I have to agree that this came out a little confusing. The
reader actually read the plan notes incorrectly. The front 1⁄16 x 5⁄16
spar is supposed to taper down to 3⁄16 inch at the tip. That means
I’m only reducing the height by 1⁄8 inch. There is a difference
when reducing “by” and reducing “to.” I E-mailed an extra photo
to the reader and he thought that was helpful, so I will include it
here.
The entire idea of tapering the three spars was to be able to
thin the airfoil as it approaches the wingtip. Had I left the three
spars a constant height, the airfoil shape going toward the tip
would have gotten progressively thicker.
You can see my hand notes in the photo. Originally I had the
front spar tapering down to 3⁄16 inch, the middle (main) spar to 1⁄4
inch, and the rear spar to 3⁄16 inch. On the final plans I kept it
simple and indicated that all three spars should taper to 3⁄16 inch.
The resulting tip airfoil is a little flat, but that is much better than
having a thicker airfoil at the tip.
My reader friend also wrote that he couldn’t find any 1⁄16 x 5⁄16
balsa since it isn’t a standard size. It is easy to cut your own spars
from sheet-balsa material using a long, steel straightedge and an
X-Acto knife. You might mess up a few spars on your first tries,
but I’ll bet you will quickly get the hang of it.
Q16: A reader was confused by the term “PCB” that he had seen
in several magazine articles. He thought the reference was to the
toxic substance material known as Polychlorinated Biphenyls.
Bob Aberle
F r e q u e n t l y A s k e d Q u e s t i o n s
E-mail: [email protected]
The wingtip portion of the Scratch One. Notice that the three
spars have been tapered as they approach the tip.
Top: Scratch One’s original eight-cell 1100 mAh NiMH pack.
Bottom: New two-cell FMA Direct/Kokam 1500 Li-Poly pack.
Since Li-Poly battery is 3.2 ounces lighter, keep it positioned
forward to help maintain proper CG position.
Hitec HS-55 and Bob Selman Designs magnetic actuators. One
controls the rudder; the other controls the elevator.
A16: The abbreviation was probably referring to a printed circuit
board. For many years it was referred to as a “PC board.” This is a
plastic board that contains copper foil strips to interconnect
electrical components that are mounted on it. I’ve recently seen
the reference change to “PCB,” hence the dual meaning.
06sig3.QXD 3/24/04 1:45 pm Page 78
June 2004 79
Rather than move throttle servo forward of firewall to obtain
correct balance point, move heavier battery pack forward or use
Harry Higley Heavy Hub.
Elevator “regular” trim lever set for full down-elevator. Lever
position gives rough idea of how much trim you are using.
With digital trims, there is no lever that gives away position of
control surface; there is only a push-button switch.
LCD screen shows how much elevator (CH 2) trim you are using
on Hitec Eclipse. “TRIM—50%” is same as full down-trim. For full
up-elevator trim it would read “TRIM + 50%.”
Q17: “I’ve already built your Scratch One electric-powered
sailplane design that appeared in the November 2003 MA and it
flies great! But with all the talk now of Lithium-Polymer
batteries, can I change over to these new cells in my Scratch
One?”
A17: The answer is a definite yes, and I have already done so. I
wrote an article published in last month’s MA titled
“Introduction to Lithium-Polymer Batteries.” In it I show you
how to replace the Scratch One’s original eight-cell 1100 mAh
NiMH battery pack that weighed 5.9 ounces with a two-cell
FMA Direct/Kokam 1500 mAh Li-Poly pack that weighs 2.7
ounces. You get a weight savings of 3.2 ounces while gaining
roughly one-third capacity. Your Scratch One will weigh less
and fly longer!
Q18: “I keep reading about ‘magnetic actuators’ to operate
control surfaces on a model aircraft and wonder how these
devices differ from the common RC servo.”
A18: You will see references to “magnetic actuators” when we
are writing about micro RC indoor models. These aircraft
typically range in weight from 1.5 ounces down to practically
nothing (a few grams)!
The tiny actuators are made up of a coil and a magnet.
Operating your RC transmitter’s control sticks causes the arm on
the actuator to displace, or move. Some magnetic actuators are
mounted directly on the control surfaces. Recent improvements
have produced actuators with regular output arms to which you
can attach small control rods.
