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Wizofoz
21st Jun 2018, 02:39
I've had an idea for a while, but lack the math/aerodynamics to verify it's practicality.

I've wondered if the vertical wind-shear in the boundaries of jet-streams could be utilized to dynamically soar a sailplane over long distances.

The question I need a guru to answer is this- what rate of vertical shear would be needed to allow a high performance glider (lets say an L/D of 50-1) to maintain a sustained climb?

FE Hoppy
21st Jun 2018, 11:42
Just long enough to run out of oxygen is my guess ;-)

meleagertoo
21st Jun 2018, 12:05
At (say) 50mph the glider is covering 4400 feet per minute. At 50:1 it is losing 4400/50 fpm, ie 88fpm. Thus rising air at only 88fpm will enable it to maintain altitude, any more than that and it will be able to climb (or stay level and go faster at a less efficient l/d ratio).
That bit sounds perfectly feasible in theorey. The problems would be simply finding the jetstream, let alone finding it's edge, and getting the glider there in the first place. Those, I suspect, are pretty much insurmountable.

Surely of far more importance would be a way for airliners to find this rising air and stay in it enabling a considerable reduction in power to maintain speed. I have flown a Jetranger several times in strong ridge lift (canyon edge) for many miles at ludicrously low power settings so the theorey appears sound.

Have I got that right?

Wizofoz
21st Jun 2018, 14:39
At (say) 50mph the glider is covering 4400 feet per minute. At 50:1 it is losing 4400/50 fpm, ie 88fpm. Thus rising air at only 88fpm will enable it to maintain altitude, any more than that and it will be able to climb (or stay level and go faster at a less efficient l/d ratio).
That bit sounds perfectly feasible in theorey. The problems would be simply finding the jetstream, let alone finding it's edge, and getting the glider there in the first place. Those, I suspect, are pretty much insurmountable.

Surely of far more importance would be a way for airliners to find this rising air and stay in it enabling a considerable reduction in power to maintain speed. I have flown a Jetranger several times in strong ridge lift (canyon edge) for many miles at ludicrously low power settings so the theorey appears sound.

Have I got that right?

No, sorry- I'm not talking about rising air, I'm talking about wind-shear- change of wind velocity with altitude. An increasing head-wind is positive wind-shear and if sufficient can allow a glider to climb without actual rising air.

pattern_is_full
21st Jun 2018, 15:40
An increasing headwind will have to keep increasing to infinite speed to do much good for more than a few seconds. Pretty rapidly, the inertia of the aircraft is overcome, and it is just drifting backwards with the headwind. No more relative headwind at the wing's leading edge, and a decrease in ground speed. Either of which will make achieving "long distances" - ummm - challenging. ;)

This is more or less just a restating of the "turn into the wind" question - unless an aircraft is fixed in position (tied down on the ground), the external wind has no effect on airspeed - which is what produces lift. Except for very brief moments (gusty turbulence or shear) where a gust may act faster than inertia can be overcome.

You fly into the increasing headwind along the edge of the jet stream, and maybe gain a few seconds of extra lift and a bit of altitude. And you fly a little further into the shear and gain a few more feet, but soon you will be in the core of the jetstream, with no more shear, just a steady headwind. What do you do? If you fly out towards the edge of the jet, you now have a decreasing headwind/shear and will lose altitude again. TANSTAAFL ("There ain't no such thing as a free lunch.")

Wizofoz
22nd Jun 2018, 03:46
An increasing headwind will have to keep increasing to infinite speed to do much good for more than a few seconds. Pretty rapidly, the inertia of the aircraft is overcome, and it is just drifting backwards with the headwind. No more relative headwind at the wing's leading edge, and a decrease in ground speed. Either of which will make achieving "long distances" - ummm - challenging. ;)

This is more or less just a restating of the "turn into the wind" question - unless an aircraft is fixed in position (tied down on the ground), the external wind has no effect on airspeed - which is what produces lift. Except for very brief moments (gusty turbulence or shear) where a gust may act faster than inertia can be overcome.

You fly into the increasing headwind along the edge of the jet stream, and maybe gain a few seconds of extra lift and a bit of altitude. And you fly a little further into the shear and gain a few more feet, but soon you will be in the core of the jetstream, with no more shear, just a steady headwind. What do you do? If you fly out towards the edge of the jet, you now have a decreasing headwind/shear and will lose altitude again. TANSTAAFL ("There ain't no such thing as a free lunch.")

You don't understand dynamic soaring. Albatrosses cross oceans using it, and modelers have achieved speeds, with gliders, of 500MPH plus.

