The Kimballs, Jim the
elder and Kevin the son,
are interesting folks.
Working out of their
private grass strip in
Zellwood, Florida, they
have carved something of a
special niche for
themselves within the
world of antique aviation.
Now, with the Pitts Model
12, known by some as the
Macho Stinker, they are in
the process of whittling
an equally impressive, and
typically unique, niche in
the world of homebuilding.
As the
purveyors of kits and
components for Curtis
Pitts' most recent biplane
design, the hairy chested,
round-motored Model 12,
they have applied their
deep knowledge of round
motored biplanes to their
version of a sorta-antique
for the homebuilder. Of
course, being a Pitts,
it's an antique with
spunk.
Before
Curtis was even close to
finishing the Macho
Stinker back in 1996,
Kevin and Jim were
standing on his doorstep
looking over his shoulder.
They were looking for
something new to add to
their repertoire and the
Model 12 tickled their
fancy. They came away with
a set of plans and started
building at the same time
as Curtis and his Biplane
Mafia.
The
Kimballs were not
strangers to biplanes. In
fact, in the years since
Jim bailed out of the
electronics wholesale
business in an effort to
save both his health and
his sanity, biplanes have
been central to their
lives. Running an
electronics company with
200 employees and an
eccentric owner had taken
it's toll and Jim simply
walked out the door and
decided it was time to do
something else with his
life. However, to keep
himself busy while he was
picking a direction, he
purchased a basement full
of parts which were
propertied to be a
Staggerwing, when
assembled, and began
working on what is widely
regarded to be one of the
most labor intensive
airplanes in the world to
restore. The result was
that he didn't have to
pick a direction for his
life. The direction came
looking for him in the
form of antique airplanes.
He was good at what he did
and he loved it.
Having finished and sold
the Staggerwing, he
purchased a Stearman and
began restoring it with
the goal of selling it for
a profit. That was the
last airplane he had to
purchase. From that point
on people were banging on
his door seeking his
skills to be applied to
their aircraft. That
single Stearman was the
first of 25 Stearman, 6
Staggergwings and
everything in-between. In
total, since they moved to
Zellwood in 1982, they
have restored over 80
antique airplanes, Cub to
Staggerwing and all of
those which have been
entered in judging have
won awards. The SM8
Stinson they built to be
an award winner cleaned up
at Sun n Fun the only year
SnF had a trophy for
overall winner.
Kevin,
who is 32 years old with
two tykes of his own, was
a tyke himself when he
started helping his dad.
"We have pictures of me
rib stitching when I was
eight years old." By the
time he graduated high
school and was ready to go
off to the University of
Central Florida to study
engineering, he had built,
rebuilt or designed
practically every part on
an airplane. This put him
in a different category
than the rest of his
mechanical engineering
class. "It was really
frustrating because the
professors would
constantly be designing
things that couldn't be
built. To them a bolt was
a bolt, there were no
different types or sizes,
or they'd come up with an
assembly on paper in which
aluminum was welded to
steel. They just didn't
get it."
One of
the reasons the Kimballs
decided to take on the
Model 12 project was
creativity and pure
practicality. "We were
tired of building things
that had to look and be
built like something else.
Our first serious
homebuilding activity was
building the Model Z Gee
Bee, but even there we had
to conform to older
practices in many areas
just as with the antiques.
In some of the antiques
we'd have to bolt a seat
to a 1/4" plywood floor,
really stupid, but that's
the way it had originally
been done, so..."
As the
Model 12 at Curtis' was
coming along, the Kimballs
began negotiating to buy
the rights to the design
to incorporate it into
their business. What they
didn't know, and Curtis
had forgotten, was that
there was a clause in the
contract under which which
he had sold the earlier
Model 11 Super Stinker
rights that gave that
purchaser first right of
refusal on all further
Pitts designs. They
exercised their option and
the Kimballs found
themselves looking for
another way into the
homebuilt biplane market.
However, when they then
negotiated to become the
parts supplier in support
of the individual who was
selling the plans, they
found themselves scratch
building Model 12 parts
anyway.
As soon as the original
Model 12 was flying, Ben
Morphew, a long time
homebuilder and G-junkie
from Dallas, journeyed
down to Homestead to fly
it. On his way back home
he called the Kimballs to
get them started on
building a Model 12
airframe for him. He,
however, had some changes
he wanted made. Morphew's
input, coupled with
several items which
surfaced once the
prototype was flying (e.g.
the original motor mount
had to be 11 inches longer
than calculated for CG
purposes), set in motion a
subtle redesign (with
Curtis' blessing every
step of the way) that
resulted in the Model 12
which the Kimballs offer
in kit and pre-finished
component form. It should
be noted that there are
actually two versions of
the airplane now: The
original, as shown on the
plans and the Kimball
version for which plans
are not available.
