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Re: Vine seeds become 'giant gliders'

Postby ARP » Sun Jan 31, 2016 3:04 pm

" Hang gliding sort of evolved from kites behind motor boots. "

Not something I would agree with. Hang gliding existed long before towing kites behind motor boats. The improved water skiing kite produced by John Dickenson did eventually evolve into a hang glider when Bill Moyes foot launched it from a mountain in 1967.
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Re: Vine seeds become 'giant gliders'

Postby JoeF » Sun Jan 31, 2016 3:44 pm

Long live the kiting spiders

http://www.energykitesystems.net/akiteis.html

A very simple kite:
Image
While flying the shown very simple kite would be changing its L/D for its wing set, tether set, and anchor set; at times the very simple line kite could be flying up, at other times flying down, and at other times flying at a near-constant altitude. Portions of the line squiggle and form various amounts of lift and drag while other portions of the line form various amounts of lift and drag; at times the regions at one end will resist the regions at the other end in such manner and form that a climbing may occur for the system. Our kite hang gliders are similarly constructed but with more constancy in form; one end forms, say, a WW Falcon 3, while the other end of the hang line forms an anchor set of clothes, harness, ligaments, etc.; the two ends of the tether kite line are each wing sets resisting each other; it is common to call one wing set the "wing" and the other wing set "the payload, pilot, anchor, ... ); the active falling gliding kite system of the piloted Falcon 3 hang glider is a kite system (abbreviate to kite hang glider or just kite); a Falcon 3 product packed in a bag is simply an object and is not then an active part of a kite. A kite has wing set, tether set, and anchor set (which is a wing set also). As ARP noted, nature does not use our words.
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Re: Vine seeds become 'giant gliders'

Postby KaiMartin » Sun Jan 31, 2016 7:27 pm

ARP wrote:Nature does not understand the terms humans give to describe how something flies. What ever you call the forces involved the spider is lifted into the air by the thread it throws out whilst it is on the ground.

When balooning, spiders don't lift from the ground. They climb as high as they can on whatever happens to be nearby. They produce a long thread which catches the wind. Then they let go, get airborn and drift wherever the wind takes them. This is very much like the seeds of the dandelion and very much unlike a human made kite.

The combination of L/D versus gravity are what gets the spider into the air. If the lift is zero then the drag vector must have a vertical component in it, to offset the gravity, which you can interpret as lift.

Well, in aerodynamic speak "lift" is defined as the component of air generated force which is vertical to the local velocity of the air. By contrast, drag is the component of the force which is in parallel to the air. Unless you redfine terms in a private way, there is no way, drag can somehow contain lift. Note, that aerodynamic lift is not necessarily vertical with respect to the ground. E.g. sails produce lift mostly parallel to ground.

No matter how you call it, the principle of operation of spider balooning is very different from the aerodynamic forces that let human made kites lift from the ground. The whole process is is very different from about every angle you look at it. For starters, a kite is able to stay aloft indefinitely while not moving with respect to the ground.

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Last edited by KaiMartin on Sun Jan 31, 2016 10:49 pm, edited 1 time in total.
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Re: Vine seeds become 'giant gliders'

Postby JoeF » Sun Jan 31, 2016 8:37 pm

The flights of ballooning and kiting spiders are not all the same. Any particular flight will differ from other spiders' flights. And in any particular flight there will be various amounts of kiting occurring; but it is astronomically greatly probably that some kiting is occurring in the natural silks being wafted by the air. The spider's body is a wing in the kite system; the silks are playing two parts: wing and tether. As the natural frequencies play over the silks there will be non-straight portions of the silks that form various and changing airfoils; as the dynamics progress there are lift and drag vectors occurring all along the changing-form silks; and the spider body is wafted and keeps changing its face to the ambient wind over its body. There will be moments in some spider flights where lift won't be enough to overcome the mass of the system ... and at those moments the system will fall lower in the stream unless thermal or vertical drafts overcome the absolute fall rate relative to the ground. A kite system need not be a great lifter; indeed kiting may occur when above-zero lift is occurring on some part of the system. Spider flights where there is zero thermal or updrafting occurring will have less distance success.
When a kite's anchor set is moving (FFAWE, moving towing anchor, kite hang glider kiting gliding flight, ), there is still kite present. When the anchor set is not moving relative to the earth surface, there can still be kiting occurring. Of special importance to some spider kiting flight concerns the wind gradient; the silks may fly in wind that is faster moving relative to the ground than the airs lower where the spider's body is reacting with the air. The upper silks are wing; the lower body is wing; the upper silk is tethered to the spider body; the spider body is tethered to the upper silks. Upper silk ends whip and undulated from the influence of various undulating reactions that occur in the system; the lifting and dragging that occurs over all parts of the system form a kite system; the system is not lighter than air, but has mass. My guess is that the spider kite system is a very poor L/D system, but one that will flow with thermals easily because of system drag; as the flow goes up or obliquely up, the system goes with that flow. My guess is that the spider system is a better parachute than a glider, but the format nevertheless forms a true kite system, however poor is the L/D; but good drag from the undulating whipping form-changing silks.

