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By Beeza
#398213
Some scans to go with the previous post.

The wind shear at the top of the wave just continues on from the lift in the lee of the wave. So everything should have been drawn within the thermal from the entry to the core.

The pendulum thing on the thermal/wave-lift page was just an "ikon", a reminder to read up on something.

There are quite a few throughout, either sketches or tracings.

They were not a suggestion that the subject was involved in some way, they were just something that might be worth looking up when more information became available.

Easier and more instant to read. Better than using a lot of words.
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By DMarley
#398218
I'm guessing bezza has never been on the ocean or very large body of water (Great Lakes) before, or never had to navigate upon the ocean on a small boat on heavy seas.
Small wavelets build within large waves, within larger waves. All these waves are being pushed by varying velocities of similar wind direction. This is most noticeable in a building sea. If there is any wind reversal (rotor), it is only on very steeply peaked waves and only occurs within a very small fraction of the wavelength leeward of the crest.
As a young adult, I spent many hours sailing upon Lake Erie (Ohio, Pennsylvania, New York), Lake Michigan, and Lake Superior. Some of the most memorable of those hours were sailing sailboards (windsurfers) and catamarans in 12 - 16 ft seas off Cleveland Harbor and Erie,PA. Never did the sails backwind as we accelerated and screamed up the wave faces while blasting upwind, launching spectacularly off the lips of the crests and landing on the backs of each wave, attempting to achieve 'major air' in each flight.. In 15-30 knots of wind, our sailboard sails were at most 45 deg to the horizon, our backsides were much of the time just kissing the water. If there was ANY wind reversal, we could not have sailed in this manner or attain the speeds that we were able to achieve. Similarly while sailing hot racing beach cats. Yes, sometimes we had to sheet in a bit while closely approaching the crests, then sheet out quickly just before launching at the crest because our apparent wind would veer forward, but that was due to wind gradient and perhaps minor rotor merely feet leeward of the lip, not wind reversal throughout the wave trough. Our paths would fluctuate throughout the wave period, such that after landing off the lip, we'd sail close hauled nearly straight down the back, fall off the wind just before reaching the trough, and maintain heading on a close reach until just approaching the lip when we would round up into close hauled again and launch.
As for all the small wavelets that are generated within large waves, these would not be building in the same direction as the major waves if there existed a wind-flow reversal within the trough.
Get out onto the ocean and see for yourself. But without actually harnessing the wind and waves and feeling the power, you will not fully understand it.
By Beeza
#398270
First page in the previous post was blank for some reason.

It's already posted in the half-size drawings. It just shows the circulation in the water and the air in the trough, next to it.

The waves in the sketches, to make it easy, were mainly drawn as being close to sine waves, so the "lift" appears to reduce after the mid-point, between the wave trough and crest.

In practice the wave will be more "peaked" so the area of maximum lift will be closer the approaching crest, only reducing just before the crest.

So the "lift" progressively increases as the albatross flies up the wave, the lift rotates 90 degrees and progressively increases (then decreases) as the bird finishes climbing and turns 90-ish degrees, ready to turn another 90-ish degrees in an increasing /decreasing downwind gradient (there is no gradient when it flies across the wind).
Assuming the bird is circling.

With a more peaked wave, there will be a wider area of lift to fly through if it wants to climb out from the surface, near the crest, to avoid breaking waves.
The "lift" will also be slightly stronger towards the end of the climb, behind the wave.
By antialias
#399695
By chance, I stumbled across a section in Flying Conditions (1979 ed.) where Pagen addresses Dynamic Soaring. One interesting bit was that he mentions you can get some of this effect coming out of ground effect on launch, provided that you run fast and pull in for extra speed:

"A hang glider and other aircraft without the good energy retention of a sailplane will probably never be able to sustain flight in this unique fashion. However, a hang glider can make use of dynamic effects occasionally. The most obvious situation occurs on take-off. If a pilot gets a good run and pulls on speed in the dead air close to the ground, he can pay off for extra altitude as he enters the stronger wind away from the hill. This is especially effective where trees surround a site and block the air near takeoff. A pilot using this technique will end up with a bit more. altitude than if he kept the same angle of attack throughout the take-off and climb."

