November 1995 (Page 76)...Reprinted with
permission
By LeRoy Cook
Well-designed
airplanes can have their basic structures adapted for many different
uses, as
well as incorporate modifications without undue effort. The Merlin GT I
flew
for this pilot report is such an airplane. It can fly with various
power
plants, carry a good load and land in just about any farm field -and it
can
even give up its wings and WI feathers to create a lightweight
offspring: the
E-Z Flyer, a plane that lives up to its name (see the sidebar).
The
Merlin GT
The
Merlin is a perky two-place
tail dragger kit aircraft designed by John Burch in 1989 as an answer
to the
need for an off-airport bushplane that was a bit more roomy and rugged
than the
tiny aluminum-frame airplanes on the market. "It was designed to land
just
about anywhere," says Burch, now general manager of Merlin Aircraft.
"For that reason, we're known as the Jeep of the kit airplane
industry."
Originally produced as the Macair Industries Merlin, the firm has been
owned
since 1993 by Reg and Kevin Adarns, operators of a large warehousing
and
transportation company, headquartered in Muskegon, Michigan. Merlin now
ships
kits to just about any part of the world where a simple-to-build,
rugged aircraft
is needed; one of the airplanes on the flight line when we visited was
headed
for Portugal. Some 200 Merlins had been sold by the end of 1993,
according to
Burch.
An
Arkansas Reunion
Because
winter had already
arrived at the Michigan factory, we met at a slightly warmer location,
the
unofficial Merlin skunk works in Jonesboro, Arkansas, situated on the
Classic
Airstrip east of town. Merlin's dealer and development specialist in
Jonesboro,
Scott Haggenmacher, was on hand with Burch to show off the company's
latest
achievement, the Forinula/N4erlin power package installed on a Merlin
GT
airframe.
Subaru
Power
The
new powerplant is a
much-enhanced conversion of the Subaru EA 81 flat-four, liquid-cooled
auto
engine, built by Formula Power in Concord, California. The
Formula/Merlin puts
out I 10 hp on the dynamometer at 4800 rpm and weighs 185 pounds with
its
1:1.84 ratio cog-belt reduction drive. All-up, ready-to-fly weight,
including
exhaust, radiator and vital fluids, is only 230 pounds. Obviously, this
is no
stock automobile engine; Formula Power adds goodies like hydraulic
valve
lifters, dual independent ignition and an airflow fuel injection
system, then
carefully balances and blueprints the engine, resulting in a conversion
ideally
suited to the Merlin. An SAE No. I prop hub mounts a three blade Great
American
fixed-pitch wood propeller on the dark-blue testbed airplane, which had
been
built up by Scott Haggenmacher and crew.
The Merlin has evolved from using the two-stroke Rotax 582/618, Re a
lot of
light kit airplanes. With the development of the Formula/Merlin
package, Merlin
Aircraft plans to offer three engine options: the Rotax 912 (which we
also flew
for comparison), the Subaru conversion, and the old reliable
Continental
small-fours of 65-85 hp. The lightweight Rotax carries its battery on
the
firewall to keep the c.g. from moving too far aft, while the Formula
and
Continental engines have the battery in the baggage compartment.
Nose
to Tail
The
GT's composite cowling is
relatively blunt, accentuated on the Formula powered airplane by the
fact that
it was operating without a spinner for test purposes. At the time of
our
flight, only 10 hours had been logged since the installation. The
24x18-inch
aluminum radiator -from a Volkswagen Scirocco- was positioned on an
adjustable
mount behind and below the engine, near the c.g. By comparison, the
Rotax 912's
radiator and oil cooler are mounted under the forward part of the
compact
engine, visible through an inlet under the spinner. In both cases, the
cowling
could be opened quickly by CamLoc fasteners for inspection or
maintenance.
The standard fuel system consists of a single 13-gallon tank above the
cabin,
its contents visible simply by looking up. Both of the demonstrator
aircraft we
flew had the popular dual-tank option, using 8-gallon aluminum tanks in
each
wing and electric gauging, which allows an overhead skylight to be
installed.
