Sailplane Classes - a different perspective

Eric Greenwell wrote:

A lot of ras pilots seem to think 15 meters is the 'natural best span',
when embodied in a low cost LS4.


And as far as performance is concerned, look at was has been achieved
with the Diana, sticking with normal sized wings. Much more than a lot
of open class gliders.


--

Michel TALON

Michel Talon wrote:

And as far as performance is concerned, look at was has been achieved
with the Diana, sticking with normal sized wings. Much more than a lot
of open class gliders.

Maximum L/D is only one little part of the story. Much more important
than 2 or even 5 nominal points are the flatness of the polar curve, how
it behaves in turbuence, with bugs, in rain, and, of course, for fun
flyers like myself, the overall feel of the glider.

E.g. many pilots in our club fly the LS8 with 15 meters rather than with
18, because above ca. 150 km/h, the L/D is better with the short wings.
I personally fly it always with 15 meters and unballasted, just because
of the feel. There's much more in a glider than maximum L/D.

Stefan

p.s. I recently listened as a 'pundit' was holding forth on the reasons for
the demise of the open class. He was saying that they were just too hard to
rig. A short distance behind him an ASH-25 owner was whistling softly to
himself as he rigged solo using simple aids.


Try a carry-out of an open class glider when you can't get the trailer
to the glider because it's in the middle of a corn field :-)

Quickly wish for short little wings.

Clinton Birch
LAK 12 (20.4m - one piece wings - 4 outlandings - three involving a
bit of carrying)

Stefan wrote:
Michel Talon wrote:

And as far as performance is concerned, look at was has been achieved
with the Diana, sticking with normal sized wings. Much more than a lot
of open class gliders.

Maximum L/D is only one little part of the story. Much more important
than 2 or even 5 nominal points are the flatness of the polar curve, how
it behaves in turbuence, with bugs, in rain, and, of course, for fun
flyers like myself, the overall feel of the glider.

E.g. many pilots in our club fly the LS8 with 15 meters rather than with
18, because above ca. 150 km/h, the L/D is better with the short wings.
I personally fly it always with 15 meters and unballasted, just because
of the feel. There's much more in a glider than maximum L/D.

Yes, and the Diana performs reasonably well at high speed, as far as i
can see on the loaded polar ...
So i was saying, and you confirm, that 15m wings allow very good
performance when good design is achieved. This also allows light enough
wings, hence easy retreival when outlanding, and doesn't take too much
room in hangars. As far as price is considered i remember that an ASH25
was something like 3 times more expensive than an LS4, which should draw
the attention of people who want more affordable gliding.


Stefan

--

Michel TALON

Andreas Maurer wrote:
For approximately 30 years the performance of gliders has hardly
advanced at all and yet we now have the tools (computer programs) and
much stronger materials (carbon composites) to surely advance the
state of the art of gliders.

Hmm... do you know something that noone else knows?
30 years ago the maximum L/D was about 46:1, now it's 70:1... I would
dare to call this anything but marginal.
Or standard class: LD went up from 35:1 to 48:1.

Absolutely true.

But let's not commit the all too common mistake of "maximum L/D"
fixation when it comes to performance.

I suppose we can agree that "performance" should include
everything that contributes to improving our cross-country
speed under varying conditions. And maximum L/D is only one
of those factors.

It is just as important to consider L/D at varying speeds.
If we do, we get even bigger differences than the above.

(eg. what was the best L/D at 180 kph 30 years ago and compare
that to today's performance).

Cheers CV

David Bingham wrote:
Class 1 be limited to 70kilos maximum
(plus safety equipment such as a ballistic parachute).

Say what ? Where is there a 70 kg glider ?????

(assuming you don't mean hang gliders - 70 kg is approx 150 pounds.)

CV

CV wrote:
David Bingham wrote:

Class 1 be limited to 70kilos maximum
(plus safety equipment such as a ballistic parachute).


Say what ? Where is there a 70 kg glider ?????

(assuming you don't mean hang gliders - 70 kg is approx 150 pounds.)

Currently, the only high performance sailplane being manufactured that
fits the class is the SparrowHawk (www.windward-performance.com/). I
think David is thinking these gliders would appear in greater numbers
when there was a specific class for them.


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

Eric Greenwell
Washington State
USA

Eric Greenwell wrote:
Bill Daniels wrote:

The first class, (Standard Class) was intended to reduce glider costs by
virtually eliminating innovation which, it was felt at the time, was
leading
to ever larger and more expensive gliders.


And it worked! Standard class gliders were a lot cheaper!


The flap enthusiasts insisted on splitting off as the 15 meter class.

