Paper Kite Posts—Rokkaku

(Paper Spars)

It's an archive of sorts, although there are no dates and times. Kite flying is timeless, don't you agree?

I trust there is plenty in here to educate, inform, and often entertain!

These short flight reports once appeared as posts in the site-blog page, although that page is no longer present on this site. Below, the latest posts come first. Just scroll down and stop at any heading that appeals :-)

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Paper Rokkaku Kite

Rok Wraps Up Testing

There were just 5 minutes left to log. This was easily achieved in the gusty moderate conditions today.

Wings in Wind Gradient

It was late afternoon, with a cool moderate breeze gusting across the small local reserve.

First up was the Paper Rokkaku prototype which now needed just over an hour of flying time to be certified for durability. The first flight was just 5 minutes and the second just 10 minutes, despite the boisterous gusts blowing paper rubbish across the grass. This was a sure sign of there being sufficient wind for any Paper Series kite! However, it was a small reserve and the amount of thread out was correspondingly short. This made it far harder for the kite to stay off the grass during longer lulls.

Looking around, I decided to really make the most of the wind direction and available space. Hence perhaps another 10 or 15 meters of thread went out with the kite still clear of major obstacles. This really seemed to do the trick and the rokkaku never came close to dropping out in a lull after that.

In fact, the opposite reason kept the kite low from time to time—excessive wind speed. The kite would get forced down to within just a few meters of the ground. At this point, the slower air down there would allow the kite to stay airborne. Sooner or later a drop in wind speed would allow the kite to climb back up.

The change in speed of airflow, from slowest at ground level to a maximum at some higher height, is called wind gradient. The rokkaku was making good use of it today, where the effect was most noticeable below about 50 feet of height. In strong wind over rough terrain, the effect can exist right up to 1000 feet or so.

While the rok was up I did some flying with the Paper Sode. After flying quite well with some extra tail added, the kite started to show signs of spar failure at the middle. This was mainly on the lower horizontal spar. So, the upper one will need to be a bit bigger/stronger and the lower one quite a bit bigger/stronger. The extra dihedral resulting from the partial failures actually made the little kite cope brilliantly with the strongest gusts! So, some extra dihedral angle will be incorporated as well, in the next prototype!

It was a good productive outing. There are only 5 minutes to go to fully certify the Paper Rokkaku while some solid info was gained to improve the Paper Sode design.

Rok Climbing—And Descending

Once again, a foray to a local reserve in the morning proved disappointing. But then, later:

Noticing some tree waving going on outside, I hastened to get back out to the same reserve with the Paper Rokkaku. Also on board was the new Paper Sode with its own winder. After some initial troubles with the thread catching and breaking over dry weeds, a good blast of warm air got the rokkaku out on plenty of thread.

Despite the almost excessive wind speeds that were powering across the reserve, the lulls were just as extreme. To my surprise the Paper Rok was soon back on the deck! It wasn't long before another almighty gust got the little kite away once again. This time, I let out as much thread as I dared, given the available space.

This flight lasted 15 minutes before a drawn-out lull once again grounded the kite. A relaunch resulted in a rather short flight, but I just let the kite sit there for a while. It was time to try out the new Paper Sode. The sode flew very stable at modest wind speeds but will need more tail for the top end of the moderate range. Anyway, back to the rok.

Some minutes later, another fierce gust managed to pop the rokkaku back into the air all on its own! This flight lasted for 15 minutes, and a very wild ride it was. Medium-sized branches were moving about, the leafy portions positively thrashing at times. The wind direction shifted by 30 degrees or more. That's a lot, considering the general strength of the wind. This wasn't "light and variable"!

Much of this final flight was somewhat concerning since the kite spent some time in fast-moving sinking air—very close to trees. At other times the kite was very high in rising air. Either way, a thread breakage might have been bad news for the kite. Getting stuck in a treetop or flattened by a car were just two possibilities.

Retreating to the car after bringing the kite down, I realized that it had been most fortunate to still have the kite. It was resolved to only fly in safer coastal conditions from now on. At least until that 3 hour durability milestone comes up in the log.

A Rok Thrown High

Earlier today, the Paper Rokkaku failed to get much air-time, but during the afternoon the breeze really picked up.

Arriving at the field, a large flock of white corellas was present on the ground. Earlier, it had been a similarly big group of magpies, plus the distant chattering of a kookaburra.

Phone in hand, I started timing shortly after starting to let out thread. There was ample wind strength and I certainly wasn't helping the kite stay airborne.

By the time the rokkaku was at around 50 feet off the ground, the corellas decided to take off and have a look at the paper bird! Perhaps it's the flailing thin ribbons of paper that birds find so intriguing. There is constant movement and a rustling sound at most wind speeds. After wheeling around several times, passing close to the kite, the noisy pure-white birds were gone.

After this I let thread straight out to 90 meters (300 feet) and anchored round a small branch of a tree. Just three turns with the winder on the ground below was enough.

