INSIDE THE ENGINE B22/B25
AeroPower Engines: general characteristics
· 4 stroke engine Otto cycle, 4 cylinder Boxer.
· Single Over Head Camshaft (SOHC), with cam follower and 2 valves per cylinder.
· Timing with gear and chain using an automatic chain tensioner with torsion spring.
· Governor for constant speed propeller with electro-hydraulic control, integrated in reduction box (optional).
· Integrated water tank with pressurized cap.
· Forced lubrication with internal gear (gerotor) pump, semi-dry sump without external pipes.
· Double injection and ignition system fully redundant, based on alfa-n strategy, with diagnosis and limp-home functionality.
· Mapped ignition with inductive coil, mapped dwell time and air temperature correction.
· Mapped fuel injection with altimeter, oil temperature, and air temperature correction.
· Fuel pump automatically controlled by the ECU.
· Auxiliary fuel pump, for take off and landing.
· Electro-hydraulic Active Damper Control (ADC System, Patent pending) to control torsional vibration in idling and low RPM condition.
· Electric starter with permanent magnet (12V 0.8kW).
· Start relay 300W.
· Inductive alternator with permanent magnet with counter-phased windings (300W).
· Voltage regulator (26A).
· Data export line for transmission between ECU and EFIS or EMS based on CAN-Aerospace protocol (optional).
AeroPower Engines: description
AeroPower engines are 2200cc (B22) or 2550cc (B25) fuel engine, with 4 cylinders, four stroke and boxer disposition: this engine layout, which is very common for aeronautic applications, reduces vibration and improve torque regularity. The B22 has a composite crankshaft, press fit and forged of high strength steel. The crankshaft is mounted with four large ball bearings.
The connecting rod is monolithic, pressed from carbon steel and uses a needle roller bearing.
The pistons are machined directly from a block of alloy with low thermal dilation.
The service shaft, placed over the crankshaft, is connected to the crankshaft using two gears, and turns at a lower speed than the crankshaft. The timing chains (one for each bank) and the oil pump are connected to the service shaft. The disengaging system for the start system is also mounted on the service shaft.
There are two camshafts, one for each engine head, driven by the timing chain that is kept at the proper tension by an automatic tensioner. The camshaft lobes move directly on the cam follower, operating on a hardened metal shim. Inside the camshaft there is a hydraulic valve lifter that is controlled by an electro valve. The hydraulic valve lifter is used to reduce the compression of the engine so that it is possible to start the engine with a small starter and battery (a failure of the hydraulic valve lifter does not compromise flight safety).
The gearbox, used to reduce revolutions from crankshaft to prop shaft, is composed by two helical gears. Each gear and respective shaft is monolithic and is mounted with a large ball bearing. Lubrication of the gearbox is separate from the engine lubrication and uses special transmission oil.
The gearbox is designed to be integrated into the hydraulic system to produce a constant propeller speed. The gearbox does not include a damping system thanks to the ADC system that avoids any vibration at low RPM.
The lubrication system uses an internal gear pump (gerotor). All of the lubrication circuit is machined in the casting (no external pipes). The oil filter is a cartridge type and the B22 does not requid re an oil radiator.
In case of an oil pump failure, the engine can run for 15 minutes with a lower power generation. The blow-by gases are vented directly from the intake manifold.
The fuel system uses a fuel pump controlled by the ECU and the fuel pressure regulator is integrated in the engine and the rail is made of steel. A second pump (auxiliary) is use when safety flight condition are requested (take off, landing): this is manually switched.
The fuel injection and ignition system uses an ECU that is installed on the top of the engine. It controls the ignition advance and injection timing based on the mapping of the RPM and throttle valve angle and then corrects the advance and injection using the mapping of the oil temperature, air temperature and battery voltage.
The electrical system has been designed so that the engine, running above 1500 RPM can run normally in case of a battery failure. The electrical system is pre-installed on the B22: two sealed connectors with safety locks are arranged to connect the engine’s electrical system to the body of the aircraft. All the connectors of the electrical system are sealed and equipped with a hold-within system to protect the wiring loom from vibration and traction stress.
The engine has four integrated rear attachments for wall mounting and four bottom attachments for floor mounting in the engine compartment. The attachments are made with a special shock absorber made of rubber with four different hardness’s.
AeroPower Engines: version and performance
AeroPower engines are been designed to generate up to 200 HP (in a future turbocharged version).
The versions that are currently available are:
· B22D – without gearbox, max power 95HP@3300RPM, max torque 21Kgm@3200 RPM, dry weight 74kg.
