August 2011 31
Designing in
CAD
by David Walker
A beginner’s guide
to designing your
own aircraft
is a modeler to do when he or she loves
to build?
The not-so-obvious answer is to
design your own kits using CAD, or
computer-aided design. Once you are
familiar with CAD there is no limit to
the aircraft you can model, whether your
interest is RC, FF, or CL.
Many aeromodelers who are
unfamiliar with CAD might find it
daunting. It used to be true that you
needed a super-powerful computer;
months, if not years, of training; and a
lot of money to use a CAD package.
Fortunately for us, CAD has also
evolved—to the point where any
modeler with basic computer knowledge
can use it on an existing computer as
long as it is less than 10 years old. And
for what we are doing, the cost can be
zero dollars. Even if you have only a
passing interest, you owe it to yourself
to learn more and try it.
But why not design a model on
good, old paper? Similar to how the
word processor replaced the typewriter,
EVOLUTION: Our hobby has been
evolving rapidly lately. From computer
radios to laser-cut kits to electricpowered
aircraft that not only rival their
glow counterparts, but often exceed
them in performance, our hobby is
changing.
Another aspect of aeromodeling that
has evolved is ARFs and RTFs. There
are great benefits to the proliferation of
these models, but a result of this
progress is that traditional kits have
almost disappeared.
If you are the way I am and still love
to build, your options are rather limited.
This is unfortunate because just as lasercutting
was becoming mainstream, the
decline of kits had already begun. What
A three-view of a Fairchild C-123
Provider downloaded from the Internet.
08sig1.QXD_00MSTRPG.QXD 6/23/11 1:33 PM Page 31
A downloaded three-view
with rough CAD overlay.
The author made this
80-inch-span foam and
plywood C-123 using a
CAD drawing that
originated from the
three-view.
The screen showing that all
objects have been changed
with one click of the mouse.
The screen showing confirmation to
change edit group object, so that all
objects with the same name get the
change.
CAD for the home user is replacing the
paper, pencil, T-square, large drawing
table, mechanical compass, and multitude
of other tools needed to properly create a
set of plans the “old way.”
Drawing model airplane plans has
evolved too, with many of the same
benefits. Sure, there is a learning curve;
but just as you adapted to using a word
processor, and likely would never use a
typewriter again, you can probably learn
and adjust to using CAD almost as easily.
My goal is not to teach you how to
design an airplane in CAD using a
specific CAD program, or even how to
use this design method, but to help you
get started and point out some of the
advantages of it with which you might be
unfamiliar.
The easiest way to begin is to
download one of the free CAD programs
listed at the end of this article and start
using it. For many of them there is plenty
of online help and support forums that are
specific to the program you are using.
Then if you find that you like using
CAD, you can explore many of the other
CAD programs that are available for
purchase. My current favorite is the free
version of Sketchup.
Once you get the basics down, you
can explore the more advanced features.
But in all honesty, the basics are really all
you need when drawing model airplanes.
With CAD you can download an
almost endless supply of free plans on the
Internet. And if the airplane is not the
scale you want, or you want to make
design changes, you can easily do that.
These plans are also a great way to pick
up on new techniques and design
possibilities.
Addtionally, there is a countless array
of parts, such as servos, hardware, etc.,
that are available to download to use in
your drawings. And you can share your
work with others around the world. There
is something gratifying about seeing
someone else fly one of your designs—
sometimes someone from halfway around
the world.
Before going into some of the important
features of CAD, it’s important to know
how it differs from conventional painting,
drawing, or photo programs, with which
you may be familiar.
CAD is vector based; that is, the
drawing is made from lines and nothing
more. Even circles or arcs are a series of
lines, albeit extremely small lines.
Photo and painting programs are
“raster” images. That simply means that
the image from one of these programs is
composed of a series of fixed-size
squares. That might seem unimportant at
first—until you try to zoom in on a raster
image.
Most of you have probably tried
this at one point. You have a nice
picture of your favorite airplane in
flight, but it looks like a small dot in
the picture. Then you zoom in, and all
you have is a larger dot with fuzzy
edges.
32 MODEL AVIATION
08sig1.QXD_00MSTRPG.QXD 6/23/11 1:37 PM Page 32
Comparison of
a zoomed-in
section of the
CAD drawing
showing a
raster vs. a
vector file.
Raster zoomed
Vector zoomed
A screen shot showing a working
drawing of an 80-inch-wingspan P-39.
34 MODEL AVIATION
The completed Provider coming
in for a landing on its first flight.
Photos by the author
Because a CAD drawing is composed
of a series of lines, you can zoom in all you
want with no loss of quality. This is
important when you want to work on fine
points of a drawing such as servo mounting
details, landing gear detail, etc.
The fact that a CAD drawing is vector
based also allows you to scale a drawing to
any size you want. This is handy if you
want to trace a three-view that you found
on the Internet and, for example, make an
8-foot model of the airplane.
The three-view might have had a
wingspan of only 6 inches when originally
drawn. However, you can easily scale it to
any size you want with a few clicks of the
mouse—and there will be no loss of quality.
