ENGINEERING

Sensational six hundreds!

The new 600kg category promises an influx of ready to fly Permit aircraft. By LAA Chief Engineer, Francis Donaldson…

At last – 600kg is go! But what do the new 600kg rules mean? Basically, it means a new selection of sub-600kg, factory-built sport aircraft can be made available to microlight and light aircraft pilots alike, on a Permit to Fly administered by either the BMAA or LAA, rather than as would previously have been the case, a Certificate of Airworthiness. The raising of the stall speed from 35kt to 45kt will allow aircraft of considerably higher performance than previous microlights.

Either a new design, or variant of an existing type, can be certified at a selected weight not exceeding 600kg to the amended BCAR Section S code and, provided the manufacturers can gain the necessary CAA design and manufacturing approvals, it can then be supplied as a factory-built aircraft but qualify for a Permit to Fly.

The less onerous Permit to Fly regime offers more flexibility on costs and the ability to incorporate many non-certified pieces of equipment that have been developed for use on microlight and amateur-built types over the years, which are often more advanced than equivalents that have not yet ‘made it’ into the certified world. It also means that the machines can be maintained and inspected, and have their Permits to Fly renewed annually by the sporting associations, including the LAA which has a great deal of experience of dealing with aircraft in this class, and have done for many years – in fact, LAA has held an approval to do just this continuously since 1948.

What it doesn’t mean is that an existing 450kg microlight can be suddenly re-classified as a 600kg aeroplane and flown at higher weights. An aircraft that’s been properly designed for 450kg would be desperately overloaded with an extra 150kg of payload – that’s like adding the weight of two extra people, after all – not to mention the question of where

Above One of a breed of high performance types is the 600kg Blackshape Prime. The similar TL Stream is another likely UK candidate.

experimenting in this field, but 600kg gives industry the opportunity to move forward in this area. Its true that an aircraft that’s to be cleared at 600kg is going to need a stronger airframe than a 450kg equivalent, and the beefing up of the airframe will eat into the 150kg increment to some degree, but even with the power density of today’s batteries, an extra 100kg or so available for battery weight will make a big difference to the potential range and endurance of such a craft.

the CofG might end up if the aircraft was overloaded in that way.

For an existing aircraft presently cleared at 450kg gross weight (or that has been allowed the option of being cleared at 472.5kg when equipped with a ballistic parachute), the new rules allow the possibility of the design of the aircraft being re-examined to determine whether it would be possible to clear it at a slightly increased weight, taking advantage of the newly extended scope of this class of aircraft. This would include needing to make strength calculations, possibly undercarriage ‘drop tests’, flight tests, changes to the pilot’s operating handbook, and changes to the operating speeds, placards and instrument markings etc.

Altogether, this would not be an exercise likely to be within the scope of a single owner, but rather, something that would be carried out by the type design organisation, if it still exists, or, if it doesn’t through one of the several engineering consultants who advertise their services in this field. This could be financed by an interested group of owners for example. Having said that, the exercise of re-stressing an aircraft for a higher weight is no small undertaking and probably not financially viable unless it was to benefit a whole fleet of aircraft rather than a single example.

Another interesting by-product of the new 600kg rule is the creation of a category of regulated single seat microlight with a gross weight (more than 300kg, but not exceeding 600kg) and/or stall speed (more than 35kt, but not exceeding 45kt) that precludes it from the present deregulated SSDR category. Because a single-seater falling into this bracket would save the weight of a crew member over its two-seat counterpart, it could have a seriously large engine – bearing in mind that the new rules impose a 45kt stall speed limit but there’s no top limit on how fast an aircraft can go in this category!

One can picture something very racy indeed that features a fairly small wing and double slotted flaps, slots and so on to achieve the 45kt landing speed. Twin engines, anybody? There’s no restriction on the number of engines, or of the type of powerplant – a small jet, perhaps?

Which brings us to another very significant benefit of the new class of aircraft, being that it would allow scope for the likely weight of batteries for a two-seat electric powered aircraft, be it all-electric or hybrid, or enough payload for experimenting with other types of powerplant.

