Duotone's Ken Winner Slams Ram Airs

[Pump me up]

Ken Winner, one of the most respected kite designers, has slammed ram airs:

Well the North team has now taken the top four places in both of the 2011 PKRA production class race series' using the new Dynos and the new raceboard, and we're starting to get some really positive feedback on the Dyno as an all-around lightwind kite, so for those interested in the technical side of the Dyno's design, here are some notes from designer Ken Winner:


Parafoil vs. Inflatable

The debate has rumbled and flared in kite forums, newsgroups and blogs like a distant storm: Which is better, inflatable or parafoil? Despite years of well-earned market-place dominance by inflatables, parafoil fans have always been able to point to one area of seemingly unquestioned parafoil superiority: super-light wind conditions. While parafoils have never fared well in high-level old-school or new-school freestyle competitions, and they are seldom seen in moderate- and strong-wind racing, they at least seem sometimes to be competitive in races that take place in super light wind. They have good power and they remain in the air in even the lowest lulls of a low-wind session.

At North we have long designed and produced parafoil kites, and have always felt that they are well suited to their correct millieu, such as training and snow-kiting, but at the same time we have remained convinced that the inflatable can and should dominate in all on-water circumstances - even in extreme light wind. Our reasoning has been that the factors which produce superior performance in other wind conditions should provide an advantage in light wind as well.

For example, the rigidity of the stucture of a parafoil is determined by the difference in internal and external air pressure: A very low number -- less than one pound per square inch. By contrast, the inflatable typically has a huge structural advantage of six psi and often more. You don't see performance-oriented aircraft with soft structures in other areas of flight. Birds, wasps, stunt kites, fighter jets and passenger aircraft are all rigid. Likewise, you should not expect performance kites to be soft.

One weakness of a soft structure is the lack of tactile feedback it offers the rider. The kite is soft so the feedback is soft and imprecise. The rigid inflatable kite by contrast provides a wealth of nuanced feedback to the rider -- feedback about kite position, rate of turn and gradations of power delivery.

Another issue with parafoils: They're thick. People sometimes look at the thickness of an inflatable leading edge and judge that to be a liability. However, the thickness of a light-wind parafoil is typically two to three times as great. Worse, much of that thickness is carried back in the profile to very near the trailing edge. Anyone who has looked closely at the trailing edge of a parafoil can easily imagine the gross aerodynamic inefficiency such thickness must entail. An inflatable trailing edge, by contast, is thin and aerodynamically efficient.

An additional issue with parafoils is weight. While the parafoil itself is typically light, the amount of air entrained by the flying parafoil can be quite heavy. This entrained air is indeed so heavy that it encumbers the parafoil and makes it slow to turn and accelerate in a dive or the upturn after a dive. Lacking nimble turning and quick accleration results in weaker dynamic power -- the power you get from flying the kite aggressively.

While there are yet other problems with parafoils, such as incredibly complex bridles and weak water relaunch, the main remaining one to mention here is wind range. Parafoils simply don't have the depowerability that a good inflatable has. This means, of course, that parafoils have more limited range of use and less inherent safety than a good inflatable.

Given all the inherent benefits of the high-pressure inflatable structure in water kites, why have inflatables not dominated parafoils in light wind? In a word, weight. All that inflatable structure comes at a cost in material weight which has made inflatables more difficult to fly in light winds. New materials and construction techniques however, have now opened the door to weight reduction in inflatables, and, as usual, North is ready to take advantage.


The Dyno

Enter the Dyno. This is the light-wind kite. It offers parked power similar to a parafoil together with superior dynamic power, better depower, more nuanced bar feel, better turning speed and superior safety (owing to inflatable elements). A versatile kite that will fly on either four lines or five, it's much like the Fuse in performance and handling, but better in the way it handles light winds and lulls.

Weight - Low weight is clearly the Dyno's main feature. To get it we took several steps. We eliminated the Lazy Pump inflation system because single-point inflation adds weight. We went to thinner bladder material and a lighter Dacron in the inflatable elements. Construction details that contribute crucially to function and durability remain, others were eliminated.

As a result, the 18-meter Dyno will fly in winds that are barely perceptible.

Quickness, Turning & Feel - The Dyno feels much like a Fuse, but with one difference. Since the Dyno is lighter, it turns and accelerates more quickly than a similarly sized Fuse would. If you're flying a sine pattern in light wind, for example, the light Dyno will turn and fly up from a dive more quickly and thus generate more power than a heavier kite would.