Early toy kite contests sometimes would not respect a kite that did not obtain a steady tether angle of 15 degrees or higher. Such was formal kite-contest ruling. But formal kite-contest rule making does not define mechanical kiting. A kite system that reacted to get a part off stream directions while involving a tether between two wings is a kite system during that deflection off stream. During the drag of spider silk some deflection off stream occurs because the silks cannot stay perfectly straight in natural real-air flows; and once some bit is off-straight, then some form reactions occur that give some non-zero lift component traverse to the ambient stream; presto: kite. In real life it is almost impossible to have an absolute non-kite parachute, no matter how much engineering takes places to sculpt a symmetrical parachute; so, almost never is there a non-kiting parachute.
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Re: Vine seeds become 'giant gliders'

Postby ARP » Mon Feb 01, 2016 5:38 am

The spider needs to get high enough for the silk to be projected into the airflow and so climbs the grass stalk. It is still connected to the ground and anchored. When the silk is in the airflow it is subject to aerodynamic forces( no matter what you call them ) the result of which provide sufficient lift to overcome the gravitational forces on the mass of the spider.

I tried a simple experiment using a thread clamped between the pages of a book. With the thread hanging down, blow on face and edge of the book and the thread moved outwards into the airflow. So despite its low Reynolds number it would seem that a force (lift ?) is being generated perpendicular to the airflow. I can see in my mind that the spider is operating a kiting system unfortunately putting it into words leaves my description of it wanting.
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Re: Vine seeds become 'giant gliders'

Postby ARP » Mon Feb 01, 2016 10:08 am

Taking the L/D concept a little further down the aerodynamic path:-

If an object is placed in a vertical airstream such as they do for freefall simulation, is it drag or lift that is keeping the skydiver up? The pressure on the under side of the skydiver is higher than that on the upper side. Once this pressure difference matches the weight of the skydiver balance is achieved and he/she no longer falls to the ground. ( Terminal velocity) The vectors are aligned so are drag and lift the same thing with only the resultant vector described by a L/D ratio?
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Re: Vine seeds become 'giant gliders'

Postby Bill Cummings » Mon Feb 01, 2016 10:39 am

ARP wrote:Taking the L/D concept a little further down the aerodynamic path:-

If an object is placed in a vertical airstream such as they do for freefall simulation, is it drag or lift that is keeping the skydiver up? The pressure on the under side of the skydiver is higher than that on the upper side. Once this pressure difference matches the weight of the skydiver balance is achieved and he/she no longer falls to the ground. ( Terminal velocity) The vectors are aligned so are drag and lift the same thing with only the resultant vector described by a L/D ratio?

Or a hail (ice)?
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Re: Vine seeds become 'giant gliders'

Postby Rick Masters » Mon Feb 01, 2016 11:58 am

RS-1 Zanonia

Image
Ross built the RS-1 in 1937 for Harvey Stephens, hence the designation. It was one of the first small-span high-performance sailplanes. The lines of the ship were inspired by the Lippisch Fafnir II and the name comes from an Australian seed with good gliding characteristics. Ross flew the RS-1 in the 1937 U.S. Nationals and placed 3rd behind Peter Riedel and Richard du Pont. The ship placed 2nd in the Easton design competition. Later, owned and piloted by John Robinson, it made American Soaring history by winning the 1940, 1941 and 1946 Nationals, placing third in 1947 and second in 1948, and setting National distance record of 466 km. /290 miles in 1940 and 523 km. /325 miles in 1947 and the world altitude record of 10,211 m. / 33,500 ft. in 1949. Robinson also completed the Worlds’s first Diamond badge using the RS-1. http://www.sailplanedirectory.com/ross.htm

