(Dynamic) Soaring

[Windy_Skies]

There are several topics and comments on this forum that touch on dynamic soaring. Here is a topic for linking to those and to any other content on dynamic soaring.

Wayback Machine

OPTIMAL DYNAMIC SOARING FOR FULL SIZE SAILPLANES

Abstract
Dynamic soaring is a unique flying technique designed to allow air vehicles to extract energy from horizontal wind shears. Dynamic soaring has been used by seabirds like the Albatross to fly hundreds of kilometers a day across the ocean. Small hobby radio controlled sailplanes have also used this technique to achieve sustained speeds of over 200 miles per hour from just a simple hand toss. Dynamic soaring, however, has never before been studied for use on full size aircraft. The primary goal of this research was to prove or disprove the viability of dynamic soaring for enhancing a full size aircraft’s total energy by using a manned sailplane as a demonstration air vehicle. The results of this study will have a direct impact on the sport of soaring, as well as the design of the next generation of large, sailplane-like, robotic planetary explorers for the National Aeronautics and Space Administration (NASA).

This research began with a point mass optimization study of an L-23 Super Blanik sailplane. The primary goal of this study was to develop and analyze optimal dynamic soaring trajectories. A prototype 6 degrees of freedom (DOF) flight simulator was then developed. This simulator helped to validate the dynamic soaring aircraft equations of motion derived for this research and built operational simulator development experience. This experience was then incorporated into a full dynamic soaring research simulator developed at the NASA Dryden Flight Research Facility (NASA DFRC). This NASA simulator was used to develop advanced dynamic soaring flight displays, flight test techniques, and aircrew coordination procedures. Flight test were successfully accomplished using an instrumented L-23 Super Blanik sailplane and advanced weather monitoring equipment. Through modeling and simulation, flight test, and mathematical analysis, this research provided the first documented proof of the energy benefits realized using dynamic soaring techniques in full size sailplanes.

[Windy_Skies]

r/aerodynamics - Books on Dynamic Soaring

[Windy_Skies]

Flying at No Mechanical Energy Cost: Disclosing the Secret of Wandering Albatrosses

PDF: Energy economy in flight - Emily L.C. Shepard

[PierreB]

Some explains on:

DYNAMIC SOARING EXPLAINED

An envisaged application for wind turbines on:
https://www.sciencedirect.com/science/article/abs/pii/S0947358023000717

Abstract

Dynamic soaring for UAVs is a flight technique that enables continuous, powerless periodic flight patterns in the presence of a wind gradient. However, sufficiently large wind gradients are uncommon over land, while at offshore locations the largest wind gradients are located close to the ocean surface, thereby limiting the scope of practical application. An intrinsic feature of wind turbines is that they inherently produce very sharp wind gradients in the near wake. Therefore, in this paper, we propose and investigate periodic stationary dynamic soaring trajectories in the near wake of wind turbines. We additionally consider the potential of dynamic soaring for revitalizing the wind turbine wake. To this end, we apply periodic optimal control based on a simplified model for the glider dynamics and the wind profile in the wake. The cost function maximizes the revitalization of the wake. We compute optimal orbits for a range of different wing spans and different mass-scaling assumptions. The largest glider configuration, with a wingspan of 10 m and a mass of 222.6 kg, achieves a wake revitalization of about 0.94% of the total turbine thrust.

Introduction

Modern wind turbines are often clustered together in large farms in order to reduce balance-of-system costs and optimize the use of land or sea concession areas. However, wind turbines generate wakes that impair the efficiency of downstream turbines when spaced too closely together. In modern wind farms, with turbine spacings of 5 to 7 turbine diameters, overall efficiency losses due to wakes can be up to 40% and more, depending on wind direction and atmospheric conditions [2]. In the current work, we propose and investigate the potential of using glider planes to speed up wake recovery, by flying dynamic soaring loops between a wind turbine near wake and the surrounding free stream.[…]

The full article is available on request on https://www.researchgate.net/publication/371620671_Dynamic_Soaring_in_Wind_Turbine_Wakes

Dynamic Soaring in Wind Turbine Wakes

• June 2023

• European Journal of Control

• Follow journal

• DOI:

• 10.1016/j.ejcon.2023.100842

• Jakob Harzer

• Jochem De Schutter

• Moritz Diehl

• Johan Meyers

[Windy_Skies]

https://www.audubon.org/news/these-masters-sky-can-fly-hours-or-days-while-barely-flapping

These Masters of the Sky Can Fly for Hours (or Days) While Barely Flapping

Seven extraordinary examples of birds that figured out how to let the wind do the work for them.

