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Ken.
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Posted: 09 October 2008 at 6:35pm | IP Logged Quote Ken.

Hi guys,
As a pilot (helicopters) I suggest a little caution on the wing tips. They are usually mounted on the end of fixed wing aircraft wings, not on the props'.
There are engineering problems associated with wingtips too, the extra lift puts greater stresses on the wing tips and overall. I've never seen wingtips put on props', There could well be a good reason and add to that the fact that these are "driven" props as opposed to "driving" props'. opens up a can of worms...I'd love to hear from an Aero' engineer on that one... A great idea to let the people at the forefront of this stuff decide what they want though!...Now about designing VAWT blades LOL

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Gill
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Posted: 09 October 2008 at 8:04pm | IP Logged Quote Gill

Yes Ken, I agree. This subject arose some time ago so I won't re argue my case against them again. The proliferation of winglets on commercial wind generators is a good indication of their application.

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Posted: 09 October 2008 at 8:44pm | IP Logged Quote Jarbar

Ken on the subject of Helicopters did you see the twin opposing rotor design on the New Inventors last night.It had adjustable wing tips that gave rotational control to the helicopter body.Instead of the usual tail mounted rotor.You need to download the whole program to see the explanation of their use.As it not shown in the demo video.As for windmills surely it would encourage less air flung off the end of the blade and reduce the vortex at the tip.One commercial model has a ring joining all three blades at the tip.

Anthony.

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oztules
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Posted: 09 October 2008 at 9:59pm | IP Logged Quote oztules

Wing tips....

This came up a day or so on otherpower in response from ULR on the AWP blades we hacked up with a chainsaw......


Quote:

" Re: Blades from scratch for the AWP (3.00 / 0) (#8)
by Ungrounded Lightning Rod on Wed Oct 8th, 2008 at 06:40:52 AM EADT
(User Info) [Edit User]

1.4 KW fully furled (1.2 KW or so usable after battery storage) is sweet.

Bringing the tips down to an edge may improve the performance by throwing the tip vortex farther out, reducing the depowering of the outer half-foot or so by air running around the end of the blade.

(I'd once thought of screwing a "wingtip" airfoil onto the end of the blade to block the run-around air, ala the "wing keel" used on shallow-draft sailboats to make a short keel act like a long one (as long as you aren't listing too badly) That would be a piecewise approximation of a ducted fan. But a NASA design document implies that you can get much of the advantage of that, with far simpler construction, by making the tips knife-edged. Which brings up the question of why wing keels work better on boats. B-) Maybe it's because, with the knife edge, you're reducing the loss of the low-pressure on the downwind side but you still lose the high pressure on the upwind side. But intuitions about fluid dynamics are notorious for being faulty.)"



.........oztules

Edited by oztules on 09 October 2008 at 10:32pm


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MadRat
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Posted: 09 October 2008 at 10:26pm | IP Logged Quote MadRat

U.S. patent # 6578798 covers the idea. It's strange that a concept that has been out since the 50's would receive a patent in 2003!?

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GWatPE
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Posted: 09 October 2008 at 10:36pm | IP Logged Quote GWatPE

I would expect that any differences would be related to effects seen with air flow with laminar flow and that with turbulent flow over the blade surface. This will be reynolds number dependent. Fluid dynamics is a tricky science. Relative surface roughness and fluid velocity play a significant part in the type of flow over the surface.

I have tested tiplets on model aeroplane wings, and the effect was similar to having a longer wing without the associated drag. The wing produced the same lift at a slightly lower airspeed.

On a windmill, the effect may be to extract more power from the wind, but at the expense of the tsr. The alternator and blade may need to be redesigned for operation at a higher rpm. The blade may appear to extract more power from the wind, but the change in tsr may erase this benefit. Extensive wind tunnel testing may be required as the difference may be minimal.

I expect that if there would be a benefit, that tiplets would be used on MW windmills already. None of the windmills of this size down the road from me have tiplets.

Gordon.