However, Kevin and Jim
make components for both
versions and, where
possible, make their parts
so they'll fit on the
original design.
Morphew, being a long time
aerobatic pilot who, among
other things, owned the
original Super Stinker
before selling it to
Aviat, wanted an airplane
that more closely fit his
personal definition of
what a sport biplane
should be. Where Curtis
had designed the airplane
to be "...an old man's
airplane", as he put it,
something which was much
tamer than Pitts usually
are, Ben wanted to put
some of the well known
Pitts hot-sauce back into
the design. Among the
changes he wanted were
shorter wings and longer
ailerons for more roll
rate. He also wanted the
canopy modified, something
which the Kimballs already
had underway.
Changes
from the original include
clipping a foot from each
wing and maintaining the
same number of ribs so
they were moved closer
together. The I-struts
were relocated to balance
inboard/outboard bending
moments. The ailerons were
extended clear to the tips
and run in one bay closer
to the fuselage. This
produced a 22 foot span
(an S-2 Pitts is 20 feet
and a Skybolt 24). At the
same time, they took most
of the dihedral out of the
lower wings leaving only
about half a degree and
that was mostly to avoid
the "droopy" look zero
dihedral wings tend to
have. As they proceeded
with the redesign, Curtis
urged them to design metal
ailerons as they'd be
lighter and easier to mass
produce than the wooden
ones on the original
airplane. The kits include
these metal ailerons
although the plans show
wooden ones.
To get
the C.G. problem worked
out and shorten the motor
mount, the Kimballs did
some redesign of the
fuselage which included
relocating the
pilot/passenger, in
relation to the wings. The
net result was that the
engine came back and the
tail came forward making
the airplane 10" inches
shorter. Kevin
re-calculated the tail
volumes and increased the
size of the rudder to give
the same amount of
authority the original
had.
The
canopy on the original
airplane was actually an
afterthought as the Macho
Stinker was supposed to be
an open cockpit airplane
until it was within
several months of flying.
At that point the sheet
metal was already
finished, so the canopy
wound up sitting on top of
the sheet metal combing
and used a locking and
sliding mechanism even
Curtis wasn't satisfied
with. Also, with the sheet
metal combing up so high,
the cockpit had a definite
gopher hole feel and
visibility suffered. On
the Kimball version, the
sheet metal combing is
eliminated and the canopy
comes clear down to the
longerons, ala Christen
Eagle. It is bonded to a
4130 frame and includes a
separate windshield for a
couple of reasons. "We
wanted the windshield so
in case you ever lost a
canopy, the windshield
would still be there
deflecting wind. Also,
without the windshield,
the canopy only has to
come back four inches to
clear the wing before
opening."
The
canopy also has an
intermediate locking
position so the airplane
can be taxied with it
partially open. Taxing a
bubble cockpit airplane of
any kind on a warm, sunny
day (the kind we all like
to fly on) with a canopy
that can't be opened is
too much torture for most
people.
By the time the Kimballs
began working with the
Vendenyev M-14P radial
engine from Russia, most
of its quirks had been
encountered by the
aviation movement, but not
all of them had been
worked out. The
difficulties with the
engine centre on three
things: first, the fact
the rocker boxes aren't
drained puts a lot of oil
into the bottom cylinders
which promotes hydraulic
locks on starting. You
have to be really careful
you clear the induction
tubes and cylinders.
Second, the starting
system is pneumatic which
requires a constant supply
of high pressure air.
Third, the engine fittings
are either metric or just
flat weird so hooking it
up to SAE or AN fittings
required a lot of
conversion gymnastics for
those putting the engine
in a non-Russian airframe.
A number of homebuilders
have faced and conquered
these problems and
Kimballs tossed their
accumulated knowledge into
the pot and brought all
the fixes together under
one roof. Now, anyone
seeking to hang one of
these engines on a
homebuilt (they've
actually put one on a UPF
WACO), only has to make
one phone call to solve
all their problems.