With the Government’s pledges for carbon neutrality in not that many years’ time, it seems inevitable that flyers will be under pressure to develop alternatives to the good old Otto cycle, and future generations won’t necessarily have the power-to-weight ratio that we’re enjoying in our present fleet.

The 450kg limit didn’t allow any weight margin for Top The earlier Tecnam Echo has been succeeded by the 600kg P92 Echo 11, a possible candidate for the UK market.

Above middle

Long-established FK Aviation has a range of aircraft including the FK14 Polaris, which boasts a cruise speed of 140mph on a 912S.

Above The Swedish Blackwing 635RG certainly made waves at AERO 2019 with its stated cruise speed of 185kt at FL75 on the 915is… and 38kt stall speed.

Some history

The changes announced by the CAA are the culmination of many months of work that have taken place jointly by experts from the LAA, BMAA, CAA and industry. This began with the announcement by EASA in 2017 of their intention to offer the possibility of countries ‘opting out’ of EASA regulation for aeroplanes with a stall speed of less than 45kt in the power off landing configuration, and a maximum gross weight not exceeding 600kg. Ironically of course, the CAA’s decision to opt out, which followed an overwhelmingly positive response to its public consultation on the subject, was then overshadowed by the UK coming out of EASA, subsequent to Brexit. Importantly however, most other EASA-participating countries also voted to opt out of EASA controlling their aeroplanes in this class, including Germany and the Czech Republic which are the main sources of sport aircraft in this weight bracket.

In some ways this is a shame, because it marks an admission of failure of EASA’s intent to apply uniform standards for small aircraft design and manufacture across Europe, which it had been hoped would allow aircraft in this class to move freely from one country to another and to be bought, sold, owned and operated anywhere within Europe without any cross-border impediments, or the need for manufacturers to go

through a whole lot of extra paperwork just to make a few extra sales in a new marketplace.

Unfortunately, with hindsight, the rule-set that EASA put in place was too onerous and certification under the EASA rules was too expensive. Most manufacturers found they were better off making their aircraft as ultralights within the 450kg definition under national rules. The few who did try the EASA certified route generally got their fingers burnt, and never saw a worthwhile return on the considerable investment that this involved.

The problem with making aircraft to sell in the 450kg ultralight category was that it was (and is) limiting in terms of what payload the aircraft can carry. Even with the most efficient weight-saving on the airframe, a two-seater with one of the state of the art four stroke engines by Rotax, Jabiru or UL-Power was inevitably restricted in the amount of fuel it could carry while keeping within the 450kg limit.

Many struggled even to meet the minimum requirement to be able to carry two people of 86kg plus enough fuel for an hour’s cruise flight, and you could only legally fill the tanks or load any significant amount of baggage onboard when flown solo. Forced to choose between either flying overweight or risking running out of fuel before reaching their destination, perhaps not surprisingly many pilots preferred to risk a ticking off from the authorities than ending up in a field.

Over time, ultralight aircraft have steadily grown more sophisticated, and while modern avionics is undoubtedly lighter than the older variety, any savings in that area have usually been overshadowed by the weight of more powerful engines, retractable undercarriages, variable pitch propellers and other features that would have been out of the question just a few years ago in this class of machine.

The empty weights of so-called ultralights on show at AERO Friedrichshafen and similar events grew to levels where it was frankly ridiculous to pretend that they were practical to operate as two seaters within their weight category. The industry clearly needed to be able to sell aircraft that could operate at a higher weight – say, 600kg – without having to jump through EASA’s expensive hoops, ideally using the tried and tested certification arrangements already in place in their own countries.

Happily, however, there is also work underway to try to ‘level up’ design standards for this class of machine between the UK, Germany and the Czech Republic and so achieve a degree of mutual acceptance in the new 600Kg category, but this is slow in coming. In parallel with the work on the 600kg class definition, as announced by the CAA in August this year, a revision to BCAR Section S has also been in process which has removed, wherever possible, the arbitrary differences between the UK, Czech and German design codes and left as few ‘national differences’ as possible that would have to be tackled in re-certifying a machine in any of the three countries.

