50+:1 15m sailplanes

"Ian Strachan" wrote in message
...
In article u, Swiftel

Snip-----

It is interesting that when Gerhard Weibal lectured at the BGA weekend
about 5 years ago, he naturally concentrated on huge-span sailplanes. I
therefore asked him in the question period what he considered the most
"cost-effective span". I expected him to say about 20 or 22 metres but
his reply was 17. Pretty close to the 16m I mentioned above, and
fortunately also to 18m which is now a separate IGC class and is
particularly suited to bearing the extra weight of a motor (whereas 15m
is a tad small for a self-launcher in a weak-thermal country).

Snip-----


Ian Strachan

Bentworth Hall West
Tel: +44 1420 564 195 Bentworth, Alton
Fax: +44 1420 563 140 Hampshire GU34 5LA, ENGLAND


Interesting.

I recall a technical discussion a long time ago asking whether there was a
"natural best wingspan" imposed by the nature of soaring weather. The
question was this: "Ignoring competition classes, is there a single best
wingspan that is suited for the widest range of soaring conditions? The
answers converged around 18 meters. Larger spans were considered too slow
in strong conditions and smaller spans suffered in weak conditions. It's
interesting that the "most cost effective wingspan" is about the same.

This makes me wonder if eventually the 18 meter class will become dominant.
It also makes me wonder if the selection of 15 meters for the two most
popular classes was an error.

Bill Daniels

Bill Daniels wrote:

I recall a technical discussion a long time ago asking whether there was a
"natural best wingspan" imposed by the nature of soaring weather. The
question was this: "Ignoring competition classes, is there a single best
wingspan that is suited for the widest range of soaring conditions? The
answers converged around 18 meters. Larger spans were considered too slow
in strong conditions and smaller spans suffered in weak conditions. It's
interesting that the "most cost effective wingspan" is about the same.

This makes me wonder if eventually the 18 meter class will become dominant.
It also makes me wonder if the selection of 15 meters for the two most
popular classes was an error.

Here's my recollection of the genesis of the 15 meter class. Real
historians please fill in the gaps and correct errors.

In the beginning, there was only One class, and it became Huge and
Expensive, so the World Gliding Body (IGC?) made the Standard Class in
1960. It was Small and therefore Cheap, and it's Leader was the Ka-6. It
was Wood and it was Good.

But then, Dick Schreder rose up and Said, "Spoilers are a False god",
and he Made a Standard Slass glider with Flaps, and it was Better.
Better enough, that the World Gliding Body became concerned, and there
was also Pressure from Libelle H301 owners, so that a New class was born
in 1974 (or thereabouts): the 15 Meter class.

And it was Very successful, and spawned Many designs, and Thousands were
built, and the Contests were full, and it was Good. But then came Carbon
fiber, and new airfoils, and Pilots that knew nothing of Wood, and they
said "the World Gliding Body made a Mistake!" And they were Right..

Whoa! Not so fast. Back then 18 meter wasn't so easy to do. The choices
are different now, and it's a mistake to revisit the decision as if the
materials and aerodynamics we have now were available then, and as if
the pilots would accept the same trade-offs for cost and size that they
are willing to do now.

I think the 18 meter class has been driven by motorglider considerations
much more than any natural "sweet spot" in performance/$. And frankly,
to even claim that 18 meters is the "sweet spot" is a subjective
judgment. Lot's of people prefer smaller gliders, and many prefer bigger
gliders; for many people, it's the cost, not the L/$, that counts;
most people, I believe, don't fly in a wide range of conditions, but fly
during the heart of the day and don't visit locations that vary much.

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

Eric Greenwell
Washington State
USA

Interesting.

I recall a technical discussion a long time ago asking whether there was a
"natural best wingspan" imposed by the nature of soaring weather. The
question was this: "Ignoring competition classes, is there a single best
wingspan that is suited for the widest range of soaring conditions? The
answers converged around 18 meters. Larger spans were considered too slow
in strong conditions and smaller spans suffered in weak conditions. It's
interesting that the "most cost effective wingspan" is about the same.

This makes me wonder if eventually the 18 meter class will become dominant.
It also makes me wonder if the selection of 15 meters for the two most
popular classes was an error.

Bill Daniels

If this was true, why do the 25m gliders win the Open class
competitions? Why aren't the LS8-18's and V2C's etc. cleaning up on
the ASH-25's?

