Author Topic: winglets  (Read 8148 times)

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bob golding

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winglets
« on: November 08, 2010, 04:04:46 PM »
i am servicing my turbine at the moment before the winter gales start to get too nasty. i need to redo the  leading edges. what do people use. araldite? i was reading the sandia article on tip shape and wondered what the current thinking on winglets is? is it worth the trouble or am i asking for problems when the blades hit a 80 mph gale. thinking if one flies off it will unbalance the other 2 bladeswhich will be a pain if nothing else.
if i cant fix it i can fix it so it cant be fixed.

Beaufort

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Re: winglets
« Reply #1 on: November 09, 2010, 12:28:11 AM »
I think the benefits of winglets are like the benefit for a nose cone for the rotor....minimal if any.  I haven't seen any numbers to show the overall benefit of winglets; if anything they present more drag surface area in the place where you don't want drag.  I don't know of any commercial products using winglets anymore; I think there was one years ago that used them in conjunction with brake deployment or something??  Others here would know.  It seems the consensus on the commercial side is to use a certain tip shape that is known to reduce vortices.  That area is a nice one to model and they've done just about all they can through tunnel testing and FEA models.   It's probably too complex to get perfect for a home-built, but some amount of uniform tapering does reduce noise compared to the standard chopped-off blade tips.  I can't vouch for a performance increase; my methods can't pick that out from the noise of other variables from one unit to the other.


DanG

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Re: winglets
« Reply #2 on: November 09, 2010, 07:53:32 AM »
Gizmag.com has written up a winglet-less vortex damper shown at this years Paris Air Show - looks like it might be fun to try and imitate...




From Enercon comes a generic (scale VERY distorted) design for their slow rotating turbines. At 132 feet long & 18.5 RPM maximum the tip is moving at 90mph.




Here is a helicopter rotor tip design used to add more stealth and a higher top speed to attack helicopters. Ignoring the knuckled leading edge I admire the slight roll-off to the winglet - something maybe the high speed RPMs of smaller HAWTs could benefit from, especially in gusty weather?



(I apologize I've lost the link to the site the helicopter picture belongs to, but I'm certain the blade has been written up many places. If anyone finds where I should attribute it to that will be promptly done - or even delete it if needed...)

SparWeb

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Re: winglets
« Reply #3 on: November 09, 2010, 04:18:09 PM »
Compare, for a moment the effect of adding 6 inches of length to the blade, versus 6 inches of winglet...

That's why winglets exist - to add an "effective" length to the tip of a wing or rotor, without actually increasing the span.  Hardly an important concern for us homebuilders, but really difficult when getting a Boeing 747 to park between airport gates 150 feet apart.

Gizmag.com has written up a winglet-less vortex damper shown at this years Paris Air Show - looks like it might be fun to try and imitate...

Another case of "proving" something with pretty FEA pictures but the real answer is in long lines of numbers.  I don't see anything in that diagram to make me believe that the wingtip tube is doing anything to reduce the vortex.  You can even see the lines curling around it, in fact.  That's a vortex being formed at the wingtip, and there's no way to know if the strength is more less or equal to that of the normal tip.

As for the chopper, lots have funny things on the tips.  That knee shape takes the cake though.  There could have mutual-interference effects between the panels, but there could be a benefit to the total blade.  That's from a Sikorsky S92.

From Wikepedia:

http://en.wikipedia.org/wiki/Sikorsky_S-92
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

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DanG

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Re: winglets
« Reply #4 on: November 09, 2010, 06:42:24 PM »
Your link defines the S-92 as four bladed rotor when the one included above is five, so much of a obvious five bladed rotor it seems you were more interested in flaming a timely informational post than in reporting any new content.

The S-92 entry did say "The four-bladed fully articulated composite main rotor blade is wider and has a longer radius than the Sikorsky S-70. The tapered blade tip sweeps back and angles downward to reduce noise and increase lift."

Reports from the glider community show increases in speed and range using very small winglets. Reducing drag in average wind conditions is a win-win situation unless your wind conditions are class four or better already.

And to your grousing about the provided vortex graphics, a link to the full article and photo gallery was included for those who do read carefully.

vawtwindy

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« Last Edit: November 09, 2010, 09:03:26 PM by vawtwindy »
endless hurdles.

