REFLECTOR: VG's

[Mark Magee]

Hi Lawrence,
You are entirely correct. The factory utilized vortilons to fix the majority of these issues in the Velocity. Mine are installed. These effectively straighten out lateral airflow toward the winglets at slow flight with virtually no drag penalty. Vortilons are the factory's solution (actually from Rutan) to slow flight problems of the laminar flow washing out laterally and greatly reducing aileron effectiveness in slow flight.
This is all well tested in the Variviggen, Varieze, Defiant and Long EZ well before all our Velo derivatives. Some folks apply trailing edge fences near the ends of the ailerons which greatly increase aileron authority at slow fight, I think they look funky.
A few VG's here and there (not discussing for cooling: only aerodynamics) IMO is acceptable. Applying them en masse on the upper surface of the main wing changes the aerodynamic profile of the entire wing. As John A mentioned, the only logical reason to do that is a serious modification to the airframe such as a markedly heavier engine grafted in, requiring markedly greater lift. Maybe the addition of a substantial belly tank Ect.
OTW I never second guess the designer(s). Large arrays of VG's change the designers design into something they did not design! You get to write the manual on that design... Actually large arrays of VG's are kin to a STOL kit for a Velocity. Look at some of the Cessna's out on the ramp, STOL kits for some of those Spam Cans are arrays of VG's probably the leading edge.
A STOL kit for a Velocity?

Mark Magee
N34XL XLFG 300 HP 80 hrs
Brady TX

"Texan by birth, Canardian by choice."



Mark B. Magee
Sent from IPhone 4

On Jun 8, 2012, at 3:53 AM, Lawrence Epstein <ljepstein at hotmail.com> wrote:

> The fact is, (on even the best designed wing) laminar flow is only present for a part of the wing. at some point, the flow separates and becomes turbulent anyway. When this happens, there is no (much less) airflow over that part of the wing that is downwind. If it happens to be the part that includes the aileron or elevator, you lose effectiveness of that control surface.
> Properly placed VG's don't decrease (by much) the wing area that "sees" laminar flow (in fact, may increase), they cause a local turbulence"just ahead" of where the flow would have separated anyway. That turbulence causes a local low pressure which "pulls" the airflow back down to the surface of the wing (where you may get a return to laminar flow) and thereby increases the efficacy of the control surface (or the net lift of the wing). 
> 
> Some VG's can actually decrease the induced drag of the wing.
> 
> 
> 
> On Thu, Jun 7, 2012 at 4:41 PM, Mark Magee <edjonesbrady at gmail.com> wrote:
> All,
> I think David frames the problem properly from the original thread (italics added):
> -------------------------------------------------------------------------------------------------------------
> On 6/6/2012 11:06 PM, David Ullman wrote:
> I now have about 27 hours on 444DX.  Getting things sorted out.  I have been
> to 10,500 ft and over 200kts (in a dive).  I have done both low and power-on
> mushes.  I cant call them stalls as it doesn't.  Around 50 kts it just
> mushes.  I still have roll and yaw control all the way down.  Overall the
> plane is very easy to handle at any speed.  I hate the thought that this may
> be due to the vortex generators.  I just cant intellectually get past the
> fact that I have put vortex generators on a laminar flow surface.
> 
> --------------------------------------------------------------------------------------------------------------
> 
> I can't either. A laminar flow surface and wings are designed to -avoid- turbulent flow of all types, particularly vortexes.
> One reason they go so fast. 
> In my mind applying VG's to a Velo is like the old F-4's flying around full throttle with the drag chute deployed in flight.
> 
> Mark
> 
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