Diva - 2005/02

GWS A-10 Warthog
18 MODEL AVIATION
Use of curved trim adjacent to straight lines on wing gives
illusion of elliptical planform. Phil looks justifiably proud!
by Phil Granderson
IN 1980 I was fortunate to compete in the Control Line World
Championships in Poland. As a member of the Combat team, I
captured the Bronze Medal for the USA.
The CL Precision Aerobatics (Stunt) contingent was the
“Dream Team” of Bob Hunt, Les McDonald, Bill Werwage, and
Wynn Paul. Bob was the defending World Champion, Les is a
three-time World Champion, and Bill is a three-time World
Champion and the first American to win a World Championships.
Those guys were there to win. And they did! Les, Bob, and Bill
took the Gold, Silver, and Bronze medals in that order.
There was a wealth of knowledge in just watching them and
learning. Today two of them are still fierce competitors and good
friends. Although Les McDonald is no longer competing, he left a
wealth of knowledge with his Stiletto series of aircraft.
I remember thinking, “As soon as I win a Combat World
Championships, I’ll switch hats and become a Stunt World
Champion.” How hard could it be? Now that you’re laughing,
let’s get to work.
Stylish, elegant CL
Stunter designed with
original thinking
@@Web Extra
February 2005 19
The entire model is covered with .2-ounce carbon mat, applied with modeling dope.
When fully cured, the carbon makes the airframe incredibly stiff.
The Diva in the foreground features a built-up Lost Foam wing, and the one in the
background was built using a foam-core wing. Both fly extremely well!
The Diva sits low and has great ground-handling qualities. An outstanding blend of
aesthetic features gives this aircraft an original flair.
Photos by Roger Grotheer
Many people are looking for simplicity in a
complex world. That was exactly my
thinking when I began the Diva odyssey six
years ago; just build a distinctive box
around a proven formula. After exploring
and observing a variety of proven formulas,
it became apparent that this approach simply
would not produce the airplane I envisioned.
So what is Diva? It is the culmination of
a few ideas and experiments that worked
well and the exclusion of many ideas and
experiments that either did not work at all or
worked poorly. It is an original work.
From the high cheek cowls, to the
canopy, to the rudder, it is different. Top,
front, and side views reveal that it is unique.
The thinking and application of power is
different. The airfoil is original.
You might ask the question, Why
reinvent the wheel? That was never my
intention, but if you look closely you will
see that the wheel was tweaked in some
unique ways.
Beginning in the late 1960s, there were
experiments with extremely long tail
moments, gapless hinge lines, variations on
rudder offset, engine side thrust and
downthrust, numerous airfoils, and far too
many ideas and experiments with engines.
Through all of that, somehow I still have old
sketches, templates, and garbled notes
tucked away in boxes and files that have
been moved countless times.
In November 1998 construction began
on the first Diva. Rather than wading into
the whole thing blindly, I applied a process
that had proved successful for me and
countless others. It was simply to formulate
a plan, make modifications when and where
required, but, most important, never lose
sight of the original goal. This had worked
quite nicely in my Combat endeavors and in
business. So here’s the plan.
First, set a goal. You’ve probably heard
the question, How will you get there if you
don’t know where you’re going? The goal
was to design and refine a world-class CL
Aerobatics airplane. The model would
someday win a World Championships—
preferably with me as the pilot. Today I’m
much closer and having so much fun that
the only slightly painful chore so far is
writing this article; I’d rather be building or
flying!
The first Diva was promptly renamed
“Ante” when my wife Kathleen made the
observation that the paint scheme I planned
did not look like a Diva. Ante was the first
airplane to emerge from my clean-slate
approach to design. Its maiden flight was
eight months after I cut the first piece of
wood.
This was the watershed project. I was
going for the whole package: distinctive
looks, front-row finish, piped engine, and
world-class performance. The results fell
somewhat short of the goal.
A summary of the results was that the
finishing system worked well and was
relatively easy to apply. Ante was a frontrow
airplane. The piped PA .65 engine
performed well. The wing with the unique
tra
20 MODEL AVIATION
A close-up shows the wraparound header that is available from Aero Products to fit the
Magnum .36. The company also handles the carbon pipe for that engine.
Phil has developed a method of using a computer to design his complete trim scheme.
This allows an infinite amount of adjusting and brainstorming.
airfoil that was developed and implemented
on the Triumph model built in 1969 worked
exactly as I remembered it, generating a great
deal of lift with no real side effects.
There were also some primary things that
didn’t work. I was completely baffled about
why the tried-and-true combination of long
tail moment and relatively small stabilizer/
elevator size suddenly didn’t work as it did
on so many of my previous designs. The
Ante had no problem turning, but it was
difficult once the turn started to get it
stopped. I also noticed that it required more
force on the handle to turn outside.
The design had an assortment of inherent
problems that could not be corrected by
adjusting, tweaking, and trimming. And
finally, the line tension was way beyond my
tolerance level.
I knew after roughly 20 flights with this
airplane that the next model would have
major modifications. Ante was left in its “best
flight condition” and would serve as a
measurement for changes and improvements
to subsequent airplanes. To this day, it is still
the control for all my experiments.
The second airplane—appropriately
painted and approved for the name Diva—
had four significant changes: equal-span
panels, less wing area, the elevator and
stabilizer were moved down closer to the
thrustline, and the stabilizer/elevator area was
increased to 26% of the wing area.
There were other changes too. The tail
moment was shortened 1⁄2 inch to compensate
for the larger stabilizer’s additional weight.
The wingtip shape was changed slightly. The
flap area was reduced by 5%, and the fueltank
compartment was expanded to allow the
tank to be moved backward and forward an
additional 2 inches. I also took much more
care in the alignment and setup of the entire
airplane.
Ultimately I installed the faithful PA .65.
It was apparent from the first flights that
these changes made significant
improvements in the overall performance.
The whole package seemed to come together.
Most noticeable was the marked
improvement in tracking. There was no more
hunting, and the overturning problem was
completely gone. Additionally, control
pressure for outside and inside maneuvers
was the same. Line tension was reduced
slightly.
The Diva’s finish was even slicker and
shinier than the one applied to the Ante. The
horizontally adjustable tank proved to be
golden for finding the perfect CG. I could
move the CG aft or forward by 1 inch
without adding weight.
Another bonus from the tank arrangement
was that the CG did not shift as much from
the beginning of the flight to the end. This
was indeed a marked improvement over
Ante. Flight scores immediately rose and
were continuing to improve. It even captured
my first Concours d’Elegance award.
I was just beginning to appreciate and
enjoy the fruits of my labor when disaster
struck. In what could only be called the
dumbest thing I’ve ever done, my brain died
and I hooked up the handle upside down and
never did a preflight check! It’s been said that
few people have ever saved an airplane from
crashing with the controls reversed. I was not
one of the few!
The Diva’s 36th flight is now
memorialized by its unique dent in the
blacktop at Whittier Narrows in Southern
California. I still chuckle when I visualize
Keith Trostle chasing it around the circle as
the nose was firmly planted and the PA .65
chewing up the carbon propeller just before
performing its brief fatal maneuver. No one
ever imagined Keith could move that fast!
Within minutes of the disaster, the
model’s remains were loaded into the van
and I started the six-hour drive home. I spent
the first three hours of the drive chewing
myself out and the next three planning my
recovery.
I arrived home at 4:24 p.m., unloaded the
van, got a sandwich, and began cutting balsa.
By 7 p.m., I had the fuselage sides cut and the
doublers clamped and laminated.
Construction of “Diva 2 Quick”
February 2005 21
Phil notches the wing LE to allow for more tank-compartment
room. This also puts the fuel’s weight closer to the model’s CG.
How is this for an inspirational photo? All components are built
and ready to assemble. Note the extremely clean workmanship.
Type: CL Aerobatics
Wingspan: 58 inches
Engine: .36-.65
Flying weight: 50-62 ounces
Construction: Balsa and plywood
Covering/finish: .2-ounce carbon mat, light-grade silkspan
and modeling dope, clear automotive topcoat
progressed at breakneck speed. It was ready
for the maiden flight August 28—just seven
weeks after cutting the first piece of wood.
There were no big changes from its
predecessor. I did make the stabilizer slightly
bigger and added ribs to make it lighter. I
lengthened the tail back to the original 21
inches used on the Ante. I also used thinner
balsa for the rudder (3⁄16) and left it flat. It
flew virtually the same as its forerunner and
was easier to trim.
By all accounts and observations,
everything worked very well. The model
looked good, it flew really well, I looked
comfortable flying it, and flight scores were
on the rise again. It was fairly easy to
“practice myself” into this airplane, but I
wanted an airplane to practice with rather
than one to practice for.
Wow, the truth can hurt! I had invested
serious time, effort, wood, and money in
creating a great airplane, and I wasn’t happy.
What would I have rather been flying? How
about an airplane that was as positive as the
Diva and as refined and nimble as a finely
tuned Classic aircraft? As I sat in my shop,
the Classic models began talking to me.
“Hey Phil, over here. I’m your Vulcan;
I’ll be nice to you. You can relax; fly me!”
“Me too! I’m your Lark; ditto what the
Vulcan said.”
The task was clear: tame and refine the
60-size airplane’s edginess and brute force. I
would have to break the mold that I
painstakingly crafted in the first three
airplanes. I would have to redesign, reengineer,
and reinvent a major portion of an
excellent airplane.
Was there a smaller, lighter engine that
would make the right kind and amount of
power? What size should the new Diva be to
score well when big airplanes generally score
better? It was impractical to simply downsize
Diva by a specific percentage.
The toughest task would be to find a
readily available engine with the right kind
and amount of power. It would also have to
Wood Weights and Measures
Thickness Length (inches) Weight (grams) Length Weight (grams)
1/16 3 x 36 8-11 4 x 36 11-14
3/32 3 x 36 12-16 4 x 36 17-21
1/8 3 x 36 18-21 4 x 36 21-28
3/16 3 x 36 24-30 4 x 36 32-43
1/4 3 x 36 32-42 4 x 36 43-57
3/8 3 x 36 48-63 4 x 36 63-83
1/2 3 x 36 62-85 4 x 36 81-110
1/16 3 x 48 11-14 4 x 48 15-18
3/32 3 x 48 17-21 4 x 48 23-28
1/8 3 x 48 21-28 4 x 48 28-37
3/16 3 x 48 33-40 4 x 48 44-56
1/4 3 x 48 44-57 4 x 48 56-75
3/8 3 x 48 63-85 4 x 48 84-112
1/2 3 x 48 86-112 4 x 48 114-150
be light and manufactured to consistently high
standards. If such an engine could be found
and possessed good Stunt fundamentals, I was
confident in my ability to identify and make
modifications if necessary.
Believing that most modern 40-size
engines had plenty of power, the quest began
to find the best one for the refined Diva. I
started collecting every 25- to 40-size engine I
could find. Since I had conducted no tests, my
only requirement was that it could not weigh
more than 91⁄2 ounces.
In December 2001 I began testing and
evaluating eight engines. In the end, the
Magnum .36 was clearly the top contender. It
weighed only 81⁄4 ounces and easily turned an
11-inch propeller more than 11,000 rpm. The
next step was to install a pipe and put the
engine in a model to see if the power could be
controlled.