I've done a bit of googling for dynamic soaring and hang gliding and never found anything quite so specific for hang gliding as what I've found in this book.

Scan of the section is here: https://goo.gl/NhkWiP
By aeroexperiments999
#399770
bickford frederick wrote:
Tue Jul 25, 2017 5:52 pm
http://www.dynamic-soaring-for-birds.co.uk

More later..
This website is complete garbage. Ignore it. The author and I have exchanged about 100 emails between mid June and mid July and nothing he said made any sense. For more detail see this discussion on this model-airplane website: http://www.rcgroups.com/forums/showthre ... ring/page1 . I am "aeronaut999" in this discussion. Pay special attention to posts #1, 3, 14, 48, 51, 52, 54, and 55. Especially post #52 https://www.rcgroups.com/forums/showpos ... stcount=52 and post #54 https://www.rcgroups.com/forums/showpos ... stcount=54 . Post #14 pertains to a web page of the British Ornithologist's Union-- in the "comments" section, various people are responding to the author's work-- https://www.bou.org.uk/dynamic-soaring/ -- they all understand that it is without merit. It's a travesty that the author of this website is wasting the time and attention of serious people with this stuff. It's complete pseudoscience, vaporware, nothingness.

Basically what you have here is a man who claims to have 16,000 hours of flying time, who believes that an aircraft naturally tends to gain airspeed and/or altitude simply by turning to face the wind. Unbelievable. And he seems to be completely unable to see the most fundamental flaw in his ideas-- that they violate the principle Galilean Invariance-- i.e. they treat the ground as as special, privileged reference frame. When challenged on this point he'll give strange and nonsensical arguments on why his ideas supposedly don't suffer from this problem. This person and his website are a fascinating case study in psychology but contribute nothing to our understanding of the physics of flight.

If you don't believe it, just try to have an email conversation with him. His contact info is given on his website. You'll soon find out that it all adds up to nothing. At least if you start with a solid understanding of the basic physics of flight. If you think his ideas make sense, you had better reexamine your own understanding of basic physical principles.

Again see the recent discussion on the model-airplane website, as linked above, for much more in the way of specifics. See for example the math error detailed in post #52.

In the discussion on the British Ornithologist's Union webpage linked above, you'll find this quote from Mr. Taylor, the author of the website in question:

"Colin Taylor replies –

"These responses are very disappointing. All of their points are covered in detail in the dynamic-soaring-for-birds website. Anybody reading it will find a reasoned argument supported by mathematical analysis which is derived directly from the principles of conservation of energy and Newton's Laws of motion. Simply stating the contrary does not constitute a valid counter-argument.

"I stand by everything in the blog and the website. I am not making anything up. The mathematics speaks for itself.

"The only thing I am confused about is why people are so keen to cling to the wind-gradient theory which was invented in 1883, before people had any experience of gliding flight."

In other words, this man really and truly believes that he is "fighting the good fight". And he is completely and utterly mistaken. It doesn't take many minutes of looking at his webpage to begin finding error after error. Again see the discussion on the model-airplane website, linked above, for more.

I am not posting from my normal login because I have had some difficulties logging in since the recent website upgrade. My normal login is aeroexperiments. I'll try to get back onto that account soon.

Happy soaring
Sincerely, Steve Seibel
#399771
Re above-- there seems to be some strange problem with the links to individual posts given above. Use to the link the whole thread https://www.rcgroups.com/forums/showthr ... ic-soaring and manually scroll to the specific posts I mentioned. Following links to specific posts may lead you to the wrong posts. I'd delete those links but find I am not allowed to further edit the post at this point.

