Kite Strings

Tad Eareckson wrote:

Davis Straub - 2012/06/27 23:48:20

That was a bloody good joke on my part. Drier humor than even you Brits are used to I'd imagine.

Mike Lake - 2012/06/28 03:33:32

Sorry, I still didn't get the bit about you being from the colonies but I appreciate any attempt at humour, especially the dry stuff.

This is my attempt.

When I look out of my window I see lots of flat fields, therefor the Earth must be flat. I too go with what is physically obvious.
Those round Earth f******s don't know nuffin.

Davis Straub - 2012/06/28 04:52:47

Nice try. I once owned a Kiss. That was one dangerous glider.

Too bad it didn't kill you. I'd have been a major contributor to the PacAir Defense Fund.

Mike Lake - 2012/06/28 08:31:09

Yeah, I know. If I can just keep alive for a bit longer I'll be able to retire mine.
Didn't you once have a forum? Now that was one dangerous place.

(How am I doing?)

Fine. Always has been, always will be.

Davis Straub - 2012/06/28 19:52:09

Good.

I have a forum and it has been extremely active lately as we discuss Jim Rooney's essays on landing.

http://ozreport.com/forum/viewtopic.php?t=28168

How would anyone who isn't a registered member and hasn't yet been banned for exposing you as the stupid lying scumbag you are know? You locked it down to the public when the incompetence of you assholes was brought to light right after the Lenami Godinez-Avila fatality two months ago.

Mike Lake - 2012/06/28 21:45

Blimey! I didn't mean that dangerous.

Try reading his essays on failure to hook in and towing sometime.

Davis Straub - 2012/06/28 19:52:09

I have a forum and it has been extremely active lately as we discuss Jim Rooney's essays on landing.

Tad

How would anyone who isn't a registered member and hasn't yet been banned for exposing you as the stupid lying scumbag you are know? You locked it down to the public when the incompetence of you assholes was brought to light right after the Lenami Godinez-Avila fatality two months ago.

Davis Straub - 2005/02/09 06:20:40

At Quest and Wallaby 130 pound test line in a loop with a fisherman's knot is used. That is two strands minus the weakness due to the knot (225 lbs).

If I put it on my Pro-Tow, then the tension on it is reduced by the cosine of the angle (results is =>300 lbs).

Davis Straub - 2005/01/11

The rope length will be increased from 60 meters to 90 meters and from spectra to poly to increase the stretch in the rope and help out with the new weaker weak links.

Davis Straub - 2009/04/21 16:27:15

210 (hook in weight) + 71 (glider weight) = 281 (total)

weaklink = 200 lbs (approximately) Halved = 400 lbs.

400/281 = 1.42 (approximately)

If the weaklink was 180 lbs then 360/281 = 1.28

Davis Straub - 2009/04/21 22:57:18

250/281 = .89

Tad Eareckson - 2009/04/22 11:12:25

Dallas,

Oops, neglected to answer these questions:

What is the breaking strength of a loop of 130 lb greenspot? Since it's not "right" what is?

On the end of a Spectra bridle I use 140 pounds.

Whether it's "right" or not depends upon what your glider weighs and how you're towing.

If the glider is 200 pounds and towing one point or 174 and towing two point it's pretty good. But for the other 95 percent of the stuff we see waiting in line it's stupid.

Davis,

Those numbers you provided all assume the glider is towing one point. I think you'll find that not to be the case for the majority of the ones in line on a Saturday afternoon.

Davis Straub - 2009/04/22 12:07:12

Pro tow?

So. It would be the same with a V-bridle.

Tad Eareckson - 2009/04/22 13:01:03

In one point towing the attachment points for the bridle/release assembly are separated by a matter of about eight inches and thus the apex angle formed by the bridle is so acute that the resultant increase in tension over the halfway mark to which the assembly is subjected is negligible.

In two point towing the separation between the attachment points - pilot and carabiner or keel - is a matter of some number of feet, the apex angle tends to be around sixty degrees, and the assembly - notably the primary release and weak link - is subjected to significantly more than half the towline tension.

Davis Straub - 2009/04/22 13:42:54

Let's see your pictures on that.

Davis Straub - 2009/04/22 13:43:27

BTW, I assume that this means you're cool with the pro-tow and Greenspot.

Tad Eareckson - 2009/04/22 14:38:53



It's why the cables droop instead of being stretched to horizontal. (Golden Gate Bridge - thanks, Wikipedia.)

Yeah, I'm totally cool with Greenspot for pro-tow - for anyone who's gonna be dead from anorexia in a couple of days anyway.