[…]

Like many other soaring birds, Great Frigatebirds use thermals to gain altitude. But unlike the others, they ride powerful thermals inside white and puffy cumulus clouds, which can elevate them 13 feet per second. “It’s the only bird that is known to enter into a cloud intentionally,” Henri Weimerskirch, lead author of the paper describing this behavior, told NPR in 2016. By doing so the birds can reach altitudes as high as 13,000 feet.

[…]

Turkey Vultures are different from other vultures throughout the world. Most vulture species rely heavily on soaring and gliding through the air at very high altitudes (up to 37,000 feet), says Katzner, and they rely heavily on sharp vision to see the carcasses of dead animals from such a height. But Turkey Vultures have adapted to fly at lower altitudes to sniff the best pieces of carrion. In fact, they have one of the best smelling systems of all birds. In 2017, after comparing them with other 32 species, a team of researchers proved that Turkey Vultures has more mitral cells, which transmit information about odors to the brain, than any of the other measured species.

These birds fly using a type of soaring called “contorted soaring.” Through this technique, Turkey Vultures ride the upward wind generated when air currents collide with treetops. This allows them to stay closer to the ground compared to other carrion eaters, like Black Vultures in North America, giving them an advantage. They can also rock side-to-side while flying to counteract the wind forces in turbulent scenarios, which allows them to have a lot of control and stability in their flight. “They can fly with almost no wind and in very turbulent settings," Katzner says. “They are just one of the coolest species in North American to me.”

Scientists Determine How Birds Soar to Great Heights

August 01, 2016

Migratory birds often use warm, rising atmospheric currents to gain height with little energy expenditure when flying over long distances.

It’s a behavior known as thermal soaring that requires complex decision-making within the turbulent environment of a rising column of warm air from the sun baked surface of the earth. But exactly how birds navigate within this ever-changing environment to optimize their thermal soaring was unknown until a team of physicists and biologists at the University of California San Diego took an exacting computational look at the problem.

In this week’s online version of the journal Proceedings of the National Academy of Sciences, the scientists demonstrated with mathematical models how glider pilots might be able to soar more efficiently by adopting the learning strategies that birds use to navigate their way through thermals.

“Relatively little is known about the navigation strategies used by birds to cope with these challenging conditions, mainly because past computational research examined soaring in unrealistically simplified situations,” explained Massimo Vergassola, a professor of physics at UC San Diego.

To tackle the problem, he and his colleagues, including Terrence Sejnowski, a professor of neurobiology at the Salk Institute and UC San Diego, combined numerical simulations of atmospheric flow with “reinforcement learning algorithms”—equations originally developed to model the behavior and improved performance of animals learning a new task. Those algorithms were developed in a manner that trained a glider to navigate complex turbulent environments based on feedback on the glider’s soaring performance.

According to Sejnowski, the “reinforcement learning architecture” was the same as that used by Google’s DeepMind AlphaGo program, which made headlines in 2016 after beating the human professional Go player Lee Sedol.

When applying it to soaring performance, the researchers took into account the bank angle and the angle of attack of the glider’s wings as well as how the temperature variations within the thermal impacted vertical velocity.

“By sensing two environmental cues—vertical wind acceleration and torque—the glider is able to climb and stay within the thermal core, where the lift is typically the largest, resulting in improved soaring performance, even in the presence of strong turbulent fluctuations,” said Vergassola. “As turbulent levels rise, the glider can avoid losing height by adopting increasingly conservative, risk-averse flight strategies, such as continuing along the same path rather than turning.”

In the two, three dimensional color graphs (shown above), the scientists illustrate how an untrained glider (at left) takes random decisions and descends, while the trained glider (at right) learns to employ the characteristic spiraling patterns in regions of strong ascending currents, as observed in the thermal soaring of birds and gliders. (The colors indicate the vertical wind velocity experienced by the glider. The green and red dots indicate the start and the end points of the trajectory, respectively.)

The researchers write in their paper that, based on their study, “torque and vertical accelerations” appear to be the sensorimotor cues that most effectively guide the most efficient soaring path of birds through thermals, rather than differences in temperature.

“Temperature was specifically shown to yield minor gains,” they write adding that “a sensor of temperature could then be safely spared in the instrumentation for autonomous flying vehicles.”

“Our findings shed light on the decision-making processes that birds might use to successfully navigate thermals in turbulent environments,” said Vergassola. “This information could guide the design of simple mechanical instrumentation that would allow autonomous gliders to travel long distances with minimal energy consumption.”

“The high levels of soaring performance demonstrated in simulated turbulence could lead to the development of energy efficient autonomous gliders,” said Sejnowski, who is also a Howard Hughes Medical Institute Investigator.

