Not Difficult, Just Different

Small in size but with plenty of performance, recent changes in legislation mean the modern microlight has become an attractive and practical aircraft.
Dave Unwin details the differences.

Well, its been a year of unprecedented negativity for the aviation industry, and although much over-used, the word ‘unprecedented’ is entirely apposite on this occasion! Amongst all the bad news two recent announcements have shed a little light on a very gloomy scene. Firstly, the MAUW for new microlights is going up to 600kg, and flight time logged on three-axis microlights will now count towards maintaining a PPL. Great news, and as far as I’m concerned, long overdue. The new legislation is clearly based on the FAA’s Light Sport Aircraft class which was introduced in 2001 to stimulate America’s light aircraft industry, which had declined drastically through the 1990s. I subsequently got to test around 25 LSAs over the next five years (the FAA approved more than a hundred), ranging from sleek composite designs such as the Pipistrel Alpha via modern all-metal machines like the Tecnam P2008 to revived classics like the Thorpedo, and although they weren’t all good, some were great.

The only problem for the British-based pilot was that most of the LSA types either weren’t available in the UK, or could only be certified as a 450kg ULA (microlight) or 750kg VLA (Very Light Aircraft). For several years, the modern microlight had been blurring the line between ‘classic’ ultralight aircraft (ULA) and the very light aircraft (VLA) class, and it was apparent that the single most unsatisfactory facet about many of them was that the 450kglimit was simply too low. In fact, to stay legal in some 450kg machines ‘two up’ you could barely carry enough fuel to even taxi.


 Microlight instrument panels have come a very long way since their first appearance in the 1980s ...

The profound advantages of an extra 150kg of useful load are obvious, particularly when you compare exactly the same type of aircraft but registered under different systems. In the UK, the German Flight Design CT-SW was considered a microlight, and had a useful load of around 156kg, whereas its American LSA counterpart had a useful load of 284kg. Now, for many pilots of traditional SEPs, the term ‘microlight’ often conjures up an image of a hang glider fitted with a lawnmower engine, but for modern microlights nothing could be further from the truth. In many – if not most respects, these machines offer performance that is superior in almost every way to the average flying club machine, while being a lot cheaper to run. Consequently, I believe that for UK GA this new initiative really is great news. And of course, being able to maintain your PPL while mostly flying a microlight means that on the odd occasion when you do need to rent a four-seater you’ll have a valid licence- so what’s not to like? Well, I think that there are two distinct aspects that could cause the unprepared aviator issues, systems knowledge and general handling. Firstly, there could be a temptation for some pilots, who may have considerable experience in what I’ll call ‘classic types’, to think that they’re stepping down in both performance and complexity. This assumption is fundamentally – and could be fatally – flawed, for such a mind-set can lead to complacency. It is a well-accepted truism that “all aircraft bite fools”, and to operate any flying machine complacently is a very foolish thing indeed. These aircraft are certainly not difficult, but they are different, and there are safety implications particularly for those who have only ever flown ‘classic’ GA types such as Cessna’s 152 and 172 or Piper’s ubiquitous PA28 series. Some of these considerations, such as paying even more attention to the weight and balance schedule are probably quite obvious, while others are perhaps less so. For example, whereas most of the traditional GA fleet are powered by direct- drive air-cooled flat-fours from either Continental or Lycoming, most 600kg microlights are fitted with Rotax’s ubiquitous ‘nine series’. The 80hp 912 engine exploded onto the General Aviation scene in 1989, and it is fair to say that the nine series transformed GA. The original 80hp 912 was soon joined by the 100hp 912S and then the turbocharged 115hp 914 and 141hp 915, while the 100hp model was subsequently marketed in both carburetted and injected versions, and either certified or ASTIM-compliant. And here’s an interesting fact – you can tell if an engine is certified or not at a glance, as the data plates are colour-coded. Many people know you can deduce the power produced by any given nine series Rotax from 50 metres away (if the cowling is open), as the heads are colour-coded. Black for 80hp, green for 100, red for 115 and blue for 141. Well, the data plates are also colour-coded. If it’s a certified engine its data plate is red, while if its black its ASTM compliant. I have been either pushed or pulled by every nine- series variant, with most of my Rotax time being logged in the Buckminster GC’s EuroFox glider tug, which is fitted with a 100hp 912iS. This is a very different engine from a 100hp Lycoming O-200! For example, at 1,352cc (82.5ci) the displacement is significantly less than the O-200’s 3,290cc (200ci). It’s worth noting that a 912iS produces more than one horsepower per cubic inch, whereas many classic American aero-engines typically only produce around half a horsepower per cubic inch. For example, most O-360s produce 180hp, O-320s are usually good for 160, while O-200s normally put out around 100.



