Debacle: Flight test of Diana-2

pbc76049 wrote:


Item 4 is subjective at best. The aircraft meets JAR 22.

I'm not aware of any standardized crash testing procedure for gliders,
and if the the manufacturer of my ASH 26 E has knowledge of such tests,
they haven't shared it with any of the customers I know. It would be
wonderful if such data was available, but if you must have this data for
any glider in production, I think you will have pay someone to do a
crash test on it.

Unless you are an engineer competent in composite design for crash
protection, I don't think you will learn anything about the design by
asking "where the Kevlar is".


Item 5 is conjecture on your part. You are
presupposng a failure mode not in evidence
by inferring that it is problematic.

I don't think any of the manufacturers test their gliders until they
flutter, because it is very dangerous. The glider is likely to be so
damaged or uncontrollable, the test pilot will have to parachute out of
it. Certification requires testing to a certain speed beyond the Vne;
above that, and you are a test pilot. If you want to "know what margin
you will have when you are in an emergency" then you should fly so that
your emergencies do not exceed Vne. Even if the manufacturer the exact
flutter speed, he would be smart not to reveal that speed, for fear that
pilots would then use that speed as the "real" Vne.


Item 13 is again subjective. Properly assembled trailing
edges do not delaminate regardless of their construction
method. Your presupposition that fabric wrapped edges
are superior is not based in fact, just an opinion you hold.
Attempting to show one Trailing Edge construction method
as superior to another again shows the limitations of your
composite construction background.

My ASH 26 E does not use fabric wrapped trailing edges, nor did my ASW
20, yet they both seem like fine machines. I would feel rather foolish
telling Gerhard Waibel or Martin Heide the proper way to build a glider!

It appears Neshe sets very high and very unusual standards for a glider.
If I were a glider manufacturer, I would pray he became interested in
some other manufacturer's glider.


--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Hi Eric,

On Sun, 16 Oct 2005 20:48:49 -0700, Eric Greenwell
wrote:


Unless you are an engineer competent in composite design for crash
protection, I don't think you will learn anything about the design by
asking "where the Kevlar is".

Well... extremely light weight of a fuselage definitely makes me
wonder about crash protection - something Germany glider manufacturers
have a lot of experience with. I think there's a good cause why their
gliders are so heavy compared to the Diana 2.


I don't think any of the manufacturers test their gliders until they
flutter, because it is very dangerous.

Wilhelm Dirks did that with the DG-600...

Flutter testst are not performed inflight, but any aircraft needs to
perform static flutter tests before it's certified in Germany (a very
expensive thing to do - these tests are usually performed by Prfessor
Niedbal).

Even if the manufacturer the exact
flutter speed, he would be smart not to reveal that speed, for fear that
pilots would then use that speed as the "real" Vne.

The design maximum speed is Vne + 15 percent - this is what the glider
is designed for (and being flight-tested). Obviously this is the
proven speed where no flutter occurs... at least in a perfectly
maintained (prototype) glider.
I certainly wouldn't risk to fly that fast... do you think that
someone is so stupid to exceed Vne? I think most flutter cases happen
at speeds between Va and Vne due to unexpected turbulence.



Bye
Andreas

Andreas Maurer wrote:

Unless you are an engineer competent in composite design for crash
protection, I don't think you will learn anything about the design by
asking "where the Kevlar is".


Well... extremely light weight of a fuselage definitely makes me
wonder about crash protection - something Germany glider manufacturers
have a lot of experience with. I think there's a good cause why their
gliders are so heavy compared to the Diana 2.

Questions about the crash protection are very sensible, but they should
be good questions. I think "how can your glider be so much lighter than
the German gliders?" would be a much better question than "where is the
Kevlar?". Or maybe: "Is the Diana 2 crash protection as good as the ASW
27 (for example)?"

snip

The design maximum speed is Vne + 15 percent - this is what the glider
is designed for (and being flight-tested). Obviously this is the
proven speed where no flutter occurs... at least in a perfectly
maintained (prototype) glider.
I certainly wouldn't risk to fly that fast... do you think that
someone is so stupid to exceed Vne?

I can easily imagine a pilot thinking "This wave has such strong winds,
I must fly very fast to get to the upwind lenticular. The air is quite
smooth, and the actual flutter speed was determined by testing at 40
knots over Vne, so I can fly at 30 knots over Vne quite safely; of
course, I will be very gentle on the stick!"

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

On Mon, 17 Oct 2005 16:02:16 -0700, Eric Greenwell
wrote:

Questions about the crash protection are very sensible, but they should
be good questions. I think "how can your glider be so much lighter than
the German gliders?" would be a much better question than "where is the
Kevlar?". Or maybe: "Is the Diana 2 crash protection as good as the ASW
27 (for example)?"

Indeed.
The 27 is a good example because its dimensions are very similar to
the Diana 2.

