Hobo A simple CL model built for fun - 2012/08

Many have told me that they were not ready for a fullbodied
airplane, yet in most cases profi le airplanes
were holding up their progress.
Many of the available profi le kits are simply recreations
of airplanes from the 1950s with thin airfoils and short
moments. This is nostalgic, but does not present an ideal
platform. A twisting, vibrating, fuselage does nothing to help
engine runs or the aerodynamic capabilities of the airplane.
A simple airplane is needed to provide the step up from the
profi les.
Although I thrive on competing in Stunt with the best
equipment available (see Top Hat in the March 2009 Flying
Models, and the Jerseyan in the September 2004 MA), I need
a fun airplane as a relief from the days of hard practice—an
airplane that will address all of the previous criteria.
I realize that most people are not interested in the
demanding practice sessions required for top-level
competition. Even those who might regularly attend
contests and strive to improve their fl ying skills might not be
interested in campaigning at an expert level, so the concept
for the Hobo was born.
In the last 20 or 25 years, there has been little addressed
toward building a full-bodied fun airplane. No airplane has
been designed with the Hobo’s options.
This is a sport airplane, but is that really enough? Visualize
a multipurpose airplane that is capable of performing the
CL Stunt pattern, but offers much more. It doesn’t have to
be pretty. It must have a full fuselage to avoid vibration and
twisting exhibited with profi le layouts. It must be simple for
fast construction.
I wanted an airplane with capabilities that may not have
been addressed in the past: a convertible airplane with a
changeable appearance. I encourage kitbashing!
It must be capable of quick-change control ratios and
The author suggests installing 1/2-ounce weight inside the
outboard wingtip. A blind nut in the plywood rib provides for
bolting on additional external weight. He does not recommend
using stick-on weights.
The center line sweep, allowing for sane and insane maneuvers, from
extremely tight loops to the Sabre Dance. It should be
capable of performing the Stunt pattern or any maneuver
that you can imagine. All of this should be packaged with the
simplicity of a monoplane.
The Hobo can be built with many variables. The controls
can be internal, or can be installed with an old-style external
pushrod that will allow for easy transition of the elevatorto-
fl ap ratio from the standard one-to-one to the excessive
elevator movement that will accommodate those wild, crazy
maneuvers.
The wing sheeting is minimal, simple, fast construction. The
wingtips are fl at, allowing the inboard one to have a simple
slot for the wingtip slider that can be adjusted for Stunt trim,
but can also be moved aft when performing crazy Hobo
maneuvers.
The outboard wingtip has a blind nut installed, allowing
additional external weight to be added. No blocks are used in
the fuselage. The engine is upright and uncowled. The nose
also allows for tank changes and adjustments.
The Hobo is a multipurpose, convertible airplane that does
not require six months or more to build. It is a simple step up
from a profi le, providing a better aerodynamic platform for
Intermediate or Advanced competition or just plane fun.
Fuselage
The top of the fuselage sides have only a short segment
that is parallel to the thrustline. The plans show tabs that are
used so that the fuselage can be assembled upside down. The
tabs are cut off after the basic fuselage sides and formers are
installed.
Most tanks are slightly wider than 2 inches, requiring the
end caps to be squeezed in a vise. The Hobo’s nose is 1/32 inch
wider than the standard 2 inches to allow the fuel tank to
slide in. The F-1 and F-2 plywood formers have tabs that key
into the fuselage, ensuring the engine mounts are properly
aligned.
Use a long straightedge to align the top of the fuselage
building tabs, and then glue the forward and the fuselage sides
together. Next, glue the 1/32-inch plywood doublers in place.
Make sure you make one left-hand and one right-hand part.
Make the engine crutch and trim the balsa spacers to fi t
between plywood formers F1 and F2. Leave at least 1/8 inch
of the engine mounts at the aft end to extend through F2.
The tank shelf (F-3) fi ts into slots in the fuselage. This ensures
proper alignment of the engine mounts. (Note: The engine mounts can be drilled for the engine
before the crutch is installed.)
