Freesteel Blog » Weekends

Monday, May 20th, 2019 at 11:57 am - - Kayak Dive

I’m carving out some valuable time from the other stuff to blog some notes and records.

The car failed its MoT inspection with 3 condemned tyres. (Some kind of bump in them that I couldn’t see.) I had an unhappy evening because I thought this had trashed our kayak diving weekend in Anglesey.

Apparently the dangerous bulge is in this picture here at bottom inside:

Yes, normally back in the 1990s I’d have driven the car anyway, because who’s going to know? But now with all the MoT records being computerized so you can’t shop around for a garage who might overlook the flaws, and all these automatic number plate recognition cameras on the motorways, I was for sure I was going to be busted by the police on our way out.

Fortunately Becka phoned up a kwikfit garage and I took it round in the morning for some new tyres at a high price, but it was worth it. We kept the fresh receipt on the dashboard as evidence that the issue had been addressed and didn’t encounter a problem. Even though we didn’t need it, it’s good price to pay for not to have this eating your mind during the whole drive.

After a stop off at Vivian Quarry for some air-fills (£4.50 for only 200bar and a long time to fill), we dropped in on the Astral Ship for an inspection.

We concluded that it wasn’t a robot friendly place, so I took it away and we were lucky to get my robot into someone else’s car for the ride back to Liverpool. More on this story some other time.

It was now 4 o’clock, and we got a kayak dive out from Cable Bay to the Euphraties, which was swarming with large spider crabs and had mounds of chain and other wreckage that blended in with the rocks so well you couldn’t tell, except by their form, what was natural or man-made.

Then we headed off late to the Tyn Rhos Camping Site Ravenspoint Road and ended up on the wrong side of a locked gate because we hadn’t approached it from Ravenspoint Road (idiot). The Liverpool Canoe Club were spending the weekend there and some of them had paddled to the Skerries durinig the day (one of the things on our bucket list). One of the other parties had passed us coming in while we were going out for our dive. They didn’t stop off to watch, as no one is particularly interested in kayak diving. In the morning we tried to see if there were any trips being planned that we could dive in the direction of, as it gives peace of mind to have a bit of company on the surface when you are underwater, but nothing presented itself. So we were back to our original plan of diving the Kimya, which I have been trying to get a decent dive on since 2004!

The wind had picked up from the northwest (it was supposed to be northeast on the forecast) and there was a bit of chop. The May bloom was overdue. It all looked like it would be another failure.

But we got there. After much anchor dragging of anchors, shouting and checking the GPS on my expensive phone in a pelicase (all my waterproof GPS’s are bust), Becka seemed to hook something at last. (After the dive she understood my outrage that it had been so difficult to hook — the wreck is massive and full of holes.)

Just as we were going down the line, a dive boat showed up. That made me feel more comfortable.

If everything went tits up, they’d probably pick up the pieces. It’s a 3km paddle from the nearest landing and there are no fishermen on the headlands, so it’s a pretty lonely spot round about here. No one is ever going to see you.


Becka collected the anchor from the bottom and carried it as we circled the wreck twice. I thought the lifeline to our kayaks was going to get tangled continually, but she skillfully kept it running free. I had thought at the start about tying the anchor to a good spot on the wreck, but it was so big you wouldn’t be sure of getting back to it again.


There were a couple of swimthroughs, and a huge hold that we sank down into towards the end of the dive. Luckily the divers from the boat hadn’t been in there to stir up the silt by then. Little splashes of bright colour from nudibranchs on any surface you cared to focus on.


And so we surfaced, climbed back on our boats, chatted with the other divers (who were from St Helens) and arm-power hauled our way back to Porth Cwyfan (the cove with the white church), and then hoofed the kit across acres of sharp low-tide rocks to the shore.

Now we would have had our tea at that spot, except that the place is very much in earshot of the Anglesey racing circuit, whose noise diary for 19 May 2019 gave their No Limits Motorcycle Track Day a noise category 2. It was pretty bad.

