Freesteel Blog » Weekends

Tuesday, July 3rd, 2018 at 7:50 pm - - Flightlogger, Hang-glide

We had a go, where I rigged my U2 hang-glider in the front garden with the VG full on to make it rigid, and then standing it on its nose so that JR could take lots of nice high definition photos of it from a variety of angles with a proper camera with a big lens.

The Agisoft Photoscan thing initially got it right, with a good looking 3D image:

But then I started doing things with the point scan — in particular finding its symmetry so as to compare the left wing with the right wing.

The code is here.

Basically, I loaded the 9653216 points from the csv file with this one Python command:

k = pandas.read_csv("hg1a1b.txt", sep=" ", names=["x","y","z","r","g","b","nx","ny","nz"])

And then worked out that I could perform vector calculations on the columns of coordinates, like this

# Reflect about the plane through x=2 parallel to the YZ plane
mv = pandas.Series({"x":2, "y":0, "z":0})
mvsq = sum(mv**2) # (scalar)
mvfac = (k.x*mv.x + k.y*mv.y + k.z*mv.z)*2/mvsq - 2  # 9million value column
kmirr = pandas.DataFrame({"x":k.x-mv.x*mvfac, "y":k.y-mv.y*mvfac, "z":k.z-mv.z*mvfac})

The alternative more memory efficient calculation method, performed row by row runs many, many times slower:

kmirr = k.apply(lambda R:R[["x","y","z"]] - mv*((R.x*mv.x+R.y*mv.y+R.z*mv.z)*2/mvsq - 2), axis=1)

There’s something curious about this column mathematics and how it applies to computational geometry.

In any case, have produced an animation melting through from one wing tip to the other, like so:

It seems that one wing is much fatter in depth than the other.

I think this is a photogrammetry error in its understanding of how far apart to put both sides of the wing. The gap at the leading edge on the fatter wing gives it away.

As is my observation in freeform CAD/CAM: you can get away with a lot of deviation from the required surface because no one can tell when it’s wrong. They can measure the flatness of the square edges, but errors in the middle of the freeform surface (so long as they are smooth) pass without notice. I suspect a lot of photogrammetry works on that principle. It’s only when we scanned something with two sides that was supposed to be symmetrical could I tell there was a big a problem.

(To be fair, the Agisoft failed when we reran it to get a better fit. It is better to

Well, so much for that. I had hoped I’d have something good enough to trace up and enter into XFLR5 as a series of contours, but it’s not quite.

However, I should just make up a series of contours based on this anyway (since it has things like the washout/twist approaching the wingtips) so that when we get good data (eg from a laser scanner) we are all ready for it.

Tuesday, July 3rd, 2018 at 5:50 pm - - Kayak Dive

# date site depth divetime
1 25 June 12:00 marine park pinnacle 20.5m 47 minutes
2 25 June 14:42 Citrine (wreck) 15.4m 52 minutes
3 26 June 10:41 Sugarloaf caves 12.7m 61 minutes
4 26 June 16:42 Thracian (wreck) 32.7m 29 minutes
5 27 June 11:00 The puddle 18.1m 58 minutes
6 27 June 17:26 Burroo 21.3m 54 minutes
7 27 June 20:14 Bay near Burroo 18.7m 56 minutes
8 28 June 11:30 Gibdale Bay 22.4m 47 minutes
9 28 June 14:24 St Mary’s Ledges 19.8m 57 minutes
10 28 June 22:19 Port Erin 11.3m 63 minutes
11 29 June 11:04 Thousla rock (wreck) 20.8m 50 minutes
12 29 June 14:04 Sugarloaf caves 11.0m 57 minutes
13 29 June 19:19 Spanish head drift 21.6m 40 minutes

Really very much good diving stuff with Discover Diving on the Isle of Man last week. We went over loaded up on our bikes (can’t find the pics) on a trip with LUSAC from the ferry terminal about a mile away from our doorstep. My logbook records over 11 hours underwater in 5 days of luxurious cold water diving.

It was insanely hot and the sea was mirror flat most of the days. We stayed on for an extra two days for a cycle to Peel and back to Douglas, though actually we spent most of those days sleeping to escape from the heat.