Install the crutch and plywood F-1
through F-3 onto one fuselage
side. Use a 90º triangle to
make sure that all parts are
perpendicular to the fuselage
side. When the glue has dried,
position the fuselage upside
down on the building tabs and
install the other fuselage side.
Using the notches and tabs, the
parts snap into place. The basic
fuselage can be built in one day.
I recommend using 30-minute or
1-hour epoxy for installing the 1/32
doublers, engine mounts, and all
plywood parts.
When the nose parts are dry, use a
centerline drawn on your table, or
a fuselage jig to align the fuselage
sides, and install the remaining balsa
formers. Do not remove the building
tabs at this time.
Wing
The Hobo’s wing can be assembled in
one evening. Laser-cut ribs are available
from Blue Sky Models. Splice the spars
and TEs as shown on the plans. Mark
the rib locations on the spars and TE.
Place the ribs onto the 1/4-inch spars,
but do not glue them into place. Use a
long straightedge at the rear of the rib
jigging feet to make sure the wing’s TE
will be straight and ensure that the ribs
are vertical and 90º to the spars and TE.
Using thin CA, attach each rib to the
lower TE and the main spars. Use cotton
swabs to wipe away excess glue before it
sets.
Check the alignment and glue the LE
and main 1/4-inch spars in place along
with the lower 3/16-inch center spar and
the top TE sheet.
Use aliphatic glue and masking tape
to install the 1/4-inch TE cap. You can
now turn the wing over and install the
3/32-inch center section sheeting. Don’t
remove the rib jigging feet at this time.
The 1/4-inch spars will be fl ush with
the center section sheeting. I advise
placing light weights over the ribs
during assembly to ensure that the wing
remains straight. Use care installing the
half ribs. They are delicate until glued
into place.
You can choose to use internal or
external controls, which is a unique
feature of the Hobo. The external
controls will allow easy control-ratio
adjustment to achieve competition-type
maneuvers or outlandish fun maneuvers.
The inner center rib must be trimmed
slightly to allow you to install the
bellcrank mount on top of the 1/4-inch
and 3/16-inch lower spars. Install the
upper center section’s 3/16-inch spar and
complete the bellcrank to fl ap controls
and install the upper center section
sheeting.
Install the inboard 1/8-inch light
plywood wingtip rib and slider. Then
install a 4-40 blind nut on the inside
of the outboard 1/8-inch light plywood
wingtip. I suggest permanently installing
approximately 1/2 ounce of weight
inside the outboard wingtip.
Final weight can be added externally
using bolt-on weights that are available
from Sig Manufacturing or Brodak
Manufacturing. Trim and sand the LE
and TE caps to shape and complete the
wing.
Assembly
If you are using external controls,
the fuselage can slide onto the wing.
If you have internal controls you can
place the fuselage upside down on the
building tabs and cut out a section of
the fuselage to install the wing and then
replace the cutout sections.
If you cut the fuselage, make sure that
you install internal 1/32-inch plywood
doublers across the slice. These can be
made from scrap material and should
extend 1 inch at each side of the joint.
I suggest that you make wingtip jigs to
help ensure that the wing is installed
square into the fuselage.
Use either a 1/8-inch wire landing gear
installed with J-bolts or .093 aluminum
gear. The forward fuselage side view
shows this installation. Several suppliers
have landing gear that will work well.
A 1/8-inch plywood plate is made, and
two sets of blind nuts can be installed so the gear can be moved forward for grass applications.
Installing wheel pants is easier with the aluminum gear.
Install a 6-32 blind nut in the plywood pant clip, and use a
jam nut on the inside of the landing gear.
The LEs and TEs of the fl aps, stabilizer, and elevator are
sanded round. Double and triple check alignments while
installing the tail surfaces and then install the tail wheel
mount.
Remove the fuselage building alignment tabs and install the
3/32-inch fuselage top and bottom with the grain going across
the fuselage. The turtledeck (optional) is then installed. The
Bill Hummel’s completed
Hobo. Hummell photo.
Two Hobos framed up. Dave Russum’s (L) has the triangular turtledeck
option shown on the plans. Photo by Bill Lee.
rudder can be cut horizontally above the fuselage to allow any
desired offset.
