Porter, manufactured in Switzerland, is now just a part of Pilatus'
considerably expanded product line. Since its original STOL flying
machine, the company now makes business jets and military trainers.
Various iterations of the Porter are seen at scale model contests
worldwide, and there are multiple kits and ARF versions available
for free flight, control line, and radio control. What makes this
particular Pilatus Porter noteworthy is its builder and pilot, Mrs.
Dolly Wischer, who appeared with it in an article in a 1963 edition
of American Modeler magazine. She researched the design,
drew the plans, built the airplane, and flew it with one of the
earlier proportional radio control systems. Its 68" wingspan and
a wing loading of just under 22 oz/sq.ft. allowed a .19 engine to
drag it around the sky handily.
AMA Plans Service (somewhere around
page 18) still sell plans for this Pilatus Porter, as well
as for 15 other versions! I told you it is a popular scale subject.
Dolly Wischer's "Yeti" Radio Controlled Pilatus Porter
Wisconsin housewife, mother of R/C Rudder
Champ, designed, built and operates this scale flyer, gives
her own story and plans-yes, drew 'em herself!
Mrs. Robert (Dolly) Wischer with her
R/C Porter entry at last year's National Meet, Glenview,
Ill., Naval Air Station.
Tail unit of Pilatus Porter; shown are
push rods for moving rudder and tailwheel.
Interior (nose upwards): plywood panel
holds switch, connecting plugs and Hillcrest throttle servo.
Annco servos at bottom.
Engine mount details: Piano wire push
rod emerges from aluminum tube; sheet aluminum covering
to protect balsa from castor oil was made from cookie sheet
(the woman's touch!).
Under-body view, aluminum liners for
the exhaust and engine cooling vents are visible.
Porter model with cowl removed, note
2·oz "clunk" type fuel tank held in place via rubber bands
and hooks. Mrs. Wischer's faithful copy is based on geared,
super-charged standard Porter powered by Lycoming GSO-480.
Cover drawing by Cal Smith depicts the Turbo-Porter with
There is considerable variation in opinion of what constitutes
a pretty airplane. Some prefer sweeping curves and elliptical wing
outlines, while others like straight lines with a long, slender
appearance. The Pilatus Porter is obviously neither of these; its
utilitarian shape is square to the extent that it seems to have
been built in long lengths which were then sawn off into shorter
chunks. However, in spite of those functional lines, her designers
have come up with an airplane that has an appeal to any person who
feels an affinity for things that fly, and I suspect that I am one
The model was inspired by the reading of the mountaineering book
"The Ascent of Dhaulagiri," a narrative of the successful 1960 Swiss
Expedition to climb the 26,795 foot mountain, Dhaulagiri, in Nepal.
At that time it was the highest unclimbed mountain in the world.
The Swiss used the airplane to supply the high camps in place of
many Nepalese porters. The Pilatus Porter made between twenty and
thirty landings at altitudes from 15,000 to 19,000 feet-and holds
the world record for a landing at 19,200 feet. All of these landings
were made with loads such as carrying 1,500 pounds of rice to a
glacier at 15,000 feet. For this type of work the Porter is equipped
with a combination of skis and wheels, the skis being hydraulically
raised or lowered depending on the surface encountered. The expedition
plane was christened "Yeti", the Nepalese word for the elusive abominable
The Porter is a product of the Pilatus Aircraft Works of Stans,
Switzerland, who generously supplied us volumes of necessary information
and drawings. It is the most outstanding of the STOL aircraft. Powered
by a geared super-charged Lycoming six cylinder engine of 340-hp,
it can lift a useful load of 1,900 pounds with a ground run of 525
feet and a landing run of only 330 feet. Cruising speed is 125-mph,
top speed is 145, and it stalls at 43. A later version employing
the Turbomeca Astazaou turboprop powerplant (see Cal Smith's cover
painting) has even more spectacular performance.