The Merlin GT's wing structure consists of a 9-inch-deep aluminum spar
with a
0.040-inch-thick web, doubled to 0.080 from the strut attachment point
inboard.
A load-carrying D-section leading edge is supplied already attached to
the
spar, with only the rib attachment rivets left out for the builder to
install.
Nose ribs are factory fitted at 6-inch intervals; the wing bay ribs,
with
24-inch spacing, are high-density foam with aluminum caps and spacers.
The
PolyFiber wing covering is pop-riveted directly to the caps. A massive
1.5-inch
drag strut runs from the rear wing-folding fuselage attachment to the
spar, and
the 2-inch tubular aluminum lift strut, streamlined with a plastic
fairing,
assures accurate dihedral.
Burch is proud of the Merlin's quick assembly and simplicity of
rigging; when
the struts and fittings mount to the fuselage, the wing is prealigned.
Wing
folding is provided for compact storage; Merlin does not recommend
routine
folding for towing or trailering, due to the possibility of damage from
road
rash. The fuselage truss is a prealigned assembly of 5/8-inch steel
tubing, a
distinguishing Merlin hallmark.
Burch prefers paint over powder coating because it is much easier to
remove,
should it ever become necessary. A 100 pound-capacity baggage
compartment of
1/4-inch plywood is behind the seats, reached by lifting the hat tray.
The
seats are not adjustable but can accommodate varying sizes of people by
installing or removing cushions. Swing-up doors are fitted on both
sides of the
fuselage, latching to the underside of the wing. They may be opened and
closed
in flight, but the long stretch into the slipstream to reach the handle
can be
a challenge.
The almost-square platform of the tail surfaces is a trademark of the
Merlin
design; the horizontal tail has a 7-foot span and a 3.58-foot chord.
The
empennage comes prebuilt, needing only covering and a couple of holes
drilled
to be ready for installation. In fact, the whole Merlin GT project
requires but
350 to 450 hours to build -a figure supported by several builders,
Burch says.
Merlin also prides itself in supplying a complete kit--engine,
propeller,
covering, tires- everything to make a flyable ready-to-paint airplane.
Comparing
the Merlin GT
Engine Options
The
day was crisp and bracing
for Arkansas -one of those days when the air will be fat with lift and
any
ripples will probably be due to your own wake turbulence. We first
climbed
aboard the maroon-colored, Rotax-powered GT to see how it performed on
the
78-hp 912; venturi-driven gyro instruments were installed, as was an
electric
turn-and-bank, and a three blade, ground adjustable Warp Drive
propeller was
fitted, replacing the standard two-blade unit.
Once aboard, there was more than ample room for two well-bundled
individuals;
the optional overhead skylight aids forward and upward visibility and
gives an
added air of openness to the cockpit. In response to the burning
question of
the day, Bruce said, yes, a cabin heater could easily be plumbed from
the
radiator; he suggested a salvaged motorcycle radiator, complete with
fan, or a
Ford Escort heater core, both perfect for the job. Toe brakes were
installed on
the left rudder pedals only, so we gladly relinquished that seat to
Burch until
we got familiar with the Merlin's handling.
A pull of the choke and a twist of the key brought the Rotax to life,
and once
it had warmed up into a stable unchoked idle we were ready to go.
Taxiing is
wonderfully straightforward, the steer-able tailwheel pivots the Merlin
on a
dime, and there's little need for brakes with proper planning. The
wide-track
Merlin is so stable on the ground that an intentional groundloop is
recommended
in an emergency short-rollout situation, usually resulting in no
damage. The
dual ignition modules were checked and the instruments set and
verified; once
the controls were tested and the trim tab was adjusted, we were out of
excuses.
It was time to fly.