The only airplane I was willing to sacrifice
with all the modifications necessary was my
15-year-old Et al, which had a 21-inch tail
moment, 600 square inches of wing area, and
weighed 54 ounces with the engine and pipe
installed and ready to fly.
The first 20 flights were interesting in that
most were spent finding the right pipe and
length. I used a Bolly 12 x 4 narrow-blade
propeller cut to 11 inches.
My suspicions about usable power were
confirmed. There was definitely a great deal
of power, and it seemed quite usable. Most of
those flights were with the engine not running
“on the pipe” and revealed a flat power curve
and the smooth delivery of more power
exactly when and where it was necessary.
At this point the pipe was just a muffler.
The engine was happy being launched at a
soft two-cycle and would break into a
controlled faster speed the moment the nose
was pointed up and then back into its soft
phase as soon as the model returned to level.
There was also no tendency to wind up or
charge at any point. It seemed to “come on” in
all the right places.
The first flight with the pipe in the range
(on the pipe) produced a noticeably stronger
feel everywhere in the pattern, and lap times
went from 5.0 to 5.4. When the needle was
turned in slightly to get to 5.2 lap times, the
engine and airplane were ecstatic, and I
couldn’t keep myself from joining in the
celebration by pushing that old model to
previously unobtainable performance levels.
Since I felt comfortable with the engine, I
was able to turn my focus to the new aircraft.
It would have to be smaller and lighter but
still have that “big airplane” presence.
Deciding that it would probably be a series of
design modifications, I decided to build the
first version only slightly smaller than the
previous .65-powered Divas.
The Ante has 750 square inches of wing
area, and the two larger Divas have 710-
square-inch wings. The wing area presented
here is only 4% less; in fact, there is as much
as in most modern .60-powered models that
are flown today. The tail moment is 18.5
inches, which is slightly longer than most
other airplanes. The fuselage is massive. The
elevator/stabilizer area is medium to small
compared to many models’.
After the first flight, it was apparent that
Diva IV was something special. My good
friend Jim Aron remarked candidly, “I’ve
seen the first flights of your previous
airplanes, and this is the first time I’ve ever
seen you smile!”
To date, there are two smaller Divas, each
weighing 57 ounces. One has a foam-core
wing with balsa sheeting, and the other uses
the Lost Foam Wing Building System
construction shown on the plans.
As an experiment, I used stick-on weights
to increase the overall weight to 64 ounces,
just to see what would happen. The only
noticeable difference was more line tension.
There was still plenty of power, and the Diva
didn’t hesitate anywhere in the pattern.
In general, the two primary components of
any design are aerodynamics and power
dynamics. Aerodynamics is the science of
solid bodies moving through air. Diva was
designed for competition from the beginning.
It is an aerodynamic package that produces a
stable solution for a set of complex and
complicated variables.
Provisions have been made and tested that
allow for the variety of adjustments necessary
to bring the entire package into your personal
comfort zone without adversely affecting
visual presentation or limiting flight
performance.
In our world, power dynamics consists of
two primary components. For our purpose, the
engine is a simple pump that converts fuel to
energy and directs the energy to a specific
output. Integral to this pump is a simple
transmission system. It comprises the
propeller and an adjustable exhaust timing
device (tuned pipe).
The propeller acts as a gear and a final
power converter. The pipe regulates the
time, delivery, and consistency of power. It
is a static throttle of sorts. The whole system
is actually quite primitive because its
components are overtly static, but it is
elegant in its simplicity. When properly
installed and adjusted, it delivers consistent,
reliable, usable power.
So if that’s all there is, why is it so
difficult to get everything working the way
you want?
How you attack a problem is the key.
When you are on the flightline, how things
work is far more important than why they
work. These two factors should not be
interchangeable, although frequently they
are.
When you ask the question “How does it
work?” the answer should be “good” or
“bad.” These answers ultimately quantify
results because if you are honest, they
confirm or deny the need for change.
When you ask “Why does it work?” the
quest for an answer suddenly becomes
complex. Ask those questions and see for
yourself. An analogy would be that you
don’t have to know why a television works
to be satisfied with how it works. This
translates to our sport quite nicely. Ask how
and make progress; ask why and ponder.
The preceding is not intended to be a
brainteaser, but rather a systematic approach
to problem solving and a foundation for
performance building and enhancement.
Before beginning construction, let’s look at
the whole package. In the past six years of
concentrated building and developing the
Diva, I have come to understand and
separate much fact from fiction. This
process is not too different from my
experiences in competitive Combat flying
and business. Following are some facts I
have learned.
• A good contest-caliber finish adds 7-10
ounces from bare wood.
• A light finish cannot save a heavy airplane.
• Good wood is 4-6 pounds per cubic foot. It
is rare to find good wood that weighs less
than 4.5 pounds, and, for our purposes, it
should never exceed 6 pounds stock.
• In an aerodynamically well-designed
airplane, weight distribution is far more
important than weight conservation.
• The three most significant trim
adjustments are CG, propeller, and control
system. You can only use as much power as
you need. Excess power will probably find a
way to work against you.
Look closely at the plans and you will
see some things that are out of the norm.
These differences are what make the whole
package work. Everything on the plans is
there for a reason.
The majority of details relate to function.
If you build the airplane per the plans—at a
finished weight of 62 ounces or less—and
build it accurately and straight, you will be
pleased. Actually, the only frill is the little
faux air scoop on the bottom of the cowl.
Following are details of note.
• The fuselage gets wider at the midpoint
and remains fairly wide where the stabilizer
is mounted.
• The tank compartment is slightly wider
than most, at 23⁄32 inches.
• The wing LE at the root inside the fuselage
has a recessed cavity for tank adjustment.
• Cheek cowls terminate on the wing top at
the high point of the root airfoil.
• The fuselage is deep at the dorsal fin. The
rudder is 1⁄8 balsa.
• There is 3° of permanent rudder offset.
• There is no engine offset.
• The airfoil is completely different at the
root than at the tip.
• The wing panels have equal spans.
• The outboard flap is 1⁄4 inch longer than
the inboard flap.
• The control system is completely adjustable.
• There is a large air inlet in the cowl.
• The air outlet in the fuselage around the pipe
is roughly three times that of the cowl inlet.
• Control horns are made from 3⁄32-inchdiameter
wire.
Construction is probably not for a
beginner, but an accomplished Advanced
competitor or builder should have no
problems. Diva makes extensive use of
molded-balsa components. The cheek cowls,
aft fuselage top block, bottom fuselage block,
most of the cowl, and LE sheeting are molded
balsa.
Having built several wings using the Lost
Foam Wing Building System, I do not hesitate
to recommend it. The Diva IV has a
traditional foam-core, balsa-sheeted wing that
performs equal to the built-up wing.
The entire model is covered with .02-
ounce carbon veil before finishing. In a builtup
wing, cover the entire structure—including
open bays and rib capstrips—with the veil and
cut the openings before final covering. See the
photo. Final wing covering of open bays is
done with silkspan.
Wood selection is crucial for strength and
weight. Today, grain type is less critical with
the use of carbon veil before the final finish.
The accompanying wood-weight chart refers
to common balsa lengths and thicknesses, but
the plans call for extensive use of .077-inchthick
wood. The weights for 1⁄16 wood in the
chart should be close to those for the .077
wood.
Most of the custom-cut, contest-gradewood
suppliers will cut the thicker wood
when requested. As a general rule, it is
preferable for thicker pieces to bias to the
lighter side of the chart. You will also find
exceptional wood that is actually lighter and
obviously usable. The chart is only a gauge.
My favorite method of building is to
complete entire components. I finish the wing
with controls installed and tips and flaps
shaped and fitted. Hinge slots and hinges are
fitted.
I complete the fuselage with the cowl and
front hold downs installed and all top blocks
and 1⁄32-inch cross-grain sheeting on the
bottom permanently glued, leaving only the
opening for the wing. This is critical for final
assembly because the fuselage can twist if
it’s not stabilized by permanent installation
of major components.
The landing-gear mount and rear cowl
hold down are integrated and can only be
installed after the wing is permanently glued
in. The elevator/stabilizer assembly is
completely built, with all hinges aligned and
test fitted. The control horn is permanently
attached to the stabilizer. The rudder is
completed with the dorsal fin. See the photos
for final-assembly clarification.
Volumes have been written about
construction methods. If you want to know
more about two-stroke engines, Larry
Scarinzi’s “Blitz” article from the mid-1960s
is a must read. Bob Gaildini’s “Olympic”
article from 1963 is the definitive work for
CL Stunt aircraft-design considerations.
Robin’s View Productions, Windy
Urtnowski, and a host of other sources have
produced videotapes chronicling everything
from wood selection to finishing to installing
tail wheels. Get your hands on as much
information as you can and digest it. Your
building will improve measurably and
quickly as you gain knowledge.
As with any successful venture, countless
people have made contributions. My
grandmother helped me with words as I
struggled to read model-airplane magazines
when I was 7 years old. My mother was my
lone defender when the house was filled with
modeling-dope fumes and the rest of the
family voted to disown me.
Mrs. Norton, who owned the local hobby
shop, extended credit to me at the age of 16
and introduced me to Ed Southwick and
Dick McCoy. This publication’s
aeromodeling editor has been a great friend
for the past 30 years, and with him I have
debated and shared thoughts on almost
everything.
I must mention Brett Buck; in my humble
opinion, he is the ultimate guru when it
comes to trimming and adjusting just about
anything on a Stunt model. There is also Jim
Aron—one of very few who could ask for
and actually get a piece of my best wood.
And I can’t leave out Ted Fancher and Dave
Fitzgerald, who are my protagonists.
I hope you’ve enjoyed the preceding and
found it informative. As you persist in your
quest for the perfect Stunt pattern, I leave
you with one simple thought: rely on the fact
that something is working to validate the
fact that it does work. MA
Phil Granderson
13250 Campus Dr.
Oakland CA 94619
(Editor’s note: We have chosen a
portion of Phil’s “Diva” article to be the
subject of our new online feature that we
call MA “Web Extra.”
As he explained, Phil designed his Diva
with a specific engine size and type in mind.
Moreover, he used a carbon-fiber tuned pipe
to augment the engine’s power and to contour
its power output to a specific rpm band. This
is an interesting subject, and not much is
written about how it works or the practical
specifics of how to properly set up and adjust
a piped system.
Whether you intend to build the Diva or
not, this online material is interesting and
educational. Give it a look; go to
www.modelaircraft.org and then to the
MA Web Extra section.)
Sources:
Lost Foam Wing Building Systems, fully
assembled Lost Foam wings, Lost Foam
video sets, building videos, foam wing cores,
covered foam wings:
Robin’s View Productions
Box 68
Stockertown PA 18083
(610) 746-0106
Building videos:
Windy Urtnowski
93 Elliott Pl.
Rutherford NJ 07070
(201) 896-8740
Magnum .36 engines, side-to-rear exhaust
manifolds, carbon-fiber AeroPipes—tuned
pipes:
Aero Products
980 Winnbrook Dr.
Dacula GA 30019
(678) 407-9376

GWS A-10 Warthog
18 MODEL AVIATION
Use of curved trim adjacent to straight lines on wing gives
illusion of elliptical planform. Phil looks justifiably proud!
by Phil Granderson
IN 1980 I was fortunate to compete in the Control Line World
Championships in Poland. As a member of the Combat team, I
captured the Bronze Medal for the USA.
