Plane Talk: Balsa USA 1/3 Scale Ercoupe on Floats-2007/04

The Balsa USA Ercoupe on 1/3-
scale Sea Commander EDO
floats is beckoned by the waters
of Lake Perris.
I ENJOY RC float-flying, so most of my models wind up on floats.
I recently completed a Balsa USA 1/3 Scale Ercoupe on floats, and
according to Balsa USA it was the first of these aircraft to
successfully fly off the water. In this article I will give an overview
of the Balsa USA kit, but I will concentrate more on the adaptation
of the model to floats.
I had never seen an Ercoupe on floats. My research revealed that
the first was the EDO/ERCO prototype, NX86951, in 1946 on the
East Coast.
It passed the CAA (now FAA) tests, but the government pilot
asked for more familiarization time. He flipped the airplane on a
crosswind takeoff or landing (per an ex-EDO employee). The floats
appear to have been standard EDO 1320 “flat-top” models, as were
used on the Piper J-3 Cub and other light aircraft of the period with
similar sizes and weights.
According to Fred Weick, one of the chief designers, the rudder
pedals were required for crosswind landings and takeoffs with floats.
The original Ercoupes were set up for optional rudder pedals, but
very few people ordered them that way so they eliminated the
hardware needed for that option in the post-war production models.
Hence the floatplane Ercoupe was no longer viable.
The second Ercoupe on floats, NX87060, was a private venture
by Howard E. Cousins in 1952 near Chicago, Illinois. Todd
Westfall’s dad Dale was the CAA pilot.
The limited elevator travel had to be increased to allow the
Three nose-wheel steering arms
are coupled to link the pull-pull
water-rudder control.
Left: The aluminum
water rudders use
standard Du-Bro nosegear
hardware. Hard
points in the fiberglass
Sea Commander floats
are installed at the
factory.
Right: The distinctive
twin tails, out of the
propeller blast, reduce
the tendency to turn
left during
a climb.
The twin
rudders may
be coupled to the
ailerons as on the fullscale
Ercoupe.
Photos by the author
Above: The big
Zenoah G-62 fits
neatly into the
Ercoupe’s huge
fiberglass cowling.
The extra power is
beneficial when
carrying the floats’
extra weight.
Above: Construction of the Balsa USA
Ercoupe’s wings closely matches that of
the full-scale version.
Right: The fuselage is built in halves—the
upper part first and then the bottom is
assembled onto the upper frame.
The large-displacement, 64-inch Sea
Commander floats with twin water
rudders provide superior water handling.
airplane to get on the step. This made it no longer spin-proof, so they
had to do spin tests. In one of those the aileron on one wing
developed flutter and the wing failed.
The airplane crashed and Todd’s dad got out just in time (per
Todd, a newspaper account, and the pilot’s log book). Therefore, no
certification was forthcoming and no more float-equipped Ercoupes
were built.
As on the full-scale Ercoupe on floats, the struts on my model
form three triangular trusses connecting the floats to the three
tricycle landing-gear hard points on the Ercoupe.
When I built my Balsa USA Ercoupe, there were no kits, plans,
or ready-made EDO 1320 flat-top floats available in 1/3 scale. All
available 1/3-scale floats, including Balsa USA’s and Sea
Commander’s, were the later round-top EDO 2000 style. Therefore,
I used the Sea Commander 64-inch EDO 2000-style round-top
fiberglass floats on my model.
I tried to get the look of the full-scale prototype using the Sea
Commander hardware and special adapter brackets I designed and
fabricated. These brackets attach the six struts to the tricycle
landing-gear hard points on the Balsa USA model. I used two water
rudders on the model, for positive water handling, driven by cables
from the nose-gear servo.
The Balsa USA Ercoupe: I had not built a big model for
approximately 10 years; the last was a Stream Schneider Sport 320
floatplane racer with a SuperTigre 3000 engine. Flying ARFs and
airplanes that others built was typically my lazy practice in the
hobby.
When Balsa USA came out with the 1/3 Scale Ercoupe kit, it
touched a nerve. There was a project that was challenging enough to
get my juices flowing.
It looked like a good candidate for the Kavan FK50 four-stroke
twin engine I was flying in a ModelTech ARF Cub at the time. The
models’ 2,400 square inches of wing area and 31-pound weight on
pinked-tape placement, and so on. I omitted several of the details
shown and/or furnished with the kit, such as the gas gauges, rivets,
pinked tape, and decals, but I did build a scale instrument panel
based on Ercoupe N87405.
I did not use the simple early-Ercoupe panel furnished with the
kit. It was fun hunting the surplus electronics stores looking for all
the tiny switches, lights, and circuit breakers. I used JTEC 1/3-scale
instruments.
I upholstered the interior with adhesive-backed fabrics I
obtained in local plastics and auto-supply stores. The full-body pilot
came from H.P. Pilots. He was too tall for the cockpit, so I had to
cut approximately an inch out of his midriff. He weighed a whole
pound, so I took him out for the initial test flights.
Model Float Installation: My strut design is based on the
prototype Ercoupe floatplane and utilizes the three tricycle landinggear-
attachment hard points, as does the full-scale version. The
struts, spreader bars, and floats form three rigid triangular trusses
and make for a sturdy float mounting system. The model’s scale
bolt-on wheel landing gear made it relatively easy to design suitable
adapter brackets to be attached in its place.
Sea Commander furnished the floats along with the material and
fasteners to make the spreader bars and struts. I designed and
fabricated the adapter brackets, water rudders, and X bracing from
material I obtained locally.
The 64-inch Sea Commander EDO 2000 floats are high-quality
fiberglass/polyester moldings. The spreader bar saddles are molded
in, and there are several internal bulkheads that separate the floats
wheels were almost identical, and the Cub was flying nicely at 40
pounds on floats.
The huge Balsa USA Ercoupe kit is not for the faint of heart,
either financially or in terms of building time and skill. The kit,
with tax and shipping, will set you back roughly $1,000.
The kit came in three packages: a conventional big kit full of
lumber, a big box with the giant fiberglass cowl and other goodies,
and a big mailing tube containing rolled thin plywood and the seven
monstrous sheets of plans. Small parts were nicely and logically
packaged in clear plastic bags with labels.
The 73-page manual had many photos. The fiberglass cowling
was impressive. It was big, light, and flexible, and all the difficult
trimming was done. It had molded-in fastener heads and panel lines.
The entire fuselage top half was built on a table. Then it was
inverted in a fixture for completion of the bottom half.
The scale operating tricycle landing gear was assembled from
massive aluminum castings and pieces of steel. I had to do quite a
bit of filing, drilling, and silver-soldering, but the necessary
precision holes and mating surfaces were already drilled and
machined. The finished landing gear, with the supplied air wheels,
weighed 4 pounds.
Wing and tail construction were conventional, except for the
scale diagonal wing ribs and complex laminated wingtips. The
removable outer wings were quite stiff and light.
Scale Detailing: My “coupe” was built as a Sport Scale model, not
meant for Expert-class competition. A separate big three-view sheet
was thoughtfully supplied in the kit, and it showed rivet location,
Stainless-steel 4-40 hardware was used throughout. The nose-strut
attachment bracket and steering servo will be hidden by the cowl.
Mounting brackets in the wing were fashioned from aluminum Tstock
and fitted into the existing main gear locations.
Sea Commander struts and hardware, with special adapter
brackets, connect the floats rigidly to the landing-gear hard points.
The Sea Commander EDO 2000 floats are supplied with fiberglass
dress covers to hide the hard points of the float.
within the strut to get the desired exact
overall end hole to end hole length of the
strut assembly, and then I match-drilled it
and fastened it. The struts were made in
left and right pairs of equal length.
I used standard 4-40 hardware to fasten
the struts to the airplane and to the floats,
with elastic stop nuts on all bolts in the
float assembly and Loctite on the main
gear adapter bracket bolts.
Finishing: The four fiberglass covers that
Sea Commander furnished were fastened
over the spreader bar saddles using #2 selftapping
screws. These covers had to be
individually trimmed and fitted to each
saddle.
From that point I disassembled
everything and painted the floats. I used
Stits Poly-Tone (Rancho Silver) with F&M
Enterprises’ Feather Coat primer. The
paint provides a scale-looking satin finish,
but a gloss top coat is available for those
who like it shinier. The paint is prethinned
for spraying, and it contains retarders,
flexibilizers, and a self-extinguishing fire
retardant.
