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ACHIEVING THE BEST REFLEXED AIRFOILS FOR FLYING WING USE IN THE SMALL PLANE CATEGORIES

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Norman

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I had to close the TE in as the CFD does not like the open rear(Its attached)
Xfoil doesn't do square trailing edges (the spline can't have any sharp angles) so the trailing edge is either closed or open. An open TE simulates a square TE just fine for panel codes because they're not actually modeling fluid dynamics, they're just calculating the pressure and estimating the friction on each panel. If you can close that gap with a line segment your CFD might work with it. My guess is that as long as the finite TE thickness is less than 2 percent of the chord it won't make much difference for a 12% thick airfoil. For very thick airfoils a truncated TE actually produces less drag than a sharp TE. In any event it's just not practical or safe for airplanes to have knife sharp trailing edges.


Does anyone know what the vertical arrow in the XFLR5 Pressure screen op point is supposed to indicate?
I belive that's the center of pressure. Each panel has a vector representing the normal pressure on that panel. If you take the sum of the vertical component of all of those vectors (both up and down) you get the center of pressure. On zero pitching moment airfoils eg NACA 5 digit, some reflexed, and symmetrical this is a stationary point withing the linear range as displayed in the Cm graph. With normaly cambered and aft loaded airfoils it moves aft of the trailing edge at some low AoA which is obviously impossible see attachment.
 

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WINGITIS

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Xfoil doesn't do square trailing edges (the spline can't have any sharp angles) so the trailing edge is either closed or open. An open TE simulates a square TE just fine for panel codes because they're not actually modeling fluid dynamics, they're just calculating the pressure and estimating the friction on each panel. If you can close that gap with a line segment your CFD might work with it. My guess is that as long as the finite TE thickness is less than 2 percent of the chord it won't make much difference for a 12% thick airfoil. For very thick airfoils a truncated TE actually produces less drag than a sharp TE. In any event it's just not practical or safe for airplanes to have knife sharp trailing edges.




I belive that's the center of pressure. Each panel has a vector representing the normal pressure on that panel. If you take the sum of the vertical component of all of those vectors (both up and down) you get the center of pressure. On zero pitching moment airfoils eg NACA 5 digit, some reflexed, and symmetrical this is a stationary point withing the linear range as displayed in the Cm graph. With normaly cambered and aft loaded airfoils it moves aft of the trailing edge at some low AoA which is obviously impossible see attachment.

Ok I will try and edit the DAT file to close it off flat instead of making it a sharp TE.


I am not sure if it can be the COP in XFLR5?

If you look at the CFD areas where there is upward pressure under the airfoil and negative pressure above the airfoil the center of those two area clearly lines up with the FORCE LINE listed in the other picture, it is also where one can imagine it should be at that AOA.

Hence I asked the question in case the XFLR5 line represents something else, its either that or there is in error.

EITHER TOOL COULD HAVE IT WRONG but there should not be that much difference?


NACA M6 CLOSED TE PRESSURE 12.5 MINUTES PROCESSING.pngNACA M6 CLOSED TE FORCE LINE 12.5 MINUTES PROCESSING.png
 

WINGITIS

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Ok here is the result from the STD TE BUT FLAT AND CLOSED IN....

THE CFD resolved and gets a lower total C/L at 17 degrees of 1.285

Unfortunately the equivalent test in XFLR5 does not resolve very often with that configuration and not all all at the higher AOA where we are comparing!

MOST UNFORTUNATE..so I am not sure a conculsion can be drawn from this!?

NACA M6 301 ORIGINAL TE BUT FLAT CLOSED OFF FOR CFD IMAGE.pngM6 FLAT TE CFD STATISTICS.pngM6 FLAT TE CFD FORCE LINE.pngM6 FLAT TE CFD PRESSURE.pngNACA M6 CLOSED FLAT TE-WOULDNT RESOLVE ON A LOT OF POINTS.png
 

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WINGITIS

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OK as no one has commented on the forced transition setting I will stick with "0" for now.

I am also happy to compare airfoils at setting "1" with my other MAGMAGEXPORT airfoil, posted previously.

Here is a new one people may have not seen before, I captured it with a spline from a printed side view in a PDF article, so its about 95% accurate.

NASA MADCAT MORPHING WING, TIP AIRFOIL.

