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Old Jun 23, 2013, 12:03 PM
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Congress, AZ
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Check out wind tunnel testing on RCSoaring

http://www.rcsoaringdigest.com

Current version has some interesting wind tunnel test results from the Ukraine.

Keep an open mind.


"Vintage Fan" has already referenced this, sorry for the double post

If you think the free flight guys have nothing to teach us, here are a couple of tidbits:

FAI free flight gliders execute a "bunt or zoom launch" off the top of the launch that doubles there altitude.

FAI power planes have been clocked (think radar gun) over 90 mph in the climb.


Gary
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Old Jun 24, 2013, 10:24 AM
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United States, SC, Mt Pleasant
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Would have been nice to find out what Re they were testing to see how relavant it is.

James.
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Old Jun 24, 2013, 11:25 AM
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F1a wings usually glide at 3-3.5m/s.Chord is about 150mm. Acceleration for launch is much higher but but in the past has not been the consideration for airfoil design.
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Old Jun 24, 2013, 12:29 PM
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Dephela,

Let's see if I can remember enough of what that class is, I'm a bit dated:

F1A, what a long time ago was known as Nordic A2? 80-100" span (just and estimate)?

Tow line launched, 50 meter line?

I seem to remember seeing some reports that altimeters show that they can reach nearly 100m after the zoom off the tow? Is that correct?

If so, that means that the glider has to moving pretty fast to gain an additional 40-50 meters of altitude. The RE must be approaching the RE of the hlg at launch, and drag should be higher, as the span is much greater.

Root chord of a Zone V2 wing is about 175mm, root chord of a XXLite is 130mm, so chords are probably comparable.

Gerald and others must have estimates or measurements of glide speed.

Not so obvious that things are so much different.

Over to Chris and Gerald for comments.

Gary
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Old Jun 24, 2013, 01:20 PM
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Yes, you have it about right.
Here's a video of a typical circle tow and accelleration to a zoom launch.
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Old Jun 24, 2013, 02:23 PM
Aurora Builder
United States, MD, Lusby
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Very interesting. The information discussing the turbulator is extremely interesting. Also suggests a lot of testing is needed for refinement. The type of testing that requires 24/7 access to a tunnel like these guys have.

Thin TE's are as well but not sure how we can go thinner back there on our composite ships? We're already down to the laminate thickness (2x layers of 0.73 oz/in^2 fiberglass in my case). Where there is a will there is a way but how much will do you have?
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Old Jun 24, 2013, 11:16 PM
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Sam,

I missed anything that they posted about how thin is thin. Did they actually specify?

Way back when, I think Mark D commented about the laminate thickness was fine.

What I find interesting is what Chris has been saying for some time. The flight conditions for those gliders (and other free flights, particularly power) might not be so far from the dlg requirements as we like to think.

Gary
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Old Jun 24, 2013, 11:32 PM
G_T
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Actually they differ in important aspects.

Once in flight, a free flight design will be optimized to hold close to min descent rate. For a DLG we utilize a wider flight speed range and achieve this through pilot input and through variable camber through flaperon adjustment.

Additionally, DLGs require handling characteristics suitable for radio control whereas a free flight model flies a nearly fixed flight pattern which need be maintained even in the presence of disturbances. A free flight model need not fly straight lines and need not turn very tightly. A DLG needs to do these things with equal aplomb.

A free flight glider isn't going to need to return from downwind... Well, that might not be true. It just won't be capable of doing it!

Gerald
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