Sailplane performance trends

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WonderousMountain

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I don't know anything about sailplanes other than they're airplanes less an engine, and they like to fly in circles.

Would be interested to hear about (pictures) what the open class competition gliders are doing that get the edge over the other guys.

Sincerely,

Wonderous Mountain
 

Topaz

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This has some great visuals, and a nice description of basic strategy.


I'm on my phone, or I'd post more detail on the aircraft themselves. Hopefully Autoreply or one of the other soaring enthusiasts will catch this thread and pick that part up.
 
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fly2kads

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Design-wise, they go for span, span, and more span. The big guys are going for integrated wing/airfoil combinations, with many purpose-designed airfoils along the span. Each airfoil is tailored for the flow conditions at that point on the wing. They are using cuffed wing roots that transition between turbulent flow around the fuselage to laminar flow farther outboard, giving a blended wing/body of sorts. Camber-changing flaps keep them at close to minimum drag at every point in the speed range. Lots of ballast to go fast.

U.S. soaring pilot Dick Butler has undertaken construction of what he hopes will be the ultimate open glass glider, and has enlisted the aid of some heavy hitters for design and technical assistance. There is an ongoing blog about what the participants are calling the Condordia project at Soaring Cafe.
CONCORDIA – SUPERSEGLER | Soaring Cafe
Reading through it will give you a good idea of what they're doing with technology, and to some extent, racing strategy. Here is an image from that site, showing how the airfoils are distributed along the span. I count 14 different airfoils:
3D_with_airfoil_names.jpg
(I'm not a soaring pilot yet, but getting the add-on rating is near the top of my personal to-do list!)
 

autoreply

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Design-wise, they go for span, span, and more span.
Actually, nowadays less and less span is popular.

But first history.

Gliding started with McReady theory. You thermal and glide to the next thermal. Optimal speed depends on the strength of the thermals. It's beneficial to fly faster than best L/D. Even though you will arrive lower at the next thermal, you are there earlier then when you would've flown best L/D and - dependent on thermal strength - you will be higher when you would have arrived, flying best L/D. The stronger the thermal, the faster you have to fly between them. Ballasting your glider shifts the same performance to higher speeds, but increases sink in thermals (a bit) and thermalling radius (by a lot).

so in the 70's, pilots ballasted their gliders and in the good areas (Texas, Spain, Namibia, South Africa, Down Under) climbed with the powerful thermals (1000-2000 fpm) and raced to the next one at speeds over 120 kts, carrying all the ballast they could.

When in late 70's, the first "true" open class gliders (N3, ASW 22) came out with their 60:1 glide ratio, made available by carbon and the next generation of airfoils, pilots started to realize that flying slower would make you fly faster.

That's against the theory (which is correct), but it works. You can exploit the energy in the air and by that I'm talking the slow rising masses in between thermals. Think of an anti-depression with it's constant 50 fpm rising air. Think of following that lane on the ground for 50 fpm less descent. Instead of the 100+ kts cruises, the "long-ears" went back to mushing forward at 60 kts, and barely having to circle again.

Then, during the 90's, the same performance of the older open class gliders came within reach of the 60ft class and even of the racing class gliders (50 ft span) and they started to fly exploiting the energy between thermals too.

The weight limit in open class has long been 750 kg (850 for a two-seater) and this meant that most open class ships suffered from a too low wing-loading, compared to the shorter-winged 60 en 50 ft classes. No problem, given their superior performance.

But when all gliders had enough performance to fly energy lines, it became clear that wingloading was way too low. For "classic" thermalling, rather low wingloadings are great because if you're too heavily loaded, you fly around the thermals and that's what you're doing 25-50% of the time. But if you're flying on energy-lines, you barely circle. A serious handicap in thermalling is then acceptable, thus the smaller gliders had an advantage, not to speak of the manouvrability of a ship with a wingspan of a 737.

Now, you see open class gliders getting smaller and smaller already. Concordia is certainly impressive, but it's likely to perform just a tad better than the other new open class ships who're between 20 and 25 meters.
A slightly lower span gives a much lower wing weight and the wing area can be smaller. Thus they can fly with much higher wing loadings:
Schleicher ASH 31 - Wikipedia, the free encyclopedia
Schempp-Hirth Quintus - Wikipedia, the free encyclopedia

Take note that those 2 have the same empty weight as Concordia with a 220 lbs engine.
 

WonderousMountain

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Balsa.....

Really good information.

I wasn't sure line lift was being used succesfully in competition. It's good span isn't the end all, but the uber-high aspect ratio isn't all that more comforting.

Expected a higher slow flight Cl. Seems like fewer are going to the larger root section. Guessing that's a low CM airfoil.

Well, now that I'm addicted it's time to catch up on the last dozen years of sailplane racing......going to need a bigger bag of popcorn.

Wonderous Mountain
 

fly2kads

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Autoreply,

I was hoping you and Topaz would jump in. Thanks for the info. It is interesting how sailplanes have evolved over time, with wing loadings having essentially doubled over the years.