We saw some amazing sights, like this bird swimming underwater:

That was at the end of the dive in the Sugarloaf Caves, which in every way (except the kayaking) outmatched our cavern dive on the LLeyn a couple of weeks before.

As usual, we had problems with the fact that air goes only upwards when you try to fill a blob. “No,” I shook my head.

We got better at deploying it later in the week. Here’s a dive to the anchor chain and half a giant anchor on the Thracian. When you release the blob to the surface you realize just how deep 32 metres actually is.

On the night dive we annoyed an octopus who was trying to do its hunting in the dark.

Our final dive was a fast(-ish) 2 knot drift with the current from Spanish Head which left us feeling happy, going with the flow.

I don’t have a lot of time to write this up. Maybe there will be some other vids later on when I’ve gone through them a bit more. (Most are terrible.)

In the meantime, here’s me in black on the deep dark wreck, startled by someone else’s light.

Thursday, June 21st, 2018 at 11:31 am - - Cave, Kayak Dive

Last week we completed the unfinished business of properly kayak diving the underwater cave at Pen-y-Cil headland Aberdaron in Bardsey Sound in perfect conditions

Just look at these conditions:

We had 10 metre visibility, lots of air, and got a nice swim through with lots of crabs.

Even did the side cave too. As Becka’s neckseal had split, I dived the Glenocum wreck on my own on the way back. It was so relaxing.

On day two we did some (very cold) snorkeling off Criccieth looking for seagrass (didn’t find any pipefish).

On day three we were going to paddle around from Whistling Sands through Bardsey Sound, but decided that would be too scary, so we went and played in the overfalls by Nefyn. The waves looked huge when we were there, but don’t amount to much in the photos.

We got air fills at Tyn Rhos Diving which surprisingly still existed. And beforehand I visited my mum for one night in Machynlleth before driving up for a night in the campsite behind Eric Jones Cafe and meeting Becka off the bus in Tremadoc, after much protesting that I didn’t want to drive up and fetch her from Caernarfon ridiculously late in the night.

Thursday, June 21st, 2018 at 10:29 am - - Kayak Dive

Not at all keeping up with any blogging of late, so here is a late report a 5 day sea kayking trip from Oban with the Liverpool Canoe Club

Those who served:
IB, SH, RC, CH, AV, Julian Todd, Becka Lawson

I’m proud of underplanning and not thinking ahead, especially when doing something new.

Becka and I had never been out for more than one night in a sea kayak, and this trip was supposed to be 5 nights in the Scottish wilderness. We had the kayaks, we had a trangia stove and enough old soda bottles for regulation supply of water. At the last minute we grabbed our one working tent that wasn’t the pop-up kind. I was sure we could simply shovel enough packets of random food from the larder into the holds around this gear to make something up each day.

Becka drove us up to Oban while I provided the entertainment by reading aloud someone’s kayak camping packing list off the kayarchy website. By the time we reached Glasgow Becka had to panic buy yet more provisions at the Aldi supermarket, so we arrived quite late.

Other last minute decisions that happened frantically in the morning included packing our thickest sleeping bags (which could barely be rammed in even when you fed them right up to the bow through the hatch), and our choice to wear our skinny wetsuits for the whole trip because we didn’t have enough confidence that we weren’t going to capsize or be able to roll.

The rest of the group were polite enough not to make it too obvious we were holding them up as we squabbled over what to take.

And then we set off south towards the slate islands.

We got lucky with the weather. It was never too windy or wavy, and it tended to rain during the day and often during the night, with brief sunny respites for a few hours most afternoons during which time we could dry out our wetsuits. That was another advantage of going on a trip lead by IB — aside from the air of competence and expert decision making — the early starts and early finishes. You got your 5 or 6 hours on the water experiencing sore arms, sore thighs and a sore back from sitting in an insanely unnatural position (those who can’t take it probably don’t go kayaking), with enough time afterwards *not* in the boat to recover and straighten out. If left to do our own planning, Becka would probably have maxxed out the paddling for a minimum of eleven hours a the day, which would have meant I’d refuse to get out of bed in the morning. On a multi-day trip you need to pace yourself sensibly; it’s not a weekend blast.