I used the same brand of paint on the
rest of the model. Stits has a special dope
into watertight compartments. A special
small bow compartment is provided for
balancing weights.
The struts and spreader bars are
streamlined 6061-T6 structural aluminum
tubing. This is not your typical soft
aluminum hobby-shop material. These
components are bigger and much stronger.
The float assembly weighs a hefty 9
pounds, but the husky Ercoupe landing
gear it replaces weighs 4 pounds. Thus we
gained only 5 pounds adding the floats, for
a 36-pound total weight. With 2,400
square inches of wing area, the wing
loading came out a reasonable 35 ounces
per square foot. The Ercoupe’s flight
characteristics resemble those of my
ModelTech ARF Cub.
Spreader Bars: The two teardrop
aluminum-tubing spreader bars were
mounted with the float centerlines 32
inches apart. I match-drilled and installed
the furnished aluminum filler bar and three
self-tapping screws at the end of each
spreader bar after I made sure the floats
were parallel and the assembly was square.
After initial assembly I disassembled
the spreader bars and hardened the screw
holes in the floats with thin cyanoacrylate
glue, and then I reassembled the floats and
spreader bars. I trimmed the ends of the
spreader bars to clear the covers to be
installed later.
Adapter Brackets: The three adapter
brackets for the model landing-gear
attachment points were made from
aluminum T section for the wing maingear
attachment point and aluminum angle
for the nose-gear attachment point. The
bolt-hole pattern in the adapters matched
the hole pattern in the wheel landing-gear
legs. I mounted the brackets onto the
model using 4-40 hardware—the same as I
used for the wheel landing gear I was
replacing.
I made four lower float-attachment
brackets from aluminum angle. I mounted
the brackets onto the spreader bars with
self-tapping screws. The forward brackets
were a bit tricky since they comprised
attach points for the nose-gear struts and
the forward main-gear struts.
Struts: I made a simple fixture to hold the
floats and the airplane in the correct
relative position so the strut lengths could
be determined. The float steps were located
at the airplane’s CG, and the flat bottom of
the wing should be parallel to the top of the
floats so the wing maintains a positive
incidence angle to the water surface.
I machined the strut end fittings from
the furnished aluminum bar. I used a band
saw and file to make the slots, a drill press
to drill the end holes, and a belt sander to
round the ends.
I match-drilled the struts and end
fittings for one end of each strut and
installed the furnished hardware to fasten
them together. I slid the other end fitting
The gentle flight characteristics of the
1/3-scale Ercoupe on floats resemble
those of a like-size Piper Cub on floats.
52 MODEL AVIATION
• Molded-in fiberglass joiner lip and side
stiffener
• Molded-in fiberglass bottom
reinforcements
• Four fiberglass-reinforced bulkheads
• Five watertight compartments
• Composite reinforcements in scale
mounting positions
• Composite reinforced transom for
water rudder mounting
• Available in sizes from 29 to 65 inches
• Floats pressure-checked for leaks
• Ready-to-paint and -install fittings
• Float kit used: 1/3 scale (64 inches)
• Price: $385.28 (floats only)
EDO 2000 Float Specifications
Engine used: Zenoah G-45 (on wheels),
G-62 (on floats)
Propeller: Master Airscrew 20 x 8
(on wheels), APC 22 x 10 (on floats)
Fuel: 24-ounce plastic (furnished)
Radio system: Futaba 9VAP transmitter
with nine-channel PCM receiver, six
Hitec RCD HS-645MG servos, two
1500 mAh Cermark 6-volt NiMH
battery packs, eight Cermark 12-inch
servo extensions
Finish: Stits Poly-Tone paint
Ready-to-fly weight: 31 pounds,
36 pounds with floats
Flight duration: Exceeds 15 minutes
Test-Model Details
Model type: Giant Scale kit
Pilot skill level: Sport/Scale fliers
who are experienced builders
Wingspan: 120 inches
Wing area: 2,400 square inches
Length: 84 inches
Weight: 28-32 pounds
Wing loading: 30 ounces/square
foot (as built)
Engine: 45-55cc two-stroke gas
or 3.0-3.5 cu. in. glow
Radio: Four-channel radio (minimum),
six servos
Construction: Conventional balsa/
plywood/basswood with fiberglass
cowling
Covering/finish: Fabric on wings,
thin fiberglass (furnished) on fuselage
and tail
Price: $899.95
Ercoupe Specifications
+
• Beautiful, good-flying scale airplane.
• Complete kit.
• Excellent construction manual.
• Scale functional landing gear.
• Scale sliding cockpit windows. -• Complex fuselage construction.
• Balsa quality issues.
• Errors in manual but no errata sheet.
Pluses and Minuses
formula (used instead of primer) that
chemically bonds to the polyester wingcovering
fabric.
Water Rudders: I cut the rudders from
.030-inch aluminum and silver-soldered
the .030 brass hinge brackets to the 5/32-
inch music-wire shafts. Standard hobbyshop
nose-gear nylon bearings and steering
arms completed the installation. The water
rudders were manually retractable and
were adjusted to kick up if they hit an
obstacle.
The Ercoupe nose-gear-steering servo
was used to steer the water rudders. I
modified a nylon steering arm to form a
April 2007 53
During the 1920s and 1930s many
private pilots were injured, killed, or scared
off by the terrible ground handling, landing
and takeoff characteristics, and poor stallspin
performance of the day’s tail-dragger
lightplanes. Ground loops during landing
were common, and the gentle stall and spin
performance of “baby carriages” such as
the Cessna 172 were unknown.
A group of engineers, including the
great Fred Weick, comprised the
Engineering Research Company, or
ERCO, which was to address these
problems. The Ercoupe Model 415C was
the result.
With performance similar to today’s
Cessna 150, the Ercoupe could not spin
and it was so certified by the CAA. The
Ercoupe was so easy to fly that a special
pilot’s-license category was assigned to it,
requiring a minimum of five hours solo
and 35 hours total flight time, as opposed
to eight hours solo and 40 hours total flight
time for conventional lightplanes at that
time.
The Ercoupe is a two-seat, low-wing
monoplane with twin vertical tail surfaces
and a tricycle landing gear. The pilot and
passenger sit in a glassed-in cockpit with
excellent all-around visibility.
Construction is modern all metal,
except for the fabric covering on the wings.
The skin-stressed (monocoque) design has
no wing or tail struts. Engines range from
65 to 90 horsepower.
The rugged Ercoupe tricycle landing
gear is configured so that the airplane can
be landed in a crab in a crosswind, and its
geometry causes the aircraft to
immediately straighten out on the runway
upon touchdown. Thus no ground looping
and easy ground handling.
With the nose wheel linked to the
pilot’s yoke, one drives it like a car. A
carlike single brake pedal controls both
main wheel brakes simultaneously.
The Ercoupe’s stall-spin resistance is
achieved through several design features.
The wing has generous dihedral, and the
ailerons and rudders are coupled so there
are no rudder pedals. Thus one cannot
cross controls in a standard Ercoupe. Turns
are coordinated, with no way to slip or
skid. Stall resistance is aided by limiting
the elevator travel.
More than 5,000 Ercoupes were built,
mostly after WW II, and an excess of
2,000 remain registered today. Several
other companies followed ERCO in
building the Ercoupe, and a number of
changes were instituted in the design,
including a sliding canopy, single tail,
rudder pedals, and larger engines. Some
of these modifications resulted in more
conventional stall-spin behavior.
The unique color scheme and
instrument panel I used on my model are
those of N87405. It was owned by Tom
Laird-McConnell in the Seattle-Tacoma
area in Washington but was sold to
Harold Gochenouer in Lake Havasu City,
Arizona.
I was “Googling” my way through
cyberspace looking for a nice color scheme
for my Ercoupe when I happened upon
Tom’s Web site: www.ercoupers.com. It
has photos of many Ercoupes that are
currently flying. When I saw Tom’s
N87405, I fell in love.
Tom was extremely generous with
photos of his airplane, and I got to see it
at Lake Havasu City Airport after the big
annual Desert Hawks float fly. I modified
the usual wing-LE location of the landing
lights so they match the type mounted on
the main landing-gear fairings of Tom’s
aircraft. His photos were extraordinarily
helpful in duplicating the interior.
Man Behind the Ercoupe: I just finished
reading the autobiography of Fred Weick
entitled From the Ground Up (from
Smithsonian Institution Press, 1988).