Other members of the research team were Gautam Reddy, a physicist at UC San Diego and the first author of the paper, and Antonio Celani of the Abdus Salam International Center for Theoretical Physics in Trieste, Italy. The study was supported by a grant from the Simons Foundation.

The study referenced above:

https://www.pnas.org/doi/10.1073/pnas.1606075113

Learning to soar in turbulent environments. G. Reddy, A. Celani, T.J. Sejnowski & M. Vergassola. Proc Natl Acad Sci U S A. published ahead of print August 1, 2016

Significance

Thermals are ascending currents that typically extend from the ground up to the base of the clouds. Birds and gliders piggyback thermals to fly with a reduced expenditure of energy, for example, during migration, and to extend their flying range. Flow in the thermals is highly turbulent, which poses the challenge of the orientation in strongly fluctuating environments. We combine numerical simulations of atmospheric flow with reinforcement learning methods to identify strategies of navigation that can cope with and even exploit turbulent fluctuations. Specifically, we show how the strategies evolve as the level of turbulent fluctuations increase, and we identify those sensorimotor cues that are effective at directing turbulent navigation.

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https://www.pnas.org/doi/10.1073/pnas.1907360117

Physical limits of flight performance in the heaviest soaring bird

Abstract

Flight costs are predicted to vary with environmental conditions, and this should ultimately determine the movement capacity and distributions of large soaring birds. Despite this, little is known about how flight effort varies with environmental parameters. We deployed bio-logging devices on the world’s heaviest soaring bird, the Andean condor (Vultur gryphus), to assess the extent to which these birds can operate without resorting to powered flight. Our records of individual wingbeats in >216 h of flight show that condors can sustain soaring across a wide range of wind and thermal conditions, flapping for only 1% of their flight time. This is among the very lowest estimated movement costs in vertebrates. One bird even flew for >5 h without flapping, covering ∼172 km. Overall, > 75% of flapping flight was associated with takeoffs. Movement between weak thermal updrafts at the start of the day also imposed a metabolic cost, with birds flapping toward the end of glides to reach ephemeral thermal updrafts. Nonetheless, the investment required was still remarkably low, and even in winter conditions with weak thermals, condors are only predicted to flap for ∼2 s per kilometer. Therefore, the overall flight effort in the largest soaring birds appears to be constrained by the requirements for takeoff.

[dougselsam]

Anyone who has been involved in hang-gliding sees birds in a whole new way.
You can feel what the bird is thinking as it lands and flies, because it’s a case of “yup, been there, done that”.
Around here people stay up all day riding thermals. Wearing winter clothing, people launch at over 100 degrees F. , ride thermals up to 16,000 feet, and have to come back down when it gets too cold up there.
Anyway, what most people don’t really notice becomes apparent - a gaggle of birds all circling in the same direction, none of them flapping their wings - we know they found a thermal and are riding in it without expending energy. Most people would just never notice the lack of flapping. Similarly, we see birds effortlessly riding the updraft when wind hits a ridge (ridge soaring), and we know what they are thinking as they play around and chase each other. When we see them lower their feet as they flare coming in for a landing, we see that they are just like us. Nothing new here folks. Soaring is an old concept. Staying well away from known dangerous obstacles like powerlines and wind turbines is rule number one!

[PierreB]

@dougselsam

Anyway, what most people don’t really notice becomes apparent - a gaggle of birds all circling in the same direction, none of them flapping their wings - we know they found a thermal and are riding in it without expending energy.

We see this every day in the countryside, with the naked eye or binoculars.

Raptors are wrapping around in thermals and rising to spot possible prey.

To covering distance, some birds leave a thermal, glide to find another thermal, and so on, as gliders do.

On the other hand, the dynamic soaring of albatrosses is more difficult to observe if we are not in a boat in the sea. It takes place just above the sea, the bird covering distance by oscillating between two layers of air.

Dynamic Soaring: How the Wandering Albatross Can Fly for Free

[dougselsam]

This video doesn’t really go into any detail about exactly how the energy transfer that allows such perpetual flight actually works.

[Rodread]

Experimental Swept Wing Transonic - Dynamic Soaring- Parker Mtn.

Wishing all our efforts dynamically soar in 2024

[Windy_Skies]

In the comments under the above video the uploader links the 56 minute talk BTD10: The 835kph Sailplane and Dynamic Soaring. I might not have linked that before.

The model will see as high as 80 G’s during a flight. (Yes, you read that correctly. Eighty times the force of gravity.) https://www.youtube.com/watch?v=nv7-YM4wno8

The wing spars must be solid carbon and/or composite of great stature?!

Loads and loads of carbon. We have measured over 100 gs.