REFLECTOR: VGs

[Scott Derrick]

Tom wrote:
> I just installed the Stolspeed VGs via the Velocity Factory templates.
> Flew this morning to test but we had a low ceiling and I couldn't get
> up high enough to do a stall series. However, first impression was not
> good. At the same power setting I generally use there was a 7 knot
> decrease in airspeed. 
Thats not good.  I figured a 2-3 knot cruise reduction at the most. 
With an analog IAS gauge it was not enough to measure.
> Takeoff broke ground 3 knots lower and my approach speed was 4 knots
> slower. This seems to be way off of other folks experiences. Some
> possible issues I see:
This was one test or multiple averaged tests?   How did you measure a 4
knot slower approach speed?  4 knots slower with same descent speed?
> 1) the Stolspeed VGs are more streamlined than the factory VGs but
> they are also about 1/3rd taller
taller may not be good.  My understanding is that  at  cruise the  VG's
are below or within the laminar flow which reduces their drag
influence.  If they are taller  maybe they are sticking up  to high?

> The canard VGs have me baffled. Why are they needed at all?? Don't I
> want the canard to stall first anyway? Looks like way too much drag
> for minimal gain as far as the canard is concerned. Tom
I had thought the factory established  the placement to maintain the
ratio of lift between the canard and the main wing.  Which would seem
optimal  to me.   This would maintain elevator placement at cruise, 
reduce the rotation speed at takeoff, etc..    If you don't have VG's on
the canard, your takeoff roll length would be mostly unaffected.

Scott

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