The Hobo is adaptable or “convertible” so you can make it
look any way you want. Finish your Hobo using your favorite
method.
As an additional caveat, the Hobo’s nose can be easily
modifi ed for electric power. Because motor mountings will
vary, these details are not shown on the drawing.
Flying and Trimming
It is important to start with the CG near the location
shown on the plans. This is approximately 2 inches behind
the LE. Remember, this is only a starting point. If you use
different engines, adjust the CG location using either nose or tail weight. The CG on all airplanes will
vary depending on wood density and
finish.
There are many methods of adding
nose weight. These include the Prathertype
weights installed on the engine
shaft, the Harry Higley aluminum and
brass propeller nuts, tongue- or tubetype
mufflers, or adding weight under
the engine. Adjusting the tail weight can
be as simple as using different size tail
wheels.
The prototype Hobos have been test
beds for several different engines. For
these adjustments, I cut a square section
out of the inboard side of the fuselage
under the elevator. I then installed a
4-40 post bolt on a 1/8-inch plywood
plate on the inside of the outboard
fuselage side. This allows bolt-on
weights to be installed on the 4-40 post
and held in place with a 4-40 locknut. I
reinstalled the square cutout as a hatch
cover held in place with clear packing
tape.
Start with about 1/2 ounce of
additional weight outside the wingtip
and then adjust as required. For novelty
maneuvers, the leadouts should be
farther aft; additional wingtip weight is
generally recommended.
Hobos using Fox .35s or Double Star
.40s generally have the CG range close to
the desired location. Nearly all airplanes
require adjustments in line sweep, wingtip
weight, and forward or aft CG.
Hobos have also been flown with
various line lengths. Engines in the .25
or .35 size might require shorter lines in
the 55-foot range; larger engines might
require longer lines. Handle line spacing is
another trim consideration. If the airplane
is happy, but still slightly sensitive, reduce
the line spacing at the handle.
In Conclusion
I want to thank Bill Hummel, Dave
Russum, and Gerald Schamp for help
with the prototype airplanes and
photographs. Here is Bill’s assessment of
his prototype Hobo:
“I flew eight more flights with the
Hobo on Wednesday—all full patterns.
The ship continues to perform
admirably!
“Using both the Double Star .40
plain bearing and a souped-up Fox 35,
the Hobo performs all the tricks nicely!
[I] also did a little fooling around with
some maneuvers not in the book ... this
little guy has character to spare, and will
do anything you ask of it! Reminds me
of a terrier we once had—no fear, and
all attitude!
“I don’t believe I would change
anything on future versions. It’s a sweet
ship to fly! Thanks again for a really
nice and innovative design, Tom!”

Many have told me that they were not ready for a fullbodied
airplane, yet in most cases profi le airplanes
were holding up their progress.
Many of the available profi le kits are simply recreations
of airplanes from the 1950s with thin airfoils and short
moments. This is nostalgic, but does not present an ideal
platform. A twisting, vibrating, fuselage does nothing to help
engine runs or the aerodynamic capabilities of the airplane.
A simple airplane is needed to provide the step up from the
profi les.
Although I thrive on competing in Stunt with the best
equipment available (see Top Hat in the March 2009 Flying
Models, and the Jerseyan in the September 2004 MA), I need
a fun airplane as a relief from the days of hard practice—an
airplane that will address all of the previous criteria.
I realize that most people are not interested in the
demanding practice sessions required for top-level
competition. Even those who might regularly attend
contests and strive to improve their fl ying skills might not be
interested in campaigning at an expert level, so the concept
for the Hobo was born.
In the last 20 or 25 years, there has been little addressed
toward building a full-bodied fun airplane. No airplane has
been designed with the Hobo’s options.
This is a sport airplane, but is that really enough? Visualize
a multipurpose airplane that is capable of performing the
CL Stunt pattern, but offers much more. It doesn’t have to
be pretty. It must have a full fuselage to avoid vibration and
twisting exhibited with profi le layouts. It must be simple for
fast construction.