This lesser-known but outstanding
aeronautical engineer was born in 1899
and was building and flying model
airplanes before World War I. He was
one of the first graduate engineers to
apply a rigorous engineering and
scientific approach to airplane design and
testing.
Fred worked for NACA and the
Airmail Service, Texas A&M, ERCO,
and Piper. He invented the modern
tricycle landing gear and did pioneering
research into safer aircraft-control
systems. He also led the team that
developed the NACA low-drag cowling
for radial engines.
Fred wrote a paper about simplified
propeller design for light aircraft, and it is
still the “bible” for home builders. He
was very active in EAA. Fred was
responsible for the design of the Ercoupe,
Piper Cherokee series, and the Ag-1,
which set the standard for modern, safer
agricultural-application aircraft (crop
dusters) such as the Piper Pawnee.
Fred’s other contributions to aircraft
efficiency and safety and his many honors
and awards are too numerous to list here.
For a summary of his career visit http://
en.wikipedia.org/wiki/Fred_Weick. MA
—Oscar Weingart
SCOOP
“COUPE”
ON THE
Oscar Weingart’s 1/3-scale Ercoupe with full-scale N87405 at Lake Havasu City
Airport. The landing lights on the model’s main landing-gear fairings were
specially made.
The model’s instrument panel is
based on N87405, with JTEC
instruments and commonly
available surplus subminiature
switches and buttons.
Length: 20 feet, 9 inches
Wingspan: 30 feet
Wing area: 142.6 square feet
Weight: 1,440 pounds (max.)
Wing loading: 10.1 pounds/
square foot
Engine: Continental C-85
Full-Scale Ercoupe Specifications
bearing and bolted it to the nose-gear
adapter bracket. A vertical music-wire
shaft was fitted with three more of these
steering arms: one for the connection to
the servo and the other two to form a tiller
bar. Cables connected this tiller bar to the
steering arms on the water rudders.
Balancing: I drilled a 1-inch-diameter
hole into the top of each float to gain
access to the bow ballast compartment. I
balanced the assembled floatplane by
installing lead weights in modeling clay in
the ballast compartments and filled the
remaining space with polyurethane soft
foam.
Scale-looking soft aluminum covers
were made for the holes and held in place
with small self-tapping screws. The edges
of the covers were coated with clear
silicone sealer.
Transportation: The 1/3-scale Balsa USA
Ercoupe has detachable outer wing panels,
which make for easy transportation. If you
have a large-enough vehicle, the Ercoupe
floats can remain attached to the model.
With our standard-length Ford Aerostar
minivan, the float assembly had to be
removed and loaded separately.
Control Setup and Programming: The
water rudders were permanently linked to
the air rudder stick in my Futaba 9VAP
transmitter using the programmable mix
function. The channel used has a knob on
the face of the transmitter, which allows
the water rudders to be trimmed
independently from the air rudders. Hitec
RCD HS-645MG high-torque, metal-gear
servos were used throughout.
The full-scale Ercoupe had no rudder
pedals. The ailerons, rudders, and nose
wheel were linked together to the pilot’s
control wheel.
A switch-selectable mix was
programmed for the model. The ailerons
and air rudders move together with the
aileron stick, but the rudder stick can still
override the coupled rudder movement. I
used the coupled aileron-air rudder mode
in flight, but I found that I preferred the
uncoupled mode for landing and takeoff.
Taxiing and Flying: The Ercoupe “turns
on a dime” with two large water rudders. I
hold full up-elevator when taxiing on
water; this keeps the water rudders well
under the surface for positive control. The
heavy, low-wing Ercoupe is not affected
much by crosswinds, but appropriate
seaplane sailing and taxiing techniques,
such as holding aileron against the wind,
can be used in stiff crosswinds.
Takeoffs and landings are the fun part
of flying RC seaplanes. The Ercoupe
initially porpoised during takeoff, but a
more powerful engine cured this condition.
Standard seaplane takeoff and landing
techniques work well on the model.
The Balsa USA 1/3 Scale Ercoupe
equipped with Sea Commander EDO 2000
64-inch floats makes a unique, attentiongrabbing
seaplane that looks great and flies
beautifully.
Many thanks are due Dave Lewis at
Balsa USA, Ryan Holm at Sea
Commander, and Chip Mull at F&M
Enterprises for their help in getting the
information and materials needed to build
the Ercoupe on floats. Tom Laird-
McConnell furnished many fine detail
photos of N87405, as well as the photos of
the prototype Ercoupe floatplane.
The full-scale airplane’s background
and history were obtained via the Google
search engine, using the key word
“Ercoupe,” and from several discussion
forums on the RC Universe Web site at
www.rcuniverse.com.
Don Lien of the Riverside RC Club
(RRCC) was a great partner in painting,
fabric covering, and cockpit-glass
installation. Initial test pilots were Dale
Yaney of RRCC and Dan Egelhoff of
Team Airtronics. They were followed by
Dave Collis of Vancouver, British
Columbia, for the test flights at Lake
Shuswap, where the Ercoupe won the
“Best on the Beach—Scale” award. MA
Oscar Weingart
[email protected]
Aircraft Kit Manufacturer:
Balsa USA
Box 164
Marinette WI 54143
(906) 863-6421
www.balsausa.com
Float Manufacturer:
Sea Commander
4768 Harvie Ave.
Powell River, BC, Canada
V8A 2P5
(877) 485-2926
www.seacommander.com
Items Used in Review:
Zenoah G-62 engine
www.horizonhobby.com
Miscellaneous hardware
www.dubro.com
Stits Poly-Tone paint
www.stits.com
1/3-scale instruments
www.jtecrc.com
1/3-scale full-body pilot
www.hppilots.com
Resources:
Ercoupers Web site
www.ercoupers.com

The Balsa USA Ercoupe on 1/3-
scale Sea Commander EDO
floats is beckoned by the waters
of Lake Perris.
I ENJOY RC float-flying, so most of my models wind up on floats.
I recently completed a Balsa USA 1/3 Scale Ercoupe on floats, and
according to Balsa USA it was the first of these aircraft to
successfully fly off the water. In this article I will give an overview
of the Balsa USA kit, but I will concentrate more on the adaptation
of the model to floats.
I had never seen an Ercoupe on floats. My research revealed that
the first was the EDO/ERCO prototype, NX86951, in 1946 on the
East Coast.
It passed the CAA (now FAA) tests, but the government pilot
asked for more familiarization time. He flipped the airplane on a
crosswind takeoff or landing (per an ex-EDO employee). The floats
appear to have been standard EDO 1320 “flat-top” models, as were
used on the Piper J-3 Cub and other light aircraft of the period with
similar sizes and weights.
According to Fred Weick, one of the chief designers, the rudder
pedals were required for crosswind landings and takeoffs with floats.
The original Ercoupes were set up for optional rudder pedals, but
very few people ordered them that way so they eliminated the
hardware needed for that option in the post-war production models.
Hence the floatplane Ercoupe was no longer viable.
The second Ercoupe on floats, NX87060, was a private venture
by Howard E. Cousins in 1952 near Chicago, Illinois. Todd
Westfall’s dad Dale was the CAA pilot.
The limited elevator travel had to be increased to allow the
Three nose-wheel steering arms
are coupled to link the pull-pull
water-rudder control.
Left: The aluminum
water rudders use
standard Du-Bro nosegear
hardware. Hard
points in the fiberglass
Sea Commander floats
are installed at the
factory.
Right: The distinctive
twin tails, out of the
propeller blast, reduce
the tendency to turn
left during
a climb.
The twin
rudders may
be coupled to the
ailerons as on the fullscale
Ercoupe.
Photos by the author
Above: The big
Zenoah G-62 fits
neatly into the
Ercoupe’s huge
fiberglass cowling.
The extra power is
beneficial when
carrying the floats’
extra weight.
Above: Construction of the Balsa USA
Ercoupe’s wings closely matches that of
the full-scale version.
Right: The fuselage is built in halves—the
upper part first and then the bottom is
assembled onto the upper frame.
The large-displacement, 64-inch Sea
Commander floats with twin water
rudders provide superior water handling.
airplane to get on the step. This made it no longer spin-proof, so they
had to do spin tests. In one of those the aileron on one wing
developed flutter and the wing failed.
The airplane crashed and Todd’s dad got out just in time (per
Todd, a newspaper account, and the pilot’s log book). Therefore, no
certification was forthcoming and no more float-equipped Ercoupes
were built.
