Berkut
Carbon Fibre Wolf Hunter
by Budd Davisson, courtesy of
www.airbum.com
The descendants of the
Mongols of central Asia
must have an intense
feeling of pleasure
knowing they'd progressed
to the point they could
command the mighty golden
eagle to do their wolf
hunting for them. Their
name for this ultimate
bird of prey is Berkut.
'Wonder how they'd feel
seeing their stately
weapon swoop to the Earth
backwards? Its tail
feathers in front?
Those of us belonging to
the tribe EAA wouldn't bat
an eye at seeing a Berkut
swoop down to the numbers
with its traditional beak
and tail pointing the
wrong direction. That's
how far we've progressed.
We now accept the unusual
as the usual, courtesy of
the sultan of weird, Burt
Rutan. We have come so far
since the original VariEze,
4EZ, blew us away at
Oshkosh '77 with its
absolutely Buck Rogers,
this-can't-really-be-happening
appearance, that nothing
surprises us any longer.
That is why an aircraft
such as Dave Ronnenberg's
wonderfully modern
rendition of the
feathered, Mongol wolf
hunter is accepted as
being only logical. It is
part of a progression, a
natural evolvement of the
unique breed of eagles
that look as if they fly
backwards and are only a
few steps removed from an
picnic cooler in
structural complexity.
Ronnenberg and his
company, Experimental
Aviation (3025 Airport
Ave., Santa Monica, CA
90405, 310-391-8645
Editor's note: this
company no longer is in
business), have taken
the basic concept of the
VariEze/LongEZ and carried
it to the next level. A
long-time builder of
LongEZs (eight to his
credit), Ronnenberg didn't
start out to have a career
building backwards flying
machines. He had been a
serious model builder
when, in his mid-twenties
the death of his brother
set him on a new
life-path.
"That
was the turning point of
my life," he remembers, "I
needed something to help
me keep my sanity, so I
decided to design and
build an airplane of my
own."
At that time he hadn't
even been in a light
airplane, but he felt he
had to build something
that flew.
"I don't know why I
thought I could do it, but
I had no reason to believe
that I couldn't do it
either. As a child I had
always felt if I had the
right tools and the right
materials I could build
anything."
He describes that first
airplane as a cross
between a Mustang and a
Spitfire built of thin
plywood and foam. Four
years later he found the
airplane had had its
desired effect.
"At that point I realized
I had survived the
emotional upheaval of my
brother's death and at the
same time realized I had a
natural feeling for
fibreglass and composites.
I looked at that airplane
and knew I had done my
kindergarten work at one
end of it and my college
thesis at the other.
"It had been a combination
education and
psychological survival
course. it had served its
purpose, so I took a saw
to most of it and the only
time it flew was as the
parts left my hand and
spun a few times before
they hit the dirt at the
Los Angeles dump."
The canopy lines and
retract gear visually
separate the Berkut from
the EZ tribe
He had become familiar
with the VariEze through
building canards for
others and then heard the
plans for the LongEZ were
about to come out.
"I drove up to Mojave and
met Sally Melville for the
first time. I asked her
when the plans would be
out and she looked at her
watch and said, 'Oh, in
about half an hour,' so I
got in line and received
the second set."
By 1983 he had built three
LongEZs for others, hadn't
yet completed his own and
still hadn't even gotten a
ride in one. That's when
Dick Rutan and Jeanne
Yeager talked him into
coming to work on the
Voyager project. While
there, he finished his own
LongEZ.
After leaving the Voyager
project he returned to the
LA basin where he
continued custom building
and became involved with
California Microwave
modifying LongEZs to use
as RPVs. At the same time,
he was doing subcontract
work for such companies as
Yamaha, showing them how
to use fibreglass for
conceptual work, designing
prototypes, building
prototypes and anything
else that came along. He
even became involved in a
three-wheel vehicle
prototype.
All the time he was doing
this work he was working
on a new airplane, a new
evolutionary step away
from the LongEZ.
"Every LongEZ I built was
non-standard. They had
different noses, different
canopies, cowls, engines,
exhaust systems, induction
systems. I kept modifying
and improving until by
1985 I had quite a wish
list of things I wanted to
incorporate into a single
airplane. Moulding the
fuselage was high on that
list along with
retractable landing gear
and a larger engine.
"Even though I didn't know
what gear I wanted to use,
I knew I wanted to stay
away from mounting it on
the outboard end of the
main spar. I talked to
Shirl Dickey about his
retract gear and saw that
by lengthening the
fuselage to both balance
the engine and give a
larger cockpit, it also
give me room to mount the
gear in the belly. Today
Dickey makes my gear legs.