Davis Straub - 2009/04/22 15:00:07

What are you talking about?

And what does the Golden Gate bridge have to do with anything?

Tad Eareckson - 2009/04/22 17:18:13

Davis,

A single loop of 130 pound Greenspot on the end of a one point bridle puts a 200 pound glider at 1.40 Gs. Great - but that's the lightest glider I know about.

And she flies two point so she's down to 1.22 Gs. Still OK.

But you start putting those things on stuff much bigger than that (like yours truly - 320 pounds) and you are asking for and getting trouble.

You shorten those bridge cables you dramatically increase the tension to which they are subjected.

You increase the bridle apex angle you increase the loads on the bridle and anything connected to it.

Let's say 400 pounds tow line tension.

One point bridle apex angle - 20 degrees - which is probably generous. The weak link is feeling 203 pounds.

Same tension loaded onto a two point bridle forming a 60 degree apex angle - 231 pounds.

Do the trig.

Davis Straub - 2009/04/22 23:08:34

281 lbs here (total with glider and 212 hook in weight). If the Greenspot is about 180 - 200 pounds which as I recall is what we found at Quest Air (not 125 lbs), well you can see the numbers above.

I'll let the forces on the V-bridle be divided by 2 and leave it at that.

Tad Eareckson - 2009/04/23 16:19:40

I don't know where you're getting those numbers. Quest says:

...that one loop (which is the equivalent to two strands) is about 260 lb. strong...

and nobody in this thread has yet referenced 125 in any context other than feet of altitude.

Let's use 140 pounds - the figure I picked as a result of testing a loop of 130 pound Greenspot formed with a Fisherman's Knot, installed on a one point Spectra bridle with a Double Lark's Head, and engaged by a spinnaker shackle or barrel release:

140*2/281 = 1.00 Gs

I'll let the forces on the V-bridle be divided by 2 and leave it at that.

Remind me to take the ferry to avoid any bridge you may have designed. If you prefer real to make-believe numbers you've gotta knock off about fifteen percent.

140/1.15*2/281 = 0.87 Gs

BUT -

As George and just about anybody who's ever towed - two and/or one point - on that crap knows all too well, virgin loops pop all the time under ambient tow tension. They can start losing their integrity as soon as the cart starts rolling.

I've measured ambient tension between a 914 Dragonfly and me at 125 pounds.

So let's run those numbers again for ya.

125/281 = 0.44 Gs

I want three times that before I start feeling safe. And I'm hooking an additional forty pounds to the towline.

Dallas Willis - 2009/04/23 20:33:25

Tad is right about the force not being split in half. The tow force on the tow rope is directly ahead towards the tug. Then the force is split into 2 sections of your bridle. Let's assume pro-tow. The force felt on the weak link or the bridle in the angled direction towards the tow rope is greater than 1/2 the total force on the tow rope. Not by much but it is greater. In words, you have to make a force vector diagram and use cosine (SOH CAH TOA, so Cosine of an angle = length of adjacent / length of hypotenuse).

I've attached a couple diagrams (yeah I know they suck) that should show this. I choose a 60 degree angle just for kicks but you can adjust this and the force "units" to your liking. But in this example with a tow line force of 100, each bridle sees 57.7 units of force in their angled direction (and thus on the weaklink) or about 15% more than "half". For a tow force of 200 units the bridle would see 115.5 units of force (again about 15% and that number should keep for all values of the tow force and a 60 degree angle).

Change the angle to 30 degrees and you end up with 51.8 units of force for a 100 unit tow line, or 103.5 units for a 200 unit tow line so about 3.5%.

I could be wrong about this, stretching back to high school and freshman year of college for this...

Davis Straub - 2009/04/23 22:16:45

...and nobody in this thread has yet referenced 125 in any context other than feet of altitude...

I suggest that you missed this and that you look again at the link that Billo provides.

I like 180 - 200 lbs, which I recall from tests by Steve Kroop that I witnessed, but I'll ask him again, just what the results of those tests were.

Steve Kroop - 2005/02/10 04:50:59

I do not know the exact tow line tension required to break this weak link but the value is somewhat moot since the weak link is not too strong so as to cause any damage to the tow plane and it is not too weak to leave the glider pilot with the towline.

Jim Rooney - 2011/08/25 04:55:25

I mean seriously... ridgerodent's going to inform me as to what Kroop has to say on this? Seriously? Steve's a good friend of mine.

Jim Rooney - 2011/08/28 06:15:12

You may not know, but Davis is a friend of mine.