As on the full-scale Ercoupe on floats, the struts on my model
form three triangular trusses connecting the floats to the three
tricycle landing-gear hard points on the Ercoupe.
When I built my Balsa USA Ercoupe, there were no kits, plans,
or ready-made EDO 1320 flat-top floats available in 1/3 scale. All
available 1/3-scale floats, including Balsa USA’s and Sea
Commander’s, were the later round-top EDO 2000 style. Therefore,
I used the Sea Commander 64-inch EDO 2000-style round-top
fiberglass floats on my model.
I tried to get the look of the full-scale prototype using the Sea
Commander hardware and special adapter brackets I designed and
fabricated. These brackets attach the six struts to the tricycle
landing-gear hard points on the Balsa USA model. I used two water
rudders on the model, for positive water handling, driven by cables
from the nose-gear servo.
The Balsa USA Ercoupe: I had not built a big model for
approximately 10 years; the last was a Stream Schneider Sport 320
floatplane racer with a SuperTigre 3000 engine. Flying ARFs and
airplanes that others built was typically my lazy practice in the
hobby.
When Balsa USA came out with the 1/3 Scale Ercoupe kit, it
touched a nerve. There was a project that was challenging enough to
get my juices flowing.
It looked like a good candidate for the Kavan FK50 four-stroke
twin engine I was flying in a ModelTech ARF Cub at the time. The
models’ 2,400 square inches of wing area and 31-pound weight on
pinked-tape placement, and so on. I omitted several of the details
shown and/or furnished with the kit, such as the gas gauges, rivets,
pinked tape, and decals, but I did build a scale instrument panel
based on Ercoupe N87405.
I did not use the simple early-Ercoupe panel furnished with the
kit. It was fun hunting the surplus electronics stores looking for all
the tiny switches, lights, and circuit breakers. I used JTEC 1/3-scale
instruments.
I upholstered the interior with adhesive-backed fabrics I
obtained in local plastics and auto-supply stores. The full-body pilot
came from H.P. Pilots. He was too tall for the cockpit, so I had to
cut approximately an inch out of his midriff. He weighed a whole
pound, so I took him out for the initial test flights.
Model Float Installation: My strut design is based on the
prototype Ercoupe floatplane and utilizes the three tricycle landinggear-
attachment hard points, as does the full-scale version. The
struts, spreader bars, and floats form three rigid triangular trusses
and make for a sturdy float mounting system. The model’s scale
bolt-on wheel landing gear made it relatively easy to design suitable
adapter brackets to be attached in its place.
Sea Commander furnished the floats along with the material and
fasteners to make the spreader bars and struts. I designed and
fabricated the adapter brackets, water rudders, and X bracing from
material I obtained locally.
The 64-inch Sea Commander EDO 2000 floats are high-quality
fiberglass/polyester moldings. The spreader bar saddles are molded
in, and there are several internal bulkheads that separate the floats
wheels were almost identical, and the Cub was flying nicely at 40
pounds on floats.
The huge Balsa USA Ercoupe kit is not for the faint of heart,
either financially or in terms of building time and skill. The kit,
with tax and shipping, will set you back roughly $1,000.
The kit came in three packages: a conventional big kit full of
lumber, a big box with the giant fiberglass cowl and other goodies,
and a big mailing tube containing rolled thin plywood and the seven
monstrous sheets of plans. Small parts were nicely and logically
packaged in clear plastic bags with labels.
The 73-page manual had many photos. The fiberglass cowling
was impressive. It was big, light, and flexible, and all the difficult
trimming was done. It had molded-in fastener heads and panel lines.
The entire fuselage top half was built on a table. Then it was
inverted in a fixture for completion of the bottom half.
The scale operating tricycle landing gear was assembled from
massive aluminum castings and pieces of steel. I had to do quite a
bit of filing, drilling, and silver-soldering, but the necessary
precision holes and mating surfaces were already drilled and
machined. The finished landing gear, with the supplied air wheels,
weighed 4 pounds.
Wing and tail construction were conventional, except for the
scale diagonal wing ribs and complex laminated wingtips. The
removable outer wings were quite stiff and light.
Scale Detailing: My “coupe” was built as a Sport Scale model, not
meant for Expert-class competition. A separate big three-view sheet
was thoughtfully supplied in the kit, and it showed rivet location,
Stainless-steel 4-40 hardware was used throughout. The nose-strut
attachment bracket and steering servo will be hidden by the cowl.
Mounting brackets in the wing were fashioned from aluminum Tstock
and fitted into the existing main gear locations.
Sea Commander struts and hardware, with special adapter
brackets, connect the floats rigidly to the landing-gear hard points.
The Sea Commander EDO 2000 floats are supplied with fiberglass
dress covers to hide the hard points of the float.
within the strut to get the desired exact
overall end hole to end hole length of the
strut assembly, and then I match-drilled it
and fastened it. The struts were made in
left and right pairs of equal length.
I used standard 4-40 hardware to fasten
the struts to the airplane and to the floats,
with elastic stop nuts on all bolts in the
float assembly and Loctite on the main
gear adapter bracket bolts.
Finishing: The four fiberglass covers that
Sea Commander furnished were fastened
over the spreader bar saddles using #2 selftapping
screws. These covers had to be
individually trimmed and fitted to each
saddle.
From that point I disassembled
everything and painted the floats. I used
Stits Poly-Tone (Rancho Silver) with F&M
Enterprises’ Feather Coat primer. The
paint provides a scale-looking satin finish,
but a gloss top coat is available for those
who like it shinier. The paint is prethinned
for spraying, and it contains retarders,
flexibilizers, and a self-extinguishing fire
retardant.
I used the same brand of paint on the
rest of the model. Stits has a special dope
into watertight compartments. A special
small bow compartment is provided for
balancing weights.
The struts and spreader bars are
streamlined 6061-T6 structural aluminum
tubing. This is not your typical soft
aluminum hobby-shop material. These
components are bigger and much stronger.
The float assembly weighs a hefty 9
pounds, but the husky Ercoupe landing
gear it replaces weighs 4 pounds. Thus we
gained only 5 pounds adding the floats, for
a 36-pound total weight. With 2,400
square inches of wing area, the wing
loading came out a reasonable 35 ounces
per square foot. The Ercoupe’s flight
characteristics resemble those of my
ModelTech ARF Cub.
Spreader Bars: The two teardrop
aluminum-tubing spreader bars were
mounted with the float centerlines 32
inches apart. I match-drilled and installed
the furnished aluminum filler bar and three
self-tapping screws at the end of each
spreader bar after I made sure the floats
were parallel and the assembly was square.
After initial assembly I disassembled
the spreader bars and hardened the screw
holes in the floats with thin cyanoacrylate
glue, and then I reassembled the floats and
spreader bars. I trimmed the ends of the
spreader bars to clear the covers to be
installed later.
Adapter Brackets: The three adapter
brackets for the model landing-gear
attachment points were made from
aluminum T section for the wing maingear
attachment point and aluminum angle
for the nose-gear attachment point. The
bolt-hole pattern in the adapters matched
the hole pattern in the wheel landing-gear
legs. I mounted the brackets onto the
model using 4-40 hardware—the same as I
used for the wheel landing gear I was
replacing.
I made four lower float-attachment
brackets from aluminum angle. I mounted
the brackets onto the spreader bars with
self-tapping screws. The forward brackets
were a bit tricky since they comprised
attach points for the nose-gear struts and
the forward main-gear struts.
Struts: I made a simple fixture to hold the
floats and the airplane in the correct
relative position so the strut lengths could
be determined. The float steps were located
at the airplane’s CG, and the flat bottom of
the wing should be parallel to the top of the
floats so the wing maintains a positive
incidence angle to the water surface.
I machined the strut end fittings from
the furnished aluminum bar. I used a band
saw and file to make the slots, a drill press
to drill the end holes, and a belt sander to
round the ends.
I match-drilled the struts and end
fittings for one end of each strut and
installed the furnished hardware to fasten
them together. I slid the other end fitting
The gentle flight characteristics of the
1/3-scale Ercoupe on floats resemble
those of a like-size Piper Cub on floats.
