Also included in this column:
• Alternatives to rubber bands
for hold-downs Eric Jedelsky’s Motorflugmodell from the 1959-61 Zaic Yearbook shows his trademark
solid-wing construction. The ribs are actually external stiffeners.
Thurman Bowls’ innovative Moffett has closed-cell polystyrene for
most of the structure. The wing offers a new take on the halfcentury-
old Jedelsky wing construction.
World War II aircraft such as the B-24 also inspired Thurman’s
Moffett design. A Ping-Pong ball serves as the rear gun turret.
JEDELSKY UPDATED: In the 1950s and
1960s Jedelsky wing construction provided an
alternative to the usual stick-and-tissue
construction. Developed by Eric Jedelsky of
Austria, the all-balsa wing was quick to build
and provided an accurate upper surface
without the sags inherent in most tissuecovered
structures.
The wing basically consisted of two pieces
of balsa joined along the wing’s high point.
The front piece was shaped like a Hand
Launched Glider wing, with a flat bottom and
curved upper surface.
The rear piece was thin sheet, bent in a
slight curve. Widely spaced ribs on the
underside of the wing helped maintain the
curve of the rear section and kept it at the
proper angle relative to the front piece. The
ribs were strictly stiffeners and were out in the
breeze rather than enclosed with tissue
covering.
Jedelsky wings were fast to build, making
them popular for beginners’ models and for
experimentation. A look through some of
Frank Zaic Yearbooks from that period shows
a wide range of models using the Jedelsky
wing construction.
Lawrence Wellman’s Idiot’s Delight A-1
from the 1964-65 Model Aeronautic
Yearbook uses a 3/16 x 11/2-inch balsa front
section and a 1/16 x 3-inch rear section to
produce a wing with a chord of 41/2 inches.
(Even at the low prices of balsa back then,
minimizing wastage of balsa was a high art.)
Ed Turner’s A-2 from the same Yearbook
used 3/8 balsa sheet for the front portion of the
wing and 1/16 sheet for the rear. A strip of
spruce affords the LE some protection from
the inevitable dings.
Construction was simple. The front
section of the wing was roughed out using a
razor plane, and then it was carefully sanded
to give it a flat surface along the top rear. That
piece was pinned to the building board upside
down with the LE elevated above the building
board.
The thinner rear section of the wing was
glued to the front section. Then the ribs were
glued in place, providing the curve to the rear
portion of the wing.
Building the wing upside-down was
Hermann Andresen’s Dust Devil Mk III from the 1964-65 Yearbook also has Jedelsky wing
construction. The one-piece model uses crinkled tissue on top of the wing for turbulation.
Bud Romak’s Moffett Rubber model features a balsa-and-plywood
saddle to hold the one-piece wing in place.
The saddle is glued down to the rear of the pylon. A nylon screw
clamps the saddle down over the wing at the front.
necessary to allow access to the undersurface
for attaching the ribs. (If I were building a
Jedelsky wing today, I would be tempted to
hot-wire a concave fixture from foam that
followed the upper curvature of the wing.)
Dihedral joints were sanded in, Hand
Launched Glider style, with thickened or
angled ribs to give extra strength. After a final
sanding the wing could be finished with
nonshrinking dope.
The next logical progression in the solidbalsa-
wing saga was to use three or more
sheets of balsa, carefully angled to create the
curvature of the undercambered airfoil. These
wings were surprisingly quick to build and
offered accurate airfoil sections top and
bottom along the span. Unlike the Jedelsky
wings, these needed no exposed ribs for
strength, although chordwise strips of carbon
fiber were sometimes attached to the upper
and lower surfaces to stiffen the wing.
The Germans, who pioneered this type of
construction, had considerable success
beginning with Gerd Erichsen’s 1963 Nordic
Glider win, followed in the 1980s by multiple
Wakefield World Championships wins by
Lothar Doring and Reiner Hofsass. But the
arrival of the much stiffer carbon D-box
construction in the early 1990s put an end to
the solid-balsa wing.
However, old ideas can be combined with
new materials. At last year’s Nats Thurman
Bowls flew an all-plastic Moffett with a
Jedelsky-type wing. Thurman is well-known
for his innovative Rubber models, including
his auto-everything P-30 that was named an
NFFS [National Free Flight Society] Model
of the Year.