I'm fine with 140 lbs also.

Yes, Dallas is correct if the bridle is short the forces are greater. Another good reason for the length of bridles that I sell. (Homemade, btw.) The angle of the lines on the bridles that I sell is very acute.

This, of course, would not be as true on the V-bridle where the distance between the pilot's chest and the line attached to the keel is much further. Thanks for that correction, Dallas.

Tad Eareckson - 2009/04/24 02:05:05

I suggest that you missed this and that you look again at the link that Billo provides.

No - I didn't miss it. It's in another thread. And it's exhausting enough to handle this one.

But OK, fine - 125 pounds is even more insanely understrength in relation to the 260 pound assumption cornerstone upon which our religion is founded.

I like 180 - 200 lbs, which I recall from tests by Steve Kroop that I witnessed...

On quarter inch braided Dacron line I've gotten a loop of Greenspot to hold to 215 pounds. It's gotta be mounted on a bridle and engaged by a release as it would in the air for the tests to mean much.

The angle of the lines on the bridles that I sell is very acute.

The apex angle formed by ANY one point bridle is so acute that the increase in tension above the fifty-fifty split is negligible.

Let's assume a 400 pound tow line tension. If the primary bridle assembly were infinitely long the barrel releases would be feeling 200 pounds.

I've estimated twenty degrees to be a generous apex angle allowance but let's go nuts and make it thirty. The barrels are now straining at 207.

At twenty degrees they're doing 203.

These differences are - for all intents and purposes - MEANINGLESS.

All you accomplish by lengthening the secondary bridle is to decrease the odds of it clearing the tow ring without tying itself in a knot. I don't give it a snowball's chance in hell to tie itself in a knot.

If you really MUST decrease the apex angle do it by increasing the distance between your shoulder and the release.

With respect to the two point bridle however...

It IS long enough to wrap and - although you can minimize the risk with good designs - there's NOTHING you can do to totally eliminate the possibility. That's why we have secondaries (not backups - SECONDARIES).

Since we're stuck with the possibility anyway there's essentially no downside to increasing its length - 'cept you gotta stow more crap after the tug goes away - so I like that one a bit on the long side - ten feet - to reduce the load on the weak link and release.

Thanks for that correction, Dallas.

The correction was mine. Dallas did the confirmation. You're welcome.

Davis Straub - 2008/04/22 14:47:00

Here is the requirement from the 2007 Worlds local rules (which I wrote) for weaklinks:

Pilots must use weaklinks provided by the meet organizers and in a manner approved by the meet organizers. All weaklinks will be checked and use of inappropriate weaklinks will require the pilot to go to the end of the launch line to change the weaklink.

Weaklinks will consist of a single loop of Cortland 130 lb Greenspot braided Dacron Tolling line and should be placed at one end of a shoulder bridle.

Davis Straub - 2011/09/02 18:37:09

Concussions are in fact very serious and have life long effects. The last time I was knocked out what in 9th grade football. I have felt the effects of that ever since. It changes your wiring.

Tad Eareckson wrote:Yeah, that sonuvabitch deserves a topic all his own.

He seems to have become a lot more active on The Jack Show since he barricaded his own swamp.

Davis Straub - 2012/07/19 23:38:30

It's difficult to understand how when the crimes are sitting right in front of them, they are thinking it was Batman that caused them. Not that the Fed is actually Batman, or that Batman is actually real.

Davis Straub - 2012/07/31 13:44:25

#156

Look, I am not misinformed at all. I have a much different point of view and set of facts than you. You may feel that your position is correct. I find that it is not.

The Euro acts like a gold standard because it restricts the national actions of the countries that adopted it, just like the gold standard does. I have plenty of evidence for this.

I realize that being confronted by someone who completely disagrees with you on the facts and the requirements for action based on those facts is uncomfortable, but claiming that I am misinformed as not going to do it.

miguel - 2012/08/01 21:58:56

I do not get the hate for Davis. I read his windoze books back in the day. People thought I knew something about computers.
His money does not color what I think of him.
The facts he spouts are not secret. They are on the internet just like the other so called facts.

Meet Alexander Hamilton
Podcast at
http://www.corbettreport.com/episode-235-meet-alexander-hamilton/

An illegitimate child born in the West Indies, Alexander Hamilton was an unlikely choice to be a founding father of the American Republic. Still, a founding father he was and he did his best to leave his mark on the fledgling American nation. Meet Alexander Hamilton, advocate of debt, central banking, corporate welfare, an elected king, a standing army, and a tyrannical central government.