NACA MADCAT MIT-Morphing-Wing.png
 

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WINGITIS

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Ok Folks here are another 5 reflexed airfoils tested for this week.

I WOULD APPRECIATE IT IF OTHERS CAN EITHER DO SOME TESTS ON THEIR OR OTHER KNOWN REFLEX AIRFOILS AND SUBMIT THEM HERE.

OR ALTERNATIVELY JUST SUBMIT THEIR TXT AIRFOIL FILE HERE AND I WILL DO THE ANALYSIS FOR THEM(The TXT is just a SELIG DAT file format renamed to upload here because DAT file extensions are not supported on this website/board)

The idea was that we would just get a pile of reflex airfoils on here so everyone who wanted to build a flying wing can hone in on and select the best one with the features that suits their project, so if others do not add to this it will just die as a thread at some point!

Lets try and aim for just 5 airfoils a week at least shall we? If I am flogging the proverbial dead horse, just let me know.................
 

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SlowFlight

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Thank you for posting. While I'm not sure I'll be looking for a flying wing unless it can be safely STOL, I'm interested in less Cm, and the wing shapes.
 

WINGITIS

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Thank you for posting. While I'm not sure I'll be looking for a flying wing unless it can be safely STOL, I'm interested in less Cm, and the wing shapes.
Thanks SlowFlight, I will include the profiles in the PDF's where I can.

What do you define as STOL, In New Zealand we have a 45 Knot Stall speed, which seems slow to me, but you may be thinkining of a slower regime?
 

Norman

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Here are a few positive Cm0 airfoil sections that I've found over the years. People have been trying to find the original ordinates of the Go 765 used on the Me 163 for years and the just don't appear to have been published so there have been a few attempts to lift them from a museum specimen. Unfortunately it's nearly impossible to get accurate measurements by hand even from a shiny new wing much less a beat up old war horse. This file "Gottingen 765 spline" is probably as close as you can get to the original Gottingen shape unless some secret WWII German tech report shows up. Next is a cleaned up version of the NACA M6. Not much improvement, just a little less drag at a couple spots on the drag polar and the L/D curve is a little wider but still that funny double hump shape. Third is a something I developed from an airfoil I found years ago. Don't know where the M35a came from or how I modified it it's been so long.


BTW The x axis on the drag polar in the PDF is Cd X 1000 to spread the curves apart
 

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WINGITIS

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Here are a few positive Cm0 airfoil sections that I've found over the years. People have been trying to find the original ordinates of the Go 765 used on the Me 163 for years and the just don't appear to have been published so there have been a few attempts to lift them from a museum specimen. Unfortunately it's nearly impossible to get accurate measurements by hand even from a shiny new wing much less a beat up old war horse. This file "Gottingen 765 spline" is probably as close as you can get to the original Gottingen shape unless some secret WWII German tech report shows up. Next is a cleaned up version of the NACA M6. Not much improvement, just a little less drag at a couple spots on the drag polar and the L/D curve is a little wider but still that funny double hump shape. Third is a something I developed from an airfoil I found years ago. Don't know where the M35a came from or how I modified it it's been so long.


BTW The x axis on the drag polar in the PDF is Cd X 1000 to spread the curves apart
Hi Norman

Thanks for that, here is the ME163 airfoil I use, its called RECOVERED but I am not sure by who?

Also a good pic I have showing the Reflex and another showing the Slot..I like slots!ME163B SHOWING WING REFLEX ORIGINAL.pngME163 slot from below ORIGINAL.png
 

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WINGITIS

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The M-35A is from the Marske Pioneer 3, I have it, I think I included that in those earlier tests I put up!?
No I cant have posted it, I only have it in 499 points version, it may have been included in tests I showed on that original thread before this one.

Ill convert it to 299 and put it here shortly.
 

WINGITIS

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No I cant have posted it, I only have it in 499 points version, it may have been included in tests I showed on that original thread before this one.

Ill convert it to 299 and put it here shortly.
I had indeed posted it with all those other Marske and similar ones..before going down to 299 points.

Here is my 499 versionconverted to 299:
 

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WINGITIS

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I got my M-35A from a PDF spline, I spent some time getting it fairly accurate.

Its not to far of yours in terms of results, less lift but more CM.

But yours is 2% thicker so that's a lot of difference!

Results to follow..
 
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