Blue Spot 2 - Flight Reports

Flight Test 1 - The unstoppable luff machine.

So, I bridled up the blue spot 2 last night, woke up this morning and hey presto! No wind. A little breeze picked up around lunchtime, so packed up the bridling kit and trotted off to Blackheath.

It inflates! It flutters around at the end of the lines! It refuses to lift off the ground!

Attempt 2. Still no brake bridle, (much) less AoA due to extended 'C' lines.

It lifts off! It pulls! It luffs! It's absolutely bloody uncontrollable!

At this point, Simon sits down, has a cigarette and watches his girlfriend flying her Rev.

Some time later, with a brake bridle attached, a set of handles found, the lines equalised and some trepidation, Attempt 3.

This time, it takes off, can be turned, powered down, landed, etc. Very civilised. Except for the luffing. Hmmmmmmmmmmmm.

More tuning and another fagbreak later, Attempt 4.

Better. Much better. Acceleration is evident, power is _definitely_ evident and it still luffs.

Then it started to look like thundery rain, so I packed up and went home.

Packing up, by the way, is rather tricky, as the damn thing refuses to deflate. I left it inflated overnight on Friday and it was still 50% inflated 8 hours later. There seems to be an initial deflation to the 50% mark over about 10 minutes, then it just sits there.

Anyroadup, this is looking good. It zaps across the window already, although it needs some[1] brake to stop it luffing, it turns on a sixpence and it's already showing signs of being a powerful little beast.

There was enough power there to buggy with (just about), although it was nowhere near controllable enough to use yet. The only other buggier on the heath was using what looked like a 4.9 blade, and he was doing more sitting than buggying.

Once I have the bridle set up so it can fly without extreme brake, and it can get some apparent wind, this promises to be a fairly evil little kite.

Flight Test 2 - Taming the monster.

So, I returned from holiday, having carried the damn thing around France for a week in a dead calm. Within an hour of returning home, I was sat looking folornly out of the window, as the wind was building up and it looked as though there was no chance of me getting out to test, what with unpacking, and all. To my surprise, however, my 'Significant Other' noticed and pointed me at the door.

15 minutes later, and I was unrolling the kite on the field. Several bridling adjustments later, and the kite was zapping around somewhat better than before - not entirely perfect, as there's still some luffs to be removed, but much better. It appears that my initial bridling calcs were nearly correct, and that letting out the 'C' line to allow it to fly 2-line was a bad move. Pretty much everything is back to the initial settings, with perhaps a tad more AoA than initially planned.

So what's still bad? Well...

• It still luffs, especially at the tips, so more tweaking is required.
• Inflation is a little slow, and one tip in particular seems not to want to inflate at all. I suspect that what's happened is that the internal seams on one side are flapping over the (minimal) crossventing (which is only at the trailing edge) and stopping that particular tip from inflating. I suspect it will be necessary to open up the TE and put more crossventing in the tips, which will be fun give the taped construction...
• Brake bridling still needs work, but as the bridling is an ongoing experiment that's to be expected.

And what's good?

• Speed. Now it's luffing less, it's getting very fast. I might need to put on longer lines that the 15m set I'm testing with, as there's precious little time to observe behaviour on passes. Acceleration is outrageous.
• Power. Enough to pull the strops out of one of my handles, although that possibly has more to do with the quality of the handles... Certainly enough power to be getting exciting. On a 15m lineset, in low wind. Admittedly, not nearly as much power as the 5.3m^2 predator I flew it back-to back with, but there you go - half tuned kite vs fully tuned beast with almost twice the area... There was a guy flying a 3.5m^2 rectangular quad - looked like a sands derivative, about a 5:1 AR, commercial kite, can't remember the name of it - and I've got that beat already. But that was, frankly, a shit kite.
• Maneouverability. It turns on a sixpence, reverses beautifully and is generally nice to fly (apart from the inevitable luffing).
• Luff recovery. When it has luffed, it is possible to recover it with a sharp tug on the brakes, even when it's trying to bowtie itself. I like valves.

And as I was by myself, still no photos ;-)

Flight test 3

The 3rd flight test occurred on an evening where the wind was rather non-ballistic and very lumpy. But performance is definitely getting better - Window is now comparable to the Skytiger Hi-40 I flew it BtB with this time (I love testing where there are other people around) although absolute pull is still a bit down. More crossventing is definitely necessary, as the tips take an age to inflate.

Something to stop the valves reversing would be a good idea - They don't reverse completely but after a slap into the ground they have a tendency to part-reverse and then won't inflate at all.

Luffing is somewhat reduced, although still there, and running on such a short lineset has given me a chance to see what's actually going on:

Hauling in one set of lines causes the entire bridle to pull across the kite (as would be expected with the arch setup). On the 'inside' wing, all is well. But on the outside wing, although the 'arched' section and the tip line stay tight, the rest goes slack. This actually happens if you 2-line anywhere in the window, but it only tends to luff at the edge. The reason the 'normally' bridled section goes slack is due to the cross-forces on the bridle pulling the secondary towpoint in towards the centre, at which point geometry takes over.

I hypothesise that due to the valving, minimal crossventing and Dribs, the canopy is rigid enough that it can't 'arch' to take up the slack in the primaries. So I end up with, for a second or so, a kite that's only bridled across 2/3 of its (significant) span. That seems to be long enough that, when near the edge, the outer tip, which is travelling fast and near the luffing point anyway, starts flapping about, loses lift, and luffs.

Oddly enough, the problem seems worse with the left wing (i.e. when pulling in the right lines), and that's where inflation best. I've put down the inflation problems to internal seams flapping over some of the crossventing and sealing the tips (all due to which way round I made the kite), and the same problem may be happening in reverse on the other side, which makes sense. Whatever, it seems that better crossventing may well help to solve the problem.

So. In summary. It's getting there.

Flight test 4

Well, It's getting good enough that I now feel confident enough to stick it on a long (25m) lineset. Wow. What a difference. It slams across the window, accelerating hard, and as it's got time to generate power, some wild slides start to occur. Still in winds I'd be more than comfortable flying a 5m+ kite. Woo-Hoo!

Not only that, but slowing it down causes the power to go away magically. Let it accelerate again and it powers up with a bang.

Having got used to the 'total-quadline' technique required, luffing is almost nonexistent, but reproducable on a whim.

Now it's getting some speed up, I can see that the tips aren't inflating above 80% - I definitely need to open up the trailing edge.

But it would definitely be good enough to buggy with now. It's easier to fly than the original Blue Spot, faster, turns faster and goes further upwind. When I've got all the bridling wrinkles ironed out, it promises to be most amusing, although winds 15-20mph+ are likely to be its forte.

Flight Test 5

Not really a flight test as such, as I didn't get to tune it any more that it already was, but it was blowing something rotten so I had to get out and try it...

The airport weather report for LCY showed 18mph winds. That's approximately the speed the evil bastard dragged me across Blackheath at. Unbelievable. Unparkable. Fun. And absolutely buggy-able.