RC servos are motor-driven devices that can be positioned in
a precise manner. However, because they require a motor and a
feedback potentiometer, the lightest servos weigh roughly 5-6
grams; a magnetic actuator can be as light as 1.5 to 2.0 grams!
We are seeing much progress in smaller and lighter-weight RC
servos. It wouldn’t surprise me to soon see servos as light as
actuators. Of course, the servos have considerably more output
torque than the magnetic actuators.
Q19: “I need extra nose weight to balance my Scale model and
was wondering if I might move my throttle servo up front,
forward of the firewall. What do you think of the idea?
A19: I’m not in favor of that idea at all. The throttle servo
would be extremely close to the engine, where it would be
subject to fuel residue and mechanical vibration; neither would
provide a long-lasting servo. Also, the average standard-size
servo weighs approximately 1.5 ounces, so you aren’t gaining
06sig3.QXD 3/24/04 1:46 pm Page 79
80 MODEL AVIATION
that much weight forward for all your
trouble.
I suggest that you move the receiver
battery pack forward, to a point just under
the engine. Wrap the pack in padding and a
plastic bag. You can access the battery for
charging purposes by using the charging
jack located on the switch harness;
presumably that will be back in the RC
compartment. By using the battery you
should be able to gain 3-4 ounces of weight
farther forward to balance your airplane.
Another suggestion is to use a Harry B.
Higley & Sons Heavy Hub, which is a 2-
ounce propeller spinner. Since it mounts on
the end of the engine’s crankshaft, the
weight is almost as far forward as you are
going to get it. It’s an easy solution to a tailheavy
model.
The only problem is that the hub isn’t
available in many propeller shaft sizes.
Check http://members.aol.com/harryhig/
EngineAccessories1.htm to see what is
available.
Q20: “I hear RC modelers refer to ‘regular
trim’ and ‘digital trim.’ Since I’m new to the
hobby, can you explain the difference to
me?
A20: Regular trim has been used for many
years. A small lever located on the outside
of the RC transmitter is connected to a
potentiometer control on the inside of the
transmitter. It provides for a vernier
adjustment of the particular channel
functions, such as the aileron, elevator,
rudder, and throttle controls.
Let’s use the elevator as an example. The
servo may move 45° on either side of the
neutral position. The trim lever can relocate
the neutral position of that same servo by,
say, plus or minus 15°. If your airplane
climbs slightly by itself, adding a small
amount of down-elevator trim will make it
fly level. The time-honored “regular trim”
has always been operated by a small lever;
its position makes it obvious how much trim
travel has been set in.
Modern RC transmitters have been going
to “digital trim.” With this concept, the trim
lever is replaced by a push-button switch.
You keep pushing, or pulsing, the trim
button to achieve new trim positions. But
since it is a button, you really don’t have
any reference to the actual trim position on
the model. Some transmitters have bar
graphs that appear on the LCD screen
showing servo position. Some others show
the trim as a percentage of travel.
Digital trim has upset many old-time RC
fliers. It took me awhile, but now I have to
admit that I like digital trim. It also makes
for much easier storage of trim positions in
the transmitter’s computer memory circuit.
That concludes the published portion this
month. With each column I will include a
few photos to supplement the text where
possible. I encourage you to write in or Email
your questions about anything with
which you are having a problem. Try me
with any and all of your inquiries. As I’ve
mentioned, if I can’t answer them, I network
with a group of experts on a regular basis to
act as my consultants. Your questions will
get answered!
And please let me know if the answers
are too broad, too detailed, too long, or not
long enough! I need your input! MA
www.modelaircraft.org
06sig3.QXD 3/24/04 2:13 pm Page 80
Edition: Model Aviation - 2004/06
Page Numbers: 78,79,80
Edition: Model Aviation - 2004/06
Page Numbers: 78,79,80
78 MODEL AVIATION
THIS IS THE second monthly FAQ column in which I try to
answer, as clearly as possible, questions you have written or Emailed
to me. Each question is given a sequential number for
identification purposes. Because publication space is somewhat
limited, part of each column will be in the magazine, and the
published portion and spillover material will be posted on the
AMA Web site. Let’s start!