I wanted an airplane with capabilities that may not have
been addressed in the past: a convertible airplane with a
changeable appearance. I encourage kitbashing!
It must be capable of quick-change control ratios and
The author suggests installing 1/2-ounce weight inside the
outboard wingtip. A blind nut in the plywood rib provides for
bolting on additional external weight. He does not recommend
using stick-on weights.
The center line sweep, allowing for sane and insane maneuvers, from
extremely tight loops to the Sabre Dance. It should be
capable of performing the Stunt pattern or any maneuver
that you can imagine. All of this should be packaged with the
simplicity of a monoplane.
The Hobo can be built with many variables. The controls
can be internal, or can be installed with an old-style external
pushrod that will allow for easy transition of the elevatorto-
fl ap ratio from the standard one-to-one to the excessive
elevator movement that will accommodate those wild, crazy
maneuvers.
The wing sheeting is minimal, simple, fast construction. The
wingtips are fl at, allowing the inboard one to have a simple
slot for the wingtip slider that can be adjusted for Stunt trim,
but can also be moved aft when performing crazy Hobo
maneuvers.
The outboard wingtip has a blind nut installed, allowing
additional external weight to be added. No blocks are used in
the fuselage. The engine is upright and uncowled. The nose
also allows for tank changes and adjustments.
The Hobo is a multipurpose, convertible airplane that does
not require six months or more to build. It is a simple step up
from a profi le, providing a better aerodynamic platform for
Intermediate or Advanced competition or just plane fun.
Fuselage
The top of the fuselage sides have only a short segment
that is parallel to the thrustline. The plans show tabs that are
used so that the fuselage can be assembled upside down. The
tabs are cut off after the basic fuselage sides and formers are
installed.
Most tanks are slightly wider than 2 inches, requiring the
end caps to be squeezed in a vise. The Hobo’s nose is 1/32 inch
wider than the standard 2 inches to allow the fuel tank to
slide in. The F-1 and F-2 plywood formers have tabs that key
into the fuselage, ensuring the engine mounts are properly
aligned.
Use a long straightedge to align the top of the fuselage
building tabs, and then glue the forward and the fuselage sides
together. Next, glue the 1/32-inch plywood doublers in place.
Make sure you make one left-hand and one right-hand part.
Make the engine crutch and trim the balsa spacers to fi t
between plywood formers F1 and F2. Leave at least 1/8 inch
of the engine mounts at the aft end to extend through F2.
The tank shelf (F-3) fi ts into slots in the fuselage. This ensures
proper alignment of the engine mounts. (Note: The engine mounts can be drilled for the engine
before the crutch is installed.)
Install the crutch and plywood F-1
through F-3 onto one fuselage
side. Use a 90º triangle to
make sure that all parts are
perpendicular to the fuselage
side. When the glue has dried,
position the fuselage upside
down on the building tabs and
install the other fuselage side.
Using the notches and tabs, the
parts snap into place. The basic
fuselage can be built in one day.
I recommend using 30-minute or
1-hour epoxy for installing the 1/32
doublers, engine mounts, and all
plywood parts.
When the nose parts are dry, use a
centerline drawn on your table, or
a fuselage jig to align the fuselage
sides, and install the remaining balsa
formers. Do not remove the building
tabs at this time.
Wing
The Hobo’s wing can be assembled in
one evening. Laser-cut ribs are available
from Blue Sky Models. Splice the spars
and TEs as shown on the plans. Mark
the rib locations on the spars and TE.
Place the ribs onto the 1/4-inch spars,
but do not glue them into place. Use a
long straightedge at the rear of the rib
jigging feet to make sure the wing’s TE
will be straight and ensure that the ribs
are vertical and 90º to the spars and TE.
Using thin CA, attach each rib to the
lower TE and the main spars. Use cotton
swabs to wipe away excess glue before it
sets.
Check the alignment and glue the LE
and main 1/4-inch spars in place along
with the lower 3/16-inch center spar and
the top TE sheet.