· B22L – with gearbox, max power 115HP@3950RPM, max torque 20.8kgm@3950RPM, max propeller speed 2400RPM, dry weight 79kg.
· B22R – with gearbox, max power 130HP@470RPM, max torque 20.5kgm@4550RPM, max propeller speed 2400RPM, dry weight 79kg.
· B25D – without gearbox, max power 110HP@3300RPM, max torque 24Kgm@3200 RPM, dry weight 74kg.
· B25L – with gearbox, max power 132HP@3950RPM, max torque 24kgm@3950RPM, max propeller speed 2400RPM, dry weight 79kg.
· B25R – with gearbox, max power 150HP@470RPM, max torque 24kgm@4550RPM, max propeller speed 2400RPM, dry weight 79kg.
The indicated weight does not include the water radiator, battery, exhaust system, water and oil.
AeroPower Engines: innovative items
The B22 has been designed to be an engine for aeronautic applications. It is a combination of a high content of active and passive safety, high technology and avant-guard performance.
The B22 is equipped with an electronic fuel injection and ignition system, thus avoiding the use of carburetors and all of the critical aspects of the carburetors. The electronic ignition system uses an inductive coil with mapped dwell time that controls the energy to the sparkplugs avoiding the risk of failure of the sparkplugs typical of magneto or distributor ignition systems. The electronic injection system reduces the consumption fuel and controls the power generation in any condition.
The B22 has everything that is necessary for the engine installed on the engine itself; Engine suspension, ECU, wiring loom, coil, sensors, thermostat, water expansion tank, pressurized cap for the cooling system, throttle synchronized command, fuel rail with fuel pressure regulator, alternator and voltage regulator, starter and starter relay. Therefore the installation of the B22 is very easy, safe and fast.
The large engine displacement (2.200 cc) allows the engine to reach a high power generation at low RPM, with considerable torque on a large range of RPM.
The crankcase integrated within the cylinder block, is in aluminium alloy with a high amount of magnesium to guarantee a high stiffness and reliability; the iron cast liners can be easily removed.
Having chosen to use a composite crankshaft it has been possible to use large ball bearings instead of plane bearings, thus avoiding the use of an oil radiator and the linkage problems connected with the installation of an oil radiator.
AeroPower Engines: safety items
· The ADC system avoids vibration at low RPM and kickback during power on and off of the engine. Using that system, the engine doesn’t need a mechanical damping system, which is very critical and typically needs a lot of maintenance.
· Wall mounting integration avoids the use of an additional frame and reduces the number of bolt/nut junctions between the aircraft and the engine.
· The simplicity of installation and the easy access reduces the check list before flying.
· The electronic fuel injection and ignition systems avoids the risk of icing caused by the Venturi effect on the carburetor and avoids the risk of having reserve fuel in the carburetor float chamber during take off.
· The ECU is installed on the engine to avoid failure of the electric system loom due to reciprocal vibration between the engine and the aircraft.
· The use of a main fuel pump controlled by the ECU (when the engine stops, the ECU stops the fuel pump) will eliminate the risk of a fuel leak from the carburetor float chamber especially in case of an accident.
· All of the tubing of the cooling system is in metal in order to avoid the more frequent deterioration of rubber hoses.
· The fuel rail installed on the engine is to simplify the installation and the tubing is metal with a small diameter in order to avoid the risk connected with rubber hoses that are sensitive to temperature and subject to more frequent deterioration especially when in contact with fuel vapours.
· The B22 is completely water cooled. This improves heat removal and can guarantee a constant temperature of the engine under any flight conditions. The water cooling system avoids the installation complexity typical of air cooled in-line or boxer engines.
· The expansion tank of the water cooling system is installed on the engine itself. This significantly reduces the risk of failure of the water cooling system due to the reciprocal vibration between the engine and the end of the chassis of the plane where it is normally attached and due to long hoses.
· The thermostat installed on the engine avoids the risk of thermal shock.
· A professionally made electric wiring loom is installed on the engine to avoid the risk of electrical failure due to incorrect installation or the use of home-made wiring looms.
· The monolithic propeller shaft reduces the risk of a fatigue fracture of the shaft itself and increases the stiffness.
· The downward direction of the exhaust system reduces the risk of overheating or burning of the other components of the engine.
· The SOHC reduces the load on the timing command, and no hydraulic adjusters or adjustment crews are necessary to maintain the nominal distance between the tappet surface and valve’s contact surface.
· The pistons are machined, to avoid deformation problems connected to a casting failure or tension connected to moulding or casting process.
· The monolithic connecting rod reduces the risk of failure of the crank due to a mounting error or due to tightness of the connecting rod cap.