Dave Robelen
M i c r o - F l y i n g
Route 4, Box 369, Farmville VA 23901; E-mail: [email protected]
The first step is marking the propeller blank with layout lines.
The author drills the shaft hole at this stage.
The propeller blank has been cut to shape and is ready for the
front and back of the blade to be carved.
The propeller-block layout and graph system has been in use for a number of years and
will result in an accurate and well-performing blade.
GREETINGS from chilly central
Virginia. As I am writing this, it is early
December. By the time you read it, it will
be winter and Christmas will have passed.
I hope all of you had a safe and joyous
Christmas and found just what you were
looking for under the tree. With the rapid
growth of the micro industry, there
certainly is plenty from which to choose.
In the last column I indicated that the
next National Indoor Remote-controlled
Aircraft Council (NIRAC)
Championships would probably be held
in Pennsylvania. There has been a
change, and it appears that we will be
back in Waterford, Michigan, in 2005.
This year the CD will be Bob Wilder,
so you can expect him to do a quality job
running the meet. Make plans now to
come out and join the fun. More periods
of organized open flying are planned, so
even if you are not a “trophy hound,”
come on out.
There is a rising star in the field of
micromodels. Scott Christensen, who is a
manager with Sig Manufacturing, is no
stranger to quality modeling. Roughly a
year ago, he was bitten by the micro bug
and obtained an RFFS-100 control
system. In practically no time, Scott had a
new design flying that he calls the
Yardsail. I saw it at the Toledo Show and
again in Waterford, and I was delighted
with the obvious quality and good flying
habits.
The model is a profile shoulder wing
with three-panel dihedral, and the drive is
mounted on a low pylon over the wing.
Although the model is not complex, the
quality and finish are superb.
Last season I had published plans for a
14-inch-span, all-balsa WACO SRE built
for micro gear and drive. This was a
project in RC MicroFlight. Shortly after
the issue was published, I received an Email
with pictures attached from Scott.
He is a fan of the WACO SRE and had
built his own from my plans.
Scott’s model was incredibly clean,
lightweight, and had a true scale color
scheme. It flew quite well, which led to
stage two. He was so pleased with his
model that he decided to build another to
contest standards.
It was hard for me to imagine much of
an improvement over the first model.
That changed when I received another Email
from him. The latest version of
Scott’s WACO is stunning! Unless you
know the size, it would be natural to
assume that it is a much larger model. It
took right off and flew like a bird.
I do not have pictures large enough to
show here, but for those who have
Internet access, check out www.rc
groups.com for a real treat in photos.
I have been carving my own propellers
from wood for a long time, and when I
applied this technique to the small
electric-powered models, the
improvement in performance was evident.
circumference (R) circumference / 2 (R/2)
pitch
The author uses lacquer sealer, Krylon Crystal Clear spray, or
modeling dope to coat the finished propeller.
The rough-carved propeller is ready to be sanded into its final
shape. A template will provide symmetry.
There is no mystery to shaping a propeller; it is a matter of
proper layout and careful cutting. I cannot take claim for this
design system. It has been in use for at least 50 years and
produces an accurate, well-performing blade.
The accompanying sketch shows the circumference of a
propeller marked along the bottom line, with the pitch marked
on the vertical line. For convenience, I usually divide both of
these numbers by two or three so they will fit a standard sheet of
paper.
Dividing the circumference by two and marking the line will
designate a point halfway out one blade. Drawing a slanted line
between this point and the pitch mark will define the pitch angle
at the middle of the blade. The maximum chord of the blade may
be marked on this line, and then a pair of lines defining the block
measurements may be drawn. The figure shows a drawing of a
typical propeller-block layout.
For most applications, hard balsa will make a satisfactory
propeller. I use an X-Acto knife with a #26 whittler’s blade to
shape the blank after cutting it out with a jigsaw. For a sturdier
propeller, I have had good results with clear, white pine, such as
you find in the home-improvement stores. In this case, I do
much of my “carving” with a drum-sanding attachment on a
Moto-Tool.
The first picture shows a propeller blank ready to have the
excess sawed away before carving. I drill the shaft hole while
the blank is still in a rectangular form. Accuracy here pays off
later.
Another picture is of the shaped blank ready for the back and
front of the blade to be carved. Again, accuracy in making a
symmetrical blank will pay off in a true-running propeller.
Rather than cut straight down the blade, I normally hold the
knife approximately 45° to the blank and cut across at a
diagonal. This can be especially helpful in shaping a small
amount of undercamber in the back of the blade.
A photo shows the completed rough-cut blade. I leave the
front surface slightly full to allow for smoothing the airfoil and
getting the propeller in balance. At this stage, the blade outline
should be cut and the remaining shaping done with sandpaper. A
template helps keep both sides symmetrical.
