Della Porta Kite Posts

This design and the physical kites are actually the property of AKFA (Adelaide Kite Flyers Association). Hence no plans or instructions will be published or sold under the MBK banner. However, I was the designer and have enjoyed doing most of the test flying :-)  There's a video near the bottom of this page.

By crossing the spars at the towing point, the kites may be easily flown in a train and require only very short single-line bridles. This variant of the classic della porta does not require any tail. It also gets by without any horizontal spars, which makes it a very straightforward design to make. The leading edge of the flying kite is under tension due to aerodynamic forces pulling the spars apart.

The photo shows the original plastic-sailed prototype. Eventually, several more kites were made, with ripstop-nylon sails.

These short flight reports once appeared in the site blog page, which is no longer present. Just scroll down and stop at any heading that appeals, below :-)

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Fun With Float-Out Climbs

The weather station was saying 5 kph up to 11 kph before I left and 5 to 9 kph on my return, so a light-wind della porta was definitely the right choice of kite.

Sunny and Light for Della Porta

Winter-like weather has been the norm here for many weeks. But today was sunny with very light winds. It was a rare opportunity to take out the tailless della-porta variant with its latest mini-bridle configuration.

Originally, the flying line was attached to a short line from the spar crossing-point. That proved too far aft, so now there is a little Y-bridle attached 11 cm from the crossing point. One knot brings the lines together while the other one holds the flying line, using a Lark's Head of course.

After I stepped out onto the damp grass of a nearby school oval, the wind didn't really know which way to blow. Being well under 5 kph in strength, the breeze would sometimes hold the kite up as it sat on its trailing edge, leaning into the wind at about 30 degrees from vertical. Sometimes it stayed there for quite a few seconds!

Eventually some promising puffs of breeze came through and up went the big della porta. When in a nose-up attitude, the kite would climb very willingly. Even so, just a few extra kph would bend the spars and abruptly end the climb.

It's all a bit of a trade-off.

The current combination of weight, spar strength, and towing point position should make for a lot of enjoyment when winds are under 10 kph. Smooth or gusty, the kite seems stable enough to cope.

Having measured 3.5 kph gustiing to anbout 5 kph at shoulder level, the kite seemed happy sitting at a roughly 40-degree line angle on its 50-pound Dacron line. So, it's still not the most efficient kite but perhaps a couple of extra kph would push it over 45 degrees. And of course, the frame isn't carrying super-light Icarex material yet!

Of Pelicans and Della Portas

Today, according to the weather data online, was the day to test a change of towing point on a big tailless low-wind della porta kite.

In order to do quick checks without creating a new sail each time, a small V-shaped bridle was attached above the spar crossing point. It seemed like 4 cm should make a noticeable difference, so the Dacron was tied on with slip knots about 4 1/2 cm along the carbon tubes.

Out at the park, the breeze was light indeed, gusting to less than 2 kph at shoulder height! So there were a few failed launches despite the great low-wind performance of the kite.

Eventually, by towing up on more than 30 meters (100 feet) of line, a respectable amount of tension developed and the kite was away. Cloud movement suggested there was 10 to 20 kph much higher up. That would be far too much for the della porta.

Alternating bright sunlight and cloud shadow was causing plenty of thermal activity. Sometimes the kite would wallow around face down—but climbing slowly. Other times saw the kite straining away at a low line-angle, in gently descending air.

The 4 cm shift in towing point had less effect than I was hoping for. The kite was still reluctant to climb when extra tension was applied to the line by pulling in. And that was not to mention an average flying-line angle of just 30 degrees or so most of the time. Well, it just means that bridle needs to be shifted up another 4 cm. We'll see how that goes, another day!

The sky was quite picturesque today with about 40% cloud cover, including many active cumulus. These clouds were gray in the middle and brilliant white around the edges.

To top it off, a small flock of pelicans soared right overhead and away downwind. They were just cruising, in a rough V-formation.

Della Portas Side By Side

The kites were trapezoidal and tailless della porta variants, to be more precise.

A few of these big and light kites had been readied for the kite festival back in April, just in case there was a day or two of very light wind. That didn't happen, but a couple of us are still committed to making small improvements to the kites from time to time. It's a fairly low-priority project, but hopefully the kites—which can be flown in a train—will be ready for a wider range of wind speeds come the next festival!

Today's flying was to test a concept—to add a tensioning line attached to three of the frame's corners. The idea being to keep the leading edge of the sail under more tension in flight. But after today, it appears to make little difference. The bending of the spars under flight loads reduces tension in the ... ahem ... tensioning line, so negating the effect. It works on the ground, but not in the air. So it's back to the drawing board, as they say.