A prominent feature is the exhaust augmenter tube which also
carries off the air used for cooling the engine. The wing trailing
edge is almost evenly divided between flaps and ailerons. The plane
can carry seven passengers plus pilot, and is easily adaptable to
photo, cargo, and parachute work. The first Porter was purchased
by Hermann Geiger, the famous Swiss alpine pilot, for utility and
rescue flights in Switzerland. "Yeti" was the third plane built,
and four others are operated by the International Red Cross in Nepal.
The first in the United States was purchased by Wein Alaska Airlines.
Our model was developed around six channel multi equipment. The
ailerons and flaps, although built separately and glued in place
for realism, could easily be made operable if eight or ten channels
are available. Since a plane like the Porter is not considered acrobatic,
ailerons are not a requirement for realistic flight. The space inside
the model is so vast that any amount of electronic gear could easily
be installed, but more power than the Veco .19 would be needed.
In order to simulate the all-metal construction of the full size
Porter, the model is entirely covered with sheet balsa. It is important
to choose only the lightest wood for this purpose in order to keep
the weight down to a reasonable five pounds or less.
The squareness of its outlines makes "Yeti" quite simple. Wing
tip ribs and root ribs are the same shape, which means that the
right and left panels will be identical until strut anchors and
end ribs are cemented in place. The airfoil employed for the model
is an NACA 2414, quite different from the reflexed high lift airfoil
of the prototype. Aerodynamically this change was not absolutely
necessary, but an undercambered airfoil is more difficult to construct
and it was considered a good idea to concur with usual R/C practice.
As it turned out the choice was a good one since the plane flew
well, without any adjustments, on its first flight. While the model
has little dihedral this does not affect its performance adversely
since the center of gravity is low.
Every scale modeler has a problem with the horizontal stabilizer
because it usually has too small an area compared with modeling
practice. In this case the decision was made to conform with the
scale area, as this helps in obtaining maximum scale points in a
contest. A bonus benefit derived from the small stab is that the
plane takes off well even though the main landing wheels are quite
far ahead of the center of gravity. The usual ground loop doesn't
develop because the tail wheel stays on the ground until a good
speed is built up, and by that time the large fin and rudder take
over to hold the plane in a straight line take-off. Past experience
had shown that an oversize stabilizer will cause the tail to lift
too early with a resultant ground loop. Once airborne the Porter
has all the stability of the full size plane, showing no bad handling
characteristics. (My husband calls it an old ladies' airplane.)
The fuselage conforms with present day R/C construction practice
with minor variations. A large hatch in the roof permits easy access
to a cavernous interior, where the Annco servos, mounted on the
floor, appear lost. Batteries and receiver are wrapped in foam and
placed at the front. Fuselage sides have doublers extending from
the cabin rear to the firewall. Forward from this point the nose
is solid balsa underneath, with a built-up balsa cowl covering the
engine and fuel tank. The unique landing gear extends from the fuselage
centerline and due to its length is quite springy. It has a very
realistic soft action in landing, and has saved the plane from damage
on occasion. Spoked Veco wheels closely simulate those used on the
prototype Porter. Dummy shock struts are actually telescoping birch
dowels, and serve no purpose in load carrying.
Fastening the wings to the fuselage sides permits the windshield
to be made in one piece for greater scale fidelity, but this means
that the wing halves must be keyed accurately by tongues extending
from the wing roots through alignment holes. Heavy rubber bands
then hold the wings snugly, but not too tightly, against the fuselage.
On a hard landing the rubber bands stretch, permitting the wings
to swing downward and forward, pivoting around the struts. This
system works well in practice, but for inverted flight the bands
must be tight. Holes through the solid nose block for engine exhaust
and ventilation could be coated with polyester resin or, as in my
"Yeti", lined with sheet aluminum to prevent soaking of the wood
with castor oil. In any case, the exhaust heat must not bear directly
on the balsa wood since this would constitute a fire hazard.
Construction. Fuselage sides are best made from 3/32" thick,
6" wide balsa sheets; can also be spliced from 3" sheets. Score
the sides on their inside surface with a razor saw at the point
where they bend inward at the cabin rear. Use cement liberally to
reinforce this score line after bending to the proper angle, using
the fuselage top view as a template. The 3/32" doublers are duplicates
of the fuselage sides except that they end at the cabin rear. Doublers
are beveled at the back end to fit the bent fuselage sides closely.
