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By Dontsink
#341330
The USAF giving it a try:


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By Flyking
#341397
looks possible but doing wingover close to the ground with a high performance glider is not a good idea :surrender:
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By Flyingseb
#341412
Flyking wrote:looks possible but doing wingover close to the ground with a high performance glider is not a good idea :surrender:
That's the problem. Every year that I grow older (this is the way it is, I know :-) ), this possibility to test it myself slowly escapes my mind.
Maybe a physic genius could calculate if doing it with a Hangglider is doable, considering how much G it can handle, and if is a dive and recovery
are efficient enough to gain some energy in each cycle.

Art of flight brought to ultimate level

Already so much exhilarating with a model slope soarer...but also much too often leading to an abrupt end :mosh: :surrender:

After all, why not simply try with a model hangglider? :goodidea:
By Beeza
#342353
"looks possible but doing wingover close to the ground with a high performance glider is not a good idea"


Perhaps that isn't a requirement?

Maybe the requirement is to circulate in the best combination of gradient and flow (lift?) so there might not really be any need to fly closer to the ground than usual.

There was a description of a fibre glass 3 axis glider in a Reichmann book of an early attempt to dynamic soar over a valley of still air with a horizontal strong wind flowing over the top. Ingo Renner was the pilot in the 1970s. They worked out that not a lot of gradient was required to stay up. (Can't remember which book. Might have been the one published by the SSA)

OK so a hang glider is a completely different animal, but there are similarities, and it might be possible to work round the differences?

Maybe go the whole hog and make a comparison with a 3 axis glider, against a single surface hang glider to emphasize the difference in performance. They are more sensitive anyway IMO.
By Beeza
#342500
A pilot sometimes reports that his glider seems to turn into wind, or that it turns easier into wind.

To show that he could be mistaken, he can be told to think of the glider as was flying in a large "block" of air, within the main mass of moving air.
No matter how the glider moves, or in whatever direction, the overall movement of the block can make no difference to the way the glider flies or "feels" when it turns within that block, whatever impressions the pilot may have. The glider is flying in its own bubble unaffected by the wider movement of the air stream.

In his model aircraft book, Martin Simons likened it to a model flying in a hanger or container in a moving aircraft carrier or ship. Others suggest comparing it to a boat manoeuvring in a river. When the boat turns upstream, the helm feels no different and the boat behaves no differently, from when it turns downstream.

Using those kind of illustrations, logically there can be no difference to the glider if it alters direction, and no change in what the pilot senses when it does.

That logic may be correct for those particular illustrations, but perhaps the examples do not accurately represent the air most glider pilots would choose to fly in, for most of the time.

The examples may be good for calm early morning first flights from the big hill, or flights made to try adjustments to the glider or test new equipment.
They may apply to evening flights, when the air is gently rising everywhere, after a hot day. And they could apply when flying between thermals.

But, if we say that most of the time the average pilot is trying to gain or maintain height, slope soaring or thermalling in less mild conditions, then the air he flies in through choice, would not likely be a large homogenous inert "block", it would more likely to be moving at varying rates within the "block", and in sometimes changing directions.

There then would be gradients in that flow of air, and the inertia of the glider/pilot might cause the glider to react in the roll, yaw or pitch axis as it moves through the air.
Turning upwind/downwind, or up gradient/down gradient will then "feel" noticably different to the pilot, and have some marked effect on the glider, whatever he has been told to the contrary.

To see the relevance of recognising the different effects of turning and climbing or dropping, either upwind or downwind in an appropriate gradient, look at the 1970s Reichmann example of a glider dynamic soaring over a valley, moving between a higher fast moving airstream and the still air below it.
From above the valley in the strong wind, to gain momentum, the pilot Ingo Renner dives down with the wind behind him into the still air, executes a sharp, on end 180 degree turn, then quickly rolls the glider flat and climbs, heading back into the fast oncoming air. Into what he might justifiably see as a "headwind".

So what happens if he next does the exact opposite by diving against the wind, to the still air below, then turns 180 degrees and climbs with an increasing tailwind?
According to the "boat in the river" idea, there should be no difference.

What happens if "flat" climbing from the still air into the "headwind", he comes out of the still air heading at say an angle of 45 to 60 degrees to the headwind, instead of directly into it? Would the pilot "feel" anything pulling at the glider from one side? Might it seem to steer into the "wind"?

