The Windward Turn Theory
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Aren't albatrosses effectively doing wave soaring
I wouldn't have thought so. The surface irregularities associated with the (comparatively) minor ocean wave profile would be unlikely to produce much perturbation in the wind trajectories.
However, even if you have an absolutely smooth surface for miles and miles around, there will be a near surface wind profile similar to the boundary layer near the surface of an aircraft in flight.
The typical atmospheric boundary layer model is the one-seventh relationship, commonly used in certification and FT work.
There are a few threads speaking to this topic .. for instance, a typical example was looking at speed additives.
Your albatross might be gliding downwind toward the ocean's surface, then wheeling around into wind and climbing into the shear to gain some energy, then wheeling around downwind and so on .. ? The penalty for the bird, of course, is that the gross flightpath inevitably is downwind.
For the ridge/wave soaring folk, one can remain more or less in the same area or, indeed, near motionless ..
I wouldn't have thought so. The surface irregularities associated with the (comparatively) minor ocean wave profile would be unlikely to produce much perturbation in the wind trajectories.
However, even if you have an absolutely smooth surface for miles and miles around, there will be a near surface wind profile similar to the boundary layer near the surface of an aircraft in flight.
The typical atmospheric boundary layer model is the one-seventh relationship, commonly used in certification and FT work.
There are a few threads speaking to this topic .. for instance, a typical example was looking at speed additives.
Your albatross might be gliding downwind toward the ocean's surface, then wheeling around into wind and climbing into the shear to gain some energy, then wheeling around downwind and so on .. ? The penalty for the bird, of course, is that the gross flightpath inevitably is downwind.
For the ridge/wave soaring folk, one can remain more or less in the same area or, indeed, near motionless ..
Vessbot, Perhaps the rudder was out and the slip indicator was wrong. 
Flew half my first B744 sim session without the slip indicator. Finally asked if it had one and instructor pointed to tiny white rectangle
Flew half my first B744 sim session without the slip indicator. Finally asked if it had one and instructor pointed to tiny white rectangle
Aren't albatrosses effectively doing wave soaring
I wouldn't have thought so. The surface irregularities associated with the (comparatively) minor ocean wave profile would be unlikely to produce much perturbation in the wind trajectories.
However, even if you have an absolutely smooth surface for miles and miles around, there will be a near surface wind profile similar to the boundary layer near the surface of an aircraft in flight.
The typical atmospheric boundary layer model is the one-seventh relationship, commonly used in certification and FT work.
There are a few threads speaking to this topic .. for instance, a typical example was looking at speed additives.
Your albatross might be gliding downwind toward the ocean's surface, then wheeling around into wind and climbing into the shear to gain some energy, then wheeling around downwind and so on .. ? The penalty for the bird, of course, is that the gross flightpath inevitably is downwind.
For the ridge/wave soaring folk, one can remain more or less in the same area or, indeed, near motionless ..
I wouldn't have thought so. The surface irregularities associated with the (comparatively) minor ocean wave profile would be unlikely to produce much perturbation in the wind trajectories.
However, even if you have an absolutely smooth surface for miles and miles around, there will be a near surface wind profile similar to the boundary layer near the surface of an aircraft in flight.
The typical atmospheric boundary layer model is the one-seventh relationship, commonly used in certification and FT work.
There are a few threads speaking to this topic .. for instance, a typical example was looking at speed additives.
Your albatross might be gliding downwind toward the ocean's surface, then wheeling around into wind and climbing into the shear to gain some energy, then wheeling around downwind and so on .. ? The penalty for the bird, of course, is that the gross flightpath inevitably is downwind.
For the ridge/wave soaring folk, one can remain more or less in the same area or, indeed, near motionless ..
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Albatrosses
Albatrosses stay fairly close to the ocean surface. Speaking as a sailor, I can assure you that what the wind is doing at the top of a 20m (60 ft) mast is often very different from what it is doing at deck level. With wave heights on the open ocean being 5m and up (they don't usually feel so big because they are not steep) it wouldn't surprise me a bit to have a lot of vertical movement of air in the space from sea level to, say, 20 or 30 meters up.
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Albatrosses and the like may be able to gain advantage by exploiting wind gradients and/or air deflected upward by waves. I wouldn't dispute that for a moment.
I am however, fairly confident that they cannot achieve a net energy gain relative to their basic gliding efficiency by turning within a homogeneous body of moving air. As nearly as I can tell, this is what it being claimed by the article linked in the first post.
