Interesting. Good spotting.
In aerodynamic terms having a void behind the LE is definitely creating an area which would add considerable drag with the low pressure behind the LE requiring constant changing pressure to neutralise the void zone inside airflow stream. ie constant turbulence & a constant reverse thrust on the LE flying forward.
The natural flow of air over an obstruction creates a void which is 5 times the height (in this case depth) of the obstruction. So if the centre of the LE is say 150mm then there is reverse thrust turbulence extending for an area of 750 inside the canopy. (NB the length of the void may be reduced by the fact that the LE is cylindrical - ask an engineer?)

But whatever it would be significant. IMO the shield as shown would negate this effect. How much better will it fly ???
Apply that other rule - demo demo demo.

Back in 2007 we experimented on kites with a cover under the leading edge, also with mesh and Velcro shaped Styrofoam inserts, was interesting but we did not get much of a performance improvement over just using thinner leading edges. This idea has been around for some time and is not too hard to come up with the idea when looking at a kite and wing. I have not seen any designer going with it long term. Will watch with interest :)

... some of the old timers here may remember the Gaastra Phoenix which came out with a double bladder LE that made it more like an oval cross section so in theory, that made the LE thinner or less drag with almost the same support. Probably didn't have big advantages because you don't see them anymore but was interesting idea.

Robbie

Puetz said..

... some of the old timers here may remember the Gaastra Phoenix which came out with a double bladder LE that made it more like an oval cross section so in theory, that made the LE thinner or less drag with almost the same support. Probably didn't have big advantages because you don't see them anymore but was interesting idea.

Robbie

Yeh I do remember back somewhere in about 2001/2002 I do remember someone having something like this Robbie. But I'm not sure but I think the wing was a lei with entire double surface ...kind of a cross between a foil and a lei...anyone remember those...?

Might not be what you are talking about here though??

eppo said..

Puetz said..



... some of the old timers here may remember the Gaastra Phoenix which came out with a double bladder LE that made it more like an oval cross section so in theory, that made the LE thinner or less drag with almost the same support. Probably didn't have big advantages because you don't see them anymore but was interesting idea.



Robbie

Yeh I do remember back somewhere in about 2001/2002 I do remember someone having something like this Robbie. But I'm not sure but I think the wing was a lei with entire double surface ...kind of a cross between a foil and a lei...anyone remember those...?

Might not be what you are talking about here though??

... the Gaastra Phoenix definetely had the double bladder LE so the LE was oval shaped, with normal canopy.

I was given a 25m and man did that thing jelly fish when loaded up, was a pretty ordinary kite but had the longest hang ever, but did nothing else good!

Robbie

Kamikuza said..

And I seem to remember reading something that stated the backwards eddies aren't a drag, as they create a buffer that mimics the effect of a double skinned kite...

Want to play with airfoils? Get a Flysurfer

We are all playing with air foils.
The LEI shield shown mimics the effect of a double skinned kite. The troughs & eddies behind a LE are the opposite.
Wouldn't put money on it but I reckon the LE shield would make a noticeable difference. Have to fly the same kite with & without to tell though.

eppo said..

It's the areodynamic inefficiency of a lot of lei designs that actually allow certain styles of riding.

Exactly!

This ASV design isn't new however, as pointed out many designers have tried similar ideas before.

....if efficiency is your game ie racing for sure. Maybe big air, hangtime wise. For everything else can't see how more efficiency would be an innovation.

Reminds me of the exact same evolution of hang-gliders back in the early eighties. The % double surface went from 15 upto 90 in the course of a few years. At the time the style and goals changed to include more distance type competition.
When I last did training you learnt on a lower aspect ratio kite with approx 30 % double surface easier to control wind range was lower i.e easier to take off / land but could not go as fast, the surface material was also slightly looser allowing easier control (weight shift loading up the side you wanted to turn to, this increased the dynamic drag on that side and lowered it on the other - presto a turn - very similar to kite surfing). The more performance orientated gliders have more aspect ratio, more double surface and could also tighten / loosen the sail in flight by using a chord (similar to depower!!) / pulley arrangement to move the main cross spars (= VB Variable Billow). To achieve the tight skin and accurate top surface profile (the bottom surface was essentially flat) you had up to 20 cambered battens to insert. It was a fantastic time to be experiencing the change and evolution as the sink rate decreased the speed range cranked up and the glide angles improved - one of the grounding factors was the under carriage did not change and you still had to land at a speed you could run at - into a wind - not an issue, but landing out in a hot fairly windless paddock with wind eddies causing odd wind directions - could get a bit exciting

Realistically most of the wind range we use is well catered to by the current designs - the trade-off will be flexibility we currently enjoy...
One main difficulty in having more than say 10% double surface comes from the bend in an inflatable kite leading edge. Most masts and wing leading edges are dominantly straight in one plain and apply a fair amount of tension to the sail or have a rigid surface to get the desired shape.
As discussed above when would improving the camber profile be useful?