Use aliphatic glue and masking tape
to install the 1/4-inch TE cap. You can
now turn the wing over and install the
3/32-inch center section sheeting. Don’t
remove the rib jigging feet at this time.
The 1/4-inch spars will be fl ush with
the center section sheeting. I advise
placing light weights over the ribs
during assembly to ensure that the wing
remains straight. Use care installing the
half ribs. They are delicate until glued
into place.
You can choose to use internal or
external controls, which is a unique
feature of the Hobo. The external
controls will allow easy control-ratio
adjustment to achieve competition-type
maneuvers or outlandish fun maneuvers.
The inner center rib must be trimmed
slightly to allow you to install the
bellcrank mount on top of the 1/4-inch
and 3/16-inch lower spars. Install the
upper center section’s 3/16-inch spar and
complete the bellcrank to fl ap controls
and install the upper center section
sheeting.
Install the inboard 1/8-inch light
plywood wingtip rib and slider. Then
install a 4-40 blind nut on the inside
of the outboard 1/8-inch light plywood
wingtip. I suggest permanently installing
approximately 1/2 ounce of weight
inside the outboard wingtip.
Final weight can be added externally
using bolt-on weights that are available
from Sig Manufacturing or Brodak
Manufacturing. Trim and sand the LE
and TE caps to shape and complete the
wing.
Assembly
If you are using external controls,
the fuselage can slide onto the wing.
If you have internal controls you can
place the fuselage upside down on the
building tabs and cut out a section of
the fuselage to install the wing and then
replace the cutout sections.
If you cut the fuselage, make sure that
you install internal 1/32-inch plywood
doublers across the slice. These can be
made from scrap material and should
extend 1 inch at each side of the joint.
I suggest that you make wingtip jigs to
help ensure that the wing is installed
square into the fuselage.
Use either a 1/8-inch wire landing gear
installed with J-bolts or .093 aluminum
gear. The forward fuselage side view
shows this installation. Several suppliers
have landing gear that will work well.
A 1/8-inch plywood plate is made, and
two sets of blind nuts can be installed so the gear can be moved forward for grass applications.
Installing wheel pants is easier with the aluminum gear.
Install a 6-32 blind nut in the plywood pant clip, and use a
jam nut on the inside of the landing gear.
The LEs and TEs of the fl aps, stabilizer, and elevator are
sanded round. Double and triple check alignments while
installing the tail surfaces and then install the tail wheel
mount.
Remove the fuselage building alignment tabs and install the
3/32-inch fuselage top and bottom with the grain going across
the fuselage. The turtledeck (optional) is then installed. The
Bill Hummel’s completed
Hobo. Hummell photo.
Two Hobos framed up. Dave Russum’s (L) has the triangular turtledeck
option shown on the plans. Photo by Bill Lee.
rudder can be cut horizontally above the fuselage to allow any
desired offset.
The Hobo is adaptable or “convertible” so you can make it
look any way you want. Finish your Hobo using your favorite
method.
As an additional caveat, the Hobo’s nose can be easily
modifi ed for electric power. Because motor mountings will
vary, these details are not shown on the drawing.
Flying and Trimming
It is important to start with the CG near the location
shown on the plans. This is approximately 2 inches behind
the LE. Remember, this is only a starting point. If you use
different engines, adjust the CG location using either nose or tail weight. The CG on all airplanes will
vary depending on wood density and
finish.
There are many methods of adding
nose weight. These include the Prathertype
weights installed on the engine
shaft, the Harry Higley aluminum and
brass propeller nuts, tongue- or tubetype
mufflers, or adding weight under
the engine. Adjusting the tail weight can
be as simple as using different size tail
wheels.
The prototype Hobos have been test
beds for several different engines. For
these adjustments, I cut a square section
out of the inboard side of the fuselage
under the elevator. I then installed a
4-40 post bolt on a 1/8-inch plywood
plate on the inside of the outboard
fuselage side. This allows bolt-on
weights to be installed on the 4-40 post
and held in place with a 4-40 locknut. I
reinstalled the square cutout as a hatch
cover held in place with clear packing
tape.