Steve
#399778
The one interesting thing I did learn from that erroneous website was that people were figuring out some of the principles of albatross dynamic soaring as early as 1883. That's pretty cool. I seem to recall that even Lilienthal with his hands-on experience in gliding and even a bit of soaring had some kind of strange ideas as to what might be going on some cases of soaring bird flight, specifically thermal soaring. (See his book "Birdflight as the basis of aviation")

Steve
#399780
Corrected url's for some specific posts critiquing the erroneous website re albatross dynamic soaring first noted five posts above-- (post #399727 )

posts 1, 3, 14, 48, 51, 52, 54, and 55 here: http://www.rcgroups.com/forums/showthre ... ic-soaring

1-- http://www.rcgroups.com/forums/showpost ... ostcount=1
3-- http://www.rcgroups.com/forums/showpost ... ostcount=3
14-- http://www.rcgroups.com/forums/showpost ... stcount=14
48- http://www.rcgroups.com/forums/showpost ... stcount=48
51-- http://www.rcgroups.com/forums/showpost ... stcount=51
52-- http://www.rcgroups.com/forums/showpost ... stcount=52
54-- http://www.rcgroups.com/forums/showpost ... stcount=54
55-- http://www.rcgroups.com/forums/showpost ... stcount=55

OK, back to your regularly scheduled discussion of ACTUAL dynamic soaring using the wind gradient etc...

Steve
By Beeza
#402522
If flying as described, with a tail down glider is done right, it isn't just a case of being near the top of the pile, the height gains can be a bit more than that.
As an example, with the first school, on one occasion when the glider had climbed as high as it could go and was circling, a light aircraft passed directly underneath, perhaps thirty or forty metres below. The other gliders were grouped just above the lower take off, so the pilot had probably seen the group of gliders but maybe hadn't seen the single one above.
From below it would likely have looked if the two were going to collide, but up there it was clearly at a lower level as it started to come in. No idea if anyone else saw it. It was a rule never to discuss flying, apart from short replies to odd comments.
The glider was around about the height of Courmettes (1250m), the top of the hill overlooking the site, with a very good view inland. An easy enough height to reach from the take off area above Gourdon but harder in my experience, to get that high directly above the lower take off near Bar sur Loup (about 450m?)
The glider was the only one up there, and the only one going in circles. It wasn't a particularly sunny day in March-ish and the thermals were not that strong.
So flying that way, the glider could reach a pretty decent height and it didn't take all day to get there.
There were some pretty reasonable flights with the other school as well. But not too many as it took most of a day to get there.

The tidied up sketches, and photocopied papers from various journals and magazines, I've never found.
Some of the sketched were sent to the SSA in the nineties, but there might have been some "rubbish" in with them. (windmill, figure of eight pattern....the figure of eight was just to avoid the suggestion that the glider had to circle close to the hill. The windmill was something separate)
Padding it out seemed like a good idea at the time. If anyone sketched forty or so pages on how to ride a bicycle, anyone else trying to follow it would probably never be able to ride a bicycle. Nothing was thrown away when redrawn, or rejected completely as an idea, so there was plenty of material for padding.
The only other sketches, (only started never finished) were how a three axis glider might be modified if it could do the same, with the pilot possibly rowing to add a little something, move the centre of gravity and straighten anything that got bent. A bit like rowing a barge with sweeps. The pilot would have been allowed to face forwards.
And with that, there was the idea that when up to speed a swan flies by nodding its head, only the head does not move. It is all done by weights, as they say. (It didn't matter how a swan actually flies, it was just to generate ideas).
The sketches were started, but at the time, only the hang gliding seemed really relevant. There isn't enough to be worth copying now, without redoing them. Just odds and sods.