I know how long it took for Schleicher to squeeze only 20 lbs out of
the forward fuselage from the ASW-27 (which then became the 27 SL with
an empty wight of 230 kg). Hard to see for me how someone is able to
save another 48 kg on a glider of similar dimensions without
sacrifying anything (the empty weight of the Diana 2 is 182 kg).

I heard that the wings of the Diana 2 are only slightly lighter than
the ones of the ASW-27, but unfortunately I didn't find more
ionformation yet.


I can easily imagine a pilot thinking "This wave has such strong winds,
I must fly very fast to get to the upwind lenticular. The air is quite
smooth, and the actual flutter speed was determined by testing at 40
knots over Vne, so I can fly at 30 knots over Vne quite safely; of
course, I will be very gentle on the stick!"

Well... definitely a proof of the existence of natural selection
then...
I could think about a different scenario with the same result:
Since the indicated Vne goes down with altitude (but the red line
doesn't move), it's easily possible to fly faster than Vne
unintentionally if one forgets to study the Vne over height (no idea
of the correct technical term in English... sorry...) limitation
table and flies at high altitude.





Bye
Andreas

Andreas Maurer wrote:
Or maybe: "Is the Diana 2 crash protection as good as the ASW
27 (for example)?"


Indeed.
The 27 is a good example because its dimensions are very similar to
the Diana 2.

I know how long it took for Schleicher to squeeze only 20 lbs out of
the forward fuselage from the ASW-27 (which then became the 27 SL with
an empty wight of 230 kg). Hard to see for me how someone is able to
save another 48 kg on a glider of similar dimensions without
sacrifying anything (the empty weight of the Diana 2 is 182 kg).

I can only speculate, because I am not familiar with the Diana 2. I know
from speaking to Gerhard Waibel that some structure on the Schleicher
gliders is much stronger than required by the flight loads. I learned
about that when I had a problem with an aileron push rod at the root of
my ASW 20. Gerhard told me I didn't have a problem, because those rods
were three times stronger than the flight loads required, due to ground
handling issues (pilots would grab the rods to keep the wing from
tipping in a wind). Similarly, the wings are much stronger in the
horizontal direction than needed in flight, because pilots and crew put
a lot of force on the wing tips when pushing the glider around on the
ground.

If a designer believed the owners of his glider would be very careful
when moving the glider on the ground, he could save weight in these
areas (and others). Of course, there are other ways to save weight: the
SparrowHawk is an extreme example of this, and one factor is the use of
pre-preg carbon fiber instead of wet lay-up. Or, perhaps, pultruded
carbon rods instead of a roving spar cap, as some gliders use.

I don't know how the Diana does it, but if I wanted a Diana 2, I would
ask questions like "How did you achieve this weight reduction without
sacrificing strength needed for ground handling or crashworthiness?".

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Eric Greenwell wrote:

I don't know how the Diana does it, but if I wanted a Diana 2, I would
ask questions like "How did you achieve this weight reduction without
sacrificing strength needed for ground handling or crashworthiness?".

Yes, Eric, but English is your first language. I don't think it is for
Naresh so he simply said "Where is the Kevlar?"

12 words and about 97 polysyllables shorter - but exactly the same
question.

Graeme Cant

Graeme Cant wrote:
Eric Greenwell wrote:

I don't know how the Diana does it, but if I wanted a Diana 2, I would
ask questions like "How did you achieve this weight reduction without
sacrificing strength needed for ground handling or crashworthiness?".


Yes, Eric, but English is your first language. I don't think it is for
Naresh so he simply said "Where is the Kevlar?"

12 words and about 97 polysyllables shorter - but exactly the same
question.

OK, how about "How come yours is so light and theirs is so heavy?"?

Actually, his written English is excellent - look at his postings and
web site. I think he asked the Kevlar question because he thought the
details about it's use would tell him (and the audience he appears to be
reaching for) important information. My point is it won't, unless you
are very knowledgeable about the details of glider structural design for
crashworthiness.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Andreas Maurer wrote:


Well... extremely light weight of a fuselage definitely makes me
wonder about crash protection - something Germany glider manufacturers
have a lot of experience with. I think there's a good cause why their
gliders are so heavy compared to the Diana 2.

Whatever the kind of vehicle, crashworthiness is definitely not
described by the mass of the vehicle itself!

All of the mass situated behind the pilot's seat is dangerous, not
protective.

Aldo Cernezzi

2cernauta2 wrote:

All of the mass situated behind the pilot's seat is dangerous, not
protective.

And, contrary to the belief of some SUV drivers, even the amount of mass
in front of the pilot doesn't tell much about crashworthyness.

Stefan

But in gliders as in SUV's, I feel better if my mass is above yours.
"Stefan" wrote in message
...
2cernauta2 wrote:

All of the mass situated behind the pilot's seat is dangerous, not
protective.

And, contrary to the belief of some SUV drivers, even the amount of mass
in front of the pilot doesn't tell much about crashworthyness.

Stefan