The Easy - 2008/09

28 MODEL AVIATION
by Dick Sarpolus
Frank Ehling’s 1949 CL Stunter
Easy
The
I WAS LEARNING how to fly inverted
50-some years ago, and it wasn’t going very
well. I needed another airplane. A local
older modeler had given me a stack of Air
Trails magazines, and in the April 1949
issue I found plans for Frank Ehling’s Easy.
I crudely scaled up the plans from the pagesize
drawings and scratch-built my version.
That model is basically a 50-inchwingspan
profile, and to help with my
inverted flying, I added a single-strut wire
landing gear with a wheel, on the top side of
the fuselage. With the help of, I believe, a
front-rotary O&R engine, and later a Forster
or OK, and finally a Fox, I did learn to fly
inverted.
Wanting recently to do some more CL
flying, I got a copy of that April 1949 Air
Trails article from the Precision Aerobatics
Model Pilots Association (PAMPA). I have
always remembered the
Easy as a good-flying
airplane, and with nostalgia
as another motive I decided
to build a new one roughly 50
years after my first one.
I constructed the new model
according to the original design, but I used
some modern materials and technologies.
I’ve flown it and I like it.
Even though it’s more
than 50 years old,
this design shows
the proven good
proportions of a
basic CL Precision
Aerobatics
model.
September 2008 29
I did get to know Frank Ehling a bit
through the years, later when he worked for
the AMA, and I think he was way ahead of
his time with this CL design. At that time,
CL flying itself was fairly new and the glow
plug had just come out in 1947. Inverted
flying had only been around for a couple
years, and flaps for Precision Aerobatics
models (Stunters) were about to be
introduced.
CL Stunt wasn’t in its “golden years”
yet. But Ehling’s Easy had plenty of wing
area, was light, and the proportions seem
right to me. He designed the model because
he wanted to make 24 CL Stunt models for
Christmas gifts in December 1948. Wow,
he was some gift giver.
Air Trails’ three-page article didn’t have
much text; the building instructions were
mainly in the photo captions. The page-size
plans in the magazine were accompanied by
a chart containing the specific dimensions
for seven—yes, seven—different sizes to
which the design could be built. This was to
accommodate engine sizes ranging from a
miniature CO2 to a .65; the wingspans
ranged from 12.5 to 50 inches. I built the
largest version.
That wing has slightly more than 500
square inches, which I thought would be
good for modern .35 power. I wanted to lay
out accurate plans, and working from the
magazine plans was interesting.
The easy thing to do
would have been to enlarge
the page-size drawing to
the size I wanted, but it
was noted that the
drawing was not done to
scale and the chart should be used for the
dimensions. That revealed some
inconsistencies.
Adding the individual component
lengths for the fuselage resulted in an
overall length of 30.25 inches. However, the
chart’s fuselage length was 32 inches.
The airfoil in the drawing looked fine.
But the photo captions indicated that the
airfoil thickness was determined by the
wing center block, which was determined
by the engine-mount bearers, and the wing
LE was 1.25 inches thick. Working with
those factors wasn’t going to provide a
reasonable airfoil section.
In the end, I worked with the enlarged
drawing and the chart dimensions to
develop what I think is an accurate
reproduction of Ehling’s large Easy. I
assume that my plans, and anyone else’s
from the article, would be legal for PAMPA
Old Time Stunt (OTS) competition.
CONSTRUCTION
When I built my Easy in the early 1950s,
everybody was putting the bellcrank inside
the wing, with holes in the ribs for the
leadouts. Ehling’s plans called for mounting
the bellcrank on the bottom of the fuselage,
with the leadouts supported by a guide
below the inboard wingtip.
Since the PAMPA OTS rules allow
modification to the control-mechanism
location, I assume that this modification is
legal. Not that I cared about rules; I was
building this thing for my own fun-flying.
A structural modification I made was to
incorporate two spars in the wing. It didn’t
change any outside dimensions, and I felt
that the spars were needed for sufficient
strength in an airplane such as this. Wingtips
are shaped from balsa blocks; it’s good to
make wood chips and sawdust.
The assembly instructions called for
building the wing with a center wood block
and then adding the fuselage pieces around
that block and the wing. Not that it wouldn’t
work that way, but I built the fuselage as a
separate assembly with a hole in it through
which to slide the wing.
I used 3/8 x 1/2 maple engine mounts,
spaced to suit the power plant being used,
with 1/8 plywood nose-section doublers, as in
typical profile construction. But then I added
1/4 balsa on each side over
the plywood to keep the
same outer fuselage
dimensions as the
original Easy had.
I kept the landing-
Adoring classics—
such as the author’s
custom ’57 Chevy
and the 1949 Easy—
go hand in hand.