The CL Precision Aerobatics (Stunt) contingent was the
“Dream Team” of Bob Hunt, Les McDonald, Bill Werwage, and
Wynn Paul. Bob was the defending World Champion, Les is a
three-time World Champion, and Bill is a three-time World
Champion and the first American to win a World Championships.
Those guys were there to win. And they did! Les, Bob, and Bill
took the Gold, Silver, and Bronze medals in that order.
There was a wealth of knowledge in just watching them and
learning. Today two of them are still fierce competitors and good
friends. Although Les McDonald is no longer competing, he left a
wealth of knowledge with his Stiletto series of aircraft.
I remember thinking, “As soon as I win a Combat World
Championships, I’ll switch hats and become a Stunt World
Champion.” How hard could it be? Now that you’re laughing,
let’s get to work.
Stylish, elegant CL
Stunter designed with
original thinking
@@Web Extra
February 2005 19
The entire model is covered with .2-ounce carbon mat, applied with modeling dope.
When fully cured, the carbon makes the airframe incredibly stiff.
The Diva in the foreground features a built-up Lost Foam wing, and the one in the
background was built using a foam-core wing. Both fly extremely well!
The Diva sits low and has great ground-handling qualities. An outstanding blend of
aesthetic features gives this aircraft an original flair.
Photos by Roger Grotheer
Many people are looking for simplicity in a
complex world. That was exactly my
thinking when I began the Diva odyssey six
years ago; just build a distinctive box
around a proven formula. After exploring
and observing a variety of proven formulas,
it became apparent that this approach simply
would not produce the airplane I envisioned.
So what is Diva? It is the culmination of
a few ideas and experiments that worked
well and the exclusion of many ideas and
experiments that either did not work at all or
worked poorly. It is an original work.
From the high cheek cowls, to the
canopy, to the rudder, it is different. Top,
front, and side views reveal that it is unique.
The thinking and application of power is
different. The airfoil is original.
You might ask the question, Why
reinvent the wheel? That was never my
intention, but if you look closely you will
see that the wheel was tweaked in some
unique ways.
Beginning in the late 1960s, there were
experiments with extremely long tail
moments, gapless hinge lines, variations on
rudder offset, engine side thrust and
downthrust, numerous airfoils, and far too
many ideas and experiments with engines.
Through all of that, somehow I still have old
sketches, templates, and garbled notes
tucked away in boxes and files that have
been moved countless times.
In November 1998 construction began
on the first Diva. Rather than wading into
the whole thing blindly, I applied a process
that had proved successful for me and
countless others. It was simply to formulate
a plan, make modifications when and where
required, but, most important, never lose
sight of the original goal. This had worked
quite nicely in my Combat endeavors and in
business. So here’s the plan.
First, set a goal. You’ve probably heard
the question, How will you get there if you
don’t know where you’re going? The goal
was to design and refine a world-class CL
Aerobatics airplane. The model would
someday win a World Championships—
preferably with me as the pilot. Today I’m
much closer and having so much fun that
the only slightly painful chore so far is
writing this article; I’d rather be building or
flying!
The first Diva was promptly renamed
“Ante” when my wife Kathleen made the
observation that the paint scheme I planned
did not look like a Diva. Ante was the first
airplane to emerge from my clean-slate
approach to design. Its maiden flight was
eight months after I cut the first piece of
wood.
This was the watershed project. I was
going for the whole package: distinctive
looks, front-row finish, piped engine, and
world-class performance. The results fell
somewhat short of the goal.
A summary of the results was that the
finishing system worked well and was
relatively easy to apply. Ante was a frontrow
airplane. The piped PA .65 engine
performed well. The wing with the unique
tra
20 MODEL AVIATION
A close-up shows the wraparound header that is available from Aero Products to fit the
Magnum .36. The company also handles the carbon pipe for that engine.
Phil has developed a method of using a computer to design his complete trim scheme.
This allows an infinite amount of adjusting and brainstorming.
airfoil that was developed and implemented
on the Triumph model built in 1969 worked
exactly as I remembered it, generating a great
deal of lift with no real side effects.
There were also some primary things that
didn’t work. I was completely baffled about
why the tried-and-true combination of long
tail moment and relatively small stabilizer/
elevator size suddenly didn’t work as it did
on so many of my previous designs. The
Ante had no problem turning, but it was
difficult once the turn started to get it
stopped. I also noticed that it required more
force on the handle to turn outside.
The design had an assortment of inherent
problems that could not be corrected by
adjusting, tweaking, and trimming. And
finally, the line tension was way beyond my
tolerance level.
I knew after roughly 20 flights with this
airplane that the next model would have
major modifications. Ante was left in its “best
flight condition” and would serve as a
measurement for changes and improvements
to subsequent airplanes. To this day, it is still
the control for all my experiments.
The second airplane—appropriately
painted and approved for the name Diva—
had four significant changes: equal-span
panels, less wing area, the elevator and
stabilizer were moved down closer to the
thrustline, and the stabilizer/elevator area was
increased to 26% of the wing area.
There were other changes too. The tail
moment was shortened 1⁄2 inch to compensate
for the larger stabilizer’s additional weight.
The wingtip shape was changed slightly. The
flap area was reduced by 5%, and the fueltank
compartment was expanded to allow the
tank to be moved backward and forward an
additional 2 inches. I also took much more
care in the alignment and setup of the entire
airplane.
Ultimately I installed the faithful PA .65.
It was apparent from the first flights that
these changes made significant
improvements in the overall performance.
The whole package seemed to come together.
Most noticeable was the marked
improvement in tracking. There was no more
hunting, and the overturning problem was
completely gone. Additionally, control
pressure for outside and inside maneuvers
was the same. Line tension was reduced
slightly.
The Diva’s finish was even slicker and
shinier than the one applied to the Ante. The
horizontally adjustable tank proved to be
golden for finding the perfect CG. I could
move the CG aft or forward by 1 inch
without adding weight.
Another bonus from the tank arrangement
was that the CG did not shift as much from
the beginning of the flight to the end. This
was indeed a marked improvement over
Ante. Flight scores immediately rose and
were continuing to improve. It even captured
my first Concours d’Elegance award.
I was just beginning to appreciate and
enjoy the fruits of my labor when disaster
struck. In what could only be called the
dumbest thing I’ve ever done, my brain died
and I hooked up the handle upside down and
never did a preflight check! It’s been said that
few people have ever saved an airplane from
crashing with the controls reversed. I was not
one of the few!
The Diva’s 36th flight is now
memorialized by its unique dent in the
blacktop at Whittier Narrows in Southern
California. I still chuckle when I visualize
Keith Trostle chasing it around the circle as
the nose was firmly planted and the PA .65
chewing up the carbon propeller just before
performing its brief fatal maneuver. No one
ever imagined Keith could move that fast!
Within minutes of the disaster, the
model’s remains were loaded into the van
and I started the six-hour drive home. I spent
the first three hours of the drive chewing
myself out and the next three planning my
recovery.
I arrived home at 4:24 p.m., unloaded the
van, got a sandwich, and began cutting balsa.
By 7 p.m., I had the fuselage sides cut and the
doublers clamped and laminated.
Construction of “Diva 2 Quick”
February 2005 21
Phil notches the wing LE to allow for more tank-compartment
room. This also puts the fuel’s weight closer to the model’s CG.
How is this for an inspirational photo? All components are built
and ready to assemble. Note the extremely clean workmanship.
Type: CL Aerobatics
Wingspan: 58 inches
Engine: .36-.65
Flying weight: 50-62 ounces
Construction: Balsa and plywood
Covering/finish: .2-ounce carbon mat, light-grade silkspan
and modeling dope, clear automotive topcoat
progressed at breakneck speed. It was ready
for the maiden flight August 28—just seven
weeks after cutting the first piece of wood.
There were no big changes from its
predecessor. I did make the stabilizer slightly
bigger and added ribs to make it lighter. I
lengthened the tail back to the original 21
inches used on the Ante. I also used thinner
balsa for the rudder (3⁄16) and left it flat. It
flew virtually the same as its forerunner and
was easier to trim.
By all accounts and observations,
everything worked very well. The model
looked good, it flew really well, I looked
comfortable flying it, and flight scores were
on the rise again. It was fairly easy to
“practice myself” into this airplane, but I
wanted an airplane to practice with rather
than one to practice for.
Wow, the truth can hurt! I had invested
serious time, effort, wood, and money in
creating a great airplane, and I wasn’t happy.
What would I have rather been flying? How
about an airplane that was as positive as the
Diva and as refined and nimble as a finely
tuned Classic aircraft? As I sat in my shop,
the Classic models began talking to me.
“Hey Phil, over here. I’m your Vulcan;
I’ll be nice to you. You can relax; fly me!”
“Me too! I’m your Lark; ditto what the
Vulcan said.”
The task was clear: tame and refine the
60-size airplane’s edginess and brute force. I
would have to break the mold that I
painstakingly crafted in the first three
airplanes. I would have to redesign, reengineer,
and reinvent a major portion of an
excellent airplane.
Was there a smaller, lighter engine that
would make the right kind and amount of
power? What size should the new Diva be to
score well when big airplanes generally score
better? It was impractical to simply downsize
Diva by a specific percentage.
The toughest task would be to find a
readily available engine with the right kind
and amount of power. It would also have to
Wood Weights and Measures
Thickness Length (inches) Weight (grams) Length Weight (grams)
1/16 3 x 36 8-11 4 x 36 11-14
3/32 3 x 36 12-16 4 x 36 17-21
1/8 3 x 36 18-21 4 x 36 21-28
3/16 3 x 36 24-30 4 x 36 32-43
1/4 3 x 36 32-42 4 x 36 43-57
3/8 3 x 36 48-63 4 x 36 63-83
1/2 3 x 36 62-85 4 x 36 81-110
1/16 3 x 48 11-14 4 x 48 15-18
3/32 3 x 48 17-21 4 x 48 23-28
1/8 3 x 48 21-28 4 x 48 28-37
3/16 3 x 48 33-40 4 x 48 44-56
1/4 3 x 48 44-57 4 x 48 56-75
3/8 3 x 48 63-85 4 x 48 84-112
1/2 3 x 48 86-112 4 x 48 114-150
be light and manufactured to consistently high
standards. If such an engine could be found
and possessed good Stunt fundamentals, I was
confident in my ability to identify and make
modifications if necessary.
Believing that most modern 40-size
engines had plenty of power, the quest began
to find the best one for the refined Diva. I
started collecting every 25- to 40-size engine I
could find. Since I had conducted no tests, my
only requirement was that it could not weigh
more than 91⁄2 ounces.
In December 2001 I began testing and
evaluating eight engines. In the end, the
Magnum .36 was clearly the top contender. It
weighed only 81⁄4 ounces and easily turned an
11-inch propeller more than 11,000 rpm. The
next step was to install a pipe and put the
engine in a model to see if the power could be
controlled.