Maybe I'm missing something... but maybe not - didn't a Ventus win
open in SA recently (I could be mistaken).

Jim

"Ian Strachan" wrote in message
...
No, but some of the German manufacturers proposed 16 m, which was so
close to the 15m flapped ships already being built (like the Pik 15)
that IGC decided to stick with 15m.

Just a bit of nit-picking, but it was Pik-20. Pik-15 "Hinu" is a towing
plane...

regards,

h

In article , Fantsu
writes

"Ian Strachan" wrote in message
...
No, but some of the German manufacturers proposed 16 m, which was so
close to the 15m flapped ships already being built (like the Pik 15)
that IGC decided to stick with 15m.

Just a bit of nit-picking, but it was Pik-20. Pik-15 "Hinu" is a towing
plane...

You are quite right, thanks for the correction. I meant the Pik 15
metre (or Pik 20).

On the motor glider front, I flew a Pik20E for some years in the UK.. I
always thought the span a bit short for our weak conditions when
carrying the extra weight of a self-launching engine. I wrote to Pik in
Finland suggesting an 18m version. They did in fact produce a 17m
version, the Pik 30E, but once DG produced the DG400 it was the DG that
sold rather than the Pik 30. I liked the Pik engineering, though, it
was nice and simple (as much as it can be with a self-launcher).

--
Ian Strachan
Lasham, UK

Never mind

It is till a good quote

(I still think it was Moffat back in the 70s)

Robert

Bob Johnson wrote:
Just to keep stuff straight, while Mr. Moffat has certainly expessed
from time to time his fondness for span, I believe "there is no
substitute for span" quote comes from Michael Bird ("Platypus") who used
to "tinsfos" us quite regularly in S & G (Brit mag) from across the pond
...

Of course I could be wrong ..

BJ


Robert Danewid wrote:

There were 2 SZD56 flying in the worlds in Sweden in 1993. They
performed nice but not astonishing. One of them even had a minor midair.

A year later or so we had one (modified) exhibited at the Annual Swedish
Cliding Conference, and as Chris writes, the cockpit were not built for
nice looking guys from the West, but supposedly for thin, starving
pilots from the eastblock...... (now that has thank God changed!)

Moffat once wrote: there is no substitute for span! If you want 50+ go
for an 18m or larger ship, if you want nice handling, easy rigging etc,
it is easy to trade in som finesse-point to achieve that in a 15m glider!

Robert
H304

Chris OCallaghan wrote:

It's been a few years, but if memory serves Gerhard said that the 27
wing could manage a Finesse (best L/D) of 100, that is, if he didn't
have to hang a fuselage off of it. However, most glider pilots like to
fly their aircraft in the first person, so he compromised and got a
Finesse around 46. The Diana, on the other hand, took the road less
travelled by and decided that pilot comfort (or in my case, presence)
were not critical marketing factors. Based on that philosophy, I
wouldn't doubt that a determined engineer could achieve a Finesse of
50+ for a 15 meter glider. However, we've learned that best L/D is a
poor means of judging sailplane performance. It is the flatness of the
drag curves on both sides of the intersection that really determine
the worth of your glider. A polar free of a low speed bucket and
relatively flat increase of sink with speed make a great glider. Might
the poles have found a new trick? A more stable high aspect ratio
airfoil that needs less tail? A better fuselage/wing transition?
Improved laminar control? Perhaps.





Paul T wrote in message ...


'DuckHawk 15m racer announced at 2003 SHA Western Workshop.
53:1glide ratio VNE 200 kts' -from Winward Performance
- anyone got anymore details?

'SZD-56-2, Diana 2: Newest 15-meter Sailplane.The technologically
advanced SZD-56-2 Diana 2 will soar on new wings next
summer. Bogumil Beres, chief design engineer of the
Diana and owner of Biuro Projektowe 'B' Bogumil Beres,
recently announced the design project of a breakthrough
Diana 2, featuring a curved wing platform with a continuously
varying airfoil and high-performance winglets. The
original Diana fuselage will be retained, but with
a lower drag fuselage-wing junction. The wing loading
range will be 6.08 - 11.7 psf. Most remarkably, the
Diana 2 will break the long-standing 15-meter glide
ratio barrier of 50/1 with room to spa forecast
performance includes a max L/D of 52/1. The prototype
Diana 2 wings will fly next August. Diana 2's will
be delivered in the Spring of 2005.'

Have the Germans got something to worry about?