We drove to Newborough Warren where the guy collecting the £5 entrance fee had already gone home, and brewed up some tea just over a sand dune from the carpark (unfortunately melting the handle on the trangia tea-pot in the process).

Then, of course, we had to walk out to and along the whole length of Ynys Llanddwyn, scrambling up and down the rocks at the far end.

I was knackered.

Becka accused me of getting soft and complained that we had done nothing all day.

Wednesday, May 8th, 2019 at 7:00 pm - - Hang-glide

Lots of adventures that have gone unreported on the blog for the last few months, including a month long stay in the city of Belfast, including a couple of dives in Strangford Lough. I’ve been putting stuff in twitter/goatchurch instead.

I haven’t finished writing up my logbook, but anyway I was on a hang-gliding competition last week where I got 12th place in spite of levels of fear before takeoff that made me question whether it was all worth it.

It turned out it was. There were some lovely flights from Builth Wells, Hay Bluff. And then there was Merthyr. Becka was there to pick me up from where I landed, and I sometimes made enough of a distance for this to be worth it.

Here are some quick pics.


Acting as a wireman to put off the fateful moment when it’s going to be my turn.


Getting low on Merthyr Hill in the grey after an hour and a half of flying in the rough air.


Finally getting up to cloud-base, at which point I decided I was done with this place and went straight off downwind.


I landed two hills back with some curious cows. Not such a result that day.

The gopro failed on the other two days, so no in-air photos are available.

I got a lot of stuff to write about, like RTK GPS, ESP32s with MQTT asyncronous mDNS capabilities, Sonoff POWs, differentiating time-series values by curve fitting polynomials. The trouble is none of it is working too well, so I’m preferring to work on it rather than report it. I’ll force myself to hammer some stuff out in the next few days whatever.

Tuesday, November 6th, 2018 at 6:51 pm - - Hang-glide

Quite a lot of work in the last week (especially at the weekend) reading a big book called Tailless Aircraft: Their Design and Characteristics, published 1994, translated from German.

The blurb on the inside cover reads:

The authors are uniquely placed to compile the first practical and comprehensive treatment of this fascinating branch of aeronautics. They have for many years collaborated on the practical and theoretical development of flying wings, applying themselves to sailplanes and powered designs ranging from models to full-size craft. In 1988, together with Klaus R, they received the “Berblinger Award” from the City of Ulm for their investivation into the design for an optimum tailless hangglider.

What the heck is the “Berblinger Award”?

The winner of the 100,000 Euro Berblinger Flight Competition was declared on Sunday 17 April, in the Ulm town hall. In all, 36 participants competed for the prize, which focussed on the use of innovative, ecological and resource-saving technologies. Of the 36 applications received, 24 aircraft were initially admitted to the competition. 13 aircraft started successfully; due to insufficient financial backing, technical difficulties or the absence of the appropriate flying licenses the remaining competitors were not able to take part in the practical phases of the competition, which was carried out at the AERO global for general aviation, in Friedrichshafen. Eight participants successfully completed the exercise of flying from Friedrichshafen to Ulm.

Two anniversaries were celebrated with an extensive programme of events during this weekend in Friedrichsau Park and the Adlerbastei: 200 years ago, King Friedrich 1st gave the Friedrichsau Park to the people of Ulm. In honour of his visit, Berblinger performed his attempt to fly across the Danube.

Who the heck is Albrecht Berblinger?

One of Berblinger’s inventions was what appears to be a hang gliderKing Frederick I of Württemberg became interested in his work and sponsored him with 20 Louis. He tried to demonstrate the glider on the evening of 30 May 1811 in the presence of the king, his three sons and the crown prince of Bavaria. The king and a large number of citizens waited for the flight but Berblinger cancelled it, claiming that his glider was damaged. The next day he made a second attempt. The King had left by this time, but his brother Duke Heinrich and the princes stayed to watch. Berblinger waited so long for a good wind that a policeman finally gave him a push and Berblinger fell into the Donau (Danube).

It sounds like the experience on some of my takeoffs.

But enough of that rabbit-hole.