I am however, fairly confident that they cannot achieve a net energy gain relative to their basic gliding efficiency by turning within a homogeneous body of moving air. As nearly as I can tell, this is what it being claimed by the article linked in the first post.
That is what is being claimed and you are right it isn't possible.
Albatrosses and the like may be able to gain advantage by exploiting wind gradients and/or air deflected upward by waves. I wouldn't dispute that for a moment.
I am however, fairly confident that they cannot achieve a net energy gain relative to their basic gliding efficiency by turning within a homogeneous body of moving air. As nearly as I can tell, this is what it being claimed by the article linked in the first post.
I am however, fairly confident that they cannot achieve a net energy gain relative to their basic gliding efficiency by turning within a homogeneous body of moving air. As nearly as I can tell, this is what it being claimed by the article linked in the first post.
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I believe it's been shown that Albatrosses can dynamically soar and make progress UP wind.
Such shouldn't be too difficult in suitable conditions with a reasonably strong gradient. A bit similar to tacking in sailing vessels .. but, probably, not an effective way to make progress ? Then, again, I guess that the bird has plenty of time on its hands, so long as the necessary fish for eating keep coming along ..
it wouldn't surprise me a bit to have a lot of vertical movement of air in the space from sea level to, say, 20 or 30 meters up.
Plenty of evidence to support that thought. However, I suspect that the bird will be doing better from the more predictable gradient profile than the more random turbulent mixing ?
Such shouldn't be too difficult in suitable conditions with a reasonably strong gradient. A bit similar to tacking in sailing vessels .. but, probably, not an effective way to make progress ? Then, again, I guess that the bird has plenty of time on its hands, so long as the necessary fish for eating keep coming along ..
it wouldn't surprise me a bit to have a lot of vertical movement of air in the space from sea level to, say, 20 or 30 meters up.
Plenty of evidence to support that thought. However, I suspect that the bird will be doing better from the more predictable gradient profile than the more random turbulent mixing ?
One study on how they do it.
https://publish.wm.edu/cgi/viewconte...ontext=reports
Spent hour upon hour watching these birds from the ships helideck, failing that, going to the bow and passing the time watching dolphins. Never ever observed the birds attempt to get airborne on no wind days, they'd just paddle out of your way. Only times ever saw them above sea level was heading offshore (flying) and a bird was soaring along in a dry front at 1,500 feet (Golden Beach JT), the other was popping out of a cloud at 500 feet to be confronted by a bird. I assume he was soaring in some localised disturbance that wasn't obvious to us.
https://publish.wm.edu/cgi/viewconte...ontext=reports
Spent hour upon hour watching these birds from the ships helideck, failing that, going to the bow and passing the time watching dolphins. Never ever observed the birds attempt to get airborne on no wind days, they'd just paddle out of your way. Only times ever saw them above sea level was heading offshore (flying) and a bird was soaring along in a dry front at 1,500 feet (Golden Beach JT), the other was popping out of a cloud at 500 feet to be confronted by a bird. I assume he was soaring in some localised disturbance that wasn't obvious to us.
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Did a bit of net trolling to see what papers might come to light.
The following story sounds to be reasonably persuasive to me and, probably, is a useful read in conjunction with Megan's link. Don't fuss too much with the mathematics .. that's just there to confuse those who haven't been mathematically anointed with this and that.
To my simple, dumb, engineer's mind, but with a pilot's overlay .. it is a matter of playing cyclically and skilfully with overshoot and undershoot shear within the surface boundary layer. A bit of skill (which the albatross has from however long its genetic lineage might be) and one can run downwind, tack across and into wind according to one's penchant at the time.
Megan, being a flingwing player of very considerable maritime experience would be expected to have a pretty intimate appreciation of what the bird folks might be doing out there over the water ... I note that his link is to an old paper .. which I will contemplate over coffee this evening for interest.
the other was popping out of a cloud at 500 feet to be confronted by a bird.
The occasional benefits of VFR become more evident .. last time I had such an experience was in a glider tug (45 or so years ago) on descent (sort of maintaining VMC, I guess) .. don't you just love gliders skimming along at the cloud base ? How we didn't kill our collective selves as young idiots often causes me no end of wonderment ..
The following story sounds to be reasonably persuasive to me and, probably, is a useful read in conjunction with Megan's link. Don't fuss too much with the mathematics .. that's just there to confuse those who haven't been mathematically anointed with this and that.
To my simple, dumb, engineer's mind, but with a pilot's overlay .. it is a matter of playing cyclically and skilfully with overshoot and undershoot shear within the surface boundary layer. A bit of skill (which the albatross has from however long its genetic lineage might be) and one can run downwind, tack across and into wind according to one's penchant at the time.
