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KiteLife article on adding weights 
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Joined: Mon Sep 29, 2003 7:43 pm
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Post KiteLife article on adding weights
.....is here.

Allow me to pull a quote for you:-
    The first item on the agenda is to explain what adding weight is going to accomplish for you. This is pretty straightforward, and it’s all about the Center of Gravity.

Is it ? Have you ever actually seen how much (or how little) effect the amounts of weight we would normally use has on the static CoG of a kite ? It's not a whole heap. And when you think of how much that same weight is going to have on the kite when subjected to aero. loads too.

"All about the CoG" - really ?

He does go on to talk about rotational effects (and even throws in a little Newton, which is good) which I personally think is where the major effect of adding mass is happening. It's tricky to explain away LE/LS and centre-T weights in terms of CoG effects, given that they are so much closer to the unweighted, static CoG in the first place. Why add 20g at the centre-T when 10g further away at the base of the spine will have the same CoG shifting effect ? (I would suggest it is to balance the pitch effects (yoyos) with rotational effects (Backspins, Susans)).

Think on this:- what would happen if a kite had two large weights set equidistant on the spine from the unweighted CoG ?

If CoG placement really is the major issue, the answer would be nothing much.

If it's polar moment of inertia :-) then this kite will roll up like a beast.

I just would like to know if I am thinking along generally accepted lines here. Or talking piffle. Not that the two are mutually exclusive. :wink:

Mike.


Thu Nov 10, 2005 7:01 pm
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WEIGHTS RAWK, DUDE!! :rockout2:


Thu Nov 10, 2005 7:05 pm
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Juha wrote:
WEIGHTS RAWK, DUDE!! :rockout2:

Well quite. Thank you Mr. Double VF Winner for that insight. :crazy:

    your kite’s Center of Gravity. This is the spot that marks the axis around which the kite will pitch when doing all those flippy-floppy moves.

You know what ? This really isn't true. Take a look at your favourite video shot from the side of the kite and the centre of rotation is frequently nowhere near the kite, let alone at the static CoG.

Agree with me dammit !!! :evil:

Mike.


Thu Nov 10, 2005 7:15 pm
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Absolutely right. Probably.

If I get time I will be getting a kite out and taking photos later.

It's frightening how much Mechanics I've lost when I used to be good at it. :(

Top of my head, I'm thinking: Momentum.

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Thu Nov 10, 2005 7:53 pm
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Andy S wrote:
Top of my head, I'm thinking: Momentum.

I am thinking; inertia, momentum, CoG might influence how the trick looks (ie; orientation and position) rather than whether or not it happens.

In my defense my education is mainly in statics not dynamics so it's altogether possible I am talking utter pigswill.

Mike.


Thu Nov 10, 2005 8:00 pm
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Definitely inertia, not much to do with momentum. I got the two terms confused.

Inertia is defined as the resistance an object has to a change in its state of motion and is SOLELY dependent upon mass.

I also agree (and intend to demostrate later, perhaps) that the CoG changes very little given a 15 or 20g weight on the tail.

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Thu Nov 10, 2005 8:14 pm
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I agree, its not all about COG but its a fairly lightweight article so I wouldn't get too worked up about it (I must be ill, normally I'm more anally retentive).

The thing that concerns me is the belief among some people that you can just whack a weight on any old piece of crap and hey presto yo-yo monster. Most good weighted kites are designed with weight in mind from the outset, you'll see traits such as a trailing edge cut quite low compared to old school kites which helps get the centre of rotation much nearer the spreaders.
Gotta stop there, I'm knackered and I'm in danger of getting on a soapbox.


Thu Nov 10, 2005 8:16 pm
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Ian Newham wrote:
you'll see traits such as a trailing edge cut quite low compared to old school kites


Or has the lower spreader moved up? :wink:


Juha


Thu Nov 10, 2005 8:28 pm
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Juha wrote:
Or has the lower spreader moved up? :wink:

Get a look at this for sale Sandpiper and tell us more about the direction that the LSs have moved over the years. :wink:

Mike.


Thu Nov 10, 2005 9:32 pm
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Zippy8 wrote:
Get a look at this for sale Sandpiper and tell us more about the direction that the LSs have moved over the years.


That certainly doesn't qualify as evidence - if you look where the spreader is located at the LE, it's not far from where it is in most modern kites. The Sandpiper just has a HUMONGOUS tail which creates an optical illusion.

Anyway.... it was just an offhand remark. I'm sure there are plenty of older kites where the lower spreader is pretty high. But take a look at any pre-2001 Level One kite. :shock:


Juha


Thu Nov 10, 2005 9:41 pm
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I dont think its all optical illusioin I think the T is a bit high on Sandpipers.

Look at something like an Opium or a Frenezy and you'll see the trailing edge looks quite low, this has the effect that you can get the point of influence of the bridle very low which gives you a much snappier roll up. If it was simply the spreaders moving up you wouldn't be getting the POI lower. Getting back nearer topic this and moving the inner standoff outward are far more effective at improving roll-up performance than doubling the amount of lead on your tail.

That said transfers do look like the spreaders have just moved up :-)


Thu Nov 10, 2005 10:06 pm
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Ian Newham wrote:
Look at something like an Opium or a Frenezy and you'll see the trailing edge looks quite low


Hmm... nevertheless - if you look at the typical "French" kite directly from the front, you'll see that the lower spreader is right at the same level with the highest point of the trailing edge. The French kites are all geared towards good backflip performance, and as you know, a low-placed lower spreader would be a big hindrance for most backflip tricks.


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That said transfers do look like the spreaders have just moved up


On the Transfer they really are higher than "normal". This (together with standoff placement and tail size/shape) leads to good backflip performance (which I'm sure was one of the goals), particularly automatic multilazies. However, as you pointed out, the lower connection points of the bridle sholdn't move up that much to facilitate snappy yoyos - and they haven't. On the Tranny the bridle attaches below the centre T and both at AND below the lower LE connectors. Best of both worlds? :-)

Juha


Thu Nov 10, 2005 10:46 pm
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On this topic: I have a virus (or rather a "Le Virus") and it yoyo-ed like crazy when I first got it. In fact, it went into backflips and yoyo's way too easy! The kite wasn't convinced to stay put in a fade neither.....
When adding weight to the lower part of the spine, all the above was corrected: yoyo's only happen when I want them to happen, a fade does stay now :-)

How it helps the above conversation, I don't know, but these are the things I noticed


Thu Nov 10, 2005 10:59 pm
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Juha wrote:
On the Tranny the bridle attaches below the centre T and both at AND below the lower LE connectors. Best of both worlds? :-)
Juha


Ah, Nice! I hadn't been close enogh to a Transfer to notice that :-)


Thu Nov 10, 2005 11:17 pm
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Juha wrote:
The Sandpiper just has a HUMONGOUS tail which creates an optical illusion.

How do you know it's not the high placed LSs giving the illusion of a humongous tail ? :goofy:

And weren't we discussing weights just a second ago ? :wink:

Mike.


Fri Nov 11, 2005 6:17 am
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