The only airplane I was willing to sacrifice
with all the modifications necessary was my
15-year-old Et al, which had a 21-inch tail
moment, 600 square inches of wing area, and
weighed 54 ounces with the engine and pipe
installed and ready to fly.
The first 20 flights were interesting in that
most were spent finding the right pipe and
length. I used a Bolly 12 x 4 narrow-blade
propeller cut to 11 inches.
My suspicions about usable power were
confirmed. There was definitely a great deal
of power, and it seemed quite usable. Most of
those flights were with the engine not running
“on the pipe” and revealed a flat power curve
and the smooth delivery of more power
exactly when and where it was necessary.
At this point the pipe was just a muffler.
The engine was happy being launched at a
soft two-cycle and would break into a
controlled faster speed the moment the nose
was pointed up and then back into its soft
phase as soon as the model returned to level.
There was also no tendency to wind up or
charge at any point. It seemed to “come on” in
all the right places.
The first flight with the pipe in the range
(on the pipe) produced a noticeably stronger
feel everywhere in the pattern, and lap times
went from 5.0 to 5.4. When the needle was
turned in slightly to get to 5.2 lap times, the
engine and airplane were ecstatic, and I
couldn’t keep myself from joining in the
celebration by pushing that old model to
previously unobtainable performance levels.
Since I felt comfortable with the engine, I
was able to turn my focus to the new aircraft.
It would have to be smaller and lighter but
still have that “big airplane” presence.
Deciding that it would probably be a series of
design modifications, I decided to build the
first version only slightly smaller than the
previous .65-powered Divas.
The Ante has 750 square inches of wing
area, and the two larger Divas have 710-
square-inch wings. The wing area presented
here is only 4% less; in fact, there is as much
as in most modern .60-powered models that
are flown today. The tail moment is 18.5
inches, which is slightly longer than most
other airplanes. The fuselage is massive. The
elevator/stabilizer area is medium to small
compared to many models’.
After the first flight, it was apparent that
Diva IV was something special. My good
friend Jim Aron remarked candidly, “I’ve
seen the first flights of your previous
airplanes, and this is the first time I’ve ever
seen you smile!”
To date, there are two smaller Divas, each
weighing 57 ounces. One has a foam-core
wing with balsa sheeting, and the other uses
the Lost Foam Wing Building System
construction shown on the plans.
As an experiment, I used stick-on weights
to increase the overall weight to 64 ounces,
just to see what would happen. The only
noticeable difference was more line tension.
There was still plenty of power, and the Diva
didn’t hesitate anywhere in the pattern.
In general, the two primary components of
any design are aerodynamics and power
dynamics. Aerodynamics is the science of
solid bodies moving through air. Diva was
designed for competition from the beginning.
It is an aerodynamic package that produces a
stable solution for a set of complex and
complicated variables.
Provisions have been made and tested that
allow for the variety of adjustments necessary
to bring the entire package into your personal
comfort zone without adversely affecting
visual presentation or limiting flight
performance.
In our world, power dynamics consists of
two primary components. For our purpose, the
engine is a simple pump that converts fuel to
energy and directs the energy to a specific
output. Integral to this pump is a simple
transmission system. It comprises the
propeller and an adjustable exhaust timing
device (tuned pipe).
The propeller acts as a gear and a final
power converter. The pipe regulates the
time, delivery, and consistency of power. It
is a static throttle of sorts. The whole system
is actually quite primitive because its
components are overtly static, but it is
elegant in its simplicity. When properly
installed and adjusted, it delivers consistent,
reliable, usable power.
So if that’s all there is, why is it so
difficult to get everything working the way
you want?
How you attack a problem is the key.
When you are on the flightline, how things
work is far more important than why they
work. These two factors should not be
interchangeable, although frequently they
are.
When you ask the question “How does it
work?” the answer should be “good” or
“bad.” These answers ultimately quantify
results because if you are honest, they
confirm or deny the need for change.
When you ask “Why does it work?” the
quest for an answer suddenly becomes
complex. Ask those questions and see for
yourself. An analogy would be that you
don’t have to know why a television works
to be satisfied with how it works. This
translates to our sport quite nicely. Ask how
and make progress; ask why and ponder.
The preceding is not intended to be a
brainteaser, but rather a systematic approach
to problem solving and a foundation for
performance building and enhancement.
Before beginning construction, let’s look at
the whole package. In the past six years of
concentrated building and developing the
Diva, I have come to understand and
separate much fact from fiction. This
process is not too different from my
experiences in competitive Combat flying
and business. Following are some facts I
have learned.
• A good contest-caliber finish adds 7-10
ounces from bare wood.
• A light finish cannot save a heavy airplane.
• Good wood is 4-6 pounds per cubic foot. It
is rare to find good wood that weighs less
than 4.5 pounds, and, for our purposes, it
should never exceed 6 pounds stock.
• In an aerodynamically well-designed
airplane, weight distribution is far more
important than weight conservation.
• The three most significant trim
adjustments are CG, propeller, and control
system. You can only use as much power as
you need. Excess power will probably find a
way to work against you.
Look closely at the plans and you will
see some things that are out of the norm.
These differences are what make the whole
package work. Everything on the plans is
there for a reason.
The majority of details relate to function.
If you build the airplane per the plans—at a
finished weight of 62 ounces or less—and
build it accurately and straight, you will be
pleased. Actually, the only frill is the little
faux air scoop on the bottom of the cowl.
Following are details of note.
• The fuselage gets wider at the midpoint
and remains fairly wide where the stabilizer
is mounted.
• The tank compartment is slightly wider
than most, at 23⁄32 inches.
• The wing LE at the root inside the fuselage
has a recessed cavity for tank adjustment.
• Cheek cowls terminate on the wing top at
the high point of the root airfoil.
• The fuselage is deep at the dorsal fin. The
rudder is 1⁄8 balsa.
• There is 3° of permanent rudder offset.
• There is no engine offset.
• The airfoil is completely different at the
root than at the tip.
• The wing panels have equal spans.
• The outboard flap is 1⁄4 inch longer than
the inboard flap.
• The control system is completely adjustable.
• There is a large air inlet in the cowl.
• The air outlet in the fuselage around the pipe
is roughly three times that of the cowl inlet.
• Control horns are made from 3⁄32-inchdiameter
wire.
Construction is probably not for a
beginner, but an accomplished Advanced
competitor or builder should have no
problems. Diva makes extensive use of
molded-balsa components. The cheek cowls,
aft fuselage top block, bottom fuselage block,
most of the cowl, and LE sheeting are molded
balsa.
Having built several wings using the Lost
Foam Wing Building System, I do not hesitate
to recommend it. The Diva IV has a
traditional foam-core, balsa-sheeted wing that
performs equal to the built-up wing.
The entire model is covered with .02-
ounce carbon veil before finishing. In a builtup
wing, cover the entire structure—including
open bays and rib capstrips—with the veil and
cut the openings before final covering. See the
photo. Final wing covering of open bays is
done with silkspan.
Wood selection is crucial for strength and
weight. Today, grain type is less critical with
the use of carbon veil before the final finish.
The accompanying wood-weight chart refers
to common balsa lengths and thicknesses, but
the plans call for extensive use of .077-inchthick
wood. The weights for 1⁄16 wood in the
chart should be close to those for the .077
wood.
Most of the custom-cut, contest-gradewood
suppliers will cut the thicker wood
when requested. As a general rule, it is
preferable for thicker pieces to bias to the
lighter side of the chart. You will also find
exceptional wood that is actually lighter and
obviously usable. The chart is only a gauge.
My favorite method of building is to
complete entire components. I finish the wing
with controls installed and tips and flaps
shaped and fitted. Hinge slots and hinges are
fitted.
I complete the fuselage with the cowl and
front hold downs installed and all top blocks
and 1⁄32-inch cross-grain sheeting on the
bottom permanently glued, leaving only the
opening for the wing. This is critical for final
assembly because the fuselage can twist if
it’s not stabilized by permanent installation
of major components.
The landing-gear mount and rear cowl
hold down are integrated and can only be
installed after the wing is permanently glued
in. The elevator/stabilizer assembly is
completely built, with all hinges aligned and
test fitted. The control horn is permanently
attached to the stabilizer. The rudder is
completed with the dorsal fin. See the photos
for final-assembly clarification.
Volumes have been written about
construction methods. If you want to know
more about two-stroke engines, Larry
Scarinzi’s “Blitz” article from the mid-1960s
is a must read. Bob Gaildini’s “Olympic”
article from 1963 is the definitive work for
CL Stunt aircraft-design considerations.
Robin’s View Productions, Windy
Urtnowski, and a host of other sources have
produced videotapes chronicling everything
from wood selection to finishing to installing
tail wheels. Get your hands on as much
information as you can and digest it. Your
building will improve measurably and
quickly as you gain knowledge.
As with any successful venture, countless
people have made contributions. My
grandmother helped me with words as I
struggled to read model-airplane magazines
when I was 7 years old. My mother was my
lone defender when the house was filled with
modeling-dope fumes and the rest of the
family voted to disown me.
Mrs. Norton, who owned the local hobby
shop, extended credit to me at the age of 16
and introduced me to Ed Southwick and
Dick McCoy. This publication’s
aeromodeling editor has been a great friend
for the past 30 years, and with him I have
debated and shared thoughts on almost
everything.
I must mention Brett Buck; in my humble
opinion, he is the ultimate guru when it
comes to trimming and adjusting just about
anything on a Stunt model. There is also Jim
Aron—one of very few who could ask for
and actually get a piece of my best wood.
And I can’t leave out Ted Fancher and Dave
Fitzgerald, who are my protagonists.
I hope you’ve enjoyed the preceding and
found it informative. As you persist in your
quest for the perfect Stunt pattern, I leave
you with one simple thought: rely on the fact
that something is working to validate the
fact that it does work. MA
Phil Granderson
13250 Campus Dr.
Oakland CA 94619
(Editor’s note: We have chosen a
portion of Phil’s “Diva” article to be the
subject of our new online feature that we
call MA “Web Extra.”
As he explained, Phil designed his Diva
with a specific engine size and type in mind.
Moreover, he used a carbon-fiber tuned pipe
to augment the engine’s power and to contour
its power output to a specific rpm band. This
is an interesting subject, and not much is
written about how it works or the practical
specifics of how to properly set up and adjust
a piped system.
Whether you intend to build the Diva or
not, this online material is interesting and
educational. Give it a look; go to
www.modelaircraft.org and then to the
MA Web Extra section.)
Sources:
Lost Foam Wing Building Systems, fully
assembled Lost Foam wings, Lost Foam
video sets, building videos, foam wing cores,
covered foam wings:
Robin’s View Productions
Box 68
Stockertown PA 18083
(610) 746-0106
Building videos:
Windy Urtnowski
93 Elliott Pl.
Rutherford NJ 07070
(201) 896-8740
Magnum .36 engines, side-to-rear exhaust
manifolds, carbon-fiber AeroPipes—tuned
pipes:
Aero Products
980 Winnbrook Dr.
Dacula GA 30019
(678) 407-9376

GWS A-10 Warthog
18 MODEL AVIATION
Use of curved trim adjacent to straight lines on wing gives
illusion of elliptical planform. Phil looks justifiably proud!
by Phil Granderson
IN 1980 I was fortunate to compete in the Control Line World
Championships in Poland. As a member of the Combat team, I
captured the Bronze Medal for the USA.
