became aware of the Buhl Aircraft
Company during the late 1950s;
one of my American friends, Steve
Ditta, sent me a Berkeley kit of the
Buhl Pup.
This interesting little Scale Free Flight
model was a fine flying machine. On one
occasion, it hooked a powerful thermal and
flew out of sight.
My next contact with models of Buhl
aircraft was through an article in our
Aeromodeller magazine, which featured a
Buhl Sport Airsedan designed by American
modeler Hurst Bowers.
From those plans—scaled up to a 72-
inch wingspan—I built my first Radio
Control model years ago. The model flew
well, but it was not very accurate. When
some information about the full-scale
aircraft came to light, I did a complete
redesign of the model.
The Buhl Sport Airsedan was a
deluxe three-place sesquiplane with a
36-foot wingspan. Being a highperformance
aircraft aimed at the
sportsman pilot, it had limited appeal;
consequently, few were built.
The lower wings were very small
compared to the upper wing—they were
roughly 1⁄4 the area, which made the aircraft
a true sesquiplane type.
Powered by a nine-cylinder 220-
horsepower Wright Whirlwind J-5 engine,
the Airsedan had a top speed of 134 mph
and would cruise at 112 mph. Later fitted
with the Wright J-6 engine, the top speed
went up to 150 mph and the cruising speed
was 125 mph.
The Airsedan had the performance of
one of the high-powered open-cockpit
sporting biplanes of the time, but it had the
added attraction of a roomy, comfortable
30 M ODEL AVIATION
With the top wing installed, this design takes on a unique look. A great deal
of wing area results in great performance.
The small lower wing on the Airsedan puts this
design in the sesquiplane category. There’s ample
radio room here!
n Phillip S. Kent
Buhl Sport Airsedan
Try a sesquiplane!
March 2001 31
This photo gives a good indication of the model’s size. Notice the great simulated radial engine detail!
The prototype of this model came in slightly heavier than predicted, but the flying
characteristics showed no ill effects. It’s a very realistic flier.
cabin for three and a payload big enough to
allow the occupants to have ample baggage.
The aircraft type took part in many of
the competitive and record events of the
time, with some success.
I got some useful information, including
a drawing with color information about the
full-scale aircraft from the June 1969 Sport
Flying magazine and photographs from U.S.
Civil Aircraft by Juptner.
The model is to 1⁄6 scale with a
wingspan of 72 inches. The earlier model
design was a similar scale and was flown
using an O.S. 48 four-stroke engine. The
later model—the subject of this article—is
flying with an old open-rocker O.S. 60
four-stroke, but anything from a 52 to a 75
four-stroke should be fine.
The prototype model, built by my friend
Jim Dobson, was heavier than expected
when finished, but that has not affected its
excellent flying characteristics.
CONSTRUCTION
The model uses conventional model
airplane construction techniques and
materials. The fuselage is a basic box built
from 1⁄4 square balsa, but it is faired out with
stringers on the sides and the top. The wings
use a rib-for-rib scale structure that also
includes the balanced aileron outline.
The small lower wings are built on a
sheet core and they plug into the
fuselage. The tail unit can also be
constructed using the core method, or
with built-up construction.
It is essential that the working rigging as
shown is used. This is not difficult to
reproduce, using the Mick Reeves fork ends
and 3⁄32 flat flying wires.
The undercarriage uses standard 51⁄4-
inch-diameter Williams Bros. Golden
Age wheels on a simple torsion bar unit
that has dummy-sprung oleo legs. The
engine is mounted on integral hardwood
bearers, and a balsa box contains the
tank behind the engine.
Fuselage: Build the first side of the fuselage
box directly over the plan. When dry, cover
with a sheet of clear polythene—covering
film or Tex backing is ideal.
Build a second side over the first. When
dry, remove both sides from the building
board. The polythene will prevent the sides
from sticking together.
Make the saw cuts where indicated on
the plan at F2, in front of and behind the
wing and in front of the tailplane. Make two
temporary formers that will fit the fuselage
at section A and at the front of the parallel
section where the wing fits.
Airsedan
The fuselage construction is strong and light, with a rigid forward box section and a
lightweight built-up aft section. Notice the crossbracing stringers.