It’s a good idea to start slowly when
learning anything new, and CAD is no
different. As you learned to fly with a
trainer, it is best to start with a simple, small
CAD project to get used to your new tool.
Choose a project that will allow some room
for error and with which you can grow.
One of the great things about computers
is that they make it almost effortless to
duplicate nearly anything; so why not learn
to draw by making something you will use
later? A servo, hardware items, a receiver,
motors/engines, etc. are perfect candidates,
and you can employ them later, when you
design your first model.
Even if you mess up beyond all hope
when making one of these early drawings,
you may have lost only 10-15 minutes of
work. But you learn valuable lessons to be
applied to your first aircraft design, thus
saving hours of work.
Just as when you learned to fly, handson
experience with CAD is best. However,
it was nice to have some guidance when I
got started. Every CAD package I have used
throughout the years has had the following
features, and they are crucial to learn.
• Drawing tools: Line, circle, and arc
function as you would expect them to.
Most CAD packages have many more, but
those are the ones you will use 90% of the
time.
• Editing tools: Once you have a line or
other object drawn, you might want to
change a few things. Trim/extend, delete,
rotate, copy, and stretch allow you to edit
objects on the screen.
• Snap: This allows you to start your next
line exactly at the end or middle of a line or
tangent to a circle or arc. You can also snap
to predefined angles such as 0°, 45°, 90°,
etc.
Snap is one of the many things that sets
CAD apart from traditional painting
programs. This is vital if you want to have
your parts laser or machine cut.
• Layers: This allows you to separate
various components of your drawings. It is
similar to drawing on clear plastic sheets,
where you can lay the various layers on top
of each other or omit some for clarity.
You can have the wing structure on
one layer and hardware on another. You
can keep the hardware layer off while
working on the detail of the wing
structure, and then turn the hardware
08sig2.QXD_00MSTRPG.QXD 6/23/11 9:19 AM Page 34
August 2011 35
layer back on to show the final product.
I separate my layers by color so I can better
visualize the various objects, but it is not
necessary.
• Groups: This function allows you to group the
many lines that comprise an object, such as a
servo. Some CAD programs call these
“blocks.” This lets you copy, move, or rotate the
servo as a unit; you don’t have to try to select all
the individual lines that make up the servo.
Let’s keep with the servo example. If you
placed six of them on your drawing and later
decide to use different servos, all you have to
do is redefine the group with the new servo and
all servos are changed automatically. Try that
with pencil and paper.
• Export to DXF: DXF is a common file type
that almost all CAD programs use. Each
package has its own proprietary file format, so
you will need to export to DXF if you want
your parts laser or machine cut; almost all
shops that offer cutting services accept these
kinds of files.
When saving your drawing while working
on it, it is best to save in its native format
because DXF does not always save all the
details of your drawing. If you do not plan on
having your parts machine cut, exporting to
DXF is not important.
Let’s cover printing; after all, what we are
after is a set of plans from which to build. Here
is where CAD for the home user has its
shortcomings.
Each CAD program I have used has its own
way of handling printing. Most have a way to
tile print with registration marks; that is, your
drawing will be produced on your standard
home printer on many sheets.
Since printers cannot print to the edge of a
sheet of paper, registration marks are printed in
the corner of the drawings so you can align all
the sheets and tape them together after
trimming the margins. This is not as tedious as
it sounds, and I have done it quite a few times
with great success.
Some CAD programs don’t offer printing
with registration marks. To deal with this, some
aeromodelers export their drawing as full-size
PDF files and use the PDF viewer to do the tile
printing.
Unfortunately printing in CAD requires
some experimentation to get acceptable results.
You could say that printing for the CAD home
user needs to evolve a little more.
I am lucky in that I have access to a 48-inch
plotter. CAD is designed to work with plotters.
Knowing this, I size my drawings accordingly.
Some towns have printing shops that will
plot your drawing for a reasonable cost, or
maybe you know a friend who has access to a
plotter. If you want to submit your drawings to
a magazine for publication or have your
drawing printed by a local company or friend, it
is best to check with them regarding the size
that is required.
The AMA Plans Service and the local
FedEx/Kinko’s requires 36-inch drawing
heights. Length can be anything you want, but
it is best to keep the length less than 60 inches
or the plans set becomes too large to use easily.
I hope this article at the very least got you
thinking about trying CAD and ultimately has
inspired you to draw your own model.
It is important to remember that you will not
create a masterpiece the first time you open the
program; you probably won’t even create a
useful drawing the first few times. But stick
with it.
Learn how to use the features I mentioned
earlier, and build on them each time you work
with CAD. Think back to the first time you
learned to use a word processor, email
program, or made your first model flight. It
might have been intimidating at first, but it
became second nature before long.
Remember, though, that using a computer
to design a model does not guarantee that you
will produce a great-flying airplane. That part
is also up to you. MA
David Walker
[email protected]
Sources:
Sketchup
http://sketchup.google.com
08sig2.QXD_00MSTRPG.QXD 6/23/11 9:20 AM Page 35
Edition: Model Aviation - 2011/08
Page Numbers: 31,32,34,35
Edition: Model Aviation - 2011/08
Page Numbers: 31,32,34,35
August 2011 31
Designing in
CAD
by David Walker
A beginner’s guide
to designing your
own aircraft
is a modeler to do when he or she loves
to build?
