Two 6M2 Pilots At Nelson 2014
Pilots and lifters are now everywhere, spreading thru the upper reaches of the sky where they lurk like some outlier cult, disturbing the peace of those below with their squabbles. But there are some positives:
Unquestionably the pilot kite/show kite train system has enabled a greater density of larger and more interesting kites to fly at festivals, and in a wider range of winds- which has contributed directly to the explosion of new kite events now evident throughout the world (and especially Asia).
Elwyn and I expect to be at kite festivals in 8 different countries in just the first 4 months of this year.
The pilot system pretty much started 25 years ago on US beaches with John Waters and Doug Hagaman, et al. Even then it was apparent that ram air inflated parafoils (including Flowforms) would become the dominant style. They clearly have- though parasleds (a hybrid ram air/single skin/carbon rod style) still have their loyalists and there remains a niche for deltas and rokakus at the small end.
Parafoils have been the type which I've mainly worked on during this period, specifically 4 cell low aspect ratio Pilots and Lifters , following the style of Dom Jalbert and John Waters.
Which is about to change- not that I'm going to abandon current designs or even stop incremental development of the parafoil type- it's more of a plateau while two other directions are explored.
But first some housekeeping:
On the peterlynnhimself site there are plans for a 6sq.m 8 bridle Pilot kite, first posted about 2 years ago.
From emails and comments on kite forums, some makers have difficulties with these plans.
Robert van Weers and I have been fielding two main types of queries:
The first is typically: "A flare, rib, and panel are sewn together in each outer lower seam, but the plans show them as having different lengths. There must be a mistake".
This one's easy to answer; the dimensions in the plans are correct; the lengths that need to match are after a seam allowance has been taken off each edge (which requires that long tapered pieces like the flares and ribs are nominally much longer than square ended pieces like panels).
The second is that the bridle dimensions are wrong.
This has been much harder to resolve, because there was a mistake in the plans as first published, a simple number transposition; (2.59m was written as 2.95m). It was corrected immediately on peterlynnhimself, but not until last week at the peterlynnkites website. Apologies for this. Bridle Dimensions.
But even with this error corrected, there have been queries which have been difficult to answer conclusively because I've never actually made a kite off these plans (they were prepared from the last of many prototypes and this actual kite was then stolen at the Weifang event in 2013). Robert van Weers has made one- but with a somewhat different bridle- and I was able to test his and a 2011 example (which turned up at the PL Kites factory) during the Nelson event in January. They both flew well (very light to quite strong wind), from which I conclude that problems are most probably caused by differences that makers innocently introduce.
Even for very simple kites like these pilots, small changes can have big effects that are not at all obvious.
What may seem like inconsequential changes or obvious "improvements" often aren't. For example, the positioning and sewing method for reinforcements is critical, as is the placement and size of cross venting. Bridling "improvements' can also be a problem if they only suit a narrow range of conditions. The published bridle dimensions for this Pilot (attached) work from 8km/hr to more than 100km/hr (with careful tuning) and in unsteady winds.
Parafoil tuning is another area that needs to be explained more clearly. Perfect lateral symmetry being unachievable (not least because of inherent asymmetries in fabric), every kite leans to one side or the other at some wind speed unless it becomes unstable or breaks first.
Kites therefore need a tuning system to correct bias- and that can also be used to keep clear of adjacent kites.
Few fliers seem to understand how to do this for parafoils.
Increasing or decreasing the bridle angle of one side of the kite is often tried, but almost never works (especially for kites that are longer than they are wide), because such changes have very different ( even opposite) effects in light and strong winds.
What does work is to increase or decrease the camber of one side relative to the other without changing the bridle angle. Increasing the camber on the side the kite is leaning to, or decreasing the camber on the opposite side will correct bias evenly across the entire wind range. .
For a Pilot with 3 bridles/side this is done by shortening or lengthening a middle bridle while leaving the forward and rear bridles unchanged. For kites with only one bridle/side, a draw string at about the maximum camber point on each outer top seam can be pulled in on one side or the other to reduce the effective camber on that side.
But this is enough housekeeping for now.
One of the two new pilot kite designs I'm moving to is itself a show kite; the Ray, first made in 1988. They've always flown well in smaller sizes, and by 10 years ago were beginning to perform adequately up to midi size, but even after thousands of hours of effort, refused to fly reliably without a pilot in larger sizes (they occasionally slide off and collapse to one side or the other). The cause of this misbehaviour has to be in a factor that doesn't scale; most likely fabric stiffness or mass/area ratio, but knowing this- for 25 years- doesn't seem to have been of much help. Three Quarter Maxi Ray as Pilot.
I'd begun to despair of ever finding a solution, then over the last year or so, better inflation- by way of a slightly different valve design initially developed for the smooth tail Rays- has finally fixed the problem (strongly suggesting that the fabric, soft as it is, provides just enough rigidity to overcome inadequate inflation in sizes up to and including midis, but not for maxis).
PL Kites Ltd now offer a 9kgm bucket-tailed ray that does not require a pilot in any wind conditions and is suitable for lifting and stabilising trains of other show kites.
They also offer a mid sized ultra light ray which not only flies well without a pilot but outflies even Pilots in very light conditions.
The other new direction is towards single skin single line kites. SSSL Prototype #4
The goal is a kite that has no rigidifying elements or ram air inflated spaces and is scalable to larger sizes that will fly stably and tailless on a single line in a suitably wide wind range.
Do such a kites already exist? I know that Robert van Weers has made at least one promising prototype but I'm not aware of any kite that yet meets the above criteria. Sure, parasails and Nasa single skin traction kites will fly single line if enough weight (like a person) is hung beneath them, but this disqualifies them.
The incentive is that for somewhat inexplicable reasons (probably magic), single skin kites are luff resistant even while using highly cambered profiles. A consequence of this is that they fly in less wind and with more pull than other kite styles. But there are two significant challenges:
The first is that for single skin kites, the angle of attack range between stalling and collapsing is almost non-existent (which is why single skin traction kites are easily provoked into flying backwards uncontrollably).
The second is that single line stability is compromised by the requirement for the centre of pressure (where the lift forces act) to be a long way back in order to prevent leading edge collapse. (For single line kites, lift forces must act at a point substantially above the centre of gravity so that the kite points itself upwards.)
These constraints have made development of single skin single line kites very difficult-but I think now that they probably are possible- because the 3rd prototype I built flew well for some hours at Nelson in January- good angle, stable, excellent light wind flying, and huge pull for its size- though its leading edge was inclined to collapse above 20 to 25km/hr. SSSL Prototype #4 at Nelson 2014 Showing Reflexive Profile.
But then the "improved" 4th and 5th prototypes didn't fly at all, in any wind, even after hours of minor bridle and skin changes. Still, the key discovery is secure; that such a kite does seem likely to be practical.
I'm almost pleased that 5 is a failure so far- because problems that are too easy to solve just aren't fun.
PETER LYNN, KUWAIT, FEB 1 2014.