Dynamic Soaring of Air masses Video

[silverdollar1]

http://www.icarusengineering.com/Dynamic-Soaring-and-SE.htm



I am trying to validate dynamic soaring versus normal thermal soaring, but both are using thermals as the power source. Dynamic soaring would mean using 2 types of air masses. One in the thermal and the second one is the inflow to the thermal.

 

[rcgldr]

The youtube video seems like conventional rc glider flight in an updraft, in this case a fairly large thermal.

Link to video of what was at the time a record 468 mph achieved by dynamic soaring with an rc model glider. It's hard to see the model, but in the last part of the video, the guy with the helmet cam flies the same model so you can see the model better in that part (his last pass is clocked at 405 mph) at 4:00 into the video.

http://www.youtube.com/watch?v=rfoxjNg-eg0&hd=1

A.T. made an animated version that shows what's going on:



Anther link about dynamic soaring:

http://www.rc-airplane-world.com/dynamic-soaring.html

An older video, 392 mph record at the time, but it's much easier to follow the model:

http://www.youtube.com/watch?v=WaQB16ZaNI4&hd=1

I've read that albatrosses generally make use of the updraft of wind off waves, called ridge lift, in addition to some dynamic soaring using the difference in wind speed close to the surface of the water and somewhat above it. It wasn't clear to me if an albatross can go long distances over relatively smooth water using just dynamic soaring.

 

[A.T.]

I am trying to validate dynamic soaring versus normal thermal soaring, but both are using thermals as the power source. Dynamic soaring would mean using 2 types of air masses. One in the thermal and the second one is the inflow to the thermal.

Thermal soaring : Gaining potential energy from the upwards movement of air.
Dynamic soaring : Gaining kinetic energy from the velocity difference between 2 air masses.

Two differences of dynamic soaring compared thermal soaring:
- Dynamic soaring is possible without any vertical air movement.
- If dynamic soaring does use vertical air movement, it can work without any upwards air movement. Just still air and some downdrafts are enough to stay in the air continuously.

 

[A.T.]

It wasn't clear to me if an albatross can go long distances over relatively smooth water using just dynamic soaring.

Potentially they can stay airborne, using only the wind gradient:
http://esoaring.com/albatros_presentation_esa.pdf In real life they might be using some ridge lift while gliding low, between the dynamic soaring turns at height:

https://www.youtube.com/watch?v=buuxFP--Ezo

 

[silverdollar1]

Rcglr you don't understand what I mean.

 

[rcgldr]

Dynamic soaring would mean using 2 types of air masses. One in the thermal and the second one is the inflow to the thermal

I'm thinking that the shear boundary layer between the inflow and updraft of a thermal is too large and the differential in air mass speed too small to be useful for dynamic soaring in the conventional sense.

 

[A.T.]

Rcglr you don't understand what I mean.

I'm not sure what you are asking either. Do you want to make sure that it is pure DS, without any TS? Then you would have to use the outer area of the thermal inflow, where the flow is purely horizontal. But this is of course far too idealized to be put in practice, even if you could see how the air moves exactly, which you can't.

Theoretically you could use the inflow area above a downdraft, where you have only horizontal and downwards air movement, so TS is impossible. But practically this seems even more difficult.

From: http://www.icarusengineering.com/Dynamic-Soaring-and-SE.htm

 

[A.T.]

Dynamic soaring would mean using 2 types of air masses. One in the thermal and the second one is the inflow to the thermal.

That's not quite the idea behind the smooth DS that you linked. In fact it uses only the inflow to the thermal. Keep in mind that the air on opposite sides of the inflow is moving in opposite directions horizontally, so you allready have the velocity difference that you need for DS. You don't fly into the center of the thermal, just circle around it, and use the horizontal velocity difference.

 

[silverdollar1]

Someone lied to me. Dynamic just means not static. It has nothing to do with the arena of having 2 of anything.

rcgldr did you only watch the first 10 seconds of the video?

 

[rcgldr]

rcgldr did you only watch the first 10 seconds of the video?

Yes, and I also went to his youtube page. I'm not sure what his point is, other than he's getting some negative comments. If a thermal is strong enough then you can do aerobatics. The model starts off so high in the video that even if it lost 100 feet in altitude doing maneuvers it would be difficult to tell.

