Freesteel Blog » Hang-glide

Friday, December 15th, 2017 at 6:48 pm - - Hang-glide

If I don’t blog it, it hasn’t happened. I have been forgetting this fact.

Yesterday I had a minor breakthrough.

For years I’d been seeing beautiful videos of simulated cloud convection online, but was never able to run them myself in order to look at the data.

The structure of thermals has been a long-term mystery to me, and I’ve noticed that some pilots seem to be able to navigate through and climb these invisible things quite reliably, yet are not able to explain how they do it. They are in the dark just as much as I am, yet they have — probably by luck (plus the necessary skill to recognize and lock it in) — struck upon the combinations of responses to inputs and gut senses that just happens to pay off spectacularly.

My gut feelings and responses to inputs don’t always work out so well because my imaginations of the air are probably too logical, incorrect and counter-productive and they require resetting and retraining to break free from their false notions.

So I’ve decided that it has got to help me if I can see what is going on, and not carry on wondering whether thermals are columns or vortex donuts, are surrounded by sinking air or tailwind incoming air, are observably warmer than their surroundings or mere upward kinetic energy.

So this time I tried harder to get to the simulation code when I had the time.

I am now pretty sure that the code for the GPU-resident Atmospheric Large-Eddy Simulation (GALES) is unpublished.

However, I did eventually establish from one of the papers that GALES is based on DALES — the Dutch Atmospheric Large-Eddy Simulation where it said the code was to be found at the broken link dales.ablresearch.org. Fortunately it does exist at github.com/dalesteam/dales.

This divulged a pile of Fortran90 code and a CMake script, and I was able to build it and run it against the cblstrong case example.

This eventually (after heating up my computer’s CPU) dumped out a file called initd03h00mx000y000.001 written by the function modstartup.f90 writerestartfiles with lines like:

write(ifoutput) (((u0 (i,j,k),i=2-ih,i1+ih),j=2-jh,j1+jh),k=1,k1)
write(ifoutput)  (((v0 (i,j,k),i=2-ih,i1+ih),j=2-jh,j1+jh),k=1,k1)
write(ifoutput)  (((w0    (i,j,k),i=2-ih,i1+ih),j=2-jh,j1+jh),k=1,k1)
write(ifoutput) (((thl0 (i,j,k),i=2-ih,i1+ih),j=2-jh,j1+jh),k=1,k1)

By the power of Python I used the module scipy.io.FortranFile to read the velocity component records like so:

ku = f.read_record(dtype="f8")
kv = f.read_record(dtype="f8")
kw = f.read_record(dtype="f8")

and determine that the number of double-float values in each array record came to 475300. Of course you can immediately tell that this factorizes into 50*70*70, so that the 3-dimensional array of vertical components of air velocity can be stated as:

kkw = numpy.resize(kw, (50,70,70))

Thus this is plotted slice-wise at a constant altitude by:

plt.imshow(kkw[16,:,:])
plt.colorbar()

to make a familiar image of computer generated thermals seen in past papers:

I didn’t stop there, and generated the following video of a melt through from the bottom to the top with black arrows denoting the horizontal wind components:

using the code:

cmdstring = ('ffmpeg','-r', '5','-f','image2pipe','-vcodec', 'png', 
             '-i', 'pipe:', "testA.avi")
p = subprocess.Popen(cmdstring, stdin=subprocess.PIPE)
X, Y = numpy.mgrid[0:70, 0:70]
for ik in range(1,50,1):
    print(ik)
    plt.figure(figsize=(11,11), frameon=False)
    Q = plt.quiver(X, Y, kku[ik,:,:], kkv[ik,:,:], color="black", headlength=4, headwidth=2)
    plt.imshow(kkw[ik,:,:], cmap=plt.get_cmap("coolwarm"), vmin=-5, vmax=5, interpolation="bilinear")
    plt.title("zslice %d" % ik)
    plt.savefig(p.stdin, format='png', pad_inches=0.0, bbox_inches='tight')
    plt.close()
p.stdin.close()

Boy have I wasted a lot of time on this so far, and I’ve got to do some other things while I catch up on some Basic Lessons on CFD (Computational Fluid Dynamics). It can only help to have some background knowledge of the field.

