Viper Article & Plans
1973 American Aircraft Modeler Article
visitor Steve G. wrote asking that I post the article for the
Viper R/C pattern ship that appeared in the January 1973 edition
of American Aircraft Modeler. The Viper won the "Best Original Design"
award and the "Most Outstanding Finish" award at the 1972 Toledo
show. Data obtained during research into a scale P-51 Mustang model
contributed heavily to the wing and fuselage design. At least four
versions of the Viper were built by designer Dario Brisighella,
but the first, which won the Toledo trophy, had not yet left the
ground at the time of the article's publication. Viper is a full-house
ship with a laminar flow foam wing, balsa fuselage, retractable
landing gear, and uses a Webra .61 Blackhead.
By Dario Brisighella, Sr.
Photos by Jonn Kozy
Viper won the "Best Original Design" award and the "Most
Outstanding Finish" award at the 1972 Toledo show.
Neat and uncomplicated engine installation. Webra rests
on Kraft-Hayes plastic mount.
Sheeted wing is ready for aileron and wing facing, then
hinging. This unusual airfoil required precision work.
Rather than bend fuselage sides to fit bulkheads under tension,
sides are water and ammonia soaked and laminated for doublers
and bent on this jig. When dry, bend stays in without tension.
Very important to accurate modeling is use of centerlines
throughout. Text describes in detail.
Thick airfoiled stab is balsa sheeting over foam. Note that
like ailerons, elevators are foam cored. This guarantees
Pro-Line retract system is flown in one plane and shown
being installed here. Violett landing gears are also considered
This shows proper lineup of the centerlines and accurate
fuselage side alignment with heavy triangles.
What looks like a canopy is built up of balsa blocks and
triangles. Space inside will house battery packs.
Before carving and sanding, fuselages sure look ugly!
A Viper takes on smooth curves. Fit the engine to aid in
shaping the nose.
Vipers 1 and 3 differ in that the latter model has less
dihedral. Several have been made by very different builders;
all perform the same.
Author with Toledo winnings. Dario still has not flown the
original plane-it is too pretty! The others fly all the
time when Dario is not making helicopters.
At rest on the gear, Viper has that look of ready action.
Note the moveable sub·fin. This is most helpful in wingovers
The 1972 Toledo design and finish winner is a state-of-the-art
pattern ship. Fast, predictable, and smooth even in gusty winds.
It is a model for the expert builder and flier.
"intention," according to Webster's "often applies to little more
than having an idea in mind, or the will to act or do a certain
thing." With this in mind, it would seem that most modelers are
inherently blessed with all manner of "good intentions/ideas." In
most cases, the only catalyst required to convert these intentions
into reality, is simply ample free time applied towards the varied
types and numbers of model subjects in mind for the future.
More often than not, we do complete some of our model-intentions.
Some require the passing of more time than others before completion.
Then there are those which are just passed over due to the advancements
in the State-of-Art, or forgotten over the years. I have dropped
a few intentions along the way, as most of us have. On the other
hand, I have managed to complete some which date back a few years.
Recently, for example, I completed an intention of twelve years-that
of restoring a full-size aircraft. Today I am the very proud owner
of a classic 1947 Stinson-Voyager, N-12-DB (Best Stinson Classic,
1971 EAA Convention). The original intention was easy to come by;
the time for actual restoration was "sumpin' else." The model presented
here, though a new design, is really the completion of another intention
that dates back to 1969.
Ostensibly, Viper began as only
an intention while completing the research covering the North American
P-51 Mustang for an ultra-scale model (another good intention).
As so often one project is shelved in lieu of another, so went the
Mustang. My scale deHavilland Hornet took its place, as did the
Stinson restoration project. The Mustang remains shelved, but that
intention is the prime contributor and factor of this design.
Obtaining the airfoils and sections employed on the Mustang
was a feat in itself. Once accomplished though, these laminar flow
designs really "turned me on." I became intrigued by the rather
unusual curves and reflexes of these high-speed sections. Thus Viper-intention
began. Someday I would experiment with these sections on a non-scale
design, or at least before completing the Mustang.
were many long discussions about this project with other modelers.
Seldom, if ever, were there any encouragements. Many had doubts
and fears. The laminar-flow sections almost became more challenge
Certainly obvious was the fact that a non-scale
design would provide the best test vehicle in the least amount of
time. My next pattern design would begin around these airfoil sections.
Undoubtedly, from the onset, there could be more gained
than lost in the experimentations. If the sections proved to be
"another bag of worms," the test model could always be fitted with
another wing - a small price to pay should it someday save the early
demise of the "still intended Mustang." Needed then was only the
free time to begin. Sound familiar?
Inadvertently, as accidents
occur, three fractured fingers left me with all sorts of time late
in 1971. This period was not what I'd consider "good time," but
I was grounded and idled. So I began the roughest of unnatural,
left-handed sketches for Viper. Now there was time to incorporate
new ideas and methods into those older ones learned through experience.
