600kg: Part 2
BCAR Section S revision
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Ben Syson explains the probable amendments to BCAR Section S to accommodate 600kg microlights…
ollowing Francis’ article describing the new 600kg microlight category in September’s Light Aviation, I’ve been asked to write a short article on the changes being made to BCAR Section S, the CAA’s airworthiness requirements document for microlight aeroplanes, which is being updated to suit the expanded Microlight definition. However, as a revised document has yet to be published – I fear I may have been stitched up! To be fair though, I have been involved as LAA Engineering’s representative in the CAA’s working group advising what should and should not go into the updated document, so I have a reasonable idea about what might appear.
BCAR Section S
45kt stall speed limits will allow many more higher performance aeroplanes into the microlight definition. Therefore, it has been decided to overhaul BCAR Section S to make it fully applicable to all aircraft in the new microlight category. It’s also been decided to realign BCAR Section S as much as possible with the Czech UL-2 and German LTF-UL documents.
Gust loads
The first ‘high speed’ requirement currently missing from BCAR Section S are gust loads – the original BCAR Section S had the gust loading requirements of JAR-22 removed. This is a justifiable omission for low-speed aircraft, as flying relatively slowly through gusts doesn’t generate loads as large as the +4/-2g manoeuvre load limits. I’m expecting traditional light aeroplane gust load requirements to be introduced into BCAR Section S, which will align it with the Czechs and Germans, as well as the American Light Sport Aircraft (LSA) requirements.
a 600kg microlight must have payload sufficient to take two 100kg people
BCAR Section S was introduced by the CAA in the mid-1980s as part of the regulation of the new, and previously unregulated, sport of microlight flying. Rather than starting from scratch, JAR-22, the then European airworthiness requirements document for powered sailplanes, was used as a starting point. The sailplane-specific requirements were removed, and the remaining requirements tweaked and toned down to suit the simple, lightweight, low-performance microlights of the day. An early version of BCAR Section S was used by the Czechs and Germans as the starting point for their ultralight airworthiness requirements, UL-2 and LTF-UL respectively. As time has gone on, the three documents, BCAR Section S, UL-2 and LTF-UL, have evolved independently, and grown apart to some extent. Although BCAR Section S has evolved – mostly for the better – it is still only fully applicable to aeroplanes with a design maximum speed not exceeding 140kt. The few microlights in the current definition that are faster than that were approved by borrowing ‘high speed’ requirements from light aircraft airworthiness requirements. The expanded 600kg take-off weight and 36 | LIGHT AVIATION | November 2021
Above The Blackshape Prime is typical of a new genre of high performance 600kg aircraft.
Flutter
The other ‘high speed’ requirement that was significantly toned down – although not entirely removed – in BCAR Section S, was flutter. Although flutter can occur at low speed, it becomes much more of a problem as airspeed increases. The German and Czech requirements are very hot on flutter, as they have a number of universities that specialise in the subject for their glider and light aeroplane industries. Unfortunately, the UK is not well endowed with this particular expertise. I’m expecting the CAA to find some middle ground for the new BCAR Section S, with some ground testing/analysis required prior to confirmatory flight testing.
Increased payload
One of the criticisms of the 450kg microlight category is that it’s possible to squeeze a conventional-style light aircraft into it – think Eurostar or Flight Design CT – but only just.
