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Why do B22 and B25 Aeropower engines use SOHC (Single OverHead Camshaft) instead of push rod (OHV) or lateral valve?


Most aeronautical engines use pushrods for the timing system (OHV): the reason is that most of these engines were designed 50 or 60 years ago. Even if the pushrod system is simpler when compared to the SOHC, it is worse when compared to an OHC system in terms of engine performance, efficiency and fuel consumption (read more http://autos.ca/articles/jk/040421.htm). For that reason most modern automotive engines adopt an OHC system: mainly DOHC (double over head camshaft) on 4 valves per cylinder and SOHC on 2 valves per cylinder. Furthermore using OHV systems, it is hard to obtain a good stiffness and timing stability at high rpm: for this reason most aeronautical engines can turn only at low RPM, which means low power density and low efficiency. Lateral valve is a very old technology and has been abandoned by all engine manufacturers since 1950 because it is not possible to obtain an adequate compression ratio and good combustion efficiency. Fuel consumption, pollution and performance is strictly dependent on this parameter. Furthermore, due to engine head geometry, the combustion chamber has an high ratio surface/volume (which means bad thermal efficiency) and the inlet duct has a very curvy design (which means bad flow dynamical efficiency). The only advantage offered by this technology is the Flat-head and the dimensions of the engine but the reduction in engine weight is compensated by the addition fuel and the high fuel consumption will have a big impact on the maintenance cost. The power/weight ratio of side valve engines is by far worse when compared with OHC engine (as the development path in engine design shows during last 40 years).


Why are the B22 and B25 Aeropower engine water cooled?


It is common in aeronautics to see air cooled engines. It is quite an old tradition and most of these designs are 50 to 60 years old. The air cooled engine is definitely simpler and it is easy to cool the engine on an airplane, at least when in flight. But there are a few disadvantages: first of all, an air cooled engine has low efficiency (high fuel consumption) and the engine temperature is basically out of control in many situations such as taxi, long descent, and whenever there is a significant change of environmental conditions. It gets even harder with six cylinder engines or with applications like gyroplane or helicopter, in which it is almost impossible to have an adequate airflow on the engine. This thermal instability produces performance decay and strong wear on mechanical components.

B22 and B25 Aeropower engines have been designed to use the most advanced technology to obtain high efficiency. Water cooling has the advantage of being able to obtain a very precise engine temperature in any flight and environmental condition. This not only improves the efficiency of the engine, but also improves the life of all engine components, because they are not subject to any thermal shock. In addition the engine is much easier to install, and the installer only needs to ensure adequate air flow through the radiator. In gyroplane or helicopter applications it is enough to increase the efficiency of the water radiator, by increasing the surface area and by using an electrical fan to force air through the radiator.


Which accessories do I need?

To run the engine it is necessary to complete the installation with a cooling system (radiator + hoses), a fuel system (fuel pump + hoses), an exhaust system (pipes + muffler) and a wiring loom between the engine and cabin. To simplfy your installation, a few different types accessories are available although not all will fit in all installations. If MWfly accessories are not suitable for your installation, Manual A (installation manual) provides all the specifications you need to design your own accessories. For any questions do not hesitate to contact an MWfly service center.


What do I need to do to cool the engine?

Keep in mind that the engine is completely water cooled: Just focus on having a good air flow across the radiator. You can improve the air flow by sealing gaps between the air intake and the radiator or by extracting the air beside the radiator with a spoiler.  For some applications (e.g. pushing, gyroplane, helicopter) it is not easy to have a good airflow across the radiator: therefore it is necessary to use a larger radiator or a fan to force the air flow across the radiator. The engine is also equipped with a thermostat, that improves the thermal stability and allows a quicker warm up: this component could be easily removed from engine if you want.


Do I need an oil radiator?

The B22 and B25 normally do not need an oil radiator. The engine is been designed to avoid any external pipes in the lubrication circuit. That’s why crankshaft supports are ball bearing and so only a low oil pressure it’s necessary to the engine for run. An oil cooler is easy to install: there is a special threaded port on the engine crankcase to connect a radiator.


Is a fuel injected engine as reliable as a carbureted engine?

MWfly engines are equipped with a fully redundant injection and ignition system. Installed on each engine are two ECU’s, two sparks for each cylinder working with different ignition coils, two different injection and ignition circuits (one pickup for each ECU). The ECU’s are working contemporary, with master and slave strategy; in case of ECU failure, the second one takes over and the engine continues to run. Furthermore, each ECU can work in Limp Home mode, in case of sensor, battery or generator failure. The ECU system is compliant with IECEDD68-2-6 (sinusoidal viration environment test).


May I use analog sensors?

All engine data is available via a CAN line with standard CAN AEROSPACE protocol, using preinstalled sensors and adding sensors connected to the ECU’s.  It is also possible to use standard analogical instrumentation: ther is a lot of space on the engine set up for pressure and temperature sensor installation. In the installation manual there is a section dedicated to the installation of sensors, or you can download the document “Instrument Compatibility” from the wesbsite.


Which is the prop rotation direction?

All engine models are available either CW or CCW. This could be a benefit in case of twin engine airplane (experimental). Most of the more popular propellers are available in either rotation.


How should I choose the propeller?

The prop is the component that transforms the engine power into aircraft performance. Like the tires of a car, if you chose the wrong ones the performance will be affected (can you imagine a sport car with the tires of a commercial vehicle!!). MWfly clients choose their engine for the performance: they also have to choose the prop to align with this concept. It is important to work with your prop manufacturer to find a solution for the performace you expect, because the prop design is based on aircraft design as well as on engine power. Today the prop choice is very large because the engines are available with right or left rotation in any configuration.   


Why does  the engine not have  the same attachment points as the  Rotax?

Those engines are different in weight, mass distribution, power and prop position: so the engine frame must be a different one.


How the airplane speed should change increasing the engine power?

If you want to increase the speed of your airplane by 10% you have to increase the engine power by 33%. Normally increasing engine power will have the effect of shortening the take off and obtaining a better climb rate thereby providing better safety during this critical situation. Using a more powerful engine will also increase the comfort level because to have the same performance as before the power set will be reduced (click here for Performance Variation Chart).


What is the difference between a new engine and a rebuilt engine?

A rebuilt engine could be an engine that has been used for testing or marketing activities; or an engine that has been returned to MWfly for heavy maintenance having reached the first TBO.  While a new engine has a life of two cycles of TBO, a rebuilt engine’s life is limited to 1 cycle of TBO. The rebuit engines are normally updated to the last version.








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