Thin Airfoil and Climb Performance

[Brad[_2_]]

As a guy who has flown thick airfoil ships and currrently owns a ship
with a 17% airfoil, I am curious what kind of performance in climb I
might see with a <14% airfoil section.

Thanks,
Brad

[[email protected]]

On Mar 27, 6:59 pm, Brad > wrote:
> As a guy who has flown thick airfoil ships and currrently owns a ship
> with a 17% airfoil, I am curious what kind of performance in climb I
> might see with a <14% airfoil section.
>
> Thanks,
> Brad

Take a look at SZD 56 Diana. It has 13% thick airfoil and climbs like
a bird.

Jacek
Pasco, WA

[[email protected]]

I am curious what kind of performance in climb I
might see with a <14% airfoil section.

Thanks,
Brad


The amount of camber in the airfoil, flaps/no flaps, wing loading and
aspect ratio are also important factors...

Bill

[Dan G]

On 28 Mar, 01:59, Brad > wrote:
> As a guy who has flown thick airfoil ships and currrently owns a ship
> with a 17% airfoil, I am curious what kind of performance in climb I
> might see with a <14% airfoil section.
>
> Thanks,
> Brad

Someone on here mentioned a presentation by Loek Boermans at the
recent SSA conference, where he stated that modern, thin, laminar-flow
sections don't climb as well as they theoretically should in bumpy
gusty thermals. Apparently research into ways round that are ongoing,
but the Jonker brothers stumbled across an airfoil for the JS-1that
doesn't suffer from this by accident!

Maybe someone who attended could expand on what was said? It sounded
very interesting.

[[email protected]]

On Mar 28, 2:02 pm, wrote:
> I am curious what kind of performance in climb I
> might see with a <14% airfoil section.
>
> Thanks,
> Brad
>
> The amount of camber in the airfoil, flaps/no flaps, wing loading and
> aspect ratio are also important factors...
>
> Bill

Probably the 17% airfoil has a higher CL number but that would occur
in a unusable angle of attack. Generally speaking the thicker the
airfoil the broader is the low drag bucket (for laminar sections of
course).
Basically the climb ratio is governed by the wing loading, the aspect
ratio and the wing planform. The main enemy here is the induced drag.
Getting a low wing loading and high A/R is the way to go up. Given no
variable camber (ie flaps) the airfoil characteristics have a small
impact. Otherwise in the high speed section of flight having a high
wing loading and an airfoil tailored for hi-speed (thin and low
camber) is desirable. That´s why the sailplanes are in the cutting
edge of aircraft design, since they have to accomplish a very broad
mission envelope with a light empty weight and a high relative payload
(water+pilot).

wladimir

[Bruce]

I'd take the accident part with a pinch of salt. They may have been pleasantly
surprised, but what I know of those two involves many years of meticulous
research and testing. Luck often plays a role, but like Edison and the lightbulb
there is a lot of plain hard work behind the "chance" discovery.

But yes the JS1 climbs well, and runs (exceptionally) well, and in the hands of
one of the Jonkers is hard to beat.

The most critical thin laminar wing I have seen is the Diana 2 - The only time I
could see relative performance I was in a Duo Discus, and the Diana had a Dr
Kawa installed so it is probably not a good comparison. However the Diana had
absolutely no difficulty outclimbing a lightly loaded Duo in light ridge/thermal
conditions. Indications are that a well designed thin section can be made to
climb well. Conversely both the DG600 and ASW24 had difficulty in strong
turbulent thermals, and suffer in South Africa. (Except when there is a
Goudriaan installed in the ASW)

So - I think the wing section does make a difference, but I strongly believe
that the difference is very small and insignificant relative to personal
performance for most of us - The software is the diagnostic bit when it comes to
ultimate performance.

A good person to ask might be Kolie (skylinesoaring.org) -he just moved from a
LS3 to a Diana 2. So far I have not heard ANY complaints about the Diana's climb
performance.

