Freesteel Blog » 2013 » May

Wednesday, May 29th, 2013 at 7:19 am - - Hang-glide

Blazingly sunny day over Wether Fell, but with blue sky above the hill all day. About 30 paragliders could be seen rising above Dodd’s Fell up ahead, but there never was quite that kind of lift where I was, with another 20 paragliders on my hill, wafting about the place, catching the once-every-half-hour breezy thermal (which I missed, as I was waiting for it to get better, which it never did. Lesson learned.)

Finally went for it at 2pm after two hours standing under the glider, and went straight down with barely a breath of lift.

There was so little wind it didn’t matter which direction I landed in.


Friday, May 24th, 2013 at 4:56 pm - - Adaptive

Believe it or not, I’ve been working on the Adaptive Clearing strategy recently, attempting to upgrade it to have multi-core capabilities. As you know, the free lunch was declared over 2005 when CPU clock-cycles stopped increasing exponentially. Now, instead, the numbers of cores are increasing. I have 8 cores on my current laptop, and when my state-of-the-art-algorithm runs on it using only 12.5% of the computing capability, it’s embarrassing.

To break the algorithm down into components that can be processed concurrently, I have separated it into 7 working threads, each of which pipes objects to the next layer through a queue. I was told that this is pretty standard architecture — even though it doesn’t look like it can be done using the concurrent.futures module in Python (where I looked for inspiration) because it looked like it needed the complete list of tasks before it could distribute them — at least in an earlier incarnation — and not a pipeline of data. I was also confused by the use of the word “futures” for processes not yet complete, which was similar to the __futures__ module which was features from a later version of Python into an earlier one. I don’t like the terminology anyway, but that’s just my opinion.

Anyway, a Queue is a structure that has functions queue.put(object) [to the front] and queue.get() [returns an object from the back], where each end can be handled by a different operator, like like this:

Let’s say op1 is sending in horizontal slices of the model (the objects obj) and op2 is calculating the clearing toolpath at each of the horizontal layers. We can run these two operations in different threads, and it will all work tickety-boo. The operating characteristics of the threads getting and putting from and into queues is that when a thread gets from a queue that it empty, it automatically sleeps (consuming no processor cycles) until something is put into the queue at the other end, at which point it automatically wakes up and retrieves the object. The opposite happens on the put if you have specified an upper bound for the capacity of the queue and you hit it.


Friday, May 24th, 2013 at 9:26 am - - Cave

I have a confession to make. The digging trip in April wasn’t quite as boring as said.

In fact, we broke through. But since it would be about a month before the digging team could get back together and do all the stuff we needed to get done before the teeming hoards went in, we kept it secret.

To recap, the dig started in the dry mud floor in this terribly obvious place here:


Monday, May 20th, 2013 at 7:46 pm - - Kayak Dive

This is paddling back along Loch Carron from Plockton to our lovely hostel in Stromeferry with a 20mph tailwind on Monday 13 May.


Thursday, May 9th, 2013 at 2:50 pm - - Hang-glide 2 Comments »

I don’t usually talk about plans like this too far in advance, due to the fear of jinxing it by some bad event, but I am too much looking forward to this, and I don’t have anyone to go with yet.


Thursday, May 9th, 2013 at 1:57 pm - - FOI

In their new executive-summary-style webpages, the UK Government sets out its case that it is fulfilling its side of the deal that allows them to remain a nuclear weapons state under the Nuclear Non-Proliferation Treaty wherein they promised to “pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament, and on a treaty on general and complete disarmament under strict and effective international control.”

Monday, May 6th, 2013 at 11:48 pm - - Hang-glide

The Long Mynd hang gliding site is sort of on the way to LLandrindod Wells where we were going to bury grandfather’s ashes. He once owned a shop in Church Stretton nearby and talked about the gliders up on the Long Mynd in the early 1960s when he was out rambling. So it seemed like a good idea to go there and take advantage of the westerly wind.

Unfortunately at a wind-speed of 20mph, it was a bit breezy, so there were not many gliders there, even though it was a bank holiday. None of the pilots were local; the locals can pick better days when it’s going to be more fun. This was going to be a gale-hang. Two people had flown. Now it was my turn, having delayed until one of them had landed and could tell me the conditions (quite smooth).

Everyone had Wills Wing gliders similar to mine, not the fancy topless kind.

I had a good time — except for the landing. Actually, the landing was fine, it was the 3 seconds before it that weren’t so good. I should consult an instructor to work out what happened and whether the harness configuration needs thinking about.

I don’t know what I’m doing. At least the camera tells me my posture is terrible. You’re supposed to pull your weight sideways to turn the glider, but it looks like my legs go the other way half the time, which means I’m simply twisting and not shifting my weight anywhere. The picture shows me that the VG cord makes a difference to the flex of the wings, though I’m too insensitive to feel it because I can’t even tell the difference between turbulence and crap flying.

Also, this new flight computer doesn’t make much sense. I can plug it into an air speed indicator, and it thought I had already taken off due to the wind speed of 20mph, which was roughly the speed of the glider. When I pulled the bar in it could go up to 30mph.

The top graph shows that I immediately rode the rising air up to 350m above take off, then straight-away bombed back down before anything else happened. This coincided with my brief excursion north along the ridge in the right hand chart. Having lost all this height so quickly, and hated it, I hung out over the take off area for the rest of the flight, not wanting to risk going anywhere else again. A sailplane buzzed up and down the ridge below me. Much later another glider joined me, rising to my altitude in no time. It went along the ridge to the left and then back towards me, and was a lot more interesting to watch than my boring flight, according to Becka.

I want to go somewhere one day so I don’t just have map scribbles. But I don’t have the guts or the skill. I get all these notions when I’m on the ground, but it completely falls apart as soon as I take off. I’m sure there something obvious I’m missing out on. It’s like I’ve learnt the wrong shape of the air.

We stayed in a nice B&B on Saturday night, then in a not so nice hotel on Sunday night with the rest of the folks. Becka headed off early Monday morning for a scary caving trip in Pool Park with its heavy steel padlocked lid over a 100m entrance pitch (she dropped the padlock) on a nasty dry 9mm rope. Too scary for me. They call it a fear of heights, but it’s actually a fear of falling. The height is not a problem if you are flying, just as the depth of water doesn’t matter if you are floating. But if your hands are tied together and you are wearing lead ankle chains, then water gets really scary. I caught a lift to Cambridge for the day, and expect to be on a train home tomorrow night.