Question came up in another thread on what the SkyWalker airfoil is.
Anyone have any details/specifications?
Looked like a Clark-Y to my uninformed eye.
This differs from what sfakias observed:

Originally Posted by sfakias

Somewhere burried in the thousants of posts regarding the skywalker, I had found a picture of the wing tip, giving a good idea of the airfoil geometry (will post it this afternoon if I manage to find it). It looked to me very similar to the NACA 4412 airfoil, which is what I decided to use, since it is well documented and tested, and works great for our application. I would bet it is not a clark-Y because the bottom of the airfoil is slightly cambered.

The chord is 240mm at the root, extending 350mm from the centerline as straight wing, with a 500mm polyhedral section at the end of the wing which ends with a 190mm chord. Dihedral step is 3 deg. Leading edge is a straight line when viewed from above. These values were deducted by reverse engineering photographs. If someone owns a skywalker and would like to shere measurements with us, it would be greatly appreciated.

Originally Posted by henkvdw

Question came up in another thread on what the SkyWalker airfoil is.
Anyone have any details/specifications?
Looked like a Clark-Y to my uninformed eye.
This differs from what sfakias observed:

I'd love to know the airfoil used. At this rate I figured I'd order another SW and cut the wing. If I do that I'll scan the wing and post it.

I found the picture I was talking about. The slightly cambered underside may be an illusion due to the lens or other factors, but it looks cambered to me.

I have used Clark-y in several of my planes, but it has significant drag associated with it. Also, it is a very old design of airfoil (I think the first trans-Atlantic flight was with a Clark-Y!). I wanted to use a more "modern" airfoil for this project to increase efficiency.

I did some research and found that NACA 4412 is a well documented airfoil, widely used, with good L/D ratio, working through a wide envelope of AoA, and with good stall behavior. It is indeed slightly cambered at its lower surface, as you can see from the attached drawing of a 240mm chord NACA4412 (from Profili V2, edited in AutoCAD). A difference between the photographed airfoil and NACA4412 is that in the photo, the leading edge radius looks bigger: that could be again an illusion, or a feature built on purpose to make stalls even more gentle.

Henkvdw, you mention that the wing you own has 4mm thick trailing edge - that is a thick trailing edge! I am sure it is not ideal from an aerodynamic point of view, but sure is better for production and for hangar rush point of view. If you trim the trailing edge of NACA 4412 240mm chord to be 4mm thick, the remaining chord is 228mm - close enough to the 232mm that you measure. If you can measure the dimensions of the ailerons, and their distance from the plane center line, I would be grateful. BTW, do you own a wing only or a complete Skywalker?

I am leaning towards using 2deg angle of incidence for the 240mm center section, and 1deg angle of incidence at the 190mm tip, to decrease the chances of a tip stall. Any thoughts on that?

Sorry for the long post - I read a lot but post rarely here, so when I post my posts end up rather long... If you read enough, usually you find the answer to the question you were about to post!

I've seen plenty of Clark-Y airfoils on sailplanes and while they're plenty lifty they act
like they've got the brakes on when you put em into a dive. I dunno if I just haven't
gone fast enough with the SW to notice, but it does not give the same impression.
It doesn't *look* like a high performance airfoil, but it does ok.

ian

I am gonna have to take out the foam wire cutter and try this out myself. Keep you updated on this. Thank you henkvdw, and sfakias for all the great info and direction.

Hows this? I can do a better one if you want.

Originally Posted by Martin Y

Hows this? I can do a better one if you want.

Thanks for the scan Martin Y. However, it involves a lot of guess work to deduct an airfoil from this picture, due to the win root features that are blended with the airfoil. To get a specific geometry, one would have to cut the wing at a plane that would result in a section of the airfoil only, without other features, as Typicalaimster suggests. Also, at least a second section, towards the wing tip, is required to get a good idea of the wing geometry.
However, to keep this in context, we must keep in mind that any scratch build plane has approximate geometry, since no CNC machined molds or parts are used - it is mostly handcraft. In my opinion, the discussion should focus on what would be a good approximation and would perform similar to the stock Skywalker. I suggest NACA4412 with 2deg angle of incidence at the root and 1 deg at the tip, and I am looking forward to other suggestions.

well what's funny is that likely 99% of all the aircraft designated "clark-y" are not.
eventually you face the fact that there are several famous LARGE named kit companies & popular designers that have sold "clark-y" airfoils where all the experienced builders would joke about the clark-y wing being "the outside tracing of X designer's size 10 shoe".
same joke many times over with most semi-symetrical wings being "X's shoe horn" claiming to be one thing or another. heh

Originally Posted by sfakias

Henkvdw, you mention that the wing you own has 4mm thick trailing edge - that is a thick trailing edge! I am sure it is not ideal from an aerodynamic point of view, but sure is better for production and for hangar rush point of view. If you trim the trailing edge of NACA 4412 240mm chord to be 4mm thick, the remaining chord is 228mm - close enough to the 232mm that you measure. If you can measure the dimensions of the ailerons, and their distance from the plane center line, I would be grateful. BTW, do you own a wing only or a complete Skywalker?

sfakias, I have 2 unbuilt SkyWalkers complete.
Will do some measurements tonight. And try getting some pics too.
Let me know what measurements you need and I'll try to get it.

just landed enough foam to cut one up. lets do this already, lol. Since my scratch-built "sky walker" plane is a bit heavier than the stock one. i will probably do a x 1.25 Thank you henkvdw, look forward to the measurements.