52 MODEL AVIATION
• Molded-in fiberglass joiner lip and side
stiffener
• Molded-in fiberglass bottom
reinforcements
• Four fiberglass-reinforced bulkheads
• Five watertight compartments
• Composite reinforcements in scale
mounting positions
• Composite reinforced transom for
water rudder mounting
• Available in sizes from 29 to 65 inches
• Floats pressure-checked for leaks
• Ready-to-paint and -install fittings
• Float kit used: 1/3 scale (64 inches)
• Price: $385.28 (floats only)
EDO 2000 Float Specifications
Engine used: Zenoah G-45 (on wheels),
G-62 (on floats)
Propeller: Master Airscrew 20 x 8
(on wheels), APC 22 x 10 (on floats)
Fuel: 24-ounce plastic (furnished)
Radio system: Futaba 9VAP transmitter
with nine-channel PCM receiver, six
Hitec RCD HS-645MG servos, two
1500 mAh Cermark 6-volt NiMH
battery packs, eight Cermark 12-inch
servo extensions
Finish: Stits Poly-Tone paint
Ready-to-fly weight: 31 pounds,
36 pounds with floats
Flight duration: Exceeds 15 minutes
Test-Model Details
Model type: Giant Scale kit
Pilot skill level: Sport/Scale fliers
who are experienced builders
Wingspan: 120 inches
Wing area: 2,400 square inches
Length: 84 inches
Weight: 28-32 pounds
Wing loading: 30 ounces/square
foot (as built)
Engine: 45-55cc two-stroke gas
or 3.0-3.5 cu. in. glow
Radio: Four-channel radio (minimum),
six servos
Construction: Conventional balsa/
plywood/basswood with fiberglass
cowling
Covering/finish: Fabric on wings,
thin fiberglass (furnished) on fuselage
and tail
Price: $899.95
Ercoupe Specifications
+
• Beautiful, good-flying scale airplane.
• Complete kit.
• Excellent construction manual.
• Scale functional landing gear.
• Scale sliding cockpit windows. -• Complex fuselage construction.
• Balsa quality issues.
• Errors in manual but no errata sheet.
Pluses and Minuses
formula (used instead of primer) that
chemically bonds to the polyester wingcovering
fabric.
Water Rudders: I cut the rudders from
.030-inch aluminum and silver-soldered
the .030 brass hinge brackets to the 5/32-
inch music-wire shafts. Standard hobbyshop
nose-gear nylon bearings and steering
arms completed the installation. The water
rudders were manually retractable and
were adjusted to kick up if they hit an
obstacle.
The Ercoupe nose-gear-steering servo
was used to steer the water rudders. I
modified a nylon steering arm to form a
April 2007 53
During the 1920s and 1930s many
private pilots were injured, killed, or scared
off by the terrible ground handling, landing
and takeoff characteristics, and poor stallspin
performance of the day’s tail-dragger
lightplanes. Ground loops during landing
were common, and the gentle stall and spin
performance of “baby carriages” such as
the Cessna 172 were unknown.
A group of engineers, including the
great Fred Weick, comprised the
Engineering Research Company, or
ERCO, which was to address these
problems. The Ercoupe Model 415C was
the result.
With performance similar to today’s
Cessna 150, the Ercoupe could not spin
and it was so certified by the CAA. The
Ercoupe was so easy to fly that a special
pilot’s-license category was assigned to it,
requiring a minimum of five hours solo
and 35 hours total flight time, as opposed
to eight hours solo and 40 hours total flight
time for conventional lightplanes at that
time.
The Ercoupe is a two-seat, low-wing
monoplane with twin vertical tail surfaces
and a tricycle landing gear. The pilot and
passenger sit in a glassed-in cockpit with
excellent all-around visibility.
Construction is modern all metal,
except for the fabric covering on the wings.
The skin-stressed (monocoque) design has
no wing or tail struts. Engines range from
65 to 90 horsepower.
The rugged Ercoupe tricycle landing
gear is configured so that the airplane can
be landed in a crab in a crosswind, and its
geometry causes the aircraft to
immediately straighten out on the runway
upon touchdown. Thus no ground looping
and easy ground handling.
With the nose wheel linked to the
pilot’s yoke, one drives it like a car. A
carlike single brake pedal controls both
main wheel brakes simultaneously.
The Ercoupe’s stall-spin resistance is
achieved through several design features.
The wing has generous dihedral, and the
ailerons and rudders are coupled so there
are no rudder pedals. Thus one cannot
cross controls in a standard Ercoupe. Turns
are coordinated, with no way to slip or
skid. Stall resistance is aided by limiting
the elevator travel.
More than 5,000 Ercoupes were built,
mostly after WW II, and an excess of
2,000 remain registered today. Several
other companies followed ERCO in
building the Ercoupe, and a number of
changes were instituted in the design,
including a sliding canopy, single tail,
rudder pedals, and larger engines. Some
of these modifications resulted in more
conventional stall-spin behavior.
The unique color scheme and
instrument panel I used on my model are
those of N87405. It was owned by Tom
Laird-McConnell in the Seattle-Tacoma
area in Washington but was sold to
Harold Gochenouer in Lake Havasu City,
Arizona.
I was “Googling” my way through
cyberspace looking for a nice color scheme
for my Ercoupe when I happened upon
Tom’s Web site: www.ercoupers.com. It
has photos of many Ercoupes that are
currently flying. When I saw Tom’s
N87405, I fell in love.
Tom was extremely generous with
photos of his airplane, and I got to see it
at Lake Havasu City Airport after the big
annual Desert Hawks float fly. I modified
the usual wing-LE location of the landing
lights so they match the type mounted on
the main landing-gear fairings of Tom’s
aircraft. His photos were extraordinarily
helpful in duplicating the interior.
Man Behind the Ercoupe: I just finished
reading the autobiography of Fred Weick
entitled From the Ground Up (from
Smithsonian Institution Press, 1988).
This lesser-known but outstanding
aeronautical engineer was born in 1899
and was building and flying model
airplanes before World War I. He was
one of the first graduate engineers to
apply a rigorous engineering and
scientific approach to airplane design and
testing.
Fred worked for NACA and the
Airmail Service, Texas A&M, ERCO,
and Piper. He invented the modern
tricycle landing gear and did pioneering
research into safer aircraft-control
systems. He also led the team that
developed the NACA low-drag cowling
for radial engines.
Fred wrote a paper about simplified
propeller design for light aircraft, and it is
still the “bible” for home builders. He
was very active in EAA. Fred was
responsible for the design of the Ercoupe,
Piper Cherokee series, and the Ag-1,
which set the standard for modern, safer
agricultural-application aircraft (crop
dusters) such as the Piper Pawnee.
Fred’s other contributions to aircraft
efficiency and safety and his many honors
and awards are too numerous to list here.
For a summary of his career visit http://
en.wikipedia.org/wiki/Fred_Weick. MA
—Oscar Weingart
SCOOP
“COUPE”
ON THE
Oscar Weingart’s 1/3-scale Ercoupe with full-scale N87405 at Lake Havasu City
Airport. The landing lights on the model’s main landing-gear fairings were
specially made.
The model’s instrument panel is
based on N87405, with JTEC
instruments and commonly
available surplus subminiature
switches and buttons.
Length: 20 feet, 9 inches
Wingspan: 30 feet
Wing area: 142.6 square feet
Weight: 1,440 pounds (max.)
Wing loading: 10.1 pounds/
square foot
Engine: Continental C-85
Full-Scale Ercoupe Specifications
bearing and bolted it to the nose-gear
adapter bracket. A vertical music-wire
shaft was fitted with three more of these
steering arms: one for the connection to
the servo and the other two to form a tiller
bar. Cables connected this tiller bar to the
steering arms on the water rudders.
Balancing: I drilled a 1-inch-diameter
hole into the top of each float to gain
access to the bow ballast compartment. I
balanced the assembled floatplane by
installing lead weights in modeling clay in
the ballast compartments and filled the
remaining space with polyurethane soft
foam.
Scale-looking soft aluminum covers
were made for the holes and held in place
with small self-tapping screws. The edges
of the covers were coated with clear
silicone sealer.
Transportation: The 1/3-scale Balsa USA
Ercoupe has detachable outer wing panels,
which make for easy transportation. If you
have a large-enough vehicle, the Ercoupe
floats can remain attached to the model.
With our standard-length Ford Aerostar
minivan, the float assembly had to be
removed and loaded separately.
Control Setup and Programming: The
water rudders were permanently linked to
the air rudder stick in my Futaba 9VAP
transmitter using the programmable mix
function. The channel used has a knob on
the face of the transmitter, which allows
the water rudders to be trimmed
independently from the air rudders. Hitec
RCD HS-645MG high-torque, metal-gear
servos were used throughout.