Bruce

Dan G wrote:
> On 28 Mar, 01:59, Brad > wrote:
>> As a guy who has flown thick airfoil ships and currrently owns a ship
>> with a 17% airfoil, I am curious what kind of performance in climb I
>> might see with a <14% airfoil section.
>>
>> Thanks,
>> Brad
>
> Someone on here mentioned a presentation by Loek Boermans at the
> recent SSA conference, where he stated that modern, thin, laminar-flow
> sections don't climb as well as they theoretically should in bumpy
> gusty thermals. Apparently research into ways round that are ongoing,
> but the Jonker brothers stumbled across an airfoil for the JS-1that
> doesn't suffer from this by accident!
>
> Maybe someone who attended could expand on what was said? It sounded
> very interesting.

[Eric Greenwell]

Dan G wrote:
> On 28 Mar, 01:59, Brad > wrote:
>> As a guy who has flown thick airfoil ships and currrently owns a ship
>> with a 17% airfoil, I am curious what kind of performance in climb I
>> might see with a <14% airfoil section.
>>
> Someone on here mentioned a presentation by Loek Boermans at the
> recent SSA conference, where he stated that modern, thin, laminar-flow
> sections don't climb as well as they theoretically should in bumpy
> gusty thermals.

I attended Boerman's lecture. The problem isn't thin, laminar flow
airfoils in general, but some specific designs over the last two decades
or so that have a "flat spot" in the lift coefficient (Cl) curve as the
angle of attack (AOA) approaches stall. Normally, the Cl increases with
increasing AOA, but in the flat spot region, it remains constant (or
nearly so) even as the AOA increases. Past this region, Cl begins to
increase again with AOA at the usual rate.

While thermalling, the glider's AOA will be near this region. If a gust
increases the AOA enough to enter the region, the climb rate is reduced
momentarily. By the top of the thermal, repeated gusts mean the glider
hasn't climbed as quickly as it might have.

In gusty conditions, the climb rate can be improved by thermalling a bit
faster, so this region is avoided (gusts can't increase the AOA enough
to enter the region). Because the "flat spot" is wider in the
thermalling flap setting and diminished or not present with more
negative flap settings, using the neutral flap setting in gusty
conditions will also avoid (or at least improve) the situation.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[Eric Greenwell]

Eric Greenwell wrote:

> I attended Boerman's lecture. The problem isn't thin, laminar flow
> airfoils in general, but some specific designs over the last two decades
> or so that have a "flat spot" in the lift coefficient (Cl) curve as the
> angle of attack (AOA) approaches stall. Normally, the Cl increases with
> increasing AOA, but in the flat spot region, it remains constant (or
> nearly so) even as the AOA increases. Past this region, Cl begins to
> increase again with AOA at the usual rate.

I should add that designers were aware of the flat spot years ago, but
did not appreciate the problems it could cause in gusty conditions.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[[email protected]]

>
> A good person to ask might be Kolie (skylinesoaring.org) -he just moved from a
> LS3 to a Diana 2. So far I have not heard ANY complaints about the Diana's climb
> performance.
>
> Bruce
In gusty conditions, the climb rate can be improved by thermalling a
bit
faster, so this region is avoided (gusts can't increase the AOA
enough
to enter the region). Because the "flat spot" is wider in the
thermalling flap setting and diminished or not present with more
negative flap settings, using the neutral flap setting in gusty
conditions will also avoid (or at least improve) the situation.