So, what does it mean to members?

Probably the first thing we’ll see is existing UK-based microlight manufacturers coming up with new, heavier variants of their existing types just as soon as the CAA release the amended BCAR Section S – or even before if the manufacturers choose to use a higherlevel code that already exists, such as CS-VLA.

Then, we’ll see new manufacturers – including some who are already familiar to us as kit manufacturers – applying to the CAA for A8-1 approval of their facilities to design and manufacture, and approval of their designs as compliant with the revised BCAR Section S design code requirements. The CAA folk at Gatwick have been working on this project for some time now and want to see good come out of it as much as we do, so we hope that with the help of the Associations, manufacturers will be able to get up and running in short order.

Hopefully it’ll be possible to provide some recognition of what regulatory hoops existing designs from abroad have already ‘jumped through’, while also ensuring a level playing field with UK-based manufacturers waving the flag for Team GB.

The rule changes won’t have any immediate impact on the existing LAA fleet of aircraft, or on building new aircraft of existing types, which will continue to operate under their existing classifications.

Reclassifying an existing kitplane SEP type as a 600kg category aircraft would mean going through a reapproval exercise against the new version of BCAR Section S, or other suitable code. In some cases this might be quite straightforward, in others well-nigh impossible – it just depends on what basis the type has been cleared up to this point.

There’s no intention to re-classify vintage types as 600kg machines, even if their weight and stall speed fall into the definition – the 600kg class is aimed at modern machines cleared against modern design codes, which will inevitably be very different to those which the vintage fleet were certified to.

There’s also no capability of transferring an aircraft that’s already been certified by EASA into the national 600kg category – it’s baked into the rules that such aircraft would continue as ‘Part 21’ CofA machines. Manufacturers of EASA type-approved types could of course, build a non-certified version of an EASA certified type, and release it on the market for operation on a 600kg national Permit to Fly, but they would need to get their manufacturing approvals and design approvals separately through the CAA.

Right Dragon Aviation’s 600kg Aeroprakt A32 is already a popular kit and plans are afoot to bring it in ready-built. A 600kg Super Sport A22 Foxbat is also available.

The changes to regulations relating to the microlight definition came into law on 19 August this year, so expect to see the first of the new class of machine doing the rounds ‘at a fly-in near you’ in the coming months. In next month’s magazine we’ll discuss the changes to Section S that are being finalised, and some of the contenders in this new class.

Watch out! E10 unleaded fuel is here… NOW

By Francis Donaldson

Due to the political pressures encouraging the use of biofuels, the government is pushing for greater use of ethanol in petrol, and has mandated that from 1 September all regular grade unleaded petrol will contain up to 10% ethanol, rather than up to 5% as previously. In the last few weeks, filling stations around the UK have been re-marking their E5 petrol pumps to show that they now supply E10 specification fuel and receiving tanker-loads blended with up to 10 percent ethanol content.

For the automotive world, this means reduced carbon dioxide emissions, which is better for the environment and, arguably in terms of ecodesirability, a small further reduction in the reliance on fossil fuel. The automotive industry has been preparing for this change, and if all goes as planned, people with vehicles registered after 2002 should be able to switch to E10 without noticing any difference.

A challenge

The additional ethanol content is bad news for aviation users though, were we to ignore the change and start putting E10 in our aircraft regardless. Ethanol is a powerful chemical solvent which can attack components, including rubberised gaskets and fuel pipes, older lacquered carburettor floats and composite or plastic components in some newer fuel systems. The doubling of the concentration of ethanol in E10 makes it much more likely that problems will be experienced if these parts are not designed to be ethanol-proof.