The model’s lower wing is built with a balsa sheet core piece. The top wings are a result
of more-normal construction, with spars and full ribs.
The O.S. 60 four-stroke engine is mounted in the inverted position, so it can be cowled
completely by the simulated Wright radial. This adds realism!
Pin the formers in place over the plan
view, and fit the sides so the structure is
built inverted. Add the crosspieces aft of the
leading edge of the wing, pulling in the
sides at the saw cuts.
Do not do anything to the nose section
forward of the wing yet.
Remove the box assembly from the
board when it is dry. Fit the inside former
F3 with epoxy.
When the epoxy has cured, “dry fit” the
beech bearers inside former F2 and inside
former Fl. When you are satisfied with the
fit, glue the bearers in place with fiveminute
epoxy.
Add the wing mounts—which are made
from 1⁄4 sheet—the outside formers at the
nose, and the top decking formers. The
stringers on top of the fuselage can be from
balsa or balsa with dowel.
Fit all undercarriage and wing-tube blocks.
Fit the main undercarriage legs into the beech
blocks and block in with the plywood
crosspiece. Add the keel with plywood inserts,
and fit the brass brackets for the undercarriage.
Add the front undercarriage bracket before
using soft balsa block for the underside of the
fuselage back to the door opening.
Add the windscreen formers, along with
the 1⁄16 plywood and the 1⁄8 balsa crosspiece
that takes the front wing-attachment dowels.
After fitting the front outside parts of the
front formers—F1-F3—cover the nose
section with 0.4mm plywood.
Fit a wire tail skid or leaf spring to the 1⁄8
plywood plate and epoxy in place. If the
elevator is to be actuated in the full-scale
manner, make the elevator horn unit from
3⁄32-diameter wire with brass horns silversoldered
in place.
Use plywood bearing plates glued to the
fuselage uprights and add the 1⁄16 sheet insert
to fit to the outside at the rear of the fuselage.
Complete the basic fuselage structure by
adding the side stringers, cutting the door,
and making the engine cowl.
Wings: Although there are four wings to
make, they are not too complicated. The
main wings follow the usual practice of
having spars and ribs, but the smaller lower
wings are different; they are built using a
1⁄16 sheet-balsa core.
Cut two 1⁄16 sheet-balsa cores to the plan
shape of the lower wings. Add the 1⁄4 x 3⁄16
leading edge and the 1⁄16 x 1⁄4 trailing edge
pieces to the top side of each core.
The shape of the root and tip ribs are
shown on the drawing. Cut these out and fit
the top halves to the core. The root rib will
be wider than the actual root of the wing,
because of the trailing edge cut back.
Add the remaining ribs cut from scrap 1⁄8
sheet, and shape them using the overlength
root rib and tip rib as a guide.
Repeat the operation for the bottom of the
lower wings. Trim the root rib to the correct
shape and fair in the second rib to suit you.
Fit the wires that locate the wings on the
fuselage. Pack around the wire with
basswood and epoxy in place. Add 1⁄4 sheet
as a spar, making sure these pieces lay
March 2001 33
Photos courtesy the author Graphic Design by Carla Kunz
34 M ODEL AVIATION
Notice the balanced elevators on the built-up tail section. Because of the long tail
moment on this design, the tail components need to be built light!
Type: RC Scale
Wingspan: 72 inches
Engine: O.S. 60 four-stroke
Flying weight: 61/2-8 pounds
Construction: Sheet and stick balsa
Covering/finish: Iron-on fabric/acrylic
lacquer
Buhl Sport Airsedan
below the covering line. Add the balsa tips
and plywood rigging inserts.
Cut a plywood rib template; using it,
produce 40 wing ribs from 3⁄32 sheet balsa.
Pin the front 1⁄4 square spar on the board.
Place suitable packing pieces at the trailing
edge and underneath the rear spar before
fitting the ribs. Shorten the ribs where the
ailerons are located before fitting.
Glue the aileron spar and the leading and
trailing edges in place. Fit the two 1⁄4 square
top spars and the add the 1⁄16 sheet webs
where indicated.