Right-sized LE Diameter - Some years ago when we were working only with "C" kites, we were able to make the leading edge diameter pretty small without paying a large penalty in shape stability. However, nowadays, on kites with flatter arcs, comes greater need for shape stability through the rigidity of the inflatable leading edge. This means it's a disaster to have too small a leading edge. How do we know? We've tried small LE in flat prototypes and ended up with narrower wind range, worse upwind performance and unstable bar feel. We've also tried small LE diameter heavily supported by an elaborate bridle to much the same effect.

Granted, if we were willing to inflate the LE to 15 or 20 psi we could get stability AND a smaller LE, but that would mean using heavier LE cloth or far more expensive LE cloth, or both. Worse, hand-pumping a big LE to 15 or 20 psi would be hard, hard work.

Therefore, and for now at least, the Dyno has a leading edge diameter that doesn't require high pressure yet gives good arc stability.

Thin Struts - Dyno struts are on the thin side so as to minimize weight and aerodynamic drag. They don't need to be pumped hard. Six psi will do.

Seven Struts - The Dyno 16 and 18 have seven struts so that stability is ensured in high wind and under the heavy load of big riders. Whether a big kite needs five, six or seven struts is a matter for debate and ideas will certainly change over time. However, since the Dyno has to work for big riders in big winds as well as light, we figured we'd play it safe and make sure the canopy would retain an aerodymanic shape under load.


Other notes

Grunt vs. Quickness
Every kite has a combination of grunt and quickness. "Grunt" is the power a kite produces when it is parked or not moving very fast. "Quickness" is the ability of a kite to turn and accelerate quickly. Small kites are typically quick. Big kites are typically grunty. Designers are always trying to make their small kites more grunty and their big kites quicker.

The big benefit of grunt is that it's easy. You sheet in, you go. The disadvantages of grunty kites are:
- often don't depower well
- often don't fly to the edge of the window and so don't go upwind well
- often don't turn well or create big power spikes
- tend not to jump high

The big benefit of quickness is that a quick kite can generate a big power spike -- the hard, sharp pull you get when diving the kite or sending it for a jump. Quick kites can also:
- turn quickly and provide satisfying handling
- jump high
- depower well
- go upwind well

The only liability of quickness is that a quick kite is less of a sheet-in-and-go type of kite.


The Case for Quickness
Two trends in kiteboarding favor a quickness bias in light-wind kites:

- light-wind boards, both twin-tips and race boards, are quite efficient. Once they get on a plane they continue planing with little power from the kite. The quick kite permits the rider to make a short, sharp dive to get onto a plane, then flies quickly to the edge of the window for staying or going upwind.

- More riders are using long, 32-meter flying lines in light winds. Longer lines give longer power spikes from diving the kite, which means riders are depending more on the quickness of the kite than its grunt.

Bottom Line: Even the Largest Dyno is more Quick than Grunty

[OzBungy]

Makes more sense to the see the original posting than a cut and paste

http://www.facebook.com/topic.php?uid=2 ... opic=17227

[Puetz]

... not exactly a slam there dude, but he does raise some interesting points though!!

For me, if Ken says it's so, then it is so, for me! Ken is a legend!!

[Pablo]

though what this guy says is probable true regarding the performance of his new kite, he certainly has no clue about aerodynamics.
"Another issue with parafoils: They're thick. People sometimes look at the thickness of an inflatable leading edge and judge that to be a liability. However, the thickness of a light-wind parafoil is typically two to three times as great. Worse, much of that thickness is carried back in the profile to very near the trailing edge. Anyone who has looked closely at the trailing edge of a parafoil can easily imagine the gross aerodynamic inefficiency such thickness must entail. An inflatable trailing edge, by contast, is thin and aerodynamically efficient."

one thing is LE thickness-diameter and another profile thickness. since the lower part of the LE (in LEIs) has no bottom skin you have to pay a huge price in drag... (actually a single skin LEI kite is closer to wright's flyer!)... if this guy was right paragliders would be inflatable too...

anyway there's no point in discussing these things here, but it really annoys me when these guys start talking like they knew what they're talking about. kite design has so many variables that the only way to make it is trial and error, only with a little tought between prototypes. KB has evolved so fast because building prototypes is cheap and quick.

they should just say "we've tried hundreds of kites and this one worked great, even better than foils in low wind" most of the other stuff is just BS. but of couse, talking fancy stuff sells better.
pablo

[Nico]

Another marketing splab by Mr Ken Winner.
Thats his job, good job I suppose.
Nico

[Toby]

any company who is releasing a light wind kite will target the Flysurfer foils PMU, guess why? Maybe because they are good and known to be the first on the water?