Megan, being a flingwing player of very considerable maritime experience would be expected to have a pretty intimate appreciation of what the bird folks might be doing out there over the water ... I note that his link is to an old paper .. which I will contemplate over coffee this evening for interest.
the other was popping out of a cloud at 500 feet to be confronted by a bird.
The occasional benefits of VFR become more evident .. last time I had such an experience was in a glider tug (45 or so years ago) on descent (sort of maintaining VMC, I guess) .. don't you just love gliders skimming along at the cloud base ? How we didn't kill our collective selves as young idiots often causes me no end of wonderment ..
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I can't decide if the appropriate comment is, "that's bold, not old" or "Canvas airships and iron pilots."
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Similar, but with an important distinction: in either case you need an inertial frame of reference that is decoupled from the moving air. A sailboat achieves this by sticking a big fin (keel or centerboard) into the water; conceivably an albatross achieves this via physical inertia while transiting the transition between layers of air that are moving in different directions relative to each other.
Ultimately their aint no free lunch, though. unless you continue to see a sharp gradient between wind velocity vectors across a very short distance, you're out of harvestable energy. I'll bet (being way to lazy to figure this out) that the albatross is fully at one with the "new" wind by the time it is 50 meters or so into it, and has run out of inertia imparted by the "old" wind by then.
All this aside, let's pause for a moment to contemplate how spectacularly beautiful the albatross is, eh?
Ultimately their aint no free lunch, though. unless you continue to see a sharp gradient between wind velocity vectors across a very short distance, you're out of harvestable energy. I'll bet (being way to lazy to figure this out) that the albatross is fully at one with the "new" wind by the time it is 50 meters or so into it, and has run out of inertia imparted by the "old" wind by then.
All this aside, let's pause for a moment to contemplate how spectacularly beautiful the albatross is, eh?
Yes I heard about the 'spin out of the cloud method" from the autobiography of an airmail pilot...back then way before 14CFR 91.3 the Post Office decided when you can fly but that all changed with the Avigation Act of 1926
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Just want to start with, I'm not a pilot, just an average joe with an engineering background so I welcome any criticisms and explaining you feel like (theres no hard feelings on the internet right). I've been reading a lot about downwind turn myth stuff and just wanted to put out how i see it and see if ive got it right. Also want to pre-empt; im not including drag forces and other stuff thats relevant for real world applications here, this is just about clearing up the concepts that have been thrown around.
- I dont agree with the author of the OP link,
- there is no change in the magnitude ground speed of the aircraft when you turn into/out of wind (assuming no motor, no drag, no friction, ignoring increase in speed due to gravity or conversion of gravitational potential energy into KE); I think the big problem is that people forget about a direction change does not equal change in magnitude.
- upon changing headwind/tailwind you will change your "true airspeed" (as far as i know true airspeed is defined as velocity of airmass relative to the aircraft).
- DS relies on wind shear gradient,
- all DS flight patterns revolve around climbing in headwind and descending in tailwind
Ok so here im sort of guessing;
DS takes advantage of
- flying into headwind which assists in generating lift due to higher true airspeed flowing over the wings (assume you turn before you stall)
- flying into tailwind does impart a little kinetic energy to the aircraft (might be one of these or a combination or maybe something else)
- lower true airspeed results in less drag forces so you get higher efficiency in converting potential gravitational energy into KE
- I assume that as the heading of the aircraft changes (during the turn) some portion of the headwind is being used as a propulsive force and not a lift gaining force (AoA and
pitch/yaw will make this relative but you get the idea).
Its the relatively high frequency of loops over short 'straight legs' which allows to DS work in the real world as 'straight' legs dont net you any increase in energy while drag will still occur. Said another way is; its the turns which could theoretically(?) add energy coupled with the wind gradient which allows for more efficient energy conversion between height and momentum which DS operates on. Side note; unless there is negative true airspeed (from trailing edge to leading edge) there can be no propulsive force exerted by the wind and lets just ignore this scenario.
By all means let me know if I've used jargon incorrectly, forgot something or theres a flaw in my logic. I'm just here to learn from people more knowledge and experience than me.
Cheers guys
- I dont agree with the author of the OP link,
- there is no change in the magnitude ground speed of the aircraft when you turn into/out of wind (assuming no motor, no drag, no friction, ignoring increase in speed due to gravity or conversion of gravitational potential energy into KE); I think the big problem is that people forget about a direction change does not equal change in magnitude.