Both classes became successful at the expense of the open class where
carbon
composites make the most difference.


Wait a minute - these classes came into being years before carbon was
used. The first really successful Standard Class glider, the Ka-6, was
wood!

In a 15 meter design, the main benefit

of carbon is lighter wings for easier assembly.


Also a higher aspect ratio leading to better L/D, and thinner wings,
leading to higher cross-country speed.


Manufacturers were forced to produce special gliders for two similar 15
meter classes. Designers were forced by the same class rules to
pursue ever
more expensive ways to improve performance such as extremely smooth
surfaces. They wound up producing expensive gliders anyway because of
short
production runs.


Baloney! Far more gliders in EACH class were produced than ever would
have been produced for even a single Open class. THe classes weren't
popular because they were FAI classes, but became popular because they
were such an outstanding combination of cost and performance. That
magical "sweet spot" some people talk about.

snip


I've heard interesting speculation that there's a 'natural best span'
around
18 - 20 meters that would be the best compromise for all conditions.
If the
market had settled on that, we might have had innovation AND low costs.
We'll never know.


The market is moving there, to some extent. Remember, the 'natural best
span' is _very_ dependent on the materials available (and their costs),
and will be different for wood, metal, fiberglass, and carbon. There is
nothing magic about 18 meters, because it depends on a value judgment
(performance versus costs). So, the market couldn't settle on 18 meters
sooner, but had to wait for technology to advance, material costs to
come down, and for pilots to decide that they were now willing to pay
for a certain level of performance.

A lot of ras pilots seem to think 15 meters is the 'natural best span',
when embodied in a low cost LS4.


Bill Daniels

p.s. I recently listened as a 'pundit' was holding forth on the
reasons for
the demise of the open class. He was saying that they were just too
hard to
rig. A short distance behind him an ASH-25 owner was whistling softly to
himself as he rigged solo using simple aids.


And taking far longer than an ASW 27, which cost far less. If your
pundit talked only about putting it together, he hasn't been around one
enough to know what a bloody pig it is on the ground, and how much real
estate they need just to be tied down, or pushed around on a ramp, or
taken down a taxiway, and how wide the runway needs to be to take off or
land on, the size of the towplane, and how many people had better show
up if he ever hopes to get it out of a field! Shucks, just trying to
push the empty trailer around to hook it up is more than my crew can
handle. It's not ignorance that keeps people from falling all over
themselves to get a 25 meter glider.

Personally I love my 15m standard class plane. Might be tempted by flaps one
day. Might be nice to have optional longer wings for the few days weak enough to
warrant them but still soarable each year.

Both of the nice to haves equate to a lot more money - think I'll settle for a
lot of flying in my cheap, simple toy... Maybe I'm just spoiled by the weather
here, but sometimes less is more.

Think about it 1:35, easy to rig, light trailer, minimal maintenance, minimal
capital cost could land in small fields (never had to so far)

Only thing I would pay for is self launch, so I can fly when the rest of the
club is not in operation. Only cost/risk of doing that is losing touch with the
mainstream, and seeing less of some friends. But to be perfectly honest my
ambition at present is to see as little as possible of them while flying as much
cross country as possible.

Eric Greenwell wrote:
Currently, the only high performance sailplane being manufactured that
fits the class is the SparrowHawk (www.windward-performance.com/). I
think David is thinking these gliders would appear in greater numbers
when there was a specific class for them.

OK, interesting concept and looks like a lot of fun.

Calling it "high performance" is a bit of a stretch
though, if we are talking conventional gliders:
Best L/D 36 at 50 KTS and 24 at 75 KTS, would put
it somewhere in the club-class performance-wise.

I'm sure it is very "high performance" within its own
UL-category.

Cheers CV

I think the number of classes has gotten out of hand also. My memory
is getting bad, but I thought when the 18M class was proposed the 15M
class was suppose to be phased out.

The logic for creating the standard class was we needed an inexpensive
class of glider so ships without flaps should were thought to fit that
bill. How much difference is there between the cost of a 15M and
Standard today? Not much.

18M was proposed as the optimum wingspan to performance to cost
solution and it was suppose to become the "racing class" in the future
and replace the 15M. Instead we now have both. As some have noted,
often the 15M ships are faster than the 18M's on any given day.

It is time to reduce the classes back down to a reasonable number; I
think standard, 15 and 18 should be combined into a "racing class"
again and with maximum wingspan of 18M. Change the "world class" to a
sub 13M class and have the open class. Then the only thing needed is
a "sports" or "club" class for those learning or flying older ships
that need a handicap.

Tim