If the climb could continue right through the gradient, higher up into uniformly flowing air, would veering a bit left and then right have the same feel to it as when the glider was at a lower level, but still climbing into the gradient? Or would it correspond to the earlier "boat manouevring in the river" or "model aircraft flying in a box" illustrations?
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By Flyingseb
#342573
Beeza wrote: From above the valley in the strong wind, to gain momentum, the pilot Ingo Renner dives down with the wind behind him into the still air, executes
a sharp, on end 180 degree turn, then quickly rolls the glider flat and climbs, heading back into the fast oncoming air. Into what he might justifiably
see as a "headwind".

So what happens if he next does the exact opposite by diving against the wind, to the still air below, then turns 180 degrees and climbs with an
ncreasing tailwind?
According to the "boat in the river" idea, there should be no difference.

What happens if "flat" climbing from the still air into the "headwind", he comes out of the still air heading at say an angle of 45 to 60 degrees to the
headwind, instead of directly into it? Would the pilot "feel" anything pulling at the glider from one side? Might it seem to steer into the "wind"?

If the climb could continue right through the gradient, higher up into uniformly flowing air, would veering a bit left and then right have the same feel
to it as when the glider was at a lower level, but still climbing into the gradient? Or would it correspond to the earlier "boat manouevring in the river"
or "model aircraft flying in a box" illustrations?
Welcome to the org, Beeza :thumbsup:

Interesting stuff.

The reasoning to the first "what if" is clear to me.
So he's flying in a wind layer, above still air. Let's say he's flying at trim, 20 mph, and the wind is the same velocity, 20 mph. Flying directly into the
wind, his ground speed is exactly 0 mph, so is his speed relative to the still air layer. If he enter this layer, then he will fall until the air speed builds
up again to 20 mph, loosing a lot of altitude in the process. Turning 180° will just cause another altitude loss, totally pointless now.

Change the flight direction by 180°, and all of a sudden, the physic work with him.

Now, with an head wind angle of 45°, in relation to your other case, I would say that the telltale effect, due to the nose angle particularly, will tend
to turn the glider into the "new" wind direction, until he loose all his momentum gain in the process. The pilot should feel the glider pulled strongly
to one side.

For the last one I'm not sure to understand your question. I would only say that the "Boat in the river" analogy is not accurate as it doesn't imply that
the water speed differ from the river bank to the middle of the river: gradient as well. The gradient is highly dependent on the river type and
characteristics.
Last edited by Flyingseb on Mon Jan 06, 2014 3:38 pm, edited 1 time in total.
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By danmoser
#342581
Dynamic soaring is regularly exploited by RC sailplane pilots.. I've seen them do this on the North Side of point of the mountain with great success.
They get the sailplane going very fast by climbing upwind into higher wind above the gradient -- which increases airspeed, then diving downwind into the wind gradient -- which also increases airspeed. They get them going around and around.. faster and faster.. hundreds of MPH.. higher & higher g-loads... BTW, they do break a few this way .. but if it doesn't break, they then pull them straight up to trade all that speed for altitude.. sometimes climbing about a thousand feet in a few seconds!!! :shock:

I've seen them do this right underneath me.. it's really quite impressive, and a little scary.

Exploiting dynamic lift of this type is much harder for a human in a hang glider .. we're larger, slower, draggier, and real wusses when it comes to high G-loads near the ground. :rofl:

But there are occasions when HGs can take advantage .. in a less spectacular way.. push away from side gusts.. a fast downwind swoop, turning back into the upwind while climbing... but that involves high ground speed, high Gs, low altitude, high bank angles in high turbulence areas .. an uncomfortable, unsafe combination.
:surrender:
Last edited by danmoser on Mon Jan 06, 2014 11:14 am, edited 1 time in total.
User avatar
By AndRand
#342661
Flyingseb wrote: Interesting stuff. The reasoning to the first "what if" is clear to me.
So he's flying in a wind layer, above still air. Let's say he's flying at trim, 20 mph, and the wind is the same velocity, 20 mph. Flying directly into the
wind, his ground speed is exactly 0 mph, so is his speed relative to the still air layer. If he enter this layer, then he will fall until the air speed builds
up again to 20 mph, loosing a lot of altitude in the process. Turning 180° will just cause another altitude loss, totally pointless .
The idea of DS is to go downwind to enter still air with excess if speed, loose as little in turn and go back in the headwind area.