Thurman’s new Moffett is a semiscale
cross between a B-24 Liberator bomber and
a troop-carrying glider from the same era. It
features twin rudders, a multiwheel landing
gear, and a tail turret crafted from a Ping-
Pong ball.
But it is the construction, both method
and material, that is most interesting. The
entire model is made from Depron sheet: a
closed-cell polystyrene material used for
insulation under laminated “floating” floor
systems that is similar to the material used
for meat trays.
Depron comes in 2mm, 3mm, and 6mm
thickness; sheets are roughly 15 x 39 inches.
Unlike open-cell foam, Depron has a smooth
surface. Stated density is 40 kilograms per
cubic meter, or approximately 21/2 pounds
per cubic foot.
An interesting feature of Depron is that it
can be heat-formed over a mold. The
temperature required is relatively low—
roughly 194°. Depron can be cut with a
sharp knife. It can also be scored and folded.
For his Jedelsky-style wings, Thurman
uses 2mm Depron, cut to approximately 11/2
times the desired wing chord. Then he scores
the sheet on the underside of the LE line and
folds it back and under to form the thicker
front portion of the wing.
A carved-balsa form is used to help hold
the curvature of the upper surface while the
glue dries. Then the form is slipped out and a
balsa spar is inserted. That’s it!
The model’s fuselage is a simple box of
3mm Depron, edged with 1/8 square balsa. On
models with a square or diamond fuselage
cross-section, Thurman cuts two sheets,
creases each down the middle, and folds 90°.
Then he joins the halves to make the fuselage.
An Internet search for Depron uncovers a
number of mail-order sources. It costs much
less than balsa. For example, a 15 x 39-inch
sheet of 2mm Depron is approximately $2.25.
Some of the dealers sell assortment packs
containing sheets of different thicknesses.
Most have minimum orders of 10 or 12
sheets.
The Internet search also uncovered a lot of
how-to information about working with
Depron for models. It’s a popular material for
small RC electrics and scale models.
Better Than Bands? For most FF models
with one-piece wings, rubber bands are the
traditional way to strap down the wing.
Rubber bands serve as a simple and
inexpensive method of keeping the wing in
place during flight, yet they allow it to pop
safely free in a crash.
However, rubber bands do have a few
drawbacks: they weaken during the day,
especially in hot weather; the rubber can be
adversely affected by model fuels; finding
bands that are just the right length and stretch
for a particular model can be difficult; and
unless properly keyed, wings can shift,
affecting model trim.
Going to a two-piece plug-in wing solves
most of the rubber-band problems and offers
the added advantage of making the
disassembled model more compact. It’s no
wonder why plug-in wings are used almost
exclusively in the three larger FAI classes.
But for smaller models the two-piece wings’
extra weight and more complicated
construction don’t make sense.
Bud Romak developed an interesting
alternative to rubber bands to attach the wing
on his Moffett rubber-powered model. The
model, based on a Carl Redlin design, uses
the usual one-piece wing that sits atop a builtup
balsa pylon. The pylon extends roughly an
inch past the wing at the front and back. An
elliptical-shaped saddle extends over the top
of the wing to hold it in place. The saddle is a
sandwich of 1/64 plywood and 1/32 balsa. The
saddle is glued to the pylon at the rear and is
flexible enough to allow the wing to be
slipped in from the front. A nylon screw
clamps the saddle down at the front, firmly
holding the wing in place. A small piece (1/2 x
1 inch) of double-stick tape helps prevent
shifting.
Bud used a rather beefy 8/32 x 1/2-inch panhead
nylon screw.
“That’s all they had at the hardware
store,” he said.
A smaller nylon screw, such as 2/56 or
4/40, would offer some weight savings and
shear off more easily in a crash. If you do try
a similar system, make sure there is access to
the bottom of the screw to allow for easy
removal if it does shear off.
(In my experience nylon screws break at
or just below the blind nut or threaded
plywood block. Unless you can get to the
other end of the screw, it will be difficult to
remove.)