The CL Precision Aerobatics (Stunt) contingent was the
“Dream Team” of Bob Hunt, Les McDonald, Bill Werwage, and
Wynn Paul. Bob was the defending World Champion, Les is a
three-time World Champion, and Bill is a three-time World
Champion and the first American to win a World Championships.
Those guys were there to win. And they did! Les, Bob, and Bill
took the Gold, Silver, and Bronze medals in that order.
There was a wealth of knowledge in just watching them and
learning. Today two of them are still fierce competitors and good
friends. Although Les McDonald is no longer competing, he left a
wealth of knowledge with his Stiletto series of aircraft.
I remember thinking, “As soon as I win a Combat World
Championships, I’ll switch hats and become a Stunt World
Champion.” How hard could it be? Now that you’re laughing,
let’s get to work.
Stylish, elegant CL
Stunter designed with
original thinking
@@Web Extra
February 2005 19
The entire model is covered with .2-ounce carbon mat, applied with modeling dope.
When fully cured, the carbon makes the airframe incredibly stiff.
The Diva in the foreground features a built-up Lost Foam wing, and the one in the
background was built using a foam-core wing. Both fly extremely well!
The Diva sits low and has great ground-handling qualities. An outstanding blend of
aesthetic features gives this aircraft an original flair.
Photos by Roger Grotheer
Many people are looking for simplicity in a
complex world. That was exactly my
thinking when I began the Diva odyssey six
years ago; just build a distinctive box
around a proven formula. After exploring
and observing a variety of proven formulas,
it became apparent that this approach simply
would not produce the airplane I envisioned.
So what is Diva? It is the culmination of
a few ideas and experiments that worked
well and the exclusion of many ideas and
experiments that either did not work at all or
worked poorly. It is an original work.
From the high cheek cowls, to the
canopy, to the rudder, it is different. Top,
front, and side views reveal that it is unique.
The thinking and application of power is
different. The airfoil is original.
You might ask the question, Why
reinvent the wheel? That was never my
intention, but if you look closely you will
see that the wheel was tweaked in some
unique ways.
Beginning in the late 1960s, there were
experiments with extremely long tail
moments, gapless hinge lines, variations on
rudder offset, engine side thrust and
downthrust, numerous airfoils, and far too
many ideas and experiments with engines.
Through all of that, somehow I still have old
sketches, templates, and garbled notes
tucked away in boxes and files that have
been moved countless times.
In November 1998 construction began
on the first Diva. Rather than wading into
the whole thing blindly, I applied a process
that had proved successful for me and
countless others. It was simply to formulate
a plan, make modifications when and where
required, but, most important, never lose
sight of the original goal. This had worked
quite nicely in my Combat endeavors and in
business. So here’s the plan.
First, set a goal. You’ve probably heard
the question, How will you get there if you
don’t know where you’re going? The goal
was to design and refine a world-class CL
Aerobatics airplane. The model would
someday win a World Championships—
preferably with me as the pilot. Today I’m
much closer and having so much fun that
the only slightly painful chore so far is
writing this article; I’d rather be building or
flying!
The first Diva was promptly renamed
“Ante” when my wife Kathleen made the
observation that the paint scheme I planned
did not look like a Diva. Ante was the first
airplane to emerge from my clean-slate
approach to design. Its maiden flight was
eight months after I cut the first piece of
wood.
This was the watershed project. I was
going for the whole package: distinctive
looks, front-row finish, piped engine, and
world-class performance. The results fell
somewhat short of the goal.
A summary of the results was that the
finishing system worked well and was
relatively easy to apply. Ante was a frontrow
airplane. The piped PA .65 engine
performed well. The wing with the unique
tra
20 MODEL AVIATION
A close-up shows the wraparound header that is available from Aero Products to fit the
Magnum .36. The company also handles the carbon pipe for that engine.
Phil has developed a method of using a computer to design his complete trim scheme.
This allows an infinite amount of adjusting and brainstorming.
airfoil that was developed and implemented
on the Triumph model built in 1969 worked
exactly as I remembered it, generating a great
deal of lift with no real side effects.
There were also some primary things that
didn’t work. I was completely baffled about
why the tried-and-true combination of long
tail moment and relatively small stabilizer/
elevator size suddenly didn’t work as it did
on so many of my previous designs. The
Ante had no problem turning, but it was
difficult once the turn started to get it
stopped. I also noticed that it required more
force on the handle to turn outside.
The design had an assortment of inherent
problems that could not be corrected by
adjusting, tweaking, and trimming. And
finally, the line tension was way beyond my
tolerance level.
I knew after roughly 20 flights with this
airplane that the next model would have
major modifications. Ante was left in its “best
flight condition” and would serve as a
measurement for changes and improvements
to subsequent airplanes. To this day, it is still
the control for all my experiments.
The second airplane—appropriately
painted and approved for the name Diva—
had four significant changes: equal-span
panels, less wing area, the elevator and
stabilizer were moved down closer to the
thrustline, and the stabilizer/elevator area was
increased to 26% of the wing area.
There were other changes too. The tail
moment was shortened 1⁄2 inch to compensate
for the larger stabilizer’s additional weight.
The wingtip shape was changed slightly. The
flap area was reduced by 5%, and the fueltank
compartment was expanded to allow the
tank to be moved backward and forward an
additional 2 inches. I also took much more
care in the alignment and setup of the entire
airplane.
Ultimately I installed the faithful PA .65.
It was apparent from the first flights that
these changes made significant
improvements in the overall performance.
The whole package seemed to come together.
Most noticeable was the marked
improvement in tracking. There was no more
hunting, and the overturning problem was
completely gone. Additionally, control
pressure for outside and inside maneuvers
was the same. Line tension was reduced
slightly.
The Diva’s finish was even slicker and
shinier than the one applied to the Ante. The
horizontally adjustable tank proved to be
golden for finding the perfect CG. I could
move the CG aft or forward by 1 inch
without adding weight.
Another bonus from the tank arrangement
was that the CG did not shift as much from
the beginning of the flight to the end. This
was indeed a marked improvement over
Ante. Flight scores immediately rose and
were continuing to improve. It even captured
my first Concours d’Elegance award.
I was just beginning to appreciate and
enjoy the fruits of my labor when disaster
struck. In what could only be called the
dumbest thing I’ve ever done, my brain died
and I hooked up the handle upside down and
never did a preflight check! It’s been said that
few people have ever saved an airplane from
crashing with the controls reversed. I was not
one of the few!
The Diva’s 36th flight is now
memorialized by its unique dent in the
blacktop at Whittier Narrows in Southern
California. I still chuckle when I visualize
Keith Trostle chasing it around the circle as
the nose was firmly planted and the PA .65
chewing up the carbon propeller just before
performing its brief fatal maneuver. No one
ever imagined Keith could move that fast!
Within minutes of the disaster, the
model’s remains were loaded into the van
and I started the six-hour drive home. I spent
the first three hours of the drive chewing
myself out and the next three planning my
recovery.
I arrived home at 4:24 p.m., unloaded the
van, got a sandwich, and began cutting balsa.
By 7 p.m., I had the fuselage sides cut and the
doublers clamped and laminated.
Construction of “Diva 2 Quick”
February 2005 21
Phil notches the wing LE to allow for more tank-compartment
room. This also puts the fuel’s weight closer to the model’s CG.
How is this for an inspirational photo? All components are built
and ready to assemble. Note the extremely clean workmanship.
Type: CL Aerobatics
Wingspan: 58 inches
Engine: .36-.65
Flying weight: 50-62 ounces
Construction: Balsa and plywood
Covering/finish: .2-ounce carbon mat, light-grade silkspan
and modeling dope, clear automotive topcoat
progressed at breakneck speed. It was ready
for the maiden flight August 28—just seven
weeks after cutting the first piece of wood.
There were no big changes from its
predecessor. I did make the stabilizer slightly
bigger and added ribs to make it lighter. I
lengthened the tail back to the original 21
inches used on the Ante. I also used thinner
balsa for the rudder (3⁄16) and left it flat. It
flew virtually the same as its forerunner and
was easier to trim.
By all accounts and observations,
everything worked very well. The model
looked good, it flew really well, I looked
comfortable flying it, and flight scores were
on the rise again. It was fairly easy to
“practice myself” into this airplane, but I
wanted an airplane to practice with rather
than one to practice for.
Wow, the truth can hurt! I had invested
serious time, effort, wood, and money in
creating a great airplane, and I wasn’t happy.
What would I have rather been flying? How
about an airplane that was as positive as the
Diva and as refined and nimble as a finely
tuned Classic aircraft? As I sat in my shop,
the Classic models began talking to me.
“Hey Phil, over here. I’m your Vulcan;
I’ll be nice to you. You can relax; fly me!”
“Me too! I’m your Lark; ditto what the
Vulcan said.”
The task was clear: tame and refine the
60-size airplane’s edginess and brute force. I
would have to break the mold that I
painstakingly crafted in the first three
airplanes. I would have to redesign, reengineer,
and reinvent a major portion of an
excellent airplane.
Was there a smaller, lighter engine that
would make the right kind and amount of
power? What size should the new Diva be to
score well when big airplanes generally score
better? It was impractical to simply downsize
Diva by a specific percentage.
The toughest task would be to find a
readily available engine with the right kind
and amount of power. It would also have to
Wood Weights and Measures
Thickness Length (inches) Weight (grams) Length Weight (grams)
1/16 3 x 36 8-11 4 x 36 11-14
3/32 3 x 36 12-16 4 x 36 17-21
1/8 3 x 36 18-21 4 x 36 21-28
3/16 3 x 36 24-30 4 x 36 32-43
1/4 3 x 36 32-42 4 x 36 43-57
3/8 3 x 36 48-63 4 x 36 63-83
1/2 3 x 36 62-85 4 x 36 81-110
1/16 3 x 48 11-14 4 x 48 15-18
3/32 3 x 48 17-21 4 x 48 23-28
1/8 3 x 48 21-28 4 x 48 28-37
3/16 3 x 48 33-40 4 x 48 44-56
1/4 3 x 48 44-57 4 x 48 56-75
3/8 3 x 48 63-85 4 x 48 84-112
1/2 3 x 48 86-112 4 x 48 114-150
be light and manufactured to consistently high
standards. If such an engine could be found
and possessed good Stunt fundamentals, I was
confident in my ability to identify and make
modifications if necessary.
Believing that most modern 40-size
engines had plenty of power, the quest began
to find the best one for the refined Diva. I
started collecting every 25- to 40-size engine I
could find. Since I had conducted no tests, my
only requirement was that it could not weigh
more than 91⁄2 ounces.
In December 2001 I began testing and
evaluating eight engines. In the end, the
Magnum .36 was clearly the top contender. It
weighed only 81⁄4 ounces and easily turned an
11-inch propeller more than 11,000 rpm. The
next step was to install a pipe and put the
engine in a model to see if the power could be
controlled.