Originally Posted by henkvdw

sfakias, I have 2 unbuilt SkyWalkers complete.
Will do some measurements tonight. An try getting some pics too.
Let me know what measurements you need and I'll try to get it.

HI Henkvdw. Please take the time to take the measurements that define the wing and the tail group. If the wing dimensions that I posted earlier are close enough, do not bother with the wing - just the width, the length and the distance of the ailerons from the plane axis. For the tail group, the dimensions that define it would be the chord at the bottom and the top of the vertical stabiliser,the angle of its leading edge to the vertical (or the horizontal), the height and the width of the rudder (moving part), the chord at the center and at the edge of the horizontal stabiliser, its span and the height and the width of the elevator (moving part). Also, The distance of the wing leading edge to the horizontal stabiliser leading edge. For the fuselage, the total length, its depth (from the bottom surface of the wing to the lower part of the fuselage), and its maximum width. Finally, the recomended CG is given by other users as25-30mm from the servo wires channels. If you could translate that to mm from the wing leading edge it would make much more sense for us scratch builders.

I know this sounds (and is) a lot of measurements, but I think it is the minimum data required to roughly define a plane. Thank you very much in advance for your valuable help.

Originally Posted by Vyas

just landed enough foam to cut one up. lets do this already, lol. Since my scratch-built "sky walker" plane is a bit heavier than the stock one. i will probably do a x 1.25 Thank you henkvdw, look forward to the measurements.

There are reports that the original Skywalker flies fine with AUW up to 3kg or more - is yours that much heavier? Lowering the wing loading is great for gliding, but it has the drawback of decreased stability if there is some wind.

Wing Pics.

Maximum thickness of wing is 1.150".
Thickness at WingTip 0.895"
Forward Spar is 1 7/16 from LE.
Rearward Spar is 5 1/2 from LE.
Servo Wire Groove at 3 1/8" from LE (Forward side, groove 1/8" wide and 0.245" deep)
TE tapers at 5 degrees to LE.
WingEnd at 102 degrees to LE.
Flap Cut-out starts at 2 5/8" from Center
Flap Cut-out is 2 5/16" front to rear and 8 1/8" L to R
Flap bottom is 1 11/16" F to R and 7 7/8" L to R
Aileron Cut-out starts at 12 7/8" from Center
Aileron Cut-out is 2 1/8" F to R and 14 1/8" L to R
Aileron bottom is 1 3/8" F to R and 13 7/8" L to R

It clearly has a different airfoil at root versus tip, and with the dihedral break
there's no way to know if it's a smooth transition from one to the other (something
you can cut with a hot wire or not).

ian

Originally Posted by sfakias

For the tail group, the dimensions that define it would be
the chord at the bottom and the top of the vertical stabiliser,

bottom 8 1/4", top 5 5/8"

Originally Posted by sfakias

the angle of its leading edge to the vertical (or the horizontal),

122 degrees to horizontal

Originally Posted by sfakias

the height and the width of the rudder (moving part),

horizontal lenth is 2 1/8", height measured at 105 degrees to horizontal is 6 5/8" (this is the angle of the hinge and trailing edge)

Originally Posted by sfakias

the chord at the center and at the edge of the horizontal stabilizer,

center 6 1/4", edge 4 1/2"
swept LE with included angle of 162 degrees
edges are at 84 degree angle to center-line of aircraft

Originally Posted by sfakias

its span and the height and the width of the elevator (moving part).

24 7/16 TE, center thickness 0.590", outside edge thickness 0.420", symmetrical profile, elevator cut-out 1 1/2" x 21 9/16", elevator bottom 1 1/4" x 21 1/4"

Originally Posted by sfakias

Also,

The distance of the wing leading edge to the horizontal stabilizer leading edge.

25 5/8" on aircraft center-line

Originally Posted by sfakias

For the fuselage,
the total length,

47" nose to top TE of rudder

Originally Posted by sfakias

its depth (from the bottom surface of the wing to the lower part of the fuselage),

7 3/4"

Originally Posted by sfakias

and its maximum width.

4 1/8" Where flat surface inside canopy starts curving up

Bottom of wing is 3" lower than than bottom of horizontal stabilizer

Hope this helps.