Re: Preliminary analysis of aerodynamics of sparrow strainers (or not)

Jay Scheevel

Hi Michael,

Not much time to fully absorb all the items you bring up, but let me hit a couple. Airfoil dimensions were normalized for my multifoil model representation including with the Eppler main wing so absolute chord equal to 1.0 (100%) is reduced for dimensional convenience to accommodate both airfoils and total lift calls. This changes Reynolds numbers slightly as well. So I am just comparing apples to apples within my  personal modeling framework.

 The difference in Angle of LS1 in the QAC  plans relative to the UIUC database was noted and discussed (in addition to actual wind tunnel data) in part 1 of the Q2xx modeling paper that I did. Have a look at that summary and see if it it squares up the discrepancy you observed. 

I am headed out of town for a week or so and I will see if I can wrap my head around the other points you make as time permits. Thanks for your inputs.


On Mar 8, 2022, at 9:50 PM, Michael Dunning <dunningme@...> wrote:


The comment was strictly about the tailoring of the hinge moment. The rest was a fun history tangent.


I noted a couple concerns in the provided LS(1) airfoil after running through the usual XFOIL file conversion hoops (remove tab delimiters, normalize the X/Y scale). While the max thickness is recovered correctly, the max thickness location, max camber and max camber location are considerably off from the published numbers:

Airfoil Tools (untrusted)

NASA TM-X-72843 (trusted, usually)

Regardless of that, my initial results at 2 degrees angle of attack are off in all respects from the first JavaFoil result you posted when using your (normalized) coordinates:

The two tools are never going to match but I do expect them to generally agree. My XFOIL results for zero lift AoA and where cl = 0.461 occurs are in line with the Airfoil Tools published numbers at RE=1M and the NASA published wind tunnel data, so I feel confident ruling out gross user error with the tool at least. The wind tunnel data in Figure 6 (PDF pg 28) is in general agreement and even the XFOIL over-prediction of max lift occurs at the typical +15%...and max lift AoA prediction is closer than usual at 15 vs 16 degrees actual.

Both my initial checks, the Airfoil Tools plot, and the NASA report show any cl < about 0.5 occurring at negative angles of attack. I'm doubtful but possibly this is due to the plans-template-level-line vs. chord line references? Again, not sure how JavaFoil works.

In the meantime, I need to stop and calibrate XFOIL with the wind tunnel data from the NASA report before I can be of any further use to you:
NASA-TM-X-72843 "Effects of thickness on the aerodynamic characteristics of an initial low-speed family of airfoils for general aviation applications"

#2827 (still thinking about planning on visualizing how to finish building)

Join to automatically receive all group messages.