Yes, the climb in an increasing headwind is finite- though the acceleration from say, 40 knots outside a Jetstream to 150 in the core, over several thousand feet, would supply more than a few seconds of climb.

But how DS works is you then reverse course and descend on the reciprocal- which now means you are descending into a reducing tailwind- that is to say ALSO an over-shoot shear, which would allow you to gain a lot of speed- sufficient, in an efficient glider- to reverse course again and start the process over.

Even if you just circle as such, you would still make progress at the same velocity as the jet- do it long enough and you could be in record breaking territory.

pattern_is_full
22nd Jun 2018, 05:22
Ahh - I didn't get the point that you don't care where you end up, so long as you go somewhere. ;) Also, DS normally involves alternating climbs and dives through the shear zone, not what I would call a sustained climb. But I see where you're going (aerodynamically, if not geographically).

Anyway, thus far a manned sailplane has managed to maintain peak altitude (350m/1100 feet) and gain some headway against the wind, by DS with and into a 40-knot shear at 1000 feet/300 meters. (42:1 glide ratio, 158 kt Vne, MGW 990 lbs, PIK-20). And maintain peak altitude (but drifting with the wind) with a different craft (glide ratio 39:1). I suspect with a manned craft, the prime limiting factor of what can be achieved will be the Vne (pop up into a shear of 70 knots with an airspeed already at 140 knots, and the wings come off). As always in aviation there is a trade-off in strength vs. weight (which will also affect glide ratio). A specially-designed craft may be necessary. Model gliders don't have to house a non-lift-producing human body, and can devote that weight to extra structural strength, and birds have nerve sensors (pain!) to warn of overspeeds.

For jet streams, you will need 1) oxygen (already mentioned - another weight penalty) and 2) a way of getting up to jet altitudes (on the order of 33000ft/10000m) - either a tow (what tow craft can climb that high at a low enough speed for safety - U-2?), or a preliminary climb in mountain waves (the traditional lift source for sailplane distance records) - perhaps a climb along the Andes wave to catch the southern subtropical jet over Argentina/Chile somewhere. GPS for location plus real-time data on the jet location as it meanders might be needed also.

I guess the first sentences in my second paragraph is as close as I can get to answering your basic question.

(Thought experiment - since jet streams have a core, and thus lateral shear as well as vertical shear (cross them sideways, and the wind speed increases into the core, and then decreases exiting the stream) - what happens if you "tack" back and forth through a jet stream, with or without vertical motion as well, at an angle to the wind so that you get to use some of its force? Or an even more complicated path of climbing, diving and tacking all at once?)

Wizofoz
22nd Jun 2018, 06:47
Ahh - I didn't get the point that you don't care where you end up, so long as you go somewhere. ;) Also, DS normally involves alternating climbs and dives through the shear zone, not what I would call a sustained climb. But I see where you're going (aerodynamically, if not geographically).

Anyway, thus far a manned sailplane has managed to maintain peak altitude (350m/1100 feet) and gain some headway against the wind, by DS with and into a 40-knot shear at 1000 feet/300 meters. (42:1 glide ratio, 158 kt Vne, MGW 990 lbs, PIK-20). And maintain peak altitude (but drifting with the wind) with a different craft (glide ratio 39:1). I suspect with a manned craft, the prime limiting factor of what can be achieved will be the Vne (pop up into a shear of 70 knots with an airspeed already at 140 knots, and the wings come off). As always in aviation there is a trade-off in strength vs. weight (which will also affect glide ratio). A specially-designed craft may be necessary. Model gliders don't have to house a non-lift-producing human body, and can devote that weight to extra structural strength, and birds have nerve sensors (pain!) to warn of overspeeds.

For jet streams, you will need 1) oxygen (already mentioned - another weight penalty) and 2) a way of getting up to jet altitudes (on the order of 33000ft/10000m) - either a tow (what tow craft can climb that high at a low enough speed for safety - U-2?), or a preliminary climb in mountain waves (the traditional lift source for sailplane distance records) - perhaps a climb along the Andes wave to catch the southern subtropical jet over Argentina/Chile somewhere. GPS for location plus real-time data on the jet location as it meanders might be needed also.

I guess the first sentences in my second paragraph is as close as I can get to answering your basic question.

(Thought experiment - since jet streams have a core, and thus lateral shear as well as vertical shear (cross them sideways, and the wind speed increases into the core, and then decreases exiting the stream) - what happens if you "tack" back and forth through a jet stream, with or without vertical motion as well, at an angle to the wind so that you get to use some of its force? Or an even more complicated path of climbing, diving and tacking all at once?)

