This design and the physical kites are actually the property of AKFA (Adelaide Kite Fliers 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 :-)
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 more kites will be made - in Icarex or similar hi-tech material for the best possible light-wind performance and durability.
These short flight reports once appeared in the site blog page - that's the one you enter via the 'what's new!' site navigation link. Just scroll down and stop at any heading that appeals :-)
The Della Porta variant
The Della Porta variant
Della Portas Side By Side
Trapezoidal and tail-less 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 2 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 3 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. 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 200ft 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. Nice day!
Oops forgot to check the online wind speeds straight after returning but it's now showing 3kph gusting to 7. Super-light.
Della Porta Dallies In Light Air
This afternoon was the perfect time to put the very-light-wind Della Porta through it's 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. 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 5kph, 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 it's 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 90m (300ft) of line, this is how the kite flew...
- 0-1kph: glides slowly upwind, losing height
- 2-3kph: wallows around wagging it's 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 give a good idea of how this kite flies!
My wind meter recorded an average of 4.6kph gusting to a maximum of 9.2kph. Up high, perhaps the strongest gusts were more like 12kph.
Della Porta Clears The Trees
The very-light-wind Della Porta went out yesterday for a fly...
A very simple kite to set up, this one, despite being fairly large in area and of the sparred variety. Step 1 - plug the 2-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 tree-top height. From this position, some slightly stronger gusts bent the spars back and demonstrated how the kite would behave near the top of it's wind range. Which was perhaps only 7 or 8 kph! The kite under this stress was stable but unwilling to climb high. Any thought of shifting the towing point (= 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 rip-stop nylon sails. 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. 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 it's 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 2 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 towards 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 3 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 rip-stop nylon for the sails.
Yesterday, I put together a prototype with 2-piece 2m (7ft) 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 it's flat condition! No bow lines or tensioning 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 10cm. Which will require a brand new sail - such is prototyping.