Image
John Robinson and the RS-1 Zanonia sailplane at Torrey Pines just prior to World War II
Photo courtesy of Torrey Pines Gliderport Historical Society and the National Soaring Museum

Image

More photos
http://flickrhivemind.net/flickr_hvmnd.cgi?method=GET&sorting=Interestingness&page=1&photo_type=250&noform=t&search_domain=Tags&photo_number=50&tag_mode=all&sort=Interestingness&textinput=rs1,zanonia&originput=rs1,zanonia&search_type=Tags
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Re: Vine seeds become 'giant gliders'

Postby KaiMartin » Sun Feb 14, 2016 1:47 am

ARP wrote:I tried a simple experiment using a thread clamped between the pages of a book. With the thread hanging down, blow on face and edge of the book and the thread moved outwards into the airflow. So despite its low Reynolds number it would seem that a force (lift ?) is being generated perpendicular to the airflow.

When you blow over the face and edge, you create an updraft behind the edge. Ask Bernoulli for the details. Dragged by the air, the thread aligns with the stream lines and points up.

Aerodynamic lift works by accelerating air differently on either side of the wing. It necessarily creates vortices. Viscosity dampens vortices. Given enough viscosity, vortexes will not develop in the first place. Try to stir an eddy in a glass of honey and you see how this works.

Whether or not vortices develop is governed by the Reynolds number. Due to its incredibly small diameter spider thread works at single digit Reynolds numbers. Recreational man made kites operate at about Reynolds number 10 000 and up. Coincidently, the viscosity of honey is about 10 000 times higher as regular water. The flow pattern of stirred honey compared to stirred tea is like the flow pattern of spider thread compared to the flow pattern of a kite. From a physics point of view it is as different as it gets.

Size matters with fluid dynamics. You cannot geometrically scale an object by a few orders of magnitude and expect the aerodynamics to be the similar or even the same. Consequently, the way spiders achieve flight is in no meaningful way comparable to the ways we use to lift our feet from the ground.

---<)kaimartin(>---
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Re: Vine seeds become 'giant gliders'

Postby ARP » Sun Feb 14, 2016 9:11 am

Kai,

I do not doubt what you say about the difference size makes in how the air behaves on wings. There are far more insects that fly than there are birds, bats, frogs, squirrels and aeroplanes all put together. Because a fly operates in the same medium and the air is more viscous to its wings than say that of a bird, it is still 'flying', that's why we call it a fly.

The term 'kite' was probably derived from the name of the bird that appeared motionless in the air as if held there by a tether to the ground. We know that a number of factors are involved in keeping the bird on station and that these can be described in engineering terms but it is the resultant that we observe and refer to as 'kite'.

I think that the observed spider does 'kite' the silk into the wind and holds it still until sufficient force is generated to lift it into the air. Whether or not this force is purely aerodynamic or there is some element of electrostatic force involved is not clear but the resultant is the spider gets lifted into the air in much the same observed manner as power kite operator does when jumping from level ground.

Interestingly 'flying ' underwater is great fun. Fish use swim bladders and humans can adjust their buoyancy to some degree and so reduce the amount of energy required in swimming. I use my arms in a birdlike wing flapping motion and can generate reasonable thrust and lift to propel myself completely underwater. Not sure where my configuration sits within the Reynolds number scale but I am able to make good headway and can operate beyond the limitations that my natural buoyancy would normally provide for, in climbing and diving. I have not tried it in honey though, preferring it spread on my toast.

Tony

p.s. I do not profess to understand the formula for working out Reynolds numbers but one of the main factors in the equation is chord length. The silk projected by the spider is of very small diameter but as its chord is its length, not its width, and that is aligned with the airflow, then the calculation might show that it has a high relative Reynolds number?
Last edited by ARP on Sun Feb 14, 2016 10:54 am, edited 1 time in total.
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