rotating wingtips?

[MCarlton]

I had a thought some time ago, and often wondered if it would work to reduce wingtip vortices. As you know, I am an aerodynamic bungler at best :)

Imagine a cylinder were mounted at a wingtip, with its axis of rotation fore/aft, with half the cylinder inside a fairing somewhat similar to a shrouded control surface.

Now imagine, mounted to that, spirally mounted small vanes, somewhat similar to stator vanes, which are hinged and sprung to allow them to fold flat against the cylinder in the opposite sense to the rotation of the cylinder so that when the cylinder rotates, they "pop" out.

The apparatus could either be rotated by a motor or allowed to freely rotate in the airstream, I was contemplating it being rotated in the opposite sense to the vortices, and imagining it might straighten the vortices?

Its just something I had in my head for a long time, and was never able to really model its potential effects.

Any ideas anyone?

[JetPlaneFlyer]

If you let it freewheel then the cylinder would spin in the direction of the vortex and do nothiing to reduce the vortex.. If you powered it such that it rotated opposite to vortex direction and it cancelled out the vortex (even if it were possible) then the energy you had to input into driving cylinder would even in a 100% efficient system be equal to the energy of the vortex itself. In reality accounting for losses the input energy would actually be much greater.. Then you have the added weight and profile drag of these cylinder devices stuck out there on the wingtips

So where does this energy to drive the cylinder come from? Maybe a battery or fuel of some sort?.. It would be far more efficient and practical to use battery or the fuel to drive a propeller and power the plane in the conventional way.

steve

[MCarlton]

I hadn't really thought through the practicalities to be honest, I was just bouncing an idea around in my head. Sometimes my ideas make sense, sometimes they don't, but as I don't claim to be an expert, or even marginally knowledgeable, I feel a bit more free to think sideways about things.

[bwalt822]

Numerous types of wintip devices have been tested including feathered looking tips like a bird and hoops. Do a google search and im sure lots of interesting things will pop up.

http://www.flightglobal.com/articles/2009/05/27/326996/aviation-partners-targets-later-summer-for-second-generation-spiroid.html

[eflightray]

Perhaps not quite what your thinking of, but here's an interesting 'rotating wing tip', scroll down a bit to see the picture.

Short Sherpa flying wing (http://en.wikipedia.org/wiki/Short_Sherpa)

[Brandano]

Ever wondered why both the V22 and the Flying Flapjack (http://www.daveswarbirds.com/usplanes/aircraft/flapjack.htm) have the lower portion of the prop spinning inwards? From a safety point of view it's a bad choice, objects can be picked from the ground and thrown into the fuselage, not to mention that prop blades shed in a crash landing would definitely slam into the fuse. But having the pops spinning in the opposite direction of the induced drag vortexes increases the pressure differential significantly, and allow for a smaller wing with consequent lower skin drag and better low altitude stability in gusty conditions. this does not reduce induced drag, though. I suspect that the vortexes behind the plane will still form, perhaps a bit delayed, but probably have more energy in them. At the end of the day the vortexes are a direct consequence of the pressure differential between the top and the bottom of the wing, you can't have lift without induced vortexes. The wing system I mean, please don't start another diatribe on Bernoulli against Newton. I think that strapping their caskets on the wingtips could be a good source of clean propulsion by now.

[mnowell129]

you can't have lift without induced vortexes.
on a finite wing

[JetPlaneFlyer]

At the end of the day the vortexes are a direct consequence of the pressure differential between the top and the bottom of the wing, you can't have lift without induced vortexes.

You can have lift without vortexes.. A wing in a wind tunnel with it's tips sealed on the tunnel walls has no downwash and no vortexes but still produces lift. Also wing in ground effect (WIG) planes produce 'almost' no tip vortexes (if they fly low enough).