Ethanol also has an affinity for absorbing water, which over time can then become acidic, attacking metal components in the fuel system and engine. Even if there was a practical way to do so in the volumes of fuel we use in our aircraft, we cannot safely remove the ethanol content from the fuel because it acts as an octane enhancer, so the washed-out fuel would be left with a reduced octane value, likely to cause detonation problems.

Another issue is that ethanol-blended fuel has a lower energy density than petrol, so to develop full power from our engines using an E10 fuel, we may need to richen the fuel/air mixture, for example using a bigger carburettor jet size.

Owners of Rotax and Jabiru engines are probably Right Always use the recommended test for ethanol when using mogas. already aware that many of these engines are supplied as being able to use E10 fuel – though with Jabiru engines in particular, it’s far from straightforward because some of the earlier engines require cylinder head modifications and reduced compression ratio if they are to avoid detonation issues when using any form of mogas. Jabiru also says that mogas of any type should not be used by Australian commercial flight schools, and only at the owners own risk.

Even with a supposedly E10-compatible engine, the chemical compatibility problems with fuel system components are such that the LAA does not at present approve the use of E10 mogas in any LAA amateur-built or vintage aircraft. For factory-built microlights and factory-built gyroplanes, where LAA is

not the approving authority but only renews the CAA’s Permit to Fly, owners need to refer to the TADS for their type for details of the approved fuel types, and monitor the service bulletins from the approved manufacturers for news of any updates.

A possible solution – 97 Super Unleaded

Fortunately, for the time being at least, for mogas users there’s a potential alternative option in the form of Super Unleaded fuels. Super Unleaded fuel supplied by garage forecourts is NOT necessarily ethanol-free, but its ethanol content will be capped at a maximum of 5%. There’s currently no legal requirement for ethanol to be present in super unleaded petrol, and in fact quite a few members have reported that their tests have shown Super Unleaded fuel to be completely ethanol-free in their areas.

Esso reports that “Synergy Supreme+ 99 is actually ethanol free (‘except, due to technical supply reasons, in Devon, Cornwall, North Wales, North England and Scotland’). Legislation requires us to place E5 labels on pumps that dispense unleaded petrol with ‘up to 5% ethanol’, including those that contain no ethanol, which is why we display them on our Synergy Supreme+ 99 pumps.”

Shell, BP, Tesco and other fuel suppliers don’t commit to such detail, merely stating their fuels ‘may contain up to 5% ethanol’.

UL91 avgas

For most aircraft engines, UL91 avgas remains the ideal fuel in that it is a tightly controlled aviation-grade fuel of a guaranteed composition, blended for long-term stability and optimal volatility for aviation use. As it is in effect the familiar 100LL avgas but supplied without its tetraethyl lead, any fuel system designed for 100LL avgas will be unaffected by using UL91 fuel or, if circumstances demand, by a mix of 100LL and UL91. Despite a pervasive misconception, UL91 fuel is NOT mogas and suffers from none of the issues associated with mogas use in aircraft. A list of engines suitable for use with UL91 fuel can be downloaded from the ‘Operating and maintaining an LAA Aircraft’ page of the LAA’s new website. Moves are afoot to increase the number of airfields supplying UL91 fuel, with full LAA backing.

Mogas woes

Of course, many LAA members have been using mogas of one sort or another for many years. For many airstrip users, the prospect of having to go to an airfield to fill up with Avgas would seem at best very off-putting, and at worst totally impractical for their style of operation. Hopefully Super Unleaded will continue to be an option using the LAA’s E5 procedure. Where 97 octane E5 super unleaded can be found that’s ethanol-free, it can be used in the broader range of LAA aircraft with engines eligible for use with E0 unleaded fuel. But it is important that mogas users take on board the fact that unlike with aviation fuels, automotive fuel specifications generally only describe the properties of the fuel blend, in terms of octane rating and other characteristics, they don’t specify the chemical make-up of the fuel.

