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

[WINGITIS]

I can use Freecad to import .dat airfoil files and scale, extrude, loft etc. the problem I have is if I want to cut an experimental shape on my cnc hotwire cutter, the ’free’ software that generates xyuz gcode requites a .dat file, I can generate dxf files of my shape but not .dat. Clearly there is paid software out ther that will do it but I was asking if anyone had knowledge of ‘freeware’. Because of the exchange rate, what appears to be cheap to the rest of the world is around double the cost here in OZ. A French free program Jedicut can cut dxf files If only someone could tell me how to get it to do that.

OK but I did not read it as you EXPLICITLY required a FREE version, I guess it could be inferred though, I missed that.

I am pretty sure I used to have something like that some time ago, but I have searched through all my directories and nothing comes up, but because I cannot remember what its name is that is probably why a search cannot find it.

I have had a bit of a search online and cannot find one either.

I did find a DAT TO DXF FREEWARE ONE in my directories, but that is not what you want.

AIR 2 DXF
Converts any .dat airfoil to .dxf
By Pere Casellas

 

[rotax618]

I don’t begrudge any software developer from making a $ from their efforts, but to since I don’t plan on using the software more than a few times it is not cost effective - there are many programs that will do the job - Devfoam, Devfuse etc but unless you are going to make many models they are not cost effective.
I have been fiddling with a french program, Jedicut which purports to cut dxfs, it does, but because of the lack of instructions and the language translation barrier it is a steep learning curve.
It is not only interesting to look at the predicted performance of an airfoil but to actually cut a 3d shape out of foam and observe its performance Is what I hope to achieve.

 

[Norman]

I can use Freecad to import .dat airfoil files and scale, extrude, loft etc. the problem I have is if I want to cut an experimental shape on my cnc hotwire cutter, the ’free’ software that generates xyuz gcode requites a .dat file, I can generate dxf files of my shape but not .dat. Clearly there is paid software out ther that will do it but I was asking if anyone had knowledge of ‘freeware’. Because of the exchange rate, what appears to be cheap to the rest of the world is around double the cost here in OZ. A French free program Jedicut can cut dxf files If only someone could tell me how to get it to do that.

If your CAD program has a function to list the points on a spline you can copy that to a text file and use search and replace to get rid of the CAD specific parts. Back in the stone age I did it that way several times. IIRC the command in ACAD is <inquire> under the tools menu.

 

[rotax618]

Thanks for the tip, I’ll try that out.

 

[sming]

If I understand you correctly, you have a dxf file from freecad that you want to cut with a machine that accept gcode right?
You should be able to find freesoftware
Doing dat > dxf > dat just to cut sounds fishy, dxf is well supported by cam software usually
If you need help with the french in jedicut, PM me. I'll take a look at it.

Edit: no luck with the path module in freecad? Path Workbench - FreeCAD Documentation
Edit2: jedicut is available in english, is the translation bad? jedicut-translations/English.xml at master · jedicut/jedicut-translations

 

[rotax618]

You don’t understand, most cnc 4 axis gcode generators (all except maybe Jedicut which is difficult to get to work) , don’t cut dxf files - (except Devwingfoam which costs over 200A$.)
All of them will let you import a .dat airfoil file and cut a wing, if you want to try a different shape than an existing airfoil you may make a CAD image but Cad programs dont export that shape as .dat, every other format but not .dat.

 

[sming]

Nope I don't understand. Are you trying to cut modified airfoil or any random shape you designed in CAD?
If the former, Xlfr5 can generate any dat of airfoil you want, in the other case, ok, it looks a bit problematic (found some random project on github that looks finicky).
Dat file are just text file with normalized XY coordinate of points so if your dxf shape is not too complex, you could do it by hand. Not very "computer aided"

 

[WINGITIS]

FOR CLARITY

I believe what he is doing is creating various shapes he likes in a CAD tool he likes, that GENERATES the DXF files.

His profile cutter combination(THAT HE PREFERS/HAS) wants a DAT file format as input.

Hence a DXF to DAT utility is required.

Is that correct ROTAX618 ????

 

[rotax618]

Spot on !!

 

[WINGITIS]

I brought the loss of resolution problem up to the administrator a few months ago but got no help. Basically he just told me that it's my fault.


OK I've been working on a real oddball problem off and on for a while. It's a drop-in replacement airfoil for the Mitchell U-2. The spar is right up against the pilot's back so the replacement airfoil must have the thickest point in the same place. The problem is that the max thickness is at 40% and reflexed airfoils tend to have low CLmax with the thickness that far aft and his modified Wortmann didn't turn out very well so the plane doesn't live up to the hype. So here's my latest attempt to make a better airfoil that can fit onto the spar of that plane without any structural modifications. I'm not recommending that anybody actually use it without further testing because panel code software doesn't provide data about stall or hysteresis but a large scale model would validate it.

Hi Norman

Sorry it has taken a while.

Here is is your NM-79 MITCHELL U2 REPLACEMENT airfoil analysis.

