Monday, April 16, 2012

April 16th, 2012

Fresh Air Matters... with Capt. YawIt is rare that things change in ‘big steps’ in aviation, and the majority of aircraft engines being flown in small planes today are still based on, if not completely, 1950’s technology.

 Last month the launch of the Rotax 912iS engine really marked a stage in ‘the evolution of aircraft engines’. Being at the launch of this new engine was a real thrill. More of a thrill was seeing that the ONLY woman so far trained on this new engine was a Ghanaian – living and working in Ghana in the light aviation sector – and she got a special mention by the management at the ‘engine-premiere’! Congratulations go to Patricia Mawuli Nyekodzi!

This engine is special. It is the result of a lot of research and development (over 10,000 hours of testing), and is exciting in the many realms of possibilities it opens up. Aircraft engines are special pieces of engineering, they are all about safety, reliability and what is called ‘redundancy’. Redundancy is about the ‘back-up’ solution. For example, each cylinder has two spark plugs, and two ‘spark generators’ (either magnetos or electrical modules). If one fails, the other continues – in other words, during normal operations, one of those spark plugs ‘is not really needed for the engine to work’, or is redundant. We call it dual ignition, and it has been the backbone of aviation piston engine reliability for many years now. Most aircraft engines have a fuel pump – or indeed two. The second one is the back-up, but may also be used during critical phases of flight, such as take-off and landing.

 The newest engine from the Rotax stables has one hundred horsepower – but is expected to burn the same, or perhaps even less, than the current eighty horsepower offering, going further, faster on the same fuel!

 The big change is really in the way the fuel and air gets mixed up and sucked into the cylinders for ignition. Traditional engines use carburettors, a simple device that mixes fuel and air in the approximate proportions of 1:15, (one part fuel, fifteen parts air) at ‘theoretical’ sea-level or thereabouts, to create that little bang that makes the power stroke. In a car that is quite easy, but in a plane we are changing altitudes, and with it, the density of the air. The fuel stays at the same density, and thus, as you climb you are running rich and burning unnecessary fuel. This can be mitigated against using ‘constant depression carburettors’ or using a ‘mixture control’ to adjust the fuel/air ratio as you climb. All the same, it is not an efficient solution.

Now, if you take away the carburettor and replace it with fuel injection, and add a little computer that measures, amongst other things, air pressure, air temperature and exhaust gas temperature, and let the computer calculate and control the exact amount of fuel going into each cylinder, so that each cylinder burns perfectly, with the optimum exhaust gas, you start to get an interesting solution. But this is not new… cars have been doing something like this for a long time… so, how is it more interesting in an aircraft?
Redundancy. What if an injector gets blocked or fails? Design a solution with two injectors per cylinder! What if the computer (called an ECU or Engine Control Unit) fails? Use a two lane ECU and ensure that it is remarkably robust (that means use a suitable computer protocol, in this case CAN Aerospace !

Let us look at the next problem. In a non-ECU aircraft engine, normally, if the battery fails the engine continues to run – it is self-perpetuating, provided it has fuel and air! So, if you put a two lane ECU on, and the power fails, they will BOTH stop working! That is not good.

Normally, a car has a battery and an alternator. This latest aircraft engine takes it a step further. The engine has TWO electrical generators (alternators built onto the rear end of the crankshaft), and a battery. This means that there are THREE sources of power for the two computers! In reality, ONE of the generators powers the ECU, where the two lanes are able to operate concurrently and independently. Should one of the lanes fail, the second lane will take over, just like the spark plugs in the dual ignition system. Now, the power needs to be ‘rectified and regulated’, to ensure clean power. So, of course, the newest engine has TWO rectifier/regulators… and if one generator/rectifier/regulator fails… it switches to the other!

EFIS (Electronic Fuel Injection Systems) are well proven in the automobile industry, but it is only now that the aviation safe, reliable aero-redundancy aware solutions are making headlines. This is not the first aircraft engine to offer the basic EFI solution, but it is probably the first to do so with such an impressive array of innovation!

What are the advantages of such an engine – which is initially about 20% more expensive than the still popular carburetted engine? Let’s take a look.

Fuel: Traditional aircraft engines require 100LL (AvGas), an expensive, and hard to find in West Africa, fuel. Rotax has provided MoGas (automobile fuel) aircraft engines for a long time, and is also able to take the modern e10 fuel (an ethanol blend used in Europe). The potential for this engine to activate a knock-sensor may make fuel accessibility much less of an issue than ever before in our region. You can’t beat getting high quality fuel, but to be able to ‘cocktail’ should the need arise maybe just around the corner, and with it new destinations and opportunities!

Consumption: Saving fuel is saving money, and also results in a reduction of emissions. The better fuel economy is also related to better combustion, and with it cleaner air, making Eco-Friendly a new term to watch out for in aircraft engines!

Maintenance: With no carburettors there is no carb-maintenance, this will reduce down time and ownership costs considerably – and eliminate the risk of ‘carb-icing’! Furthermore, imagine flying along and being able to carry out a ‘health check’ of your engine. Not just the temperature of the oil and cylinder heads, but a health check on the computers and all of the many sensors. THAT is what this new engine, when installed with an appropriate instrument system, offers!

When will we see such an engine flying in West Africa? Probably sooner than you think! But you can be sure that I will let you know about it here, in Fresh Air Matters – and you can be certain that it will be installed by, and flown by, local locally trained personnel, and used as an education tool for sustainable light aviation in our sub-region.

Ghana is amongst the continents leaders in many aspects of light aviation, and now leading in the engineering of modern, exciting ‘mechatronic’ power plants, including the industrial standard CANAerospace Data Bus based instrumentation systems, in the fastest growing sector of aviation worldwide!

Learning to fly and owning an aircraft in West Africa, for business and/or for pleasure, just became a little bit more interesting – and probably one step closer to enabling the growth curve, of this needed aviation sector, take a steeper climb!

Capt. Yaw is Chief Flying Instructor and Chief Engineer at WAASPS, and lead Pilot with Medicine on the Move, Humanitarian Aviation Logistics ( e-mail

1 comment:

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