Yet Another Wickerbill Question

[Rick Iverson]

Gents;

We are all on the same sheet of music here regarding Gurney flaps. But I had a thought regarding the shape as viewed from the end. The typical application is a piece of right angle aluminum extrusion with varying leg dimensions of say, 0.5” x 0.75” for canards, winglets, and rear wing elements, and 0.75” x 0.75” for the diffuser.

But what about a bent 6061-T6 lip that will require a substantial bend radius. The angle will be up to 90 degrees (perhaps samples starting at 45 degrees and working up to 90 to experiment), but the laminar transition over a smooth bend to say, 90 degrees as opposed to an abrupt 90 degree angle my be more aerodynamically efficient.

Thoughts?

[R. Pare]

I doubt that it will make any difference at all - it is what the airfow on the blunt back side does that is important, not the front side.

[alangbaker]

The whole point of a wicker is to create a small area of low pressure that helps the flow on the bottom surface to stay attached.

I doubt you could measure the difference in drag between a hard 90 degree wickerbill, and one that has a 90 degree back surface with a more flowing front facing surface.

[phantomjock]

Here are a few pennies (.02 USD) to consider. (Using 'em while they have some value )

I prefer "Gurney" to "Wicker bill" out of deference to a remarkable driver/engineer/designer/team chief (and one of my Heroes). Hopefully the following images might be helpful. Both are from an AIAA document that is based on a series of wind tunnel tests of Gurneys and T-Strips. [Note the study was on wings - so invert for downforce] I will share the pdf for anyone interested.

The authors of the study found there was a shift in the aerodynamic center (ac), pitching moment, and as well as an increase in Cl (vs AOA) - much like lowering flaps. The flow field shown is clearly attached on the surface opposite the flap, and the pressure area clear. Other studies relate the size and impact of the low pressure are to the height of the flap as I recall.


The T-Strips are an interesting application as there in little to no shift in ac or moment change, and Cl curves more like adding slats - an increase in AOA an increase in Cl, generally along the slope of the original curves.


Now, back to the your question. I agree with R.Pare and alangbaker; "...don worry 'bout it."

Cheers - Jim
Fun video clip:
https://clip.cafe/green-book-2018/dont-worry-bout-it/