The next step will be to investigate how to program the initial boundary conditions and setup to create a single idealized thermal, which is an evolutionary structure in time and space that a glider like mine might encounter. And while a glider is flying and circling and climbing in it, the thermal is evolving, so your experience can only be expressed as a slice that runs like a diagonal corkscrew through the spacetime continuum fluid in four dimensions.

There’s no way this is ever going to make sense, but if it challenges my intuition to break out into another state where the flight of my wings flows through the air better, then it will have certainly worked for me.

Monday, August 28th, 2017 at 4:44 pm - - Hang-glide

Not been getting very many things to conclusion recently. Sitting around in campsites waiting for people to finish caving. Sitting at home waiting for people to come home from caving. Things have been in stasis. And my flying has been somewhat less than epic.

I have been breaking quite a few less bits of glider lately, which is a surprise given the sort of place I chose to park it yesterday.
bradwellbamland

I came round the tree behind the nose of the glider and landed up the slope that I didn’t know was going to be there when I chose this field. If I had aimed any further along the field I’d have gone over the hump and then I don’t know what I’d do on the downslope except crash into a hedge.

It was a close enough landing that I was able to walk back to the top of the hill in an hour and a half. Here is the track drawn over the terrain:

bamford

And this is the altitude trace where I managed to circle for a time less than 200m above the ground in air that was rising not quite fast enough to keep me from going down.
bamfordalti

These diagrams were made in an ipython notebook.

Flying in weak air is a new capability. After the debacle of my previous XC flight on a day when somebody else flew 200kms from Long Mynd to Cambridge, I went back to school and watched some videos which explained how I had to set up my vario so that it makes sounds when it is going down as well as going up, so that I can tell the difference at different rates of going down without having to glance at the number.

I’m also trying to learn now to work OpenFoam, as well as learn some Aerodynamics. And now I’ve got to read a dissertaion on bicycles which involved sensors and a kinematic model of a bike on a treadmill, as this represents ten years of research in the area beyond where I am at with my glider sensors.

This is actual aggregating technical progress, not the latest forgettable choss on spacebook. I just cannot keep up!

Thursday, July 27th, 2017 at 12:45 pm - - Hang-glide

Before I dampened and broke my brand new computer by keeping it overnight in the tent I was trying some simulations of Kalman filters derived from open source implementations in order to get a handle on the overly complex mathematical formulations of this technology in, say, one dimensional filter data.

It appears that the one dimensional kalman filter is a worthless beast that obscures a simple trivial exponential filter behind it.
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Wednesday, July 19th, 2017 at 10:05 am - - Hang-glide

Sometimes things you’ve always dreamed of happening grab you by pure chance.

beckabefore3

I could have organized this event at great expense in England on some boring ridge soaring ridge, but I got unlucky during a competition, and then got real lucky to do this.

At the start of the day I was mixing it up at cloud-base with all these competition hang-gliders.

beckabefore1

And then 20 minutes later I got found out and scraped down into a wheat field 10kms to the north of take-off.

beckabefore2

Luckily one of the other competition pilots came down near me, and his retrieve driver (who, unlike my retrieve drivers isn’t more often retrieved by the pilot than the correct way round) picked us both up, and I persuaded them to take me up to the top of the hill for one last flight on Monte Cucco at the end of the holiday.

And just then, Becka was about to take off on her tandem flight which we had been rescheduling day after day during the week.

Her tandem flight lasted long enough for me to completely rig my glider, take off, and climb up to them close enough for a wave.

Later, I carried on flying for too long and landed in the field while they were trying to give the prize giving. This was delayed because of me as they needed my tracklog from my crappy flight before they could officially calculate and release the figures.

When I finally showed up I was invited to stand on the winners podium and be humiliated in front of everyone while the contest scorer squirted a water pistol at me.

Becka does not have a photo.

Tuesday, July 11th, 2017 at 4:32 pm - - Canyon, Hang-glide

I sneaked in a couple of gorgeous flights in between canyonning adventures with Becka in the last three days.