30 MODEL AVIATION
Left: The engine is a modern Thunder Tiger
.36 Pro that has had the timing changed to
suit CL Stunt flying and is fitted with a
custom, lightweight tube-type muffler.
Below: The engine sits on a molded nylon
shim plate for a few degrees of out thrust. The
fuel tank is held in place with rubber bands.
The Easy is legal for PAMPA Old Time
Stunt competition. Its flight performance
with a modern engine is superior to
traditional options.
Photos by the author
The Easy features traditional profile construction, a simple wing structure, and sheetbalsa
tail surfaces. The wire landing gear, lightweight foam wheels, and subrudder has
the model sitting at a good angle on the ground. This Easy is finished with a butyratepainted
fuselage and tail surfaces and transparent MonoKote on the wings.
gear location in the same place as on the
original plans, but I have it removable in
two pieces from the fuselage rather than
building the gear into the wing. I figured I’d
be removing the gear legs to straighten them
after some poor landings.
I had to shape the LE and TE balsa, but
nobody said that would be easy. I used a
standard 3-inch bellcrank and flexible
leadouts and a 3/32-inch wire pushrod with
one support off the fuselage side. I did
install an adjustable leadout guide as a nod
to modern technology.
I used sheet balsa for the tail surfaces, as
was done on the original. I don’t know if
Frank Ehling used rudder offset, but I put in
1/4 inch of offset with the rear upper rudder
section.
Back in the day I used a lot of colored
silk and clear dope to finish wings, with
painted fuselage and tail surfaces. This time
around, I finished the fuselage and tail
surfaces with butyrate dope, but I went for
transparent Top Flite MonoKote on the
wings; it reminds me of the old clear-dope
finishes.
I opted to use lightweight foam wheels. I
had a stock of fuel tanks and used a profile
type, which is held in place with rubber
bands and J hooks, as in the old days.
Flying: I made the first few flights on this
new Easy with an old .35 I had on hand. I
omitted the muffler, for nostalgia I guess,
but after noticing the engine shake, I figured
Below: The 3/32-inch-diameter wire
pushrod running from the bellcrank to the
control horn is supported with a fuselage
brace made from a nylon control horn.
Easy Specs
Type: CL Old Time Stunt
Designer: Frank Ehling
Origin: April 1949 Air Trails magazine
Skill level: Beginner builder/pilot
Wingspan: 50 inches
Wing area: 530 square inches
Weight: 44 ounces
Wing loading: 12 ounces/square foot
Length: 34 inches
Engine: Thunder Tiger .36 Pro (modified for Stunt)
Propeller: Pro Zinger 11 x 5
Construction: Balsa
Covering/finish: Aircraft dope, heat-shrink film
September 2008 31
that engine technology must have
progressed in the past 50 years. I like
nostalgia and tradition, but not enough to
fly with an old engine when better power
plants are available.
For some modern power, I obtained a
Thunder Tiger .36 Pro engine and a custom
CL venturi, needle valve, and lightweight
tube muffler from Stuka Stunt Works. The
Thunder Tiger power plant fit exactly into
the old .35 mounting holes.
I can understand that today’s
Schnuerle-ported engines with ball
bearings and better materials are designed
to suit RC, and changing the port timing,
compression ratio, venturi, etc. would
result in a better engine for CL Stunt. I was
lucky to have a knowledgeable engine guy
do the rework. Tom Hampshire, a New
Jersey modeling friend, helped me a great
deal by retiming the Thunder Tiger to suit
CL use. Why not fly with a modern, CLsuitable
engine?
The reworked .36 happily turns an 11 x
4 propeller and delivers its power precisely
the way we need it to for CL aerobatic
flying. And I quickly learned that it’s a
pleasure to fly this neat, old model with an
up-to-date engine.
Years ago I flew with a Hot Rock E-ZJust
large handle, but I guess my reflexes
aren’t what they used to be. To smooth
things out, I put a longer control horn on
the elevator and got an adjustable handle,
set to 31/4-inch line spacing. I’m using 62-
foot lines—much better for me. It felt great to have that handle in my
hand. Although my patterns are probably
only recognizable to me, practice may help.
I even looked at my old Mirror Meet flight
pattern but put that scary one away for now.
This stuff is fun.
