Adrian Law
Oct 18, 2002, 01:00 AM
<blockquote><strong>Dynamic Soaring, The Dark side of the hill</strong></blockquote>
<blockquote>Welcome to the world of Dynamic Soaring (DS), a relatively new and exciting part of slope flying. Before I start, I had better introduce myself. I am based in the UK in a city called Southampton on the south coast. I mainly fly Slope/DS, and my model collection currently consists of an Acacia and a foamy. The Acacia is an F3F model and details can be found on <a href="http://www.f3x.com">F3X.com</a> (USA) and <a href="http://www.soarhigh.co.uk/">Soarhigh Models</a> (UK). The foamy is currently a rare bird called a Duck. It is a 60-inch span "plank" flying wing using an airfoil section designed by Joe Wurts. The Duck doubles as a great foamy DS model and is also competitive in the UK EPP60 man on man pylon league.</blockquote>
<p align="center"><a href="/articles/liftzone/2002/oct/darkside/acacia.jpg"><img src="http://static.rcgroups.com/articles/liftzone/2002/oct/darkside/acacia_t.jpg" border="2"></a></p>
<p><big>Exactly what is DS?</p></big>
<blockquote>Andy Ellison wrote the following. I couldn't have done it better so why try!</blockquote>
<blockquote>Dynamic soaring is not a new concept by any stretch of the imagination. DS has long been associated with Albatross flight. They and other seabirds, as masters of the air, extract energy from the wind gradient by alternating climbing and diving, upwind and downwind, between air moving at differing velocities over the sea. The concept is really quite simple, but practically impossible for model sailplanes to emulate.</blockquote>
<blockquote>It is widely acknowledged that the first person to recognize a similar phenomenon while flying a model glider was the American Joe Wurts who has won just about every model gliding championships there is to win. Joe recognized the phenomenon in 1995 during a foamie 'combat' session at Parker Mountain in California. Parker Mountain has a ridge with a rounded, but narrow top. Pilots had long since known about the turbulent backside air and knew to keep well away during landing. Joe Wurts however noticed that when his combat wing was knocked down the back of the hill, he turned it around and flew it out again with more energy than it had when it entered.
</blockquote>
<blockquote>The engineer in him began to theorize the reasons behind this, and subsequently experimented to derive Dynamic Soaring as we know it today. Dynamic Soaring is the acceleration in flight of model gliders on the side of a hill opposite to the 'front-side' lift, by extracting energy from two adjacent air masses moving at different velocities.</blockquote>
<blockquote>Basically, Dynamic Soaring is fast, very fast. In fact, it is possible to soar a glider so fast that it will far exceed the speeds that you may be able to achieve flying on the front side of the hill. It is true that sometimes this can cause the models or equipment within to fail, but if you approach DS sensibly with the right equipment, suitable site, and correct frame of mind, then it should be no more dangerous than any other form of 'conventional' high energy model glider flying. Please however always show consideration towards the other slope users and the wishes of your fellow fliers. DS is known to exploit weaknesses in your model and installation so extra care must be taken. Metal geared servos and total elimination of control surface slop would be the norm as would be better control over spectators because believe me, you will get some!
</blockquote>
<blockquote>To give you some idea of what is possible during DS, it is worth noting that the fastest speed actually recorded by radar gun during DS to date is 186mph. This of course is with a specially prepared model under appropriate controls at a recent Dynamic Soaring Festival in the USA. While the theory does suggest that speeds approaching 300mph are possible, it is not likely that they will be attained.</blockquote>
<p><big>So, do you fancy a go?</p></big>
<blockquote>It is essential that you approach your first foray into DS with the correct mindset and the correct model for the job. Foamies are very good for your first flights behind the hill, and some like the JW pictured are even purpose built for the job. At all times though, safety must come first. Lookouts should always be posted in areas known for public access. Local club rules must be followed, and other pilots must be made aware of your presence, as you will probably be flying on a different part of the hill to them.</blockquote>
<blockquote>I have often found that the best form of learning is watching others and then doing it yourself. Unless you can find someone local to you to go and watch dynamic soaring, your learning curve will be much, much steeper.</blockquote>
<blockquote>Aside from the speed, the one thing that hits you when you first see someone DS'ing a model is the noise that it makes as it moves around the circuit. Sound is very important to the prospective DS pilot anyway, but the sheer noise made by a hollow molded model traveling at speeds between 100 and 200mph is simply awesome. Couple this with the hollow "Whuumpp!" as the model crosses the boundary layer between the two air masses and you can get a sound that you can physically feel in your chest!</blockquote>
<blockquote>Before I go on to describe what is happening during DS, I feel that some kind of health warning is appropriate.</blockquote>
<blockquote>DS will change your life! It is extremely addictive. You will never ever look at your favorite slope sites in the same way again. Small mounds of grass, dams, banks of trees and even rooftops that you spy from your car window on the way to work will all become new slope soaring possibilities. You will develop a sudden urge to construct one of those foamie gliders that you previously abhorred. You will travel immense distances for a few laps on the backside of nationally known DS sites with like-minded company. But worse of all, flying around on the front of the hill, which until now was perhaps your favorite pastime, will become just something to pass the time while you're waiting for the wind to turn onto your local DS site. You have been warned. Now, read on if you dare!</blockquote>
<blockquote>DS differs from conventional soaring in that it doesn't use rising air to sustain flight. Energy is extracted from the air by flying in and out of air masses moving at different speeds. This is similar to the wind gradient exploited by the Albatrosses, but happens in a much smaller space. If you select the right kind of hill, the two different air masses are basically adjacent to each other, and the contrasting airspeeds between them are much greater. The best sites for good DS are sharp peaked ridges like Rushup Edge in the Peak District or Cat Bells in the Lake District. There are however many smaller hills and coastal sites that work perfectly well dotted around the country. Even small ditches on the edge of the slope like the Westbury White Horse or Minera in North Wales make small but adequate DS spots for EPP foamie models.