Apart from specifying broad maxima and minima for those components that the powers-that-be wish to either encourage or discourage, the specifications leave to the fuel supplier the choice of how to blend the fuel to achieve the described properties. In some cases, it’s the relatively small amounts of additives that cause compatibility issues, rather than the main components of the fuel – and the mix of additives may vary from one batch to the next. So, for example, the fuel specification EN228 allows suppliers the choice of achieving a 95 RON octane rating using a better or worse ‘cut’ of petroleum-based hydrocarbons, requiring respectively a lesser or greater quantity of octane-enhancing additives made up of oxygenates including methanol, ethanol and others to achieve the necessary detonation resistance.

The government’s push for greater use of ethanol in petrol involves quotas for fuel companies to use increasing proportions of ethanol in their products, or be fined for failing to meet their quotas. Depending on the changing prices of ethanol in relation to other octane enhancers on the world market, at certain times fuel companies have found it financially advantageous to underachieve on their ethanol targets and pay the fines, rather than pay a high price for ethanol, leading to periods where fuel supplied as E5 petrol (up to 5% ethanol) actually had no ethanol in it at all. More recently however, with the ramping-up of the quota system to ever more ambitious levels, it has been more and more difficult to find ethanol-free E5 unleaded fuel on garage forecourts.

Ever changing fuel blends

The consequence is that with mogas of any type, what you get from the pump one week may be different to what you got the week before. The fact that your fuel system pump diaphragms, seals, composite tanks and so on might have been unaffected by mogas up till now does not guarantee that they will be OK with the blend that the next tanker-load brings to your garage forecourt.

Unfortunately, there is no simple answer to this, and the only way to mitigate this problem is by constant vigilance, and thoughtful adaptation of your maintenance schedule to check for signs of problems developing before they create a safety issue – more frequent checking of filters, changing of fuel lines etc.

Things to watch out for include swelling of rubber components like diaphragms, fuel valve seals and O-rings, fuel pipes hardening or developing surface cracks, and fuel tank sealants wrinkling or detaching from the internal surfaces of fuel tanks. Varnishes on cork floats may go gummy, or plastic carburettor floats absorb fuel and lose buoyancy, causing a rich mixture and rough running. Also, watch out for discolouration of the fuel you take out as fuel samples, which may imply something dissolving somewhere in the system, and for corrosion in the bases of your carb float bowls and gascolator.

Avoid letting mogas go stale in your fuel system – drain it out before a long period of disuse. But don’t leave the tanks empty for a long period – better to fill them with avgas which will reduce condensation and also, particularly with plastic tanks, prevent the tank’s internals drying out which can cause problems with shrinkage, and in extreme cases, the tanks splitting open. Likewise O-rings and other rubber parts are best kept submerged in fuel continuously.

Avoid long-term storage

vapours created by the break-down products in stale mogas after being left unattended over a single winter. Mogas is blended with the expectation that in a car it will be used within a few weeks of being supplied, so it doesn’t need to be as stable over a long period of time as an aviation fuel.

If a composite or plastic fuel tank is built into your aircraft, and if you are tempted to depart from best practice, consider carefully the risk of having to replace the tank should it deteriorate with mogas exposure, with all that implies. With an integral tank in a wet-wing Jabiru, the answer should be certainly not – a new pair of wings would likely write-off the aircraft. Even with the embedded polyethylene fuel tank in a Europa’s fuselage, changing the fuel tank is not an operation for the faint-hearted, involving cutting out quite large parts of the fibreglass cockpit module to release the tank, and then scarfing them back again afterwards, in-situ.

The Europa kit was first produced in the era of four-star mogas, a very different blend to what we find at the pumps today.

The future

For the foreseeable future the demand for fuels for pre-2002 registered cars is likely to give us continued access to Super Unleaded 97 octane E5 fuel on garage forecourts. In the longer term, we have been working with fuel suppliers and the DfT and hope to see wider access to UL91 avgas at airfields and airstrips. For owners of LAA aircraft with E10 eligible engines, a procedure for approving E10’s compatibility with aircraft fuel systems will be provided in due course. This will inevitably be more straightforward with aircraft of recent manufacture supplied with E10-compatible components than it will be for a vintage aircraft, or homebuilts where the fuel system components most likely differ from one example to the next, and are quite likely of an unknown specification.

