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Ground Slammer
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PostPosted: Fri May 12, 2017 4:11 pm    Post subject: Help with the Fleg-2 Fleg-3 Airfoil Reply with quote #1   
Hey everyone-I'm working on a Full Scale model of a Quicksilver wing that collapses like a Fleg-1 and has a Fleg-2--3 airfoil. I no longer have my Fleg-2 and was hopeful that someone out there could help me with a few tracings of the Fleg airfoil (2 or 3). I need to make a mock-up sail-put it on the scale wing-- and see if the collapsing feature will work with the partial double surface. Can't make the sail until I know how much fabric the camber takes up. Also I have to install the ribs (battens) so to confirm that it's going to work. Thanks in advance.
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TjW
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PostPosted: Sat May 13, 2017 6:29 pm    Post subject: Reply with quote #2   
I think I have a set of Fledge IIB battens around here somewhere. I can run a magic marker around the top edge of the battens to give you an idea of the airfoil thickess. I can't vouch for their precision, and I don't think all the reflex would be appropriate for a tailed glider.

But within reasonable limits, you can design for the thickness of airfoil you want, and small changes in camber or how camber is distributed won't make much difference.

The rear spar pocket is several inches wide (and you could conceivably make it an inch wider yet). It's sewn on loose enough that it will accommodate the spar thickness (and batten thickness -- batten pockets are between the spar and sail) without bulging the sail up. The geometry of this is such that sliding the sail a quarter of an inch forward or aft to acommodate more or less camber in the airfoil forward of the rear spar makes only a small change in how tight the spar pocket is.

Unlike the Quicksilver, the chordwise tension on the sail is not set by the position of the rear spar, but by the batten tensioners on the trailing edge of the sail, just like on flex wings.

I think originally the tensioners were Velcro, but tied strings in grommets or the more recent latching flip clips would also work. Flip clips would be more adjustable.
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Ground Slammer
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PostPosted: Sun May 14, 2017 9:42 am    Post subject: Reply with quote #3   
Thank you TJW- I can tell there is a little confusion as to how I'm looking at putting the sail on the QS.
Imagine the Fleg 2 sail made rectangular. Now add a trailing edge pocket at the rear of the sail--one that folds around a 1 inch tube and then comes around the bottom and is sewn several inches up from the trailing edge -so to have the air flow smooth. This becomes a second zone of double surface- very thin. I'll add a smaller diameter tube to the back edge of the trailing edge tube-when the fabric wraps around the two tubes the rear edge becomes a streamline shape. The second tube is non structural just to give the trailing edge taper.

Now you may note that this means some of the compression struts length runs outside the bottom of the fabric! But no zippers-small price to pay. Also one can try to collapse the wing via the Fleg 1 way-much slicker, quicker, and lighter than the Fleg 2 way. Finally the bottom surface of the wing get a three planar undercamber this way!!! I can use the angles and widths of the 3 zones to create a undercamber that approximates a curvetilinear one.
The Fleg 2 sail is one of the hardest sails to make-the easiest of all was the Quicksilver B. Back in the day one got a kit with no sail and instructions on how to sew one up. The difference between the original QS sail and the one I'm contemplating---- almost nothing-just the pocket widths.
I would like to keep this short and I don't have sketches ready yet, but I came to work saw TJW response andI wished to respond to him.
TJ- the ribs I am interested in are center to midspan-they are flat as a board from about 20% back all the way to their end. They are if I remember correctly, 45 degrees of arc with a 1.5 foot radius. PM me after you find they and we'll hook up.
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TjW
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PostPosted: Mon May 15, 2017 11:18 am    Post subject: Reply with quote #4   
Ground Slammer wrote:
Thank you TJW- I can tell there is a little confusion as to how I'm looking at putting the sail on the QS.
Imagine the Fleg 2 sail made rectangular. Now add a trailing edge pocket at the rear of the sail--one that folds around a 1 inch tube and then comes around the bottom and is sewn several inches up from the trailing edge -so to have the air flow smooth. This becomes a second zone of double surface- very thin. I'll add a smaller diameter tube to the back edge of the trailing edge tube-when the fabric wraps around the two tubes the rear edge becomes a streamline shape. The second tube is non structural just to give the trailing edge taper.

Now you may note that this means some of the compression struts length runs outside the bottom of the fabric! But no zippers-small price to pay. Also one can try to collapse the wing via the Fleg 1 way-much slicker, quicker, and lighter than the Fleg 2 way. Finally the bottom surface of the wing get a three planar undercamber this way!!! I can use the angles and widths of the 3 zones to create a undercamber that approximates a curvetilinear one.
The Fleg 2 sail is one of the hardest sails to make-the easiest of all was the Quicksilver B. Back in the day one got a kit with no sail and instructions on how to sew one up. The difference between the original QS sail and the one I'm contemplating---- almost nothing-just the pocket widths.
I would like to keep this short and I don't have sketches ready yet, but I came to work saw TJW response andI wished to respond to him.
TJ- the ribs I am interested in are center to midspan-they are flat as a board from about 20% back all the way to their end. They are if I remember correctly, 45 degrees of arc with a 1.5 foot radius. PM me after you find they and we'll hook up.