If you would like a copy of the old Air
Trails article about Frank Ehling’s Easy,
ask me; I’ll send one to you. MA
Dick Sarpolus
[email protected]
Sources:
PAMPA
15107 SE 145th Pl.
Renton WA 98059
www.control-line.org
MonoKote
(800) 637-7660
www.monokote.com
Stuka Stunt Works
(317) 497-1487
www.clstunt.com

28 MODEL AVIATION
by Dick Sarpolus
Frank Ehling’s 1949 CL Stunter
Easy
The
I WAS LEARNING how to fly inverted
50-some years ago, and it wasn’t going very
well. I needed another airplane. A local
older modeler had given me a stack of Air
Trails magazines, and in the April 1949
issue I found plans for Frank Ehling’s Easy.
I crudely scaled up the plans from the pagesize
drawings and scratch-built my version.
That model is basically a 50-inchwingspan
profile, and to help with my
inverted flying, I added a single-strut wire
landing gear with a wheel, on the top side of
the fuselage. With the help of, I believe, a
front-rotary O&R engine, and later a Forster
or OK, and finally a Fox, I did learn to fly
inverted.
Wanting recently to do some more CL
flying, I got a copy of that April 1949 Air
Trails article from the Precision Aerobatics
Model Pilots Association (PAMPA). I have
always remembered the
Easy as a good-flying
airplane, and with nostalgia
as another motive I decided
to build a new one roughly 50
years after my first one.
I constructed the new model
according to the original design, but I used
some modern materials and technologies.
I’ve flown it and I like it.
Even though it’s more
than 50 years old,
this design shows
the proven good
proportions of a
basic CL Precision
Aerobatics
model.
September 2008 29
I did get to know Frank Ehling a bit
through the years, later when he worked for
the AMA, and I think he was way ahead of
his time with this CL design. At that time,
CL flying itself was fairly new and the glow
plug had just come out in 1947. Inverted
flying had only been around for a couple
years, and flaps for Precision Aerobatics
models (Stunters) were about to be
introduced.
CL Stunt wasn’t in its “golden years”
yet. But Ehling’s Easy had plenty of wing
area, was light, and the proportions seem
right to me. He designed the model because
he wanted to make 24 CL Stunt models for
Christmas gifts in December 1948. Wow,
he was some gift giver.
Air Trails’ three-page article didn’t have
much text; the building instructions were
mainly in the photo captions. The page-size
plans in the magazine were accompanied by
a chart containing the specific dimensions
for seven—yes, seven—different sizes to
which the design could be built. This was to
accommodate engine sizes ranging from a
miniature CO2 to a .65; the wingspans
ranged from 12.5 to 50 inches. I built the
largest version.
That wing has slightly more than 500
square inches, which I thought would be
good for modern .35 power. I wanted to lay
out accurate plans, and working from the
magazine plans was interesting.
The easy thing to do
would have been to enlarge
the page-size drawing to
the size I wanted, but it
was noted that the
drawing was not done to
scale and the chart should be used for the
dimensions. That revealed some
inconsistencies.
Adding the individual component
lengths for the fuselage resulted in an
overall length of 30.25 inches. However, the
chart’s fuselage length was 32 inches.
The airfoil in the drawing looked fine.
But the photo captions indicated that the
airfoil thickness was determined by the
wing center block, which was determined
by the engine-mount bearers, and the wing
LE was 1.25 inches thick. Working with
those factors wasn’t going to provide a
reasonable airfoil section.
In the end, I worked with the enlarged
drawing and the chart dimensions to
develop what I think is an accurate
reproduction of Ehling’s large Easy. I
assume that my plans, and anyone else’s
from the article, would be legal for PAMPA
Old Time Stunt (OTS) competition.
CONSTRUCTION
When I built my Easy in the early 1950s,
everybody was putting the bellcrank inside
the wing, with holes in the ribs for the
leadouts. Ehling’s plans called for mounting
the bellcrank on the bottom of the fuselage,
with the leadouts supported by a guide
below the inboard wingtip.
Since the PAMPA OTS rules allow
modification to the control-mechanism
location, I assume that this modification is
legal. Not that I cared about rules; I was
building this thing for my own fun-flying.
A structural modification I made was to
incorporate two spars in the wing. It didn’t
change any outside dimensions, and I felt
that the spars were needed for sufficient
strength in an airplane such as this. Wingtips
are shaped from balsa blocks; it’s good to
make wood chips and sawdust.
The assembly instructions called for
building the wing with a center wood block
and then adding the fuselage pieces around
that block and the wing. Not that it wouldn’t
work that way, but I built the fuselage as a
separate assembly with a hole in it through
which to slide the wing.
I used 3/8 x 1/2 maple engine mounts,
spaced to suit the power plant being used,
with 1/8 plywood nose-section doublers, as in
typical profile construction. But then I added
1/4 balsa on each side over
the plywood to keep the
same outer fuselage
dimensions as the
original Easy had.
I kept the landing-
Adoring classics—
such as the author’s
custom ’57 Chevy
and the 1949 Easy—
go hand in hand.
