REFLECTOR:Vortex Generators on XL

Scott reflector@tvbf.org
Fri, 05 Dec 2003 14:15:17 -0700


>Not sure what you mean by "messed up".  I did not alter either the main 
>wing or the
>canard other than to install VGs.  Jim Price (who is the best authority 
>available to
>us on the matter) discussed with me how he did his, and why he did them 
>the way he
>did.  I followed his lead.

There is a ratio of lift between the main wings and the canard.  Say 20/80 
respectively just for grins.

Now the placement of the VG's will effect how much "extra" lift they will 
impart to the flying surface.  Some places will give no extra lift, as the 
placement for the GU canard to cure the loss of lift in visible moisture 
does.  This is not the same placement that the factory established for 
generating extra lift from both wings for the standard velocity.

Just sticking um anywhere won;t work right? Thats why you followed Jim P's 
lead.

So it would be possible to install the VG's on the Canard as to impart 
maximum lift, and then install them on the Main wings and not get the same 
ratio of lift as you got on the canard.  This would change the designed 
lift ration and possibly allow a person to deep stall his airplane.  I 
really don't know if this would do it, cause I don't know how sensitive the 
center of lift is and how much the VGs could change it.  But we all know 
the possibility is there, until someone proves otherwise.

>If one were to install VGs on the wing or canard and not the other, it 
>might "mess up"
>the "lift ratio".  I used the same VGs in the same pattern and location on 
>both
>surfaces.  No reason to believe that would "mess up" anything.

I installed my VG's on my canard and main wings using the Factory 
templates.  These came about by some engineering and rail an error on the 
factory prototype, until they felt they had achieved a lift that maintained 
the design ration.  The spacing, placement and pattern are not the same on 
my canard and main wings per the factory templates.  So I wonder what if 
your placement is doing the same thing(lift ratio) mine is?

>BTW, do you know how the guys selling them for a buck a pop "establish" 
>that they
>aren't "messing up" anything?  I'd bet dollars to doughnuts they don't 
>have *near* as
>good science *or* experience in the matter as Mr. Price.

I don't know where you can get the Buck a Pop VG's.  I paid $.050 a piece 
and glued them on right out of the bag.  Certainly more than you paid for 
yours, but They are proven, and most likely will out last the airplane.  I 
also didn't need to make them, time is money.  I appreciate a savings 
though and will certainly consider your HomeDepot VG's when I need to do 
another airplane.

CCI doesn't supply a template for the Velocty, they do supply one for the 
GU Canard for the loss of lift problem.  I don;t think they supply any 
templates but that one which was released by Rutan in the public domain.

>And, of course if I have NOT added more proportional ..... than .... I 
>have NOT set
>myself up for a damned thing.  Price said *nothing* that might indicate 
>that VGs on
>both surfaces shift the Aerodynamic Center forward.  I'll have to go with 
>his analysis
>unless you have something compelling and credible.

I wasn't trying to piss you off but it appears I did. Sorry.  Moving the 
aerodynamic center is what you are trying to minimize. Moving it forward is 
the worst direction I think? Moving it back would make takeoffs longer and 
the canard would stall at a lower speed, right?.  Moving it forward  would 
allow much easier rotation and possibly allow a main wing stall.  Though as 
I said above it would recover naturally so  its not a deep stall as I said 
on my first email.

>I've no idea what you're talking about here.  Is "forward flow" from 
>trailing edge
>toward leading edge?

I wasn't clear, I meant air flow generated by forward speed, so when the 
speed dropped below a certain point the VG's would become ineffective thus 
restoring the No-VG type airflow.

I think once again we find ourselves P-V-O-R-T.  Like the proverbial 
ten-cent tail
>wagging the forty-dollar dog.

PVORT??

Jim I wasn't trying to rag on your parade. I initially thought you were 
installing these on an XL, so I wondered how you came up with the placement 
to maintain the lift ration?

Scott