Small nylon screws in standard and metric
sizes are available from Small Parts, Inc
(www.smallparts.com). MA
Edition: Model Aviation - 2007/02
Page Numbers: 142,143,144
Edition: Model Aviation - 2007/02
Page Numbers: 142,143,144
Also included in this column:
• Alternatives to rubber bands
for hold-downs Eric Jedelsky’s Motorflugmodell from the 1959-61 Zaic Yearbook shows his trademark
solid-wing construction. The ribs are actually external stiffeners.
Thurman Bowls’ innovative Moffett has closed-cell polystyrene for
most of the structure. The wing offers a new take on the halfcentury-
old Jedelsky wing construction.
World War II aircraft such as the B-24 also inspired Thurman’s
Moffett design. A Ping-Pong ball serves as the rear gun turret.
JEDELSKY UPDATED: In the 1950s and
1960s Jedelsky wing construction provided an
alternative to the usual stick-and-tissue
construction. Developed by Eric Jedelsky of
Austria, the all-balsa wing was quick to build
and provided an accurate upper surface
without the sags inherent in most tissuecovered
structures.
The wing basically consisted of two pieces
of balsa joined along the wing’s high point.
The front piece was shaped like a Hand
Launched Glider wing, with a flat bottom and
curved upper surface.
The rear piece was thin sheet, bent in a
slight curve. Widely spaced ribs on the
underside of the wing helped maintain the
curve of the rear section and kept it at the
proper angle relative to the front piece. The
ribs were strictly stiffeners and were out in the
breeze rather than enclosed with tissue
covering.
Jedelsky wings were fast to build, making
them popular for beginners’ models and for
experimentation. A look through some of
Frank Zaic Yearbooks from that period shows
a wide range of models using the Jedelsky
wing construction.
Lawrence Wellman’s Idiot’s Delight A-1
from the 1964-65 Model Aeronautic
Yearbook uses a 3/16 x 11/2-inch balsa front
section and a 1/16 x 3-inch rear section to
produce a wing with a chord of 41/2 inches.
(Even at the low prices of balsa back then,
minimizing wastage of balsa was a high art.)
Ed Turner’s A-2 from the same Yearbook
used 3/8 balsa sheet for the front portion of the
wing and 1/16 sheet for the rear. A strip of
spruce affords the LE some protection from
the inevitable dings.
Construction was simple. The front
section of the wing was roughed out using a
razor plane, and then it was carefully sanded
to give it a flat surface along the top rear. That
piece was pinned to the building board upside
down with the LE elevated above the building
board.
The thinner rear section of the wing was
glued to the front section. Then the ribs were
glued in place, providing the curve to the rear
portion of the wing.
Building the wing upside-down was
Hermann Andresen’s Dust Devil Mk III from the 1964-65 Yearbook also has Jedelsky wing
construction. The one-piece model uses crinkled tissue on top of the wing for turbulation.
Bud Romak’s Moffett Rubber model features a balsa-and-plywood
saddle to hold the one-piece wing in place.
The saddle is glued down to the rear of the pylon. A nylon screw
clamps the saddle down over the wing at the front.
necessary to allow access to the undersurface
for attaching the ribs. (If I were building a
Jedelsky wing today, I would be tempted to
hot-wire a concave fixture from foam that
followed the upper curvature of the wing.)
Dihedral joints were sanded in, Hand
Launched Glider style, with thickened or
angled ribs to give extra strength. After a final
sanding the wing could be finished with
nonshrinking dope.
The next logical progression in the solidbalsa-
wing saga was to use three or more
sheets of balsa, carefully angled to create the
curvature of the undercambered airfoil. These
wings were surprisingly quick to build and
offered accurate airfoil sections top and
bottom along the span. Unlike the Jedelsky
wings, these needed no exposed ribs for
strength, although chordwise strips of carbon
fiber were sometimes attached to the upper
and lower surfaces to stiffen the wing.
The Germans, who pioneered this type of
construction, had considerable success
beginning with Gerd Erichsen’s 1963 Nordic
Glider win, followed in the 1980s by multiple
Wakefield World Championships wins by
Lothar Doring and Reiner Hofsass. But the
arrival of the much stiffer carbon D-box
construction in the early 1990s put an end to
the solid-balsa wing.
However, old ideas can be combined with
new materials. At last year’s Nats Thurman
Bowls flew an all-plastic Moffett with a
Jedelsky-type wing. Thurman is well-known
for his innovative Rubber models, including
his auto-everything P-30 that was named an
NFFS [National Free Flight Society] Model
of the Year.