I think you're over-complicating the structure. The Fledge and every high performance blade wing ever built do just fine with the ribs supporting a fabric trailing edge. If you don't want to deal with the double surface, then just make it single surface.




But I'll poke around in the garage attic.
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Ground Slammer
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PostPosted: Mon May 15, 2017 7:03 pm    Post subject: Reply with quote #5   
This may help---------In the top sketch we see a side profile of a QS--the LE and TE are all but planar to the stabilizer except for theta- the stabilizer angle of incidence.

In sketch 2 a Fledge leading edge and rear spar are attached to the center tube---but note that the trailing edge of the airfoil drops below the center tube---a line from the LE to trailing edge, the 0 degree angle of attack puts the stabilizer boom way too high and the stabilizer angle of incidence too high (way too high).

In sketch 3 (drawn to scale) my solution solves this and the sail fits on a conventional QS frame. Note the TE detail.

One should also note that the king post, which needs to be paced as near the center of pressure as one can-- is not in a good place in #2. Because the wing is unswept there is too little triangulation from the KP to TE. The wire to the LE triangulates, and pulls the wing rearward. But the KP to TE wire has too little triangulation to effectively pull the wing forward--these two forces are needed, and must be in balance.

The main thing to note-that the sail I propose will fit to a QS frame- Strip the old sail ----- install the new sail and ribs NOTHING MORE-NOTHING!

I hope this help exsplanes (sic) my idea-there may be more than one way to skin a cat----my idea, the only frame changes are -are---are--well nothing! Beat that! Laughing



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TjW
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PostPosted: Tue May 16, 2017 6:48 am    Post subject: Reply with quote #6   
If you're using the Quicksilver tailboom approach, I would just attach the tailbooms to the top of the rear spar with a bracket.
This would let you set the decalage to pretty much anything you want using the rigging, though you'd probably want a compression/antidrag strut from the attach point to the noseplate.

Sketcth #3 is essentially how the Fledge 2b sail is built , except that the rear spar is in a pocket attached to the upper surface, at around 50% chord.
The double surface covers the pocket and spar, but it's nowhere near 100% double surface

Instead of wrapping around, and providing the chordwise tension, it just holds the upper surface (or only surface, on the original Fledge) down to the rear spar.

Using sophisticated ASCII art, the cross section of the pocket looks like:

\O/

The O is the rear spar.. You'll have to imagine the top surface of the sail, and that the slashes and underline actually are one piece, and the angles are somewhat shallower.

But anyway, I found 'em, I drew the three straight inner ribs on a piece of Mylar.
You are right about the sophistication of the airfoil.
Dave Cronk said the original airfoil for the Quicksilver was a "670-15". That is, they bent the ribs around a 670-15 tire.


Check your PMs, or PM me.
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Ground Slammer
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PostPosted: Tue May 16, 2017 1:35 pm    Post subject: Reply with quote #7   
Thank again TJ- when I envision the approach that TJW advocates I would cut through the top of the sail behind the rear spar and go in. The QS has a diagonal strut that runs from the LE just at it's root , and hits the TE at the juxtaposition spot to the tail booms. I also think it will give an aerodynamic cleaner sail. Placing the booms on top will induce a torque on the TE tube unless you raise the diagnal strut..

What I did wish to post is that in my trailing edge as per above --there is a region at the rear of the undersurface-the exit ramp.The under camber in slow speed ,high lift sections has--the nose convexity---the entry ramp--the zone of maximum concavity-and the exit ramp. The exit ramp, if left as a single variable- has an optimum angle, as well as a optimum width. By finding what this angle and width is ,one can optimize the airfoil- making it more efficient than the original. One may need to use a larger in diameter tube in the trailing edge to get better results. This method of creating three stage undercambers in fabric and tube wings is not new. This form of construction is in mass production in UL and Sport Light aircraft as we speak. It may even be that in order to create an exit ramp that has the best angle and width a wider TE tube is needed.
The Fledge airfoil rear section could not stand a negative ramp at the TE --it is a flying wing and can't have the negative pitch that this induces. On a QS frame our hands are not tied--We have the means--we poses the technology-we can rebuild it-make it better than it was.
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Ground Slammer
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PostPosted: Wed May 17, 2017 6:18 pm    Post subject: Reply with quote #8   
Thanks to all--- section coming in the mail.I leave you with then and now.


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