Start with about 1/2 ounce of
additional weight outside the wingtip
and then adjust as required. For novelty
maneuvers, the leadouts should be
farther aft; additional wingtip weight is
generally recommended.
Hobos using Fox .35s or Double Star
.40s generally have the CG range close to
the desired location. Nearly all airplanes
require adjustments in line sweep, wingtip
weight, and forward or aft CG.
Hobos have also been flown with
various line lengths. Engines in the .25
or .35 size might require shorter lines in
the 55-foot range; larger engines might
require longer lines. Handle line spacing is
another trim consideration. If the airplane
is happy, but still slightly sensitive, reduce
the line spacing at the handle.
In Conclusion
I want to thank Bill Hummel, Dave
Russum, and Gerald Schamp for help
with the prototype airplanes and
photographs. Here is Bill’s assessment of
his prototype Hobo:
“I flew eight more flights with the
Hobo on Wednesday—all full patterns.
The ship continues to perform
admirably!
“Using both the Double Star .40
plain bearing and a souped-up Fox 35,
the Hobo performs all the tricks nicely!
[I] also did a little fooling around with
some maneuvers not in the book ... this
little guy has character to spare, and will
do anything you ask of it! Reminds me
of a terrier we once had—no fear, and
all attitude!
“I don’t believe I would change
anything on future versions. It’s a sweet
ship to fly! Thanks again for a really
nice and innovative design, Tom!”

Many have told me that they were not ready for a fullbodied
airplane, yet in most cases profi le airplanes
were holding up their progress.
Many of the available profi le kits are simply recreations
of airplanes from the 1950s with thin airfoils and short
moments. This is nostalgic, but does not present an ideal
platform. A twisting, vibrating, fuselage does nothing to help
engine runs or the aerodynamic capabilities of the airplane.
A simple airplane is needed to provide the step up from the
profi les.
Although I thrive on competing in Stunt with the best
equipment available (see Top Hat in the March 2009 Flying
Models, and the Jerseyan in the September 2004 MA), I need
a fun airplane as a relief from the days of hard practice—an
airplane that will address all of the previous criteria.
I realize that most people are not interested in the
demanding practice sessions required for top-level
competition. Even those who might regularly attend
contests and strive to improve their fl ying skills might not be
interested in campaigning at an expert level, so the concept
for the Hobo was born.
In the last 20 or 25 years, there has been little addressed
toward building a full-bodied fun airplane. No airplane has
been designed with the Hobo’s options.
This is a sport airplane, but is that really enough? Visualize
a multipurpose airplane that is capable of performing the
CL Stunt pattern, but offers much more. It doesn’t have to
be pretty. It must have a full fuselage to avoid vibration and
twisting exhibited with profi le layouts. It must be simple for
fast construction.
I wanted an airplane with capabilities that may not have
been addressed in the past: a convertible airplane with a
changeable appearance. I encourage kitbashing!
It must be capable of quick-change control ratios and
The author suggests installing 1/2-ounce weight inside the
outboard wingtip. A blind nut in the plywood rib provides for
bolting on additional external weight. He does not recommend
using stick-on weights.
The center line sweep, allowing for sane and insane maneuvers, from
extremely tight loops to the Sabre Dance. It should be
capable of performing the Stunt pattern or any maneuver
that you can imagine. All of this should be packaged with the
simplicity of a monoplane.
The Hobo can be built with many variables. The controls
can be internal, or can be installed with an old-style external
pushrod that will allow for easy transition of the elevatorto-
fl ap ratio from the standard one-to-one to the excessive
elevator movement that will accommodate those wild, crazy
maneuvers.
The wing sheeting is minimal, simple, fast construction. The
wingtips are fl at, allowing the inboard one to have a simple
slot for the wingtip slider that can be adjusted for Stunt trim,
but can also be moved aft when performing crazy Hobo
maneuvers.
The outboard wingtip has a blind nut installed, allowing
additional external weight to be added. No blocks are used in
the fuselage. The engine is upright and uncowled. The nose
also allows for tank changes and adjustments.
