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'Funsized' Rev kites ?


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#21 Choccy

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Posted 25 March 2008 - 01:23 AM

Having been dragged all over Dunstable Downs last weekend, I fully understand your concerns.


Having bumped into Sailor yesterday, he now *fully* realises my predicament!

The blustery gales had me running/being dragged down the hill, even with a vented B-series, "Bluey".
Whilst Sailor just serenely stood still floating and twirling "Primrose" his gold vented B-series.

Not fun when you have to watch out for rabbit holes too.
It's an exhausting way to learn to fly.

It was a pleasure to meet Sailor, and attempt to fly with him for a while. ;)
It will be better once my purple vented B has arrived and Groz can have Bluey, rather than a standard SLE.
Oh and when I have learnt a lot more.
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#22 Sailor99

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Posted 25 March 2008 - 04:00 AM

One thing that occurred to me afterwards. I find on a blowy day, if you double up the rods on the leading edge not only is the kite more robust but it also seems to reduce the pull a little. I think it has something to do with reducing the flex, as the sail of course "sags" in the middle when the leading edge flexes. I think it is this change in shape that seems to generate more power than had the edge not flexed.

Not explained very well, but hopefully understandable. I would be interested if others find doubling the leading edge reduces the power too, or if it is just my imagination!
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#23 Choccy

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Posted 25 March 2008 - 04:28 AM

One thing that occurred to me afterwards. I find on a blowy day, if you double up the rods on the leading edge not only is the kite more robust but it also seems to reduce the pull a little.

I believe we had both the 3 and 4 wrap rods in together, is that what you mean by doubling up?
I should have moved the knot to more power on though, as well.
Still maybe I ought not to fly in such conditions or maybe get a super super vented kite ;)
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#24 Sailor99

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Posted 25 March 2008 - 04:46 AM

Yep, that's what I meant. I guess you meant "less power" though
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#25 Choccy

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Posted 25 March 2008 - 04:53 AM

Yep, that's what I meant. I guess you meant "less power" though

Schoolgirl error!
I kind of meant the kite deals with the more power so I don't have too :kid_smartass:
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#26 Sailor99

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Posted 25 March 2008 - 04:57 AM

Well, you need to watch out for a cheapo second hand 1.5 then take your soldering iron to it - Voila! One super-vented Teabag.
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#27 Stone in Shoe Bob

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Posted 25 March 2008 - 06:50 AM

One thing that occurred to me afterwards. I find on a blowy day, if you double up the rods on the leading edge not only is the kite more robust but it also seems to reduce the pull a little. I think it has something to do with reducing the flex, as the sail of course "sags" in the middle when the leading edge flexes. I think it is this change in shape that seems to generate more power than had the edge not flexed.

Not explained very well, but hopefully understandable. I would be interested if others find doubling the leading edge reduces the power too, or if it is just my imagination!

Funny you should say that Gary and I were discussing the same thing Sunday we were both flying vented's I had a Rev Equipped SLE he was flying skiney Rev Equipped.
Stone in Shoe Bob

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#28 Sailor99

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Posted 25 March 2008 - 07:29 AM

What did you guys conclude?
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#29 steveb

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Posted 25 March 2008 - 09:12 AM

Vented Rev II - smaller sail, plus the vents reduce the pull and twitchiness, making it quite manageable in blustery winds.
vented_revII_1.jpg vented_revII_4.jpg

#30 Stone in Shoe Bob

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Posted 25 March 2008 - 09:17 AM

What did you guys conclude?

Pretty much the same as you, too much dishing in the sail creates too much drive.

Though strangely, at the other end of the scale the opposite seems to be true.

Pre Race Rods, if my sul would not fly with a Pro Use frame, I would try a P90 which being considerably lighter would allow me to fly in even lower winds. The down side was that it made the kite extremely floppy, which is strange but interesting experience. Race Rods are clearly much stiffer than P90 and probably, (I haven’t checked) quite a bit heavier. Yet I know a race frame will take wind range down even lower than P90.

Now we get to the pseudo science bit, and to be honest I’m not really sure I entirely understand this so it may be total bollocks but here goes. I wonder if in the same way my old physics teacher would tell us off for confusing “weight” and “mass” we are confusing “lift” and “drive”.

Lift comes from the amount of sail area offered to the wind and a flatter kite can offer a greater area (shortest distance between two points and all that).

Drive on the other hand, comes from the amount of air deflected by the sail, now this really is rocket science, Isaac Newton and all that. The bowed sail allows more air to be collected and channelled over the trailing edge.
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#31 Sailor99

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Posted 25 March 2008 - 09:40 AM

I THINK we are probably not confusing the two. A sail doesn't really derive drive from air 'blowing' off the back, although that is what your intuition would tell you. It is the flow of air over it that causes lift. The lift works at right angles to the sail, in the opposite direction to the lines. If you start off in hover the force is exactly in alignment with the lines, which is why the kite moves neither forwards or backwards. Tilt the sail towards you (thumbs back) and the force line also tilts. Now the force is not in alignment with the lines, it is pointing forward of the lines, so the kite moves forward. In effect some of the lift force is being converted into forward movement. I think what happens when the kite over-flexes is that the center portion of the sail flops backwards, which is the same as it being tilted forwards, and the kite shoots off.

I am no hydrodynamic physicist, so may be way off the mark. But that is how it happens with boat sails anyway! It would be loads easier to explain what I mean with a diagramme, but that doesn't work too well in a forum!
Over - Jeremy

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#32 Jonesey

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Posted 25 March 2008 - 12:25 PM

Hey Jeremy ...

I have to say that as a fellow sailor and having worked for several sailmakers and mast makers over the years I have been looking at my new rev experience from a similar angle.. my thinking so far and flame away by all means...