It is unseasonably HOT here in Texas, and the thermal forecasts are already calling for updraft velocities of 500-600 fpm here in my area, and 900 fpm in the western half of the state. If this keeps up, things should be hopping for the contestants in Uvalde later this summer. I hope to be able make a trip down there to observe, but I will have to wait and see....
 

autoreply

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Balsa.....
The logic of that escapes me until the present day too..
I wasn't sure line lift was being used succesfully in competition.
Fortunately enough it is now, almost doubling the "typical" XC here. Fortunately enough here in Europe there's lots of pnenomena that trigger energy lines. Think of cloud streets (frequent strong wind from see, plus warm land and cold airmass), the numerous mountain areas that are lined up 90 degrees with the typical winds and so on. Even the sea, with it's strong temperature gradients often gives strong cloud streets and more than once we've been out over the sea with the nearest land 15 NM or more from us.
It's good span isn't the end all, but the uber-high aspect ratio isn't all that more comforting.
It dampens turbulence quite nicely and makes for a much more comfortable flight.
Expected a higher slow flight Cl. Seems like fewer are going to the larger root section. Guessing that's a low CM airfoil.
Reasonably low, and having limited flap deflections helps a lot, especially in ships with flaperons.

Slower flight (thermalling at higher Cl) doesn't make that much sense usually. You're making more drag since you're leaving the laminar envelope and a bit more bank and pulling some G's is usually better. That also gives you a bit more margin. In the open class ships for example one tip flies about 10% slower as you, the other 10% faster. Thermals often are pretty to very turbulent and you need that extra speed to prevent you from complete uncontrollability (you will stall occasionally).
 

bmcj

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I wasn't sure line lift was being used succesfully in competition.
You will sometimes see articles about flying with "microlift", where the philosophy is that it is often better to head off on your cross country trek and, rather than circling in light lift where you would waste valuable time trying to eke aout a small altitude gain, you simply fly in the general direction of your goal while making small turns toward lift as you encounter it. In short, you don't change your overall direction... you just kind of zig-zag a bit "leaning" toward the lift pockets, but not circling unless it is big lift.

I've not really tried this, just read about it (a bit), so anyone who knows for sure please feel free to jump in or correct me.

Bruce :)
 

autoreply

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I've not really tried this, just read about it (a bit), so anyone who knows for sure please feel free to jump in or correct me.
Here's an example of the Dutch nationals:
OLC Flight information - Sikko Vermeer (NL) - 24.05.2011

(the google maps button gives a better view)

Flying an alternating course is much more efficient. For such a flight; going straight from turnpoint to turnpoint might cost you as much as 40% of your average speed. In fact, for his average thermal (2.2 m/s), his maximum McReady speed would've been around 90 km/h. He flew well over 120. His maximum glide ratio is just over 50 to 1. During this flight he got 109 to 1, more than double his original best L/D.
 

Aircar

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If nothing else this should convince the CAFE people that 'race' flight over mountainous terrain in summer makes so called 'performance comparison' of fuel efficiency by powered aircraft (most being pseudo sailplanes) actually a test of who can best plan his flight path to intercept atmospheric energy --meanwhile splitting hairs in flight testing fuel use goes out the window ( it is also more efficient to do a sawtooth flight profile climbing using maximum power at minimum specific fuel consumption and then glide down before repeating (with a retractable prop and engine this is even more advantageous )

Not all sailplanes are so sophisticated as to not require stopping to thermal and only a few days are this good or the best mode so newcomers to soaring might get a somewhat distorted outlook -- the cost of modern gliders is just crazy for what was a poor man's sport to begin with but soaring is still the most thoroughly absorbing way to fly --boredom is not an option.
 

Aircar

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I guess the Kasper article is about dynamic soaring -- a really interesting concept if viable but mostly turbulence seems to only decrease performance in laminar sailplanes presumably due to hysterisis effects on flow re attachment -- very light gliders can 'surf' gusty thermals by pulling back in surges and this is noticeable when soaring in 'formation' with heavier gliders . I recall reports of micro lift soaring in the Carbon Dragon and I guess some hang gliders must have low enough inertia in pitch but also high induced drag -- extracting energy from wing flexing indirectly is another concept I covered in my 1971 paper and this could also reduce gust loads felt in the cockpit.
 

henryk

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I guess the Kasper article is about dynamic soaring -- a really interesting concept

another concept I covered in

my 1971 paper

and this could also reduce gust loads felt in the cockpit.
-whare can I get this paper?

-Kaspers BEKAS-N is now restored for flying condition to examine the 100_3315.jpgBEKAS Wings.jpg"gust inducet soaring"...Yours opinion?
 
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autoreply

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Well, that's the theory about Diana-2 here is the real glider Diana 2 s/n3 case The company gave a junk to this unlucky female pilot.
Ah, and surprisingly that "unlucky female pilot" was you wasn't it? Welcome Hana.


For others, just know that virtually all reports about the DII have been (very) positive and people like Dick Johnson and Sebastian Kawa do have some authority to speak from.

This Hana had lots of problems and surprisingly, many of her observations were mutually exclusive and contradictionary. All this was strongly backed up... by exactly nobody, except some other users that in the end were the same Hana. Just one big gossip campaign, by what I guess is a bitter woman. If you search the internet you'll find her gossip campaign everywhere, but if you dig a little deeper, there's nobody backing anything up, just wonder why...
 
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