Better Boundary Layers

On Tue, 8 Jul 2003 17:08:46 -0700, Eric Greenwell
wrote:



No, but Dick only tested one glider, and a very early one (early '94
production). Several changes have been made in the wing since then,
such as more blowholes, adding winglets, an additional flap position,
and using NACA ducts instead of pitot tubes. My experience flying my
ASH 26 E (built in early '95, retrofitted with NACA ducts and
winglets, and no profiling or sanding of the surfaces) against DG 800s
and Ventus 2 CMs is that all three have nearly indistinguishable
performance differences.

But the 26 is the only one with blow turbulators and it goes no better
than the two gliders without. I think you just made my point.

Mike

In article ,
says...
On Tue, 8 Jul 2003 17:08:46 -0700, Eric Greenwell
wrote:



No, but Dick only tested one glider, and a very early one (early '94
production). Several changes have been made in the wing since then,
such as more blowholes, adding winglets, an additional flap position,
and using NACA ducts instead of pitot tubes. My experience flying my
ASH 26 E (built in early '95, retrofitted with NACA ducts and
winglets, and no profiling or sanding of the surfaces) against DG 800s
and Ventus 2 CMs is that all three have nearly indistinguishable
performance differences.

But the 26 is the only one with blow turbulators and it goes no better
than the two gliders without. I think you just made my point.

I was answering your comment about the "terrible" ASH 26 polar. For
the blow turbulators, I previously tried to make the point that they
may indeed be the best choice for the airfoil that Schleicher chose.
The fact that it didn't give Schleicher a "definitive" advantage
doesn't mean this isn't true, as performance is affected by other
factors, such as the wing design (area, aspect ratio, winglets, etc),
fuselage and tail design, and so on.

Regardless of whether the ASH 26 would work just as well with zig-zag,
it is obvious to the pilot the blow turbulators are doing something!
Taping over just one NACA duct elicits an loud and eery chorus that
the Louek Boermanns, the airfoil designer, says is a vortex forming
behind the trailing edge of the wing. I can also hear the vortex in
wave conditions when the flaps are not set properly.
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directly

Eric Greenwell
Richland, WA (USA)

"Mike Borgelt" wrote in message
But the 26 is the only one with blow turbulators and it goes no better
than the two gliders without. I think you just made my point.

Mike



So how's that prove BHs are ineffective? One could also say the 26e design
is somehow otherwise aerodynamically slightly inferior to the other gliders
mentioned. And that the BHs make up for this by bringing the 26's
performance up to par. Not saying I really buy this, but it makes about as
much sense.

I suspect blow turbulators provide a slight incremental improvement and
other manufactures don't think the gain justifies expense. Either way, it
doesn't much matter to me . . . they're on my 26e and they are way cool. To
those less fortunate "blowholeless pilots", I say, "tough"!

--
bumper
"Dare to be different . . . circle in sink."
to reply, the last half is right to left






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But the 26 is the only one with blow turbulators and it goes no better
than the two gliders without. I think you just made my point.

Mike
In the case of the 26 and 27 one must not narrow it down to just the
blow holes. Aside from the structural features, the gliders have
incorporated truly aerodynamic advances. For the gliders to
perform as they do everything had to work just right. Consider the
fact it has the smallest wing area of the " three" the Diana is even
smaller. It has the highest dry wing loading of any 15meter class glider.
Still it is able to soar with the lightest in its class, with only the
slightest
disadvantage. As soon as the wingloading goes up, when conditions
allow, this glider is in a class by it self.
At the time I thought Waible should have gone about it incrementally,
rather then design a radical new glider for production.
Look at the fuselage shape only, it required a new wing/fuselage juncture.
The others still use the wing straight into the fuselage.
The airfoil had to generate more lift due to smaller wing area as well make
it thinner to reduce drag. A small gain could be realized with the higher
aspect ratio that came with this wing lay out. Waibel was the man that
knew/felt
laminar flow could be obtained past 90% of chord across a hinge line. He
pursued that goal with the help from Loek Boermans.
Also the wing fuselage intersection was L. Boermans doing.
The blow holes are not an insignificant part in making the glider what it
is.
If it could just shed 75lb of its empty weight and we would not have this
discussion about blow holes.
Regards
Udo

The Idafleig tests show that the '27 polar is in a class of its own, and
significantly better than the Ventus 2. See page 168 of Fundamentals of
Sailplane Design by Fred Thomas.


"Udo Rumpf" wrote in message
...
But the 26 is the only one with blow turbulators and it goes no better
than the two gliders without. I think you just made my point.

Mike
In the case of the 26 and 27 one must not narrow it down to just the
blow holes. Aside from the structural features, the gliders have
incorporated truly aerodynamic advances. For the gliders to
perform as they do everything had to work just right. Consider the
fact it has the smallest wing area of the " three" the Diana is even
smaller. It has the highest dry wing loading of any 15meter class glider.
Still it is able to soar with the lightest in its class, with only the
slightest
disadvantage. As soon as the wingloading goes up, when conditions
allow, this glider is in a class by it self.
At the time I thought Waible should have gone about it incrementally,
rather then design a radical new glider for production.
Look at the fuselage shape only, it required a new wing/fuselage juncture.
The others still use the wing straight into the fuselage.
The airfoil had to generate more lift due to smaller wing area as well
make
it thinner to reduce drag. A small gain could be realized with the higher
aspect ratio that came with this wing lay out. Waibel was the man that
knew/felt
laminar flow could be obtained past 90% of chord across a hinge line. He
pursued that goal with the help from Loek Boermans.
Also the wing fuselage intersection was L. Boermans doing.
The blow holes are not an insignificant part in making the glider what it
is.
If it could just shed 75lb of its empty weight and we would not have this
discussion about blow holes.
Regards
Udo

On Thu, 10 Jul 2003 00:20:05 GMT, "John Morgan"
wrote:


"Mike Borgelt" wrote in message
But the 26 is the only one with blow turbulators and it goes no better
than the two gliders without. I think you just made my point.

