Sign in, say "hi", ... and be welcomed.

Re: Vine seeds become 'giant gliders'

Postby KaiMartin » Sat Feb 20, 2016 4:04 pm

ARP wrote:It may have electrostatic forces though ?

Electrostatics is responsible for the spread of threads (common polarity repels). Electrostatic forces do not provide lift, because there is no significant upward pointing electrostatic field. Ground is on ground potential, after all.

---<)kaimartin(>---
KaiMartin
User avatar
Contributor
Contributor
 
Posts: 146
Joined: Tue Apr 21, 2015 11:43 am

Re: Vine seeds become 'giant gliders'

Postby ARP » Sun Feb 21, 2016 4:33 am

Not sure how the electrostatic charge might develop with the silks being "stroked" with the increased speed of the upper airflow. There are some experiments that show lift being generated by a light weight grid with some form of electrostatic generation sufficient for it to become airborne. The generation of lightening is due to differences in the movement of air & temperature in the atmosphere causing high voltages to develop. Whilst the spider is "earthed" is the energy dissipated and if so what happens when it is no longer grounded?

What is the electrical property of the material of the spiders legs/feet. Are they insulators or conductors? Does the moister content of the air change matters so when it rains the spider stays put?

Some answers here maybe:-

http://blogs.discovermagazine.com/d-bri ... sm8LGbcthg

http://arxiv.org/pdf/1309.4731v1.pdf
ARP
User avatar
Contributor
Contributor
 
Posts: 280
Joined: Thu Jun 14, 2012 1:46 am

Re: Vine seeds become 'giant gliders'

Postby KaiMartin » Tue Mar 01, 2016 4:05 pm

ARP wrote:Some answers here maybe:-
http://arxiv.org/pdf/1309.4731v1.pdf

Seems plausible at first glance. Looking closer I am not quite convinced.
The paper is irritatingly theoretical with quite a bit of hand waving involved. E.g. they assert that the heights and distances spiders were reported requires some sort of active form of lift. However, it is well known that pollen, dandelion seeds and even full scale leaves can rise to surprising heights once they strike a thermal. The authors did not observe/measure spider take-off speeds themselves but rely on anecdotal reports. They did not measure the charge of the threads either. Instead they deduce from reported geometry of thread spread.

The argument involving electrical fields around Darwin's ship rests on particularly shaky ground. The authors did a 2D simulation. This either means rotational symmetry -- disks instead of a boom. Or planar symmetry -- booms and mast become planes. Both would yield field geometries that differ from the "real" 3D masts and booms.

That said, electric buoyancy might well contribute to spider balooning. If it is true, it would make the flight of spiders even more different from the mechanism a human built kite uses to lift from the ground.

---<)kaimartin(>---
KaiMartin
User avatar
Contributor
Contributor
 
Posts: 146
Joined: Tue Apr 21, 2015 11:43 am

Re: Vine seeds become 'giant gliders'

Postby Bill Cummings » Tue Mar 01, 2016 7:53 pm

Salticidae.PNG
Salticidae.PNG (164.96 KiB) Viewed 2461 times

While in my back yard today I watched a spider float by on on a silk strand and land on my plastic recycle bin.
When I moved in for a closer look it jumped several times and then turned to look at me.
It was one of many kinds of jumping spiders with more eyes than I have. I looked jumping spiders up and found this link:
http://ednieuw.home.xs4all.nl/Spiders/S ... icidae.htm
On the east and west coast it may be rare to use a trick that I use here is the desert southwest to aid me when I'm assessing the wind conditions at launch.
Rare partly because I'm assuming that that the pollen count is lower on average near coastal areas as well as the migrating spider count.
This trick works best on blue sky days.
Holding ones hand at arms length to shade the direct sun from shining in one eye any pollen or spider silk becomes much easier to see as it floats by almost directly (but not quite) in between the sun and the eye. Try to shade your eye the best that you can from direct sunlight.
The slower moving sightings are usually farther from ones eye as compared to the closer and faster moving silk and pollen that flashes past ones eye.
On days without white clouds in the way of the sun this will tell me, higher above launch, if the wind is crossing from what I'm feeling on the Rim.

