Prenosim zanimljiv komentar na clanak objavljen u "British Hang Gliding and Paragliding Association's magazine". I sam clanak je u prilogu posta (pdf).


Is EN B always EN B? Philipp Medicus on categories and certification


The September edition of the British Hang Gliding and Paragliding Association's magazine Skywings, contained an opinion piece entitled "EN-lightenment". (PDF-download here). In the article, author Kelly Farina claims that the EN B class has grown far too large. The trend for ever higher aspect ratio means some wings are too demanding for average recreational pilots. Farina also alleges that this is made possible because some manufacturers cheated during the EN tests. In the latest edition of Skywings, NOVA head of Design and Development Philipp Medicus replied to the article. Thanks to Joe Schofield (Skywings editor) and Kelly Farina for permission to quote and re-publish the article here.

"I recently found some time to put down my thoughts on your interesting EN-lightenment article in September’s Skywings. The article observed that the modern EN B market has become unacceptably wide, with ever-higher aspect ratios leading to some gliders becoming too hot for the average recreational pilot to handle. It also suggested that it had become possible for manufacturers to cheat the testing criteria.

I wouldn't say that manufacturers have learned how to cheat the testing criteria; however I do think the test criteria were executed more strictly a few years ago than they are now. An example: If a glider’s reaction after two out of ten test-collapses was outside the EN/LTF norm, some years ago the wing would have failed the certification. If a glider’s reaction after two out of ten test-collapses is within the EN/LTF-norm today, the wing usually passes the certification.

It’s also true that paragliding flight test will always involve a huge grey area. A skilled test pilot knows lots of different ways to induce a collapse. Often seemingly small details make a huge difference, like exactly when you shift your weight, or exactly what direction (downwards, inside-downwards and so on) you pull the A-risers.

So a skilled test pilot can make a glider look good or look bad to correspond to the EN/LTF norm. I'm not talking about a high-level EN B glider that could have been tested with one or two C ratings; rather I’m talking about an EN B glider that would be outside the D class if it was tested differently.

In the past, with the DHV monopoly, the (one and only) test house was probably focusing more on the weak points of a paraglider. If a test pilot considered a glider’s reaction to be potentially dangerous it didn't pass. No matter if the wing showed this reaction in just two out of ten cases.
Today we have competing test houses, and this development has changed the motivation of the test houses and the test pilots. Many of those test pilots are freelancers, and it's quite obvious that super-strict testing won't lead to more customers (i.e. money) in the long run. So if a wing shows a potentially dangerous reaction in just two out of ten cases, the judgement is likely to be different from the test pilot I mentioned above.

I think it's really hard to find a solution to this problem. It definitely can't be solved by making the criteria more strict, as your article suggested, for example by reducing the degree of turn allowed after a collapse. The problem of the huge grey area will remain, and I don't see a way of getting rid of it to an acceptable extent.



From the manufacturer’s point of view, however, I think that it's not clever in the long run to sell a super-high-aspect ratio EN B wing. That's why we haven't increased the aspect ratio in the fifth generation of our high-level B wings (from Mamboo and Mentor 1 to Mentor 4). The MENTOR 4 targets the very same group of pilots as the Mentor 3, the Mentor 2 and the Mentor 1 did. Accordingly it's not more difficult to fly. In the long run it would be stupid to constantly increase the demands on the pilots. Who would be able to fly a Mentor 8?

I hope that pilots and manufacturers will begin to stop focusing so much on the EN certification. I can clearly understand the pilot who wants an independent judgement of the glider he entrusts his life to. But even in a perfect certification world the EN rating would say nothing about a glider’s stability in turbulence, which is crucial for its safety. That's what a good manufacturer has to work on. There are also a couple of other important things that the EN tests can never test.

So, to summarise: certification flight tests are clearly overrated by most pilots. EN B – or EN D – says very little about a glider’s safety. Every manufacturer knows a lot more about his wing’s safety than the EN tests can ever say. I hope that more and more pilots come to realise that. And I think that most of the manufacturers will act responsibly. As I said before, in the long run it would be simply mad to increase the demands from one wing to its successor. It could be that this trend of high-aspect ratio EN B wings is already nearly over.”