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The
HKS 700E is a 60HP, horizontally opposed, two cylinder,
four-stroke engine. The 700E uses a combination of high
technology and simplicity to achieve the twin goals of high
power output and reliability. The 700E is a very high quality
product. Every major component was designed for light aircraft
use and is made from the best materials and techniques
available.
In power to weight ratio, the 700E matches conventional
two-strokes. The real difference, however, is in the high peak
torque (62ft.lbs) of the engine and the very flat torque curve.
This allows the 700E to pull better in a climb or hold a higher
prop load (pitch) than the 60 horsepower rating would suggest.
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The
integral gearbox on the 700E uses straight cut gears with a
spring-washer type torsional coupling ahead of the large flywheel. The
gearbox is attached to the flywheel case; the gears are lubricated by
the main engine oil system, the same as a Rotax 912 four-stroke. The
gearbox can be run up or down and is changed by rotating the flywheel
case around. The large flywheel mass and attention to the internal
balance of the engine are the keys to the smooth running and low
vibration of the 700E. At lower RPMs you can hear the gears singing, not
clattering. The standard gear ratio is 2.58 to one. As the Max
permissible RPM is 6200, the RPM at the prop is 2400, similar to a 3 to
1 gearbox on a Rotax two stroke.
The prop hub bolt pattern is the popular 75MM pattern; the direction of
rotation is the same as a Rotax two-stroke. HPower has conducted
baseline tests of several popular propellers, including the Ivo-prop,
Power-fin and Sport props. In tests, the 700E can swing a 74" two
blade and a three blade 68" was typical. The engine was just as
smooth with a two blade prop as three. This also allows the use of a
light wood two-blade for certain applications.
The induction system of the 700E has been optimized for a wide torque
band. The runner lengths are tuned for this purpose. The carburetors are
the Bing Constant velocity type, which varies the mixture with
horsepower and provides a modest amount of altitude compensation. These
are the same carburetors used on the Rotax 912 four-stroke.
The valve train of the 700E is operated with pushrods off of a single,
centrally located camshaft; valve lash is adjusted automatically with
hydraulic lifters. The crankshaft and connecting rods are forged, and
run in split shell type bearings. During overhaul the crank and
connecting rods won't have to be replaced, just the bearings. The
cylinder bores are Nickel-ceramic coated for wear resistance and thermal
compatibility with the expansion of the piston.
The dual CDI (Capacitive Discharge Ignition) is a programmed smart type
that varies the timing for ease of starting, smooth idle and detonation
resistance. The connectors to the electrical system are large sealed
type and can only attach to the correct component. The charging system
is 15 Amp-180 Watt. HPower has tested several tachometers and can help
you choose the correct type for your plane.
The exhaust systems that are provided in the complete packages are
beautiful. Made from steel feature attractive aluminum electroplated
coatings for corrosion resistance, they come in four configurations (two
manifold types, two mufflers) and can be modified with optional stock
components. HKS is a big producer of performance exhaust systems for all
types of cars and their expertise clearly shown in the design and
fabrication of the manifolds and the mufflers.
HPower has been testing the 700E on a Flightstar-IISC test bed since
July'97 and the results have been impressive. The engine has been easy
to start, very fuel efficient and reliable in operation. The range of
the Flightstar-IISC was effectively doubled with the switch out of the
standard 503. The fuel specifics sent from Japan indicated a fuel burn
higher than we achieved in testing; the factory spec is based on a
constant peak torque load while dyno testing. This would be the
equivalent of a very high pitch prop and full throttle. Our testing with
typical, fixed pitch propellers showed an average fuel consumption of
between 1.8 and 2.25 gallons an hour at typical cruise settings. |
