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Saturday, March 5, 2016

Questions for designers...

Hannes Papesh Interview 5 March 2016 .

Z- What’s your opinion about :  "Softer leading edge do collapse often but they also recover faster and smoother, harder leading edge with a smaller AoA are very resistant but the collapses are more aggressive".
Do you agree? or no...and why?

Hannes: We're dealing with that issue since mid of the 90’s. During the X-act development we were trying to find an airfoil which is collapse resistant and in the case, collapsing very soft and unspectacular.
As "to collapse" is a fundamental issue of the safety concept of a paraglider, this scenario should be very well predictable.
During the very intensive discussion about folding lines (see attachment) I've been arguing with the "dynamic history" of a collapse: the airfoil should deform, loose air and fold in the middle, to create a soft collapse. In this procedure the static weak points are important. They are given by the suspension points and the airfoil shape (and some internals maybe). When you mount folding lines on new suspensions (where there is no load during normal flight), you're faking new static weak points.
So we should spend some engineering and development effort to find an airfoil / solution that can do both: to be collapse resistant AND collapse soft and recover easy.
-Not just make "a quick cheat".
-Some in the scene are specialists for that, as we all know!

Z-Do you believe for instance that in order to see the real thing, the exact collapse in each individual glider regardless of their construction is to remove the test pilot ability to 'pull' the A's...

Hannes: Pulling the A's is good.
Sometimes it's not possible without mounting some separate lines (in case of an A/B fork).
Important is, that you pull on a suspension point, which is highly loaded during normal flight.
Experience shows, that the static weak points in real flight are between the suspension points: there the airfoil kinks in the case of a collapse deformation.
The simulated collapses should show the same deformation behavior as the real flight collapse.
Putting force on the airfoil further in front does enlarge the "deformation arm": resulting in softer collapses.

Z-Another idea could be to send a paramotor or some machine to create heavy turbulence that passes exactly 10 m in front of the test pilot over a lake...That way it will be clear on the videos how much the glider endure the collapse and how it will react.
-Do you think that this could be an evolution for future test houses ? Can you comment on that please ?

Hannes: It is not easy to create the standard rotor.
And will be quite hard to do: but that kind of testing could offer some more real life results.

The general problem is the exclusion of cheating actions.
We all have had airfoils which were flying fine and collapsed late. But they showed a very nasty and hard collapse behavior.
But you need really some "cheating creativity" to get the idea to mount folding lines far in front to get softer collapses.
With that technique you can get every airfoil look nice.
Because of that possibility and the very bad experiences of cheating by one manufacturer, the WG6 working group decided to limit those folding lines (invented by the same manufacturer) to the D class.

My philosophy (specially in the low classes) is to have a wide "green area". No special "best case scenarios / techniques" are needed. The wing should behave fine however the collapse is produced.


Luc Armant answer to the question:

Z-What's your opinion about :  "Softer leading edge do collapse often but they also recover faster and smoother, harder leading edge with a smaller AoA are very resistant but the collapses are more aggressive".
Do you agree? or no...and why?

Luc:   I disagree. I don’t see that at equal speed airspeed or AoA. from equal speed, fragile profile can easily have much worse recovery than more solid one. There is no strong rule here. Add to that the fact that collapsing is always more dangerous than not collapsing. In Ozone, we are searching for the best “real safety” design. We want gliders that we assess will be the safest to fly for pilots making cross country. We don’t want to compromise that.

Z- What's the benefit that a Delta 2 pilot will get flying the Delta 3 in order to disregard the certification at accelerated mode?

Luc: Best benefit for a Delta2 pilot, should be slightly higher speed and more performance at speed. We will not make anything special to try to convince pilot about recovery and EN rating, apart from a notice trying to explain things. Like usual, we will release our product and the pilot will make their choice. But again, we know that if we release it EN D we would for sure lose sell because many pilots still think that EN rating is their best way of knowing which wing to buy regardless of what the manufacturer is even recommending.

Z- The Delta 2 and Alpina 2 are still in personal view 'legends' in the C category. Many new C's that came after were more difficult to handle in rough air, except the Carrera plus. Was this only related to the back positioning A's on the leading edge ?

Luc: Of course not even though it’s an important one. There are a lot of other parameters. Too much parameters !  We believe that Aspect Ratio is one of the strongest one .

Z : Now seeing that the Carrera plus has similar performance or very close to the Alpina 2, Delta 2,
that GIN aimed for a B certification as a marketing strategy that could lead to larger sales.With the D3 going in the D category, OZONE is going on the exact opposite way in marketing strategy. Which leads to the question:
With the D3 certified as an EN-D, how will Ozone convince the Rush 4 pilots to move on the D3 ?

 Luc: That would not be marketing strategy. We know we would lose significant sell because of that. But that’s the way it is. Good products are our priority.


FlyinOrange said...

"Good products are our priority. " -> and that they have, and that they have.

"very bad experiences of cheating by one manufacturer" -> that cheating having made arguably the best wing of its year.

Heres to hoping the -3 sells beyond anyones expectations and puts the WG6 on notice that they are quickly becoming a dinosaur facing a Chicxulub on their own making.

dannau said...

Ziad, do you know who's in the WG6?

Ziad Bassil said...

Working Group 6.
The WG6 goal was to create a four-level glider certification standard, with the least stable level (D) being ‘safer’ than the previous certification schemes’ top levels, and with the most stable level (A) being ‘safer’ than any gliders then in production. To ensure that the WG kept on track (writing, testing and validating EN926 took the best part of ten years!) a simple description of these four classes was set down early on.

Kelly Reid said...

I do not believe in the statement that all collapses are bad especially when they are soft and always re-open easily. If I never get a collapse and then 5 years later have a bad collapse and because for instance I'm heavy on the glider it doesn't open easily this scenario is way worse then if I had many little collapses kinda showing me what I'm doing wrong! We do not want to simplify this scenario to the point where we are misguided! Its way more dynamic then that especially with the human mind.

mjd said...

To me, the proof is in the success of the design. The Delta 2/ Alpina / M6 family have proven to be some of the most solid and flyable gliders of all time.

Hannes comments sound childish when he uses the word "cheating" many times. He seems more worried about what other manufactures are doing instead of his own. Luc's comment on the other hand can be summarized as: "we don't care what others think, we just want to make awesome paragliders."

Let that sink in, it's pretty obvious who is being more rational, then quit worrying about how these tests are conducted.

Axis Paragliding said...
This comment has been removed by the author.
Axis Paragliding said...

Wow, Hannes needs to grow up! I am really surprised at such negativity. he creates good designs which many appreciate, and so do Ozone. To my mind they certainly did not cheat the pilots producing such a good design that still has almost no equal, and has had thousands of pilots having good experiences on D2s and Alpina 2s.