Other big differences are that the nine series utilises dry sump forced lubrication with a separate oil tank, and that the propeller is driven through a gearbox via a reduction ratio of 2.43:1, reducing an engine speed of 5,800rpm to a much more efficient – and neighbourly – 2,400rpm at the prop. The 912 iS variant also features FADEC (Full Authority Digital Engine Control), as the electronic fuel injection and ignition systems are controlled by a dual channel Rockwell Collins ECU. Buckminster GC’s EuroFox is also fitted with a Stock Flight Systems Engine Monitoring Unit. Sometimes referred to as a ‘Stock Box’ this fully integrated digital EMU was developed by German engineer Michael Stock in conjunction with Rotax, and can display (and record) a wide range of parameters in a variety of different units.


  The Avid Speedwing is one of the earlier microlight designs, built from a kit. (Michael Benson)

By now you may well be feeling (to paraphrase F.E. Smith) much better informed, but none the wiser – and what does all the above have to do with flight safety? Patience! I’m coming to that. I suspect that quite a few pilots may be tempted to try a modern 600kg microlight, and may think that they don’t need a formal checkout, because they have say 1,000 hours in a Bonanza or Comanche. In fact, these things really are quite different, hence the need for ‘differences training’. Some of the differences can be quite subtle;- for example, before the Buckminster GC got the EuroFox we had a DR400 Remorquer, and when checking people out on the Remorquer I always pointed out that an excellent indicator that the tyre pressures were on the low side was when it became hard to pull by yourself. Well, you can move a EuroFox with one hand and the tyres are really quite flat. The only way to check the tyres is to use a pressure gauge.

Even checking the oil is different, and for a variety of reasons. Firstly, because Lycomings and Continentals have ‘wet sumps’ the oil system is an integral part of the engine, and secondly, the quantities involved are very different. The Remorquer’s O-360 takes eight quarts (7.6 litres), six is a good operating amount and its perfectly normal to simply slop a quart in if the level’s a bit low on the dipstick. On the EuroFox, the maximum is 2.6 litres, and the minimum 2.1. When refilling, the quantity needs to be measured very accurately to avoid overfilling. You may be wondering why I said, “on the EuroFox”. Surely all 912s are the same, in the same way that an O-360 holds eight quarts, irrespective of the aircraft the engine is in? Well, no. Nine series engines are used in over 260 different types of aircraft, and the dry sump design means the location and size of the separate oil tank is down to the designer. The proof of the pudding is in the installation, and it is inevitable that the installation of some is probably ‘perhaps not quite as good as it could be.’ Also, the dry sump system and the separate oil tank means that its prudent to ‘gurgle’ (I prefer ‘burp’) the engine by removing the oil filler cap and then pulling the propeller through slowly until the engine burps, before checking the oil level. Failure to do this will almost certainly result in over-filling and remember, on some installations the difference between ‘Max’ and “Min’ may be as little as 400ml. Obviously, great care should be exercised when pulling it through. Some people will tell you that a 912 will not fire below 250rpm. They are wrong.

Another aspect of the 912 that you may well be unfamiliar with on an aero-engine is the cooling arrangement, and it’s quite remarkable how much ignorance there is regarding this very important system. You will often hear pilots refer to the nine series as ‘water-cooled’ engines but this is incorrect in several regards – the cylinder heads are liquid-cooled but ram-air is used to cool the cylinders, and the coolant is not water. Consequently, when servicing it is imperative that the correct grade of coolant is used. Furthermore, during the pre-flight pilots will often note that the coolant level appears low in the expansion bottle and top it up. Don’t. The only way to check the coolant level properly is to remove the radiator cap (and having done this, don’t neglect the cooling system’s hoses either). Finally, the 912 is not a Rolls-Royce Merlin or Daimler-Benz 605, and it will not fail catastrophically and within minutes if you lose all the coolant.


  The Evektor Eurostar is available both as a factory-built aircraft or as a kit; over 1,200 have
  been produced since the late 1990s.  (Geoff Hall)


The next big difference clearly demonstrates the difference in the design philosophies between the modern microlight and a classic GA type. Essentially, aircraft like the C152 were designed, built and then weighed, whereas because control of the empty weight is so critical on a modern microlight, the weight of each component is considered before the aircraft is built. Consequently, their fixtures and fittings are simply not as strong as on an American aircraft designed in the 1960s. The airframe is; – it will be stressed to +4/-2g, but components such as the rudder pedals and door latches just simply aren’t that strong, so if you’ve got used to climbing in, slamming the door and then using the rudder pedals to push yourself back in the seat prior to fastening your harness, you will break things. Incidentally, the importance of controlling the empty weight is why some types are often delivered unpainted.