Q15: A reader questioned the tapering of the wing spars on my
Scratch One design. He read the plans to indicate that the front 1⁄16
x 5⁄16 (high) spar tapered down by 3⁄16 inch; that left only 1⁄8 inch
of material on the spar at the tip.
A15: I have to agree that this came out a little confusing. The
reader actually read the plan notes incorrectly. The front 1⁄16 x 5⁄16
spar is supposed to taper down to 3⁄16 inch at the tip. That means
I’m only reducing the height by 1⁄8 inch. There is a difference
when reducing “by” and reducing “to.” I E-mailed an extra photo
to the reader and he thought that was helpful, so I will include it
here.
The entire idea of tapering the three spars was to be able to
thin the airfoil as it approaches the wingtip. Had I left the three
spars a constant height, the airfoil shape going toward the tip
would have gotten progressively thicker.
You can see my hand notes in the photo. Originally I had the
front spar tapering down to 3⁄16 inch, the middle (main) spar to 1⁄4
inch, and the rear spar to 3⁄16 inch. On the final plans I kept it
simple and indicated that all three spars should taper to 3⁄16 inch.
The resulting tip airfoil is a little flat, but that is much better than
having a thicker airfoil at the tip.
My reader friend also wrote that he couldn’t find any 1⁄16 x 5⁄16
balsa since it isn’t a standard size. It is easy to cut your own spars
from sheet-balsa material using a long, steel straightedge and an
X-Acto knife. You might mess up a few spars on your first tries,
but I’ll bet you will quickly get the hang of it.
Q16: A reader was confused by the term “PCB” that he had seen
in several magazine articles. He thought the reference was to the
toxic substance material known as Polychlorinated Biphenyls.
Bob Aberle
F r e q u e n t l y A s k e d Q u e s t i o n s
E-mail: [email protected]
The wingtip portion of the Scratch One. Notice that the three
spars have been tapered as they approach the tip.
Top: Scratch One’s original eight-cell 1100 mAh NiMH pack.
Bottom: New two-cell FMA Direct/Kokam 1500 Li-Poly pack.
Since Li-Poly battery is 3.2 ounces lighter, keep it positioned
forward to help maintain proper CG position.
Hitec HS-55 and Bob Selman Designs magnetic actuators. One
controls the rudder; the other controls the elevator.
A16: The abbreviation was probably referring to a printed circuit
board. For many years it was referred to as a “PC board.” This is a
plastic board that contains copper foil strips to interconnect
electrical components that are mounted on it. I’ve recently seen
the reference change to “PCB,” hence the dual meaning.
06sig3.QXD 3/24/04 1:45 pm Page 78
June 2004 79
Rather than move throttle servo forward of firewall to obtain
correct balance point, move heavier battery pack forward or use
Harry Higley Heavy Hub.
Elevator “regular” trim lever set for full down-elevator. Lever
position gives rough idea of how much trim you are using.
With digital trims, there is no lever that gives away position of
control surface; there is only a push-button switch.
LCD screen shows how much elevator (CH 2) trim you are using
on Hitec Eclipse. “TRIM—50%” is same as full down-trim. For full
up-elevator trim it would read “TRIM + 50%.”
Q17: “I’ve already built your Scratch One electric-powered
sailplane design that appeared in the November 2003 MA and it
flies great! But with all the talk now of Lithium-Polymer
batteries, can I change over to these new cells in my Scratch
One?”
A17: The answer is a definite yes, and I have already done so. I
wrote an article published in last month’s MA titled
“Introduction to Lithium-Polymer Batteries.” In it I show you
how to replace the Scratch One’s original eight-cell 1100 mAh
NiMH battery pack that weighed 5.9 ounces with a two-cell
FMA Direct/Kokam 1500 mAh Li-Poly pack that weighs 2.7
ounces. You get a weight savings of 3.2 ounces while gaining
roughly one-third capacity. Your Scratch One will weigh less
and fly longer!
Q18: “I keep reading about ‘magnetic actuators’ to operate
control surfaces on a model aircraft and wonder how these
devices differ from the common RC servo.”
A18: You will see references to “magnetic actuators” when we
are writing about micro RC indoor models. These aircraft
typically range in weight from 1.5 ounces down to practically
nothing (a few grams)!