The sea was flat enough to let us go round the far side of the Garvellachs and camp by the site of the monestry on the same patches of grass where the previous kayakers had camped the day before where they’d left their two-way radio.

The next day we headed back to the coast in a horrible wind and rain through the Grey Dogs north of Scarba and around to the south end to look at the Bothy that overlooks the Corryvrecken. Here we met our first group of other kayakers just getting ready to head out to sea (pretty lazy), and gave them back their missing radio. Then we had lunch in the bothy, which is a depressingly ruined not-cosy two story cottage, before moving on to a campsite on the mainland.

The most notable wildlife were the geese who liked to fly back and forth overhead honking wherever we walked. Someone saw an otter. Every so often there was a seal head poking out of the waves. There were no midges at all because it was too early in the season and too cold. In the evenings SH entertained us with different ways of not lighting a fire (apparently the driftwood was too salty) until he used a lighter. Becka and I had neglected to pack whiskey. We also worked out that a one man tent was too small for two people.

The final night (cutting short one day because of the wind forecast) put us on the north coast of Shuna on a gusty headland of squelchy mud and cow-pats where we gave a demonstration of how a married couple decides which of two spots a metre apart to pitch their tent. So we put it onto the wetter ground with the door facing into the weather across two cow-pats that Becka scooped and thrown over her shoulder using a paddle as a shovel. I sulked and didn’t come out for the remainder of the soggy day. I only had sandals and the mud sank up to your ankles, which would have made the sleeping bag filthy.

Final day before the wind really picked up involved shooting through the Bridge over the Atlantic before the tide changed and then an approach around the back of Kerrera Island to Oban. Here I was able to practice my downwind surfing, which we had been taught to do on surfskis earlier in the year on our train trip to Spain. It was fun, except I had to keep ignoring Ian who kept calling me back to the shelter of shoreline where the waves crashed on the rocks and the paddling was just a right slog.

It got very hard around the north of the island where we now had to paddle south directly into wind. No matter how much force I applied to the paddle, all the others seemed to pull away into the wind at twice my apparent speed. They waited for me to catch up in the shelter of a small island, and pulled away again and got to the shore miles ahead of me. By the time we packed everything back on cars and vans the wind had almost died and children were out on the middle of the sound on a raft made of barrels.

We all went out to dinner in the slap-up Wetherspoons Pub in Oban called the Corryvrecken.

Monday, June 4th, 2018 at 9:13 pm - - Kayak Dive

I’ve been having some adventures, including one successful flight over the Black Mountains (I didn’t get round to blogging about), a five day kayak trip out of Oban (I wrote up and Becka decided to rewrite, so maybe I’ll post my original here), and an unsuccessful flight in Yorkshire where I deserved to crash horribly, but got away with an on-the-spot landing across a single track road between two dry stone walls (I should never have got to that place).

At the weekend we were in the Farne Islands and had a lovely time with the seals.

You always get a little nervous when they open their big toothy mouth.

That was the shallow dive. Then we dived the Knivestone and shook hands with a lobster (one among many, they’re under every rock),

… and resisted the temptation to bother the octopus.

I got to do a bit more blogging, announcing various electronics work (of which there is lots), but so much is ongoing I can’t be bothered to report it. I’ve now forgotten what’s missing (nearly everything). Maybe it’s because I’m putting things in twitter instead. Oh well.

Tuesday, April 24th, 2018 at 2:05 pm - - Kayak Dive

Some old pictures of kayak diving in the Isle of Arran from 2016 that I had failed to blog about at the time are below.

The weekend before last I took a fellow DoESLiverpool-er diving in the Menai Strait, which was okay. The weather was gorgeous, but the viz was average and there were No Fish (except one butterfish I caught in my hand at the start of the dive).

Here’s us shinnying back up the sponge encrusted telephone cable back towards the Northwest shore after experiencing the current. We stayed underwater for another 20 minutes under the shelter of the main bridge pillar, but didn’t find the encrusted admiralty anchor that is reputed to be there.

I’m not sold on the idea of these side-mounted cylinders. Looked more like front mounted and dragging on the ground to me.

The weekend after that one (ie last weekend) I bagged an available place on his club trip to Eyemouth with some deep Nitrox type dives. I don’t like deep diving, but was persuaded to go anyway. It was awful. The algae had come out, the water visibility was about 2 metres, and at 40metres down it was as black as the night.