--
Eric Greenwell - Washington State, USA



I've had my Diana 2 almost two years - moved up from a 304cz. The
Diana 2 has climbed
out of valleys late in the day that would have swallowed the cz.
Remember the Diana is 25 years younger
(and how many generations?) than the cz... The 304cz is a great glider
and I loved mine dearly. When the
lift gets strong and bumpy here in SoCal, one needs to speed up to
maintain control anyway.
As I said in an earlier post, and Wladimir expanded on, it isn't just
the airfoil that determines climbing performance.
Bill

[Dan G]

On Mar 29, 7:50*am, Bruce > wrote:
> I'd take the accident part with a pinch of salt. They may have been pleasantly
> surprised, but what I know of those two involves many years of meticulous
> research and testing. Luck often plays a role, but like Edison and the lightbulb
> there is a lot of plain hard work behind the "chance" discovery.
>
> But yes the JS1 climbs well, and runs (exceptionally) well, and in the hands of
> one of the Jonkers is hard to beat.

Yeah, "by accident" was a poor choice of words (though the original
poster, iirc, implied that the Jonkers were interested in Boerman's
lecture as it provided an explanation for what they'd found). The JS1
looks very impressive and I wonder if it will become the "Diana 2 of
the 18 m Class".

[Dan G]

On Mar 29, 4:35*pm, Eric Greenwell > wrote:
> Dan G wrote:
> > On 28 Mar, 01:59, Brad > wrote:
> >> As a guy who has flown thick airfoil ships and currrently owns a ship
> >> with a 17% airfoil, I am curious what kind of performance in climb I
> >> might see with a <14% airfoil section.
>
> > Someone on here mentioned a presentation by Loek Boermans at the
> > recent SSA conference, where he stated that modern, thin, laminar-flow
> > sections don't climb as well as they theoretically should in bumpy
> > gusty thermals.
>
> I attended Boerman's lecture. The problem isn't thin, laminar flow
> airfoils in general, but some specific designs over the last two decades
> or so that have a "flat spot" in the lift coefficient (Cl) curve as the
> angle of attack (AOA) approaches stall. Normally, the Cl increases with
> increasing AOA, but in the flat spot region, it remains constant (or
> nearly so) even as the AOA increases. Past this region, Cl begins to
> increase again with AOA at the usual rate.

Thanks Eric. Which are the specific designs? The likes of the LS7/
DG600/ASW24?

[Andreas Maurer[_1_]]

On Thu, 27 Mar 2008 18:59:40 -0700 (PDT), Brad >
wrote:

>As a guy who has flown thick airfoil ships and currrently owns a ship
>with a 17% airfoil, I am curious what kind of performance in climb I
>might see with a <14% airfoil section.

If you are talking about the Wortman FX67-K170: The FX 62-K131 of the
ASW-20 from the same era climbs at least as well as the former.

The very thin airfoils of current gliders (e.g. ASW-27) climb like
homesick angels.
Bye
Andreas

[[email protected]]

On Mar 27, 9:59 pm, Brad > wrote:
> As a guy who has flown thick airfoil ships and currrently owns a ship
> with a 17% airfoil, I am curious what kind of performance in climb I
> might see with a <14% airfoil section.
>
> Thanks,
> Brad

I have not yet been outclimbed in my Antares, with
its a very thin airfoil and 9lb/ft2 min wingloading,
when flying against newer 18-meter, 15-meter, and
standard designs at lower wing-loadings. Of course,
they don't catch me after the first thermal, so my
experience is limited ;-)

Different gliders have different capabilities, but
your thermalling skill and ability to fly the particular
glider as it demands will play a huge part.

Climb performance is only part of the equation,
unless you are limiting yourself to floating about
the home drome. XC performance requires
good run performance, climb performance,
handling, and performance in transitions.

Ask about the particular machine you're lusting
after and perhaps a more specific answer
can be had !