The
Kimballs interconnect all
of the rocker arms and
drain the induction tubes
into a common drain. Then
they have a gear pump that
in 30 seconds after shut
down scavenges the sump
completely drying it out
and pumping that oil into
the oil tank. The oil tank
has a shutoff valve that
stops oil from gravity
feeding into the sump
which eliminates the
problem of oil pooling on
the back of the bottom
pistons and seeping past
what they say are weak oil
rings to flood the lower
cylinders. To eliminate
the fear of cranking the
engine with the oil turned
off, the shut-off valve
has a micro-switch that
disables the starting
circuit until the valve is
turned on and oil starts
into the sump. The
Kimballs have been using a
similar system on
antiques, especially those
with Wright engines, for
years.
The air
start system depends on a
smallish bottle
pressurized to 800-900 PSI
which works through a
distributor to pump air
into cylinders in
sequence. The Kimballs
have a complete starting
system kit mounted on a
single firewall panel that
the builder just takes out
of the box, bolts to the
firewall and hooks up. The
scavenger hunt to find the
right parts has been
eliminated. One thing the
Kimballs don't use, which
Curtis did, is a shut off
on the air tank. That's
the only way to guarantee
it won't bleed down and
they say a shut off valve
is probably in their
future.
As for
the hardware to mate the
engine to "normal" hoses,
electrics, etc., they've
worked with a number of
folks and come up with a
complete fitting kit that
makes it hook up like it
was a Lycoming.
When
the airplane made its
public debut at Sun 'n Fun
the super slick cowling on
the Kimballs airplane drew
more than its share of
comments. "The problem
with making the cowl is
that the firewall is a
really weird shape, so the
cowling can't be round and
fit. We did a CAD-CAM
model of the cowling,
blending it from a
Twin-Beech sort of ellipse
to the firewall in the
computer. Then we
generated individual cross
sections at each station
and a friend with a CNC
cutter cut the cross
sections out of foam. We
stacked them up like a
wedding cake and sanded
them to shape. That went
to our fibreglass guy who
made a mould for us. The
final weight of the
cowling is 24 pounds but
we'll do it in carbon
fibre, if someone wants
it. That saves about 13
pounds but it runs about
$120 per pound saved."
The
fire wall on both versions
of the Model 12 are the
same so they make the
cowlings long enough that
they'll fit the originals
while those building the
newer version have to
whack a section off the
back of the fibreglass
unit. Kevin says they are
planning on putting a foot
square door on each side
of the cowling to make
maintenance easier.
The
massive landing gear
sports a unique
streamlining technique: A
custom extruded rubber
fairing bonds to the rear
of the gear leg and the
brake lines run through
holes in the extrusion.
The
kit, in its complete form,
has all the welded
components finished and
powder coated. There is no
welding to be done. The
ailerons are assembled and
finished and instrument
panels are ready to be
punched for instruments.
The turtle deck is
completely pre-formed. The
wings come as a wood kit
with the spars finished
and drilled but the ribs
have to be assembled. The
Kimballs have designed a
cute rib assembly jig. The
kit includes seven rib
jigs that are 3/4"
particle board with the
outline of the rib routed
deeply into the board.
Holes are drilled in the
bottom of the channel for
each leg of the rib truss.
When the jig is used, it
is blocked up off the work
bench by 1 by 2 scrap.
Short pieces of wooden
dowels (supplied) are
inserted in the holes in
the rib channels and the
rib is then assembled.
When the gussets (supplied
precut as is all the
corner blocking) are in
place, the jig is simply
tapped down against the
work bench and the dowels
force the ribs out of the
jig.
Many of
the parts, wood and metal
are laser cut with the raw
edges of the metal that
won't be welded dressed
back to eliminate any
hardening from the
laser-cutting process.
Even the plywood nose ribs
are laser cut. The leading
edges, by the way, are
plywood and formed for the
Kimballs by Steve Wolf.
As of
this writing, they had
delivered nine kits since
the first of the year and
had orders for 21. This
doesn't include numerous
parts kits they've
produced for those who are
scratch building from
plans, which is another of
the airplane's strong
points. An individual
doesn't need to pony up
all the money for the kit
because they can scratch
build it a piece at a
time. 'Have enough money
for some steel tubing?
Start building the
elevators. The money can
go in at the rate an
individual wants. The
engines, incidentally, are
still reasonably plentiful
and the prices have
plateaued for the last
couple of years at $16,000
for a brand new one.
With
all the formal stuff
behind us, it's time to
talk the important stuff:
How does it fly?