It has its max lift centered at 20 degrees which is good and low drag depending on how much of a % laminar flow it can get on the top surface.

Many thanks for submitting it.

Cheers
Kevin

 

[WINGITIS]

Hi Folks

I dug up these three NASA reflexed airfoils from the early 80's......it was a lot of typing in....

They are not great at low Reynolds numbers, they suit Higher Reynolds than the HBA wings would typically use.

I have included them here for anyone that wants to have a look at them.

They are three thickness distributions built on the same camber line.

 

[WINGITIS]

Also here is information about the Spratt control wing airfoil that I migrated from another thread on the HBA,

pjphilli had started this off and provided the images and the plan PDF's

so people can see it here:

I have extracted the AIRFOIL image from the SPRATT Seaplane plans and compared it to Normans original one(NACAG 231) mentioned in a link above and they are both the same.

The 23112 generated from the Airfoil Tools site formula is different and is similar to Normans BTB one is the same link.

(SEE PDF FOR BETTER IMAGES)

I got excited and did the first phase for you, someone can please check my numbers, before I go on to create the DAT file.

A few issues I found:

1: The LE is not on the reference line, this can be rectified in XFLR5 with the Normalize and De-rotate features later in the process.

2: Where the tape is at the TE the station lengths are not the same, so it has been taped incorrectly.

3: The tape covers some of the measurements, I used a bit of math to solve for those missing points, using the slopes and intercept method(Overkill for this example, its more useful when the X axis values are to 6 decimal places and not equidistant, but I use it for all straight line interpolations as a rule)

Most of the other numbers are fairly readable, but it does not mean I have misread or mistyped 1 or 2, SO PLEASE CHECK!

Kevin

Ok I have finished the conversion from the PLAN dimensions to a SELIG DAT, then De-rotated it and here it is compared to Normans NACAG 231 version, they are almost the same.

There is a little work for me to do on the nose yet, theres a point missing, and then that may bring it even closer during the De-rotate procedure.

Then I will do the Polar's analysis and re-post.


OK here is the SPRATT 23112 version I have just finished the nose on and compared to the airfoil tools 23112.

The SPRATT version has no advantages and appears to have some issues at the nose, as Norman has suggested, that may be the way it is lofted, although it also has a flatter lower forward surface.

As Phil has just listed a few changes above I will check those, but here is the polar comparison and the DAT file in TXT format.

 

[WINGITIS]

MORE:

 

[henryk]

Планеры со стартом с ног

объясняет почему. =и на А бывает,и на Б бывает... -60 кг/60 лет ?!

reaa.ru

MH-78 airfoil,
L/D=16 ,
59 kg !

 

[WINGITIS]

Планеры со стартом с ног

объясняет почему. =и на А бывает,и на Б бывает... -60 кг/60 лет ?!

reaa.ru

MH-78 airfoil,
L/D=16 ,
59 kg !

Thanks for that, the video footage was good.

I will do an analysis of the MH-78 shortly.

Cheers
K

 

[WINGITIS]

Here is the MH-78 analysis compared to a few others.

Its pretty good.

 

[WINGITIS]

HI FOLKS,

MARC W has kindly posted a link to a NACA Paper on the thread below that has a fair bit of useful information in it, including on some Flying Wing airfoils.

43012, 2R212

Airfoil selection for an aircraft out there?

That is a high Reynolds number for most E-AB airplanes with flaps deployed. Yes, the Re would be a bit lower (Bigfoils uses 6m as a default), but would not change what I was trying to show. The point I am making is at stall, the unflapped portion of the wing is at a MUCH lower AoA, and...

www.homebuiltairplanes.com

The paper is here:

Airfoil Section Characteristics as Affected by Variations of the Reynolds Number - NASA Technical Reports Server (NTRS)

Report presents the results of an investigation of a systematically chosen representative group of related airfoils conducted in the NACA variable-density wind tunnel over a wide range of Reynolds number extending well into the flight range. The tests were made to provide information from which...

ntrs.nasa.gov

It is VERY GOOD in many ways!

It could very well take up QUITE A FEW WORTHWHILE hours of every ones time...

Regards
Kevin

 

[nestofdragons]

I reaaaaally need to read this all. Currently busy with a low aspect ratio FAR103 idea (link is to the post page in this forum). I don't want to make the mistake and choose the proven Fauvel 14% if i read that more modern airfoils have much better performance.

 

[cluttonfred]

On paper, Martin Hepperle MH 78 does seem very good, though the highest Reynolds number for which I found data is about 1 million, not the 3-4 million of your application.

MH 78 14.47% (mh78-il)

Details of airfoil (aerofoil)(mh78-il) MH 78 14.47% Martin Hepperle MH 78 for flying wings (hang glider)

airfoiltools.com

 

[Norman]

On paper, Martin Hepperle MH 78 does seem very good, though the highest Reynolds number for which I found data is about 1 million, not the 3-4 million of your application.

Oh we can do a little better than that.