50+:1 15m sailplanes

"Ian Strachan" wrote in message
...
In article , Bob Johnson
writes
..........
It refers to the "easiest way to increase performance" (max L/D I
suppose), contrasting the relative simplicity of adding span compared to
the complexities of adding flaps, new airfoil sections, new
configurations, etc.
........

ahhh - I like this remark Ian,
wouldn't it have been very wise if the IGC would have had this insight
before they created the 15m class.
Isn't it true that already then, several manufacturers proposed 18m wingspan
instaed of the PIKs 15m?
Or can you tell us why the racing class really got 15 instead of 18m
wingspan?
Chris

I hope that they will give the wing a bit more AOA related to the
cockpit/fuselage.
The Dianas I have seen always had bad visibility in the landing approach and
in
high speed the tail always hang a bit low in the airstream.
One of the factory guys from Poland told me in Borlaenge, that the
performance
could be increased by fixing that problem, but these days they had no money
to do
so.
The design shows some clever features, but I heard German designers having
some
doubts if the glider really would pass all JAR requirements.
CHo



"Paul T" wrote in message
...
Here's the figures on the American DuckHawk (got to
be one of the most awful names for a sailplane) from
the promo sheet.

Windward Performance LLC takes its advanced technology
to the racing class.


Specifications
Empty Weight 300 LBS
Gross Weight 900 LBS
Wing Span 49.17 FT
Wing Area 74.93 FT^2
Aspect Ratio 32.2:1
Length 20.6 FT
Horizontal Span 6.8 FT
Vertical Height 4.5 FT

Structural Limits
+11.0 / -9.0 g's
Va, Vb = 165 KTS
Vne = 200 KTS

Performance
At 500 LBS, 6.7 Lbs/FT^2
Best Glide 50:1 at 50 KTS
Min Sink 94 FPM at 40 KTS
Stall Speed 35 KTS

At 900 LBS, 12.0 Lbs/FT^2
Best Glide 52:1 at 67 KTS
Min Sink 122 FPM at 57 KTS
Stall Speed 47 KTS
(data for 900 LBS, 12 PSF)

Airfoils
Inboard 12.7 % t/c
Outboard 10.2 % t/c


The DuckHawk has the broadest wing loading range available,
the highest maneuvering and redline speeds, and the
lowest inertias for snappy handling. The lower flying
mass within the 15m span constraint gives an induced
drag advantage of 49% at 500 LBS and 33% at 900 LBS
(span loading squared) compared to the competition


Time will tell - my money is on the Diana 2 which is
a development of the SZD-56-1 Diana. (Whose cockpit
is bigger than a Ventus a!). Incedently at Leszno they
were also talking about an 18m version and 22m Open
class version.

In article u, Swiftel
writes
"Ian Strachan" wrote in message
...
In article , Bob Johnson
writes
.........
It refers to the "easiest way to increase performance" (max L/D I
suppose), contrasting the relative simplicity of adding span compared to
the complexities of adding flaps, new airfoil sections, new
configurations, etc.
.......

ahhh - I like this remark Ian,
wouldn't it have been very wise if the IGC would have had this insight
before they created the 15m class.
Isn't it true that already then, several manufacturers proposed 18m wingspan
instaed of the PIKs 15m?

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.

From memory the date was 1974 or so, when I was the UK delegate to IGC.
It was actually a BGA proposal to IGC that the old standard class rules
(under which the K6 was designed) be left alone, and the new class
should only be span-limited.

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).

Or can you tell us why the racing class really got 15 instead of 18m
wingspan?

I have written up my perspective on this for Sailplane and Gliding and
it may be published shortly. But basically as above. 18m was never
discussed by IGC in 1974 although this span was used in older wooden
designs such as the Skylark 3 and 4, etc.

--
Ian Strachan

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

"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.

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

Eric Greenwell
Washington State
USA

"Eric Greenwell" wrote in message
...
Bill Daniels wrote:

Snip--(A pretty good history)

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.

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

Eric Greenwell
Washington State
USA


Since this is early January we can knock this one around a bit. The "sweet
spot" argument for 18 meters ignores all but weather and wingspan.

It seems to me that the Skylark 4 was 18 meters as were several 1960's
vintage wood and metal gliders so 18 meters could and was done then, albeit
with a bit more effort than 15. I have never been too comfortable with the
idea that cost and wingspan had a high correlation. Most designers I have
talked to say that adding wingspan is the cheapest way to add performance.

For a decision made in the early 1970's, 15 meters was arguably not a bad
choice. The error, if there was one, is not too have allowed for
improvement in aerodynamics and materials. (Not too sure how they would
have done that.) The "low cost" goal for the Standard Class doesn't seem to
have worked out too well though.

Bill Daniels

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

My recollection is a little different. I could be wrong, but I
distinctly remember discussion of a future 17M racing class, and that
the Kestrel 17 was the first glider designed to compete in it. The year
before the first FAI 17M competitions were to take place, there was
much gnashing of teeth and wailing amongst to be heard from the H301
owners that they would all have to replace their 3 or 4 year old gliders
with Kestrels to be competitive. There were a lot of prominent Libelle
owners, and very few Kestrel owners. The IGC meeting came and went,
there was a new 15M racing class, and everyone acted like there had
never been any discussion of a 17M class.

I think that was my first inkling of just how political this sport can
be. Some things never change...

Marc

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

"Jim Phoenix" wrote in message
om...
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

Hi, Jim.

I like big gliders too.

I don't think these guys were talking about existing gliders. They were
just asking, if you designed a glider for speed, what wingspan would you
choose, ignoring all else? The consensus was 18 meters.

With carbon rods, you could probably build a 60 meter glider but would it go
fast? Probably not. There is likely to be an upper limit imposed by
soarable meteorological conditions. There may also be a sweet spot
somewhere around 18 meters. If that turned out to be the case, and it was
also the most "cost effective span", the 18 meter class would be a "natural
class". I find that a pleasing thought.

Bill Daniels
Nimbus 2C

"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