The tiny actuators are made up of a coil and a magnet.
Operating your RC transmitter’s control sticks causes the arm on
the actuator to displace, or move. Some magnetic actuators are
mounted directly on the control surfaces. Recent improvements
have produced actuators with regular output arms to which you
can attach small control rods.
RC servos are motor-driven devices that can be positioned in
a precise manner. However, because they require a motor and a
feedback potentiometer, the lightest servos weigh roughly 5-6
grams; a magnetic actuator can be as light as 1.5 to 2.0 grams!
We are seeing much progress in smaller and lighter-weight RC
servos. It wouldn’t surprise me to soon see servos as light as
actuators. Of course, the servos have considerably more output
torque than the magnetic actuators.
Q19: “I need extra nose weight to balance my Scale model and
was wondering if I might move my throttle servo up front,
forward of the firewall. What do you think of the idea?
A19: I’m not in favor of that idea at all. The throttle servo
would be extremely close to the engine, where it would be
subject to fuel residue and mechanical vibration; neither would
provide a long-lasting servo. Also, the average standard-size
servo weighs approximately 1.5 ounces, so you aren’t gaining
06sig3.QXD 3/24/04 1:46 pm Page 79
80 MODEL AVIATION
that much weight forward for all your
trouble.
I suggest that you move the receiver
battery pack forward, to a point just under
the engine. Wrap the pack in padding and a
plastic bag. You can access the battery for
charging purposes by using the charging
jack located on the switch harness;
presumably that will be back in the RC
compartment. By using the battery you
should be able to gain 3-4 ounces of weight
farther forward to balance your airplane.
Another suggestion is to use a Harry B.
Higley & Sons Heavy Hub, which is a 2-
ounce propeller spinner. Since it mounts on
the end of the engine’s crankshaft, the
weight is almost as far forward as you are
going to get it. It’s an easy solution to a tailheavy
model.
The only problem is that the hub isn’t
available in many propeller shaft sizes.
Check http://members.aol.com/harryhig/
EngineAccessories1.htm to see what is
available.
Q20: “I hear RC modelers refer to ‘regular
trim’ and ‘digital trim.’ Since I’m new to the
hobby, can you explain the difference to
me?
A20: Regular trim has been used for many
years. A small lever located on the outside
of the RC transmitter is connected to a
potentiometer control on the inside of the
transmitter. It provides for a vernier
adjustment of the particular channel
functions, such as the aileron, elevator,
rudder, and throttle controls.
Let’s use the elevator as an example. The
servo may move 45° on either side of the
neutral position. The trim lever can relocate
the neutral position of that same servo by,
say, plus or minus 15°. If your airplane
climbs slightly by itself, adding a small
amount of down-elevator trim will make it
fly level. The time-honored “regular trim”
has always been operated by a small lever;
its position makes it obvious how much trim
travel has been set in.
Modern RC transmitters have been going
to “digital trim.” With this concept, the trim
lever is replaced by a push-button switch.
You keep pushing, or pulsing, the trim
button to achieve new trim positions. But
since it is a button, you really don’t have
any reference to the actual trim position on
the model. Some transmitters have bar
graphs that appear on the LCD screen
showing servo position. Some others show
the trim as a percentage of travel.
Digital trim has upset many old-time RC
fliers. It took me awhile, but now I have to
admit that I like digital trim. It also makes
for much easier storage of trim positions in
the transmitter’s computer memory circuit.
That concludes the published portion this
month. With each column I will include a
few photos to supplement the text where
possible. I encourage you to write in or Email
your questions about anything with
which you are having a problem. Try me
with any and all of your inquiries. As I’ve
mentioned, if I can’t answer them, I network
with a group of experts on a regular basis to
act as my consultants. Your questions will
get answered!
And please let me know if the answers
are too broad, too detailed, too long, or not
long enough! I need your input! MA
www.modelaircraft.org
06sig3.QXD 3/24/04 2:13 pm Page 80
Edition: Model Aviation - 2004/06
Page Numbers: 78,79,80
78 MODEL AVIATION
THIS IS THE second monthly FAQ column in which I try to
answer, as clearly as possible, questions you have written or Emailed
to me. Each question is given a sequential number for
identification purposes. Because publication space is somewhat
limited, part of each column will be in the magazine, and the
published portion and spillover material will be posted on the
AMA Web site. Let’s start!
