REFLECTOR:Vortex Generators on XL

[Jim Sower]

Was said:

> 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.

GU canard moisture curing VGs are IIRC waaay aft, at maybe 50% or 60% of chord.
My VGs are placed to ensure they are forward of where the flow separates so as to best
energize it.

> This is not the same placement that the factory established for
> generating extra lift from both wings for the standard velocity.

What, precisely, is the "factory established" placement?  20%? 25%? 30%?
Over the years, I have heard any number of positioning schemes.  Most folks had some
anecdotal evidence justifying their particular scheme.  Some had some science.  Some
had nothing much at all.  Often it was difficult to tell who had what so I decided to
go with what made the most sense to me.

The first time out, I made mine wedge shaped (for no other reason in the world than
that's what everyone seemed to be doing) and positioned them at 25% chord since that's
where convention puts the Aerodynamic Center.  Made sense to me and satisfied my level
of aeronautical engineering background.
I have no clue as to the quantity or quality of engineering that went into the
"factory" setup.  Can anyone help me out on that?  My placement seemed to work.  I was
satisfied, particularly since I didn't have a lot of resources invested in it and
could change it any time I wanted at very little cost.

> Just sticking um anywhere won;t work right?

Sort of.  Anywhere within reason will work.  I regard "within reason" as 20% - 30% MAC

> Thats why you followed Jim P's lead.

Sort of.  As best I could discern, Jim P. was pretty much the undisputed VG champion
with the best credentials and experience of anybody I've heard of.  What he said made
sense to me.  As I said in my earlier post, I thought 20% should be only very
marginally different from 25%, and square only very marginally better than round.  But
I'd already decided that when Jim P is talking, Jim S needs to be listening, so I did
it.  Not surprisingly, his stuff worked better.

> 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.

I suppose you could say that.  I would prefer something specific.  Unsupported
generalities are of no particular value to me.

> This would change the designed
> lift ration and possibly allow a person to deep stall his airplane.

Under some unspecified circumstances that might well be the case.  Again, unsupported
generalities ....

> I really don't know if this would do it,

Get back to us when and if you have something to support your suspicion

> 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,

The possibility is always there.  For likelihood we need supporting evidence ....

> until someone proves otherwise.

Am I now supposed to prove a negative??

> >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,

How much and by whom?

> 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?

If there is a report somewhere detailing their tests and analysis, and outlining
precisely why they adopted this placement scheme and rejected that one and that one
and that one I would be very interested in reading up on the subject.

> >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.

>From some post on this thread.  I carefully selected the most outrageous price :o))

>  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.

Mine are also proven (to my satisfaction).  Outlasting the airplane was not a design
criteria.

> 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.

Agreed.  I spent a lot less time making mine than I would have spent finding out where
to get yours

> 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.

You didn't.  I felt you were coming at me with a bunch "suppose this" and "suppose
that" that was not backed up by much that I could determine in the way of science.  So
I yanked your chain a little.  Hope I didn't piss you off :o)

> Moving the aerodynamic center is what you are trying to minimize. Moving it forward
> is
> the worst direction I think?

True
Moving it back would make takeoffs longer and the canard would stall at a lower speed,
right?
It would make takeoffs longer, landings faster because the canard would stall at a
*higher* speed.
Moving it forward  would allow much easier rotation and possibly allow a main wing
stall.
Agreed.

Though as I said above it would recover naturally so  its not a deep stall as I said
on my first email.
I'll need some help on this one.

> >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.

Are you sure about that?

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

[P]ole [V]aulting [O]ver [R]at [T]urds

> Jim I wasn't trying to rag on your parade.

You didn't

> 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?

I don't think the "lift ratio" is all that sensitive to VG placement schemes if you
try and maintain some reasonable level of symmetry between canard and wing (like both
at same chord position, both in same pattern).  I would guess that VGs placed with
modest attention to aerodynamic effect would have less impact on AC than non-standard
pilots have on CG.  Like operating manuals I've seen provide an FS at which the weight
of pilot, co-pilot, etc. can be said to act.  I've discovered that lighter pilots
actually do fit that "standard" pretty well, but with the heavier folks (like moi :o)
the pilot weight acts at a FS quite different (like a couple of inches forward) of
what the manual suggests.  When computing CG, I've got to where I ignore the "school
solution" FS of pilot weight and climb into the airplane, weigh it with ME in it,
dressed like I do when I fly and compute what the moment arm is.

> Scott

Actually, as much fun as this back-and-forth is, we might best take it off line and
not clutter up the list any more with stuff that's pretty much all been said ...  Jim
S

>
>
> _______________________________________________
> To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector
>
> Visit the gallery!  www.tvbf.org/gallery
> user:pw = tvbf:jamaicangoose
> Check new archives: www.tvbf.org/pipermail
> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html

--
Jim Sower
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T