DanG

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Re: winglets
« Reply #6 on: November 09, 2010, 10:55:28 PM »
Vawtwindy - thanks for posting... It's good that mystery is solved even if it has nothing to do with the cutting edge of low technology. Although, if anyone cares to invest in active electronics with piezoelectric damping elements for their 17' dual-rotor I think ghurd has a kit coming out soon...

http://www.mandhsoaring.com/Why%20Winglets/WL-Soaring.pdf has a good review of winglets on sail aircraft.

bob golding

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Re: winglets
« Reply #7 on: November 10, 2010, 03:57:30 AM »
ohh active control via piezoelectric damping elements. think it might work better if i glue the circuit boards to the end of the blades?.
 i agree longer blades will do more than any amount of gizmo's but as an add on to already made blades it might  be worth a try. still trying to find the patent link to the minix device anyone had any luck finding it? think for now i will just round them off as per the sandia article.
if i cant fix it i can fix it so it cant be fixed.

ghurd

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Re: winglets
« Reply #8 on: November 10, 2010, 07:11:44 AM »
While researching my active piezo dampening circuit for 17'-ers,
I came accross a lot of disputes about what actually works.

Apparently, most comercial versions have the winglets on 'top', while they know they work better on the 'bottom'.
The only example I can think of that uses a single sided winglet on the bottom is the U2.  Probably a good example, because they did not care what it looked like, or what it cost.
http://images.morris.com/images/lubbock/mdControlled/cms/2009/05/01/435251506.jpg

I seem to recall one reason they added top mounted, curved corner, winglets was for a somewhat self leveling property.
As the plane moved away from level, the effective upward lift of the lower wing increased because the blade effectively "got longer".
Maybe that's not correct.

The active piezo dampening circuit for 17'-ers was a bust.
So many parts that it required an 18' diameter circuit board that blocked the wind.
Which did make it quieter.   :D
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SparWeb

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Re: winglets
« Reply #9 on: November 10, 2010, 01:01:09 PM »
And to your grousing about the provided vortex graphics, a link to the full article and photo gallery was included for those who do read carefully.

It was carefully read.  Key word in article is "claims".  Gizmag is not a technical journal.  In fact I cannot find technical articles regarding any tests of the device, not even on the minix website.  I also cannot find the inventor's name associated with any university or professional background other than the minix invention.  If they want proof, they have to put up their own cash, mount it on an aircraft, and actually fly it.  With instruments sensitive enough to measure the effectiveness, too.  Computer simulations are not proof, not in the commercial aviation world.

You got me on the S-92, though.
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

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zap

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Re: winglets
« Reply #10 on: November 10, 2010, 04:12:02 PM »
From :http://www.airspacemag.com/flight-today/wing.html
Quote
In 1976, shortly after an energy crisis sent fuel prices skyward, Richard Whitcomb, a NASA aerodynamicist, published a paper that compared a wing with a winglet and the same wing with a simple extension to increase its span. As a basis for comparing both devices, the extension and the winglet were sized so that both put an equal structural load on the wing. Whitcomb showed that winglets reduced drag by about 20 percent and offered double the improvement in the wing's lift-to-drag ratio, compared with the simple wing extension.
Quote
The airflow around winglets is complicated... Cant, the angle to which the winglet is bent from the vertical, and toe, the angle at which the winglets' airfoils diverge from the relative wind direction, determine the magnitude and orientation of the lift force generated by the winglet itself. By adjusting these so that the lift force points slightly forward, a designer can produce the equivalent of thrust. A sailboat tacking sharply upwind creates a similar force with its sail while the keel squeezes the boat forward like a pinched watermelon seed.


Apparently, most comercial versions have the winglets on 'top', while they know they work better on the 'bottom'.
The only example I can think of that uses a single sided winglet on the bottom is the U2.  Probably a good example, because they did not care what it looked like, or what it cost.
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Ungrounded Lightning Rod

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Re: winglets
« Reply #11 on: November 10, 2010, 05:15:29 PM »
Winglets don't prevent tip vortices.  Those are inherent in the wing/whatever having lift.  The air (or water in a hydrofoil) is deflected by the passage of the airfoil/waterfoil where its surface is, but not out beyond its end.  The relative velocity of the fluid turns into a vortex after the foil has passed.

What they do is interfere with airflow around the tip of the wing, keeping it from bringing air (or water) around from the high pressure side to the low pressure side and reducing the pressure difference, partially depowering the end of the foil.  So the foil is fully powered all the way to the end.

The same is done on sailboats with "wing keels" - a keel design where the end of a long fin keel (which is mostly depowered by the tip vortex and present just to keep the base of the keel working) is replaced by a stubby horizontal airfoil.  This fights sideslip as well as the longer keel but lets the boat work in much shallower water.  (Downside is that, due to its shortness, it loses more power when the boat heels over in a crosswind.  So it tends to be used only for boats intended for shallow harbors.)

