REFLECTOR:Trailing Edge

[Scott]

>I disagree, at least to a degree, that the vortilons and the VGs play very 
>different rolls.  The main function of the VGs is to generate a vortex 
>over the upper wing surface at high angles of attack, thereby breaking up 
>the spanwise flow and encouraging the flow to remain attached.  VGs do the 
>same thing, most likely more effectively on a smaller scale. So there is 
>some overlap of function.

No VG's have nothing to do with span wise flow. At least not directly.  VG 
or Vortex Generators, create small vortices that excite the boundary layer, 
this allows or forces ten boundary layer to stay attached to the wing at a 
higher angle of attack, this can do two things for your,  increase lift and 
also reduce the wings stall speed.

Span wise flow is when the wind over the wing starts to move in an outward 
direction instead of straight back.

Vortilons are a device to reduce span wise flow on swept wings at high 
angles of attack..

At least that's how I understand their function.

Scott

>The fences provide a means of stopping the spanwise flow, which is the 
>worst coming down off the sides of the fuselage, and heading 
>outward.  Without VGs some spanwise flow probably re-establishes outboard 
>of the first fence, which to me seems the only reason to have more fences 
>outboard of the aileron.  Having them out there probably provides further 
>stability, but would expect to reduce roll rate.
>
>VGs probably cause more drag a high speed than a fence, and the vortilons 
>likely cause negligible drag except at high angles of attack.  I’m going 
>to guess that a roughly optimum arrangement for increased low speed 
>response, good roll rate and minimum drag is having a fence inboard of the 
>aileron, and a few VGs forward of the aileron; probably on the outer half 
>of the aileron length.  And leave the vortilons where they are.  Like I 
>said, it’s my guess.
>
>The tuft testing on the EZs showed little deviation from straight back 
>flow on the underside of the wing at any flyable speed.  That leads me to 
>wonder why Klaus suggests that the fence should extend below the wing, but 
>wouldn’t disagree.  Until there is solid evidence to the contrary, I see 
>no reason not install the vortilons as specified, even with the 
>installation of VGs.
>
>And all these conclusions are only worth what it cost you.  I didn’t do 
>any flight testing on my airplane – yet.
>
>Al
>
>Oh BTW; that aileron fence?  Corrugated cardboard core – another 
>inovation.  Couldn’t locate any thin foam, and knew that mostly what was 
>needed was to maintain airspace between the fine BID plys until they 
>cured.  After cutting out I recessed and filled around the edges with 
>micro.  After glassing to the wing they are very rigid, very light, and 
>just under 3/16” thick.


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