Another speculative thread - adding forward sweep to solve CG problems

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bhooper360

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Wing tip vortices might have a different point to this conversation ?


I found this sentence incomprehensible, and I am irritated. First of all, wing tip vortices are not people but mere physical phenomena , so they cannot contribute to a conversation. And furthermore, you don't say, "have a different point"; you say "add a different point" or "have a different view."

Grammatical nitpicking aside, your one-sentence post basically just related Topic A to Topic B, and put a question mark at the end. You didn't put much effort into formulating an actual question, so it's impossible to know how to address the topics or to understand what the intent would be. For starters, what actual topics did you even want the discussion to address? The post you're referencing states that the most notable characteristics of a design were related to its power system. You basically said, wing tip vortices, then you linked a boldmethod (yuck) article about aspect ratio. So, uhm... huh???

Anyway, there are factors things besides sweep angle that influence the extent of the tip vortices. It all factors into an optimization problem which is context-specific, and includes other factors like strength.

By the way, would you please do me a huge favor and set up a firewall rule to block any traffic pertaining to boldmethod? If you ever find yourself with excess free time and brain cells, you could always try aviation stack exchange.
 

WonderousMountain

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Wing tip vortices might have a different point to this conversation ?

Upwash, caused by the airfoil leading edge, along with downwash at
trailing edge may contribute to deteriorative effects, yet mild sweep
in the forward direction has tendancy to fight inflow, so no real issue.
 

Sraight'nlevel

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I found this sentence incomprehensible, and I am irritated. First of all, wing tip vortices are not people but mere physical phenomena , so they cannot contribute to a conversation. And furthermore, you don't say, "have a different point"; you say "add a different point" or "have a different view."

Grammatical nitpicking aside, your one-sentence post basically just related Topic A to Topic B, and put a question mark at the end. You didn't put much effort into formulating an actual question, so it's impossible to know how to address the topics or to understand what the intent would be. For starters, what actual topics did you even want the discussion to address? The post you're referencing states that the most notable characteristics of a design were related to its power system. You basically said, wing tip vortices, then you linked a boldmethod (yuck) article about aspect ratio. So, uhm... huh???

Anyway, there are factors things besides sweep angle that influence the extent of the tip vortices. It all factors into an optimization problem which is context-specific, and includes other factors like strength.

By the way, would you please do me a huge favor and set up a firewall rule to block any traffic pertaining to boldmethod? If you ever find yourself with excess free time and brain cells, you could always try aviation stack exchange.


Sorry..I had no idea wing tip vortices are not real people...my bad.
 

Sraight'nlevel

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Upwash, caused by the airfoil leading edge, along with downwash at
trailing edge may contribute to deteriorative effects, yet mild sweep
in the forward direction has tendancy to fight inflow, so no real issue.


I always tought wing tip vortices can be dealt with by just adding forward sweep.
 

Riggerrob

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Sorry..I had no idea wing tip vortices are not real people...my bad.

"Paging Doctor McWhorter! Paging Doctor McWhorter!"
Professor John McWhorter is a professor of linguistics who wrote the textbook "Words on the Move" about how word meanings and usage change over time.
 

User27

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The basic reason for sweeping glider wings forward is to get the CG in the correct place in a 2-seater. Without sweep forward the CG would be too far forward, or the rear seater would be sat between the wings unable to see anything and making the structural joint of the wing spars difficult. I would guess than any aero benefit is a lucky side effect.
 

Sraight'nlevel

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The basic reason for sweeping glider wings forward is to get the CG in the correct place in a 2-seater. Without sweep forward the CG would be too far forward, or the rear seater would be sat between the wings unable to see anything and making the structural joint of the wing spars difficult. I would guess than any aero benefit is a lucky side effect.
Yes, but can it solve the wingtip vortices ?
 

Riggerrob

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Yes, but can it solve the wingtip vortices ?

I suspect that you need more than the 10 degrees of forward sweep to cancel wing tip vortices.
Bolkow Junior, Sisler Cygnet and most gliders haves 10 degrees or less of forward sweep.
Also remember that wing tip shape makes a huge difference in the size and shape of vortices: square versus rounded teardrop (ala. Cherokee) versus Hoerner versus up-swept Schumann, etc..
 

