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Old May 03, 2012, 07:04 PM
Father of Fr3aK, DLG Pilot
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John.

If you align the airfoils in XFLR (derotate) then export to Rhino, you will have the proper zero reference for a no washout wing. You can use the "rotate" function and the centerline via ortho in Rhino to set washout before you loft, or you can loft the wing and use a "twist" function to get washout after it's modeled. If you use the twist function, the twist should be around the "quarter chord" line of the wing to be accurate to XFLR modeling.

HTH....

Tom
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Old May 03, 2012, 08:18 PM
G_T
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IMO, the difference in rotation point, quarter chord or other, with respect to XFLR5 modeling will be meaningless. XFLR5 is doing a composite 2D technique. Rotate about the hingeline would be best, assuring a straight hingeline. But of course whatever you do, the parting plane is likely to be a bit of fun.

That said, there is no washout and no rotation to be applied with this particular foil family. It was designed to be easy to work with - hence no washout and no parting plane issues. The foils are not at their zero lift angle. They are at an angle where the front of the foil is at the same "height" in the coordinates as the rear of the foil. This is how all the foils are oriented to each other in this series. I do not use a convention of orienting a foil with respect to its zero lift angle. Heck, that angle is a function of Reynolds number anyway!

Gerald
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Old May 04, 2012, 03:27 PM
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Tom and Gerald -

Thanks very much for the clarification. I am indeed modeling the wing as you'd previously suggested, Gerald, without any washout. Consequently, it sounds like I can take the foils directly as output from XFLR and they will be oriented as far as AOA is concerned properly to each other.

One question Gerald: you state that the foils are "at an angle where the front of the foil is at the same "height" in the coordinates as the rear of the foil". This doesn't appear to be the case in your posted .wpa file; the forgiving foils all have a trailing edge that droops below the X axis (Y<0; see attached screen capture). I'm guessing this is because the foils are in cruise configuration (hence the "+2" in the foil names) and that the speed mode configuration of the foils would reflect a trailing edge on the X axis (Y=0). In any case, the trailing edges all appear to be about the same distance below the X axis, so I think I can safely derotate them (for easier digital manipulation and subsequent fabrication) and still maintain the proper foil-to-foil relationship. I'd appreciate it if you could let me know if any of this sounds incorrect.

Okay, one more question: it looks like you're not using XFLR's built-in flap modeling to place this foil in cruise mode (flap settings are at zero in the foil list). Is this because you do your primary design in cruise mode (so that's the "baseline"), or you don't like the way XFLR models flaps, or some other reason? Curious about the process as I'm just becoming familiar with XFLR. Thanks as always for your contributions and guidance.

-John
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Old May 04, 2012, 04:27 PM
Father of Fr3aK, DLG Pilot
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Gerald... get off the phone (with me) and answer the bloody question!

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Old May 04, 2012, 04:34 PM
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You guys are such slackers!

;-)
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Old May 04, 2012, 04:53 PM
G_T
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Derotation should be pretty close but might not give the exact answer. What you get from it is possibly a function of the curvature of the leading edge. Upon rotation, the program could possibly decide that a different point at the front is the real "front" of the airfoil and shift it vertically. One can play with this for amusement by going back and forth between "derotate" and "normalize" functions.

Easiest thing is likely to just change the flap angles upwards 2 degrees from 70% hingeline, lower surface (not the default 50% or whatever it uses).

Sorry, I had forgotten that I'd released these at 2 degrees rather than at 0.

Gerald

PS - Yes I did the development in cruise mode for these.
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Old May 07, 2012, 03:37 PM
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There's an English chap named Denis Oglesby who's been playing with turbulators for 40 years and designed a series of F3B airfoils some fifteen years ago specifically using them (AH- ( Andrew Hollom) series) using XFoils
Denis sent me turbulator positions (on top surface) and thicknesses to try for a thermal section he designed (and I used on a model 15 years ago, it's very like AG 35!) but I could never 'feel' any difference, they just cut penetration and speed without inproving duration or 'float'

The problem is there's so many variations, thickness, width, shape (using wife's pinking scizzors to produce Zig-Zag shaped turbs), position, and at the end of the day they appear to do very little unfortunately........... so forget them, you are re-inventing the wheel!