The only design parameters that can provide the exacting
performance required of our pattern competition models are those
found by the tried and proven methods. This will include many hours
of testing, modifying and testing again. Reynolds Numbers, lift-drag
ratios/coefficients, scale effect, etc., have little effect on RC
as we know it today. Designs based upon these terms generally turn
About the same results can be expected of the
"Averager Design," a phrase coined recently by one well-known RC
editor, in which the averages compiled from some sixty-odd good
models are used in achieving the ultimate in design. However, when
employing average design methods, one should expect an average,
not ultimate, model. Averagers can only lead to averages! Those
items or combinations of items which perform well for one model
seldom, if ever, perform well in combination with another set of
conditions. I am not proposing that all designs begin on a "hit-or-miss"
basis. In the Viper, other than the laminar-flow sections, combinations
known and learned through experience were the only guidelines. Inspired
by the new wing sections, it lead to some newer approaches toward
the overall design. The six available weeks helped, too. The completion
of the drawings and the arrival of New Years Eve, 1972 were simultaneous.
The Toledo Conference was but 56 days off as the first balsa
sheets were cut. Things went along smoothly even though some of
the construction techniques were slightly unorthodox (foam ailerons),
in an effort to maintain alignment and retention of the laminar
sections. This "Toledo-bound" model was first presented, unpainted,
at the January meeting of the Milwaukee Flying Electrons, nine days
after its start. It was not alone - another member also displayed
Viper Number Two the same night. The old doubts and fears were more
in evidence that night than the models themselves.
remaining 47 days before Toledo, 37 passed during the final assembly
and finishing. Five more days passed for the display stand, leaving
four days for some needed arm resting before the long drive to Toledo.
Friday night in the Rec-Hall Viper made its formal debut, as yet,
The model stirred more than just casual interest.
I noticed the apprehensive faces of the onlookers, who were aware
of its distinctive airfoils, knowing it still was earthbound. My
spouse, who was in charge of babysitting my models, began to have
her own doubts of the venture, after overhearing the comments of
Toledo is where it's at! To even "place" there
is more than ample reward for one's efforts when viewing the quality
of craftsmanship on display. If you've not tried it, let me tell
you there are some very tough acts to follow! The awards I received
there for Viper were far above my wildest expectations! I again
extend my all too simple "Thank You" to all the Weak Signal members.
Mother Nature saw fit to prevent any test-flying of Viper
No. Two until April Fool's Day. All of us in attendance braved the
cold winds, sloshed through the still remaining snow, standing water
puddles and sticky mud. It may have been springtime around the country,
but here in Wisconsin one would never have known it. A single but
brief flight ended the doubts and fears concerning the laminar flow
The model displayed some amazing speeds as it
cut through the choppy cold winds, rock-steady! (Something not expected
due to the rather sharp leading edges.) The next question was just
how fast must this thing be flown in order to bring it down in one
piece? The new Black-Head decided to quit when the question cleared
my mind; the position the model was in at the time could never have
been more dangerous. To make the open part of the field would require
a very tight turn as the model's altitude was less than 20 ft. Even
the tight turn and stretched-out glide required for the landing
proved to be no problem whatsoever, as Viper settled at a snail's
pace. Only one flight, and everything learned added up to the black
side of the ledger! Speedy, rock-stable, good penetration, ample
response in the ailerons with no indication of any tip stalling
tendencies at ultraslow speeds - some display for one flight! As
we left the field, the doubts left too.
continued throughout the following weeks; the weather improved slightly.
With most any new design not all its characteristics are going to
be on the plus side. Viper's only undesirable trait proved to be
a slight rolling tendency when yaw control (rudder) was applied.
The balance of its performance left little, or nothing, to be desired
in pattern maneuvers. Modifications were made on the field to the
fin-rudder combination, with little effect. There were of course
many comments as to the cause - most cited the airfoil, naturally.
I was convinced the cause lay elsewhere, and
was willing to modify or try anything, but not the wing sections!
The wing, I felt, offered the superior performance in pattern work
- too much to give up! In further evaluation flights I concluded
the problem lay in the wing dihedral angle. Another model was near
completion at this time, and was modified with less angle. In a
week testing began again with Viper No. Three and the problem ended.
No. Two was then modified and confirmed the results, even though
it still wore the modified fin/rudder combination. These models
were soon joined by Viper No. Four built by yet another flier. The
original Viper No. One (shown at Toledo) awaits this modification
before it leaves the ground - another intention?
flying and competition have done much to really prove the design.
We who have flown the Viper are convinced that the laminar
sections do make great difference over the more conventional sections.
I claim no knowledge of exactly how these sections join in making
Viper the speed demon it is and yet give it the super-stability
it has in slow flight. Nor can I explain how it can be so docile
and predictable in any maneuver, in most any wind conditions (It
is well suited in choppy crosswinds.)