"I wanted to move
everything forward because
of the LongEZ's ability to
have an aft CG
accidentally built into
it. Also, I wanted at
least 360 cubic engines
behind the firewall
because I knew the
LongEZ's gross weight was
primarily a factor of its
ability to climb or
perform at higher density
altitudes. It all worked
together to give more room
and more power with a
cleaner airframe."
The carbon fibre gear legs
tuck up into the wings
While redesigning the
fuselage he worked on
another of his wish list
items; a completely
moulded fuselage and wing
strake package. To keep
the weight down he has
gone to carbon fibre in as
many places as possible
which he says also gives
him parts that are totally
stable once cured. He has
taken advantage of the
parts consistency by
incorporating much of his
jigging indices into the
moulds so the parts
themselves incorporate the
important match points.
It's a high tech variation
on the Tab-A-into-Tab-B
concept.
The fuselage skins, for
instance have a waterline
clearly moulded into them
along with positioning
points for the strake
skins. This eliminates the
alignment difficulties
often associated with
attaching wing strakes to
the fuselage so they are
matched and have the
proper angle.
In as many places as
possible, similar match
points are tooled in. They
are often moulded-in-place
protrusions which provide
self-alignment for another
assembly. The landing gear
assembly, for instance, is
installed this way. Rich
Riley, their
writer/PR/Do-Everything
guy has been quoted as
saying they ought to carry
the concept to the extreme
and just print the plans
on the parts.
The only parts of the
airframe that still adhere
to the original Rutan
concept of mouldless
construction in which
hot-wired cores are then
covered in glass are the
wing panels, winglets and
canard. But even in those
parts Dave applies a
different building
technique.
After laboriously
correcting the problems
endemic in hot-wiring
(wire drag, undercutting,
chatter, etc) in the cores
in his own projects, he
searched for a way for the
builder to produce
cleaner, truer cores. If
the core is perfect, the
part will also be perfect
and won't require extra
weight in the form of
fill.
The kit is supplied with
hot-wired cores that are
approximately 1/4"
oversize. Aluminium
airfoil templates are also
supplied which are used as
sanding guides. The
builder makes a long, true
sanding block covered in
36 grit which he slides
back and forth on the
templates to rough the
core to shape. Then finer
sandpaper is used until
the surface is smooth and
straight. According to
Ronnenberg, this system
always yields a part that
is die straight with a
flawless surface.
Incidentally, the kit also
includes plans for a
vacuum pump to use in
bagging the lay-ups that
costs $20 to make
utilizing an old
refrigeration unit. One of
their builders came up
with it and calls it The
Cheap Little Sucker.
The power package is a
Lycoming IO-360-B1B
utilizing one mag and an
electronic ignition unit
from Klaus Savier's Light
Speed Engineering company.
During mag checks it was
interesting to note the
normal 50-75 rpm drop on
the mag while the
electronic ignition didn't
drop a single rev. It
acted as if the mag hadn't
even been switched off.
The prop on the prototype
at the time we caught up
with it at Copperstate was
another Savier product. A
black, evil looking,
highly twisted thing, it
was a maple/composite unit
with specially shaped
blades for their aerobatic
demos but used the same
dimensions as their normal
cruise prop, 67" diameter
and 91"(!) pitch.
Norm Howell, F-16 test
pilot from Edwards and all
around homebuilt freak,
was doing the honours when
I got a chance to fly the
airplane.
I was especially glad for
Howell's restraint in not
laughing when I did the
Berkut Boogie in
scrambling aboard. The
accepted boarding method
is to place one hand on
the canard and another on
the canopy rail. Then with
a minimum of grunting you
leap and turn at the same
time, pirouetting around
to hook part of your rear
on the canopy rail.
Fearful of looking like a
wimp, I over did it and
nearly launched myself
tail first into the
cockpit.
Now comes the obligatory
prototype statement: The
kits make provision for a
step. And a step of some
sort is sorely needed,
especially if the pilot is
even less athletic than I
am (hard to believe) or
has a few female
friends/spouse who want a
more dignified way of
boarding.
Prototypes being what they
are...prototypes...they
always have a bunch of
things that "...will be
taken care of in the
kits..." In the dozens of
demonstrators we've flown,
not one has been
as-kitted, so the Berkut
is far from being alone in
that respect.
A word about canard
airplanes and especially
those with a tandem
configuration: Canards are
different than other
airplanes, both in the way
they fit and in the way
they fly. The differences
aren't huge and are easily
acclimated to by a pilot
with some adaptability
built into him. To a Spam
can driver who has limited
homebuilt experience,
however, just sliding down
into the airplane will
make him or her feel as if
they are boarding an F-16.
