Open Class

At 19:59 14 February 2015, Jonathan St. Cloud wrote:
I had read where SH is no longer publishing polars for it's gliders.
Anyon=
e know the true polars of the JS1-C, Quintus and/or Anteres 23. Has any
cl=
ub or organization started doing the glide test that Dick Johnson for so
ma=
ny years provided the gliding community. I have been away from gliding
for=
a while, much has changed. I have much time in Nimbus 4, Nimbus 4D,
Nimbu=
s 3D. I assume the shorter wing birds could get much more out of the
ther=
mal, but I would think the long wing birds would be better at dolphin
flyin=
g. Any comments. Would love to hear from pilots that have flown in or
aga=
inst the shorter wing open versus the longer wing opens.



It is all about the wing loadings!

Actually, it is not all about wing loading. It is the magical mix of the right aspect ratio, wing loading (high or low depending on the day), laminar flow wetted area...etc. Since I have been away from soaring I did notice shorter wing open class are making a splash, instead of just longer and longer wing birds. So what I was hoping for was an intellegent discussion among those that fly open class as to the merits and demerits of short wing birds, vs long wing birds. I loved flying the nimbuses, but are the newer shorter wing birds better? Any pilots out there than fly or have flown both the newest generation and the birds from one generation ago where it was thought long and long span would increase performance?

This article covers most of the basics:
http://soaringcafe.com/2011/01/desig...ion-sailplane/

Assuming you want to stay within the constraints of EASA CS22, wing loading can't exceed 60 kg/m2 much.

A higher aspect ratio not only means a higher L/D max, it also means that L/D max occurs at lower and lower relative speeds. In other words, going from AR=32 to AR=57, L/D max might go up substantially but fully ballasted, performance at 70 kts barely changes. For many long-ears L/D max already occurs at speeds one will only fly while thermalling.

On Saturday, 14 February 2015 02:29:03 UTC+2, Jonathan St. Cloud wrote:
I have been away from soaring for 12 years and have noticed the open class now has long wing and much shorter wing birds (JS-1C) competing. I am curious how do the 21 and 23 meter new ships keep up with the ASW-22BL's and Nimbus-4's. Are the new shorter wing gliders better overall (better L/D, better penetration ) or just better on strong days when wing loading counts more than the ability to stay in the air?

New shorter wing open class ship probably outperform these older ships easily, but according to few pilot friends that have flown latest open class comps think there still is no substitute for span. At Leszno one pilot flying new 23m ship thought that EBs ran better (plus Concordia, of course). I've seen calculations that shorter span ships can come pretty close when avg. speeds are very high, but not that much better even then, and 99% of comps have several days of pretty lousy weather that you really will have all the span you can buy.

On Saturday, February 14, 2015 at 1:57:36 PM UTC-6, J. Nieuwenhuize wrote:
The smaller the wing (area, not span), the bigger the relative drag of the fuselage becomes.

On that note, what happened to the 18 meter Diana II that was rumored to come out?

Maybe the same thing that happened when someone asked Greg Cole (Duckhawk designer) if he was going to make an 18 meter version. He said "Why would you want to make it slower?" :-)

A few observations from one who flies a Nimbus 3 now and previously raced a 604.

Climb is dictated more by span squared loading. 604 and Nimbus 3 both at 750 KG, both at about 9.2 psf, Nimbus 3 has slightly lower sink rate (from the polars) but noticeably better climb. Based on my experiences with 22 meter 604 and 22.9 plus winglets Nimbus 3 and 25.5 meter Nimbus 3. Why? More span and aspect ratio.

Run is dictated most by percent of total area getting laminar flow (or maybe amount of surface NOT getting laminar flow) and close second by wing loading. Again with my 604 and Nimbus 3 comparison. Same weight, roughly same wing loading, but at 80 knots, the 604 just falls away. Why? Less of the wing has laminar flow (more of it does not), and the wing is a LOT thicker (so the wake is bigger, too). So, it presents a much larger frontal area to the air.

Now, we will step to Nimbus 3/4 and ASW22 to JS1. With the Nimbus 4 or ASW22 at 850KG, and the span at 26.5 or greater, the span loading is much lower on the bigger wing ships, so they should have an advantage in climb. They are also at a lower wing loading, so in theory, they can fly slower, turn tighter, etc.

Roll out of he thermal and go running. Not only is the JS1 at a MUCH higher wing loading, it has 40-50 square feet less wing area. So, MUCH less wetted area that is not laminar even if they have the same percentage of laminar flow. And, the wing is a little thinner, so the run is likely much better at speed on the shorter wing ship.

I can only guess that the EB 29 goes well because it has low span loading for climb, and high wing loading for cruise. Sort of like Concordia. I watched it go by my Nimbus 3 about as fast and with as much better glide angle as the Nimbus 3 had over my 604.