The not-so-obvious answer is to
design your own kits using CAD, or
computer-aided design. Once you are
familiar with CAD there is no limit to
the aircraft you can model, whether your
interest is RC, FF, or CL.
Many aeromodelers who are
unfamiliar with CAD might find it
daunting. It used to be true that you
needed a super-powerful computer;
months, if not years, of training; and a
lot of money to use a CAD package.
Fortunately for us, CAD has also
evolved—to the point where any
modeler with basic computer knowledge
can use it on an existing computer as
long as it is less than 10 years old. And
for what we are doing, the cost can be
zero dollars. Even if you have only a
passing interest, you owe it to yourself
to learn more and try it.
But why not design a model on
good, old paper? Similar to how the
word processor replaced the typewriter,
EVOLUTION: Our hobby has been
evolving rapidly lately. From computer
radios to laser-cut kits to electricpowered
aircraft that not only rival their
glow counterparts, but often exceed
them in performance, our hobby is
changing.
Another aspect of aeromodeling that
has evolved is ARFs and RTFs. There
are great benefits to the proliferation of
these models, but a result of this
progress is that traditional kits have
almost disappeared.
If you are the way I am and still love
to build, your options are rather limited.
This is unfortunate because just as lasercutting
was becoming mainstream, the
decline of kits had already begun. What
A three-view of a Fairchild C-123
Provider downloaded from the Internet.
08sig1.QXD_00MSTRPG.QXD 6/23/11 1:33 PM Page 31
A downloaded three-view
with rough CAD overlay.
The author made this
80-inch-span foam and
plywood C-123 using a
CAD drawing that
originated from the
three-view.
The screen showing that all
objects have been changed
with one click of the mouse.
The screen showing confirmation to
change edit group object, so that all
objects with the same name get the
change.
CAD for the home user is replacing the
paper, pencil, T-square, large drawing
table, mechanical compass, and multitude
of other tools needed to properly create a
set of plans the “old way.”
Drawing model airplane plans has
evolved too, with many of the same
benefits. Sure, there is a learning curve;
but just as you adapted to using a word
processor, and likely would never use a
typewriter again, you can probably learn
and adjust to using CAD almost as easily.
My goal is not to teach you how to
design an airplane in CAD using a
specific CAD program, or even how to
use this design method, but to help you
get started and point out some of the
advantages of it with which you might be
unfamiliar.
The easiest way to begin is to
download one of the free CAD programs
listed at the end of this article and start
using it. For many of them there is plenty
of online help and support forums that are
specific to the program you are using.
Then if you find that you like using
CAD, you can explore many of the other
CAD programs that are available for
purchase. My current favorite is the free
version of Sketchup.
Once you get the basics down, you
can explore the more advanced features.
But in all honesty, the basics are really all
you need when drawing model airplanes.
With CAD you can download an
almost endless supply of free plans on the
Internet. And if the airplane is not the
scale you want, or you want to make
design changes, you can easily do that.
These plans are also a great way to pick
up on new techniques and design
possibilities.
Addtionally, there is a countless array
of parts, such as servos, hardware, etc.,
that are available to download to use in
your drawings. And you can share your
work with others around the world. There
is something gratifying about seeing
someone else fly one of your designs—
sometimes someone from halfway around
the world.
Before going into some of the important
features of CAD, it’s important to know
how it differs from conventional painting,
drawing, or photo programs, with which
you may be familiar.
CAD is vector based; that is, the
drawing is made from lines and nothing
more. Even circles or arcs are a series of
lines, albeit extremely small lines.
Photo and painting programs are
“raster” images. That simply means that
the image from one of these programs is
composed of a series of fixed-size
squares. That might seem unimportant at
first—until you try to zoom in on a raster
image.
Most of you have probably tried
this at one point. You have a nice
picture of your favorite airplane in
flight, but it looks like a small dot in
the picture. Then you zoom in, and all
you have is a larger dot with fuzzy
edges.
32 MODEL AVIATION
08sig1.QXD_00MSTRPG.QXD 6/23/11 1:37 PM Page 32
Comparison of
a zoomed-in
section of the
CAD drawing
showing a
raster vs. a
vector file.
Raster zoomed
Vector zoomed
A screen shot showing a working
drawing of an 80-inch-wingspan P-39.
34 MODEL AVIATION
The completed Provider coming
in for a landing on its first flight.
Photos by the author
Because a CAD drawing is composed
of a series of lines, you can zoom in all you
want with no loss of quality. This is
important when you want to work on fine
points of a drawing such as servo mounting
details, landing gear detail, etc.
The fact that a CAD drawing is vector
based also allows you to scale a drawing to
any size you want. This is handy if you
want to trace a three-view that you found
on the Internet and, for example, make an
8-foot model of the airplane.
The three-view might have had a
wingspan of only 6 inches when originally
drawn. However, you can easily scale it to
any size you want with a few clicks of the
mouse—and there will be no loss of quality.