As a technique it worked.....as far as I was concerned......and as long as the glider ran into a suitable thermal. Which was a bit hit or miss if quality time wasn't spent slope soaring.
Couldn't do anything with my own glider which was way too stable and way too slow, took too long to assemble, had the control bay too far forward, and had too much negative dihedral so you couldn't see what was coming when taking off. If there was no lift, top to bottom from the lower site was five minutes, fifteen minutes from the upper one. The disadvantage of the upper one was having to leave early to avoid the parachutes, before conditions had settled so it was a Galloping Gertie ride over Gourdon, and then it usually had to follow a set route with the sea breeze. A bit disappointing. (Bought it without trying it, due to a hand injury...that's my excuse). Probably need a flabby old glider to make it work now.
Doubt if anyone would still make a 1980's glider, and an old one probably wouldn't take being thrown around.
At that time when the hang point was usually from the keel, the glider was more sensitive to where the load was placed, and to any (sudden) increase in load. The hang point only had to be moved a small amount to allow for different pilot weights. The only double surface gliders we flew with the schools were "almost" single surfaces, only the cross boom was enclosed and there were no lower surface battens.
In my view having the control bar further forward seemed to make it take longer to get the glider to turn steeply. If it was closer to chest level as on an older glider, the feet could be moved over slightly before the main body weight giving an almost instant, on end turn if required. Having the bar forward made it more likely that the body would just twist from the hang point if a sudden turn was attempted. Steep turns took way too much time with my glider.
On the plus side it was very steady in a "normal" turn and on landing seemed to cushion the air nicely without any twitchiness if the air was variable. It also folded into a two metre package, which is really why it was bought.
Never tried one, but it would have been nice to (try) have a Magic 4. Didn't like the look of the new improved versions they were making, so it would have meant looking round for a decent used one, and that would have taken too long. A new one would have also cost a bit more, and money was tight.
By Beeza
#402650
Just to be clear, the steep turns are not forced or exaggerated.
If the pilot is tired, the effort will always be the minimum required to haul an ungainly glider around. He will have little energy left to overdo things.
The turn is just a progressive roll up, ending in a steep bank and fast recovery, to quickly turn the glider away from the hill with the gradient helping, as it makes the glider much lighter in roll.
(Compared to the heavier roll of a tail down glider in straight and level flight).
Whatever maximum angle of bank is reached, it is just momentary. The pilot is not specifically aiming for an "on end" turn, he is just finishing turning by a sharp roll up and instant roll "flat", to be ready to impact the gradient, when the glider will become very heavy in roll. The angle of bank actually reached in the turn, seems to sort itself out.
The glider seems to be bouncing of the side wall of the thermal. That increase in load pulls the bar forward automatically at the point of maximum bank, it's then instantly grabbed in as the glider drops and is rolled flat. The two increases in load come in quick succession and seem to join as the circuit speeds up.
To speed things up the glider (quickly) turns back, to the direction of the hill before it has completely scrubbed off its speed in the climb. The turn is made earlier that it was the first time(s) round.
One comment, often repeated at one school, was that I was "too brutal and too nervous". To which the reply was always "It isn't me, it's the glider".
It was the biggest glider they had so it wasn't worth trying another one, as was sometimes suggested. The reply to that was that I'd prefer to try the same one with the hang point moved. That was probably the limit of any discussion of flying. Apart from "can't you telephone before you turn up?".
And miss out on a grim sense of satisfaction? No I couldn't. I'd paid for my thirty flights and was having them, however annoying the situation was becoming.

Gliders that are sensitive to where the load is placed (or sensitive to varying load) have the holes for the hang point, very close together.
On the school gliders of the time they were about 1/2" to 5/8" apart, with the pilot suspended from the keel. My glider had the hang point on the mast, and only had three holes (for the mast) spread over about 15".
A floating cross boom with enough double surface to enclose it, maybe a 120 degree nose angle, keel pocket, shaped battens, control bar not too far forward, and probably no underside battens, are as advanced as the glider needs to be, to do this. In my view.
Improvements in gliders that came after, probably make the glider too insensitive to do much with, at least at the start.
By Beeza
#402664
Just point out that"Nervous" in French means "quick", not nervous as in problems with nerves.

It's just how a pig of a tail down glider has to be flown sometimes.