30 MODEL AVIATION
Left: The engine is a modern Thunder Tiger
.36 Pro that has had the timing changed to
suit CL Stunt flying and is fitted with a
custom, lightweight tube-type muffler.
Below: The engine sits on a molded nylon
shim plate for a few degrees of out thrust. The
fuel tank is held in place with rubber bands.
The Easy is legal for PAMPA Old Time
Stunt competition. Its flight performance
with a modern engine is superior to
traditional options.
Photos by the author
The Easy features traditional profile construction, a simple wing structure, and sheetbalsa
tail surfaces. The wire landing gear, lightweight foam wheels, and subrudder has
the model sitting at a good angle on the ground. This Easy is finished with a butyratepainted
fuselage and tail surfaces and transparent MonoKote on the wings.
gear location in the same place as on the
original plans, but I have it removable in
two pieces from the fuselage rather than
building the gear into the wing. I figured I’d
be removing the gear legs to straighten them
after some poor landings.
I had to shape the LE and TE balsa, but
nobody said that would be easy. I used a
standard 3-inch bellcrank and flexible
leadouts and a 3/32-inch wire pushrod with
one support off the fuselage side. I did
install an adjustable leadout guide as a nod
to modern technology.
I used sheet balsa for the tail surfaces, as
was done on the original. I don’t know if
Frank Ehling used rudder offset, but I put in
1/4 inch of offset with the rear upper rudder
section.
Back in the day I used a lot of colored
silk and clear dope to finish wings, with
painted fuselage and tail surfaces. This time
around, I finished the fuselage and tail
surfaces with butyrate dope, but I went for
transparent Top Flite MonoKote on the
wings; it reminds me of the old clear-dope
finishes.
I opted to use lightweight foam wheels. I
had a stock of fuel tanks and used a profile
type, which is held in place with rubber
bands and J hooks, as in the old days.
Flying: I made the first few flights on this
new Easy with an old .35 I had on hand. I
omitted the muffler, for nostalgia I guess,
but after noticing the engine shake, I figured
Below: The 3/32-inch-diameter wire
pushrod running from the bellcrank to the
control horn is supported with a fuselage
brace made from a nylon control horn.
Easy Specs
Type: CL Old Time Stunt
Designer: Frank Ehling
Origin: April 1949 Air Trails magazine
Skill level: Beginner builder/pilot
Wingspan: 50 inches
Wing area: 530 square inches
Weight: 44 ounces
Wing loading: 12 ounces/square foot
Length: 34 inches
Engine: Thunder Tiger .36 Pro (modified for Stunt)
Propeller: Pro Zinger 11 x 5
Construction: Balsa
Covering/finish: Aircraft dope, heat-shrink film
September 2008 31
that engine technology must have
progressed in the past 50 years. I like
nostalgia and tradition, but not enough to
fly with an old engine when better power
plants are available.
For some modern power, I obtained a
Thunder Tiger .36 Pro engine and a custom
CL venturi, needle valve, and lightweight
tube muffler from Stuka Stunt Works. The
Thunder Tiger power plant fit exactly into
the old .35 mounting holes.
I can understand that today’s
Schnuerle-ported engines with ball
bearings and better materials are designed
to suit RC, and changing the port timing,
compression ratio, venturi, etc. would
result in a better engine for CL Stunt. I was
lucky to have a knowledgeable engine guy
do the rework. Tom Hampshire, a New
Jersey modeling friend, helped me a great
deal by retiming the Thunder Tiger to suit
CL use. Why not fly with a modern, CLsuitable
engine?
The reworked .36 happily turns an 11 x
4 propeller and delivers its power precisely
the way we need it to for CL aerobatic
flying. And I quickly learned that it’s a
pleasure to fly this neat, old model with an
up-to-date engine.
Years ago I flew with a Hot Rock E-ZJust
large handle, but I guess my reflexes
aren’t what they used to be. To smooth
things out, I put a longer control horn on
the elevator and got an adjustable handle,
set to 31/4-inch line spacing. I’m using 62-
foot lines—much better for me. It felt great to have that handle in my
hand. Although my patterns are probably
only recognizable to me, practice may help.
I even looked at my old Mirror Meet flight
pattern but put that scary one away for now.
This stuff is fun.
If you would like a copy of the old Air
Trails article about Frank Ehling’s Easy,
ask me; I’ll send one to you. MA
Dick Sarpolus
[email protected]
Sources:
PAMPA
15107 SE 145th Pl.
Renton WA 98059
www.control-line.org
MonoKote
(800) 637-7660
www.monokote.com
Stuka Stunt Works
(317) 497-1487
www.clstunt.com