Ethanol-proof rubber hoses are available. In particular SAE J30/R9 or the European equivalent DIN 7339 D3 are automotive hose standards that are widely available from auto factors. The SAE spec

J30/R14 is a lower pressure, more pliable version

for carburettor systems. These should be used in preference to the older SAEJ30/R6 standard hose which is more permeable to fuel vapour and will harden and crack more rapidly, particularly using fuel containing ethanol.

Watch out for cheap imitations – the real McCoy should come from a reputable manufacturer, be marked with the SAE number along its length, and will likely cost at least £10 a metre.

Paul Hendry-Smith, MD of TLAC at Little Snoring, the company factory-building the Sherwood Ranger, Scout and Kub, as well as supplying the Ikarus C42, advises that he is currently adapting their range of aircraft to make them E10 compatible, including, for the Ranger, a new aluminium main fuel tank to replace the fibreglass originals.

He’s concerned by reports that fuel suppliers sometimes use car petrol as a means of getting rid of unwanted chemicals – for example one supplier apparently stands accused of blending impure methanol and xylene into the fuel, which Paul describes as ‘a great mix for paint stripper’.

This eliminates the costs of safely disposing of otherwise non-saleable (impure) product and allows car owners to burn it and use their catalytic converters for the job. This is certainly happening within some EU Member states. Paul also reports on one Sherwood Ranger’s fuel tank degrading with mogas fuel, despite being made from an ethanol proof resin – those undefined other additives in the fuel presumably being responsible.

What can we do to help the situation?

It may be that off-the-shelf drop-in-the-tank additives can be used to mitigate some of the problems with E10 fuel, in particular stabilisers and anti-corrosion products, just as they are routinely in the marine and race-car world. Not knowing what’s in them, I’d steer clear of any additives that claim to boost the fuel’s octane. Definitely avoid additives that claim to actively enhance an engine’s power or fuel economy (other than just to restore proper performance by giving the carburettor jets and orifices an occasional clean-up) which like those ‘powerful rare-earth magnets you can install alongside the fuel line’ are the preserve of the snake oil salesmen, often with offerings seemingly aimed at flat-earthers or enthusiasts of perpetual motion.

Where we need to be particularly careful in reading-across from (hopefully) a trouble-free transition to E10 in automotive use is the difference between our petrol cars and the way our aircraft engines are configured.

Our cars generally have submerged fuel pumps in their petrol tanks and a sealed fuel system. In our aircraft we have an open-vented tank and usually a fuel pump several feet away, often mounted in a hot area of the engine bay near to the engine exhaust, dragging the fuel through a fairly convoluted pipework system, a filter and fuel selector – all features encouraging a vapour lock – and then to make matters worse, we want to climb up to altitude and operate in reduced atmospheric pressure.

Our modern car will have a fuel injection system rather than carburettors, a circulating fuel system designed to purge any vapour forming in the fuel line, and an ECU that monitors the engine’s parameters constantly and adjusts the fuel mixture strength and ignition timing to prevent damage to the engine – and if all else fails and the engine should ‘pink’, we can hear it from the driver’s seat and drop down a gear to lighten the load.

Because of the much higher background noise level in our aircraft, detonation cannot be heard, and the pilot’s first indication of a problem may be when the first piston crown disintegrates, or a valve head departs its stem.

In conclusion – E10 is now not only coming, it’s here, and it is presently not recommended nor approved for use in LAA aircraft. ‘Hoping for the best’ and using E10 fuel in your aircraft regardless could risk ruining the fuel system components, fibreglass tanks falling to bits, engine failure through contamination of the fuel or ruptured fuel pump diaphragms etc, or more serious engine damage. For most of our engines, UL91 Avgas is the best choice, but 97 octane E5 Super Unleaded remains an alternative to the now-obsolete E5 spec

mogas. ■