THE NO-WIND KITE!
Plus a useable single skin single line kite and a better 9sq.m pilot.
Quite a few things can limit kite flying at events; rain, snow, too much wind, gustiness, lack of space, no anchors, - and ever more often now; "health and safety", and infestations of "kite tourists" who are too lazy to do what they are invited for (which I assume is to fly kites- but I must be wrong). 22sq_m Airbanners Balloon enabled Lifter flying in very light wind
But by far the most common is lack of wind.
Which stops the show perhaps 10 times as often as all other causes in total.
Including on 10 out of 14 days at the 6 events I've been to in the last 4 weeks- undoubtedly the worst run I've yet experienced in 30+ years of international kite festivals.
But a combination of the desperation this engendered and the availability of helium balloons at some of these events has provided one quite practical answer:
Putting spherical helium balloons INSIDE a 22 sq.m Airbanners Lifter. 22sq_m Airbanners Lifter flying with internal balloon assist following Gavin home
This was spurred by how kitefliers now routinely use clusters of the organiser's promotional helium balloons to hold their kites up in the absence of wind at events like Chengdu, Chongqing and Uiseong.
Putting the kites inside is just the next step; a way to allow the kite to remain in the air when the wind comes up rather than having to pull it down to take the balloons off (lacking streamlined shape, tethered balloons are pushed to the ground in even moderate winds).
Yes indeed; like for many inventions, this one too was fathered by laziness!
Previously, most of my thoughts about lighter than air kites have been in relation to ram air traction kites, and for these, the minimum size that would be easily self-supporting is around 20 sq.m- which could be achieved either by using bladders shaped to fit every cell, or by using fabric that is helium proof.
I've never made such a kite, either way, but I'd generally favour the bladder approach, because when the wind is strong enough, the bladders could be removed and the remaining fabric kite would then be lighter and fly better. 22sq_m Airbanners Lifter fitting balloons.
For single line Pilot/Lifter kites, the smallest practical size for lighter-than-air self-support is less than for traction kites because, being proportionally fatter, they have relatively more internal volume. With fitted bladders, a 10 sq.m pilot could probably be self-supporting. But by 22 sq.m, the bladders don't need to be especially shaped; 4 spherical helium balloons, each a bit more than 1.2 m diameter will fit inside without distortion and provide enough lift for positive buoyancy.
The advantage of this approach is that such balloons are inexpensive and widely available off-the-shelf.
Although the balloons we used in Uiseong (Korea) for the first trial were undersize (around 1m diameter), and over-weight (rubber rather than Mylar), four of them could still almost lift themselves plus a standard weight 22 sq.m four cell Airbanners Lifter.
So, problem solved!? 22sq_m Airbanners Lifter with internal balloon assist
Well not completely, because this 'balloon enabled' Lifter is not (yet?) reliably stable without removing the balloons above perhaps 25km/hr, which isn't very satisfactory.
For smaller sizes I always aim for a 100km/hr upper limit but 60km/hr is acceptable for this larger size as above this there's more pull than can be reasonably be used.
This early-onset instability happens because the lift from the lighter than air gas, its placement and containment inevitably changes the relationships between shape, forces, weight and mass that determine stability for single line kites. As all aspiring kite builders soon find out, if even one of these variables is outside a narrow range, at ANY wind speed, you no longer have a kite but an angry object thrashing around on the end of a piece of string- so I don't expect that getting a lighter than air kite to fly stably over the full range will be anything but very difficult-
Luckily, it doesn't wander around during the initial transition from balloon lift to aerodynamic lift as I thought it would- recalling the 1960's "Kitoon" (?) a balloon that was specially shaped to generate aerodynamic lift and also fly as a kite, which reportedly did behave like this. I'm not sure why this Lifter/balloon combination doesn't have this problem, but it's not a gift I'm about to turn down! 22sq_m Airbanners Lifter with external balloon assist, Chongqing 2014
But I also expected that the balloons would cause the onset of volatile instability at a lower wind speed than the kite would otherwise exhibit- and this did seem to be the case.
I also anticipate that the tendency to volatility should decrease again in even stronger winds as aerodynamic forces overwhelm the puny balloon lift, but haven't tested for this yet.
What I can say now with confidence is that that a 22 sq.m Airbanners Lifter containing four 1.2m diameter helium balloons (near the leading edge in each cell) will reduce the minimum wind speed required to zero without effecting the kite's stability until at least 20km/hr. For useful lift, some wind is still necessary- but a LOT less than previously. And, with internal balloons the kite becomes self-inflating and self-launching, even in flukey conditions.
Ultra-light (35gm/sq.m fabric instead of the standard 50gm/sq.m) 22 sq.m Airbanners Lifters from now will be fitted with internal cords in each cell for attaching balloons.
And, at Uchinada (Japan, April 27th), we used SSSL 19 as a pilot kite (above a Ray) for the first time. It was excellent; very steady, higher flying angle and an unbelievable amount of pull for its size (less than 2 sq.m) by comparison to an 8sq.m pilot. When the wind dropped off in time for packing later in the afternoon (as should be arranged at all kite festivals) it hung on about as well as any of the standard pilots and lifters there. This was a big relief, as light wind reliability is by far the most difficult problem I've encountered with single line single skin kite development so far. 22sq_m Airbanners Lifter flying with internal balloon assist.
But even for kites that don't have balloon assist, standard pilots and lifters no longer set the light wind standard.
Because at the same time, a latest model (mid April) 9sq.m Airbanners Pilot didn't even seem to notice that the wind had dropped- and had useful pull even when everything else was lying limp on the ground.
Which is also a pleasant surprise; 10 years of concerted effort to lower the threshold wind required for Pilot kites had yielded barely an extra km/hr or two (the PL Kites Ltd 8 sq.m ultra-light pilot being the recent benchmark), then suddenly it just happened.
The gain came from reducing leading edge depth and increasing camber- which is obvious enough- though that this model has been able to accept these L/D improving changes without becoming unstable is another stroke of blind luck that I am delighted to accept.
Not a bad month!
PETER LYNN, Ashburton, 1st May 2014
(Back to winter here. I won't be at Vung Tau on the 10-12th May- need some sewing machine time to refine the above developments- but Elwyn and I will be at Kelantan later in the month.)
Peter Lynn Kites Ltd
105 Alford Forest Rd
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