You can achieve a similar effect by making the end of the wing sharp like the trailing edge (rounding it into the leading edge at the corner).  The sharp end causes the high pressure air to jet off with enough speed that, by the time it gets turned around, the low-pressure side has moved on.  So you get about half the effect of the winglet without its added drag.

Or at least that's how I understand it (from combining some stuff in a NASA article on a windmill blade design where they described why they made the end sharp with stuff about wing keels on boats.)
« Last Edit: November 10, 2010, 05:37:59 PM by Ungrounded Lightning Rod »

bob golding

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Re: winglets
« Reply #12 on: November 11, 2010, 06:10:17 AM »

You can achieve a similar effect by making the end of the wing sharp like the trailing edge (rounding it into the leading edge at the corner).  The sharp end causes the high pressure air to jet off with enough speed that, by the time it gets turned around, the low-pressure side has moved on.  So you get about half the effect of the winglet without its added drag.



will give that a try. very easy to do. not sure i will be able to notice the difference but will try it anyway. plus i can just about get my head around how it works, just in case anyone asks me to explain. i assume the blades are cut off square with just a small rounded bit to the leading edge?
if i cant fix it i can fix it so it cant be fixed.

Ungrounded Lightning Rod

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Re: winglets
« Reply #13 on: November 11, 2010, 11:15:57 AM »

You can achieve a similar effect by making the end of the wing sharp like the trailing edge (rounding it into the leading edge at the corner).  The sharp end causes the high pressure air to jet off with enough speed that, by the time it gets turned around, the low-pressure side has moved on.  So you get about half the effect of the winglet without its added drag.



will give that a try. very easy to do. not sure i will be able to notice the difference but will try it anyway. plus i can just about get my head around how it works, just in case anyone asks me to explain. i assume the blades are cut off square with just a small rounded bit to the leading edge?

I don't recall if they were square or angled slightly, but I don't think square would be an issue.  I'd have to dig around for the NASA document.  (It was referenced here a couple years back.  A research paper on a windmill design.)  The "rounding" consists of the corner, where the leading edge ends, becoming a quarter sphere on the forward/out section, with the back smoothing teardrop-style into the sharp edge.

Regardless, you should be able to get the corner OK by doing the edge then smoothing the corner into it by hand.  Anything that feels like a smooth transition will probably hold the airflow attached and do what you want.

kevbo

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Re: winglets
« Reply #14 on: December 06, 2010, 01:55:13 PM »
Sailplane pilot here.

Winglets increase the effective span.  There are two classes of competition sailplanes (flapped and not) that are rule limited to 15m wingspan, so you can get the efficiency effect of a longer wing and still be within the rules by using winglets.  You get larger and slower turning tip vortices.

The downside:
The winglets on a windmill would need to be on the lee side of the blades, which would decrease tower clearance in tailed designs.  They would also cause some flexing load due to the out of plane mass.  This would be opposite that due to the wind/lift...so might not be a bad thing, but the blades would need to stand up to this. Note that aircraft wings don't have this issue, and the helicopter blades that do use much shorter winglets.

Really though, you don't have competition rules like the sailplanes, nor gate spacing issues like the transports, so there is little benefit to reducing the diameter a little but adding the complications of winglets.  Maybe for some peculiar circumstance where you need a little more span but can't lower the upper guys on the tower?


Ungrounded Lightning Rod

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Re: winglets
« Reply #16 on: March 07, 2011, 02:47:46 PM »
Sailplane pilot here.

The downside:
The winglets on a windmill would need to be on the lee side of the blades, which would decrease tower clearance in tailed designs

As I understand it the winglets on aircplanes and helicopters are on the more convex side of the wing (the top) only because of ground/peoples'-head clearance, not because they work better on one side, the other, or on both.  Should work fine on the upwind side of the blade.

Quote
Really though, you don't have competition rules like the sailplanes, nor gate spacing issues like the transports, so there is little benefit to reducing the diameter a little but adding the complications of winglets.  Maybe for some peculiar circumstance where you need a little more span but can't lower the upper guys on the tower?

I agree with you there.  Why do winglets when making the blade longer works just fine?

Only reason I can think of is that it might be easier to fabricate something to screw onto a flat, stubby end of a blade than to fabricate the blade longer, with a thin, sharp tip, and then keep the tip intact through the rest of the construction and raising process.