Nick Rolls
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Old May 07, 2012, 03:58 PM
G_T
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In the case of this section, and possibly others, the intent is not to improve float, but to improve speed. Yes, that is contrary to how turbulators have been used for some old foils and possibly other Reynolds number ranges.

Gerald
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Old May 08, 2012, 07:58 AM
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Sorry if this is 'off the subject', don't always know where to post things, sorry Gerald!
I notice one subscriber was interested in boom stiffness, and why it's important.
I worked in a company that made very high speed camera's, and in one of the tests they photographed an aluminium arrow in flight, fired by an archer, from the side and behind, and it was quite amazing to see the sinewave type flexing and magnitude of it along the shaft!
I can only think any movement of the fin/elevator (must look like a fish moving in water) puts the airfoils in a draggy part of the drag polar, the drag bucket is very narrow on these thin foils
Clever of the Swedes etc to find this out on their own!
The SAL-Peter has it's boom and pod moulded in one, nice if you can get it

Nick Rolls
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Old May 08, 2012, 08:55 AM
G_T
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Nick,

Dynamic flow and static flow are not the same thing. The polars you are used to seeing are static. In transient flow, even thin foils can generate a lot more lift than you might think.

Otherwise, how would people break tailbooms on launch? That force comes from the vertical tail.

Gerald
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Old May 08, 2012, 02:26 PM
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Your brain is better than mine Gerald!, I am very much an 'empirica'l modeller, not sure I always trust what computers say. Do your latest foil design programmes take into account leading edge radius/shape?, I think the old ones didn't. To me leading edge radius/shape is critical.
Interesting you saying about the sideways torque induced by the vertical tail, my friends JJEdge has a markedly horizontal oval sectioned boom!

Watching a video of Joe Wurtz launching a DLG, we need to get running as well as weight lifting! He seems to put in a radiused turn immediately after launch that I havent seen anyone else do, is he picking up extra speed from the oncoming wind?, sort of DSing? I don't think he does anything without a good, well thought out reason.

Nick Rolls
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Old May 08, 2012, 02:39 PM
G_T
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All of my foils have had considerable care in establishing the leading edge radius and shape. The vast majority of my airfoil development work is via inverse modeling, where it is difficult to produce a shape that appears "circular" at the leading edge. That sometimes the shape is not really quite circular is not necessarily a flaw; sometimes it is a feature. It is the expectation that it appear a certain way or be some particular size that is the flaw!

The torque produced by an asymmertic airfoil of a vertical tail is a small component, thankfully in the direction that offsets the torque produced by the drag of the throwing blade. These forces are small, and have no bearing on the choice of whether to ovalize a boom or not.

Joe can comment on Joe, but it sounds like just some variation of turn and burn from what you are saying. We all pick up extra airspeed from the wind during the launch. More knowledgeable and more experienced pilots will use this available energy a little more effectively than the run of the mill pilot.

Gerald
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Old Jul 26, 2012, 10:59 AM
G_T
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Just a quick note to everyone. I named the first version of these foils Synergy. Hopefully that isn't taken by anything that is close enough to a DLG to cause confusion.

Gerald
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Old Jul 26, 2012, 11:05 AM
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Have a wing drawn up with the Synergy, performance looks very good on the comp. Will start prototyping it after the Neos finishes it's upgrades in late Aug.
2 versions of the wing right now, ~20dm^2 and a ~21dm^2 options, 21dm^2 is looking great though. Graphs look very promising.
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Old Jul 26, 2012, 11:20 AM
Father of Fr3aK, DLG Pilot
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Excellent. The airfoils formerly known as the "Forgiving foils" will forever now be known as "Synergy"

A name is a good start.
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