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Canard planes swept wing outer VG's?



 
 
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  #1  
Old December 11th 03, 08:55 AM
Paul Lee
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Posts: n/a
Default Canard planes swept wing outer VG's?

I have the copy of the CAFE test of Cozy Mk IV canard where it states
that swept wings tend to start stalling at the tip rather than the root.
This moves the center of lift forward and is a bigger problem for aft
CG.

While canard planes swept wings typically already have those
"vortilon" tabs, has anyone investigated placing a few vortilons near
outer wing part to compensate for the early tip stall tendency?

I am talking about the main swept wing of a typical canard and not the front
canard wing itself.

----------------------------------------------------
Paul Lee, SQ2000 canard project: www.abri.com/sq2000
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  #2  
Old December 11th 03, 07:20 PM
David Lednicer
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I have the copy of the CAFE test of Cozy Mk IV canard where it states
that swept wings tend to start stalling at the tip rather than the root.
This moves the center of lift forward and is a bigger problem for aft
CG.


By the very nature of a canard configuration, if the aft wing stalls,
the tip will stall first, as it it in the upwash caused by the tip
vortex coming off the canard. The inboard part of the aft wing is in
downwash from the canard. With that said, the aft wing of a canard
aircraft should NEVER be allowed to stall. If it does, the neutral
point will shift forward and the aircraft will become longitudinally
unstable. The idea is for the canard to stall first. This makes the
airplane more stable and causes the nose to pitch down.

While canard planes swept wings typically already have those
"vortilon" tabs, has anyone investigated placing a few vortilons near
outer wing part to compensate for the early tip stall tendency?


The vortilons are always placed on the outer part of the aft wing of a
canard configured aircraft, to keep the outer aft wing from stalling.
There is no sense on placing them on the inboard wing, unless the
aircraft is really screwed up.

On early VariEzes, it was found that the outboard portion of the aft
wing, of poorly built aircraft, would stall. Rutan retrofitted a cuff
on the outboard aft wing, to prevent this stalling.

  #3  
Old December 12th 03, 12:52 AM
Paul Lee
external usenet poster
 
Posts: n/a
Default

I know about what should be about CG and main wing should
not be allowed to stall, etc. etc. But my question is about
possible further improvement.

I mistyped the last sentence question.
"..has anyone investigated placing a few vortilons near
outer wing part to compensate for the early tip stall tendency?.."

Should have been
...has anyone investigated placing a few vortex generator tabs near
outer wing part to compensate for the early tip stall tendency?

I am talking about the popular small VG tabs on top of the wings.
And if a few could be placed near the last 1 or two feet of the outboard
wing part to improve wing stall. The usual vortilon tabs used on swept
wings are not really on the extreme part of wing outboard but rather almost
mid wing.

Inboard (imagine wing sweep)
---------------------------------------------------------------

/ \ / \ - extra VG's
---------------------------------------------------------------
| | | - current vortilons



David Lednicer wrote in message ...
I have the copy of the CAFE test of Cozy Mk IV canard where it states
that swept wings tend to start stalling at the tip rather than the root.
This moves the center of lift forward and is a bigger problem for aft
CG.


By the very nature of a canard configuration, if the aft wing stalls,
the tip will stall first, as it it in the upwash caused by the tip
vortex coming off the canard. The inboard part of the aft wing is in
downwash from the canard. With that said, the aft wing of a canard
aircraft should NEVER be allowed to stall. If it does, the neutral
point will shift forward and the aircraft will become longitudinally
unstable. The idea is for the canard to stall first. This makes the
airplane more stable and causes the nose to pitch down.

While canard planes swept wings typically already have those
"vortilon" tabs, has anyone investigated placing a few vortilons near
outer wing part to compensate for the early tip stall tendency?


The vortilons are always placed on the outer part of the aft wing of a
canard configured aircraft, to keep the outer aft wing from stalling.
There is no sense on placing them on the inboard wing, unless the
aircraft is really screwed up.

On early VariEzes, it was found that the outboard portion of the aft
wing, of poorly built aircraft, would stall. Rutan retrofitted a cuff
on the outboard aft wing, to prevent this stalling.

