Clark Y-15 airfoil plot?

Ok, I ran into a little problem...

I'm laying out the rib design for a 1931 Georgias Special and it uses a
Clark Y-15 airfoil. The coordinates (stations if you will) for upper
and lower surfaces start at the leading edge and go back to the rear
edge. Chord is supposed to be 48". Adding up the distances in the
drawings (the 1931 Flying and Glider Manual, reprinted by EAA) add up to
54 inches. So...does anyone have the airfoil coordinates for this
airfoil (and I assume they would be expressed as something like 2% (aft
of leading edge), bottom =0.75" lower surface and 1.5" upper surface, 5%
(aft of leading edge), bottom surface = 0.25", upper surface = 2.25",
etc.)? It would be even easier if someone had the coordinates for one
with a 48" chord

Thanks for any help!

Scott

I could not find info on a plain old Y-15. Did find some references to
the Clark Y, Clark YH, Clark YM15, etc. They all apear to have a
slightly curved bottom plot all the way back to the trailing edge,
whereas the Y-15 in the Georgias plans is flat from about 15% back from
the leading edge all the way to the trailing edge.

Scott wrote:

Ok, I ran into a little problem...

I'm laying out the rib design for a 1931 Georgias Special and it uses a
Clark Y-15 airfoil. The coordinates (stations if you will) for upper
and lower surfaces start at the leading edge and go back to the rear
edge. Chord is supposed to be 48". Adding up the distances in the
drawings (the 1931 Flying and Glider Manual, reprinted by EAA) add up to
54 inches. So...does anyone have the airfoil coordinates for this
airfoil (and I assume they would be expressed as something like 2% (aft
of leading edge), bottom =0.75" lower surface and 1.5" upper surface, 5%
(aft of leading edge), bottom surface = 0.25", upper surface = 2.25",
etc.)? It would be even easier if someone had the coordinates for one
with a 48" chord

Thanks for any help!

Scott

Dear Scott,

If you'll contact me directly with a valid email address I can attach a
DeltaCAD drawing of the Clark Y15 - 48 to the return message.

But it's easy enough to dig out for yourself.

Use Google or other search engine to locate 'Profili,' a popular
airfoil profiling program written by an Italian fellow and offered free
to the aviation community. (The program was apparently written
specifically for MODEL airplane builders, so think big :-)

Once you find it and get it installed on your computer, use the task
bar to locate the Airfoil Library, click on that then simply go down
the list until you find the Clark Y-15 (which is there; keep looking
:-)

Once you have it, Profili will print it out for you in any chord (be
sure to select 'inches;' output is normally in millimeters).

If you select .dxf as the output file type you can enter the result
directly into DeltaCAD, which is also available free, at least for a
time-crippled copy.

Once you have the airfoil in DeltaCAD you can do ANYTHING YOU WANT with
it, such as drawing in the verticals & diagonals, figuring out the best
shape of the gussets and so forth.

To make up your rib jig simply print the airfoil full-scale (DeltaCAD
allows any scale), glue it to your board, give it a coat of varnish and
there it is.

Since it will print-out on several sheets, to aid in their alignment I
usually overlay a 2" grid of light blue lines. I use them to align the
sheets on a light-table (or sliding glass door) BEFORE gluing them to
the board.

---------------------------------------------------------------------

You're message is pretty good evidence that you don't have Profili
installed. (And maybe not even DeltaCAD, although it has become a de
facto standard for homebuilders.) In that case, it may sound like a
lot of trouble.

Trust me here, Scott. Profili is a useful tool for the homebuilder.
It's always something of a pain in the ass when you have to learn to
use a new tool, especially one you may need to use only once, which is
why I offered to send you the .dxf file. But once you have a tool
available you tend to find uses for it, such as laying out symmetrical
airfoils for fairings and the like, which takes only a moment when you
have Profili and DeltaCAD.

-R.S.Hoover

PS -- For those not familiar with the airfoils of Virginius Clark, the
Clark-Y is approximately 12% thickness (11.73) whilst the Clark-Y15 is
the same airfoil but a full 15% depth.

Scott wrote:
I could not find info on a plain old Y-15. Did find some references to


Download the freeware version of "Profili". Learn how to use it. It
has the Clark Y-15 airfoil along with hundreds of others in its
database.


John Kimmel

On Sat, 02 Dec 2006 21:36:48 +0000, Scott
wrote:

I could not find info on a plain old Y-15. Did find some references to
the Clark Y, Clark YH, Clark YM15, etc. They all apear to have a
slightly curved bottom plot all the way back to the trailing edge,
whereas the Y-15 in the Georgias plans is flat from about 15% back from
the leading edge all the way to the trailing edge.