Thurman’s new Moffett is a semiscale
cross between a B-24 Liberator bomber and
a troop-carrying glider from the same era. It
features twin rudders, a multiwheel landing
gear, and a tail turret crafted from a Ping-
Pong ball.
But it is the construction, both method
and material, that is most interesting. The
entire model is made from Depron sheet: a
closed-cell polystyrene material used for
insulation under laminated “floating” floor
systems that is similar to the material used
for meat trays.
Depron comes in 2mm, 3mm, and 6mm
thickness; sheets are roughly 15 x 39 inches.
Unlike open-cell foam, Depron has a smooth
surface. Stated density is 40 kilograms per
cubic meter, or approximately 21/2 pounds
per cubic foot.
An interesting feature of Depron is that it
can be heat-formed over a mold. The
temperature required is relatively low—
roughly 194°. Depron can be cut with a
sharp knife. It can also be scored and folded.
For his Jedelsky-style wings, Thurman
uses 2mm Depron, cut to approximately 11/2
times the desired wing chord. Then he scores
the sheet on the underside of the LE line and
folds it back and under to form the thicker
front portion of the wing.
A carved-balsa form is used to help hold
the curvature of the upper surface while the
glue dries. Then the form is slipped out and a
balsa spar is inserted. That’s it!
The model’s fuselage is a simple box of
3mm Depron, edged with 1/8 square balsa. On
models with a square or diamond fuselage
cross-section, Thurman cuts two sheets,
creases each down the middle, and folds 90°.
Then he joins the halves to make the fuselage.
An Internet search for Depron uncovers a
number of mail-order sources. It costs much
less than balsa. For example, a 15 x 39-inch
sheet of 2mm Depron is approximately $2.25.
Some of the dealers sell assortment packs
containing sheets of different thicknesses.
Most have minimum orders of 10 or 12
sheets.
The Internet search also uncovered a lot of
how-to information about working with
Depron for models. It’s a popular material for
small RC electrics and scale models.
Better Than Bands? For most FF models
with one-piece wings, rubber bands are the
traditional way to strap down the wing.
Rubber bands serve as a simple and
inexpensive method of keeping the wing in
place during flight, yet they allow it to pop
safely free in a crash.
However, rubber bands do have a few
drawbacks: they weaken during the day,
especially in hot weather; the rubber can be
adversely affected by model fuels; finding
bands that are just the right length and stretch
for a particular model can be difficult; and
unless properly keyed, wings can shift,
affecting model trim.
Going to a two-piece plug-in wing solves
most of the rubber-band problems and offers
the added advantage of making the
disassembled model more compact. It’s no
wonder why plug-in wings are used almost
exclusively in the three larger FAI classes.
But for smaller models the two-piece wings’
extra weight and more complicated
construction don’t make sense.
Bud Romak developed an interesting
alternative to rubber bands to attach the wing
on his Moffett rubber-powered model. The
model, based on a Carl Redlin design, uses
the usual one-piece wing that sits atop a builtup
balsa pylon. The pylon extends roughly an
inch past the wing at the front and back. An
elliptical-shaped saddle extends over the top
of the wing to hold it in place. The saddle is a
sandwich of 1/64 plywood and 1/32 balsa. The
saddle is glued to the pylon at the rear and is
flexible enough to allow the wing to be
slipped in from the front. A nylon screw
clamps the saddle down at the front, firmly
holding the wing in place. A small piece (1/2 x
1 inch) of double-stick tape helps prevent
shifting.
Bud used a rather beefy 8/32 x 1/2-inch panhead
nylon screw.
“That’s all they had at the hardware
store,” he said.
A smaller nylon screw, such as 2/56 or
4/40, would offer some weight savings and
shear off more easily in a crash. If you do try
a similar system, make sure there is access to
the bottom of the screw to allow for easy
removal if it does shear off.
(In my experience nylon screws break at
or just below the blind nut or threaded
plywood block. Unless you can get to the
other end of the screw, it will be difficult to
remove.)