I have designed and
flown a few models over the years, but I feel none can begin to
compare with Viper's performance. It just must be experienced to
be appreciated! The laminar flow wing design does make the difference.
A word of caution, however, is in order. Viper requires a little
extra space and time in which to burn off some of its speed, so
give it a little room. Don't expect it to slow in an instant for
those short-field landings.
Rather than bore you or challenge
your abilities with pages of construction details, I'll only touch
on the subject and pass on a few ideas I use which can be employed
on any other model as well. When cutting out the various formers,
doublers, fuselage sides, etc., try cutting the templates and, with
Sanford's Rubber Cement, cementing directly to the required materials,
thereby eliminating the chance of error found in transposition.
You can save the original plans by tracing off the various templates
onto tracing paper first and cementing these tracings onto the materials.
Don't forget the all-important centerlines too!
the subject of centerlines, here's a little trick I use. While the
paper template is cemented on the work piece, I drill a 1/16" hole
through the piece, directly on the centerlines, this way when the
template is removed I can locate and scribe the centerlines on both
sides of the workpiece with accuracy. In the case of fuselage sides
top blocks, etc., even after final shaping and sanding, the centerlines
can always be located and rescribed for final alignment and reference.
The small holes can be easily filled just before the final finish.
Preforming the required curve of the fuselage sides
is a simple task if done while cementing the doublers in place in
the laminating process. (See the small sketch on the plans.) The
sides are actually over-bent in this case at the start, but when
the pressure is released, you'll find the finished curve is just
right. The drawings do not show the top-view of the fuselage but
this should offer no challenge to those who prefer to build over
a drawing. Checking the various cross-sections, you'll find the
actual fuselage sides are flat, parallel to each other, across the
wing-saddle section to a point mid-way, the fuel tank area. Oh,
yes. You'll have to buy the little woman a bottle of hand lotion
if you want a fuel tank.
Build the canopy as a complete
component, including the triangular stock reinforcements before
cementing to the fuselage itself. Any model will fly only as true
as it has been built, so watch those centerlines!
looked at the drawings at all, you'll be aware that the ailerons
and the elevators are actually part of the original foam cores.
These make the job a lot easier than it looks. Simply sheet the
cores, add and shape the leading and trailing edges, remove the
narrow section indicated for the 1/4" spar, which in turn becomes
one of the hinge edges. Remove another 1/4" for the other hinge
edge of the control surfaces involved and the task is complete.
Use the "female" section of the core blocks to retain alignment
and don't forget the centerlines! You can save the messy job of
cementing the wire horns later by inserting the small section of
matching brass tubing into the control surfaces during construction.
When assembling the wire horns, simply slip into place without the
epoxy messing up your finish. I have made no attempt to shape the
ailerons of balsawood, as the shapes involved are too complex. This
is how the foam control surfaces came about. I find this method
faster and more accurate than any other method, too. Keep the centerline
hole idea in mind for the hinge line spars - they do help!
When the model is complete and all the equipment is in place,
be sure to balance the model along both its longitudinal and lateral
axis, don't forget the muffler if you use one. A few regular nails
pushed into the left-hand wing panels will overcome the side-mounted
engine. The CG as noted on the plans is only my preferred location,
and can be used as a starting point for locating your own preference.
The originals have been tested with the CG located up to one in.
forward and one in. aft of the position shown with no ill effects,
though it is more docile when placed as indicated.
you are looking to me for that all-perfect, award-winning finish
in three easy steps, forget it! There is just no easy way! How many
others have written about sanding, sanding, and more sanding? To
this I can only add: rubbing, rubbing and still even more rubbing!
The Toledo model is finished in that "old standby," dope over two
coats of laminating resin. This included approximately 50 sheets
of assorted wet and dry sandpaper, ten coats of white dope as a
base, ten coats of each color of the paint scheme, followed by still
another ten coats of clear dope over "The Whole Thing." Between
every coat of dope was a lot of wet sanding with 600 grit, then
before applying the next coat, the surface was wiped dry with DuPont
Prep-Sol to remove any particles of dust, fingerprints, etc.
When you get this far, the model should look great, now the
work really begins. That's right, now starts the rubbing, rubbing,
and more rubbing! What I look for in a finish is not the shine,
but rather the luster, and the only way to this luster is in the
buffing or rubbing process. In my own estimation, most all epoxy-type
finishes impart only a shine; real luster comes only from lacquer-based
paints. A really great finish is made up of millions of microscopic
scratches, reflecting the available light.
The more minute
these scratches are, the greater the visible luster. The actual
grit of the buffing compound used in the final rubbing is therefore
very important. This grit must be quite fine, and like wet-sanding,
the more water used, the better the results. As in the sanding process,
when you think you have it done to perfection, take a break, look
at it again, and start over or at least continue.
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 September 23, 2013