7. AIRCRAFT and SYSTEMS DESCRIPTION
GENERAL
The AVID Mk4 Speedwing is a side by side metal tube and fabric covered sport aircraft designed
by Dean Wilson and first flown in the late 1980’s. There are several hundred Avid Mk 4 aircraft in
operation. Most are equipped with the Rotax 582 2-cycle engine. Others are equipped with
Rotax 912, Jabiru and Subaru engines, among others.
The Aerobatic Speedwing version of the aircraft differs from others of the same model
designation in its wingspan, wing area, wing aerofoil section and its wing structure. The
Aerobatic Speedwing has an aluminium leading edge, a semi-symmetrical wing section and a 6’
shorter wingspan than the standard Avid Mk4. Consequently, it cruises and stalls faster and is
stressed to be fully aerobatic
When operated at a weight of 1050 pounds, the design is fully aerobatic to ?? G’s positive and
negative, ultimate strength is ?? G’s. The roll rate is ???? degrees per second. However, the
aircraft has no inverted fuel or oil systems and so inverted and sustained negative G maneuvers
are no permitted.
ENGINE
The Jabiru 2200 engine is an 80 HP aviation engine manufactured in Australia and certified by
the Australian Civil Aviation Safety Authority. The engine is a 4-cylinder 4-stroke horizontally
opposed air-cooled engine. The engine is direct crankshaft driven and does not use a reduction
gearbox. The crankshaft features a removable propeller flange, which enables the easy
replacement of the front crankshaft seal and provides for a propeller shaft extension to be fitted,
should this be required for particular applications.
The crankcase halves, cylinder, crankshaft, starter motor housings, gearbox cover (the gearbox
powers the distributor rotors) and coil mounts together with many smaller components are
machined using CNC machine tools. The sump (oil pan) is cast. The cylinders are machined
from solid bar 4140 chrome molybdenum alloy steel, with the pistons running directly in the steel
bores. The crankshaft is machined from solid bar 4140 chrome molybdenum alloy steel, the
journals of which are precision ground prior to being Magnaflux inspected. Conrods are
machined from 4130 alloy steel, the 45mm big end bearings are of the automotive slipper type.
Various components of the engines are sourced from Honda including camshaft followers, the
Bendix gear in the starter motor and the ignition coils.
An integral alternator using rare earth magnets, provides alternating current for battery charging
and electrical accessory drive. The alternator is attached to the flywheel and is driven directly by
the crankshaft. The ignition system is a transistorised electronic system; two fixed coils mounted
adjacent to the flywheel are energised by rare earth magnets attached to the flywheel. The
passing of the coils by the magnets creates the high voltage current which is then transported by
high tension leads to the center post of two automotive type distributors (which are simply rotors
and caps) before distribution to automotive spark plugs, two in the top of each cylinder head.
The ignition system is fixed timing and, therefore, removes the need for timing adjustment. It is
suppressed to prevent radio interference. The ignition system is fully redundant, self-generating
and does not depend on battery power.
The crankshaft is designed with a double bearing at the propeller flange end and a main bearing
between each big end; it therefore does not have flying webs. 48mm main bearings are also of
the automotive slipper type. Thrust bearings are located for and aft of the front double bearing
allowing either tractor or pusher installation.
Pistons are General Motors aftermarket re-machined to include a piston pin circlip groove. They
are fitted with 3 rings, the top rings being cast iron to complement the chrome molybdenum
cylinder bores. Valves are 7mm (stem dia) which are purpose manufactured for the Jabiru
engine.
The valve gear includes pushrods from the camshaft from the camshaft followers to valve
rockers which are CNC machined from steel plate, induction hardened and polished on contact
surfaces and mounted on a shaft through an aluminium bronze bush. Valve guides are
manufactured from aluminium/bronze, as is found in larger aero engines and high performance
racing engines. Replaceable valve seats are of nickel steel and are shrunk into the aluminium
cylinder heads. The valve gear is lubricated from the oil gallery.
An internal gear pump, direct mounted on the camshaft and incorporating a small automotive
spin-on filter, provides engine lubrication. An oil cooler adapter is provided.
The engine is fitted with a 1 kw starter motor, which is also manufactured by Jabiru and provides
effective starting in all conditions. The engine has very low vibration levels, however it is also
supported by four large rubber shock mounts attached to the engine mounts at the rear of the
engine.
The fuel induction system comprises a BING pressure compensating carburetor. Following
carburetion, the fuel/air mixture is transported to a small plenum chamber in the sump casting, in
which the mixture is warmed prior to entering short induction tubes attached to the cylinder
heads.
The engine is fitted with two RAMAIR cooling ducts, which have been developed by Jabiru to
facilitate cooling using direct air from the propeller to the critical areas of the engine, particularly
the cylinder heads and barrels.
A stainless steel exhaust and muffler system is fitted as standard equipment, and results in
aircraft noise of approximately 62dB in a 1000' full power flyover.
4 Stroke
4 Cylinder Horizontally Opposed
Naturally Aspirated - Pressure
Compensating
1 Central Camshaft 6 Bearing Crankshaft
Over Head Valves (OHV) Ram Air Cooled
Wet Sump Lubrication Direct Propeller Drive
Dual Transistorized Magneto Ignition Integrated AC Generator
Electric Starter Mechanical Fuel Pump
Push Rods
The engine is rated at 80 horsepower at 3200 RPM. Cylinders are numbered 1) right forward, 2)
left forward, 3) right aft and 4) left aft. Each cylinder has a cylinder head temperature probe
located under one of the two spark plugs in each cylinder. There are four exhaust gas
temperature probes located in each exhaust pipes. The two transistorized magnetos are timed
to fire at 25 degrees BTC. The timing is not adjustable.
The engine mount is of steel tube construction. Cooling air flows through the RAMAIR cylinder
shrouds, over the cylinders and downward. Cooling air also flows through the converging space
between the engine sump and oil cooler mounted below the sump.
Induction air is drawn through a hole in the lower cowling ahead of the left front cylinder through
a combined alternate air box and air filter housing which is mounted on the firewall and into the
carburetor. The alternate air may be manually selected by a push-pull control located in front of
the instrument panel ahead of the pilot seat. Heated air enters the alternate air inlet from a
shroud mounted behind the muffler.