It’s a good idea to start slowly when
learning anything new, and CAD is no
different. As you learned to fly with a
trainer, it is best to start with a simple, small
CAD project to get used to your new tool.
Choose a project that will allow some room
for error and with which you can grow.
One of the great things about computers
is that they make it almost effortless to
duplicate nearly anything; so why not learn
to draw by making something you will use
later? A servo, hardware items, a receiver,
motors/engines, etc. are perfect candidates,
and you can employ them later, when you
design your first model.
Even if you mess up beyond all hope
when making one of these early drawings,
you may have lost only 10-15 minutes of
work. But you learn valuable lessons to be
applied to your first aircraft design, thus
saving hours of work.
Just as when you learned to fly, handson
experience with CAD is best. However,
it was nice to have some guidance when I
got started. Every CAD package I have used
throughout the years has had the following
features, and they are crucial to learn.
• Drawing tools: Line, circle, and arc
function as you would expect them to.
Most CAD packages have many more, but
those are the ones you will use 90% of the
time.
• Editing tools: Once you have a line or
other object drawn, you might want to
change a few things. Trim/extend, delete,
rotate, copy, and stretch allow you to edit
objects on the screen.
• Snap: This allows you to start your next
line exactly at the end or middle of a line or
tangent to a circle or arc. You can also snap
to predefined angles such as 0°, 45°, 90°,
etc.
Snap is one of the many things that sets
CAD apart from traditional painting
programs. This is vital if you want to have
your parts laser or machine cut.
• Layers: This allows you to separate
various components of your drawings. It is
similar to drawing on clear plastic sheets,
where you can lay the various layers on top
of each other or omit some for clarity.
You can have the wing structure on
one layer and hardware on another. You
can keep the hardware layer off while
working on the detail of the wing
structure, and then turn the hardware
08sig2.QXD_00MSTRPG.QXD 6/23/11 9:19 AM Page 34
August 2011 35
layer back on to show the final product.
I separate my layers by color so I can better
visualize the various objects, but it is not
necessary.
• Groups: This function allows you to group the
many lines that comprise an object, such as a
servo. Some CAD programs call these
“blocks.” This lets you copy, move, or rotate the
servo as a unit; you don’t have to try to select all
the individual lines that make up the servo.
Let’s keep with the servo example. If you
placed six of them on your drawing and later
decide to use different servos, all you have to
do is redefine the group with the new servo and
all servos are changed automatically. Try that
with pencil and paper.
• Export to DXF: DXF is a common file type
that almost all CAD programs use. Each
package has its own proprietary file format, so
you will need to export to DXF if you want
your parts laser or machine cut; almost all
shops that offer cutting services accept these
kinds of files.
When saving your drawing while working
on it, it is best to save in its native format
because DXF does not always save all the
details of your drawing. If you do not plan on
having your parts machine cut, exporting to
DXF is not important.
Let’s cover printing; after all, what we are
after is a set of plans from which to build. Here
is where CAD for the home user has its
shortcomings.
Each CAD program I have used has its own
way of handling printing. Most have a way to
tile print with registration marks; that is, your
drawing will be produced on your standard
home printer on many sheets.
Since printers cannot print to the edge of a
sheet of paper, registration marks are printed in
the corner of the drawings so you can align all
the sheets and tape them together after
trimming the margins. This is not as tedious as
it sounds, and I have done it quite a few times
with great success.
Some CAD programs don’t offer printing
with registration marks. To deal with this, some
aeromodelers export their drawing as full-size
PDF files and use the PDF viewer to do the tile
printing.
Unfortunately printing in CAD requires
some experimentation to get acceptable results.
You could say that printing for the CAD home
user needs to evolve a little more.
I am lucky in that I have access to a 48-inch
plotter. CAD is designed to work with plotters.
Knowing this, I size my drawings accordingly.
Some towns have printing shops that will
plot your drawing for a reasonable cost, or
maybe you know a friend who has access to a
plotter. If you want to submit your drawings to
a magazine for publication or have your
drawing printed by a local company or friend, it
is best to check with them regarding the size
that is required.
The AMA Plans Service and the local
FedEx/Kinko’s requires 36-inch drawing
heights. Length can be anything you want, but
it is best to keep the length less than 60 inches
or the plans set becomes too large to use easily.
I hope this article at the very least got you
thinking about trying CAD and ultimately has
inspired you to draw your own model.
It is important to remember that you will not
create a masterpiece the first time you open the
program; you probably won’t even create a
useful drawing the first few times. But stick
with it.
Learn how to use the features I mentioned
earlier, and build on them each time you work
with CAD. Think back to the first time you
learned to use a word processor, email
program, or made your first model flight. It
might have been intimidating at first, but it
became second nature before long.
Remember, though, that using a computer
to design a model does not guarantee that you
will produce a great-flying airplane. That part
is also up to you. MA
David Walker
[email protected]
Sources:
Sketchup
http://sketchup.google.com
08sig2.QXD_00MSTRPG.QXD 6/23/11 9:20 AM Page 35
Edition: Model Aviation - 2011/08
Page Numbers: 31,32,34,35
August 2011 31
Designing in
CAD
by David Walker
A beginner’s guide
to designing your
own aircraft
is a modeler to do when he or she loves
to build?