The first deep dive was to the U74. I reached it, then got freaked out by the strobe that had been tied to the shotline to “help” us find the way back, stirred up a cloud of the silt on the metal, and took the first available option to leave, passing all the other divers coming down the rope.

I have very little tolerance for danger when the fear-to-fun ratio is too high.

Second dive was just to 12m in Pettico Wick (normally a shore dive in bad weather), supposedly to the peanut wreck. I found some bits of metal, but mostly blank boulders. But then things really cheered up when I stumbled across the rock called Wick Gaunt and dropped into a slot behind it (I think on the West side) which turned into quite a nice cave.

The other divers were not amused and didn’t follow me in. I couldn’t find the other entrance when I swam around to the other side. This would be a great place with some more visibility — and done as a kayak dive.

I will be back, having obtained a copy of the 32 page A5 booklet detailing 18 dives in St Abbs and Eyemouth from the dive centre — a booklet which is not mentioned anywhere on the marine reserve website or available from Amazon. I intend to spend about a week there when I can, because it looks like the last time we gave it a go was eleven years ago in 2007.

I tried to persuade the other divers on the trip of the benefits of kayak diving, but they thought it was a bit dangerous. That’s because a 37m horrorshow dive in poor visibility with not enough lights to a section of shingly the seabed somewhere in the vicinity of the Glanmire wreck (the shot had been pulled off it) is considered A-okay.

No it wasn’t.

As we quit early, Al and I stopped off at the Kagyu Samye Ling Monastery and Tibetan Centre near Lockerbie for some quiet moments of meditation in the temple where we overlapped into a session that involved people coming in and doing a bit of chanting.

Noisy lever-latch door handles on sprung swing doors at the temple entrance. Really? This has got to be one place it’s worth investing in some subtle silent autosealing door technology. But instead they’ve blown their tech budget on motorizing all the prayer wheels around the stupa.

We took a herbal tea, and I noticed a poster about their new off-shore retreat on Holy Isle, also in Scotland.

It turned out this was where I had a nice weekend kayak diving around this particular island with Becka in August 2016 and never blogged about it.

I had liaised with some fellow from Arran COAST who had campaigned for the Lamlash Bay no take zone to get some dive site information. (They’ve not yet produced a book like the St Abbs people have.)

Unfortunately the viz wasn’t very good, and we had quite a lot of current on our attempt at a deeper dive in the south channel.

He was kind enough to take these pics of us struggling on the surface to get kitted up in the tidal stream going past our kayaks that was pulling the buoy underwater.

We did also land and climb the peak on the island and discovered a dead data logger in the heather.

Just checking on the tech, you know.

Thursday, April 12th, 2018 at 4:29 pm - - Flightlogger, Hang-glide

Okay, so that last flying day at Meduno wasn’t very adventurous on the scale of the top pilots, but I was extremely pleased with it; I did just as well as anyone else in our xtc-paragliding (hang-gliding week) group and felt perfectly up with it.

Often you come down disappointed, and can watch everyone else from the landing field going higher and further and having more fun, and you’re down wholly because of your lack the skill and competence. But this wasn’t one of those days.

Here is the page of everyone’s tracklogs.

I was particularly happy with the part of the flight where I maintained my altitude over the flat lands at about 700m for 11 minutes before finally the air currents strengthened enough to carry me up. I had a sense of calm and flow rather than panic and disappointment this time.

It doesn’t look particularly low in the picture, but it felt like it.

I thought it was rising air from a pig farm I could see below and towards the dry river bed (because it smelled as such) but it couldn’t be as this as it was about 700m cross wind. I had consistently the wrong idea of the wind direction. It shows that even with totally mistaken ideas, I was still able to stay with the weakly rising air.

At one point I was passed high over a rifle range. The pops of the guns were like tap-taps on my breastbone.

I overflew the takeoff at the end of the day and took a photo of this cute pink training glider on the ramp beside the wood pile in the car park.

Then I tried to narrate part of my glide down to landing to the camera, which doesn’t work at all with my full face helmet.

One of the folks on the hill was SashaZ whose long blogpost about surfskis is what caused me to book my Tarifa trip with Becka.