Much of the time, the kite was being blown down low. The full flight envelope was being explored! Standing directly underneath the kite I measured a gust to 26 kph. No doubt things were even hairier up higher.

The Paper Rokkaku kite climbed during drops in wind speed and occasionally soared even higher in small patches of weak rising air.

A few drops of rain were falling, but it was very minimal so I kept flying.

For nearly half the time during the flight I sat on a mound and watched the changing shape of the thread as tension rose and fell and wind shifts came through. It was just paper up there, doing all that flying. Magical.

The little rok put on a show, exhibiting a few different behaviors. For example, steady flight, flicking left and right in rough air, doing large arcs in fresh gusts, vertical dives and recoveries, and drifting a long way left and right as the wind direction changed.

Finally, the average wind speed dropped a little. The kite descended all the way to just 5 meters or so, before climbing away again.

Not long after, raindrops became frequent and it was time to get the kite down in a real hurry. No damage was done though.

What a great flight!

Rok Rides Super-Gusts

The weather station was reporting 26 kph gusting to 35 kph down at the coast, which was not that far away.

After only brief hesitation, I hopped in the car and made for the nearest large reserve. The Paper Rokkaku prototype and kite gear bag were already stowed. Like a fireman, a dedicated kite flyer has to be ready at a moment's notice ;-)

Sure enough, the trees were thrashing around in line with the reported wind speeds. Flying the little rok would be a calculated risk, but by now I was very familiar with its flying characteristics. Launching was a breeze, and I guess that pun was more or less intended.

I didn't waste any time letting out thread to most of its length. While I sat on a mound at the perimeter of the grassed area, the MBK Paper Rokkaku soared around at fairly low line-angles most of the time. This was due to the kite being frequently over-powered and having to regain height, time after time. However, everything held. The paper spars and the thread held, to be precise!

After a while, the average wind speed seemed to drop somewhat. Deep lulls allowed the rok to descend a long way on its face. Finally, there was no climbing back and the kite settled face-down on the grass and weeds. At least some flight time could be logged—10 minutes.

Within a minute, I had relaunched the kite with a firm pull-in of the thread. You have to be extremely careful doing this with all-paper kites since if anything catches, much damage can be done to the spars. However, the kite had settled smoothly in a face-down, nose-into-wind position so it popped up into a climb with no problems.

Another 10-minute flight ensued before the kite drifted down in a repeat of the first descent and landing. Oh well, that was another 10-minute flight that would be logged, so the outing had been worthwhile.

There are just under 2 hours of flying to go now, to certify durability before the design can be published. For the next outing, I might go to the beach to get a lot of air time in smoother conditions!

Chasing the Wind

I did quite a bit of driving today, chasing opportunities to log air time with the Paper Rokkaku prototype.

Firstly, it was down to a local reserve to take advantage of the predicted wind strength. Unfortunately, the breeze died much sooner than anticipated so after a 5-minute flight it was all over.

But perhaps it wasn't over after all... A sea breeze managed to penetrate inland to the same reserve around the middle of the day. This was just after I had checked out a couple of coastal locations! The sea breeze had not been predicted, so I didn't hang around by the sea.

It was on the way home that the tree tops started waving! However, after a couple of short flights that were terminated by lulls, the breeze close to home died out.

Down at the coast, the breeze was still pumping in at moderate speeds. So, after lunch I ended up down at another reserve which was not far inland from one of the coastal weather stations.

Sure enough, there was plenty of wind, although quite gusty due to its trip inland across houses and trees.

There was some fiddling around with frustrating short flights and the thread catching on weeds. But finally the MBK Paper Rokkaku sailed clear of the treetops and flew about in gentle air that gusted into the mid-moderate range occasionally.

On 90 meters (300 feet) of polyester thread, the little rok just made 200 feet off the ground. That was height certified! Also, the kite finally sank to the grass just over 25 minutes after takeoff. And so that was duration certified too.

In the end, after some setbacks, a decent amount of flying time was finally achieved. That was a good start to getting the 3 hours required for certifying durability.

Will there be another sea breeze tomorrow?

Gulls Rok Their World

That was the most interesting thing to happen during the main flight today.

Two seagulls briefly interacted with the Paper Rokkaku kite as the slowly freshening breeze pushed it close to its current limitations. The gulls hovered very close, peering at the kite as it swirled about within a small area. One gull flinched as the kite's tail flicked in its direction. Or perhaps the gull had flown into the kite's wake in the 18 kph airstream. How do you say all that in 5 words or less? See the title :-)

The flight had started in a very promising way, the little rok launching straight up in a very smooth 14 to 16 kph breeze off the sea. The sail alterations and side tails were evidently making a big difference, compared to the last outing.

After taking some video with the kite on a fairly short line, I walked closer to the waves and set the bag down on some slightly damp sand.

With the kite on nearly 30 meters (100 feet) of polyester thread now, it continued to fly well, reaching a pleasing 50 degrees of line angle at times. Hey, it's just copier paper! However, the wind speed seemed to be creeping up.