- upon changing headwind/tailwind you will change your "true airspeed" (as far as i know true airspeed is defined as velocity of airmass relative to the aircraft).
- DS relies on wind shear gradient,
- all DS flight patterns revolve around climbing in headwind and descending in tailwind
Ok so here im sort of guessing;
DS takes advantage of
- flying into headwind which assists in generating lift due to higher true airspeed flowing over the wings (assume you turn before you stall)
- flying into tailwind does impart a little kinetic energy to the aircraft (might be one of these or a combination or maybe something else)
- lower true airspeed results in less drag forces so you get higher efficiency in converting potential gravitational energy into KE
- I assume that as the heading of the aircraft changes (during the turn) some portion of the headwind is being used as a propulsive force and not a lift gaining force (AoA and
pitch/yaw will make this relative but you get the idea).
Its the relatively high frequency of loops over short 'straight legs' which allows to DS work in the real world as 'straight' legs dont net you any increase in energy while drag will still occur. Said another way is; its the turns which could theoretically(?) add energy coupled with the wind gradient which allows for more efficient energy conversion between height and momentum which DS operates on. Side note; unless there is negative true airspeed (from trailing edge to leading edge) there can be no propulsive force exerted by the wind and lets just ignore this scenario.
By all means let me know if I've used jargon incorrectly, forgot something or theres a flaw in my logic. I'm just here to learn from people more knowledge and experience than me.
Cheers guys
- there is no change in the magnitude ground speed of the aircraft when you turn into/out of wind (assuming no motor, no drag, no friction, ignoring increase in speed due to gravity or conversion of gravitational potential energy into KE); I think the big problem is that people forget about a direction change does not equal change in magnitude.
- upon changing headwind/tailwind you will change your "true airspeed" (as far as i know true airspeed is defined as velocity of airmass relative to the aircraft).
- upon changing headwind/tailwind you will change your "true airspeed" (as far as i know true airspeed is defined as velocity of airmass relative to the aircraft).
Supposing you fly an ordinary powered aircraft at altitude in a constant 30 degree banked turn, in a constant airmass. You don’t know what the wind velocity is, and don’t care. The aircraft will go round and round in circles. The indicated airspeed (and true airspeed) won’t change at all. The magnitude of the groundspeed will be constantly changing, as long as the wind velocity is greater than zero. The position of your orbits will be moving across the ground due to the wind, but the aircraft doesn’t know this.
Most pilots would agree with all the above, yet a few of those same pilots (some with 20000+ hrs) still believe that their indicated airspeed will increase as they turn onto final into a strong wind. I’m not sure how the aircraft now knows it’s turning towards a runway, and they never seem able to explain this.
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A friend of mine gave me a simple example to understand it: Imagine you are on walking on a transportation belt moving at 30 km/h. No matter if you turn or not, your speed reference to the belt will be exactly the same as long as the belt keeps a steady 30 km/h speed.
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Only half a speed-brake
It's inertia, INTBH. Those 20k+ pilots must have flown commercially, i.e. heavier planes, where the effect can be seen. Although like you say the craft is moving within a practically uniform parcel of air, Newton's laws still apply. The inertial system is the spheres, so the physics is there.
I have no claim how pronounced or measurable the effect is on those beauties with low wing loading, but our aircraft do show. Level flight, fixed thrust, steady heading with 90° cross-wind: there is a difference in which way you'd turn.
I have no claim how pronounced or measurable the effect is on those beauties with low wing loading, but our aircraft do show. Level flight, fixed thrust, steady heading with 90° cross-wind: there is a difference in which way you'd turn.
Last edited by FlightDetent; 11th Jul 2018 at 17:26.
It's inertia, INTBH. Those 20k+ pilots must have flown commercially, i.e. heavier planes, where the effect can be seen. Although like you say the craft is moving within a practically uniform parcel of air, Newton's laws still apply. The inertial system is the spheres, so the physics is there.
I have no claim how pronounced or measurable the effect is on those beauties with low wing loading, but our aircraft do show. Level flight, fixed thrust, steady heading with 90° cross-wind: there is a difference in which way you'd turn.
I have no claim how pronounced or measurable the effect is on those beauties with low wing loading, but our aircraft do show. Level flight, fixed thrust, steady heading with 90° cross-wind: there is a difference in which way you'd turn.
I fly the same heavy commercial jets (and previously, things with much higher wing loading again), and contend that the effect can’t be seen, because it doesnt exist.. When you’re flying a holding pattern up in a jetstream, what happens to your IAS - a.) alternating stall and overspeed warnings, or b.) nothing ?