The Hobo is a multipurpose, convertible airplane that does
not require six months or more to build. It is a simple step up
from a profi le, providing a better aerodynamic platform for
Intermediate or Advanced competition or just plane fun.
Fuselage
The top of the fuselage sides have only a short segment
that is parallel to the thrustline. The plans show tabs that are
used so that the fuselage can be assembled upside down. The
tabs are cut off after the basic fuselage sides and formers are
installed.
Most tanks are slightly wider than 2 inches, requiring the
end caps to be squeezed in a vise. The Hobo’s nose is 1/32 inch
wider than the standard 2 inches to allow the fuel tank to
slide in. The F-1 and F-2 plywood formers have tabs that key
into the fuselage, ensuring the engine mounts are properly
aligned.
Use a long straightedge to align the top of the fuselage
building tabs, and then glue the forward and the fuselage sides
together. Next, glue the 1/32-inch plywood doublers in place.
Make sure you make one left-hand and one right-hand part.
Make the engine crutch and trim the balsa spacers to fi t
between plywood formers F1 and F2. Leave at least 1/8 inch
of the engine mounts at the aft end to extend through F2.
The tank shelf (F-3) fi ts into slots in the fuselage. This ensures
proper alignment of the engine mounts. (Note: The engine mounts can be drilled for the engine
before the crutch is installed.)
Install the crutch and plywood F-1
through F-3 onto one fuselage
side. Use a 90º triangle to
make sure that all parts are
perpendicular to the fuselage
side. When the glue has dried,
position the fuselage upside
down on the building tabs and
install the other fuselage side.
Using the notches and tabs, the
parts snap into place. The basic
fuselage can be built in one day.
I recommend using 30-minute or
1-hour epoxy for installing the 1/32
doublers, engine mounts, and all
plywood parts.
When the nose parts are dry, use a
centerline drawn on your table, or
a fuselage jig to align the fuselage
sides, and install the remaining balsa
formers. Do not remove the building
tabs at this time.
Wing
The Hobo’s wing can be assembled in
one evening. Laser-cut ribs are available
from Blue Sky Models. Splice the spars
and TEs as shown on the plans. Mark
the rib locations on the spars and TE.
Place the ribs onto the 1/4-inch spars,
but do not glue them into place. Use a
long straightedge at the rear of the rib
jigging feet to make sure the wing’s TE
will be straight and ensure that the ribs
are vertical and 90º to the spars and TE.
Using thin CA, attach each rib to the
lower TE and the main spars. Use cotton
swabs to wipe away excess glue before it
sets.
Check the alignment and glue the LE
and main 1/4-inch spars in place along
with the lower 3/16-inch center spar and
the top TE sheet.
Use aliphatic glue and masking tape
to install the 1/4-inch TE cap. You can
now turn the wing over and install the
3/32-inch center section sheeting. Don’t
remove the rib jigging feet at this time.
The 1/4-inch spars will be fl ush with
the center section sheeting. I advise
placing light weights over the ribs
during assembly to ensure that the wing
remains straight. Use care installing the
half ribs. They are delicate until glued
into place.
You can choose to use internal or
external controls, which is a unique
feature of the Hobo. The external
controls will allow easy control-ratio
adjustment to achieve competition-type
maneuvers or outlandish fun maneuvers.
The inner center rib must be trimmed
slightly to allow you to install the
bellcrank mount on top of the 1/4-inch
and 3/16-inch lower spars. Install the
upper center section’s 3/16-inch spar and
complete the bellcrank to fl ap controls
and install the upper center section
sheeting.
Install the inboard 1/8-inch light
plywood wingtip rib and slider. Then
install a 4-40 blind nut on the inside
of the outboard 1/8-inch light plywood
wingtip. I suggest permanently installing
approximately 1/2 ounce of weight
inside the outboard wingtip.
Final weight can be added externally
using bolt-on weights that are available
from Sig Manufacturing or Brodak
Manufacturing. Trim and sand the LE
and TE caps to shape and complete the
wing.
Assembly
If you are using external controls,
the fuselage can slide onto the wing.