I’ve been attempting to replicate some of these graphs and diagrams from the book, like these ones:

After many days and many attempts, I got to this matching version:

This was not helped by the mistake in Formula (2.7.5)!

I could not replicate the other four lines for the “neutral point” (some details about dc_l/d(alpha) has been left out).

In the process of this I have wasted no pencil and paper, and proved the power of SymPy, which I think all mathematics should be written using.

The details are all on the Horten sailplanes Jupyter notebook. It’s probably a good thing I don’t have the technology to inline mathematics into this blog.

Wednesday, October 31st, 2018 at 12:24 pm - - Kayak Dive

A quick weekend to take advantage of Becka’s trip to Southampton University to work as an examiner. Unfortunately the university library was card controlled, so I hung out in the Burgess Road Public Library skimming through a tourist book about the Isle of Wight (containing no useful information) and then reading part of a Douglas Adams book.

We drove over on the ferry on Friday afternoon to stay with an old hang-gliding buddy, who is now the last hangie on the island. This, down from a time when, during the 1980s and 1990s, one of the largest hang-glider manufactures in the world was in operation.

It was too windy for that game, and blowing from the north, so we took our kayaks, went out of Freshwater Bay and paddled to The Needles.

It seemed too windy and scary to get out to the far needle, so we got back and gave our friend a trip round the bay, then walked up to the battery to see the stunning white cliffs from another angle. It was cold and windy.

On Sunday we took the cycle trail from Newport to Sandown, emptied all our tuppences into a machine, and cycled back again, pumping up the tyres every couple miles due to a slow puncture.

I’ve been doing my best to get through the book Tailless Aircraft in theory and practice that I nicked from my friend’s bookshelf on the way out. More on this later. The mathematics in it feels a bit shoddy, which might be why I’ve never got through such engineering books before. Foundational assumptions, such as the optimality of the elliptical lift distribution, are stated in passing because the practitioners have so internalized them they don’t even notice. It’s as basic to the equations as the conventions of using (x,y,z) for the axes and t for time. Also, these engineering guys will divide anything by anything just to get a dimensionless constant.

Then on Monday I put it in practice by driving over to Treak Hill in the peak district and bombing out to the bottom landing field, while everyone else had a lovely time flying all round Mam Tour. (The airforce glider is a two person glider that also went down, because it’s quite heavy. I packed it up while the pilot went up for a proper fly.)

Maybe tomorrow.

Monday, October 22nd, 2018 at 4:33 pm - - Kayak Dive

Still not getting out much at all. Mostly just doing work (not paid of course). The time seems to go somewhere; still not sure what I’m getting done, if anything. I’m not even generating much 3D printing scrap, like I used to every week.

Anyways, we got tempted out on a kayak dive last Saturday, which went very well.

However, the point of the dive was to demonstrate kayak diving to the duttons divers, who do training in their own Vivian Quarry and run dive boat trips out to Puffin Island. We had their timetable, and they were about an hour and a half late (they were supposed to be in the water at 11am). Sometime after 12 we gave up waiting and did a dive anyway, in the drop-off on the north side of the island, in the stiff along-shore breeze. It was terrible timing. They then came by and dived without us while we were underwater. Ho hum. So I’ve failed to spread the goodness of kayak diving, as I’d hoped, because we didn’t faff enough.

Paddling back was a bit of a slog against the wind, almost making no progress across the sound past Perch Rock. Then, back on the mainland, we gave up trying to paddle up the coast to where our car was parked, landed, send Becka to get the car and bring it back, while paying the £3 car parking at the end.

Then it was back for lunch and apple pie with our friend in Menai Bridge, and then off to meet people at Vivian Quarry a couple hours later once they’d finally got off the boat and finished faffing. It was cold. We drove home, dropped me off, and Becka went off to Yorkshire to dig gravel while I washed up the gear and did another day of unaccountable work. Today I skipped a chance to go flying to watch Fahrenheit_11/9 at its single screening, which Becka thought was a bit heavy for daytime entertainment. I still feel guilty at not having gone to the People’s Vote march.

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.