Or the space shuttle. And
that's not far from being
the truth. The environment
alone is enough to get the
juices flowing, both the
good ones and the bad,
which makes flying the
airplane that much more of
a challenge.
In the case of an airplane
like the Berkut, almost
every aspect of it has to
be looked at from two
points of view: The first
is how it would be viewed
by someone with experience
in canard aircraft. The
second is how it would be
looked at by the average
pilot/builder (300-500
hours total time, 35-50
hrs per year) with no tiny
airplane or canard
experience.
For instance, sliding down
into the cockpit requires
threading both legs
through cut-outs in the
bottom edge of the panel
and slinking down into a
semi-supine seating
position. To a LongEZ
driver the fit will feel
almost luxurious in both
elbow room and general
accommodations. Everything
fits the way a
high-performance pilot
sees it in his dreams. A
C-172 pilot, on the other
hand, is going to feel as
if he is being loaded into
an artillary shell. Even
though it's not even
remotely tight (how much
moving around do you
actually do on a cross
country?), it will be
perceived that way by a
big airplane pilot. To him
or her, the smallish
instrument panel is going
to feel like a lap top
computer is strapped
across his legs. Once the
pilot is accustomed to the
environment, his biggest
problem will be in staying
awake, it is so
comfortable.
As it happens, the rudder
pedals were too far away
for my what are apparently
stubbier than average legs
and we had to put a thick
pack behind me. That,
unfortunately, moved me so
far forward it screwed up
the ergonomics of the
stick placement and the
canopy curvature. It was
nothing major, but
noticeable.
Here it is again:
Kit-build aircraft have
the option of adjustable
rudder pedals.
Norm went through the
litany of avionics,
switches etc. and it was
time to crank. The
Lycoming lit off and I
felt it, rather than heard
it start barking. The
airframe is so stiff there
was no doubt when the
air/fuel mixture was right
for firing.
The brakes at first give
the impression of being
mushy, but we hadn't moved
20 feet when I began to
like the way they were
modulated. Some
steer-by-brake systems are
touchy, others not
positive enough. This one
had a nice soft feel that
developed pressure just
before actually getting
braking so it was easy to
steer.
A problem I always have
with canards is keeping my
feet off the pedals when
they aren't needed. Since
the rudders are
independent, my usual
technique of keeping
pressure on both pedals
always backfires because
it deploys both rudders at
the same time. Not
critical but certainly
strange looking to an
observer.
The Berkut canopies
probably add a lot of
complexity and cost to the
kit, but from my
perspective they are worth
every penny. The ability
to taxi with one or both
canopies open, ala F-4
Phantom, is worth its
weight in AN hardware (or
gold, which ever is
higher). The usual canopy
on a canard can't be
opened during taxi
although you can crack
them to the safety notch
on the latch. Taxiing the
Berkut like a convertible
was nice. Then, just reach
up and pull, remembering
to get the hands out of
the way when it starts
down.
Once the canopy was down,
I found my forward seating
position put the forward
canopy combing in a
position that blocked part
of the top row of
instruments including the
airspeed. Again,
adjustable pedals will
solve that.
As we lined up on the
centerline of the big
Williams-Gateway 12R, I
was conscious of a lot of
pressure on the side stick
from the elevator trim
springs. Norm had said it
was trimmed okay for
takeoff, but there was no
trim indicator so that was
an educated guess.
The plan was to accelerate
to 90 mph, smoothly rotate
and climb out. With that
in mind, I eased the power
in, remembering I might
need some brake to steer.
It took only one tiny poke
with the brakes before the
rudders took over. Then it
was just a matter of
waiting a few seconds
until the needle started
towards 90 mph. I gently
increased back pressure on
the stick and found I was
still fighting a lot of
trim pressure. Norm had
said the elevator would
blow up to neutral and
lighten the trim load.
Apparently it needed the
trim rolled further back
because it took a lot of
muscle to get the nose up.
When the nose cleared the
runway, the airplane
started off the ground and
I went to check the nose
and hold that exact
attitude. When I did, the
nose dropped far more than
I wanted with the help of
the trim springs and I
skipped off the runway.
Embarrassing! That was
okay, though, because I'd
embarrass myself much more
later in the flight.
A quick fix for the trim
problem would be a trim
indicator, which could be
nothing more than a paint
stripe on the inboard end
of a canard tip where the
elevator mates.