Q15: A reader questioned the tapering of the wing spars on my
Scratch One design. He read the plans to indicate that the front 1⁄16
x 5⁄16 (high) spar tapered down by 3⁄16 inch; that left only 1⁄8 inch
of material on the spar at the tip.
A15: I have to agree that this came out a little confusing. The
reader actually read the plan notes incorrectly. The front 1⁄16 x 5⁄16
spar is supposed to taper down to 3⁄16 inch at the tip. That means
I’m only reducing the height by 1⁄8 inch. There is a difference
when reducing “by” and reducing “to.” I E-mailed an extra photo
to the reader and he thought that was helpful, so I will include it
here.
The entire idea of tapering the three spars was to be able to
thin the airfoil as it approaches the wingtip. Had I left the three
spars a constant height, the airfoil shape going toward the tip
would have gotten progressively thicker.
You can see my hand notes in the photo. Originally I had the
front spar tapering down to 3⁄16 inch, the middle (main) spar to 1⁄4
inch, and the rear spar to 3⁄16 inch. On the final plans I kept it
simple and indicated that all three spars should taper to 3⁄16 inch.
The resulting tip airfoil is a little flat, but that is much better than
having a thicker airfoil at the tip.
My reader friend also wrote that he couldn’t find any 1⁄16 x 5⁄16
balsa since it isn’t a standard size. It is easy to cut your own spars
from sheet-balsa material using a long, steel straightedge and an
X-Acto knife. You might mess up a few spars on your first tries,
but I’ll bet you will quickly get the hang of it.
Q16: A reader was confused by the term “PCB” that he had seen
in several magazine articles. He thought the reference was to the
toxic substance material known as Polychlorinated Biphenyls.
Bob Aberle
F r e q u e n t l y A s k e d Q u e s t i o n s
E-mail: [email protected]
The wingtip portion of the Scratch One. Notice that the three
spars have been tapered as they approach the tip.
Top: Scratch One’s original eight-cell 1100 mAh NiMH pack.
Bottom: New two-cell FMA Direct/Kokam 1500 Li-Poly pack.
Since Li-Poly battery is 3.2 ounces lighter, keep it positioned
forward to help maintain proper CG position.
Hitec HS-55 and Bob Selman Designs magnetic actuators. One
controls the rudder; the other controls the elevator.
A16: The abbreviation was probably referring to a printed circuit
board. For many years it was referred to as a “PC board.” This is a
plastic board that contains copper foil strips to interconnect
electrical components that are mounted on it. I’ve recently seen
the reference change to “PCB,” hence the dual meaning.
06sig3.QXD 3/24/04 1:45 pm Page 78
June 2004 79
Rather than move throttle servo forward of firewall to obtain
correct balance point, move heavier battery pack forward or use
Harry Higley Heavy Hub.
Elevator “regular” trim lever set for full down-elevator. Lever
position gives rough idea of how much trim you are using.
With digital trims, there is no lever that gives away position of
control surface; there is only a push-button switch.
LCD screen shows how much elevator (CH 2) trim you are using
on Hitec Eclipse. “TRIM—50%” is same as full down-trim. For full
up-elevator trim it would read “TRIM + 50%.”
Q17: “I’ve already built your Scratch One electric-powered
sailplane design that appeared in the November 2003 MA and it
flies great! But with all the talk now of Lithium-Polymer
batteries, can I change over to these new cells in my Scratch
One?”
A17: The answer is a definite yes, and I have already done so. I
wrote an article published in last month’s MA titled
“Introduction to Lithium-Polymer Batteries.” In it I show you
how to replace the Scratch One’s original eight-cell 1100 mAh
NiMH battery pack that weighed 5.9 ounces with a two-cell
FMA Direct/Kokam 1500 mAh Li-Poly pack that weighs 2.7
ounces. You get a weight savings of 3.2 ounces while gaining
roughly one-third capacity. Your Scratch One will weigh less
and fly longer!
