RC Gliders, Sailplanes and Slope Soaring Discuss rc gliders,rc sailplanes and slope soaring in this forum. Thermaling techniques, airfoils, tips, etc

Thermal Glider Question

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Old 08-05-2018, 11:19 AM
  #1  
ButteredCat
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Default Thermal Glider Question

I've recently been getting into thermalling. First with a foamie and now with an Albatros (Bird of Time).
The Albatros is good in certain conditions but it is a bit heavy so I'm looking to get another thermal glider - a Circle Dancer, Bubble Dancer, AVA, something like that.
But some of these have no ailerons. Now there must be a logical reason for this but as a newbie to this part of the hobby I struggle to see it. When you find a thermal with your wingtip getting into that thermal is going to be far easier with ailerons.
Can someone please explain in what scenario a glider without ailerons might be better.
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Old 08-06-2018, 12:54 AM
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I don't dare to explain that but at least here's an explanation what a full-house wing is good for.

I have both, and while the aileron glider with little dihedral has more potential for performance it is more stressful to fly. It's heavier and sleeker, so faster and it's harder to stay in thermals. It's better for roaming in search for thermals but it has to be controlled all the time. The rudder-elevator glider is lighter, thermals better because it's slower and flies on its own for a while. No problem to turn it into a thermal, sometimes it does it even by itself, and stays in a thermal by itself. The aileron glider just can't do that because it needs top aileron when circling. (A more technical article on that is here.)

If I'm out for a challenge I take the aileron glider and try to squeeze the last bit of thermal out of it, fighting for the best lift close to the center of thermals. It's hard work and after half an hour I'm tired. Most times I end up taking the rudder-elevator glider for relaxed flying, just bringing the model to thermal altitude and trimming it to stay in a thermal. One or even two hour flights are normal (with electric drive for climb).
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Old 08-06-2018, 12:17 PM
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Thanks for that. I guess if nobody tries to convince me otherwise I'll go for an aileronless version.
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Old 08-06-2018, 11:08 PM
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I'm building a Bird of Time. Never heard of it being called an Albatross before. There seems to be a renaissance of RES
(Rudder, Elevator, Spoiler) sailplanes of late. But ailerons are fine, if that's the way you want to go. Personally, I like the simplicity of RES. They fly just fine and can be quite maneuverable. But, no propellers allowed! Then, it's not a sailplane any more. It's a motor glider. But feel free to go in whatever direction you want.
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Old 08-07-2018, 01:29 AM
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Oh yes, it's a motorglider, I admit!

I started as a purist but have been proselytized by practice. Except being required due to limited space for flying, an electric drive makes flying even more relaxed for me. Thermals come in clusters so every now and then there are no thermals at all and the pure glider comes back to the ground. I've learned from the birds that it's not ignominious to use power to avoid coming down and to get to a better place. I ceased feeling remorse for having a motorglider and henceforth even used the drive to hold the airplane at an altitude with good prospects for thermals, usually about 100 meters. Goes without saying that a drive makes landings easier. In case of strong thermals the drive replaces spoilers by acting as a propeller brake. In normal flight, the folded prop's drag is small because flight speed is low. And drives are so small and lightweight today (for instance this one) even if not cheap.

Maybe I'm just lazy but most times I go flying to relax, not for a challenge. Actually I find an airplane should be flown with ailerons, but then again it's very hard to fly neat circles when the glider is up at 300 meters and at a 45 degrees angle. From that perspective it's all but impossible to see if the airplane climbs or sinks and if it flies straight or slips in circles. So even if I try to fly neat circles I won't succeed. Of course one could build a glider with much dihedral and ailerons, but that wouldn't help. The rudder-elevator glider circles smoothly on its own. (Eventually I eqipped my aileron glider with a gyro that really can coordinate circling, see link in post #2, and that makes the glider easier and more pleasant to fly.)

Let me go one better: I'm using a variometer from early on. Not only clean circling, climb and sink as well are hard to see from the ground. I don't have to call on the birds again, in this case the full-size gliders are our example: Soaring catched on in the 1930s when variometers were used for the first time, and today full-size gliders have even three variometers, one with total energy compensation. We need only one simple vario in a model, but we need one because thermals not only come in clusters but are different in size - some big ones and umpteen small ones. The variometer actually makes for the long flight times while the drive bridges the rare times without any thermal.
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Old 08-07-2018, 11:41 AM
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Originally Posted by born2build View Post
I'm building a Bird of Time. Never heard of it being called an Albatross before. There seems to be a renaissance of RES
(Rudder, Elevator, Spoiler) sailplanes of late. But ailerons are fine, if that's the way you want to go. Personally, I like the simplicity of RES. They fly just fine and can be quite maneuverable. But, no propellers allowed! Then, it's not a sailplane any more. It's a motor glider. But feel free to go in whatever direction you want.
https://www.topmodelcz.cz/index.php?...etail&id=10984
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Old 08-07-2018, 12:30 PM
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I see. Well, that's not really a Bird of Time at all, is it? Over the years, Dave Thornburg's original design has been "borrowed" many times. There was even a 2-meter version available at one point.
I wonder if the "Ol' Buzzard" didn't get his inspiration from Frank Zaic's Thermic design, or even the Minimoa.
Whatever you decide to build, buy, or fly, I wish you...green air!
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Old 08-07-2018, 12:39 PM
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Originally Posted by born2build View Post
I see. Well, that's not really a Bird of Time at all, is it? Over the years, Dave Thornburg's original design has been "borrowed" many times. There was even a 2-meter version available at one point.
I wonder if the "Ol' Buzzard" didn't get his inspiration from Frank Zaic's Thermic design, or even the Minimoa.
Whatever you decide to build, buy, or fly, I wish you...green air!
No, not really a Bird of Time. But the similarities are obvious. A modern take on a classic design.
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