The finished product is shown before any coatings are
applied. I have used lacquer sealer, Krylon Crystal Clear spray,
and modeling dope with equally good results. If it is for a Scale
model, put the correct colors on the blade for a finished
appearance.
Shown are an assortment of propellers made using this
method. The basic layout will apply to any size of propeller.
For sometime Hal Stewart, the editor of the newsletter CNYIFS
Thermals (Central New York Indoor Flying Society), has kept
me on his mailing list. Thanks, Hal!
The most recent issue had two handy tips I will pass along.
According to Hal, these were originally in the newsletter of the
Arizona Cactus Squadron of the Flying Aces Club.
The first item concerns pinning sticks or other parts. Purchase
a long, round eraser, generally found at stationery stores. Cut
slices from the eraser ranging from 1⁄8-inch to 1⁄4-inch thick. Push
a straight pin through the slice, slightly off center.
When you pin down sticks or cut out parts, you can place the
pin outside the piece and push down, letting the rubber hold the
part. It doesn’t split and only requires two pins at angles to the
piece—roughly half the number of pins you would normally use.
Another advantage is that the rubber isn’t as likely to mark the
piece, causing a stress riser.
The second tip is a balsa-density and weight-identification
system. This simple method helps you identify and select the
grade of balsa for each use on your model.
One cu. in. of 4-pound-per-cubic-foot-density balsa weighs
close to 1 gram. A sheet of 1⁄16 x 3 x 36 is equal to 3 x .062 x 36
= 6.7 cu. in. If the sheet is actually 4-pound-per-cubic-foot balsa,
it should weigh 6.7 grams. If the sheet weighs 10 grams, it is
10/6.7 x 4 = 6 pound-per-cubic-foot-density balsa. If it weighs
15 grams, it is 9 pounds per cubic foot density.
These numbers are rounded off slightly but are close. After
you weigh a sheet and know its density, color-code the end with
a marking pen, ink, or crayon. This should save time later in your
building project when you select the density of balsa you want
for a given part.
It is time to sign off again. I would love to see and hear from
you regarding those neat projects. Cheers! MA
Any size of propeller can be made with the basic block layout.
Edition: Model Aviation - 2005/03
Page Numbers: 146,147
Edition: Model Aviation - 2005/03
Page Numbers: 146,147
Dave Robelen
M i c r o - F l y i n g
Route 4, Box 369, Farmville VA 23901; E-mail: [email protected]
The first step is marking the propeller blank with layout lines.
The author drills the shaft hole at this stage.
The propeller blank has been cut to shape and is ready for the
front and back of the blade to be carved.
The propeller-block layout and graph system has been in use for a number of years and
will result in an accurate and well-performing blade.
GREETINGS from chilly central
Virginia. As I am writing this, it is early
December. By the time you read it, it will
be winter and Christmas will have passed.
I hope all of you had a safe and joyous
Christmas and found just what you were
looking for under the tree. With the rapid
growth of the micro industry, there
certainly is plenty from which to choose.
In the last column I indicated that the
next National Indoor Remote-controlled
Aircraft Council (NIRAC)
Championships would probably be held
in Pennsylvania. There has been a
change, and it appears that we will be
back in Waterford, Michigan, in 2005.
This year the CD will be Bob Wilder,
so you can expect him to do a quality job
running the meet. Make plans now to
come out and join the fun. More periods
of organized open flying are planned, so
even if you are not a “trophy hound,”
come on out.
There is a rising star in the field of
micromodels. Scott Christensen, who is a
manager with Sig Manufacturing, is no
stranger to quality modeling. Roughly a
year ago, he was bitten by the micro bug
and obtained an RFFS-100 control
system. In practically no time, Scott had a
new design flying that he calls the
Yardsail. I saw it at the Toledo Show and
again in Waterford, and I was delighted
with the obvious quality and good flying
habits.
The model is a profile shoulder wing
with three-panel dihedral, and the drive is
mounted on a low pylon over the wing.
Although the model is not complex, the
quality and finish are superb.
Last season I had published plans for a
14-inch-span, all-balsa WACO SRE built
for micro gear and drive. This was a
project in RC MicroFlight. Shortly after
the issue was published, I received an Email
with pictures attached from Scott.
He is a fan of the WACO SRE and had
built his own from my plans.
Scott’s model was incredibly clean,
lightweight, and had a true scale color
scheme. It flew quite well, which led to
stage two. He was so pleased with his
model that he decided to build another to
contest standards.
It was hard for me to imagine much of
an improvement over the first model.