Build the ailerons on a 1⁄16 sheet bottom,
using the cutoff pieces of rib and a 1⁄4 sheet
spar. Fit the sheet balsa tips and build up
with sheet or laminations at the outside.
Both wings may be joined when they are to
this stage. Block up the last full rib 3⁄4-inch at
the front spar and cut the spars at 90° to the
building board. Fit the center ribs, then join the
wings. Cut slots and fit the plywood dihedral
braces at all spars and the leading edge.
Fit the plywood wing-bolt retaining
piece, then build up the rear fairing. The
wing can be retained with one or two nylon
bolts that fit into tapped holes in the
plywood plate. Fit the plywood brace that
carries the locating dowels for the wing into
the central wing ribs.
Return the wing to the blocking pieces
and fit all the top capping strips, including
the capping for the aileron spar. Note the
direction of the grain. Fit the capping strips
and sheeting to the underside of the wing.
Cap the aileron ribs and add the balsa mass
balances and hinge blocks.
Make cutouts in the wings for the
balances and the hinges setup. The drawing
shows details of the wing section with
Robart hinges in position.
Fix the wing to the fuselage for final
fitting of the block balsa front fairing and
the built-up rear fairing.
Tail Assembly: The fin and rudder use a 1⁄16
sheet-balsa core. Cut out and mark the
positions of the ribs on both items. Fit the 1⁄4
square spar and the 1⁄4 x 1⁄8 leading edge on
the fin, then fit the 1⁄8 sheet ribs.
The rudder has a 1⁄4 square spar, which
should be fitted first. Add the ribs and the
soft-balsa block capping. Repeat these
operations on each side.
You can use the core method of
construction on the tailplane, but the
prototype model had a built-up structure.
Build the parts directly over the plan, using
the wood sizes indicated.
Pack up the trailing edge of the elevator.
When complete, sand to the section shown
on the drawing.
Gathering the Loose Ends: The dummy
engine is one of the main features of the
model. The prototype had 1⁄6-scale Williams
Bros. Wright Whirlwind cylinders fitted to
the removable cowl. It is easy to hide the
model power unit in the cowl if the engine
is mounted inverted.
The prototype model originally had an old
O.S. 60 open-rocker four-stroke engine, but it
has been replaced with an up-to-date version.
The model should weigh
approximately 61⁄2 pounds if built per the
plan. The prototype was heavier, at more
than eight pounds, but it did not affect
the performance.
The large cabin provides plenty of space for radio, the installation, and scale detailing.
There are no upper wing-alignment problems with this design.
March 2001 35
Make and fit all the working rigging—it
holds the model together in flight. The
prototype had 3⁄32 flat wires, with Mick
Reeves fork-end fittings on the wings and
fishing trace for the tailplane.
The model was covered with one of the
heat-shrink iron-on fabric materials. That is
what you should use for a model of a fabriccovered
full-scale airplane; it is easy to
apply, and it looks the part when painted.
The model was finished with cellulose
car paint (yes, it’s still available in the UK),
but use what you like best.
The color scheme was taken from Sport
Flying magazine, but there must be other
designs available. A specialist decal
manufacturer (there are many around)
produced the logo and license numbers.
The model was finished in autumn, but
we had to wait for suitable flying weather.
There was some apprehension on the part
of the builder, because the model was
heavier than expected.
However, after the customary
photograph session, the model made an
uneventful first flight in the capable hands
of test pilot Andy Bowman. The Airsedan
has pleasing flying characteristics, and it
looks its best making slow, low flybys.
This Scale model is not too difficult for
the modeler who has experience building
from plans. A few special techniques are
required, but accuracy in cutting and
fitting parts is essential.
Keep the model light by selecting
your materials carefully, and do not
modify the structure; it is more than
adequate if built as in the drawing.
Pilots who are competent with an
aileron model will have no problems
with the Airsedan. Mix the ailerons and
rudder for flying; it does make things
easier. On most radios, this means the
rudder can still be operated on its own
for takeoff, landing, and stall turns.
Have fun with this little-known classic from
the Golden Age of aviation. MA
Phillip S. Kent
32 Moorbottom
Cleckheaton
West Yorkshire
BD19 6AD
England
Full-Size Plans Available —see page 173