The full-scale Ercoupe had no rudder
pedals. The ailerons, rudders, and nose
wheel were linked together to the pilot’s
control wheel.
A switch-selectable mix was
programmed for the model. The ailerons
and air rudders move together with the
aileron stick, but the rudder stick can still
override the coupled rudder movement. I
used the coupled aileron-air rudder mode
in flight, but I found that I preferred the
uncoupled mode for landing and takeoff.
Taxiing and Flying: The Ercoupe “turns
on a dime” with two large water rudders. I
hold full up-elevator when taxiing on
water; this keeps the water rudders well
under the surface for positive control. The
heavy, low-wing Ercoupe is not affected
much by crosswinds, but appropriate
seaplane sailing and taxiing techniques,
such as holding aileron against the wind,
can be used in stiff crosswinds.
Takeoffs and landings are the fun part
of flying RC seaplanes. The Ercoupe
initially porpoised during takeoff, but a
more powerful engine cured this condition.
Standard seaplane takeoff and landing
techniques work well on the model.
The Balsa USA 1/3 Scale Ercoupe
equipped with Sea Commander EDO 2000
64-inch floats makes a unique, attentiongrabbing
seaplane that looks great and flies
beautifully.
Many thanks are due Dave Lewis at
Balsa USA, Ryan Holm at Sea
Commander, and Chip Mull at F&M
Enterprises for their help in getting the
information and materials needed to build
the Ercoupe on floats. Tom Laird-
McConnell furnished many fine detail
photos of N87405, as well as the photos of
the prototype Ercoupe floatplane.
The full-scale airplane’s background
and history were obtained via the Google
search engine, using the key word
“Ercoupe,” and from several discussion
forums on the RC Universe Web site at
www.rcuniverse.com.
Don Lien of the Riverside RC Club
(RRCC) was a great partner in painting,
fabric covering, and cockpit-glass
installation. Initial test pilots were Dale
Yaney of RRCC and Dan Egelhoff of
Team Airtronics. They were followed by
Dave Collis of Vancouver, British
Columbia, for the test flights at Lake
Shuswap, where the Ercoupe won the
“Best on the Beach—Scale” award. MA
Oscar Weingart
[email protected]
Aircraft Kit Manufacturer:
Balsa USA
Box 164
Marinette WI 54143
(906) 863-6421
www.balsausa.com
Float Manufacturer:
Sea Commander
4768 Harvie Ave.
Powell River, BC, Canada
V8A 2P5
(877) 485-2926
www.seacommander.com
Items Used in Review:
Zenoah G-62 engine
www.horizonhobby.com
Miscellaneous hardware
www.dubro.com
Stits Poly-Tone paint
www.stits.com
1/3-scale instruments
www.jtecrc.com
1/3-scale full-body pilot
www.hppilots.com
Resources:
Ercoupers Web site
www.ercoupers.com

The Balsa USA Ercoupe on 1/3-
scale Sea Commander EDO
floats is beckoned by the waters
of Lake Perris.
I ENJOY RC float-flying, so most of my models wind up on floats.
I recently completed a Balsa USA 1/3 Scale Ercoupe on floats, and
according to Balsa USA it was the first of these aircraft to
successfully fly off the water. In this article I will give an overview
of the Balsa USA kit, but I will concentrate more on the adaptation
of the model to floats.
I had never seen an Ercoupe on floats. My research revealed that
the first was the EDO/ERCO prototype, NX86951, in 1946 on the
East Coast.
It passed the CAA (now FAA) tests, but the government pilot
asked for more familiarization time. He flipped the airplane on a
crosswind takeoff or landing (per an ex-EDO employee). The floats
appear to have been standard EDO 1320 “flat-top” models, as were
used on the Piper J-3 Cub and other light aircraft of the period with
similar sizes and weights.
According to Fred Weick, one of the chief designers, the rudder
pedals were required for crosswind landings and takeoffs with floats.
The original Ercoupes were set up for optional rudder pedals, but
very few people ordered them that way so they eliminated the
hardware needed for that option in the post-war production models.
Hence the floatplane Ercoupe was no longer viable.
The second Ercoupe on floats, NX87060, was a private venture
by Howard E. Cousins in 1952 near Chicago, Illinois. Todd
Westfall’s dad Dale was the CAA pilot.
The limited elevator travel had to be increased to allow the
Three nose-wheel steering arms
are coupled to link the pull-pull
water-rudder control.
Left: The aluminum
water rudders use
standard Du-Bro nosegear
hardware. Hard
points in the fiberglass
Sea Commander floats
are installed at the
factory.
Right: The distinctive
twin tails, out of the
propeller blast, reduce
the tendency to turn
left during
a climb.
The twin
rudders may
be coupled to the
ailerons as on the fullscale
Ercoupe.
Photos by the author
Above: The big
Zenoah G-62 fits
neatly into the
Ercoupe’s huge
fiberglass cowling.
The extra power is
beneficial when
carrying the floats’
extra weight.
Above: Construction of the Balsa USA
Ercoupe’s wings closely matches that of
the full-scale version.
Right: The fuselage is built in halves—the
upper part first and then the bottom is
assembled onto the upper frame.
The large-displacement, 64-inch Sea
Commander floats with twin water
rudders provide superior water handling.
airplane to get on the step. This made it no longer spin-proof, so they
had to do spin tests. In one of those the aileron on one wing
developed flutter and the wing failed.
The airplane crashed and Todd’s dad got out just in time (per
Todd, a newspaper account, and the pilot’s log book). Therefore, no
certification was forthcoming and no more float-equipped Ercoupes
were built.
As on the full-scale Ercoupe on floats, the struts on my model
form three triangular trusses connecting the floats to the three
tricycle landing-gear hard points on the Ercoupe.
When I built my Balsa USA Ercoupe, there were no kits, plans,
or ready-made EDO 1320 flat-top floats available in 1/3 scale. All
available 1/3-scale floats, including Balsa USA’s and Sea
Commander’s, were the later round-top EDO 2000 style. Therefore,
I used the Sea Commander 64-inch EDO 2000-style round-top
fiberglass floats on my model.
I tried to get the look of the full-scale prototype using the Sea
Commander hardware and special adapter brackets I designed and
fabricated. These brackets attach the six struts to the tricycle
landing-gear hard points on the Balsa USA model. I used two water
rudders on the model, for positive water handling, driven by cables
from the nose-gear servo.
The Balsa USA Ercoupe: I had not built a big model for
approximately 10 years; the last was a Stream Schneider Sport 320
floatplane racer with a SuperTigre 3000 engine. Flying ARFs and
airplanes that others built was typically my lazy practice in the
hobby.
When Balsa USA came out with the 1/3 Scale Ercoupe kit, it
touched a nerve. There was a project that was challenging enough to
get my juices flowing.
It looked like a good candidate for the Kavan FK50 four-stroke
twin engine I was flying in a ModelTech ARF Cub at the time. The
models’ 2,400 square inches of wing area and 31-pound weight on
pinked-tape placement, and so on. I omitted several of the details
shown and/or furnished with the kit, such as the gas gauges, rivets,
pinked tape, and decals, but I did build a scale instrument panel
based on Ercoupe N87405.
I did not use the simple early-Ercoupe panel furnished with the
kit. It was fun hunting the surplus electronics stores looking for all
the tiny switches, lights, and circuit breakers. I used JTEC 1/3-scale
instruments.
I upholstered the interior with adhesive-backed fabrics I
obtained in local plastics and auto-supply stores. The full-body pilot
came from H.P. Pilots. He was too tall for the cockpit, so I had to
cut approximately an inch out of his midriff. He weighed a whole
pound, so I took him out for the initial test flights.
Model Float Installation: My strut design is based on the
prototype Ercoupe floatplane and utilizes the three tricycle landinggear-
attachment hard points, as does the full-scale version. The
struts, spreader bars, and floats form three rigid triangular trusses
and make for a sturdy float mounting system. The model’s scale
bolt-on wheel landing gear made it relatively easy to design suitable
adapter brackets to be attached in its place.
Sea Commander furnished the floats along with the material and
fasteners to make the spreader bars and struts. I designed and
fabricated the adapter brackets, water rudders, and X bracing from
material I obtained locally.
The 64-inch Sea Commander EDO 2000 floats are high-quality
fiberglass/polyester moldings. The spreader bar saddles are molded
in, and there are several internal bulkheads that separate the floats
wheels were almost identical, and the Cub was flying nicely at 40
pounds on floats.