Scott wrote:

Ok, I ran into a little problem...

I'm laying out the rib design for a 1931 Georgias Special and it uses a
Clark Y-15 airfoil. The coordinates (stations if you will) for upper
and lower surfaces start at the leading edge and go back to the rear
edge. Chord is supposed to be 48". Adding up the distances in the
drawings (the 1931 Flying and Glider Manual, reprinted by EAA) add up to
54 inches. So...does anyone have the airfoil coordinates for this
airfoil (and I assume they would be expressed as something like 2% (aft
of leading edge), bottom =0.75" lower surface and 1.5" upper surface, 5%
(aft of leading edge), bottom surface = 0.25", upper surface = 2.25",
etc.)? It would be even easier if someone had the coordinates for one
with a 48" chord

Thanks for any help!

Scott


what you need scott is the abbott and von doehnoff classic book.

clark Y has a flat bottom and the ordinates are from a line through
the flat bottom.
the more usual ordinates are from the chord line.
NACA 4415 is the 15% clark Y with the ordinates referenced to the
chord line.

if you are carving a prop the naca 44xx series IS the clark Y at
various thicknesses.

dont ask how we know this but there is an aero engineer who will smile
at the thought of the discussion/argument we had before we realised
this.

btw the clark YH is a modification to the standard clark Y to
constrain the centre of pressure. the clark Y has a cp that wanders
with speed and angle of attack making for an aircraft that requires
constant trim attention. the YH was supposedly an improvement.

if you want a really sweet flying classic aerofoil the naca23012 with
washout to tame the stall is superb.

Stealth Pilot

Thanks! You're the second to recommend that (veeduber beat you to it!),
so I will check it out!

Scott
Corben Junior Ace



guynoir wrote:
Scott wrote:

I could not find info on a plain old Y-15. Did find some references to



Download the freeware version of "Profili". Learn how to use it. It
has the Clark Y-15 airfoil along with hundreds of others in its
database.


John Kimmel

A couple guys turned me on to Profili software, so I will take a look
there as well. I was planning on using the Y15 since that was used on
the original and I'm not an engineer and not qualified to analyze the
different aspects of airfoils. I'm sure there ARE better and possibly
more modern airfoils, but I think it might be best to stick with the
design in this case. I could always build new wings later on for
something to do

Scott
Corben Junior Ace




Stealth Pilot wrote:

On Sat, 02 Dec 2006 21:36:48 +0000, Scott
wrote:


I could not find info on a plain old Y-15. Did find some references to
the Clark Y, Clark YH, Clark YM15, etc. They all apear to have a
slightly curved bottom plot all the way back to the trailing edge,
whereas the Y-15 in the Georgias plans is flat from about 15% back from
the leading edge all the way to the trailing edge.

Scott wrote:


Ok, I ran into a little problem...

I'm laying out the rib design for a 1931 Georgias Special and it uses a
Clark Y-15 airfoil. The coordinates (stations if you will) for upper
and lower surfaces start at the leading edge and go back to the rear
edge. Chord is supposed to be 48". Adding up the distances in the
drawings (the 1931 Flying and Glider Manual, reprinted by EAA) add up to
54 inches. So...does anyone have the airfoil coordinates for this
airfoil (and I assume they would be expressed as something like 2% (aft
of leading edge), bottom =0.75" lower surface and 1.5" upper surface, 5%
(aft of leading edge), bottom surface = 0.25", upper surface = 2.25",
etc.)? It would be even easier if someone had the coordinates for one
with a 48" chord

Thanks for any help!

Scott



what you need scott is the abbott and von doehnoff classic book.

clark Y has a flat bottom and the ordinates are from a line through
the flat bottom.
the more usual ordinates are from the chord line.
NACA 4415 is the 15% clark Y with the ordinates referenced to the
chord line.

if you are carving a prop the naca 44xx series IS the clark Y at
various thicknesses.

dont ask how we know this but there is an aero engineer who will smile
at the thought of the discussion/argument we had before we realised
this.

btw the clark YH is a modification to the standard clark Y to
constrain the centre of pressure. the clark Y has a cp that wanders
with speed and angle of attack making for an aircraft that requires
constant trim attention. the YH was supposedly an improvement.

if you want a really sweet flying classic aerofoil the naca23012 with
washout to tame the stall is superb.

Stealth Pilot