Here are some other pics from previous days.

We had some long drives there and back in someone else’s car. Becka spent the whole time at SpeleoCamp caving, and so this shouldn’t count as a hang-gliding holiday.

Oh, I might as well put down my notion of the physics of flight here, while I have it worked out. It goes like this:

A heavier than air object with a mass of 100kg wishes to avoid accelerating downwards to the ground under a gravitational force amounting to 10 metres per second per second.

As each second that passes there is 100×10 = 1000 kg m/s of momentum that must be accounted for by blowing a volume air downwards at a speed k m/s.

Suppose the craft encloses a horizontal area a square metres within which it blows the air downwards at k m/s. In one second this would be ak cubic metres, which, with a density of about 1 kg per cubic metres, is ak kilograms, sent downwards with a momentum of ak2 kg m/s.

If the area a was circular, then you could cover it with a circular propellor like a helicopter, and maintain your altitude by blowing the air at sqrt(1000/a) metres per second downwards to counteract the gravity.

But imagine the shape of a is rectangular, and instead of a rotating blade, the blade moves horizontally on rails of length v and has a width w. This is somewhat like a wing with a span w flying at a velocity v.

My glider has a wingspan of the order of 10m, and an airspeed of 16 m/s, so the air needs to be blown downwards at a speed of sqrt(1000/(10*16)) = 10/4 = 2.5 m/s.

The kinetic energy embodied in this is 1/2 * mv2 = 0.5*160*2.5*2.5*2.5 = 1250 Joules/second.

If I weigh 100kg I can generate 1250 Joules from potential energy if I sink at 1.2 m/s — which is about the rate that my glider sinks on a steady glide.

This is a story of what needs to happen to the air to keep you up, not how it is done with aerofoils, vortices, induced drag or any stuff like that. And it also suggests that our lovely gliders have already hit certain limits of what they could physically achieve for their size and speed.

One way to get them to go up will be to add an electric motor to give you that extra to get off the ground, or to find a thermal when you’re going down.

That ad says they have 24 Ah in their 57.8V battery, which equates to 24*57.8*60*60=5Megajoules. This can maintain a horizontal flight for 27 minutes, which means it’s at the rate of 3000 Watts. That’s about a 50% conversion rate from the battery to powered energy, which is plausible.

It also gives a “max summit height” of 750m, which is a budget of 6660 Joules per metre. I need to give it 1000 Joules per metre in potential energy, so suppose my climb rate is k m/s then it will take me 750/k seconds to get up there, consuming 3000*750/k + 750*1000 = 5Megajoules which computes to a climb rate of 0.53 m/s over 23 minutes.

I can’t afford this stuff. I should be happy with the massive amount that I’ve already got.

Thursday, April 5th, 2018 at 10:02 pm - - Flightlogger, Hang-glide

I’ve been deeply not keeping up with blogging on this Slovenia hang-gliding trip. Telegram and Twitter seem to take the wind out of such activities. So maybe this thing is for mainly technical reports. There are a lot of dead blogs out there that only have such things. This blog was started for technical content, and then I began putting all my own activities into it.

I’ve been working on this technical thing to do with gliding and tracklogs for so long without any breakthrough that I finally decided I had to start reporting negative results.

My latest failure was attempting to use a Hough transform to derive wind speed and direction from the 2second interval GPS sample point of a glider flying around in the air mass.

There are many made up algorithms for doing this, but I wanted something mathematical. This time I based it on the assumption that the glider is mostly flying at a constant speed, so that changes in its GPS/ground speed were entirely due to flying with or against the wind. In particular, given three consecutive positions p0, p1, p2 with td seconds between them, then the correct wind velocity w would satisfy the following equation:

|p1 - p0 - wtd| = |p2 - p1 - wtd|

There is no unique solution for w in this equation; the solutions all lie along a line. So if we add some spread and combine the probability fields of solutions for every sequence of three points in the track, then the peak probability will be the best guess at the wind direction.

It’s all explained here in this jupyter notebook.

After so many failures, I’m much pleased with this result. The actual wind was blowing towards the northeast, and the bad guesses are when the glider was on glide and not doing any circles.