The huge Balsa USA Ercoupe kit is not for the faint of heart,
either financially or in terms of building time and skill. The kit,
with tax and shipping, will set you back roughly $1,000.
The kit came in three packages: a conventional big kit full of
lumber, a big box with the giant fiberglass cowl and other goodies,
and a big mailing tube containing rolled thin plywood and the seven
monstrous sheets of plans. Small parts were nicely and logically
packaged in clear plastic bags with labels.
The 73-page manual had many photos. The fiberglass cowling
was impressive. It was big, light, and flexible, and all the difficult
trimming was done. It had molded-in fastener heads and panel lines.
The entire fuselage top half was built on a table. Then it was
inverted in a fixture for completion of the bottom half.
The scale operating tricycle landing gear was assembled from
massive aluminum castings and pieces of steel. I had to do quite a
bit of filing, drilling, and silver-soldering, but the necessary
precision holes and mating surfaces were already drilled and
machined. The finished landing gear, with the supplied air wheels,
weighed 4 pounds.
Wing and tail construction were conventional, except for the
scale diagonal wing ribs and complex laminated wingtips. The
removable outer wings were quite stiff and light.
Scale Detailing: My “coupe” was built as a Sport Scale model, not
meant for Expert-class competition. A separate big three-view sheet
was thoughtfully supplied in the kit, and it showed rivet location,
Stainless-steel 4-40 hardware was used throughout. The nose-strut
attachment bracket and steering servo will be hidden by the cowl.
Mounting brackets in the wing were fashioned from aluminum Tstock
and fitted into the existing main gear locations.
Sea Commander struts and hardware, with special adapter
brackets, connect the floats rigidly to the landing-gear hard points.
The Sea Commander EDO 2000 floats are supplied with fiberglass
dress covers to hide the hard points of the float.
within the strut to get the desired exact
overall end hole to end hole length of the
strut assembly, and then I match-drilled it
and fastened it. The struts were made in
left and right pairs of equal length.
I used standard 4-40 hardware to fasten
the struts to the airplane and to the floats,
with elastic stop nuts on all bolts in the
float assembly and Loctite on the main
gear adapter bracket bolts.
Finishing: The four fiberglass covers that
Sea Commander furnished were fastened
over the spreader bar saddles using #2 selftapping
screws. These covers had to be
individually trimmed and fitted to each
saddle.
From that point I disassembled
everything and painted the floats. I used
Stits Poly-Tone (Rancho Silver) with F&M
Enterprises’ Feather Coat primer. The
paint provides a scale-looking satin finish,
but a gloss top coat is available for those
who like it shinier. The paint is prethinned
for spraying, and it contains retarders,
flexibilizers, and a self-extinguishing fire
retardant.
I used the same brand of paint on the
rest of the model. Stits has a special dope
into watertight compartments. A special
small bow compartment is provided for
balancing weights.
The struts and spreader bars are
streamlined 6061-T6 structural aluminum
tubing. This is not your typical soft
aluminum hobby-shop material. These
components are bigger and much stronger.
The float assembly weighs a hefty 9
pounds, but the husky Ercoupe landing
gear it replaces weighs 4 pounds. Thus we
gained only 5 pounds adding the floats, for
a 36-pound total weight. With 2,400
square inches of wing area, the wing
loading came out a reasonable 35 ounces
per square foot. The Ercoupe’s flight
characteristics resemble those of my
ModelTech ARF Cub.
Spreader Bars: The two teardrop
aluminum-tubing spreader bars were
mounted with the float centerlines 32
inches apart. I match-drilled and installed
the furnished aluminum filler bar and three
self-tapping screws at the end of each
spreader bar after I made sure the floats
were parallel and the assembly was square.
After initial assembly I disassembled
the spreader bars and hardened the screw
holes in the floats with thin cyanoacrylate
glue, and then I reassembled the floats and
spreader bars. I trimmed the ends of the
spreader bars to clear the covers to be
installed later.
Adapter Brackets: The three adapter
brackets for the model landing-gear
attachment points were made from
aluminum T section for the wing maingear
attachment point and aluminum angle
for the nose-gear attachment point. The
bolt-hole pattern in the adapters matched
the hole pattern in the wheel landing-gear
legs. I mounted the brackets onto the
model using 4-40 hardware—the same as I
used for the wheel landing gear I was
replacing.
I made four lower float-attachment
brackets from aluminum angle. I mounted
the brackets onto the spreader bars with
self-tapping screws. The forward brackets
were a bit tricky since they comprised
attach points for the nose-gear struts and
the forward main-gear struts.
Struts: I made a simple fixture to hold the
floats and the airplane in the correct
relative position so the strut lengths could
be determined. The float steps were located
at the airplane’s CG, and the flat bottom of
the wing should be parallel to the top of the
floats so the wing maintains a positive
incidence angle to the water surface.
I machined the strut end fittings from
the furnished aluminum bar. I used a band
saw and file to make the slots, a drill press
to drill the end holes, and a belt sander to
round the ends.
I match-drilled the struts and end
fittings for one end of each strut and
installed the furnished hardware to fasten
them together. I slid the other end fitting
The gentle flight characteristics of the
1/3-scale Ercoupe on floats resemble
those of a like-size Piper Cub on floats.
52 MODEL AVIATION
• Molded-in fiberglass joiner lip and side
stiffener
• Molded-in fiberglass bottom
reinforcements
• Four fiberglass-reinforced bulkheads
• Five watertight compartments
• Composite reinforcements in scale
mounting positions
• Composite reinforced transom for
water rudder mounting
• Available in sizes from 29 to 65 inches
• Floats pressure-checked for leaks
• Ready-to-paint and -install fittings
• Float kit used: 1/3 scale (64 inches)
• Price: $385.28 (floats only)
EDO 2000 Float Specifications
Engine used: Zenoah G-45 (on wheels),
G-62 (on floats)
Propeller: Master Airscrew 20 x 8
(on wheels), APC 22 x 10 (on floats)
Fuel: 24-ounce plastic (furnished)
Radio system: Futaba 9VAP transmitter
with nine-channel PCM receiver, six
Hitec RCD HS-645MG servos, two
1500 mAh Cermark 6-volt NiMH
battery packs, eight Cermark 12-inch
servo extensions
Finish: Stits Poly-Tone paint
Ready-to-fly weight: 31 pounds,
36 pounds with floats
Flight duration: Exceeds 15 minutes
Test-Model Details
Model type: Giant Scale kit
Pilot skill level: Sport/Scale fliers
who are experienced builders
Wingspan: 120 inches
Wing area: 2,400 square inches
Length: 84 inches
Weight: 28-32 pounds
Wing loading: 30 ounces/square
foot (as built)
Engine: 45-55cc two-stroke gas
or 3.0-3.5 cu. in. glow
Radio: Four-channel radio (minimum),
six servos
Construction: Conventional balsa/
plywood/basswood with fiberglass
cowling
Covering/finish: Fabric on wings,
thin fiberglass (furnished) on fuselage
and tail
Price: $899.95
Ercoupe Specifications
+
• Beautiful, good-flying scale airplane.
• Complete kit.
• Excellent construction manual.
• Scale functional landing gear.
• Scale sliding cockpit windows. -• Complex fuselage construction.
• Balsa quality issues.
• Errors in manual but no errata sheet.
Pluses and Minuses
formula (used instead of primer) that
chemically bonds to the polyester wingcovering
fabric.
Water Rudders: I cut the rudders from
.030-inch aluminum and silver-soldered
the .030 brass hinge brackets to the 5/32-
inch music-wire shafts. Standard hobbyshop
nose-gear nylon bearings and steering
arms completed the installation. The water
rudders were manually retractable and
were adjusted to kick up if they hit an
obstacle.
The Ercoupe nose-gear-steering servo
was used to steer the water rudders. I
modified a nylon steering arm to form a
April 2007 53
During the 1920s and 1930s many
private pilots were injured, killed, or scared
off by the terrible ground handling, landing
and takeoff characteristics, and poor stallspin
performance of the day’s tail-dragger
lightplanes. Ground loops during landing
were common, and the gentle stall and spin
performance of “baby carriages” such as
the Cessna 172 were unknown.
A group of engineers, including the
great Fred Weick, comprised the
Engineering Research Company, or
ERCO, which was to address these
problems. The Ercoupe Model 415C was
the result.
