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

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.

--
-----
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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

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

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.


I don't think span is important. Instead it is aspect ratio. Any builder
can make span cheaply. A longer wingspan with larger mean
chord is useless and trivial. If all we wanted was span, this
would be VERY cheap.

Hmmm...it also strikes me that weight is very important to this discussion.
A 100# solo pilot is probably not getting the best performance for the
dollar from a DG-1000.

What I'd want is a minimum wing loading that, with me as the pilot,
supported a polar I like. What polar I like depends on the
conditions I fly in (floater or penetrator). I wouldn't want
to have to add ballast for every flight to get the polar I normally
like, since this would mean I paid for too much wing.

Having picked the wing loading, I'd now buy the highest aspect ratio
I could afford. As technology advances, this means I get more
and more span.

But technology for reducing weight seems to have outpaced
technology for increasing aspect ratio. So at the end of this
discussion, I'd like a Sparrowhawk for the dollar, instead of
something else. I'd prefer a much lighter glider with a
shorter wingspan and no ballast to a heavier one with more
span and the same aspect ratio.

I actually like LESS wing area with the same loading as my ideal
polar. Because the min sink part of the polar is 20 to 100 ft/min
less, the high speed part also gains this advantage. At the
super light weight, we can use a MUCH slicker airfoil and get the
same stall speed as a glider twice the weight. And we don't have
to beef up the fuse for heavy wings, then make the
wings larger for the weight, etc... (diminishing returns).

The tough decisions a is retract worth the extra weight? And is
the glider sturdy enough to be flown in/out of typical strips
at my skill level (bumps and ruts included)? The Sparrowhawk
is an excellent concept theoretically, but is it sturdy?
As a very lightweight pilot, I'd be very interested in a
similarly light glider, but I sure wouldn't want to BREAK it.
Tiny main and tailwheels, and a fragile tailboom, can be a
real practical drawback...

It sure is fun to browse all the exciting equipment at each extreme...

(Mark James Boyd) wrote in message news:3ffef018$1@darkstar...

Hmmm...it also strikes me that weight is very important to this discussion.
A 100# solo pilot is probably not getting the best performance for the
dollar from a DG-1000.

It's not the weight of the pilot, it's the weight of the plane that
counts. That's what ballast is for. Sure, you could build a 99/100th
scale DG-1000 just for the 100 lb pilot - but why? And it wouldn't be
cheap!

What I'd want is a minimum wing loading that, with me as the pilot,
supported a polar I like. What polar I like depends on the
conditions I fly in (floater or penetrator). I wouldn't want
to have to add ballast for every flight to get the polar I normally
like, since this would mean I paid for too much wing.

The problem with this approach is that you are tailoring your glider
to one specific condition - and give away the wonderful game of
tailoring a glider's wingloading to the actual condition you are
flying in. A floater in the spring is nice, but is no fun in the
middle of summer when 10 knotters roam the desert and you need an IFR
clearance to climb to cloudbase! BTW, that is probably a big part of
the PW-5 problem - too much of a one-trick pony...IMHO.


Having picked the wing loading, I'd now buy the highest aspect ratio
I could afford. As technology advances, this means I get more
and more span.

But technology for reducing weight seems to have outpaced
technology for increasing aspect ratio. So at the end of this
discussion, I'd like a Sparrowhawk for the dollar, instead of
something else. I'd prefer a much lighter glider with a
shorter wingspan and no ballast to a heavier one with more
span and the same aspect ratio.

I actually like LESS wing area with the same loading as my ideal
polar. Because the min sink part of the polar is 20 to 100 ft/min
less, the high speed part also gains this advantage. At the
super light weight, we can use a MUCH slicker airfoil and get the
same stall speed as a glider twice the weight. And we don't have
to beef up the fuse for heavy wings, then make the
wings larger for the weight, etc... (diminishing returns).

The tough decisions a is retract worth the extra weight? And is
the glider sturdy enough to be flown in/out of typical strips
at my skill level (bumps and ruts included)? The Sparrowhawk
is an excellent concept theoretically, but is it sturdy?
As a very lightweight pilot, I'd be very interested in a
similarly light glider, but I sure wouldn't want to BREAK it.
Tiny main and tailwheels, and a fragile tailboom, can be a
real practical drawback...

The whole Sparrowhawk thing scares me to death! When I'm bashing
around at 130 knots, I want my glider to have a certain structural
authority! Same thing when landing on some strange desert airstrip
for the first time. And don't get me started on the whole unregulated
ultralight glider thing!!! IMPORTANT SAFETY TIP FOR ANY NON-LICENCED
"PILOT" DROOLING OVER A SPARROWHAWK BROCHU Get the training, take
the damn test, get a licence, and fly a real glider, for goodness
sake! Or at least make me the beneficiary on you life insurance
policy...

As a very lightweight pilot, you have the advantage of an even greater
wingloading spread available to use, which can be a nice advantage
early in the season or late in the day - why give it away?

It sure is fun to browse all the exciting equipment at each extreme...

You're damn right about that! And congratulations on your CFIG, BTW!

Kirk
A not very lightweight pilot

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