The not-so-obvious answer is to
design your own kits using CAD, or
computer-aided design. Once you are
familiar with CAD there is no limit to
the aircraft you can model, whether your
interest is RC, FF, or CL.
Many aeromodelers who are
unfamiliar with CAD might find it
daunting. It used to be true that you
needed a super-powerful computer;
months, if not years, of training; and a
lot of money to use a CAD package.
Fortunately for us, CAD has also
evolved—to the point where any
modeler with basic computer knowledge
can use it on an existing computer as
long as it is less than 10 years old. And
for what we are doing, the cost can be
zero dollars. Even if you have only a
passing interest, you owe it to yourself
to learn more and try it.
But why not design a model on
good, old paper? Similar to how the
word processor replaced the typewriter,
EVOLUTION: Our hobby has been
evolving rapidly lately. From computer
radios to laser-cut kits to electricpowered
aircraft that not only rival their
glow counterparts, but often exceed
them in performance, our hobby is
changing.
Another aspect of aeromodeling that
has evolved is ARFs and RTFs. There
are great benefits to the proliferation of
these models, but a result of this
progress is that traditional kits have
almost disappeared.
If you are the way I am and still love
to build, your options are rather limited.
This is unfortunate because just as lasercutting
was becoming mainstream, the
decline of kits had already begun. What
A three-view of a Fairchild C-123
Provider downloaded from the Internet.
08sig1.QXD_00MSTRPG.QXD 6/23/11 1:33 PM Page 31
A downloaded three-view
with rough CAD overlay.
The author made this
80-inch-span foam and
plywood C-123 using a
CAD drawing that
originated from the
three-view.
The screen showing that all
objects have been changed
with one click of the mouse.
The screen showing confirmation to
change edit group object, so that all
objects with the same name get the
change.
CAD for the home user is replacing the
paper, pencil, T-square, large drawing
table, mechanical compass, and multitude
of other tools needed to properly create a
set of plans the “old way.”
Drawing model airplane plans has
evolved too, with many of the same
benefits. Sure, there is a learning curve;
but just as you adapted to using a word
processor, and likely would never use a
typewriter again, you can probably learn
and adjust to using CAD almost as easily.
My goal is not to teach you how to
design an airplane in CAD using a
specific CAD program, or even how to
use this design method, but to help you
get started and point out some of the
advantages of it with which you might be
unfamiliar.
The easiest way to begin is to
download one of the free CAD programs
listed at the end of this article and start
using it. For many of them there is plenty
of online help and support forums that are
specific to the program you are using.
Then if you find that you like using
CAD, you can explore many of the other
CAD programs that are available for
purchase. My current favorite is the free
version of Sketchup.
Once you get the basics down, you
can explore the more advanced features.
But in all honesty, the basics are really all
you need when drawing model airplanes.
With CAD you can download an
almost endless supply of free plans on the
Internet. And if the airplane is not the
scale you want, or you want to make
design changes, you can easily do that.
These plans are also a great way to pick
up on new techniques and design
possibilities.
Addtionally, there is a countless array
of parts, such as servos, hardware, etc.,
that are available to download to use in
your drawings. And you can share your
work with others around the world. There
is something gratifying about seeing
someone else fly one of your designs—
sometimes someone from halfway around
the world.
Before going into some of the important
features of CAD, it’s important to know
how it differs from conventional painting,
drawing, or photo programs, with which
you may be familiar.
CAD is vector based; that is, the
drawing is made from lines and nothing
more. Even circles or arcs are a series of
lines, albeit extremely small lines.
Photo and painting programs are
“raster” images. That simply means that
the image from one of these programs is
composed of a series of fixed-size
squares. That might seem unimportant at
first—until you try to zoom in on a raster
image.
Most of you have probably tried
this at one point. You have a nice
picture of your favorite airplane in
flight, but it looks like a small dot in
the picture. Then you zoom in, and all
you have is a larger dot with fuzzy
edges.
32 MODEL AVIATION
08sig1.QXD_00MSTRPG.QXD 6/23/11 1:37 PM Page 32
Comparison of
a zoomed-in
section of the
CAD drawing
showing a
raster vs. a
vector file.
Raster zoomed
Vector zoomed
A screen shot showing a working
drawing of an 80-inch-wingspan P-39.
34 MODEL AVIATION
The completed Provider coming
in for a landing on its first flight.
Photos by the author
Because a CAD drawing is composed
of a series of lines, you can zoom in all you
want with no loss of quality. This is
important when you want to work on fine
points of a drawing such as servo mounting
details, landing gear detail, etc.
The fact that a CAD drawing is vector
based also allows you to scale a drawing to
any size you want. This is handy if you
want to trace a three-view that you found
on the Internet and, for example, make an
8-foot model of the airplane.
The three-view might have had a
wingspan of only 6 inches when originally
drawn. However, you can easily scale it to
any size you want with a few clicks of the
mouse—and there will be no loss of quality.