With performance similar to today’s
Cessna 150, the Ercoupe could not spin
and it was so certified by the CAA. The
Ercoupe was so easy to fly that a special
pilot’s-license category was assigned to it,
requiring a minimum of five hours solo
and 35 hours total flight time, as opposed
to eight hours solo and 40 hours total flight
time for conventional lightplanes at that
time.
The Ercoupe is a two-seat, low-wing
monoplane with twin vertical tail surfaces
and a tricycle landing gear. The pilot and
passenger sit in a glassed-in cockpit with
excellent all-around visibility.
Construction is modern all metal,
except for the fabric covering on the wings.
The skin-stressed (monocoque) design has
no wing or tail struts. Engines range from
65 to 90 horsepower.
The rugged Ercoupe tricycle landing
gear is configured so that the airplane can
be landed in a crab in a crosswind, and its
geometry causes the aircraft to
immediately straighten out on the runway
upon touchdown. Thus no ground looping
and easy ground handling.
With the nose wheel linked to the
pilot’s yoke, one drives it like a car. A
carlike single brake pedal controls both
main wheel brakes simultaneously.
The Ercoupe’s stall-spin resistance is
achieved through several design features.
The wing has generous dihedral, and the
ailerons and rudders are coupled so there
are no rudder pedals. Thus one cannot
cross controls in a standard Ercoupe. Turns
are coordinated, with no way to slip or
skid. Stall resistance is aided by limiting
the elevator travel.
More than 5,000 Ercoupes were built,
mostly after WW II, and an excess of
2,000 remain registered today. Several
other companies followed ERCO in
building the Ercoupe, and a number of
changes were instituted in the design,
including a sliding canopy, single tail,
rudder pedals, and larger engines. Some
of these modifications resulted in more
conventional stall-spin behavior.
The unique color scheme and
instrument panel I used on my model are
those of N87405. It was owned by Tom
Laird-McConnell in the Seattle-Tacoma
area in Washington but was sold to
Harold Gochenouer in Lake Havasu City,
Arizona.
I was “Googling” my way through
cyberspace looking for a nice color scheme
for my Ercoupe when I happened upon
Tom’s Web site: www.ercoupers.com. It
has photos of many Ercoupes that are
currently flying. When I saw Tom’s
N87405, I fell in love.
Tom was extremely generous with
photos of his airplane, and I got to see it
at Lake Havasu City Airport after the big
annual Desert Hawks float fly. I modified
the usual wing-LE location of the landing
lights so they match the type mounted on
the main landing-gear fairings of Tom’s
aircraft. His photos were extraordinarily
helpful in duplicating the interior.
Man Behind the Ercoupe: I just finished
reading the autobiography of Fred Weick
entitled From the Ground Up (from
Smithsonian Institution Press, 1988).
This lesser-known but outstanding
aeronautical engineer was born in 1899
and was building and flying model
airplanes before World War I. He was
one of the first graduate engineers to
apply a rigorous engineering and
scientific approach to airplane design and
testing.
Fred worked for NACA and the
Airmail Service, Texas A&M, ERCO,
and Piper. He invented the modern
tricycle landing gear and did pioneering
research into safer aircraft-control
systems. He also led the team that
developed the NACA low-drag cowling
for radial engines.
Fred wrote a paper about simplified
propeller design for light aircraft, and it is
still the “bible” for home builders. He
was very active in EAA. Fred was
responsible for the design of the Ercoupe,
Piper Cherokee series, and the Ag-1,
which set the standard for modern, safer
agricultural-application aircraft (crop
dusters) such as the Piper Pawnee.
Fred’s other contributions to aircraft
efficiency and safety and his many honors
and awards are too numerous to list here.
For a summary of his career visit http://
en.wikipedia.org/wiki/Fred_Weick. MA
—Oscar Weingart
SCOOP
“COUPE”
ON THE
Oscar Weingart’s 1/3-scale Ercoupe with full-scale N87405 at Lake Havasu City
Airport. The landing lights on the model’s main landing-gear fairings were
specially made.
The model’s instrument panel is
based on N87405, with JTEC
instruments and commonly
available surplus subminiature
switches and buttons.
Length: 20 feet, 9 inches
Wingspan: 30 feet
Wing area: 142.6 square feet
Weight: 1,440 pounds (max.)
Wing loading: 10.1 pounds/
square foot
Engine: Continental C-85
Full-Scale Ercoupe Specifications
bearing and bolted it to the nose-gear
adapter bracket. A vertical music-wire
shaft was fitted with three more of these
steering arms: one for the connection to
the servo and the other two to form a tiller
bar. Cables connected this tiller bar to the
steering arms on the water rudders.
Balancing: I drilled a 1-inch-diameter
hole into the top of each float to gain
access to the bow ballast compartment. I
balanced the assembled floatplane by
installing lead weights in modeling clay in
the ballast compartments and filled the
remaining space with polyurethane soft
foam.
Scale-looking soft aluminum covers
were made for the holes and held in place
with small self-tapping screws. The edges
of the covers were coated with clear
silicone sealer.
Transportation: The 1/3-scale Balsa USA
Ercoupe has detachable outer wing panels,
which make for easy transportation. If you
have a large-enough vehicle, the Ercoupe
floats can remain attached to the model.
With our standard-length Ford Aerostar
minivan, the float assembly had to be
removed and loaded separately.
Control Setup and Programming: The
water rudders were permanently linked to
the air rudder stick in my Futaba 9VAP
transmitter using the programmable mix
function. The channel used has a knob on
the face of the transmitter, which allows
the water rudders to be trimmed
independently from the air rudders. Hitec
RCD HS-645MG high-torque, metal-gear
servos were used throughout.
The full-scale Ercoupe had no rudder
pedals. The ailerons, rudders, and nose
wheel were linked together to the pilot’s
control wheel.
A switch-selectable mix was
programmed for the model. The ailerons
and air rudders move together with the
aileron stick, but the rudder stick can still
override the coupled rudder movement. I
used the coupled aileron-air rudder mode
in flight, but I found that I preferred the
uncoupled mode for landing and takeoff.
Taxiing and Flying: The Ercoupe “turns
on a dime” with two large water rudders. I
hold full up-elevator when taxiing on
water; this keeps the water rudders well
under the surface for positive control. The
heavy, low-wing Ercoupe is not affected
much by crosswinds, but appropriate
seaplane sailing and taxiing techniques,
such as holding aileron against the wind,
can be used in stiff crosswinds.
Takeoffs and landings are the fun part
of flying RC seaplanes. The Ercoupe
initially porpoised during takeoff, but a
more powerful engine cured this condition.
Standard seaplane takeoff and landing
techniques work well on the model.
The Balsa USA 1/3 Scale Ercoupe
equipped with Sea Commander EDO 2000
64-inch floats makes a unique, attentiongrabbing
seaplane that looks great and flies
beautifully.
Many thanks are due Dave Lewis at
Balsa USA, Ryan Holm at Sea
Commander, and Chip Mull at F&M
Enterprises for their help in getting the
information and materials needed to build
the Ercoupe on floats. Tom Laird-
McConnell furnished many fine detail
photos of N87405, as well as the photos of
the prototype Ercoupe floatplane.
The full-scale airplane’s background
and history were obtained via the Google
search engine, using the key word
“Ercoupe,” and from several discussion
forums on the RC Universe Web site at
www.rcuniverse.com.
Don Lien of the Riverside RC Club
(RRCC) was a great partner in painting,
fabric covering, and cockpit-glass
installation. Initial test pilots were Dale
Yaney of RRCC and Dan Egelhoff of
Team Airtronics. They were followed by
Dave Collis of Vancouver, British
Columbia, for the test flights at Lake
Shuswap, where the Ercoupe won the
“Best on the Beach—Scale” award. MA
Oscar Weingart
[email protected]
Aircraft Kit Manufacturer:
Balsa USA
Box 164
Marinette WI 54143
(906) 863-6421
www.balsausa.com
Float Manufacturer:
Sea Commander
4768 Harvie Ave.
Powell River, BC, Canada
V8A 2P5
(877) 485-2926
www.seacommander.com
Items Used in Review:
Zenoah G-62 engine
www.horizonhobby.com
Miscellaneous hardware
www.dubro.com
Stits Poly-Tone paint
www.stits.com
1/3-scale instruments
www.jtecrc.com
1/3-scale full-body pilot
www.hppilots.com
Resources:
Ercoupers Web site
www.ercoupers.com