Mike



So how's that prove BHs are ineffective? One could also say the 26e design
is somehow otherwise aerodynamically slightly inferior to the other gliders
mentioned. And that the BHs make up for this by bringing the 26's
performance up to par. Not saying I really buy this, but it makes about as
much sense.

I suspect blow turbulators provide a slight incremental improvement and
other manufactures don't think the gain justifies expense.

That is about what I said. Nobody can point to a definitive real world
advantage held by any production glider with blow hole turbulators.
Hence blow turbulators have not become universal.

Mike

Yeah but sure they're cool when showing your new glider to your friends...

I prefer old fashioned zigzag tape. Easier to mantain and clean.

Good flights
Jose M. Alvarez
ASW24

"Mike Borgelt" escribió en el mensaje
That is about what I said. Nobody can point to a definitive real world
advantage held by any production glider with blow hole turbulators.
Hence blow turbulators have not become universal.

Mike

Earlier, Mike Borgelt wrote:

...I'm of the belief that glider performance
ran into a brick wall 20 years ago. The LS8,
still a top standard class ship, is really
an LS6 with flaps fixed and could have been
built at the same time...

I agree that span-balanced performance has been relatively stagnant
for the last decade or so. Of course, there's no guarantee that some
unforseen new development won't unstick it on a moment's notice.

What I notice about the LS-8 and LS-6 is generally along the lines of
what Mike asserts. The slightly funny thing is that the LS-6 is not
exactly a top 15 meter contender these days; but of course that could
be due to a variety of factors independent of its performance. The
LS-8, on the other hand, has been chosen by lots of Standard class
pilots and has been well-placed on the scoreboards.

My take on the situation is that the basic LS-6/LS-8 platform, with
about 10.5 m^2 of area, is actually a bit large for 15-meter
contention but about right for the current standard class. I notice
that most of the "hot" 15-meter ships have in the neighborhood of 9.5
to 10 m^2. Also, I see that the new LS-10 has a 10 m^2 area more in
line with the "hot" 15m ships. And that makes me wonder what the next
standard-class LS offering will be like. Will it combine the
elliptical leading edge with the LS-8's 10.5 m^2 area? Inquiring minds
want to know!

Even further off-topic, when I was laying out the HP-24, I originally
gave it a 9.75 m^2 area because I wanted it to go fairly well
unballasted, as most sport pilots fly. However, in line with
increasing gross weight and possible motorglider options, I later
increased the area to a round 10 m^2.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24

On 10 Jul 2003 10:39:41 -0700, (Bob Kuykendall)
wrote:

Earlier, Mike Borgelt wrote:

...I'm of the belief that glider performance
ran into a brick wall 20 years ago. The LS8,
still a top standard class ship, is really
an LS6 with flaps fixed and could have been
built at the same time...

I agree that span-balanced performance has been relatively stagnant
for the last decade or so. Of course, there's no guarantee that some
unforseen new development won't unstick it on a moment's notice.

Maybe that new boundary layer control device? Nice thing is it might
be retrofittable.

What I notice about the LS-8 and LS-6 is generally along the lines of
what Mike asserts. The slightly funny thing is that the LS-6 is not
exactly a top 15 meter contender these days; but of course that could
be due to a variety of factors independent of its performance. The
LS-8, on the other hand, has been chosen by lots of Standard class
pilots and has been well-placed on the scoreboards.

There's no explaining fashion.

My take on the situation is that the basic LS-6/LS-8 platform, with
about 10.5 m^2 of area, is actually a bit large for 15-meter
contention but about right for the current standard class. I notice
that most of the "hot" 15-meter ships have in the neighborhood of 9.5
to 10 m^2. Also, I see that the new LS-10 has a 10 m^2 area more in
line with the "hot" 15m ships. And that makes me wonder what the next
standard-class LS offering will be like.

You mean the new DG standard class offering.


Will it combine the
elliptical leading edge with the LS-8's 10.5 m^2 area? Inquiring minds
want to know!

Even further off-topic, when I was laying out the HP-24, I originally
gave it a 9.75 m^2 area because I wanted it to go fairly well
unballasted, as most sport pilots fly. However, in line with
increasing gross weight and possible motorglider options, I later
increased the area to a round 10 m^2.

I don't think you need to worry all that much. I suspect the
optimisation currve is very flat. More area = increased chord= higher
reynolds number = lower profile drag coefficient.
The Duo Discus is an excellent example of this effect.

Mike

In article ,
says...
Yeah but sure they're cool when showing your new glider to your friends...

I prefer old fashioned zigzag tape. Easier to mantain and clean.

My ASH 26 E has blow holes on the wing and zig-zag on the tail. I can
keep the blow holes clean, but when I clean the tail, threads get
caught on the zig-zag points, and wax builds up in the zigs. How do
you avoid this?
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directly

Eric Greenwell
Richland, WA (USA)