Point is it is hard to find suitable conditions for HG. Vertical gradient needs vertical trajectory (energy consuming), horizontal gradients (IE. between ridge lift and lee side rotor) are usually too small.
I think one of imaginable trajectory would be not circular but spiral ie along ridge.
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By brian scharp
#342677
AndRand wrote:Point is it is hard to find suitable conditions for HG. Vertical gradient needs vertical trajectory (energy consuming), horizontal gradients (IE. between ridge lift and lee side rotor) are usually too small.
I think one of imaginable trajectory would be not circular but spiral ie along ridge.
Dynamic soaring, lee and windward. :)
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By danmoser
#343118
Speed record now well over 400 mph
These guys are nuts!
At those speeds, it could blow your head off! :shock: :ahh: :surrender:

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By AndRand
#343196
I doubt it can be much useful in hg. Speed envelope is not that big. Maybe ridge racers could see any advantage of going max speed swerving from lift band to still air zone and back along ridge. But it looks like much of dangerous effort with little gain.
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By jjcote
#343210
I've read comments about this many times, and it seems that maybe people are thinking about this wrong, because they have the wrong objective in mind. The concern seems to be that the g-loading is too high, and the speed range would need to be too wide. But don't think of this like the RC guys who are trying for insanely high speeds. What if the question is simply whether it's possible to exploit horizontal wind shear, in the absence of rising air, to simply stay up? You fly downwind in the upper air mass until you hit the shear layer, then do a 180 and fly downwind in the lower air mass, then you push out and zoom, and when you hit that upper air mass again, you've got substantial airspeed that you can trade off for altitude. Not trying for any huge gain, just enough to survive for another go-round as you bide your time waiting for a thermal. I still don't know if it's practical, the devil is in the details, but there is energy available in that horizontal shear, and it might be possible to tap enough of it to stay in the air.
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By AndRand
#343225
IMHO the shear should be really sharp so that glider would gain airspeed using its momentum, otherwise it will not change airspeed, just groundspeed.
Also I wouldn't try 180s as they are energy consuming. I would rather imagine trajectory like with a skateboard with momentum wheel attached to wheels riding on sidewalk and conveyor. Jumping back and forth you can gain speed almost indefinitely ;) because every switch can add speed.

I don't know other such shears than on ridge that are sharp enough for glider not to loose much energy on turns.
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By danmoser
#343226
I've seen Dave Gibson do a bit of dynamic soaring at the South Side .. whether intentional or not.

He leaves the ridge lift, flying fast downwind, descending into the wind gradient at high speed right over the top landing area .. then banks it hard, almost wingtip touching the ground .. then levels it, heading back upwind, pushing out to climb back into the higher speed wind layer above the gradient ..
He typically gets back into the lift band at about the same altitude he left it.
Ya gotta admire the guy .. :thumbsup:
He's got a helluva lot more nerve than me! :lol:
By Beeza
#344391
The previous post suggested that the glider is affected by the prevailing wind when it is flying in a gradient. A pilot may feel changes in that gradient.

If there is no gradient in the local air mass, the glider/pilot will not feel any change of "wind" direction, or of "wind" strength, on the glider, when it is climbing or dropping, or turning in or out of "wind"
A pilot could be justified in thinking about the prevailing wind direction, when flying in a gradient.

In the Reichman example there is a climb in to wind and a drop with a tailwind.
Looking at a pilot slope soaring, trying to get hooked into a small well defined thermal that is passing through. If using his vario, the hanglider pilot ends up perfectly centered in the thermal, there is no gradient, so there is no "feel" from the "prevailing wind".
If he has no vario, he has to rely on feel. He can decide not to fly perfectly centered, but to deliberately fly slightly off center so that there is enough feel to allow him to judge where he is in relation to the thermal core.
On entering directly the glider will pitch up, entering to one side the pilot counters the rising wing, and turns into the thermal, or quickly turns around if there is room, and hopefully enters more directly.
Entering with speed in hand, the pilot climbs away from the hill but turns back as speed is scrubbed off, and before he drops out the far side. If he judges that there is room to complete a 360, he turns back to the hill in a tailwind ready to turn a 180 as soon as he feels a slight drop, or he decides that that is close enough.
The high banked turn is made no closer to the hill than he would normally fly. He is aiming to circuit in the gradient to position himself by "feel", not fly through all the gradient to try dynamic soaring. (Like Renner......Did he fly through all the gradient to stay circuiting over one place on the ground?)
The turn obviously should be made quickly, to avoid dropping out the back of the thermal, or flying into the hill if the pilot has misjudged it.
The pilot anticipating and trying to forestall the drop before the sharp turn, flies back then rolls the glider up and bangs it flat as he turns back into wind. it is one sharp movement .The glider wants to be completely flat before it impacts the gradient going back in, and is pitched up as it flies away from the hill. The control bar has to be pulled in and forcefully restrained while the glider is climbing. It can be eased out only as the pull (against the pilot's efforts) on it, diminishes.

