Bensen G2 - Clark YS - And other beveled trailing edge Airfoils

curtisscholl

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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?
 

Seagasm

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Interesting comments above. I have been looking at profiles and information relating to making a set of wooden rotor blades. I have used the UIUC Airfoil Data Site for reference and offer the following profiles Curtis mentions:



 

curtisscholl

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Seagasm

There is another diagram of the VR-7 with a tab on the trailing edge. Chuck Beaty wrote on that one in the Rotary Forum. The airfoil tools web site has the diagram of it. And so does the UIUC DB


Curtis Schollvr7b.gif
 
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curtisscholl

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Saline, MI
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Building Gyrobee
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Jim

Yeah...the lifting body cargo carrier....
You are showing your age....and I remember that show... too...
 
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