Thanks POF, yes we are now on the same page.

Most modem gliders have oxygen- it would just mean an extra or bigger pottles.

Yes, getting there is a problem, but I think there would be turbine aircraft like a Caravan that should be able to climb high enough at a low enough IAS to prove a tow.

You mentioned a 40 knot shear- over what vertical distance? Are you talking about lea soaring or was this in free air? I read that Ingo Renner once demonstrated DS on a morning where there was a distinct surface inversion, but there would still have to be a transition between the streams, and whether that transition is steep enough in the boundary of a jet-stream is the factor I'm not equipped to calculate.

Your "tacking idea" is also intriguing- again I'd need some math to sort out if it's viable.

Thanks for the input.

DavidN
9th Jul 2018, 10:57
I actually have a similar project in the works and was curious about DS in the JS.

Just curious, any updates on this project? how is the planning going, I've been looking the approval requirements, curious as to where you hope to fly and what are your legal requirements over there (although my project is about UAV/RPA)

Also curious as to which Jet you plan on flying and any special design considerations you had to make that i might need to be aware of?

meleagertoo
9th Jul 2018, 23:14
modelers have achieved speeds, with gliders, of 500MPH plus.

I'd love to see proof of that!

clark y
10th Jul 2018, 02:25
Lots of videos on Yoo toob etc. Just look for dynamic soaring. You can even make yourself airsick watching with one or two onboard videos.

compressor stall
10th Jul 2018, 05:36
There’s a glider that will do Mach 0.6. Not dynamic soaring though.

Google Perlan project Omega Tau. Excellent podcast.

Denti
10th Jul 2018, 08:01
The RC gliders doing up to 600 MPH ground speed with DS have to be extremely sturdy though, as they experience accelerations in excess of 100g over quite some part of their elliptical flight path. Which would be, well, not quite healthy for humans on board.

Piltdown Man
10th Jul 2018, 08:21
The biggest problem is the constant hard work and g loading for the pilot. Possible maybe, not sustainable.

PM

Wizofoz
11th Jul 2018, 00:34
The biggest problem is the constant hard work and g loading for the pilot. Possible maybe, not sustainable.

PM

Would not be necessary with what I'm proposing- you'd climb in the increasing head wind, turn and descend, turn again and repeat- it's over thousands of feet, not the couple of hundred with lea-soaring.

DavidN
11th Jul 2018, 21:03
Would not be necessary with what I'm proposing- you'd climb in the increasing head wind, turn and descend, turn again and repeat- it's over thousands of feet, not the couple of hundred with lea-soaring.

Dont want to sound hostile or calling you out or anything (im genuinely interested) but are you planning on testing and flying in the jetstream or more like having an interesting hypothetical discussion about feasibility?... have you considered which of the two jetstreams (polar or subtropical jetstream) to fly in because the conditions seem quite different, or what kind of speeds you think you'd experience in terms of ground speed since the JS moves relative to a fixed point on the ground (unlike those leeward DS gliders).

Just interested in this myself and plumbing the web for info.

Wizofoz
12th Jul 2018, 06:24
Dont want to sound hostile or calling you out or anything (im genuinely interested) but are you planning on testing and flying in the jetstream or more like having an interesting hypothetical discussion about feasibility?... have you considered which of the two jetstreams (polar or subtropical jetstream) to fly in because the conditions seem quite different, or what kind of speeds you think you'd experience in terms of ground speed since the JS moves relative to a fixed point on the ground (unlike those leeward DS gliders).

Just interested in this myself and plumbing the web for info.

No, your interest is appreciated-

If I found the math worked, I'd try and get interest in testing the concept. I live in Australia, so my interest would be in sub-tropical for the moment!

The ground speed is the point- this would be a way to stay airborne for long periods while travelling at large goundspeeds- it occurs ro me as a way to set absolute gliding distance and speed records- the ultimate dream being a trans-continental flight Eastbound over Australia.

So, nothing to grandiose……..

jimjim1
12th Jul 2018, 12:27
https://www.flightglobal.com/news/articles/dynamic-soaring-may-suit-mars-missions-210697/


During the tests, which involved the USAF Test Pilot School and Air Force Institute of Technology (AFIT) together with NASA's Dryden Flight Research Center, a heavily instrumented Let L-23 Super Blanik sailplane was flown at high speeds and low altitudes in boundary-layer windshears over the dry lake bed at Edwards AFB, California.

Google search - [Let L-23 Super Blanik dynamic soaring]

returns a lot of hits about the program.