If it's heading directly back in to the hill and accelerating not many pilots would take their time doing a nice well coordinated, genteel turn with their little finger in the air. Anyone with a bit of common sense would grab a handful of control bar and point it in the other direction as quickly as possible. More so if the pilot is tired.

Comments like that, went in one ear and out the other. As they should.
By Beeza
#403247
A few of the sketches show leading edge vortices.
Leading edge vortices are widely accepted as being an integral part of some kinds of flapping flight. (For birds as well as insects)
It is hard to find a paper on bird flight that does not mention them.
In delta winged powered aircraft a leading edge vortex gives increased lift, but with a big increase in drag, that requires a big increase in power to overcome.
When Witold Kasper's vortex, on his glider appeared, the aircraft was effectively parachuting. The vortex was not helping it whizz around like a Swift or House Martin.
For a bird like a swift in flapping flight, a leading edge vortex exists very briefly on each flap, increasing lift to raise the wing, and move it back (relative to the body mass) and maybe producing thrust when it is shed.
In gliding flight for the bird, the same vortex arrangement would not last much longer. It would slow the bird in a moment, or allow a quick change of direction, appearing on one or both wings. Vortices would help the wing change direction with sharply increased lift and drag, to lift and slow (or turn) the aircraft/bird with the increase on both wings or turn it/drag it round with more lift(drag) on one side than the other.
The more the sweepback, and/or the steeper the angle of attack of the wing, the easier a leading edge vortex appears. It could start at the point where the wing is at the highest angle of attack, beginning at the trailing edge and move forward like a stall on a sail. That could be moving forward from the wing tip, along the leading edge or appearing at the "nose" of the wing and spreading back along the leading edge.
For a tail down hang glider, (if flying off-centre can really be considered as a model of flapping flight, with the gradient doing most of the flapping), the vortex could also form briefly on either or both wings lifting the nose, if it forms there, or dragging back and lifting either wing as the glider is slammed flat as it impacts the increasing airflow of the gradient. The gradient may prolong the existence of the vortex fractionally, but it will still be short lived. (This is in a slope soaring environment with a thermal coming through. There is some gradient of air flow over the hill, even without the thermal)
If there is an element of side slip one side of the wing will effectively have greater sweepback which may also help formation on that side.
When circling off-centre, the hang glider is hitting the gradient at an angle, not straight on, so a brief vortex may lift and drag on one or both wings. It may be dragged into the "thermal" or dragged/rolled out. That will be in addition to whatever the varying lift from the thermal would be trying to do to the glider in roll (without the leading edge vortex), which ideally is forcefully overruled by the pilot trying to turn in.
It's hard to say what exactly the contribution will be from any brief appearance of a (partial) leading edge vortex on one or both wings, and anyway it will vary from circuit to circuit.
One thing that leading edge vortices may do, is help convince the pilot that he is still in the thermal when he has already climbed out the front of it, and is continuing to climb in slope soaring lift. (Without using a vario, which might give the game away).
(Re: The joke about the thermals going straight up with the circuits inclined, when everyone else did horizontal circuits and their thermals were inclined).
It probably means that apart from the first few circuits in a tight thermal, flying off-centre with a tail down hang glider may not be a very good way of centring in a thermal.
But it could be a very effective way of climbing, inside or outside of the thermal.
It needed more work.
(In or outside the "thermal" the style of flying remains exactly as described.....the pilot behaves as if he was trying to climb in a thermal by feel, with the glider trimmed tail down).
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By Beeza
#403248
Found this yesterday, thought it was of interest.

By Eleanor Lutz an artist.

https://media.giphy.com/media/abjoposej6Kxa/giphy.gif

https://bestgifsdotnet.wordpress.com/20 ... nstructed/


The fruit bat gif shows the wing tips or the bat following the same path as the hang glider, flying the way described. The tips produce most of the thrust.
Bats (some bats?) produce more lift on the upstroke than downstroke. (Maybe. can't find the link).
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