Once off the ground I
found holding the pitch
attitude required some
careful isometrics of me
against the springs until
I had enough sense to
reach up with a thumb and
toggle the lollipop trim
switch on top the stick
back a couple times. Then
life became much more
livable.
The airplane was moving
around a little because I
hadn't yet learned to
appreciate how rapidly the
airplane responded to any
kind of aileron pressure.
Any kind!
Retracting the gear was
strictly a matter of
throwing the small switch
between my legs up. If the
lights hadn't winked I
would have never known
anything had gone on,
since the airplane didn't
do anything unusual.
Norm Howell
pilots the
Berkut past the
Superstition
Mountains east
of Phoenix. The Berkut may owe
some of it's
lines and
concept to the
Rutan EZ lines,
but the design
is entirely new.
Norm's patient, reassuring
voice in the Bose
noise-cancelling headsets
(which really worked and
are a necessity) told me
anything over 100 mph was
good for climb. I was
doing a solid 110 before I
pulled up into the climb
and we started upstairs
like a bullet. The
literature says 2,000 fpm
which looks about right,
but the airplane felt much
better the faster it went.
The difference in actual
climb rate between 110 mph
and 140 mph wasn't enough
to really notice, but the
airplane seemed much
happier and was much more
stable at those speeds.
It is important you
picture what flying
something like the Berkut
looks and feels like from
inside the Raybans. For
one thing, compared to
most airplanes, you're
practically laying on your
back, which is, of course,
an illusion. It's supine,
but not very. The
instrument panel is just
above your knees gently
caressing your Levi's and
your legs are straight out
in front of you. All
rudder work is strictly
from the ankles down. The
legs never move. Glass
wraps from just above your
elbows, over your head and
sweeps down to the top of
the panel, giving the
feeling the airplane stops
just in front of the
panel, since practically
none of it can be seen.
Although the canard is out
there, it never occurs to
you to look at it. It is
mentally invisible.
The tiny throttle sticks
up under your outstretched
left arm and your right
arm is slightly, only
slightly, bent so your
hand can wrap around the
side stick. The trim
switch is on top the
stick, but a small square
box on the side of it has
a bunch of push buttons
that flip-flop the comm
and nav and let you talk
to the outside world.
The movements required to
control the airplane
aren't movements at all.
Especially in roll. The
old saying about the
airplane reading your mind
absolutely applies here.
In normal manoeuvring, the
stick doesn't move at all.
Just the gentlest of
pressures is all that's
required to whip one wing
down. The pressures
required are so slight,
sometimes its hard to tell
whether you actually
touched the stick or not.
The ailerons have
absolutely no break-out
forces. Nothing. None.
Nada. They offer no
resistance so centring the
stick is strictly a visual
affair because there is no
small notch between
pressure build-ups letting
you know you've found
centre.
Furthering the feeling of
mind-over-matter aviating
is the tremendous roll
response/acceleration
right around neutral. Just
the slightest pressure
results in 5-10 degrees of
bank instantly.
But, the illusion of
whipping around the
longitudinal axis is just
that...an illusion. The
actual roll rate isn't all
that high and the aileron
pressures required to get
max rate are also far from
being light, especially
when measured against the
response and pressures
right around neutral. The
pressures aren't linear.
This is just an analysis
of the aileron feel, not a
criticism. However, things
happen very quickly right
at neutral and it is no
place for a ham handed
pilot. The feel isn't that
much different than a lot
of canards, but the
response is much higher,
which is a welcome change.
The airplane also has yaw
characteristics that are
probably typical of highly
swept wings. They give a
huge amount of dihedral
effect with yaw, so there
is a definite coupling of
roll with yaw. Swing the
nose side ways with rudder
and you get some definite
roll with it.
The adverse yaw is also
interesting. At cruise
speeds adverse yaw is
close to being
non-existent. In fact,
because of the roll-yaw
couple, you're better off
keeping your feet on the
floor. Something I never
did do very well.
At slow speeds, the
airplane has a bunch of
adverse yaw. Actually, at
slow speeds it has what
might be considered to be
"normal" coordination
requirements while at
cruise speed it acts more
like a jet.
Once trimmed out in level
flight, the airplane just
sits there requiring
little or no input from
the pilot. If upset by
turbulence, however, the
airplane takes a while to
recover on its own. A few
pitch stability tests
showed the airplane to be
statically positive, but
not strongly so. Pulled 15
knots off cruise and
released, it gently
started back down and then
surprised me by not over
shooting the original
speed by more than about 8
knots. It damped out
completely with no long
terms in two very
leisurely cycles.