It’s a good idea to start slowly when
learning anything new, and CAD is no
different. As you learned to fly with a
trainer, it is best to start with a simple, small
CAD project to get used to your new tool.
Choose a project that will allow some room
for error and with which you can grow.
One of the great things about computers
is that they make it almost effortless to
duplicate nearly anything; so why not learn
to draw by making something you will use
later? A servo, hardware items, a receiver,
motors/engines, etc. are perfect candidates,
and you can employ them later, when you
design your first model.
Even if you mess up beyond all hope
when making one of these early drawings,
you may have lost only 10-15 minutes of
work. But you learn valuable lessons to be
applied to your first aircraft design, thus
saving hours of work.
Just as when you learned to fly, handson
experience with CAD is best. However,
it was nice to have some guidance when I
got started. Every CAD package I have used
throughout the years has had the following
features, and they are crucial to learn.
• Drawing tools: Line, circle, and arc
function as you would expect them to.
Most CAD packages have many more, but
those are the ones you will use 90% of the
time.
• Editing tools: Once you have a line or
other object drawn, you might want to
change a few things. Trim/extend, delete,
rotate, copy, and stretch allow you to edit
objects on the screen.
• Snap: This allows you to start your next
line exactly at the end or middle of a line or
tangent to a circle or arc. You can also snap
to predefined angles such as 0°, 45°, 90°,
etc.
Snap is one of the many things that sets
CAD apart from traditional painting
programs. This is vital if you want to have
your parts laser or machine cut.
• Layers: This allows you to separate
various components of your drawings. It is
similar to drawing on clear plastic sheets,
where you can lay the various layers on top
of each other or omit some for clarity.
You can have the wing structure on
one layer and hardware on another. You
can keep the hardware layer off while
working on the detail of the wing
structure, and then turn the hardware
08sig2.QXD_00MSTRPG.QXD 6/23/11 9:19 AM Page 34
August 2011 35
layer back on to show the final product.
I separate my layers by color so I can better
visualize the various objects, but it is not
necessary.
• Groups: This function allows you to group the
many lines that comprise an object, such as a
servo. Some CAD programs call these
“blocks.” This lets you copy, move, or rotate the
servo as a unit; you don’t have to try to select all
the individual lines that make up the servo.
Let’s keep with the servo example. If you
placed six of them on your drawing and later
decide to use different servos, all you have to
do is redefine the group with the new servo and
all servos are changed automatically. Try that
with pencil and paper.
• Export to DXF: DXF is a common file type
that almost all CAD programs use. Each
package has its own proprietary file format, so
you will need to export to DXF if you want
your parts laser or machine cut; almost all
shops that offer cutting services accept these
kinds of files.
When saving your drawing while working
on it, it is best to save in its native format
because DXF does not always save all the
details of your drawing. If you do not plan on
having your parts machine cut, exporting to
DXF is not important.
Let’s cover printing; after all, what we are
after is a set of plans from which to build. Here
is where CAD for the home user has its
shortcomings.
Each CAD program I have used has its own
way of handling printing. Most have a way to
tile print with registration marks; that is, your
drawing will be produced on your standard
home printer on many sheets.
Since printers cannot print to the edge of a
sheet of paper, registration marks are printed in
the corner of the drawings so you can align all
the sheets and tape them together after
trimming the margins. This is not as tedious as
it sounds, and I have done it quite a few times
with great success.
Some CAD programs don’t offer printing
with registration marks. To deal with this, some
aeromodelers export their drawing as full-size
PDF files and use the PDF viewer to do the tile
printing.
Unfortunately printing in CAD requires
some experimentation to get acceptable results.
You could say that printing for the CAD home
user needs to evolve a little more.
I am lucky in that I have access to a 48-inch
plotter. CAD is designed to work with plotters.
Knowing this, I size my drawings accordingly.
Some towns have printing shops that will
plot your drawing for a reasonable cost, or
maybe you know a friend who has access to a
plotter. If you want to submit your drawings to
a magazine for publication or have your
drawing printed by a local company or friend, it
is best to check with them regarding the size
that is required.
The AMA Plans Service and the local
FedEx/Kinko’s requires 36-inch drawing
heights. Length can be anything you want, but
it is best to keep the length less than 60 inches
or the plans set becomes too large to use easily.
I hope this article at the very least got you
thinking about trying CAD and ultimately has
inspired you to draw your own model.
It is important to remember that you will not
create a masterpiece the first time you open the
program; you probably won’t even create a
useful drawing the first few times. But stick
with it.
Learn how to use the features I mentioned
earlier, and build on them each time you work
with CAD. Think back to the first time you
learned to use a word processor, email
program, or made your first model flight. It
might have been intimidating at first, but it
became second nature before long.
Remember, though, that using a computer
to design a model does not guarantee that you
will produce a great-flying airplane. That part
is also up to you. MA
David Walker
[email protected]
Sources:
Sketchup
http://sketchup.google.com
08sig2.QXD_00MSTRPG.QXD 6/23/11 9:20 AM Page 35
Edition: Model Aviation - 2011/08
Page Numbers: 31,32,34,35
August 2011 31
Designing in
CAD
by David Walker
A beginner’s guide
to designing your
own aircraft
is a modeler to do when he or she loves
to build?