User27

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Yes, but can it solve the wingtip vortices ?
Its not possible to "solve" wingtip vortices! With no vortex there will be no lift...
It is possible to reduce the strength of the vortex, or make it work to your advantage (tip sails).
Forward sweep is usually destabilizing from an S&C perspective as the aero centre moves forward more than the CG (what a 2 seat glider wants), it is also structurally destabilizing as lift at the tip tends to twist the wing leading edge up which increases lift which increases twist, etc. So a forward swept will have to be stiffer (=heavier) than a zero sweep, or swept back, wing.
One of the X-planes had a lot of forward sweep, a rear set wing and a canard. I can't remember what the outcome was, but no-one has used that configuration for a production aeroplane.
Everything is a compromise, will the increase in drag from the increased weight be less than the drag reduction from the better control of the tip vortex? Can the design handle the reduced static margin/less good longitudinal handling, or increase in weight & drag from a larger HS to compensate? Few production aeroplanes use a forward swept wing, the conclusion must be most designers did not find it was overall a benefit.
 

Vigilant1

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Reynolds Number of 400.
 

Sraight'nlevel

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Holy Moses....vortices are still there ?

But it is a short aspect ratio wing ?
 
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Riggerrob

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What if you try something like a British Experimental Rotor Program (see Eh-101 Merlin and Cormorant helicopters)?
BERP has an extension to the leading edge that generates another vortex that rotates in the opposite direction from the tip vortex?
Say that you are examining a right wing tip vortex that rotates counter-clockwise (as seen from the rear), then what if you install a notch that generates a clockwise vortex a bit inboard of the wingtip. Will the counter-rotating vortexes cancel out each other?

Fixed wing examples include the bend in the leading edges of main wings on SAAB Viggen, Sukhoi 57 and HAL Tejas. They have shallow sweep to the their inboard leading edges, but steep sweep on their outer leading edges. The Sukhoi and Tejas add variable leading edge flaps. They are hinged a the rear and tilt leading edge down to increase lift for landings. The bend produces its own vortex that trails back across the top of the wing.

How do you tailor a wing bend, wing fence, wing slot, notch, dog's tooth, or other type of leading edge extension to generate a vortex close to the strength of the wing tip vortex? ... but rotating in the opposite direction??????

I am contemplating a test rig that starts like a tip tank on a Learjet. Then you bolt on various horizontal fins/slats to both inboard and outboard sides and photograph how the two vortices interact farther downstream???????

The 1945-vintage, low aspect-ratio, Vought Flying Flapjack claimed to cancel wing-tip vortices with propellers that rotated in the opposite direction of wing tip vortices.
The current production CV-22 Osprey tilt-rotor claims to do the same thing with outboard-rotating prop/rotors.

But I am thinking more in terms of passive, fixed, tailored leading edges to generate "counter-vortices." Did I just invent a new term???? Hah! Hah!
 
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User27

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Vortex theory says there must always be a ring of vortex if there is lift, so no vortex = no lift.
The vortex can be controlled but it cannot be cancelled out.
 

Sraight'nlevel

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Vortex theory says there must always be a ring of vortex if there is lift, so no vortex = no lift.
The vortex can be controlled but it cannot be cancelled out.
I bet it can be almost be eliminated and you still have enermous lift.

It is just structurally almost impossible to get any gain as it gets heavier ( the wing ).
 

Vigilant1

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Vortex theory says there must always be a ring of vortex if there is lift, so no vortex = no lift.
The vortex can be controlled but it cannot be cancelled out.
I bet it can be almost be eliminated and you still have enermous lift.
I'll take that bet.
Just build a 2D wing. NASA apparently does it for their airfoil performance diagrams, NACA apparently knew how to do it many decades ago, yet they won't release the secret to the public. I sense another conspiracy, like the still secret 200mpg carburetor and the 200,000 mile car tire. ;)
 
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