When
Steve Wolf and I got ready
to saddle up (Steve is
campaigning the airplane
for the airshow season) we
had a serious discussion
about which seat I should
sit in because he was
worried about the air
supply for starting. I
didn't really care which
seat I was in, having
flown it from the rear in
the past, so I scrambled
up front making any
starting problems Steve's
fault. I didn't realize at
the time what I was
getting myself in for as
the front seat is so wide
and low it is really, as
in REALLY, blind. Oh,
well. Between that and a
gusty, 90 degree crosswind
it would be a test for
both me and the machine.
The
start went exactly as
planned (I could've done
that...maybe) in that the
pneumatics kicked the
engine into life in just a
few blades. Ben had told
me if it doesn't start on
the first several
revolutions, stop because
something else is wrong.
As soon as the engine was
running, the engine-driven
pump started replacing the
air it had used starting.
I'm
glad I had set in the back
seat of the new airplane
because the visibility
back there is greatly
improved from the
original. In fact, it is
no worse than most other
taildraggers. Although the
length and width of the
nose gives the impression
it's blinder, it's not. Up
front, however, with the
huge instrument panel (the
cockpit is nearly two
people wide) and low
windshield with wide
framing, I had to S-turn
more deeply than usual to
make sure we didn't taxi
over a hangar or something
of similar size.
Fortunately, the Aviation
Products steerable
tailwheel made ground
handling a breeze...even
in the breeze.
Takeoff
can only be described in
two words...a blast! What
an absolute kick in the
shorts! It's not often I'm
caught unawares by an
airplane on takeoff, but
this one did. I brought
the power up smoothly
working to keep the tiny
wedge of runway I could
see right where it was on
the windshield frame. When
the throttle was about
2/3rds of the way in, the
prop went into governor
range and the surge felt
like I'd just slapped it
into afterburner. I was
congratulating myself on
doing such a great job and
had just started to pick
the tail up when the
airplane lost patience and
leaped/clawed/bounded into
the air. I was behind the
airplane in no uncertain
terms. Wow! I doubt if the
process had taken more
than 4-5 seconds. In less
time than I could think
about it, the airplane was
rocketing through 300 feet
and, between the hard
crosswind and
wrong-turning prop, I was
clear over the right side
of the runway.
I just
let it find a groove to
climb in and I guessed we
were going up about 2,500
fpm. Then I looked at the
airspeed. We were doing
130 mph! We blasted
through pattern altitude
less than halfway up the
runway and doubled pattern
altitude even as I turned
out to find a legal piece
of airspace in which to
play.
Unfortunately, we had an
unpredictable low cloud
condition so, as we
climbed on top, Steve and
I both kept a nervous eye
on where we thought the
airport was. Getting lost
in the local area is
always embarrassing.
On
takeoff we were showing
about 33-34 inches of
manifold pressure (it's
mildly super charged,
remember) which should
have given us the full 360
horses. And it felt like
it. Bringing the power
back to what Steve said
would give us a normal
cruise at about 13-14
gallons an hour left the
airspeed hanging at about
175 mph and it was truing
much higher than that.
I
wracked the wings back and
forth feeling out the
pressures and adverse yaw
and found you could tell
the difference in the
wings from the original.
It reacted to aileron
input much more quickly
and the roll rate was
noticeably higher. Since
Curtis had designed the
airplane to be more
gentlemanly than most of
his designs, when he
hinged the ailerons, he
didn't go as far aft on
the hinge point as his
other symmetrical "Super
Stinker" technology wings
because he didn't want the
ailerons that light. For
that reason, hustling
along at Bonanza speeds,
the aileron pressures are
higher than I wish they
were, a thought echoed by
Ben Morphew and a few
others. Kevin has said he
doesn't want to put spades
on it, but Curtis
reportedly told him he
might as well give in and
make the spades so he is
the one making the money
out of them rather than
someone else.
Incidentally, saying the
ailerons need to be
lighter is a relative
statement: Compared to
most "normal" airplanes
they are light enough, but
then, this isn't a normal
airplane is it? We're
talking rock and roll
here. Not foxtrots.
First
an aileron roll. Then a
positive-G 4-point. Then a
slow roll. Then a regular
four point. Then lay it on
its back and let it groove
into a hard left turn.
Yeehah! Steve told me to
loop it from level flight,
so I pulled with my right
hand and pushed with my
left and a curious feeling
coursed through the
airframe and into my body:
It was as if I was being
pulled uphill by a tractor
which had so much torque
and brute force it didn't
care that it was going up
hill carrying a heavy
load. It just kept on
chugging and I could feel
it pulling us up and over
and hardly giving up any
speed in the process. It
was as if I could feel the
lift vector that was
defying gravity shift
slowly from the wings to
the prop blades and back
to the wings again.