Steve

[Brandano]

The different pressure zones will eventually collapse and merge and this will create a vortex. In real world conditions the air in never smooth enough to just resume the original state as if it were a rubber mattress.An interesting side effect of this behavior is that the two vortexes behind the wingtips of large liners tend to merge in a single vortex further down, one of them switching direction. This single large vortex in the case of a 747 can persist for several minutes, and must be taken into account by the ATC whenever a small plane has to land after an heavy.

[bwalt822]

You can have lift without vortexes.. A wing in a wind tunnel with it's tips sealed on the tunnel walls has no downwash and no vortexes but still produces lift. Also wing in ground effect (WIG) planes produce 'almost' no tip vortexes (if they fly low enough).

Steve

A wing in a wind tunnel that spans the walls is just a section of an infinite wing though.

[MCarlton]

What about annular wings? Don't they provide lift without vortices?

[Brandano]

They try to, they ultimately don't

[vintage1]

The plural of vortex is vortices..gentlemen..Let's have some scholarship here. It's not the foamie forum after all.. :D :D :D

[wyowindworks]

The plural of vortex is vortices..gentlemen..Let's have some scholarship here. It's not the foamie forum after all.. :D :D :D

Both vortexes or vortices are acceptable. :) See this. (http://dictionary.reference.com/search?q=vortexes)

Wing vortices are a product of pressure differential between the top and bottom surface and downwash. Both of these could be eliminated by using wings that generate no lift.:D

[VeeOneRotate]

Interesting idea, why not just put the props on the wingtips rotating in the opposite direction of the vortices? The spiral slipstream might help to balance out the vortices, maybe...
Or you could just use wing fences and winglets to reduce spanwise flow like everybody else.

[JaRaMW]

Interesting idea, why not just put the props on the wingtips rotating in the opposite direction of the vortices? The spiral slipstream might help to balance out the vortices, maybe...

Structural strength considerations... and a roll rate penalty due to the mass at the wing tips.
This may not cancel the vortices, but I would expect the prop slipstream to shift the vortex formation more outwards, effectively increasing the wingspan.

[Flight Engineer]

Both vortexes or vortices are acceptable. :) See this. (http://dictionary.reference.com/search?q=vortexes)

Wing vortices are a product of pressure differential between the top and bottom surface and downwash. Both of these could be eliminated by using wings that generate no lift.:D

quintessentially correct but rather vulgar. I'm sticking with vortices.

[eflightray]

So......how about........... no wing tips ? :D

[VeeOneRotate]

Structural strength considerations... and a roll rate penalty due to the mass at the wing tips.
This may not cancel the vortices, but I would expect the prop slipstream to shift the vortex formation more outwards, effectively increasing the wingspan.

The way I understand it, putting the motors on the wingtips would reduce strain on the wing to fuse joints (in the air anyway, not on the ground). I have trouble putting the reason into words, but it's why airliners fill up thier wing fuel tanks before thier fuselage fuel tanks.

I think you're probably right about the vortices. Whatever happened, i don't think it would e pretty. Aynone got a wnid tunnel?

eflightray - Bingo! Problem solved!

[JaRaMW]

The way I understand it, putting the motors on the wingtips would reduce strain on the wing to fuse joints (in the air anyway, not on the ground). I have trouble putting the reason into words, but it's why airliners fill up thier wing fuel tanks before thier fuselage fuel tanks.

True... concentrating mass in the lifting surface reduces strain on the wing root fuse during flight. I was rather thinking of the strain on the wing tips when maneuvering.

[eflightray]

This picture of a C-17's wing tip vortices through the flare smoke is quite fascinating.

From the Wikipedea Wingtip Vortices (http://en.wikipedia.org/wiki/Wingtip_vortices)

A google on wingtip vortices seems to show quite a few patents have been registered.

[VeeOneRotate]

Thats a great link! I particularly like the photo of vortices forming on the tips of a prop.
There does seem to be a huge number of strange and fantastic ideas around for reducing wingtip vortices. I'm going to have to do some experimenting when I get back to the hangar (by hangar I mean my parents conservatory :p ).