On the up side, it was a pleasant enough short outing. Two big colorful kites were in the air side by side on 60 meters (200 feet) of line, until the modified one came to ground in a lull. That kite was on a heavier flying line though. Gentle winter thermals were nudging both kites higher from time to time. Blue sky stretched overhead and banks of boiling cumulus circled the horizon. What a nice day!

Oops ... I forgot to check the online wind-speeds straight after returning but it's now showing 3 kph gusting to 7 kph. That's super light.

Della Porta Dallies in Light Air

This afternoon was the perfect time to put the very-light-wind della porta through its paces at height.

Barely a leaf was stirring, but occasional movement in the tops of trees gave away some gentle thermal activity in the area. Now and again, a little movement could be felt on my face. It was definitely light-wind kite weather!

Trying to get some movie footage was a bit tricky down low. I kept flying the kite up into a sudden wind-shadow. The breeze was wafting past the tree trunks you see, but the foliage higher up was a big block to the airflow. Eventually I did get some footage and it was time to break some height records for this kite! With the average speed of the breeze around 5 kph, the lightly built della porta soon surged up to a modest line-angle.

The modified della porta is not a super-high-performing kite it seems, in terms of aerodynamic efficiency. But this one is certainly rock-steady over most of its wind range, with no tails and no bow lines. Flying as it is, from the spar crossing point only, there should be no problem flying a number of these on the one line—a kite train.

From today's flights, the last of which was on 90 meters (300 feet) of line, this is how the kite flew:

• 0–1kph: glides slowly upwind, losing height
• 2–3kph: wallows around wagging its tail end, maintaining height
• 3–4kph: sits up and tries to climb
• 4–5kph: climbs smoothly and settles out around a 45-degree line angle
• 6–7kph: spars start to bend, trailing edge flaps a little
• 8–9kph: spars bend more, kite loses some height but stays very steady
• 10kph+: kite moves to one side and may porpoise slightly

These speeds are not precise or 100% accurate, but they give a good idea of how this kite flies!

My wind meter recorded an average of 4.6 kph gusting to a maximum of 9.2 kph. Up high, perhaps the strongest gusts were more like 12 kph.

Della Porta Clears the Trees

The very-light-wind della porta was taken out yesterday for a fly.

It's a very simple kite to set up, this one, despite being fairly large in area and of the sparred variety. Step 1—plug the two-piece spars together. Step 2—insert the tips into the corner pockets. Done!

After assembly, the flying line was attached to the single-point bridle by the simple time-honored method of a Larks Head knot. Down low, even this kite found almost nothing to lift the sail. A few gentle tow-ups were the way to go.

Soon, the kite was several meters over the grass. A few wisps of breeze tightened up the flying line for a moment or two.

After several short flights and glide backs to where I stood, a tow-up on a longer line finally got the kite near treetop height. From this position, some slightly stronger gusts bent the spars back and demonstrated how the kite would behave near the top of its wind range. This was perhaps only 7 or 8 kph! The kite, under this amount of stress, was stable but unwilling to climb high. Any thought of shifting the towing point (at the spar crossing point) even further aft was dismissed at this point.

The next step, with the help of other AKFA members, will be to turn out a couple more della portas with sewn ripstop-nylon sails. That's the beginnings of a kite train!

Della Porta Debuts

The local kite-club has need of an extreme-light-wind design, in time for the festival in a few weeks time. This is just in case winds drop out.

After months of dithering around with various ideas, the time had come for action. The della porta was chosen for its simplicity and suitability for the display of artwork—although we might only have time to make a few plain ones this time around.

A standard della porta is a rectangle with just two spars, going corner to corner. Mine is modified to fly stable from the crossing point, which of course can't remain right in the middle. Shifting the crossing point toward the top edge makes the top edge shorter and the lower edge longer, distorting the rectangle. But still, it's a nice large flat surface for an artist to work with!

Why fly these from the crossing point? To train them of course! The intent is to have at least three kites on the one line, stretching way up into the air when nearly all other kites are grounded due to lack of wind. To achieve this end, the kites will be large and very light, using carbon tube for the spars and ripstop nylon for the sails.

Yesterday, I put together a prototype with two-piece 2 m (7 ft.) carbon-tube spars and a plastic sail. Trying the kite in puffs of wind on the back lawn, it was clear that the towing point was too far forward. The kite would take every opportunity to flop face-down and rarely pulled much tension into the line. However, it actually seemed to fly stable in its flat condition! No bow line or tensioning was required. Evidently, the small amount of billow in the sail on the sides was very fortuitous.

The next step will be to shift the spar crossing-point aft by 10 cm. This will require a brand-new sail—such is prototyping.

 

 

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