The not-so-obvious answer is to
design your own kits using CAD, or
computer-aided design. Once you are
familiar with CAD there is no limit to
the aircraft you can model, whether your
interest is RC, FF, or CL.
Many aeromodelers who are
unfamiliar with CAD might find it
daunting. It used to be true that you
needed a super-powerful computer;
months, if not years, of training; and a
lot of money to use a CAD package.
Fortunately for us, CAD has also
evolved—to the point where any
modeler with basic computer knowledge
can use it on an existing computer as
long as it is less than 10 years old. And
for what we are doing, the cost can be
zero dollars. Even if you have only a
passing interest, you owe it to yourself
to learn more and try it.
But why not design a model on
good, old paper? Similar to how the
word processor replaced the typewriter,
EVOLUTION: Our hobby has been
evolving rapidly lately. From computer
radios to laser-cut kits to electricpowered
aircraft that not only rival their
glow counterparts, but often exceed
them in performance, our hobby is
changing.
Another aspect of aeromodeling that
has evolved is ARFs and RTFs. There
are great benefits to the proliferation of
these models, but a result of this
progress is that traditional kits have
almost disappeared.
If you are the way I am and still love
to build, your options are rather limited.
This is unfortunate because just as lasercutting
was becoming mainstream, the
decline of kits had already begun. What
A three-view of a Fairchild C-123
Provider downloaded from the Internet.
08sig1.QXD_00MSTRPG.QXD 6/23/11 1:33 PM Page 31
A downloaded three-view
with rough CAD overlay.
The author made this
80-inch-span foam and
plywood C-123 using a
CAD drawing that
originated from the
three-view.
The screen showing that all
objects have been changed
with one click of the mouse.
The screen showing confirmation to
change edit group object, so that all
objects with the same name get the
change.
CAD for the home user is replacing the
paper, pencil, T-square, large drawing
table, mechanical compass, and multitude
of other tools needed to properly create a
set of plans the “old way.”
Drawing model airplane plans has
evolved too, with many of the same
benefits. Sure, there is a learning curve;
but just as you adapted to using a word
processor, and likely would never use a
typewriter again, you can probably learn
and adjust to using CAD almost as easily.
My goal is not to teach you how to
design an airplane in CAD using a
specific CAD program, or even how to
use this design method, but to help you
get started and point out some of the
advantages of it with which you might be
unfamiliar.
The easiest way to begin is to
download one of the free CAD programs
listed at the end of this article and start
using it. For many of them there is plenty
of online help and support forums that are
specific to the program you are using.
Then if you find that you like using
CAD, you can explore many of the other
CAD programs that are available for
purchase. My current favorite is the free
version of Sketchup.
Once you get the basics down, you
can explore the more advanced features.
But in all honesty, the basics are really all
you need when drawing model airplanes.
With CAD you can download an
almost endless supply of free plans on the
Internet. And if the airplane is not the
scale you want, or you want to make
design changes, you can easily do that.
These plans are also a great way to pick
up on new techniques and design
possibilities.
Addtionally, there is a countless array
of parts, such as servos, hardware, etc.,
that are available to download to use in
your drawings. And you can share your
work with others around the world. There
is something gratifying about seeing
someone else fly one of your designs—
sometimes someone from halfway around
the world.
Before going into some of the important
features of CAD, it’s important to know
how it differs from conventional painting,
drawing, or photo programs, with which
you may be familiar.
CAD is vector based; that is, the
drawing is made from lines and nothing
more. Even circles or arcs are a series of
lines, albeit extremely small lines.
Photo and painting programs are
“raster” images. That simply means that
the image from one of these programs is
composed of a series of fixed-size
squares. That might seem unimportant at
first—until you try to zoom in on a raster
image.
Most of you have probably tried
this at one point. You have a nice
picture of your favorite airplane in
flight, but it looks like a small dot in
the picture. Then you zoom in, and all
you have is a larger dot with fuzzy
edges.
32 MODEL AVIATION
08sig1.QXD_00MSTRPG.QXD 6/23/11 1:37 PM Page 32
Comparison of
a zoomed-in
section of the
CAD drawing
showing a
raster vs. a
vector file.
Raster zoomed
Vector zoomed
A screen shot showing a working
drawing of an 80-inch-wingspan P-39.
34 MODEL AVIATION
The completed Provider coming
in for a landing on its first flight.
Photos by the author
Because a CAD drawing is composed
of a series of lines, you can zoom in all you
want with no loss of quality. This is
important when you want to work on fine
points of a drawing such as servo mounting
details, landing gear detail, etc.
The fact that a CAD drawing is vector
based also allows you to scale a drawing to
any size you want. This is handy if you
want to trace a three-view that you found
on the Internet and, for example, make an
8-foot model of the airplane.
The three-view might have had a
wingspan of only 6 inches when originally
drawn. However, you can easily scale it to
any size you want with a few clicks of the
mouse—and there will be no loss of quality.