There's a local slope site I fly at and you can do something similar. At the slope you have an updraft, and at some point above the ridge line the wind is mostly horizontal. This allows a pump manuever where the model is flown upwards above the updraft, then flown downwards back into the updraft, and back up again. This can be done with stall (rudder only) turns, continuous cuban 8 pattern (s turn), or even just a large loop. The common factor is that the model dives downwards towards the updraft, and does a partial loop back upwards while in the updraft.

One aspect of dynamic soaring that hasnt been well covered in this thread and some of the links is the fact that a glider crossing a shear boundary into a relative headwind doesn't increase it's energy relative to the ground. The glider is being flown in a loop like pattern, so that after crossing the shear boundary, there's an increase in lift which is a centripetal force as the glider pitches relatively "upwards" in the loop like maneuver. Since the glider continues the loop pattern, what is a centripetal force at one moment in time translates into increased forward speed at a later moment in time. In some of the dynamic soaring videos, you can see the wing flexing when the models cross the shear boundary.

 

[A.T.]

Dynamic just means not static. It has nothing to do with the arena of having 2 of anything.

"Dynamic" is a very general word. "Dynamic soaring" requires a velocity difference between two air masses.

One aspect of dynamic soaring that hasnt been well covered in this thread and some of the links is the fact that a glider crossing a shear boundary into a relative headwind doesn't increase it's energy relative to the ground.

That is true. The kinetic energy relative to the ground is increased when it makes a downwind turn within an airmass that moves relative to the ground. It accelerates the air in the opposite direction, slowing it down relative to the ground, and thuse extrating energy from the true wind. But to do this continuously you need a second airmass with a different velocity, so the energy gain is not reversed again when you turn in the opposite direction.

 

[CWatters]

What he said.

 

[silverdollar1]

This isn't a slope (confined/contained/limited). So flying in only one air mass would be impossible. Flying aerobatics which makes flying even wider than small circling would make dynamic soaring take place by default. Looks like I answered my own question.

 

[rcgldr]

This isn't a slope (confined/contained/limited) and all bagged up like a specimen. So trying to prove only one air mass extends beyond the area is something you can never do.

I don't understand your point here. I already mentioned there are two air masses at a slope site, an updraft along the slope, and a horizontal wind once sufficiently above the ridge line of the slope.

At higher altitude, such as shown in the video, there probably isn't much inflow into the thermal other than shear effect. So the two air masses are the upflow at the core and somewhat stationary air surrouding the flow. So a model could dive into the thermal from outside the thermal, then do a partial upwards loop while in the thermal. The point of my previous post is that the model needs to enter somewhat downwards, then turn (partial loop) upwards in the direction of the air mass in the thermal, to gain energy from the thermal. In this case, the model is able to achieve higher speed by maintaining average altitude instead of using the thermal's energy to increase altitude.

 

[silverdollar1]

I don't understand your point here. I already mentioned there are two air masses at a slope site, an updraft along the slope, and a horizontal wind once sufficiently above the ridge line of the slope.

At higher altitude, such as shown in the video, there probably isn't much inflow into the thermal other than shear effect. So the two air masses are the upflow at the core and somewhat stationary air surrouding the flow. So a model could dive into the thermal from outside the thermal, then do a partial upwards loop while in the thermal. The point of my previous post is that the model needs to enter somewhat downwards, then turn (partial loop) upwards in the direction of the air mass in the thermal, to gain energy from the thermal. In this case, the model is able to achieve higher speed by maintaining average altitude instead of using the thermal's energy to increase altitude.

My point is that some have said that pumping is possible within lift and its just one air mass.

Is that true? Do you really need the horizontal wind when pumping on a slope? Think of a skydivers vertical wind tunnel. They can open and close their suits and get higher and lower so...same?

 

[rcgldr]

My point is that some have said that pumping is possible within lift and its just one air mass. Is that true?

Yes it is possible. The model does not need to be flown above the updraft when doing aerobatic maneuvers. It would be similar to a model doing aerobatic maneuvers while descending in a no wind, no updraft condition (for example a model that has a motor only used for short bursts to gain altitude). This is why it's not clear to me what is going on in the first video mentioned in this thread.