In setting up for cruise
the aerobatic prop made
itself known, however, the
extreme effort for fuel
efficiency also showed. At
2600 rpm, the electronic
monitoring panel showed
only 19.5 inches of
manifold pressure! We were
truing a shade under 180
knots (207 mph).
Apparently Dave and his
guys wind it up a lot
faster, around 2800 rpm in
cruise, but that seemed
awfully fast to those of
us used to normal looking
numbers. With their
earlier engine, which was
slightly hot rodded, their
speed tests showed 75%
cruise to be about 208
knots true at 8,000 feet
(1228 mile range, 10.3
gph) and the economy
cruise was 187 knots (1514
mile range with 30 minute
reserve, 7.7 gph). Race
speeds which were
officially recorded at
various canard bashes ran
between 240 mph and 248
mph. It would take a fast
wolf to escape this
Berkut.
The extreme stiffness of
the airframe was very
noticeable when cutting
through turbulence. Since
we were whistling along at
over 200 mph and nothing
in the airframe was
flexing to absorb energy,
even moderate chop
hammered at us with sharp
edges.
'Wondering about how I
embarrassed myself the
second time? The belly
board speed brake is a
T-shaped handle on the
left side of the throttle.
The mixture is a much
smaller, but still vaguely
T-shaped handle on the
right side. Guess which
one I pulled during slow
speed tests for gear and
speed brake effects? Like
I said, embarrassing.
The gear speed is 150 mph,
so it can be used to slow
you down, but it really
doesn't add that much drag
and there is very little
pitch change. It doesn't
require retrimming at all.
The belly board does pitch
the nose down and does a
lot for increasing speed
stability when slow. If
the power is up when the
board is down there's a
lot of buffeting from the
prop working in dirty air
but that all disappears
when the throttle comes
back.
The airplane takes some
planning in approach just
to get rid of the speed.
Then it needs careful
attention to keep the
speed down. Norm wanted
100 on down wind and 90
down close to ground
effect to leave enough
canard authority in the
bank to flair comfortably.
Keeping it at 100 mph was
a chore in the beginning,
since just the tiniest
nose pitch change gave an
extra 10 mph. Once it got
down to 90, it was much
easier to control and was
close to being speed
stable at 85. In this
respect, it was very
canard-like.
The visibility over the
nose is awesome on short
approach. Also, once the
airplane is slow with the
speed brake out, it
actually comes down at a
much steeper angle than
you'd expect for such a
clean bird. Many canards
need very flat approach
angles. When the glide is
broken it takes some
concentration to keep from
over rotating because the
nose is so low it is
almost out of sight. In
fact, an attitude that
looks to be nearly level
is actually a good landing
attitude.
Norm was intoning height
above the runway as I
willed the airplane down
the last 5 feet. It was an
interesting balancing act
between me, the trim
springs and an airplane
that I knew would dart at
the runway if I released
any back pressure but
would be all too happy to
balloon if I increased
angle of attack a fraction
of a degree. I just kept
working at it until the
mains thumped on. The nose
stayed in the air until I
tried to gently lower it,
at which time, it decided
it had had enough and
dropped to the ground as
if relieved the flight was
over.
Solid braking stopped us
at the intersection and it
showed no urge at all to
do anything but roll
straight ahead.
About that time I took my
first breath since
downwind.
Certainly one of the most
asked questions about the
Berkut is Ronnenberg's
relationship with Burt
Rutan.
Dave's response is, "When
designing this airplane,
there were several things
I wanted to address and
number one was I didn't
want to anger Burt Rutan.
He's a friend and we have
conversations but we don't
talk engineering, I don't
ask for advise or help.
He's keeping an arm's
length relationship with
me which I think is
necessary.
"The airplane exists
because of Burt, but only
because he designed the
airplane from which it
evolved. But it evolved
without his assistance. He
was completely and totally
separate. He had nothing
to do with the program
whatsoever and I think
he'd like people to know
that.
We didn't discuss the
subject with Burt, but
maybe we didn't have to.
For one thing, the
semi-finished Berkut in
the Experimental Aviation
booth at Oshkosh had the
owner's name on it...Dick
Rutan. Also, Ronnenberg
recounted an incident at a
past Rutan forum where
Burt was saying he would
never be involved in the
sale of kits and plans
again, but said something
to the effect of, "...but
if you'd like to see
something I like, go see
the Berkut..."
At this point in time
there are nearly 50 kits
in the field and Dave
Ronnenburg expects at
least three at Oshkosh 95.
In the meantime, keep your
wolves under cover. The
Berkuts are coming.
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