126 MODEL AVIATION
IN THE LAST few columns I addressed some of the ways foam
can be useful in building RC Giant models. This month I’ll describe
the method I used to construct the large wing fillets on my 1/4-scale
Russian Polikarpov I-16 “Rata.” This is another fine example of
how blue foam can
make a seemingly
daunting task easier
to manage.
The wing fillets
on this subject are
extremely big, both
in width and length.
At their widest
point, the fillets add
approximately 10
inches to the width of the fuselage and extend past the TE of the
wing to just shy of the horizontal stabilizer. In addition, the fillet
shape makes it difficult, at least for me, to plank using strips of 1/8
balsa.
If I had attempted this method, I’m sure I would have sanded
through the material in many places or left paper-thin areas that
would have been too weak to handle, even with an outer layer of
fiberglass cloth.
I started making the fillets by creating the correct lower outline.
This is where the part meets the wing. I did that by using 1/32
aircraft-grade plywood that extended and formed the fillet outline
How to make wing fillets using blue foam
[[email protected]]
Radio Control Giants Sal Calvagna
Also included in this column:
• Custom fuel dots
• Junior Pacheco’s B-17
The large fillet area and single fillet former on the author’s 1/4-scale
Polikarpov. The fillet base/wing saddle is made from 1/32 aircraftgrade
plywood.
Blue foam fills most of the void and is sanded to a rough shape.
Heavy first coat of finishing resin mixed with microballoons. Pacer Technology Z-Poxy finishing resin.
and would act as the wing saddle. Please refer to the photo.
This step is fairly easy. I installed the wing on the fuselage, taped
sheets of printer paper onto the wing alongside the fuselage, and
drew the shape of the fillet. I did this on only one side of the
fuselage.
When I was happy with my drawing, I used my trusty band saw
to cut two layers of 1/32 aircraft plywood. That made identical
saddles/fillet bases—one for each side of the fuselage.
An important reason for using 1/32 aircraft-grade plywood was
that it created a strong, hangar-rash resistant, sharp edge where the
fillet met the wing. The plywood creates a smooth transition from fillet
to wing that tapers at the outside to a fine edge. Balsa would not
provide the strength needed and would be too thick for a crisp
transition.
The next step was to mark the proper height on the fuselage. I
penciled a line on its surface where the fillet should have ended.
At this point I had the fillet shape where it met the wing and where
it would meet the fuselage. However, that did not give me the radius or
curve that the fillet would take from the high point on the fuselage to
the low point of the wing. I was able to determine that by making two
fillet formers from 1/8 balsa—one for each side of the fuselage.
No mathematics were required; I simply eyeballed what I thought
was correct from the reference photos. Once installed, I had the curve
template that would carry through the entire fillet.
It was time to fill in the large voids. I rough-cut pieces of blue
foam, epoxied them in place, and used a hobby knife to whittle the
foam to the approximate shape. I didn’t worry about getting anywhere
close to the correct shape; I would use handheld 80-grit sandpaper to
contour further.
Even during sanding, it is unimportant to get the foam fillet to a
finished shape. It is better to remove more foam than needed, because
the finished product will be obtained by applying a coat of finishing
resin mixed with microballoons, which can be easily shaped and
sanded when dry.
If you don’t know what the heck microballoons are, following is a
description I found on the Internet.
“Microballoons are a lightweight free-flowing white powder
consisting of microscopic, hollow, glass ball clusters. Microballoons
are a specially processed silica glass, classified to insure uniform
particle size and product performance and is hydrophopic (does not
readily adsorb moisture).
“It disperses extremely well when mixed with various resins or
plaster. Microballoons do not absorb resin and therefore provide
maximum filler function. Cured systems are more water resistant and
have a higher temperature resistance in addition to being more thermal
and electrical resistive.”
A photo shows how I spread the first, heavy layer of finishing resin
mixed with microballoons. Keep in mind that when mixing
microballoons, the more material you add to the resin, the easier it will
be to sand when dry.