On all kites when you have to bar out to stop the kite from stalling on the up stroke - upto approx 30% double surface would give a large improvement with diminishing returns after that.
On straight line speed runs - to compete with the sailing aero foils - i.e. in it to win it with a show pony.
On snow / land kites.
I could see a new range of high wind kites for on the water with 30-50 % double surface (once the teething troubles are sorted) would likely drop the kite size down possibly along these lines..
8M = 5-6M
6M = 4M
etc.
So an inflatable for the structural shape and a ram-air double surface for the profile performance and water proofing... a quality control nightmare using current build techniques

But it would be great to get the wind / water speed record back

Cheers
AP

The problem back then was conditioning - designers following & mimicking existing shapes foils or inflatables...

One kite had to do everything but make dinner :)

Now we have specialised kite shapes for various styles of riding.

Someone ought to get back to the drawing board and get creative with existing technology - change the shape 'against popular opinion' (can you say Sigma ;) design it purely for speed and reverse launchable only...

No but but buts and break the speed record...

The traditional hull shape that broke the wind/water record actually was not touching the water when they broke it - Hey

Shape Change outside your box

sir ROWDY said..

eppo said..

It's the areodynamic inefficiency of a lot of lei designs that actually allow certain styles of riding.

Exactly!

This ASV design isn't new however, as pointed out many designers have tried similar ideas before.

Even the older ASV design is not new, it is a blatant copy of the Ozone Edge. No ifs or buts about that, put them side by side they are identical. The skin on the underside of an LEI has been done before, and abandoned for good reasons.

@ Kamikuza - how come FS have dropped the mixer on their latest kite? How come they make an LEI too? Just asking, I'm a big fan of foils, but not a big fan of complexity that does not deliver worthwhile results.

The ? remains.. Is the ASV under foiled shield effective?
How much would the Edge & the other high aspect racers benefit from the LEI shield.
I concede its been done & tried before but we are now entering an age of competition kites where every slight advantage becomes a priority.
Just consider the charlatans that are promoting spray on slip & slide nano-concoctions for surf board hulls.
If theres an advantage to be had at all it has to be negligible even amongst the top performers - but reports are they are selling heaps to all sorts of wannabe champions.
Im not claiming rights here but imo the turbulence preventing under-shield foil will become a standard of future kite design. If not on all kites then at the very least on performance race kites. Its a super low (almost zero) cost add-on to production which, by scientific rules of nature, has to have some advantageous effect those pushing the boundaries will benefit from & require of their kit.

sir ROWDY said..

^Can't tell if serious or trolling.

I guess the reason you think im trolling - is the same reason thats holding us back from the 'Speed' record.

I left a very good clue in my yarn about going forward in kite design.. Reverse launch !!!!

I noticed everyone is "still" throwing the traditional foil & LeI design back n forth - nothings changed since way back

Funny how all water kites are performance limited, by their relaunch ability

eppo said..

Puetz said..

... some of the old timers here may remember the Gaastra Phoenix which came out with a double bladder LE that made it more like an oval cross section so in theory, that made the LE thinner or less drag with almost the same support. Probably didn't have big advantages because you don't see them anymore but was interesting idea.

Robbie

Yeh I do remember back somewhere in about 2001/2002 I do remember someone having something like this Robbie. But I'm not sure but I think the wing was a lei with entire double surface ...kind of a cross between a foil and a lei...anyone remember those...?

Might not be what you are talking about here though??

you talking about the black mosquito kites that elliot used to ride eppo?

Got to love the knowledge and experience that AP and STW are throwing in this discussion, must have been an incredible time to be involved in gliders. One thing that must have driven the development, was the urge or desire to "go further", and that there was a demand, in a commercial sense, that funded the development.
The minds behind brands like FS and Ozone are the same ones that were involved in PG and glider design, amongst many others I've never heard of for sure, and it stands to reason that developments in improved efficiency in kites will come from brands like this. Possibly other innovations will come from outside these fermentors of creativity, and although it seems like sigma had its roots more in wanting to be commercially different and to capture the wallets and minds of an eager public wanting something unique and better, it would seem that the idea had it a source in improved aerodynamics. There have been some very innovative designs that never made a commercial light of day, things like the Seasmik, and PL C-Quad, as well as LEI's with a filled in lower surface.
The problem with all of them is that they had practical and ease of use limitations, and therefore they had limited commercial success, and consequently died a natural death. I wonder if in these affluent times, someone with deep enough pockets, will take the gamble to think and produce outside the square?