It’s a good idea to start slowly when
learning anything new, and CAD is no
different. As you learned to fly with a
trainer, it is best to start with a simple, small
CAD project to get used to your new tool.
Choose a project that will allow some room
for error and with which you can grow.
One of the great things about computers
is that they make it almost effortless to
duplicate nearly anything; so why not learn
to draw by making something you will use
later? A servo, hardware items, a receiver,
motors/engines, etc. are perfect candidates,
and you can employ them later, when you
design your first model.
Even if you mess up beyond all hope
when making one of these early drawings,
you may have lost only 10-15 minutes of
work. But you learn valuable lessons to be
applied to your first aircraft design, thus
saving hours of work.
Just as when you learned to fly, handson
experience with CAD is best. However,
it was nice to have some guidance when I
got started. Every CAD package I have used
throughout the years has had the following
features, and they are crucial to learn.
• Drawing tools: Line, circle, and arc
function as you would expect them to.
Most CAD packages have many more, but
those are the ones you will use 90% of the
time.
• Editing tools: Once you have a line or
other object drawn, you might want to
change a few things. Trim/extend, delete,
rotate, copy, and stretch allow you to edit
objects on the screen.
• Snap: This allows you to start your next
line exactly at the end or middle of a line or
tangent to a circle or arc. You can also snap
to predefined angles such as 0°, 45°, 90°,
etc.
Snap is one of the many things that sets
CAD apart from traditional painting
programs. This is vital if you want to have
your parts laser or machine cut.
• Layers: This allows you to separate
various components of your drawings. It is
similar to drawing on clear plastic sheets,
where you can lay the various layers on top
of each other or omit some for clarity.
You can have the wing structure on
one layer and hardware on another. You
can keep the hardware layer off while
working on the detail of the wing
structure, and then turn the hardware
08sig2.QXD_00MSTRPG.QXD 6/23/11 9:19 AM Page 34
August 2011 35
layer back on to show the final product.
I separate my layers by color so I can better
visualize the various objects, but it is not
necessary.
• Groups: This function allows you to group the
many lines that comprise an object, such as a
servo. Some CAD programs call these
“blocks.” This lets you copy, move, or rotate the
servo as a unit; you don’t have to try to select all
the individual lines that make up the servo.
Let’s keep with the servo example. If you
placed six of them on your drawing and later
decide to use different servos, all you have to
do is redefine the group with the new servo and
all servos are changed automatically. Try that
with pencil and paper.
• Export to DXF: DXF is a common file type
that almost all CAD programs use. Each
package has its own proprietary file format, so
you will need to export to DXF if you want
your parts laser or machine cut; almost all
shops that offer cutting services accept these
kinds of files.
When saving your drawing while working
on it, it is best to save in its native format
because DXF does not always save all the
details of your drawing. If you do not plan on
having your parts machine cut, exporting to
DXF is not important.
Let’s cover printing; after all, what we are
after is a set of plans from which to build. Here
is where CAD for the home user has its
shortcomings.
Each CAD program I have used has its own
way of handling printing. Most have a way to
tile print with registration marks; that is, your
drawing will be produced on your standard
home printer on many sheets.
Since printers cannot print to the edge of a
sheet of paper, registration marks are printed in
the corner of the drawings so you can align all
the sheets and tape them together after
trimming the margins. This is not as tedious as
it sounds, and I have done it quite a few times
with great success.
Some CAD programs don’t offer printing
with registration marks. To deal with this, some
aeromodelers export their drawing as full-size
PDF files and use the PDF viewer to do the tile
printing.
Unfortunately printing in CAD requires
some experimentation to get acceptable results.
You could say that printing for the CAD home
user needs to evolve a little more.
I am lucky in that I have access to a 48-inch
plotter. CAD is designed to work with plotters.
Knowing this, I size my drawings accordingly.
Some towns have printing shops that will
plot your drawing for a reasonable cost, or
maybe you know a friend who has access to a
plotter. If you want to submit your drawings to
a magazine for publication or have your
drawing printed by a local company or friend, it
is best to check with them regarding the size
that is required.
The AMA Plans Service and the local
FedEx/Kinko’s requires 36-inch drawing
heights. Length can be anything you want, but
it is best to keep the length less than 60 inches
or the plans set becomes too large to use easily.
I hope this article at the very least got you
thinking about trying CAD and ultimately has
inspired you to draw your own model.
It is important to remember that you will not
create a masterpiece the first time you open the
program; you probably won’t even create a
useful drawing the first few times. But stick
with it.
Learn how to use the features I mentioned
earlier, and build on them each time you work
with CAD. Think back to the first time you
learned to use a word processor, email
program, or made your first model flight. It
might have been intimidating at first, but it
became second nature before long.
Remember, though, that using a computer
to design a model does not guarantee that you
will produce a great-flying airplane. That part
is also up to you. MA
David Walker
[email protected]
Sources:
Sketchup
http://sketchup.google.com
08sig2.QXD_00MSTRPG.QXD 6/23/11 9:20 AM Page 35