  #4  
Old December 12th 03, 08:17 PM
Peter Dohm
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Posts: n/a
Default

My recollection, from an aerodynamics class long ago, is that the tendency
of a wing to stall first at the tip and progress inward is not a function
of sweep. The sweep just makes it LETHAL.

Assuming that the wing has no twist, also known as wash-out, and that the
wing is well constructed and finished; then:
1 A straight (Hershey Bar) wing will stall from the root outward.
2 An elliptical wing will stall all at once.
3 A radically tapered (2:1) wing will stall from the tip inward.
4 A moderately tapered wing will approximate an elliptical wing.

The earlier comment regarding the canard vortex on the Vari-Eze is an
excellent note of caution, as it will tend to simulate reverse wash-out
of the main wing. Therefore, it the main wing was ever allowed to stall,
it could be expected to do so in the manner of a wing with a much more
radical taper ...

BTW, radically swept tapered wings have the reputation of being impossible
to recover from a stall -- if you allow it to occur!

Peter

Paul Lee wrote:

I know about what should be about CG and main wing should
not be allowed to stall, etc. etc. But my question is about
possible further improvement.

I mistyped the last sentence question.
"..has anyone investigated placing a few vortilons near
outer wing part to compensate for the early tip stall tendency?.."

Should have been
..has anyone investigated placing a few vortex generator tabs near
outer wing part to compensate for the early tip stall tendency?

I am talking about the popular small VG tabs on top of the wings.
And if a few could be placed near the last 1 or two feet of the outboard
wing part to improve wing stall. The usual vortilon tabs used on swept
wings are not really on the extreme part of wing outboard but rather almost
mid wing.

Inboard (imagine wing sweep)
---------------------------------------------------------------

/ \ / \ - extra VG's
---------------------------------------------------------------
| | | - current vortilons

David Lednicer wrote in message ...
I have the copy of the CAFE test of Cozy Mk IV canard where it states
that swept wings tend to start stalling at the tip rather than the root.
This moves the center of lift forward and is a bigger problem for aft
CG.


By the very nature of a canard configuration, if the aft wing stalls,
the tip will stall first, as it it in the upwash caused by the tip
vortex coming off the canard. The inboard part of the aft wing is in
downwash from the canard. With that said, the aft wing of a canard
aircraft should NEVER be allowed to stall. If it does, the neutral
point will shift forward and the aircraft will become longitudinally
unstable. The idea is for the canard to stall first. This makes the
airplane more stable and causes the nose to pitch down.

While canard planes swept wings typically already have those
"vortilon" tabs, has anyone investigated placing a few vortilons near
outer wing part to compensate for the early tip stall tendency?


The vortilons are always placed on the outer part of the aft wing of a
canard configured aircraft, to keep the outer aft wing from stalling.
There is no sense on placing them on the inboard wing, unless the
aircraft is really screwed up.

On early VariEzes, it was found that the outboard portion of the aft
wing, of poorly built aircraft, would stall. Rutan retrofitted a cuff
on the outboard aft wing, to prevent this stalling.

  #5  
Old December 14th 03, 12:27 AM
Paul Lee
external usenet poster
 
Posts: n/a
Default

Peter,

That is certainly nice iformation to know.

But back to my original question - to help the situation.

"..has anyone investigated placing a few vortilons near
outer wing part to compensate for the early tip stall tendency?.."

This could be done with a standard EZ by observing if the bobing stall
frequency increases with addition of a few outboard vortex generators.

Any EZ volunteers out there? Here is the procedu Measure the stall
bobing frequency as a position of CG. Then measure it again after
the few outboard VG's are installed and see if the frequency increases
or decreases with CG position. Would not be very expensive, just time
consuming.

I am building a SQ2000 canard but KLS Composites has designed
the thing so that there is no bobing stall frequency - it simply descends
at a constant rate. KLS demonstated that to me in their factory bird.
So I can't do the test - at least in the same way.

----------------------------------------------------
Paul Lee, SQ2000 canard project: www.abri.com/sq2000

Peter Dohm wrote in message ...
My recollection, from an aerodynamics class long ago, is that the tendency
of a wing to stall first at the tip and progress inward is not a function
of sweep. The sweep just makes it LETHAL.