Turning (say) to the right (I always turned the same way....one less decision) when climbing into wind scrubbing off speed, pitched up, with the glider "flat" the glider will tend to yaw into the gradient, into increasing "wind". Towards the end of the climb as the glider slows, the pilot may have to put more effort into resisting the inner wing rising. That will lessen as the pilot reaches the core (or what he thinks is the core).

At the top of the climb the pilot is flying just above minimum sink speed, but with a bit of speed in hand. he then turns back to the hill and repeats the maneuver.
After a circuit roughly mapping out the thermal he can close the pattern up, make it smaller, but each section should have roughly the feel each time round.

Flying out from the hill turning, if the glider does not lift a wing, or lifts with less force he could assume he has moved sideways, too far through the core, so he continues quickly round to the steep banked turn back into "wind". He is aiming to keep a regular, similar lift of the wing each time round. If he is circling to the right, clockwise viewed from above, it will always be the right wing that lifts.
If he has not flown too far back, there will be no pause before the glider impacts the gradient and climbs, after he has rolled it flat. If he flies too far forward the glider drops out of the thermal. Side to side positioning relies on the consistent regular resisting of the inner wing lifting.

It may help if the glider is trimmed slightly tail down in normal flight, so that the bar is always slightly pulled in. but not enough that it stalls. (on the point of wallowing)
The cross bar is better at chest height in normal flight. The modern position is to have it almost under the chin, which does not really help if you have to throw the glider about.
Older gliders had keel pockets instead of a Y shaped bridle in the lower rear rigging. The sail moving over easily in the climb, with a keel pocket, might make things easier.
The ideal to try it, is probably a larger sized single surface glider.
Having the hang point on the keel instead of the mast may also be an advantage. More effort means more feel, more sensitive feedback.
By Beeza
#344392
The previous post suggested that the glider is affected by the prevailing wind when it is flying in a gradient. A pilot may feel changes in that gradient.

If there is no gradient in the local air mass, the glider/pilot will not feel any change of "wind" direction, or of "wind" strength, on the glider, when it is climbing or dropping, or turning in or out of "wind"
A pilot could be justified in thinking about the prevailing wind direction, when flying in a gradient.

In the Reichman example there is a climb in to wind and a drop with a tailwind.
Looking at a pilot slope soaring, trying to get hooked into a small well defined thermal that is passing through. If using his vario, the hanglider pilot ends up perfectly centered in the thermal, there is no gradient, so there is no "feel" from the "prevailing wind".
If he has no vario, he has to rely on feel. He can decide not to fly perfectly centered, but to deliberately fly slightly off center so that there is enough feel to allow him to judge where he is in relation to the thermal core.
On entering directly the glider will pitch up, entering to one side the pilot counters the rising wing, and turns into the thermal, or quickly turns around if there is room, and hopefully enters more directly.
Entering with speed in hand, the pilot climbs away from the hill but turns back as speed is scrubbed off, and before he drops out the far side. If he judges that there is room to complete a 360, he turns back to the hill in a tailwind ready to turn a 180 as soon as he feels a slight drop, or he decides that that is close enough.
The high banked turn is made no closer to the hill than he would normally fly. He is aiming to circuit in the gradient to position himself by "feel", not fly through all the gradient to try dynamic soaring. (Like Renner......Did he fly through all the gradient to stay circuiting over one place on the ground?)
The turn obviously should be made quickly, to avoid dropping out the back of the thermal, or flying into the hill if the pilot has misjudged it.
The pilot anticipating and trying to forestall the drop before the sharp turn, flies back then rolls the glider up and bangs it flat as he turns back into wind. it is one sharp movement .The glider wants to be completely flat before it impacts the gradient going back in, and is pitched up as it flies away from the hill. The control bar has to be pulled in and forcefully restrained while the glider is climbing. It can be eased out only as the pull (against the pilot's efforts) on it, diminishes.

Turning (say) to the right (I always turned the same way....one less decision) when climbing into wind scrubbing off speed, pitched up, with the glider "flat" the glider will tend to yaw into the gradient, into increasing "wind". Towards the end of the climb as the glider slows, the pilot may have to put more effort into resisting the inner wing rising. That will lessen as the pilot reaches the core (or what he thinks is the core).

At the top of the climb the pilot is flying just above minimum sink speed, but with a bit of speed in hand. he then turns back to the hill and repeats the maneuver.
After a circuit roughly mapping out the thermal he can close the pattern up, make it smaller, but each section should have roughly the feel each time round.

Flying out from the hill turning, if the glider does not lift a wing, or lifts with less force he could assume he has moved sideways, too far through the core, so he continues quickly round to the steep banked turn back into "wind". He is aiming to keep a regular, similar lift of the wing each time round. If he is circling to the right, clockwise viewed from above, it will always be the right wing that lifts.
If he has not flown too far back, there will be no pause before the glider impacts the gradient and climbs, after he has rolled it flat. If he flies too far forward the glider drops out of the thermal. Side to side positioning relies on the consistent regular resisting of the inner wing lifting.