Small nylon screws in standard and metric
sizes are available from Small Parts, Inc
(www.smallparts.com). MA
Edition: Model Aviation - 2007/02
Page Numbers: 142,143,144
Also included in this column:
• Alternatives to rubber bands
for hold-downs Eric Jedelsky’s Motorflugmodell from the 1959-61 Zaic Yearbook shows his trademark
solid-wing construction. The ribs are actually external stiffeners.
Thurman Bowls’ innovative Moffett has closed-cell polystyrene for
most of the structure. The wing offers a new take on the halfcentury-
old Jedelsky wing construction.
World War II aircraft such as the B-24 also inspired Thurman’s
Moffett design. A Ping-Pong ball serves as the rear gun turret.
JEDELSKY UPDATED: In the 1950s and
1960s Jedelsky wing construction provided an
alternative to the usual stick-and-tissue
construction. Developed by Eric Jedelsky of
Austria, the all-balsa wing was quick to build
and provided an accurate upper surface
without the sags inherent in most tissuecovered
structures.
The wing basically consisted of two pieces
of balsa joined along the wing’s high point.
The front piece was shaped like a Hand
Launched Glider wing, with a flat bottom and
curved upper surface.
The rear piece was thin sheet, bent in a
slight curve. Widely spaced ribs on the
underside of the wing helped maintain the
curve of the rear section and kept it at the
proper angle relative to the front piece. The
ribs were strictly stiffeners and were out in the
breeze rather than enclosed with tissue
covering.
Jedelsky wings were fast to build, making
them popular for beginners’ models and for
experimentation. A look through some of
Frank Zaic Yearbooks from that period shows
a wide range of models using the Jedelsky
wing construction.
Lawrence Wellman’s Idiot’s Delight A-1
from the 1964-65 Model Aeronautic
Yearbook uses a 3/16 x 11/2-inch balsa front
section and a 1/16 x 3-inch rear section to
produce a wing with a chord of 41/2 inches.
(Even at the low prices of balsa back then,
minimizing wastage of balsa was a high art.)
Ed Turner’s A-2 from the same Yearbook
used 3/8 balsa sheet for the front portion of the
wing and 1/16 sheet for the rear. A strip of
spruce affords the LE some protection from
the inevitable dings.
Construction was simple. The front
section of the wing was roughed out using a
razor plane, and then it was carefully sanded
to give it a flat surface along the top rear. That
piece was pinned to the building board upside
down with the LE elevated above the building
board.
The thinner rear section of the wing was
glued to the front section. Then the ribs were
glued in place, providing the curve to the rear
portion of the wing.
Building the wing upside-down was
Hermann Andresen’s Dust Devil Mk III from the 1964-65 Yearbook also has Jedelsky wing
construction. The one-piece model uses crinkled tissue on top of the wing for turbulation.
Bud Romak’s Moffett Rubber model features a balsa-and-plywood
saddle to hold the one-piece wing in place.
The saddle is glued down to the rear of the pylon. A nylon screw
clamps the saddle down over the wing at the front.
necessary to allow access to the undersurface
for attaching the ribs. (If I were building a
Jedelsky wing today, I would be tempted to
hot-wire a concave fixture from foam that
followed the upper curvature of the wing.)
Dihedral joints were sanded in, Hand
Launched Glider style, with thickened or
angled ribs to give extra strength. After a final
sanding the wing could be finished with
nonshrinking dope.
The next logical progression in the solidbalsa-
wing saga was to use three or more
sheets of balsa, carefully angled to create the
curvature of the undercambered airfoil. These
wings were surprisingly quick to build and
offered accurate airfoil sections top and
bottom along the span. Unlike the Jedelsky
wings, these needed no exposed ribs for
strength, although chordwise strips of carbon
fiber were sometimes attached to the upper
and lower surfaces to stiffen the wing.
The Germans, who pioneered this type of
construction, had considerable success
beginning with Gerd Erichsen’s 1963 Nordic
Glider win, followed in the 1980s by multiple
Wakefield World Championships wins by
Lothar Doring and Reiner Hofsass. But the
arrival of the much stiffer carbon D-box
construction in the early 1990s put an end to
the solid-balsa wing.
However, old ideas can be combined with
new materials. At last year’s Nats Thurman
Bowls flew an all-plastic Moffett with a
Jedelsky-type wing. Thurman is well-known
for his innovative Rubber models, including
his auto-everything P-30 that was named an
NFFS [National Free Flight Society] Model
of the Year.