Assuming that the wing has no twist, also known as wash-out, and that the
wing is well constructed and finished; then:
1 A straight (Hershey Bar) wing will stall from the root outward.
2 An elliptical wing will stall all at once.
3 A radically tapered (2:1) wing will stall from the tip inward.
4 A moderately tapered wing will approximate an elliptical wing.

The earlier comment regarding the canard vortex on the Vari-Eze is an
excellent note of caution, as it will tend to simulate reverse wash-out
of the main wing. Therefore, it the main wing was ever allowed to stall,
it could be expected to do so in the manner of a wing with a much more
radical taper ...

BTW, radically swept tapered wings have the reputation of being impossible
to recover from a stall -- if you allow it to occur!

Peter
..

  #6  
Old December 14th 03, 05:56 AM
Paul Lee
external usenet poster
 
Posts: n/a
Default

Dang it... I copied the wrong question again... here is the correct stuff..

back to my original question - to help the situation.

...has anyone investigated placing a few vortex generator tabs near
outer wing part to compensate for the early tip stall tendency?

This could be done with a standard EZ by observing if the bobing stall
frequency increases with addition of a few outboard vortex generators.

Any EZ volunteers out there? Here is the procedu Measure the stall
bobing frequency as a position of CG. Then measure it again after
the few outboard VG's are installed and see if the frequency increases
or decreases with CG position. Would not be very expensive, just time
consuming.

I am building a SQ2000 canard but KLS Composites has designed
the thing so that there is no bobing stall frequency - it simply descends
at a constant rate. KLS demonstrated that to me in their factory bird.
So I can't do the test - at least in the same way.

----------------------------------------------------
Paul Lee, SQ2000 canard project: www.abri.com/sq2000
  #8  
Old January 3rd 04, 06:39 PM
J&D Kahn
external usenet poster
 
Posts: n/a
Default


"Neal Fulco" wrote in message
m...
(Paul Lee) wrote in message

. com...
Dang it... I copied the wrong question again... here is the correct

stuff..

back to my original question - to help the situation.

..has anyone investigated placing a few vortex generator tabs near
outer wing part to compensate for the early tip stall tendency?

This could be done with a standard EZ by observing if the bobing stall
frequency increases with addition of a few outboard vortex generators.

Any EZ volunteers out there? Here is the procedu Measure the stall
bobing frequency as a position of CG. Then measure it again after
the few outboard VG's are installed and see if the frequency increases
or decreases with CG position. Would not be very expensive, just time
consuming.

I am building a SQ2000 canard but KLS Composites has designed
the thing so that there is no bobing stall frequency - it simply

descends
at a constant rate. KLS demonstrated that to me in their factory bird.
So I can't do the test - at least in the same way.

----------------------------------------------------
Paul Lee, SQ2000 canard project:
www.abri.com/sq2000



Not an answer to your question, but would someone educate me
here....Just how do those "vortilons" on the outer portion of the main
wing inhibit the stall on that portion of the wing? I see them all
the time on the EZ's but I don't know how they work. Thanks

Neal



A vortilon delays detachment of the airflow and therefore increases stalling
AOA and improving airleron effectiveness, by creating vortices along the top
surface that mix free stream air in with the turbulent boundry layer air.
Same as the small vortex generators that are popular on top of leading
edges. However a vortex generator array on top of the leading edge produces
vortices all the time and the vortices are small.

Vortilons poduce much larger and stronger vortices but only at high AOA
because of the low position on the LE (the stagnation point has to move down
to below where the vortilon is). At low AOA the vortilon is mostly just a
fin sticking out in the underwing flow and has a minimal drag penalty. As
AOA increases the vortilon ends up above the stagnation point, and is now in
the upper flow stream, and functions as a big VG. Vortilons work best with
a lot of natrual spanwise flow at high AOA so they can produce vortices
without being angled into the airstream (and resultant drag penalty at low
AOA), which means swept wing a/c.

The Embraer 145 has vortilons that were added during certification, a
classic post-design aerodynamic band-aid to deal with tip stall problems,
same as the EZ.

John


 




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