The freshening breeze was handy since I was planning to shift to another beach further north later, where the breeze was currently stronger. The idea being to test the whole wind range of the kite.

As it turned out, the breeze ended up reaching 18 kph gusting to 21 kph. This was a little too much, with the cream-colored kite S-turning and throwing the occasional loop or three to the right.

It was interesting being able to follow the behavior of the kite as it changed in close synch with the readings on the wind meter. At this point there was no reason to go to the other location to chase more wind!

A little more tightening of the sail plus more length on the side tails should push the Paper Rokkaku's capability well into the moderate range. Then, I can start logging air time and putting the kite through its certification trials.

Rok—Paper Sheet Perplexities!

So confident that the changes made would increase stability, I didn't bother with transferring the side tails from the previous prototype.

However, down at the beach in a perfect breeze for testing, the Paper Rokkaku still had a very limited wind range. The side tails will definitely be necessary.

At just the right wind speed, the rok would accelerate straight up, only to descend again shortly after. Tight S-turns and loops to either side resulted when the gust put on just a few extra kph. Not good.

I didn't waste much more time down there, but noticed that the paper sail was not billowing anything like a traditional Rok does. Instead, the semi-rigid paper was holding almost no dihedral across the middle. It's simply the way a solid sheet behaves when bent around two axes at once, where the axes are at 90 degrees to one another. To simulate a traditional rokkaku, this kite has dihedral in the horizontal spars AND the vertical spar or spine.

Back at home, it was clear that some extra side-area might be obtained by cutting in from the sides and overlapping the resulting edges by just a few millimeters. This caused the side edge of the sail to go nearly in a straight line from one horizontal spar tip down to the other spar tip. Viewed from the side, the kite definitely had more area to help it weathercock into wind.

These changes plus those extra side tails, should help. From this point on, it will be a matter of piling on more tail length until the darn thing behaves itself right up to 28 kph!

Between a Rok and a Hard Call

With a refitted and rather fancy vertical spar, there were no strength issues today.

The Paper Rokkaku kite performed better today than ever before. The kite flew high at times in the gusty gentle to moderate breeze with no spar failures at all. In fact, during one furious gust, the kite managed to snap the polyester thread!

Bottom side-corner tails were added after being cut from the previous prototype. That certainly helped stability but this design is still quite twitchy near the top of its wind range—to the point of forcing the kite way down low during tight loops and S-turns.

It's a hard call. Making all the spars lighter will help stability, at the cost of strength. Adding yet more tail will also help, at the cost of extra weight. Increasing the dihedral angle will help too, at the cost of raising the kite's minimum wind speed. All-paper kites are a challenge!

So ... perhaps a small tweak to all three factors will do the trick! That way, the changes to strength and weight will be minimal while there should be a solid increase in stability from all three factors working together. It means building up a complete new kite though *sigh*.

Rok With a Spinal Injury

That just about sums it up.

The Paper Rok is in the process of test it / break it / test it again. This time it was the spine (the vertical spar) that gave way. I had a feeling the current dimensions were a little optimistic. So, I'm going to try the same approach as used by the horizontal spars. That is, nice and wide in the middle and tapering to quite thin out at the sail corners.

Even with ample dihedral, this little rok is going to need tails on the lower sail corners to damp out "the flicks." Descriptive enough? The main tail does a reasonable job most of the time but is less effective when the kite is at low line angles.

It's a pity to make the design more complex, but it will probably help a lot to introduce a slight kink in the vertical spar. This would have the same effect as the graceful curve that a traditional rok takes on when under pressure. With rigid paper spars of course, there's no bending! Holding a slight angle between two straight bits is the best you can do.

Hopefully I can put together a new vertical spar and retrofit it to the current kite tomorrow. Perhaps there will be time to fly as well.

Paper Rok Needs Some Work

The first prototype of the Paper Rokkaku didn't cope too well with the warm inland breeze which was gusting right to the top of the moderate range.

Suspecting that the towing point might be a fraction too far back, I tied a tiny Loop knot into the forward leg of the bridle. This made some difference, but the kite still got overpowered from time to time. Soon it was clear that something had failed since the rok had started to loop tightly in one direction.

With the kite on the ground I discovered the upper horizontal spar had failed on one side, quite close to the middle. After some careful pinching and re-forming of the spar shape, the kite again took to the air.

This time the wind strength was lower. The pale-cream copier-paper kite flew more or less normally for a while. This was all the encouragement I needed to let out quite a bit more thread, to see what would happen.

This kite mainly needs more stability. This will keep it higher and hence out of the "power zone" that subjects spars to great strain. So, the next step will be to crank up the dihedral angle a bit more on both horizontal spars. Plus tails will be added to the outside bottom corners of the sail. Having a lot more sail area than the Paper Diamond, the extra tail weight should not bother this rokkaku.

After the kite folded once again, it was time to give up and go home.

 

 

 

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