The only airplane I was willing to sacrifice
with all the modifications necessary was my
15-year-old Et al, which had a 21-inch tail
moment, 600 square inches of wing area, and
weighed 54 ounces with the engine and pipe
installed and ready to fly.
The first 20 flights were interesting in that
most were spent finding the right pipe and
length. I used a Bolly 12 x 4 narrow-blade
propeller cut to 11 inches.
My suspicions about usable power were
confirmed. There was definitely a great deal
of power, and it seemed quite usable. Most of
those flights were with the engine not running
“on the pipe” and revealed a flat power curve
and the smooth delivery of more power
exactly when and where it was necessary.
At this point the pipe was just a muffler.
The engine was happy being launched at a
soft two-cycle and would break into a
controlled faster speed the moment the nose
was pointed up and then back into its soft
phase as soon as the model returned to level.
There was also no tendency to wind up or
charge at any point. It seemed to “come on” in
all the right places.
The first flight with the pipe in the range
(on the pipe) produced a noticeably stronger
feel everywhere in the pattern, and lap times
went from 5.0 to 5.4. When the needle was
turned in slightly to get to 5.2 lap times, the
engine and airplane were ecstatic, and I
couldn’t keep myself from joining in the
celebration by pushing that old model to
previously unobtainable performance levels.
Since I felt comfortable with the engine, I
was able to turn my focus to the new aircraft.
It would have to be smaller and lighter but
still have that “big airplane” presence.
Deciding that it would probably be a series of
design modifications, I decided to build the
first version only slightly smaller than the
previous .65-powered Divas.
The Ante has 750 square inches of wing
area, and the two larger Divas have 710-
square-inch wings. The wing area presented
here is only 4% less; in fact, there is as much
as in most modern .60-powered models that
are flown today. The tail moment is 18.5
inches, which is slightly longer than most
other airplanes. The fuselage is massive. The
elevator/stabilizer area is medium to small
compared to many models’.
After the first flight, it was apparent that
Diva IV was something special. My good
friend Jim Aron remarked candidly, “I’ve
seen the first flights of your previous
airplanes, and this is the first time I’ve ever
seen you smile!”
To date, there are two smaller Divas, each
weighing 57 ounces. One has a foam-core
wing with balsa sheeting, and the other uses
the Lost Foam Wing Building System
construction shown on the plans.
As an experiment, I used stick-on weights
to increase the overall weight to 64 ounces,
just to see what would happen. The only
noticeable difference was more line tension.
There was still plenty of power, and the Diva
didn’t hesitate anywhere in the pattern.
In general, the two primary components of
any design are aerodynamics and power
dynamics. Aerodynamics is the science of
solid bodies moving through air. Diva was
designed for competition from the beginning.
It is an aerodynamic package that produces a
stable solution for a set of complex and
complicated variables.
Provisions have been made and tested that
allow for the variety of adjustments necessary
to bring the entire package into your personal
comfort zone without adversely affecting
visual presentation or limiting flight
performance.
In our world, power dynamics consists of
two primary components. For our purpose, the
engine is a simple pump that converts fuel to
energy and directs the energy to a specific
output. Integral to this pump is a simple
transmission system. It comprises the
propeller and an adjustable exhaust timing
device (tuned pipe).
The propeller acts as a gear and a final
power converter. The pipe regulates the
time, delivery, and consistency of power. It
is a static throttle of sorts. The whole system
is actually quite primitive because its
components are overtly static, but it is
elegant in its simplicity. When properly
installed and adjusted, it delivers consistent,
reliable, usable power.
So if that’s all there is, why is it so
difficult to get everything working the way
you want?
How you attack a problem is the key.
When you are on the flightline, how things
work is far more important than why they
work. These two factors should not be
interchangeable, although frequently they
are.
When you ask the question “How does it
work?” the answer should be “good” or
“bad.” These answers ultimately quantify
results because if you are honest, they
confirm or deny the need for change.
When you ask “Why does it work?” the
quest for an answer suddenly becomes
complex. Ask those questions and see for
yourself. An analogy would be that you
don’t have to know why a television works
to be satisfied with how it works. This
translates to our sport quite nicely. Ask how
and make progress; ask why and ponder.
The preceding is not intended to be a
brainteaser, but rather a systematic approach
to problem solving and a foundation for
performance building and enhancement.
Before beginning construction, let’s look at
the whole package. In the past six years of
concentrated building and developing the
Diva, I have come to understand and
separate much fact from fiction. This
process is not too different from my
experiences in competitive Combat flying
and business. Following are some facts I
have learned.
• A good contest-caliber finish adds 7-10
ounces from bare wood.
• A light finish cannot save a heavy airplane.
• Good wood is 4-6 pounds per cubic foot. It
is rare to find good wood that weighs less
than 4.5 pounds, and, for our purposes, it
should never exceed 6 pounds stock.
• In an aerodynamically well-designed
airplane, weight distribution is far more
important than weight conservation.
• The three most significant trim
adjustments are CG, propeller, and control
system. You can only use as much power as
you need. Excess power will probably find a
way to work against you.
Look closely at the plans and you will
see some things that are out of the norm.
These differences are what make the whole
package work. Everything on the plans is
there for a reason.
The majority of details relate to function.
If you build the airplane per the plans—at a
finished weight of 62 ounces or less—and
build it accurately and straight, you will be
pleased. Actually, the only frill is the little
faux air scoop on the bottom of the cowl.
Following are details of note.
• The fuselage gets wider at the midpoint
and remains fairly wide where the stabilizer
is mounted.
• The tank compartment is slightly wider
than most, at 23⁄32 inches.
• The wing LE at the root inside the fuselage
has a recessed cavity for tank adjustment.
• Cheek cowls terminate on the wing top at
the high point of the root airfoil.
• The fuselage is deep at the dorsal fin. The
rudder is 1⁄8 balsa.
• There is 3° of permanent rudder offset.
• There is no engine offset.
• The airfoil is completely different at the
root than at the tip.
• The wing panels have equal spans.
• The outboard flap is 1⁄4 inch longer than
the inboard flap.
• The control system is completely adjustable.
• There is a large air inlet in the cowl.
• The air outlet in the fuselage around the pipe
is roughly three times that of the cowl inlet.
• Control horns are made from 3⁄32-inchdiameter
wire.
Construction is probably not for a
beginner, but an accomplished Advanced
competitor or builder should have no
problems. Diva makes extensive use of
molded-balsa components. The cheek cowls,
aft fuselage top block, bottom fuselage block,
most of the cowl, and LE sheeting are molded
balsa.
Having built several wings using the Lost
Foam Wing Building System, I do not hesitate
to recommend it. The Diva IV has a
traditional foam-core, balsa-sheeted wing that
performs equal to the built-up wing.
The entire model is covered with .02-
ounce carbon veil before finishing. In a builtup
wing, cover the entire structure—including
open bays and rib capstrips—with the veil and
cut the openings before final covering. See the
photo. Final wing covering of open bays is
done with silkspan.
Wood selection is crucial for strength and
weight. Today, grain type is less critical with
the use of carbon veil before the final finish.
The accompanying wood-weight chart refers
to common balsa lengths and thicknesses, but
the plans call for extensive use of .077-inchthick
wood. The weights for 1⁄16 wood in the
chart should be close to those for the .077
wood.
Most of the custom-cut, contest-gradewood
suppliers will cut the thicker wood
when requested. As a general rule, it is
preferable for thicker pieces to bias to the
lighter side of the chart. You will also find
exceptional wood that is actually lighter and
obviously usable. The chart is only a gauge.
My favorite method of building is to
complete entire components. I finish the wing
with controls installed and tips and flaps
shaped and fitted. Hinge slots and hinges are
fitted.
I complete the fuselage with the cowl and
front hold downs installed and all top blocks
and 1⁄32-inch cross-grain sheeting on the
bottom permanently glued, leaving only the
opening for the wing. This is critical for final
assembly because the fuselage can twist if
it’s not stabilized by permanent installation
of major components.
The landing-gear mount and rear cowl
hold down are integrated and can only be
installed after the wing is permanently glued
in. The elevator/stabilizer assembly is
completely built, with all hinges aligned and
test fitted. The control horn is permanently
attached to the stabilizer. The rudder is
completed with the dorsal fin. See the photos
for final-assembly clarification.
Volumes have been written about
construction methods. If you want to know
more about two-stroke engines, Larry
Scarinzi’s “Blitz” article from the mid-1960s
is a must read. Bob Gaildini’s “Olympic”
article from 1963 is the definitive work for
CL Stunt aircraft-design considerations.
Robin’s View Productions, Windy
Urtnowski, and a host of other sources have
produced videotapes chronicling everything
from wood selection to finishing to installing
tail wheels. Get your hands on as much
information as you can and digest it. Your
building will improve measurably and
quickly as you gain knowledge.
As with any successful venture, countless
people have made contributions. My
grandmother helped me with words as I
struggled to read model-airplane magazines
when I was 7 years old. My mother was my
lone defender when the house was filled with
modeling-dope fumes and the rest of the
family voted to disown me.
Mrs. Norton, who owned the local hobby
shop, extended credit to me at the age of 16
and introduced me to Ed Southwick and
Dick McCoy. This publication’s
aeromodeling editor has been a great friend
for the past 30 years, and with him I have
debated and shared thoughts on almost
everything.
I must mention Brett Buck; in my humble
opinion, he is the ultimate guru when it
comes to trimming and adjusting just about
anything on a Stunt model. There is also Jim
Aron—one of very few who could ask for
and actually get a piece of my best wood.
And I can’t leave out Ted Fancher and Dave
Fitzgerald, who are my protagonists.
I hope you’ve enjoyed the preceding and
found it informative. As you persist in your
quest for the perfect Stunt pattern, I leave
you with one simple thought: rely on the fact
that something is working to validate the
fact that it does work. MA
Phil Granderson
13250 Campus Dr.
Oakland CA 94619
(Editor’s note: We have chosen a
portion of Phil’s “Diva” article to be the
subject of our new online feature that we
call MA “Web Extra.”
As he explained, Phil designed his Diva
with a specific engine size and type in mind.
Moreover, he used a carbon-fiber tuned pipe
to augment the engine’s power and to contour
its power output to a specific rpm band. This
is an interesting subject, and not much is
written about how it works or the practical
specifics of how to properly set up and adjust
a piped system.
Whether you intend to build the Diva or
not, this online material is interesting and
educational. Give it a look; go to
www.modelaircraft.org and then to the
MA Web Extra section.)
Sources:
Lost Foam Wing Building Systems, fully
assembled Lost Foam wings, Lost Foam
video sets, building videos, foam wing cores,
covered foam wings:
Robin’s View Productions
Box 68
Stockertown PA 18083
(610) 746-0106
Building videos:
Windy Urtnowski
93 Elliott Pl.
Rutherford NJ 07070
(201) 896-8740
Magnum .36 engines, side-to-rear exhaust
manifolds, carbon-fiber AeroPipes—tuned
pipes:
Aero Products
980 Winnbrook Dr.
Dacula GA 30019
(678) 407-9376

GWS A-10 Warthog
18 MODEL AVIATION
Use of curved trim adjacent to straight lines on wing gives
illusion of elliptical planform. Phil looks justifiably proud!
by Phil Granderson
IN 1980 I was fortunate to compete in the Control Line World
Championships in Poland. As a member of the Combat team, I
captured the Bronze Medal for the USA.