Thurman’s new Moffett is a semiscale
cross between a B-24 Liberator bomber and
a troop-carrying glider from the same era. It
features twin rudders, a multiwheel landing
gear, and a tail turret crafted from a Ping-
Pong ball.
But it is the construction, both method
and material, that is most interesting. The
entire model is made from Depron sheet: a
closed-cell polystyrene material used for
insulation under laminated “floating” floor
systems that is similar to the material used
for meat trays.
Depron comes in 2mm, 3mm, and 6mm
thickness; sheets are roughly 15 x 39 inches.
Unlike open-cell foam, Depron has a smooth
surface. Stated density is 40 kilograms per
cubic meter, or approximately 21/2 pounds
per cubic foot.
An interesting feature of Depron is that it
can be heat-formed over a mold. The
temperature required is relatively low—
roughly 194°. Depron can be cut with a
sharp knife. It can also be scored and folded.
For his Jedelsky-style wings, Thurman
uses 2mm Depron, cut to approximately 11/2
times the desired wing chord. Then he scores
the sheet on the underside of the LE line and
folds it back and under to form the thicker
front portion of the wing.
A carved-balsa form is used to help hold
the curvature of the upper surface while the
glue dries. Then the form is slipped out and a
balsa spar is inserted. That’s it!
The model’s fuselage is a simple box of
3mm Depron, edged with 1/8 square balsa. On
models with a square or diamond fuselage
cross-section, Thurman cuts two sheets,
creases each down the middle, and folds 90°.
Then he joins the halves to make the fuselage.
An Internet search for Depron uncovers a
number of mail-order sources. It costs much
less than balsa. For example, a 15 x 39-inch
sheet of 2mm Depron is approximately $2.25.
Some of the dealers sell assortment packs
containing sheets of different thicknesses.
Most have minimum orders of 10 or 12
sheets.
The Internet search also uncovered a lot of
how-to information about working with
Depron for models. It’s a popular material for
small RC electrics and scale models.
Better Than Bands? For most FF models
with one-piece wings, rubber bands are the
traditional way to strap down the wing.
Rubber bands serve as a simple and
inexpensive method of keeping the wing in
place during flight, yet they allow it to pop
safely free in a crash.
However, rubber bands do have a few
drawbacks: they weaken during the day,
especially in hot weather; the rubber can be
adversely affected by model fuels; finding
bands that are just the right length and stretch
for a particular model can be difficult; and
unless properly keyed, wings can shift,
affecting model trim.
Going to a two-piece plug-in wing solves
most of the rubber-band problems and offers
the added advantage of making the
disassembled model more compact. It’s no
wonder why plug-in wings are used almost
exclusively in the three larger FAI classes.
But for smaller models the two-piece wings’
extra weight and more complicated
construction don’t make sense.
Bud Romak developed an interesting
alternative to rubber bands to attach the wing
on his Moffett rubber-powered model. The
model, based on a Carl Redlin design, uses
the usual one-piece wing that sits atop a builtup
balsa pylon. The pylon extends roughly an
inch past the wing at the front and back. An
elliptical-shaped saddle extends over the top
of the wing to hold it in place. The saddle is a
sandwich of 1/64 plywood and 1/32 balsa. The
saddle is glued to the pylon at the rear and is
flexible enough to allow the wing to be
slipped in from the front. A nylon screw
clamps the saddle down at the front, firmly
holding the wing in place. A small piece (1/2 x
1 inch) of double-stick tape helps prevent
shifting.
Bud used a rather beefy 8/32 x 1/2-inch panhead
nylon screw.
“That’s all they had at the hardware
store,” he said.
A smaller nylon screw, such as 2/56 or
4/40, would offer some weight savings and
shear off more easily in a crash. If you do try
a similar system, make sure there is access to
the bottom of the screw to allow for easy
removal if it does shear off.
(In my experience nylon screws break at
or just below the blind nut or threaded
plywood block. Unless you can get to the
other end of the screw, it will be difficult to
remove.)
Small nylon screws in standard and metric
sizes are available from Small Parts, Inc
(www.smallparts.com). MA