That was from a four hour mega flight all round the three ridges near Gorzia where at one point I got lifted smoothly one thousand metres into the blue sky at the rate of 5m/s. I could see from the capital city inland to the container ships on the Adriatic.

Here’s a picture after landing from a lesser flight today where the clouds were pretty low on the ridge.

I need to grab some self-portraits from the other folks some point real soon of me taking off, and me landing quite properly on my feet. I’m starting to hanker after a new glider, one that’s sleeker and goes faster. This one’s beginning to feel sluggish all of a sudden. I can’t afford anything else now, and it would be quite naughty. And after my spectacular failure of an XC last week on Bradwell, I don’t deserve an upgrade.

Monday, March 12th, 2018 at 4:53 pm - - Kayak Dive, Weekends

Earlier I published the bus and train itinerary. Now for some pics.


Friday, March 2nd, 2018 at 4:12 pm - - Kayak Dive, Weekends 1 Comment »

Just done 2 weeks (feels like 2 months) tour round southern Spain, culminating in 4 days of Surfski lessons in Tarifa. The conditions were gentle, which was perfect for people who don’t know how to paddle them properly.

We generally stayed cheaply in hostel dorm rooms (while going touristing) where all the jetsetting youth cluttering up the bunks didn’t seem to believe that there were actually train tracks all the way between where we were and England.

So to prove it, below is a table of our travel itinerary.

I’ll give a special shout-out to which we only found out about on our first day in Madrid when we asked the guy behind the desk in the hostel where was the best place to buy our bus tickets. We very quickly got used to waving our phone with a downloaded PDF of a QR code at the train or bus conductor to be scanned, as well as the excellent wifi on the buses.

Type From To Euros Minutes km kph km/Euro Road-minutes Date Purchased Method
Train Liverpool London 26 139 350 151.08 13.46 280 2018-02-12 2018-01-12 Virgin
Train London Paris 78 144 457 190.42 5.86 366 2018-02-13 2017-11-09 Loco2
Train Paris Barcelona 49 390 1037 159.54 21.16 600 2018-02-13 2017-11-09 Loco2
Train Barcelona Madrid 49.55 165 650 236.36 13.12 360 2018-02-13 2017-11-09 Loco2
Bus Madrid Granada 18.59 300 420 84.00 22.59 260 2018-02-15 2018-02-14 GoEuro
Bus Granada Cordoba 17.29 144 201 83.75 11.63 135 2018-02-17 2018-02-16 GoEuro
Train Cordoba Seville 15.2 45 140 186.67 9.21 100 2018-02-17 2018-02-16 GoEuro
Train Seville Cadiz 16.05 100 122 73.20 7.60 85 2018-02-19 2018-02-18 GoEuro
Bus Cadiz Tarifa 10.2 105 105 60.00 10.29 75 2018-02-19 2018-02-18 GoEuro
Bus Tarifa Gibraltar 4.45 65 42 38.77 9.44 43 2018-02-25 2018-02-24 GoEuro
Bus Gibraltar Malaga 11.7 180 130 43.33 11.11 100 2018-02-25 2018-02-25 Station
Train Malaga Barcelona 59.05 350 996 170.74 16.87 550 2018-02-27 2018-02-18 GoEuro
Train Barcelona Lyon 39 300 639 127.80 16.38 367 2018-02-28 2017-11-09 Loco2
Train Lyon London 78 300 933 186.60 11.96 547 2018-02-28 2017-11-09 Loco2
Train London Liverpool 26 143 350 146.85 13.46 280 2018-03-01 2018-02-11 Virgin

Our losses amounted to several USB cables, one hat, one scarf, my logbook (only started this year), and one blocked ear for Becka from a freezing cold dive out of Tarifa on what is called the boiler wreck, where we were shown a brick from Scotland.

There was also the incident of the large monkey with teeth in Gibraltar that almost stole our passports out of the top of Becka’s backpack but couldn’t unzip the pocket in time before I scared it off. (Actually, it scared me away as I shouted for Becka to bat it off her back.)

We thought thought this had been an amazing no-flight adventure, but then it turned out we got home too late to see the ignite talk by Graham Hughes who claims to have visited every country in the world without flying.

So it’s really nothing to write home about. I hope to get some pictures in due course.