Better Boundary Layers

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