On the 8th July, while staying at Tramoniti di Sotto we did the canyons Torrent La Foce and Rio Carlo Gasparini in the morning (the latter of which is not in Si Flower’s book and should be), followed by Becka driving me up and leaving me behind on top of the hill above Meduno (Italy).

As usual, very few of the photos were any use. This is from La Foce.

And this is from Gasparini, selected based on a tip-off from 4lander.it website listed in a canyoning leaflet.

The canyon ends by joining the much larger Torrente Arzino where you bob along in the swiftly flowing blue-green crystal clear water until the climbing out point. Magical.

This is my BWG (boring white glider, which describes the top surface) on behind the Meduno takeoff. As I explained to Becka, I would be consumed by jealousy if I saw one of these and didn’t have one of my own.

And here it is being boring and white in the bottom landing field with no bent aluminium. For once I timed the flare perfectly and landed on my feet like a pro. Boy was I grinning.

meduno

The next day (9th July) we did Torrente Cosa, which passes through the property of the showcave Grotte di Pradis (see the walkways in the background). The canyoneer’s advice is to write a note in Italian saying what you are doing and hand it in at the showcave so they don’t get annoyed at people unexpectedly traipsing through, but the man in the ticket booth didn’t really know what to make of it and waved us away.

Cosa had one scary bit where I abseiled into a cauldron of water in a dark cavey section and couldn’t easily fight past the swirling current while dangling on the rope.

Then we had a late lunch before the long drive to Camp Gabrje near Tolmin.

The next day we cycled over for a quick tour of the relatively underwhelming and costly Tolmin Gorges before I caught the taxi up to the top of the Kobala takeoff.

tolmintop

The lift looked weak. For a while there was a wall of paragliders directly in front of takeoff and none getting higher. Then I saw two birds circling behind them, waited for a gap, and then thermalled directly up to cloudbase.

I lost it all crossing over to the next ridge to the West where I soared ineffectively for the rest of the afternoon not daring to venture into the mountains behind. I’d never been here before and hadn’t looked at a map. The wings felt totally natural on me. I’ve really grown to like them.

tolminlanding

And for a second time in a row, I landed on my feet with no bent aluminium.

Then I had a 45 minute walk back to the campsite in the sweltering humid heat to pack up the tent, fetch the car, drive back to the landing field, pick up my glider, and then go on a chase after Becka who was busy road-cycling to the Italian border via Bovec.

I’ve made a habit of having to retrieve my retrieve driver.

Now we are at Expo base camp in Austria where Becka is going to do a lot of caving and I am going to make myself bored until I start doing the chores that I have been putting off until now. Which includes writing up my logbook, blogging and looking at forgotten flight data.

Sunday, June 25th, 2017 at 8:16 pm - - Hang-glide

It’s been the fourth day of hang-gliding in a row and the first of the competition. My god today was something. The comp is at Monte Cucco, and the drill is you drive up the hill and get set a task in the form of a series of GPS coordinates with cylinder radii around them, and your job is to race from one to another and tag each one. Your track log verifies your score.

This is quite different from free flying, because you are forced to go to places you wouldn’t naturally go to if you were following the air — and get back from them.

Here is what the course looked like against the terrain map:

flightmap

This leaves out all the forests, cliffs, canyons, sprawling suburbs at the base of the mountains and power lines. The beginning of the journey was absolutely terrifying because any escape routes to lower ground were into wind and unlandable. You had to learn to trust the ridge lift.

I didn’t trust it, and instead spent the first 30 minutes wheeling around these scary wind turbines on take off unable to find a satisfactory way on.

windmills

Then the clouds really began suck and I raced back north to the second turn-point. The third point was the landing field. There was such an uprushing of air in the valley I could not get down. Well I did eventually, by pulling all sorts of stunts (tight circles) that are the exact opposite of efficient gliding. Then, when I gave it a rest for too long, the air sucked me right back up again.

Hang-gliding is a sport for turning long pieces of aluminium into short pieces of aluminium. That happened yesterday when I broke an upright. I have no more spares. Today I got away with skinning my knees (I’m wearing trousers from now on). Clearly I do not deserve to fly this higher performance glider (a Wills Wing U2) since landing is the compulsory part of every flight.