Use contact cement to fasten sides to doublers making certain that
there is a firm bond at the point where the sides were bent. Now
add the short doublers at the point where the stabilizer will be
attached. At this time cut-outs for the windows and windshield openings
should be made.
Cement all longerons and vertical braces to each side before
joining the sides with bulkhead F-1 and the cross braces thru the
cabin section. Then add cross braces from rear of cabin to tail.
Bend the landing gear wires to shape. Note that each half is formed
from a single piece of wire. Cut plywood floor F-3 and insert landing
gear into the notches after which the ends of wire are bound with
iron wire and soldered. Cement F-3 to fuselage bottom and add 1/8"
x 3/8" plywood pieces above landing gear followed by 3/8" sheet
balsa back-up blocks. Rigidity here is a necessity as a hard landing
would force the landing gear levers upward.
Complete fuselage structure by adding sheet balsa top and bottom,
bulkhead F-2. and cowl top. Tailpost is 1/2" square balsa sanded
to cylindrical shape.
Fuselage nose blocks are best built in layers in order to obtain
the two openings for exhaust and air vents. Use white glue to fasten
the block to bulkhead F-l and then sand to shape. Also use white
glue to assemble the engine mount to the nose block and bulkhead.
Note that three cross braces at the landing gear are made from 3/8"
square birch or maple. A 3/32" plywood gusset at the tail is used
for fastening tail wheel bracket. Just forward of this gusset is
an opening for access to elevator push rod.
Wings are identical, left and right, except for the plywood end
ribs and location of strut anchors. Ribs are assembled to spars
directly over the plan, then leading and trailing edges are added.
Cement strut anchors, with blind nuts attached, into the notched
ribs, then cover lower wing surface with 1/16" sheet balsa making
certain to leave a hole for the wing strut screw into the blind
nut. Cement plywood keys with piano wire hooks to root end of each
wing before adding the top 1/16" sheet balsa planking. A 1/16" plywood
tip rib is added next. The 3/32" plywood root rib must have holes
to slip over the keys. Make two more ribs identical with these root
ribs from 1/16" plywood and cement them to the fuselage sides in
exact position shown on plan to obtain 1 1/2 degrees of incidence,
making certain that both wings will have identical incidence.
The separate ailerons and flaps are made in a long strip which is
cemented in position in final assembly after finishing. Although
sheet balsa planking on the wing adds weight it also adds realism
and strength permitting a lighter interior.
Tail surfaces are built up similar to the wing and covered with
soft 1/16" sheet balsa. The hinge is of the concealed type for realism
but could be a thread hinge, the same as used on most R/C models
for much less effort in building. When hinging elevator to stabilizer
care must be taken to be sure that no cement creeps into the 3/32"
brass tube to bind.
The entire model should be given 3 coats of clear dope and then
covered with silk. To prevent warping, the hatch requires silk on
both sides. (Careful, I had to make three.) Apply 5 coats of clear
dope sanding lightly between coats and follow with 2 or 3 coats
of sanding sealer, again sanding between coats for a blemish-free
surface. Two coats of color should then be sufficient to cover the
silk but many more may be added if a superior built-up finish is
desired, keeping in mind that additional coats add weight.
The flying characteristics of a model invariably suffer when
the finish weight is too high. The March-April, 1963 issue of American
Modeler contains an excellent summary of finishing techniques by
Paul Plecan, an expert in the art.
Pilatus Porter Plans (sheet 1)
Pilatus Porter Plans (sheet 2)
The AMA Plans Service offers a full-size
version of many of the plans show here at a very reasonable cost. They will scale the plans any size for you. It is always
best to buy printed plans because my scanner versions often have distortions that can cause parts to fit poorly. Purchasing
plans also help to support the operation of the Academy of Model
Aeronautics - the #1 advocate for model aviation throughout the world. If the AMA no longer has this plan on file, I
will be glad to send you my higher resolution version.
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Posted April 11, 2015