 

[silverdollar1]

Yes it is possible. The model does not need to be flown above the updraft when doing aerobatic maneuvers. It would be similar to a model doing aerobatic maneuvers while descending in a no wind, no updraft condition (for example a model that has a motor only used for short bursts to gain altitude). This is why it's not clear to me what is going on in the first video mentioned in this thread.

Well youll have to get out your slide ruler and do some math. What does physics say would be the greater vertical boost- falling thru the lift and pulling up in lift, or falling thru still or slightly sinking air just before entering and pulling up in soaring lift. l meant soaring lift in each case.

And if you are doing aerobatics in just an updraft alone what is the term for it in physics?

 

[rcgldr]

What does physics say would be the greater vertical boost.

If the model is just circled around a horizontal plane at minimal sink speed, then altitude is gained at the quickest rate as long as the model in in the updraft. A model can continue to climb as long as it is in an updraft, but a model can only go some finite distance above the updraft shear boundary in the two mass case.

The main difference in the two air mass case for a slope site is that the model is descending in a horizontal wind during a dive, so less vertical component of aerodynamic force opposing the descent, allowing a bit more vertical speed when it reaches the shear boundary. Assume a model is flown horizontally in the updraft just below the shear boundary, it reaches some maximum speed, and is then flown upwards above the updraft, reaching some maximum altitude. The question is if the model is now flown downwards back into the updraft and then pulled upwards again, will it achieve an even higher alititude, and I'm not sure if it will. I would assume that the size of the shear boundary, speed of the updraft, and the efficiency of the model would be factors. If the slope and the induced upwash are not wide enough for the model to achieve it's maximum speed in a horiztonal glide, then the pump maneuver should allow more maximum altitude.

Trying to apply math to this problem, note that the lift is related to speed² while the duration of time spent doing a partial loop upwards in the updraft is related to some constant / speed. This means the impulse (force x time) should increase with increased velocity from the dive, resulting in more momentum change, the updraft decelerated more and the glider accelerated more.

In the case of extreme dynamic soaring like 468 mph, I think the models are achieving speeds greater than their terminal velocity would be in a straight dive.

And if you are doing aerobatics in just an updraft ... term?

I'm not aware of a special term for this, so I assume it's just aerobatics done in updraft.

 

[silverdollar1]

41burhan has just replied to a thread you have subscribed to entitled - Dynamic Soaring
of Air masses Video - in the Classical Physics forum of Physics ForumsNew reply?

I talked to Taras K on the phone. He said since all thermals are bumpy that some dynamic soaring takes place within any thermal with high G vectors.

He also taught me that its not possible to gain the speed and height without the extra energy from ds in my videos without going out of the thermal and re entering.

Turns out its been done for the last 35 years in full scale gliders...

 

[A.T.]

Turns out its been done for the last 35 years in full scale gliders.

If you pull the stick back, when entering the updraft, and push it forward on exit, you are definitively doing it.

But even if you do nothing and cross the shear layers perpendicularly, the plane will "bounce" between the air-masses, and reduce their velocity difference. So there is a certain DS component.

 

[A.T.]

Here is a video of a vulture soaring above a wind turbine (and getting hit by the blade):

https://www.youtube.com/watch?v=na6HxKQQsAM

My question is: Is just a coincidence that it chooses the soar there? Is it because the turbine is build on a hill, the creates updrafts (slope soaring). Or is it maybe also doing some dynamic soaring, between the wake of the turbine and the free stream?

 

[A.T.]

It wasn't clear to me if an albatross can go long distances over relatively smooth water using just dynamic soaring.

There is a new paper, where they (apparently for the first time) tracked an albatross with GPS, and examined the energy extraction:
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041449

 

[A.T.]

Here is another one on potential UAV usage: "Dynamic Soaring in Hurricanes"
http://vader.cse.lehigh.edu/publications/icuas2012_gre_mon.pdf

 

[A.T.]

I've read that albatrosses generally make use of the updraft of wind off waves, called ridge lift,

Could it be that flying fish use that, to glide up to 200m far at low altitude?

https://www.youtube.com/watch?v=9uFjmeWnFZ4

In the second video it seems, they occasionally dip the tail into the water and accelerate by wiggling it. They glide very low, so it could be ground effect too.

https://www.youtube.com/watch?v=OmWRCdUw17E