That changed when I received another Email
from him. The latest version of
Scott’s WACO is stunning! Unless you
know the size, it would be natural to
assume that it is a much larger model. It
took right off and flew like a bird.
I do not have pictures large enough to
show here, but for those who have
Internet access, check out www.rc
groups.com for a real treat in photos.
I have been carving my own propellers
from wood for a long time, and when I
applied this technique to the small
electric-powered models, the
improvement in performance was evident.
circumference (R) circumference / 2 (R/2)
pitch
The author uses lacquer sealer, Krylon Crystal Clear spray, or
modeling dope to coat the finished propeller.
The rough-carved propeller is ready to be sanded into its final
shape. A template will provide symmetry.
There is no mystery to shaping a propeller; it is a matter of
proper layout and careful cutting. I cannot take claim for this
design system. It has been in use for at least 50 years and
produces an accurate, well-performing blade.
The accompanying sketch shows the circumference of a
propeller marked along the bottom line, with the pitch marked
on the vertical line. For convenience, I usually divide both of
these numbers by two or three so they will fit a standard sheet of
paper.
Dividing the circumference by two and marking the line will
designate a point halfway out one blade. Drawing a slanted line
between this point and the pitch mark will define the pitch angle
at the middle of the blade. The maximum chord of the blade may
be marked on this line, and then a pair of lines defining the block
measurements may be drawn. The figure shows a drawing of a
typical propeller-block layout.
For most applications, hard balsa will make a satisfactory
propeller. I use an X-Acto knife with a #26 whittler’s blade to
shape the blank after cutting it out with a jigsaw. For a sturdier
propeller, I have had good results with clear, white pine, such as
you find in the home-improvement stores. In this case, I do
much of my “carving” with a drum-sanding attachment on a
Moto-Tool.
The first picture shows a propeller blank ready to have the
excess sawed away before carving. I drill the shaft hole while
the blank is still in a rectangular form. Accuracy here pays off
later.
Another picture is of the shaped blank ready for the back and
front of the blade to be carved. Again, accuracy in making a
symmetrical blank will pay off in a true-running propeller.
Rather than cut straight down the blade, I normally hold the
knife approximately 45° to the blank and cut across at a
diagonal. This can be especially helpful in shaping a small
amount of undercamber in the back of the blade.
A photo shows the completed rough-cut blade. I leave the
front surface slightly full to allow for smoothing the airfoil and
getting the propeller in balance. At this stage, the blade outline
should be cut and the remaining shaping done with sandpaper. A
template helps keep both sides symmetrical.
The finished product is shown before any coatings are
applied. I have used lacquer sealer, Krylon Crystal Clear spray,
and modeling dope with equally good results. If it is for a Scale
model, put the correct colors on the blade for a finished
appearance.
Shown are an assortment of propellers made using this
method. The basic layout will apply to any size of propeller.
For sometime Hal Stewart, the editor of the newsletter CNYIFS
Thermals (Central New York Indoor Flying Society), has kept
me on his mailing list. Thanks, Hal!
The most recent issue had two handy tips I will pass along.
According to Hal, these were originally in the newsletter of the
Arizona Cactus Squadron of the Flying Aces Club.
The first item concerns pinning sticks or other parts. Purchase
a long, round eraser, generally found at stationery stores. Cut
slices from the eraser ranging from 1⁄8-inch to 1⁄4-inch thick. Push
a straight pin through the slice, slightly off center.
When you pin down sticks or cut out parts, you can place the
pin outside the piece and push down, letting the rubber hold the
part. It doesn’t split and only requires two pins at angles to the
piece—roughly half the number of pins you would normally use.
Another advantage is that the rubber isn’t as likely to mark the
piece, causing a stress riser.
The second tip is a balsa-density and weight-identification
system. This simple method helps you identify and select the
grade of balsa for each use on your model.
One cu. in. of 4-pound-per-cubic-foot-density balsa weighs
close to 1 gram. A sheet of 1⁄16 x 3 x 36 is equal to 3 x .062 x 36
= 6.7 cu. in. If the sheet is actually 4-pound-per-cubic-foot balsa,
it should weigh 6.7 grams. If the sheet weighs 10 grams, it is
10/6.7 x 4 = 6 pound-per-cubic-foot-density balsa. If it weighs
15 grams, it is 9 pounds per cubic foot density.
These numbers are rounded off slightly but are close. After
you weigh a sheet and know its density, color-code the end with
a marking pen, ink, or crayon. This should save time later in your
building project when you select the density of balsa you want
for a given part.
It is time to sign off again. I would love to see and hear from
you regarding those neat projects. Cheers! MA
Any size of propeller can be made with the basic block layout.