The CL Precision Aerobatics (Stunt) contingent was the
“Dream Team” of Bob Hunt, Les McDonald, Bill Werwage, and
Wynn Paul. Bob was the defending World Champion, Les is a
three-time World Champion, and Bill is a three-time World
Champion and the first American to win a World Championships.
Those guys were there to win. And they did! Les, Bob, and Bill
took the Gold, Silver, and Bronze medals in that order.
There was a wealth of knowledge in just watching them and
learning. Today two of them are still fierce competitors and good
friends. Although Les McDonald is no longer competing, he left a
wealth of knowledge with his Stiletto series of aircraft.
I remember thinking, “As soon as I win a Combat World
Championships, I’ll switch hats and become a Stunt World
Champion.” How hard could it be? Now that you’re laughing,
let’s get to work.
Stylish, elegant CL
Stunter designed with
original thinking
@@Web Extra
February 2005 19
The entire model is covered with .2-ounce carbon mat, applied with modeling dope.
When fully cured, the carbon makes the airframe incredibly stiff.
The Diva in the foreground features a built-up Lost Foam wing, and the one in the
background was built using a foam-core wing. Both fly extremely well!
The Diva sits low and has great ground-handling qualities. An outstanding blend of
aesthetic features gives this aircraft an original flair.
Photos by Roger Grotheer
Many people are looking for simplicity in a
complex world. That was exactly my
thinking when I began the Diva odyssey six
years ago; just build a distinctive box
around a proven formula. After exploring
and observing a variety of proven formulas,
it became apparent that this approach simply
would not produce the airplane I envisioned.
So what is Diva? It is the culmination of
a few ideas and experiments that worked
well and the exclusion of many ideas and
experiments that either did not work at all or
worked poorly. It is an original work.
From the high cheek cowls, to the
canopy, to the rudder, it is different. Top,
front, and side views reveal that it is unique.
The thinking and application of power is
different. The airfoil is original.
You might ask the question, Why
reinvent the wheel? That was never my
intention, but if you look closely you will
see that the wheel was tweaked in some
unique ways.
Beginning in the late 1960s, there were
experiments with extremely long tail
moments, gapless hinge lines, variations on
rudder offset, engine side thrust and
downthrust, numerous airfoils, and far too
many ideas and experiments with engines.
Through all of that, somehow I still have old
sketches, templates, and garbled notes
tucked away in boxes and files that have
been moved countless times.
In November 1998 construction began
on the first Diva. Rather than wading into
the whole thing blindly, I applied a process
that had proved successful for me and
countless others. It was simply to formulate
a plan, make modifications when and where
required, but, most important, never lose
sight of the original goal. This had worked
quite nicely in my Combat endeavors and in
business. So here’s the plan.
First, set a goal. You’ve probably heard
the question, How will you get there if you
don’t know where you’re going? The goal
was to design and refine a world-class CL
Aerobatics airplane. The model would
someday win a World Championships—
preferably with me as the pilot. Today I’m
much closer and having so much fun that
the only slightly painful chore so far is
writing this article; I’d rather be building or
flying!
The first Diva was promptly renamed
“Ante” when my wife Kathleen made the
observation that the paint scheme I planned
did not look like a Diva. Ante was the first
airplane to emerge from my clean-slate
approach to design. Its maiden flight was
eight months after I cut the first piece of
wood.
This was the watershed project. I was
going for the whole package: distinctive
looks, front-row finish, piped engine, and
world-class performance. The results fell
somewhat short of the goal.
A summary of the results was that the
finishing system worked well and was
relatively easy to apply. Ante was a frontrow
airplane. The piped PA .65 engine
performed well. The wing with the unique
tra
20 MODEL AVIATION
A close-up shows the wraparound header that is available from Aero Products to fit the
Magnum .36. The company also handles the carbon pipe for that engine.
Phil has developed a method of using a computer to design his complete trim scheme.
This allows an infinite amount of adjusting and brainstorming.
airfoil that was developed and implemented
on the Triumph model built in 1969 worked
exactly as I remembered it, generating a great
deal of lift with no real side effects.
There were also some primary things that
didn’t work. I was completely baffled about
why the tried-and-true combination of long
tail moment and relatively small stabilizer/
elevator size suddenly didn’t work as it did
on so many of my previous designs. The
Ante had no problem turning, but it was
difficult once the turn started to get it
stopped. I also noticed that it required more
force on the handle to turn outside.
The design had an assortment of inherent
problems that could not be corrected by
adjusting, tweaking, and trimming. And
finally, the line tension was way beyond my
tolerance level.
I knew after roughly 20 flights with this
airplane that the next model would have
major modifications. Ante was left in its “best
flight condition” and would serve as a
measurement for changes and improvements
to subsequent airplanes. To this day, it is still
the control for all my experiments.
The second airplane—appropriately
painted and approved for the name Diva—
had four significant changes: equal-span
panels, less wing area, the elevator and
stabilizer were moved down closer to the
thrustline, and the stabilizer/elevator area was
increased to 26% of the wing area.
There were other changes too. The tail
moment was shortened 1⁄2 inch to compensate
for the larger stabilizer’s additional weight.
The wingtip shape was changed slightly. The
flap area was reduced by 5%, and the fueltank
compartment was expanded to allow the
tank to be moved backward and forward an
additional 2 inches. I also took much more
care in the alignment and setup of the entire
airplane.
Ultimately I installed the faithful PA .65.
It was apparent from the first flights that
these changes made significant
improvements in the overall performance.
The whole package seemed to come together.
Most noticeable was the marked
improvement in tracking. There was no more
hunting, and the overturning problem was
completely gone. Additionally, control
pressure for outside and inside maneuvers
was the same. Line tension was reduced
slightly.
The Diva’s finish was even slicker and
shinier than the one applied to the Ante. The
horizontally adjustable tank proved to be
golden for finding the perfect CG. I could
move the CG aft or forward by 1 inch
without adding weight.
Another bonus from the tank arrangement
was that the CG did not shift as much from
the beginning of the flight to the end. This
was indeed a marked improvement over
Ante. Flight scores immediately rose and
were continuing to improve. It even captured
my first Concours d’Elegance award.
I was just beginning to appreciate and
enjoy the fruits of my labor when disaster
struck. In what could only be called the
dumbest thing I’ve ever done, my brain died
and I hooked up the handle upside down and
never did a preflight check! It’s been said that
few people have ever saved an airplane from
crashing with the controls reversed. I was not
one of the few!
The Diva’s 36th flight is now
memorialized by its unique dent in the
blacktop at Whittier Narrows in Southern
California. I still chuckle when I visualize
Keith Trostle chasing it around the circle as
the nose was firmly planted and the PA .65
chewing up the carbon propeller just before
performing its brief fatal maneuver. No one
ever imagined Keith could move that fast!
Within minutes of the disaster, the
model’s remains were loaded into the van
and I started the six-hour drive home. I spent
the first three hours of the drive chewing
myself out and the next three planning my
recovery.
I arrived home at 4:24 p.m., unloaded the
van, got a sandwich, and began cutting balsa.
By 7 p.m., I had the fuselage sides cut and the
doublers clamped and laminated.
Construction of “Diva 2 Quick”
February 2005 21
Phil notches the wing LE to allow for more tank-compartment
room. This also puts the fuel’s weight closer to the model’s CG.
How is this for an inspirational photo? All components are built
and ready to assemble. Note the extremely clean workmanship.
Type: CL Aerobatics
Wingspan: 58 inches
Engine: .36-.65
Flying weight: 50-62 ounces
Construction: Balsa and plywood
Covering/finish: .2-ounce carbon mat, light-grade silkspan
and modeling dope, clear automotive topcoat
progressed at breakneck speed. It was ready
for the maiden flight August 28—just seven
weeks after cutting the first piece of wood.
There were no big changes from its
predecessor. I did make the stabilizer slightly
bigger and added ribs to make it lighter. I
lengthened the tail back to the original 21
inches used on the Ante. I also used thinner
balsa for the rudder (3⁄16) and left it flat. It
flew virtually the same as its forerunner and
was easier to trim.
By all accounts and observations,
everything worked very well. The model
looked good, it flew really well, I looked
comfortable flying it, and flight scores were
on the rise again. It was fairly easy to
“practice myself” into this airplane, but I
wanted an airplane to practice with rather
than one to practice for.
Wow, the truth can hurt! I had invested
serious time, effort, wood, and money in
creating a great airplane, and I wasn’t happy.
What would I have rather been flying? How
about an airplane that was as positive as the
Diva and as refined and nimble as a finely
tuned Classic aircraft? As I sat in my shop,
the Classic models began talking to me.
“Hey Phil, over here. I’m your Vulcan;
I’ll be nice to you. You can relax; fly me!”
“Me too! I’m your Lark; ditto what the
Vulcan said.”
The task was clear: tame and refine the
60-size airplane’s edginess and brute force. I
would have to break the mold that I
painstakingly crafted in the first three
airplanes. I would have to redesign, reengineer,
and reinvent a major portion of an
excellent airplane.
Was there a smaller, lighter engine that
would make the right kind and amount of
power? What size should the new Diva be to
score well when big airplanes generally score
better? It was impractical to simply downsize
Diva by a specific percentage.
The toughest task would be to find a
readily available engine with the right kind
and amount of power. It would also have to
Wood Weights and Measures
Thickness Length (inches) Weight (grams) Length Weight (grams)
1/16 3 x 36 8-11 4 x 36 11-14
3/32 3 x 36 12-16 4 x 36 17-21
1/8 3 x 36 18-21 4 x 36 21-28
3/16 3 x 36 24-30 4 x 36 32-43
1/4 3 x 36 32-42 4 x 36 43-57
3/8 3 x 36 48-63 4 x 36 63-83
1/2 3 x 36 62-85 4 x 36 81-110
1/16 3 x 48 11-14 4 x 48 15-18
3/32 3 x 48 17-21 4 x 48 23-28
1/8 3 x 48 21-28 4 x 48 28-37
3/16 3 x 48 33-40 4 x 48 44-56
1/4 3 x 48 44-57 4 x 48 56-75
3/8 3 x 48 63-85 4 x 48 84-112
1/2 3 x 48 86-112 4 x 48 114-150
be light and manufactured to consistently high
standards. If such an engine could be found
and possessed good Stunt fundamentals, I was
confident in my ability to identify and make
modifications if necessary.
Believing that most modern 40-size
engines had plenty of power, the quest began
to find the best one for the refined Diva. I
started collecting every 25- to 40-size engine I
could find. Since I had conducted no tests, my
only requirement was that it could not weigh
more than 91⁄2 ounces.
In December 2001 I began testing and
evaluating eight engines. In the end, the
Magnum .36 was clearly the top contender. It
weighed only 81⁄4 ounces and easily turned an
11-inch propeller more than 11,000 rpm. The
next step was to install a pipe and put the
engine in a model to see if the power could be
controlled.