Another point to consider is that these machines will almost certainly have significantly more sophisticated systems than the club 152. These may include airbrakes, dual electric fuel pumps, oil cooler flaps, turbocharger, a rocket-powered ballistic recovery system, electric trim, a negative flap setting, digital autopilot … The avionics will almost certainly be infinitely more capable, and may even incorporate facets that until recently you would only have found in a turbine powered aircraft, such as synthetic vision, a Highway-in-the-Sky presentation, and an Alpha indicator. I would definitely recommend spending an hour or two in the cockpit with the manual before going flying. Also remember that the ignition system of many nine series engines doesn’t use magnetos but electronic capacitive discharge units that rely on a functioning electrical system. If the alternator goes offline the engine will stop, hence the second (emergency) battery. In fact, checking that the alternator is online after start-up is quite important. The iS alternators (it has two) will charge quite cheerfully at 2,000rpm, but they won’t go online until the rpm has been above 2,500 for several seconds. Therefore, if you start up, turn on the myriad electrical systems and then set off on a long taxi, you will flatten the battery and the engine will stop. This is very different to a Continental or Lycoming. Indeed, smaller American engines may well not even have a battery or alternator. Before we start the engine, a word of warning. Some 912 installations use a stupidly powerful spring on the throttle, and if the friction lock isn’t set correctly and you let go of it the engine may go to full power in a second. This obviously has the potential to be extremely dangerous (and particularly so on a hard surface). Before starting make sure there’s nothing immediately in front (or behind), set the friction lock and never let go of the throttle if there’s anything within a 45° arc of the nose. OK, you’ve got it going (and if it’s a carburetted version almost certainly used some choke, yet another difference) and the alternator is generating. Because of the gearbox, you must not idle the engine too slowly, while on a hard surface it will want to taxi too fast. Don’t ride the brakes, you’ll just wear them out (and – like the rest of the aircraft – they are generally quite lightweight, with thin discs and small pads). Its more efficient to let it slowly accelerate, and when the speed becomes uncomfortable brake to a standstill and start again. One more thing, some installations display engine rpm, others prop speed. Probably best to know before you go.

And as for the actual flying, if you’re used to the indifferent take off and climb performance, solid stability and stolid handling of most ‘classic’ GA types you’re in for a treat. Expect exciting take off characteristics, with ground rolls of around 100m and climb rates in excess of 1,000ft/min when solo. Indeed, flown at a lightweight from a tarmac runway and with a stiff breeze down the centreline you’ll be airborne almost before the throttle hits the stop! However, remember that full power (5,800rpm engine speed) is limited to a maximum of five minutes, while METO or ‘max continuous’ is 5,500.

The handling will almost certainly be crisper and the stability more relaxed than you’re used to, particularly in pitch as some are relatively short-coupled. They are also much more affected by gusts and turbulence, and when converting I’d suggest flying at or close to MAUW whenever practical for a higher wing loading. Even ground handling requires extra care. Cruise speeds are on a par or superior to most ‘classic’ GA types, for about half the fuel burn, and many modern microlights will have a negative flap setting for high speed cruising. Stall speeds can be ridiculously low, and it’s worth noting that most LSA types are not cleared for aerobatic manoeuvres or intentional spins. In the unlikely event of an engine failure, some have remarkably flat glide angles and all will have better minimum sink speeds than regular GA types.

Finally, landing. Obviously, being relatively lightweight aircraft they have low inertia, and consequently the time-honoured final approach speed of 1.3 x Vso is entirely inappropriate, as when you close the throttle and flare they decelerate expeditiously! The exceptions here are the very aerodynamically ‘clean’ types, like the Pipistrels (some have airbrakes as well as flaps) or the Flight Design CT series, which will float forever in ground effect if you’re not careful and come in a bit ‘hot’. It’s also worth noting that the difference between a suitable approach speed and Vfe can be as low as ten knots, so if you do decide to go around be prepared to pitch up a long way to keep the speed down, and/or reconfigure quickly. Don’t use full flap in a crosswind, particularly if the aircraft is fitted with flaperons, as these do degrade roll authority. Lastly, when you shut the engine down a 912 does stop quite abruptly, due to the combination of relatively high compression ratios and the reduction gearbox. I’ve never got used to it, and doubt I ever will, but it is perfectly normal.

I hope that this article will tempt you to try a modern microlight, and has emphasized the importance of adequate conversion training. As I said earlier, these machines are not difficult, but they are different, so get someone familiar with the type to check you out, and also check out your licence. If you hold a PPL with SEP you must undertake ‘differences training’ to fly a microlight, but if you fly on a NPPL with a SSEA rating you’ll need to add a microlight class rating to the licence. At the risk of repeating myself, please don’t just do the bare minimum of training, and then try and fill in the gaps as you go. Always remember that anyone who teaches themselves to fly has an idiot for an instructor, and a simpleton for a student.


  The Italian Tecnam Eaglet is a development of the earlier P92.  This particular example is
  based in New Zealand. (Tecnam Aircraft)