It may help if the glider is trimmed slightly tail down in normal flight, so that the bar is always slightly pulled in. but not enough that it stalls. (on the point of wallowing)
The cross bar is better at chest height in normal flight. The modern position is to have it almost under the chin, which does not really help if you have to throw the glider about.
Older gliders had keel pockets instead of a Y shaped bridle in the lower rear rigging. The sail moving over easily in the climb, with a keel pocket, might make things easier.
The ideal to try it, is probably a larger sized single surface glider.
Having the hang point on the keel instead of the mast may also be an advantage. More effort means more feel, more sensitive feedback.
By Beeza
#344911
A hang glider will pitch up when the wing loading is increased suddenly.
The increase in load can be a from sudden increase in lift, a gust, or the glider rapidly changing direction.
An increase in lift is more immediately noticed than a drop in lift. In sink it can be several moments before the pilot realizes he is going down (flying without a vario)
Moving into increasing lift the harness is immediately squeezed in and the control bar tries to pull forward. Circling off-center in the thermal with periodically changing lift gives a regular, repeated pull upwards on the harness. It could be used as an aid to judge position in the thermal.

Continuing on from the last post, let's say the circuit flown is pear shaped, viewed from above. The narrow radius is nearer the hill, the climb is flatter than the return, and the wider "base" part of the pear is where the glider flies across the "wind" before returning.
The radius represents the angle of bank of the glider, not the actual path flown, which to an observer viewing from above may be more circular or elliptical.
Imagine a line drawn out from the hill side. With the pilot always turning right, trying to center in what he thinks is the thermal, the area to the left of the center line where the glider flies away from the hill, is the upwind leg.
To the right is the downwind leg, where the pilot flies back towards the hill. (This can be compared directly to the Renner/Reichmann demonstration of dynamic soaring).

The pilot has done one circuit, has turned and rolled the glider flat and is starting to head away from the hill again with a good excess of speed.
On entering the thermal (if it is still there), the glider will pitch up as it impacts the gust, the gradient of increasing airflow. The pilot keeps the bar firmly pulled in until the pressure from the control bar pulling against him eases.
The glider may still be pitched up even while the pilot is still grimly holding the control bar in during the climb.
If the climb is very steep both glider and pilot are pitched up, with the bar firmly held in. At the top of the climb if the pilot has scrubbed off of all the excess speed, the nose of the glider drops by itself, and the bar returns to its normal position (just held in, if it is trimmed tail down).
In a "stick thermal"with no gradient, the pilot pulls speed then eases the bar out and pushes it forward slightly to get the glider to climb. Flying in the described gradient, there is no need to push the bar out to climb. So it is not a stick thermal, or a stick thermal imposed on a gradient. The bar is only eased out as the climb slackens.

Just before the climb, the drop from the sharp bank has been suddenly arrested by the pilot banging the glider flat, causing an increase in load, so the glider pitches up. The bar is held in.
Just before that, when the pilot threw the glider up into a steep bank the load increased, causing the glider to pitch up in the turn. Only "up" is more towards the center of the turn. He may have the impression of bouncing of the wall of the thermal if he is flying with speed in hand. The pull on the bar may momentarily ease before the glider goes "flat".
The three load increases follow on from each other and effectively run almost continuously, but the impact from the thermal (if it is still there) is usually the most marked.
So fly back in a tail wind, start to bank, rapidly roll up, bounce, bang flat, hit the thermal, and climb steeply up into the prevailing wind.
The final roll up and roll flat must be one movement.
The maximum bank will be before the apex of the turn (assuming an elliptical pattern), the roll flat will be completed just after the apex, before the glider has turned completely outwards to face the wind.

This is for a small well defined thermal that might be found when a pilot is trying to go from slope soaring to circling in a thermal. The first circuit maps out the thermal roughly, the pattern then closes up, and becomes smaller as the moves become regular and repeated with less hesitation, (possibly becoming more circular). If successful, as the glider climbs, the pattern opens right up again till the pilot can climb no higher. He can maintain height by swooping round in circles, but if he faces into wind like everyone else the glider fairly quickly drops down again.

The pilot is not trying to dynamic soar, he is trying to roughly center in a thermal (real or imagined) without a vario, using the regular repeated change of feel from flying off center. When successful he anticipate what is (should be) coming next (in the sequence)and make adjustments (and adjust) , helped by flying with speed in hand, to keep up the steady rhythm.

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