curtisscholl
Gold Supporter
Chuck et al:
The Clark YS has been around for a long time.
The Wallis Airfoil looks to be a flat bottomed but thicker version of a Bensen G2 to me. The flat underside started about where the metal strap did and the upper curve was more blunt than a Clark Y. After the curve over the spar it became flat to the reflex portion of the blade.
The Bensen G2 airfoil had a reflex that utilized an upward bevel on the trailing edge that was the thickness of the bottom plywood sheet (1/8" 3MM) . the airfoil depth was not as an 8H12 and the G2 was flat as a pancake on the underside.
It looks as though the Wallis blade bottom plank was 1/8" to 3/16" if I am looking at a picture correctly.
The Clark YS is a 11.7% chord airfoil that utilizes an upward bevel from the 80% to 100% chord line starting at the flat underside at -.035 chord to the waterline of the airfoil. on a 7" chord that was around .245, ( very nearly 1/4") deep from waterline and 5.6" aft of the nose. (but the datapoints suggest .085 top, .035 bottom for .12 thickness at 30%)
There are others that do not have the bevel, but have a reflex tab all the way the length of the blade.
The Clark YS has a Cm of .04 near the 15 degree AOA depending on the Reynolds number.
The 8H12 has a Cm of .02 at the same AOA depending on Reynolds number and does not swing a lot.
The VR7 with tab has a Cm of around .01 at 15 deg aoa but wow...wild up until that AOA
Cl/Cd of 8H12 at 15 deg aoa was 120
Cl/Cd of VR7 with tab at 15 deg AOA was 120
ClCd of Clark YS at 15 deg aoa was 80.
The Wallis blade was built with Hydulignum and I cannot find that stuff in North America. Monte Hoskins did his with Birch.
Would a conclusion that the Clark YS is a draggy airfoil like the Bensen G2?
That a flat tab like the VR7 is sufficient without the upward bevel?
That a totally flat bottomed Clark Y with a tab like a VR7 might be sufficient and not be a hard starter?
The Clark YS has been around for a long time.
The Wallis Airfoil looks to be a flat bottomed but thicker version of a Bensen G2 to me. The flat underside started about where the metal strap did and the upper curve was more blunt than a Clark Y. After the curve over the spar it became flat to the reflex portion of the blade.
The Bensen G2 airfoil had a reflex that utilized an upward bevel on the trailing edge that was the thickness of the bottom plywood sheet (1/8" 3MM) . the airfoil depth was not as an 8H12 and the G2 was flat as a pancake on the underside.
It looks as though the Wallis blade bottom plank was 1/8" to 3/16" if I am looking at a picture correctly.
The Clark YS is a 11.7% chord airfoil that utilizes an upward bevel from the 80% to 100% chord line starting at the flat underside at -.035 chord to the waterline of the airfoil. on a 7" chord that was around .245, ( very nearly 1/4") deep from waterline and 5.6" aft of the nose. (but the datapoints suggest .085 top, .035 bottom for .12 thickness at 30%)
There are others that do not have the bevel, but have a reflex tab all the way the length of the blade.
The Clark YS has a Cm of .04 near the 15 degree AOA depending on the Reynolds number.
The 8H12 has a Cm of .02 at the same AOA depending on Reynolds number and does not swing a lot.
The VR7 with tab has a Cm of around .01 at 15 deg aoa but wow...wild up until that AOA
Cl/Cd of 8H12 at 15 deg aoa was 120
Cl/Cd of VR7 with tab at 15 deg AOA was 120
ClCd of Clark YS at 15 deg aoa was 80.
The Wallis blade was built with Hydulignum and I cannot find that stuff in North America. Monte Hoskins did his with Birch.
Would a conclusion that the Clark YS is a draggy airfoil like the Bensen G2?
That a flat tab like the VR7 is sufficient without the upward bevel?
That a totally flat bottomed Clark Y with a tab like a VR7 might be sufficient and not be a hard starter?