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oztules
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Posted: 09 October 2008 at 11:18pm | IP Logged Quote oztules

Gordon,

I'd go with the flow.... if the big boys don't use em, then I see no reason to do it either.... money where their mouth is so to speak.

I have enough difficulty getting a tenuous grasp on it as it is..... I don't need further complications of questionable worth....so it is simple twist, simple taper, and the hack blades work better than the beautifully shaped AWP originals...(huge root, sculptured curves and all) not sure how or why, they just do.


Gizmo,
Are these extrusions solid plastic? If so I may have an idea for them Re extrude - single pass cnc, and end up with the Danb profile.... or do you want the concave front for some reason?... (strength?)



........oztules

Edited by oztules on 09 October 2008 at 11:40pm


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Ken.
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Posted: 10 October 2008 at 7:55am | IP Logged Quote Ken.

Jarbar wrote:
Ken on the subject of Helicopters did you see the twin opposing rotor design on the New Inventors last night..One commercial model has a ring joining all three blades at the tip.

Anthony.

Hi anthony, no I didn't catch the new inventors There are several very different designs out there these days. Most of them are for specialist jobs like lifting. The K'MAX is a good example. A nightmare to fly but Awesome for lifting. The problem with Heli' blade design is that there are 3 quite different flight modes, Hover, Forward flight(Translation)and Autorotation. The blades must perform well in all of them. Wingtips in the hover would work great but in fwd flight would create obvious problems. But this is a wind power forum and not a pilots forum so we should stay on subject in the hope of coming up with the most efficient mass produced blade we can At least wind genny blades only have one mode to contend with so this should be easy considering the calibre of members and their experience on here. I'll dig out my old aerodynamics books and see if I can learn something about Autorotatioanl flight that might help. (Unlikely)

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sodes
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Posted: 10 October 2008 at 9:49am | IP Logged Quote sodes

Hi all just reading this article jogged my memory as I was sure I'd seen a wingtip on a prop on some ultralights somewhere. This prop is called the windspoon and is made of carbon fibre and is said to be a very efficient and quiet design would be great to trial a prop just to see how it'd perform, they make these ground adjustable at the hub as well. They're a nice piece of work though! Heres a link http://www.duc-helices.com/anglais/windspoon.htm

Sodes




Edited by sodes on 10 October 2008 at 9:52am


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Posted: 12 October 2008 at 12:59pm | IP Logged Quote domwild

Ken,

From memory, I posted a link or picture of a large mill with Rutan/Boeing tips on fieldlines.com some time back. So they do get built that way. It looked like a one to two Meg monster mill to me.

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Ken.
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Posted: 13 October 2008 at 7:34pm | IP Logged Quote Ken.

Hi Dom,
I havn't seen the pics. Please don't get me wrong...I'm not against the idea of wingtips!
I only made the comments to exercise caution with them. The engineers thet designed the big ones you speak of spent a long time testing the aerodynamics in wind tunnels with a bunch of guys in white coats and thick glasses who live and breath this stuff to work it out exactly. None of us have access to the same level of technology.(or R+D funding)
I'm all for people "having a go". Can you imagine the guy who first took his drawings of a helicopter to the boss and said "Mate..I think it'll fly"...He musta had balls as big as watermelons!....(excuse the language)

But it takes "risk takers" to make advancements. It's just if you're going to make a production model blade, it should be a tried and true design to the best of our abillity..not an experiment.
Cheers

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Posted: 16 October 2008 at 4:29am | IP Logged Quote SparWeb

Winglets are fine, even for wind turbines, but don't imagine that nobody's thought about this before! A large amount of research has been done on aircraft propellers, wind turbine propellers, helicopter rotor blades, and all sorts of other rotating-wing machines and no doubt the effect of the tip is of interest in each case.

US Langley Technical Reports
NACA Technical Reports
NASA Technical Reports
Danish Wind Research Laboratory
US military STINET
NREL National Renewable Energy Laboratories

Don't reinvent the wheel. Read up and you will find the answer.

Then again, you can't tell everybody "it's been tried before", they just want to try for themselves.

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