The 912 wound up quickly to 5200 rpm, hopping us off in a few hundred
feet at
40 mph indicated. We pulled up quickly into a steep 50-mph climb,
resulting in
a solid 600-fpm ascent with two aboard, later improving to 800 fpm when
we flew
solo. We leveled at 1000 feet to set up a routine 4600 rpm cruise,
which
resulted in an 82-mph IAS. Handling was predictable, with acceptable
stick-free
stability in pitch and a modicum of yaw-roll coupling to allow us to
rudder a
wing back up if our hands were busy. While the long Junkers-style
ailerons
generated some adverse yaw, there was plenty of rudder power to
persuade the
Merlin to start and stop turns. The Rotax muffler on the 912 resulted
in an
extremely quiet cockpit for a light aircraft; most of the noise was
from the
rush of the wind and the rattling of the doors.
In stalls, we found a good burble and mild break at 42 mph power off,
slowing
to 35 mph when we cranked in some throttle. If aggravated, the Merlin
would
drop a wing, but it allowed us plenty of time to get out before that
occurred.
Back at the home port, we shot a few approaches at 60 mph, slipping off
excess
altitude when we arrived a bit high. Burch eschews flaps or flaperons,
avoiding
the added complexity and degraded aileron effectiveness. Landings were
an easy
transition from a tailwheel-first touchdown to fast taxiing. We
consistently
turned around at the 800-foot point, even while landing over a set of
power
lines. Ground roll was probably 300-400 feet, with no brakes needed.
One caveat
was pointed out by Burch: The slope of the cowling sides causes the
nose to
taper in toward the front of the engine, leading one to touch down with
the
aircraft pointed at the side of the runway, rather than the centerline.
Once
noted, it can be accommodated by a top of the rudder.
Behind
the
Formula/Merlin Engine
Switching over to the Subaru-conversion Merlin, we found a somewhat
heavier,
more solid-feeling airplane. Choke and timing are entirely automatic,
so
starting and runup is a non-event; there is a mixture control, unlike
the Rotax
installations, and two electric fuel pumps are standard, one full-duty
pump and
a second standby pump switched on for takeoff and landing. Starting
requires
some priming action by the primary fuel pump, after which it is turned
off to
avoid flooding; once the engine is cranked into life, the fuel pump is
brought
on line to smooth the idle.
Taxiing reveals the extra weight of the Formula power package; some
leaning
helps keep the engine smoother during taxi. Runup was elementary, as
there was
no ignition check (the developmental engine did not have the production
powerplant's redundant pickups, coils and modules), few instruments to
scan and
the engine was still warm from a previous test hop, At full power we
hopped off
with 4800 rpm in the climbout; we netted about 700 fpm with the two of
us
aboard, holding about 55 mph for the climb. Leveled into cruise, we saw
an easy
93 mph at 4500 rpm, and 4200 rpm maintained about 90 mph; the engine
was very
smooth at this power setting, after the busy climbout power.
The aircraft's heavier feel resulted in friendly manners at cruise.
With the
c.g. moved forward by the heavier engine, pitch stability was
noticeably
improved. The controls were stiffer, from both added weight and speed.
The
noise level was... well, loud. The prototype exhaust lashup was to be
changed
to a more effective system, Burch said.
Landing approaches were flown at 60-65 mph, completely power off, and
the
Merlin touched down at 45-50 mph, rolling out in less than 500 feet. As
with
the, Rotax-powered airplane, the wide gear and docile handling made
landings
simple, as long as we remembered the curve of the cowling.
Given that the Formula/Merlin engine can deliver more than 30 extra
horsepower for
$1000 or so less investment and with but 50 pounds of added weight, it
seems to
be a good bet for a Merlin GT powerplant. I had few complaints about
the way
the Merlin flew; I would prefer the dual throttle setup, so I could
retain my
right-hand-on-stick, left-hand-on-throttle geometry, and it would be
nice to
have the elevator trim twist-knob between the seats, rather than under
the
pilot's left knee. All in all, however, the sturdy little Merlin is
exactly
what it is claimed to be; a rugged boondocks airplane that isn't afraid
to get
dirty. KP
Reprinted/Distributed
with
permission
By LeRoy Cook; Kitplanes magazine; November 1995
copyright 1995