We have one launch here that if I detect any more right crosswind, higher above launch, greater than 225 degrees, I will not launch due to much mechanical turbulence. This time of year the spiders are on the move here in southern New Mexico. Soon after the Cottonwood pollen that is much easier to see will mark the wind direction at great distances above launch. Spider silk has saved me at times from being in the air and wishing I was still on the ground. (Okay to move this if it is too far off topic.)
Bill Cummings
User avatar
Contributor
Contributor
 
Posts: 3352
Joined: Wed Jul 13, 2011 6:20 pm
Location: Las Cruces NM 88005 (Region 4)

Re: Vine seeds become 'giant gliders'

Postby Bob Kuczewski » Mon Jun 17, 2024 12:18 am

ChopperGirl's recent post ("Aunt Viola" video in the Volmer Jensen J-17 Trainer topic) prompted me to check out her web site:

      http://air-war.org/

There's a lot of interesting video there, and it's worth visiting (I hope to see some of it here on U.S. Hawks). But I was really fascinated by this short video about flying fish. I had no idea that they could fly as far as they can - "hundreds of meters":



I thought about starting a new topic for that video, but instead, I searched for "flying fish" to see if there were any existing topics that might be appropriate. Sure enough, I found this topic started by Doug in early 2016. Back on the first page, Frank wrote:

Frank wrote:If the earth had no birds or insects for us to see flying, we certainly would not be flying now.


KaiMartin replied:

KaiMartin wrote:Well, there would still be bats, flying squirrels, flying snakes and flying fish :-)


That was good enough for me. I hope you enjoy the video as well as the discussion from nearly a decade ago. :)
Join a National Hang Gliding Organization: US Hawks at ushawks.org
View my rating at: US Hang Gliding Rating System
Every human at every point in history has an opportunity to choose courage over cowardice. Look around and you will find that opportunity in your own time.
Bob Kuczewski
User avatar
Contributor
Contributor
 
Posts: 8244
Joined: Fri Aug 13, 2010 2:40 pm
Location: San Diego, CA

Re: Vine seeds become 'giant gliders'

Postby Frank Colver » Mon Jun 17, 2024 11:53 am

The flying fish are my favorite things when crossing to Catalina and back.

GBW - I didn't intend to exclude all other things that take to the air in that old statement about birds and insects.
Frank Colver
User avatar
Contributor
Contributor
 
Posts: 1292
Joined: Tue May 24, 2011 11:21 am

Re: Vine seeds become 'giant gliders'

Postby Bob Kuczewski » Mon Jun 17, 2024 12:09 pm

Frank Colver wrote:The flying fish are my favorite things when crossing to Catalina and back.

I've seen dolphins riding our bow wave between LA and the channel islands, but I've never seen flying fish. :(

Frank Colver wrote:GBW - I didn't intend to exclude all other things that take to the air in that old statement about birds and insects.

I know. Your point was that seeing anything flying was a boost to our "monkey see, monkey do" brains. I am sure you're right. I believe we would have had manned flight by now either way, but without natural examples it would have taken a bit longer.

Balloons were already used during the Civil war, and I think they were discovered through the observation of rising air from fires (no plants or animals needed other than as fuel for the fires). The ability to see distances by climbing hills or trees was already well known, so trying to get higher would have been a natural desire in warfare even if nothing else was flying. Similarly, extending one's hand outward in an airflow (riding a horse, horseless carriage, or wind storm) would have revealed the potential for generating lift from the air. I think those things alone would have pointed in the direction of heavier than air flight even if nothing in nature was leading the way. Certainly, in today's modern world, some modern scientist or engineer would have come up with the concept of flight and probably gotten us into the air very quickly. So I think we would have flight by now without natural example, but it would have been a much more compressed (and far less colorful) progression from gliders to jets.
Join a National Hang Gliding Organization: US Hawks at ushawks.org
View my rating at: US Hang Gliding Rating System
Every human at every point in history has an opportunity to choose courage over cowardice. Look around and you will find that opportunity in your own time.
Bob Kuczewski
User avatar
Contributor
Contributor
 
Posts: 8244
Joined: Fri Aug 13, 2010 2:40 pm
Location: San Diego, CA

Re: Vine seeds become 'giant gliders'

Postby Chris McKeon » Mon Jun 17, 2024 8:40 pm

Ok, OK: I will just come out and Say it: For I began Flying Hang Gliders back I am pretty Shure that I made My First Flight at a Costal Site, Remuera that was not too Far from Auckland. I believe that it was called Miramar But I might have the Spelling incorrect. From the moment My Feet left the sand I was awed! mean as I floated over the sand Gor I am not so Shure, it was Maybe a flight that covered oh I do not know, I am sure that the Flight did not cover no more than Fifty Feet. But from that moment, I was totally Hooked.
Chris McKeon
User avatar
Contributor
Contributor
 
Posts: 1421
Joined: Wed Jul 31, 2013 7:46 pm

Previous
Forum Statistics

Who is online

Users browsing this forum: Chris McKeon and 40 guests

Options

Return to Hang Gliding General