The mixture I use is not scientific. I add microballoons to the
mixed resin until the paste has lost all its sheen. You can usually obtain
microballoons at your local hobby store or from any of the large
Internet hobby suppliers.
Check in upcoming columns for the finished results of the fillet and
more about the Rata build!
Custom Fuel Dots: If you want to dress up that Cub with a scalelooking
gas cap, take a look at what Tom Tyler of Patchogue Hobbies
made for an RC Giant-size Piper Cub.
The ubiquitous Cub’s fuel tank sat directly in front of the instrument
panel. For a fuel gauge, it relied on a floating cork attached to a thick
piece of wire that protruded up through the fuel cap on top of the
engine cowling. As the fuel emptied, the cork descended into the fuel
tank, showing less and less wire above the cowling. A great video on
YouTube shows exactly how the gauge looks in flight.
Tom can make custom fuel dots in a variety of anodized colors. For
more information, give him a call. See the source listing.
A photo shows the business end of a B-17 that Junior Pacheco built
and finished as “Fuddy Duddy.” It spans 138 inches and is powered by
four O.S. .91 glow engines.
According to Junior, the full-scale aircraft was built too late to see
action during World War II and was retired in the mid-1950s.
Columbia Pictures purchased it in 1960, and after a short movie career
it was sold and converted to an air tanker.
The National Warplane Museum in Geneseo, New York, bought
the B-17 in 1986 and subsequently restored it. The California-based
Martin Aviation acquired the aircraft in the mid-2000s.
That’s all for now. I’ll be back next month! MA
Sources:
Cub fuel-gauge video
www.youtube.com/watch?v=sVZLCnI2r3o
Patchogue Hobbies
(631) 475-8856
[email protected]
Pacer Technology
(863) 607-6611
www.franktiano.com
Edition: Model Aviation - 2008/08
Page Numbers: 126,128
Edition: Model Aviation - 2008/08
Page Numbers: 126,128
126 MODEL AVIATION
IN THE LAST few columns I addressed some of the ways foam
can be useful in building RC Giant models. This month I’ll describe
the method I used to construct the large wing fillets on my 1/4-scale
Russian Polikarpov I-16 “Rata.” This is another fine example of
how blue foam can
make a seemingly
daunting task easier
to manage.
The wing fillets
on this subject are
extremely big, both
in width and length.
At their widest
point, the fillets add
approximately 10
inches to the width of the fuselage and extend past the TE of the
wing to just shy of the horizontal stabilizer. In addition, the fillet
shape makes it difficult, at least for me, to plank using strips of 1/8
balsa.
If I had attempted this method, I’m sure I would have sanded
through the material in many places or left paper-thin areas that
would have been too weak to handle, even with an outer layer of
fiberglass cloth.
I started making the fillets by creating the correct lower outline.
This is where the part meets the wing. I did that by using 1/32
aircraft-grade plywood that extended and formed the fillet outline
How to make wing fillets using blue foam
[[email protected]]
Radio Control Giants Sal Calvagna
Also included in this column:
• Custom fuel dots
• Junior Pacheco’s B-17
The large fillet area and single fillet former on the author’s 1/4-scale
Polikarpov. The fillet base/wing saddle is made from 1/32 aircraftgrade
plywood.
Blue foam fills most of the void and is sanded to a rough shape.
Heavy first coat of finishing resin mixed with microballoons. Pacer Technology Z-Poxy finishing resin.
and would act as the wing saddle. Please refer to the photo.
This step is fairly easy. I installed the wing on the fuselage, taped
sheets of printer paper onto the wing alongside the fuselage, and
drew the shape of the fillet. I did this on only one side of the
fuselage.
When I was happy with my drawing, I used my trusty band saw
to cut two layers of 1/32 aircraft plywood. That made identical
saddles/fillet bases—one for each side of the fuselage.