[Kamikuza]

Slow as usual, PMU or should we say "Ken" Already put that one to rest ... and all I had to do was pick holes in the logic of his (sorry, your) 'arguments' ...
viewtopic.php?f=1&t=2369595

[Feng]

You don't see performance-oriented aircraft with soft structures in other areas of flight. Birds, wasps, stunt kites, fighter jets and passenger aircraft are all rigid. Likewise, you should not expect performance kites to be soft.

What about paraglider ?
As far as I understand, paraglider are not exactely "hard structure".
The word "performance" has no meaning if you do not precise the metric associated too.
Handgliders (i.e. hard structure) are aerodynamically better than paraglider (soft structure) but the number of paraglider pilot is declining sharply.
Why? Because Handglider have less performances when you have to carry the whole thing on your back to walk to the take off. It is all about the associated metric

Worse, much of that thickness is carried back in the profile to very near the trailing edge. Anyone who has looked closely at the trailing edge of a parafoil can easily imagine the gross aerodynamic inefficiency such thickness must entail. An inflatable trailing edge, by contast, is thin and aerodynamically efficient.

I am not very sure about this statement (I am not an aerodynamic expert, I have only the basic scientic backgroud).
In aerodynamic you want narrow but long wing (i.e. big aspect ratio => reduce drag). Due to their structure, foils can offer better aspect ratio than inflatable.

This entrained air is indeed so heavy that it encumbers the parafoil and makes it slow to turn and accelerate in a dive or the upturn after a dive. Lacking nimble turning and quick accleration results in weaker dynamic power -- the power you get from flying the kite aggressively.

This is probably the main point why inflatables have "better" performances that foils.
Because the inflatables are more rigid, we can turn them quicker so you can create faster your own apparent wind (the lift is basically a product of the speed on the air going through the wing). Basically, the rider can use better its own muscle (its arms) through the control bar ("S" figure) to increase quickly the apparent wind and then add lift when needed (i.e. when the breeze is temporally decreasing after a gust).
But in smooth constant wind (typical of light condition) a foil has probably better aerodynamic performance.

I am also wondering if the shape (reverse "V") does not make the inflatables less stable (in an aerodynamic sence) that helps the quick turning and again helps the creation of apparent wind.
To take an example, flighter plane wing are like a reverse "V" (just look at a picture facing the plane). This makes flighter planes less stable so they can turn quicker which is a very important factor of survival during dog fight.
On the other hand, sail plane have a "V" shape (just look at a picture facing the plane). This makes the sail plane more stable. It is harder to turn but in other hand it "automatically" adjusts itself to make the best use of the air flow on both wing and therfore maximize the lift.

[Mr_Weetabix]

Given all the inherent benefits of the high-pressure inflatable structure in water kites, why have inflatables not dominated parafoils in light wind? In a word, weight.

Given that this thread could be renamed as "man selling kites says that his kites are better than kites sold by somebody else", I'll assume that Ken isn't the most objective commentator, but if North's new materials get over the inherent weight problem in big pumpy kites (without compromising durability), kudos to them. I'm waiting for a side-by-side comparison between the Dyno and the Speed3.

After finally getting a chance to get my Speed3 in the air last weekend, I'll admit to being a convert to the foil camp as far as light wind kiting is concerned (my 17m Contra is now doomed to be a beach shelter for the kids, unless someone wants to buy it). However, I'm not about to go all Ram-Air Fanboi and ditch my smaller tube kites. I would rather have a simpler bridle, and it is reassuring to have a kite that you can use as a raft if all else fails. If someone without an agenda (hahahaha... on this forum?) shows that the Dyno will stay in the air under the same conditions as the Speed3 (and the lightweight materials don't cause durability issues) then it will be my next light wind kite. Until then, on light wind days, I'll be the guy flying the giant pillowcase.

[voodoospirit]

well, i hope he didn t base his statement after using north foils (low aspect open cell slow foils)....theyr are stable...but they are probably trainer-side than fast and performance kites...
anyway, he might be good in races and kite design but he seems kinda clueless about modern foils.
every 6monthes, we hear that new kites are THE best kites ever created...
he should try to see if its kite is better than the zephyr....

they might need 32m lines because their kites dont have an enough high aspect ratio to park it immediatly at the edge of the window and to get off the water at the same time..so i can unerstand they need to work them to get a powerstroke to get apparent wind and then park them.