Hope this helps,
Best Regards, Dave "YO electric" (see August
Soaring cover)

[[email protected]]

On Mar 29, 11:43 am, Eric Greenwell > wrote:
> Eric Greenwell wrote:
> > I attended Boerman's lecture. The problem isn't thin, laminar flow
> > airfoils in general, but some specific designs over the last two decades
> > or so that have a "flat spot" in the lift coefficient (Cl) curve as the
> > angle of attack (AOA) approaches stall. Normally, the Cl increases with
> > increasing AOA, but in the flat spot region, it remains constant (or
> > nearly so) even as the AOA increases. Past this region, Cl begins to
> > increase again with AOA at the usual rate.
>
> I should add that designers were aware of the flat spot years ago, but
> did not appreciate the problems it could cause in gusty conditions.
>
> --
> Eric Greenwell - Washington State, USA
> * Change "netto" to "net" to email me directly
>
> * Updated! "Transponders in Sailplanes"http://tinyurl.com/y739x4
> * New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more
>
> * "A Guide to Self-launching Sailplane Operation" atwww.motorglider.org

If I understood Loek correctly, "gusty" isn't perhaps the right
description. Better "high frequency changes in vertical velocity,
causing momentary increases in required CL" ? Its not something
you'd necessarily feel as a pilot if I understood correctly.
Eric ?

[Eric Greenwell]

wrote:
> On Mar 29, 11:43 am, Eric Greenwell > wrote:
>> Eric Greenwell wrote:
>>> I attended Boerman's lecture. The problem isn't thin, laminar flow
>>> airfoils in general, but some specific designs over the last two decades
>>> or so that have a "flat spot" in the lift coefficient (Cl) curve as the
>>> angle of attack (AOA) approaches stall. Normally, the Cl increases with
>>> increasing AOA, but in the flat spot region, it remains constant (or
>>> nearly so) even as the AOA increases. Past this region, Cl begins to
>>> increase again with AOA at the usual rate.
>> I should add that designers were aware of the flat spot years ago, but
>> did not appreciate the problems it could cause in gusty conditions.

>
> If I understood Loek correctly, "gusty" isn't perhaps the right
> description. Better "high frequency changes in vertical velocity,
> causing momentary increases in required CL" ? Its not something
> you'd necessarily feel as a pilot if I understood correctly.
> Eric ?

I don't recall the presentation well enough to say for sure, but my
impression is the pilot would be aware that it's not smooth air,
probably enough that the pilot would be making some control corrections.
It would be better to ask Loek, or someone like Dan Somers or Mark
Maughmer, who are also aware of it.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[Udo]

Eric,
what is the title of Loek Boerma's presentation?
Is it available in paper form?
Udo


> I attended Boerman's lecture. The problem isn't thin, laminar flow
> airfoils in general, but some specific designs over the last two decades
> or so that have a "flat spot" in the lift coefficient (Cl) curve as the
> angle of attack (AOA) approaches stall. Normally, the Cl increases with
> increasing AOA, but in the flat spot region, it remains constant (or
> nearly so) even as the AOA increases. Past this region, Cl begins to
> increase again with AOA at the usual rate.
>
> While thermalling, the glider's AOA will be near this region. If a gust
> increases the AOA enough to enter the region, the climb rate is reduced
> momentarily. By the top of the thermal, repeated gusts mean the glider
> hasn't climbed as quickly as it might have.
>
> In gusty conditions, the climb rate can be improved by thermalling a bit
> faster, so this region is avoided (gusts can't increase the AOA enough
> to enter the region). Because the "flat spot" is wider in the
> thermalling flap setting and diminished or not present with more
> negative flap settings, using the neutral flap setting in gusty
> conditions will also avoid (or at least improve) the situation.
>
> --
> Eric Greenwell - Washington State, USA
> * Change "netto" to "net" to email me directly
>
> * Updated! "Transponders in Sailplanes"http://tinyurl.com/y739x4
> * * * New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more
>
> * "A Guide to Self-launching Sailplane Operation" atwww.motorglider.org

[Eric Greenwell]

Udo wrote:
> Eric,
> what is the title of Loek Boerma's presentation?
> Is it available in paper form?
> Udo

I don't recall the title. It might be published somewhere. The OSTIV
journal would be the first place I'd check.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org