If you have internal controls you can
place the fuselage upside down on the
building tabs and cut out a section of
the fuselage to install the wing and then
replace the cutout sections.
If you cut the fuselage, make sure that
you install internal 1/32-inch plywood
doublers across the slice. These can be
made from scrap material and should
extend 1 inch at each side of the joint.
I suggest that you make wingtip jigs to
help ensure that the wing is installed
square into the fuselage.
Use either a 1/8-inch wire landing gear
installed with J-bolts or .093 aluminum
gear. The forward fuselage side view
shows this installation. Several suppliers
have landing gear that will work well.
A 1/8-inch plywood plate is made, and
two sets of blind nuts can be installed so the gear can be moved forward for grass applications.
Installing wheel pants is easier with the aluminum gear.
Install a 6-32 blind nut in the plywood pant clip, and use a
jam nut on the inside of the landing gear.
The LEs and TEs of the fl aps, stabilizer, and elevator are
sanded round. Double and triple check alignments while
installing the tail surfaces and then install the tail wheel
mount.
Remove the fuselage building alignment tabs and install the
3/32-inch fuselage top and bottom with the grain going across
the fuselage. The turtledeck (optional) is then installed. The
Bill Hummel’s completed
Hobo. Hummell photo.
Two Hobos framed up. Dave Russum’s (L) has the triangular turtledeck
option shown on the plans. Photo by Bill Lee.
rudder can be cut horizontally above the fuselage to allow any
desired offset.
The Hobo is adaptable or “convertible” so you can make it
look any way you want. Finish your Hobo using your favorite
method.
As an additional caveat, the Hobo’s nose can be easily
modifi ed for electric power. Because motor mountings will
vary, these details are not shown on the drawing.
Flying and Trimming
It is important to start with the CG near the location
shown on the plans. This is approximately 2 inches behind
the LE. Remember, this is only a starting point. If you use
different engines, adjust the CG location using either nose or tail weight. The CG on all airplanes will
vary depending on wood density and
finish.
There are many methods of adding
nose weight. These include the Prathertype
weights installed on the engine
shaft, the Harry Higley aluminum and
brass propeller nuts, tongue- or tubetype
mufflers, or adding weight under
the engine. Adjusting the tail weight can
be as simple as using different size tail
wheels.
The prototype Hobos have been test
beds for several different engines. For
these adjustments, I cut a square section
out of the inboard side of the fuselage
under the elevator. I then installed a
4-40 post bolt on a 1/8-inch plywood
plate on the inside of the outboard
fuselage side. This allows bolt-on
weights to be installed on the 4-40 post
and held in place with a 4-40 locknut. I
reinstalled the square cutout as a hatch
cover held in place with clear packing
tape.
Start with about 1/2 ounce of
additional weight outside the wingtip
and then adjust as required. For novelty
maneuvers, the leadouts should be
farther aft; additional wingtip weight is
generally recommended.
Hobos using Fox .35s or Double Star
.40s generally have the CG range close to
the desired location. Nearly all airplanes
require adjustments in line sweep, wingtip
weight, and forward or aft CG.
Hobos have also been flown with
various line lengths. Engines in the .25
or .35 size might require shorter lines in
the 55-foot range; larger engines might
require longer lines. Handle line spacing is
another trim consideration. If the airplane
is happy, but still slightly sensitive, reduce
the line spacing at the handle.
In Conclusion
I want to thank Bill Hummel, Dave
Russum, and Gerald Schamp for help
with the prototype airplanes and
photographs. Here is Bill’s assessment of
his prototype Hobo:
“I flew eight more flights with the
Hobo on Wednesday—all full patterns.
The ship continues to perform
admirably!
“Using both the Double Star .40
plain bearing and a souped-up Fox 35,
the Hobo performs all the tricks nicely!
[I] also did a little fooling around with
some maneuvers not in the book ... this
little guy has character to spare, and will
do anything you ask of it! Reminds me
of a terrier we once had—no fear, and
all attitude!
“I don’t believe I would change
anything on future versions. It’s a sweet
ship to fly! Thanks again for a really
nice and innovative design, Tom!”