Q18: “I keep reading about ‘magnetic actuators’ to operate
control surfaces on a model aircraft and wonder how these
devices differ from the common RC servo.”
A18: You will see references to “magnetic actuators” when we
are writing about micro RC indoor models. These aircraft
typically range in weight from 1.5 ounces down to practically
nothing (a few grams)!
The tiny actuators are made up of a coil and a magnet.
Operating your RC transmitter’s control sticks causes the arm on
the actuator to displace, or move. Some magnetic actuators are
mounted directly on the control surfaces. Recent improvements
have produced actuators with regular output arms to which you
can attach small control rods.
RC servos are motor-driven devices that can be positioned in
a precise manner. However, because they require a motor and a
feedback potentiometer, the lightest servos weigh roughly 5-6
grams; a magnetic actuator can be as light as 1.5 to 2.0 grams!
We are seeing much progress in smaller and lighter-weight RC
servos. It wouldn’t surprise me to soon see servos as light as
actuators. Of course, the servos have considerably more output
torque than the magnetic actuators.
Q19: “I need extra nose weight to balance my Scale model and
was wondering if I might move my throttle servo up front,
forward of the firewall. What do you think of the idea?
A19: I’m not in favor of that idea at all. The throttle servo
would be extremely close to the engine, where it would be
subject to fuel residue and mechanical vibration; neither would
provide a long-lasting servo. Also, the average standard-size
servo weighs approximately 1.5 ounces, so you aren’t gaining
06sig3.QXD 3/24/04 1:46 pm Page 79
80 MODEL AVIATION
that much weight forward for all your
trouble.
I suggest that you move the receiver
battery pack forward, to a point just under
the engine. Wrap the pack in padding and a
plastic bag. You can access the battery for
charging purposes by using the charging
jack located on the switch harness;
presumably that will be back in the RC
compartment. By using the battery you
should be able to gain 3-4 ounces of weight
farther forward to balance your airplane.
Another suggestion is to use a Harry B.
Higley & Sons Heavy Hub, which is a 2-
ounce propeller spinner. Since it mounts on
the end of the engine’s crankshaft, the
weight is almost as far forward as you are
going to get it. It’s an easy solution to a tailheavy
model.
The only problem is that the hub isn’t
available in many propeller shaft sizes.
Check http://members.aol.com/harryhig/
EngineAccessories1.htm to see what is
available.
Q20: “I hear RC modelers refer to ‘regular
trim’ and ‘digital trim.’ Since I’m new to the
hobby, can you explain the difference to
me?
A20: Regular trim has been used for many
years. A small lever located on the outside
of the RC transmitter is connected to a
potentiometer control on the inside of the
transmitter. It provides for a vernier
adjustment of the particular channel
functions, such as the aileron, elevator,
rudder, and throttle controls.
Let’s use the elevator as an example. The
servo may move 45° on either side of the
neutral position. The trim lever can relocate
the neutral position of that same servo by,
say, plus or minus 15°. If your airplane
climbs slightly by itself, adding a small
amount of down-elevator trim will make it
fly level. The time-honored “regular trim”
has always been operated by a small lever;
its position makes it obvious how much trim
travel has been set in.
Modern RC transmitters have been going
to “digital trim.” With this concept, the trim
lever is replaced by a push-button switch.
You keep pushing, or pulsing, the trim
button to achieve new trim positions. But
since it is a button, you really don’t have
any reference to the actual trim position on
the model. Some transmitters have bar
graphs that appear on the LCD screen
showing servo position. Some others show
the trim as a percentage of travel.
Digital trim has upset many old-time RC
fliers. It took me awhile, but now I have to
admit that I like digital trim. It also makes
for much easier storage of trim positions in
the transmitter’s computer memory circuit.
That concludes the published portion this
month. With each column I will include a
few photos to supplement the text where
possible. I encourage you to write in or Email
your questions about anything with
which you are having a problem. Try me
with any and all of your inquiries. As I’ve
mentioned, if I can’t answer them, I network
with a group of experts on a regular basis to
act as my consultants. Your questions will
get answered!
And please let me know if the answers
are too broad, too detailed, too long, or not
long enough! I need your input! MA
www.modelaircraft.org
06sig3.QXD 3/24/04 2:13 pm Page 80