1. Angle of attack ... most of what makes rev flying so unique is the way you can control the angle of attack of the two 'sails' independently for rotation as well as the whole kite to generate lift whatever the orientation of the kite.

2. Sail shape/power ... from what I can see there is very little seam shaping or 'luff curve' in the kite construction so the flying shape is a result of what you and I would call sheet tension but in this case its the shock cord (bungee) that holds the verticals.. tighter = flatter, slacker = fuller sail so perversely the sail gets fuller and more powerfull in a gust and flatter (less powerfull) in a lull (do people ever replace the bungee with alternatives?) however this is more then compensated for by the bend in the leading edge which in effect dumps the power and introduces twist so the sail de-powers automatically (more bend = less power) ... much like a windsurfer mast which responds to gusts by flexing etc etc (oops straying off sport again)...

So the logic to me is the bendier the leading edge the more forgiving the kite will be to gusty conditions and the less it will pull ... Try a shockwave in 20+ knots, all together stiffer structure is very much on/off in terms of power and you can only really control the amount of power via angle of attack/break.

Obviously the key to the Rev experience is matching the right rods with the right kite and the right wind strength to automate this gust response and finding the sweet spot... case in point vented B-series ... No SLE so nice and forgiving, perfectly balanced and as a result wonderfully flattering for us newbies to fly!

Looking at the rev range it seems the more you progress (?) towards the power/speed series the more 'locked in' the flying shape becomes and the more 'challenging' the flying experience .... I will test this theory when my blast 2.4 arrives and my ambition:ability ratio plummets into the negative!

Good times :kid_devlish:

#33 Choccy

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Posted 25 March 2008 - 12:40 PM

Looking at the rev range it seems the more you progress (?) towards the power/speed series the more 'locked in' the flying shape becomes and the more 'challenging' the flying experience .... I will test this theory when my blast 2.4 arrives and my ambition:ability ratio plummets into the negative!

Hello Jonesey
You make for interesting reading/points with your sail knowledge.
Although fluid dynamics was never my strong point (yuck!) ;)

Do you have a B-series in your collection ?... of course you have ;)
Looks like there is getting to be quite a little 'collection' of Bees in the county!

I'll leave you big chaps to play with your Blasts/shockwaves and the like :blue_wink:

Good winds.
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#34 Sailor99

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Posted 25 March 2008 - 12:44 PM

Yep, I see your point about power dumping. A bit like mast prebend or putting bend in a light rig with the vang. But doesn't that assume you have some chord precut in the sail so the bend can take it out and flatten the sail? I need to think it through some more.
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#35 Jonesey

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Posted 25 March 2008 - 12:47 PM

oops .. just checked again (thanks Sparky) and there is in fact a degree of curve in the sails leading edge.... I suspect that the lighter the kite (SUL) the more curve (havent got one yet to check ... another reason to buy more) so on any given kite when the leading edge bend matches the curve in the sails leading edge the sail is in effect flat (not withstanding tip/sheet tension) any less bend the sail 'powers up' any more bend the sail de-powers and its probably time to change up to a stiffer rod.... Make sense??

Think I need to stop thinking and start doing....

#36 Sparky

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Posted 25 March 2008 - 01:22 PM

Jonesey,

No seaming, about 3 inches luff curve.

Spar bend exagerted by bridle being attached to the spar ends in addition to wind power & bungees.

If bungees replaced by fixed line at both ends, I would expect a more progressive power up/down as the sheet tension remains the same.

Have you started builing yet?!

Sparky

#37 Sparky

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Posted 25 March 2008 - 01:30 PM

Jonesey,
Your next analysis is to establish the comparitive stiffness of the spars.
If you build the spar and then put one end on the bathroom scales - you will need 0.1kg accuracy, and then push down on the other end. After a reasonsable amount of bend you will notice that the weight will not increase, so that becomes spar bend weight. Once you have done the analysis you can post the results for the rest of us. Clearly you will need to do the mixed spar (lighter tip spars) as well as the standard, 2, 3, 4, Race, SLE rods.

Secondly sail load will increase if bungees are replaced by fixed line, so plastic cringles may be requried to prevent sail ripping.

Standing by...

Sparky

#38 Jonesey

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Posted 25 March 2008 - 02:15 PM

Sparky ...

Happy to start analysis as per your request ... I assume you are happy to apportion a percentage this years Olympic budget to the project or would you prefer to fund a longer term test with a view towards 2012 where I assume you will have used your influence to have Weymouth hosting the first Quad line demonstration event??

P.S.

Only other area we havent discussed is the effect of panel layout/thread orientation and cloth weights ...... any takers??

#39 Sparky

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Posted 25 March 2008 - 02:59 PM

Jonesey,
You have just pointed out, without realising it as usual, that Chisel beach is an excellent flying venue. N or S winds allow clear breeze and the oportunity for you to develop your underwater techniques.

My tech budget cannot deal with current product, however we will of course step in when we find there is a hole in the spar range that need new rods. What about one piece rods? This would prevent the hard spots where the current Rev spars join, and give us a better constant luff curve bend. I didn't look this morning, however I doubt this hard point is taken into account in the current luff curve.


I think Airx 500N - VMG (31 grams /sqm) would be ideal, athough it is very difficult to print onto. Hard finish, little stretch - work for a long time then break, so you know it is done!
Probably want to orientate warp parrallel with leading edge. Difficult one this, I think I can argue for fill parrallel with leading edge too.
Agree?

Sparky

#40 Jonesey

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Posted 25 March 2008 - 03:38 PM

Probably.... But obviously anything not Rev stock is cheating! (not to mention copyright/patent etc!)

might email Lolly and see what custom materials options are or if a 'bring your own' material option exists!!

On the other hand we could just practice more and learn to fly what we have properly first ...




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