The days of just more span for more overall performance are gone. Span leads to area which leads to reduced high speed performance, even if you get the wing loading up. Low speed, best L/D, you can get almost as much with less span and more aspect ratio. Each generation of airfoil sections gets more laminar flow. And can get it at lower Reynolds Numbers. So, aspect ratio can be boosted again. 604 was high aspect ratio at 28.6. Nimbus 1 was amazing at 31. JS1 and Quintus seem almost "low" at 36. My thoughts from several years back were 22 meter span and 40 aspect ratio.

So, what would I like as my stepup up from my Nimbus 3? JS1C, Quintus, and Antares 23E sure look good to me... JS1C probably at the top of my list because for the added cost of the engine in the others, I can buy a whole lot of tows! But, I think there is another thread somewhere that talks about the merits of self launch...

Steve Leonard

On Monday, February 16, 2015 at 8:10:08 PM UTC-7, Steve Leonard wrote:
A few observations from one who flies a Nimbus 3 now and previously raced a 604.

Climb is dictated more by span squared loading. 604 and Nimbus 3 both at 750 KG, both at about 9.2 psf, Nimbus 3 has slightly lower sink rate (from the polars) but noticeably better climb. Based on my experiences with 22 meter 604 and 22.9 plus winglets Nimbus 3 and 25.5 meter Nimbus 3. Why? More span and aspect ratio.

Run is dictated most by percent of total area getting laminar flow (or maybe amount of surface NOT getting laminar flow) and close second by wing loading. Again with my 604 and Nimbus 3 comparison. Same weight, roughly same wing loading, but at 80 knots, the 604 just falls away. Why? Less of the wing has laminar flow (more of it does not), and the wing is a LOT thicker (so the wake is bigger, too). So, it presents a much larger frontal area to the air.

Now, we will step to Nimbus 3/4 and ASW22 to JS1. With the Nimbus 4 or ASW22 at 850KG, and the span at 26.5 or greater, the span loading is much lower on the bigger wing ships, so they should have an advantage in climb. They are also at a lower wing loading, so in theory, they can fly slower, turn tighter, etc.

Roll out of he thermal and go running. Not only is the JS1 at a MUCH higher wing loading, it has 40-50 square feet less wing area. So, MUCH less wetted area that is not laminar even if they have the same percentage of laminar flow. And, the wing is a little thinner, so the run is likely much better at speed on the shorter wing ship.

I can only guess that the EB 29 goes well because it has low span loading for climb, and high wing loading for cruise. Sort of like Concordia. I watched it go by my Nimbus 3 about as fast and with as much better glide angle as the Nimbus 3 had over my 604.

The days of just more span for more overall performance are gone. Span leads to area which leads to reduced high speed performance, even if you get the wing loading up. Low speed, best L/D, you can get almost as much with less span and more aspect ratio. Each generation of airfoil sections gets more laminar flow. And can get it at lower Reynolds Numbers. So, aspect ratio can be boosted again. 604 was high aspect ratio at 28.6. Nimbus 1 was amazing at 31. JS1 and Quintus seem almost "low" at 36. My thoughts from several years back were 22 meter span and 40 aspect ratio.

So, what would I like as my stepup up from my Nimbus 3? JS1C, Quintus, and Antares 23E sure look good to me... JS1C probably at the top of my list because for the added cost of the engine in the others, I can buy a whole lot of tows! But, I think there is another thread somewhere that talks about the merits of self launch...

Steve Leonard

Paul MacCready once told me the essence of a racing sailplane was a glider with the lowest span loading and the highest wetted area loading shaped to attain the greatest % of laminar flow.

On Friday, February 13, 2015 at 9:49:02 PM UTC-8, Bruce Hoult wrote:

...but they lose badly to the new thin airfoils at high speed...

It's kind of a nitpick, but there's really nothing new about thin airfoils. What has changed in the last decade and a half is the cost-effectiveness of the structure required to implement them in competitive sailplanes.

Thanks, Bob K.

On Friday, February 20, 2015 at 10:09:07 PM UTC-6, Bob Kuykendall wrote:
On Friday, February 13, 2015 at 9:49:02 PM UTC-8, Bruce Hoult wrote:

...but they lose badly to the new thin airfoils at high speed...

It's kind of a nitpick, but there's really nothing new about thin airfoils. What has changed in the last decade and a half is the cost-effectiveness of the structure required to implement them in competitive sailplanes.

Thanks, Bob K.

I think there is something new about the thin airfoils in use today, though, Bob. Laminar flow over a greater percentage of chord. Laminar flow over that chord at much lower reynolds numbers. Ability to maintain low drag to higher C/L.

Chicken and egg sort of question. Did structural design philosophy dictate airfoil design in terms of thickness, or did the airfoil design encourage continued use of the same old structural design techniques?

Steve Leonard

On Saturday, February 21, 2015 at 5:09:07 PM UTC+13, Bob Kuykendall wrote:
On Friday, February 13, 2015 at 9:49:02 PM UTC-8, Bruce Hoult wrote:

...but they lose badly to the new thin airfoils at high speed...

It's kind of a nitpick, but there's really nothing new about thin airfoils. What has changed in the last decade and a half is the cost-effectiveness of the structure required to implement them in competitive sailplanes.

Sure, carbon spars enabled them.