The only airplane I was willing to sacrifice
with all the modifications necessary was my
15-year-old Et al, which had a 21-inch tail
moment, 600 square inches of wing area, and
weighed 54 ounces with the engine and pipe
installed and ready to fly.
The first 20 flights were interesting in that
most were spent finding the right pipe and
length. I used a Bolly 12 x 4 narrow-blade
propeller cut to 11 inches.
My suspicions about usable power were
confirmed. There was definitely a great deal
of power, and it seemed quite usable. Most of
those flights were with the engine not running
“on the pipe” and revealed a flat power curve
and the smooth delivery of more power
exactly when and where it was necessary.
At this point the pipe was just a muffler.
The engine was happy being launched at a
soft two-cycle and would break into a
controlled faster speed the moment the nose
was pointed up and then back into its soft
phase as soon as the model returned to level.
There was also no tendency to wind up or
charge at any point. It seemed to “come on” in
all the right places.
The first flight with the pipe in the range
(on the pipe) produced a noticeably stronger
feel everywhere in the pattern, and lap times
went from 5.0 to 5.4. When the needle was
turned in slightly to get to 5.2 lap times, the
engine and airplane were ecstatic, and I
couldn’t keep myself from joining in the
celebration by pushing that old model to
previously unobtainable performance levels.
Since I felt comfortable with the engine, I
was able to turn my focus to the new aircraft.
It would have to be smaller and lighter but
still have that “big airplane” presence.
Deciding that it would probably be a series of
design modifications, I decided to build the
first version only slightly smaller than the
previous .65-powered Divas.
The Ante has 750 square inches of wing
area, and the two larger Divas have 710-
square-inch wings. The wing area presented
here is only 4% less; in fact, there is as much
as in most modern .60-powered models that
are flown today. The tail moment is 18.5
inches, which is slightly longer than most
other airplanes. The fuselage is massive. The
elevator/stabilizer area is medium to small
compared to many models’.
After the first flight, it was apparent that
Diva IV was something special. My good
friend Jim Aron remarked candidly, “I’ve
seen the first flights of your previous
airplanes, and this is the first time I’ve ever
seen you smile!”
To date, there are two smaller Divas, each
weighing 57 ounces. One has a foam-core
wing with balsa sheeting, and the other uses
the Lost Foam Wing Building System
construction shown on the plans.
As an experiment, I used stick-on weights
to increase the overall weight to 64 ounces,
just to see what would happen. The only
noticeable difference was more line tension.
There was still plenty of power, and the Diva
didn’t hesitate anywhere in the pattern.
In general, the two primary components of
any design are aerodynamics and power
dynamics. Aerodynamics is the science of
solid bodies moving through air. Diva was
designed for competition from the beginning.
It is an aerodynamic package that produces a
stable solution for a set of complex and
complicated variables.
Provisions have been made and tested that
allow for the variety of adjustments necessary
to bring the entire package into your personal
comfort zone without adversely affecting
visual presentation or limiting flight
performance.
In our world, power dynamics consists of
two primary components. For our purpose, the
engine is a simple pump that converts fuel to
energy and directs the energy to a specific
output. Integral to this pump is a simple
transmission system. It comprises the
propeller and an adjustable exhaust timing
device (tuned pipe).
The propeller acts as a gear and a final
power converter. The pipe regulates the
time, delivery, and consistency of power. It
is a static throttle of sorts. The whole system
is actually quite primitive because its
components are overtly static, but it is
elegant in its simplicity. When properly
installed and adjusted, it delivers consistent,
reliable, usable power.
So if that’s all there is, why is it so
difficult to get everything working the way
you want?
How you attack a problem is the key.
When you are on the flightline, how things
work is far more important than why they
work. These two factors should not be
interchangeable, although frequently they
are.
When you ask the question “How does it
work?” the answer should be “good” or
“bad.” These answers ultimately quantify
results because if you are honest, they
confirm or deny the need for change.
When you ask “Why does it work?” the
quest for an answer suddenly becomes
complex. Ask those questions and see for
yourself. An analogy would be that you
don’t have to know why a television works
to be satisfied with how it works. This
translates to our sport quite nicely. Ask how
and make progress; ask why and ponder.
The preceding is not intended to be a
brainteaser, but rather a systematic approach
to problem solving and a foundation for
performance building and enhancement.
Before beginning construction, let’s look at
the whole package. In the past six years of
concentrated building and developing the
Diva, I have come to understand and
separate much fact from fiction. This
process is not too different from my
experiences in competitive Combat flying
and business. Following are some facts I
have learned.
• A good contest-caliber finish adds 7-10
ounces from bare wood.
• A light finish cannot save a heavy airplane.
• Good wood is 4-6 pounds per cubic foot. It
is rare to find good wood that weighs less
than 4.5 pounds, and, for our purposes, it
should never exceed 6 pounds stock.
• In an aerodynamically well-designed
airplane, weight distribution is far more
important than weight conservation.
• The three most significant trim
adjustments are CG, propeller, and control
system. You can only use as much power as
you need. Excess power will probably find a
way to work against you.
Look closely at the plans and you will
see some things that are out of the norm.
These differences are what make the whole
package work. Everything on the plans is
there for a reason.
The majority of details relate to function.
If you build the airplane per the plans—at a
finished weight of 62 ounces or less—and
build it accurately and straight, you will be
pleased. Actually, the only frill is the little
faux air scoop on the bottom of the cowl.
Following are details of note.
• The fuselage gets wider at the midpoint
and remains fairly wide where the stabilizer
is mounted.
• The tank compartment is slightly wider
than most, at 23⁄32 inches.
• The wing LE at the root inside the fuselage
has a recessed cavity for tank adjustment.
• Cheek cowls terminate on the wing top at
the high point of the root airfoil.
• The fuselage is deep at the dorsal fin. The
rudder is 1⁄8 balsa.
• There is 3° of permanent rudder offset.
• There is no engine offset.
• The airfoil is completely different at the
root than at the tip.
• The wing panels have equal spans.
• The outboard flap is 1⁄4 inch longer than
the inboard flap.
• The control system is completely adjustable.
• There is a large air inlet in the cowl.
• The air outlet in the fuselage around the pipe
is roughly three times that of the cowl inlet.
• Control horns are made from 3⁄32-inchdiameter
wire.
Construction is probably not for a
beginner, but an accomplished Advanced
competitor or builder should have no
problems. Diva makes extensive use of
molded-balsa components. The cheek cowls,
aft fuselage top block, bottom fuselage block,
most of the cowl, and LE sheeting are molded
balsa.
Having built several wings using the Lost
Foam Wing Building System, I do not hesitate
to recommend it. The Diva IV has a
traditional foam-core, balsa-sheeted wing that
performs equal to the built-up wing.
The entire model is covered with .02-
ounce carbon veil before finishing. In a builtup
wing, cover the entire structure—including
open bays and rib capstrips—with the veil and
cut the openings before final covering. See the
photo. Final wing covering of open bays is
done with silkspan.
Wood selection is crucial for strength and
weight. Today, grain type is less critical with
the use of carbon veil before the final finish.
The accompanying wood-weight chart refers
to common balsa lengths and thicknesses, but
the plans call for extensive use of .077-inchthick
wood. The weights for 1⁄16 wood in the
chart should be close to those for the .077
wood.
Most of the custom-cut, contest-gradewood
suppliers will cut the thicker wood
when requested. As a general rule, it is
preferable for thicker pieces to bias to the
lighter side of the chart. You will also find
exceptional wood that is actually lighter and
obviously usable. The chart is only a gauge.
My favorite method of building is to
complete entire components. I finish the wing
with controls installed and tips and flaps
shaped and fitted. Hinge slots and hinges are
fitted.
I complete the fuselage with the cowl and
front hold downs installed and all top blocks
and 1⁄32-inch cross-grain sheeting on the
bottom permanently glued, leaving only the
opening for the wing. This is critical for final
assembly because the fuselage can twist if
it’s not stabilized by permanent installation
of major components.
The landing-gear mount and rear cowl
hold down are integrated and can only be
installed after the wing is permanently glued
in. The elevator/stabilizer assembly is
completely built, with all hinges aligned and
test fitted. The control horn is permanently
attached to the stabilizer. The rudder is
completed with the dorsal fin. See the photos
for final-assembly clarification.
Volumes have been written about
construction methods. If you want to know
more about two-stroke engines, Larry
Scarinzi’s “Blitz” article from the mid-1960s
is a must read. Bob Gaildini’s “Olympic”
article from 1963 is the definitive work for
CL Stunt aircraft-design considerations.
Robin’s View Productions, Windy
Urtnowski, and a host of other sources have
produced videotapes chronicling everything
from wood selection to finishing to installing
tail wheels. Get your hands on as much
information as you can and digest it. Your
building will improve measurably and
quickly as you gain knowledge.
As with any successful venture, countless
people have made contributions. My
grandmother helped me with words as I
struggled to read model-airplane magazines
when I was 7 years old. My mother was my
lone defender when the house was filled with
modeling-dope fumes and the rest of the
family voted to disown me.
Mrs. Norton, who owned the local hobby
shop, extended credit to me at the age of 16
and introduced me to Ed Southwick and
Dick McCoy. This publication’s
aeromodeling editor has been a great friend
for the past 30 years, and with him I have
debated and shared thoughts on almost
everything.
I must mention Brett Buck; in my humble
opinion, he is the ultimate guru when it
comes to trimming and adjusting just about
anything on a Stunt model. There is also Jim
Aron—one of very few who could ask for
and actually get a piece of my best wood.
And I can’t leave out Ted Fancher and Dave
Fitzgerald, who are my protagonists.
I hope you’ve enjoyed the preceding and
found it informative. As you persist in your
quest for the perfect Stunt pattern, I leave
you with one simple thought: rely on the fact
that something is working to validate the
fact that it does work. MA
Phil Granderson
13250 Campus Dr.
Oakland CA 94619
(Editor’s note: We have chosen a
portion of Phil’s “Diva” article to be the
subject of our new online feature that we
call MA “Web Extra.”
As he explained, Phil designed his Diva
with a specific engine size and type in mind.
Moreover, he used a carbon-fiber tuned pipe
to augment the engine’s power and to contour
its power output to a specific rpm band. This
is an interesting subject, and not much is
written about how it works or the practical
specifics of how to properly set up and adjust
a piped system.
Whether you intend to build the Diva or
not, this online material is interesting and
educational. Give it a look; go to
www.modelaircraft.org and then to the
MA Web Extra section.)
Sources:
Lost Foam Wing Building Systems, fully
assembled Lost Foam wings, Lost Foam
video sets, building videos, foam wing cores,
covered foam wings:
Robin’s View Productions
Box 68
Stockertown PA 18083
(610) 746-0106
Building videos:
Windy Urtnowski
93 Elliott Pl.
Rutherford NJ 07070
(201) 896-8740
Magnum .36 engines, side-to-rear exhaust
manifolds, carbon-fiber AeroPipes—tuned
pipes:
Aero Products
980 Winnbrook Dr.
Dacula GA 30019
(678) 407-9376