It’s 9pm now. I’m finding I don’t really give a damn about anything else, eg reading and answering emails, or thinking about work. It’s too hot here even if I wasn’t flying.

Bed time.

Monday, June 5th, 2017 at 11:52 am - - Hang-glide

Some friendly competition in Derbyshire between hangies and paragliders on Saturday meant I got to witness the scale, organization and infrastructure of the paragliders — which included following me on xcrt.aero and being at the nearest road before I’d even had time to pick myself off the ground.

Then I was in the car for an hour as they drove madly up and down the M1 taking wrong turnings in an effort to collect three other paragliders strewn in the area.

Motto: write the logbook on the day and edit the video as quick as possible without wasting too much time.

My flight datalogger failed to record anything, so I can’t see if my thermal detector collected any signals.

Not that I had any spare brain capacity. For two hours I was continually trying to visualize and feel the structure of the air convection wafts while making constant adjustments to my circling.

I’m also learning how to stay in very weak air where you are gradually losing height — but at a slower rate than if you were on a desperate glide to nowhere — which moves you forward in time for something else to develop. It’s like skipping a turn in a card game.

Here’s a screen-grab of the livetrack24 view of my flight, which receives updates from an app running on your mobile phone.

livetrack

This is not to be confused with the latest AirWhere technology thing, also done by the paragliders recently which create an ad-hoc Lorawan network among themselves that displays their distance and climb rates of your neighbours on the network.

A small amount of additional calculation and they’ll be able to circle the ones who are in thermals you should fly to and join. This helps people haven’t learnt how to judge distances, times and glide angles.

I just cannot keep up with the tech.

Here’s some plots that I did salvage the data.

flightterrain

flightterrainside

Friday, June 2nd, 2017 at 3:32 pm - - Hang-glide

This is the follow-on of my Loser Plateau article of last year in Skywings magazine.

4 page PDF version

I should find something new to write about next time. Now that I am flying my BWG (Boring White Glider), which is a more advanced U2 I got second hand off Tim who no longer needs it because he’s got a whole hang-glider factory. Helen the bright orange HSMWorks glider is a Sport2, and I’m not ready to let go of her yet.

swp1

swp2

swp3

swp4

Thursday, June 1st, 2017 at 4:06 pm - - Flightlogger, Hang-glide

I’ve been flying around my data logger on my hang-glider and doing my own data processing with mixed results for two years now.

During this time I’ve been on the lookout for someone else’s work that I can copy.

Just yesterday I discovered the existence of Dropsondes and then Radiosondes (devices that get lifted by a weather balloon with a radio link; nothing to do with sound-waves).

The fact of their existence has been staring me in the face for years.

raspsoundings

Those little red *S* symbols in the rasp forecast are not weather symbols for sunshine, but in fact the locations of half a dozen atmospheric “sounding” stations.

Until now I’d believed they were something involving a fancy radar beams shining up through the clouds, but it turns out it’s a freaking weather balloon with a humidity, temperature and gps sensors (they don’t bother with the barometer anymore and just use the gps altitude) that radio back data for an hour and a half till the latex balloon bursts at 25,000m and the device falls under a biodegradable parachute with a 95% of never being seen again.

The US government has a complete tour of the procedure, but the MetOffice has some automated stations which assemble and let off a new balloon every 12 hours from a robot building.
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Tuesday, May 30th, 2017 at 6:11 pm - - Flightlogger, Hang-glide

First, here’s a picture of me and my cheezy grin high up in wave over Wether Fell with about a dozen other gliders last Sunday

wavegrin

I was able to generate my incomplete Tephigram as before to illustrate the warm dry air encountered way up there.

tephi

Unfortunately, the fancy Python tephigram software released by the MetOffice doesn’t work for me as it’s designed to plot graphs that go ten times higher in the atmosphere.

Tephigram is short for “Temperature” and “Entropy/phi” plot and was invented in 1915. I don’t understand all of it yet. But this science goes back a long way.

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