An important reason for using 1/32 aircraft-grade plywood was
that it created a strong, hangar-rash resistant, sharp edge where the
fillet met the wing. The plywood creates a smooth transition from fillet
to wing that tapers at the outside to a fine edge. Balsa would not
provide the strength needed and would be too thick for a crisp
transition.
The next step was to mark the proper height on the fuselage. I
penciled a line on its surface where the fillet should have ended.
At this point I had the fillet shape where it met the wing and where
it would meet the fuselage. However, that did not give me the radius or
curve that the fillet would take from the high point on the fuselage to
the low point of the wing. I was able to determine that by making two
fillet formers from 1/8 balsa—one for each side of the fuselage.
No mathematics were required; I simply eyeballed what I thought
was correct from the reference photos. Once installed, I had the curve
template that would carry through the entire fillet.
It was time to fill in the large voids. I rough-cut pieces of blue
foam, epoxied them in place, and used a hobby knife to whittle the
foam to the approximate shape. I didn’t worry about getting anywhere
close to the correct shape; I would use handheld 80-grit sandpaper to
contour further.
Even during sanding, it is unimportant to get the foam fillet to a
finished shape. It is better to remove more foam than needed, because
the finished product will be obtained by applying a coat of finishing
resin mixed with microballoons, which can be easily shaped and
sanded when dry.
If you don’t know what the heck microballoons are, following is a
description I found on the Internet.
“Microballoons are a lightweight free-flowing white powder
consisting of microscopic, hollow, glass ball clusters. Microballoons
are a specially processed silica glass, classified to insure uniform
particle size and product performance and is hydrophopic (does not
readily adsorb moisture).
“It disperses extremely well when mixed with various resins or
plaster. Microballoons do not absorb resin and therefore provide
maximum filler function. Cured systems are more water resistant and
have a higher temperature resistance in addition to being more thermal
and electrical resistive.”
A photo shows how I spread the first, heavy layer of finishing resin
mixed with microballoons. Keep in mind that when mixing
microballoons, the more material you add to the resin, the easier it will
be to sand when dry.
The mixture I use is not scientific. I add microballoons to the
mixed resin until the paste has lost all its sheen. You can usually obtain
microballoons at your local hobby store or from any of the large
Internet hobby suppliers.
Check in upcoming columns for the finished results of the fillet and
more about the Rata build!
Custom Fuel Dots: If you want to dress up that Cub with a scalelooking
gas cap, take a look at what Tom Tyler of Patchogue Hobbies
made for an RC Giant-size Piper Cub.
The ubiquitous Cub’s fuel tank sat directly in front of the instrument
panel. For a fuel gauge, it relied on a floating cork attached to a thick
piece of wire that protruded up through the fuel cap on top of the
engine cowling. As the fuel emptied, the cork descended into the fuel
tank, showing less and less wire above the cowling. A great video on
YouTube shows exactly how the gauge looks in flight.
Tom can make custom fuel dots in a variety of anodized colors. For
more information, give him a call. See the source listing.
A photo shows the business end of a B-17 that Junior Pacheco built
and finished as “Fuddy Duddy.” It spans 138 inches and is powered by
four O.S. .91 glow engines.
According to Junior, the full-scale aircraft was built too late to see
action during World War II and was retired in the mid-1950s.
Columbia Pictures purchased it in 1960, and after a short movie career
it was sold and converted to an air tanker.
The National Warplane Museum in Geneseo, New York, bought
the B-17 in 1986 and subsequently restored it. The California-based
Martin Aviation acquired the aircraft in the mid-2000s.
That’s all for now. I’ll be back next month! MA
Sources:
Cub fuel-gauge video
www.youtube.com/watch?v=sVZLCnI2r3o
Patchogue Hobbies
(631) 475-8856
[email protected]
Pacer Technology
(863) 607-6611
www.franktiano.com