And
speaking of props. They
are using the MT composite
three blade prop and
recommend either those or
the similar Whirlwind
rather than the original
two blade units for a
number of reasons. The
original Russian props are
time-limited and are
getting harder to find at
a decent price. Also by
actual pull tests (a
fishing scale between the
tail and a stout hangar),
the three-blade composites
are putting out 25% more
thrust. Right. As if the
airplane needs more
thrust. The Hoffman three
blade is also a good and
less expensive
alternative.
We kept
watching the cloud layer
playing with the ground
and decided it was a good
idea to go back and shoot
some landings. The bottom
edge of the cloud layer
was right at pattern
altitude, so, as I came
rocketing down hill, we
had a real feeling of
speed as we flashed down
through the openings at
200 mph plus. At first I
thought I was going to
have trouble slowing it
down, but bringing the
power back and letting the
prop flatten out
practically throws you
forward in your seat.
Also, there were other
airplanes in the pattern
and about the only way I
could keep track of them
was to make sure I knew
where one was and pull the
airplane hard into a space
behind him which I was
positive no one else
occupied. That slowed the
airplane down too. Low
visibility in a blind
airplane and a crowded
pattern really keeps your
head on a swivel.
I had
to make the first approach
behind some yo-yo who was
making a cross country out
of his or her approach. I
avoided centerline and
kept the runway in sight
by flying a steep angle to
final from the left which
let me see the runway and
the traffic at the same
time. I had no idea what
the glide angle would be
so I kept it intentionally
high intending to slip
down in the usual Pitts
landing. This is what I
did. Sorta, but between
unfamiliarity and the
crosswind pushing us
towards final, it wasn't
very pretty. I wanted to
hold 100 mph, but wasn't
working too hard at it as
I'd already seen that any
time I wanted to kill
speed, all I had to do was
pull the power and hold
the nose in a given
position. The prop took
care of the rest.
As the
ground came up at me, I
brought it around and
lined it up with the
runway and did something I
tell my students never to
do: I was staring at only
one side of the runway.
Usually I like to look at
both sides to judge drift
and alignment. This time,
however, it took too long
to glance form side to
side, so I just snuggled
up against what I could
see of the left side of
the runway and held that.
I was a
little fast and the gusts
were doing their best to
push us off the runway,
but the little airplane
wouldn't let them. As with
all Pitts designs, it's a
terrific crosswind
airplane.
I
thought I had the three
point attitude nailed ,
but I kissed off the
ground with the mains
giving us a nice little
bounce. No big deal, just
keep it straight and don't
let it drift. Proing! It
was back down again and it
stuck this time. My feet
kept waiting for something
to happen, as it rolled
out, but other than the
occasional tap, it didn't
need anything.
I knew
a Cherokee had taken off
just in front of us and I
debated whether to make it
a touch and go, knowing
I'd catch up with him in a
heart beat. but, I
couldn't miss the
opportunity to do another
one. Power coming up, prop
surging, we leap off and I
make a slight right turn
as soon as the gear clears
looking for the Cherokee.
I kept climbing and
turning and finally
located him about 100 feet
off the right side of the
runway where he'd let the
wind push him. I just kept
the nose and power up,
whizzing up to pattern
altitude and turning over
him while he struggled
through two hundred feet.
On this
approach the wind was
really working us but I
was determined to do
better. I didn't. I kissed
it off the mains again and
hung there for a second
until it came back down.
Same deal as last time as
the airplane didn't do
anything stupid. The
conditions couldn't have
been too much worse and I
was doing much less than a
sterling job but the
airplane still behaved
like a gentleman. A very
macho gentleman.
Is this
a hard airplane to fly?
It's no cub, but other
than the lower than normal
visibility and higher than
normal climb rate, it's
much easier than any other
Pitts to fly. In fact, I
think I'd put it right in
with the Skybolt in terms
of being a terrific
airplane that can be flown
by most people. And then
there's the other question
about the prop turning the
"wrong" way. Yes, I
noticed it, but only if I
thought about it. The rest
of the time you just use
which ever foot is needed
to do what ever it is
you're trying to do.
How do
I feel about the airplane
in general? Perhaps my
wife and soul mate Marlene
summed it up best when we
were standing by the ramp
waiting for the two Model
12's to arrive at Winter
Haven. As they taxied up
and the Vendenyev's were
making that characteristic
Bearcat rumble, she looked
across the top of the car
at me with big round eyes,
grinned and said, "Now,
that's where the word
'bitchin'' came from."