The following diagram gives a visual indication of what the air is doing over a typical DS hill. The path of the model takes the form of an inclined 'loop' and crosses the boundary or shear layer behind the hilltop twice in each circuit.</blockquote>
<p align="center"><a href="/articles/liftzone/2002/oct/darkside/julian.jpg"><img src="http://static.rcgroups.com/articles/liftzone/2002/oct/darkside/julian_t.jpg" border="2"></a></p>
<blockquote>I have come across many different explanations of the DS phenomena lately, but the easiest I have found to understand is this abridged one based on Joe Wurts' original musings.</blockquote>
<blockquote>Assuming a wind speed of 10mph and ignoring any losses from model drag, turning, etc, we can see that a model heading downwind over the top of the hill with an airspeed of 30mph and a ground-speed of 40mph (30mph airspeed plus the 10mph wind speed) crosses the shear boundary into the still air where immediately the airspeed becomes equal to the ground speed i.e. 40mph. You will notice the model wobble slightly as it accelerates.</blockquote>
<blockquote>Now, if the model makes a 180 degree turn in the dead air on the back of the hill and crosses the shear boundary on its way out towards the front of the hill, its airspeed will immediately rise to 50mph as it crosses the shear boundary (40mph ground speed plus 10mph wind speed which is now a head wind).</blockquote>
<blockquote>If the model now immediately turns back 180 degrees to the downwind direction where it began, its ground speed will be 50mph airspeed plus 10mph wind speed equaling 60mph. A gain of 20 mph in a single 360 degree turn! Now imagine this with a wind speed of 50mph!</blockquote>
<blockquote>Obviously it is not quite so simple, as there are factors which affect the net speed gain per circuit. The least of these are the drag of the model, the size of the circuit, and the interference from the pilots' thumbs.</blockquote>
<blockquote>Aside from the buzz to the pilot from flying an extremely fast model so close to the ground, there is definitely an art to flying proper DS. Mastering the perpetual energy increases and accelerating the model to a much higher velocity than it would normally see as its terminal velocity, in say a prolonged front side dive, is not at all easy to do. You will also find that if your DS is successful, the speed of the model is directly proportional to the grin on the pilot's face and the net fun had during the day!</blockquote>
<blockquote>DS can have a serious side too. I have recently read of DS techniques being used to fly out slots in thermal competitions or build up speed to gain altitude during slope cross-country events. I do believe in each case the pilot's actions were frowned upon by both the organizers and their fellow competitors. Perhaps if they'd thought of it too, it wouldn't have been so bad, eh?</blockquote>
<blockquote>An awful lot has been written elsewhere on how best to get started with dynamic soaring, and I'm afraid that space negates me saying too much here. However if you really are interested in a new and exiting challenge to try with your slope models, try looking here first. <a href="http://www.dynamic-soaring.co.uk">Dynamic Soaring</a>.</blockquote>
<blockquote>Adrian Laws' web site will pretty much lead you everywhere you need to go. It is dedicated to the UK DS scene. There is a lot of information here. Ade is extremely enthusiastic, and he and his hard core cluster of DS mates are experimenting all the time. If you get onto your favorite Internet search engine and look up Dynamic Soaring, I am sure you'll turn up the Albatross stuff. However, most of what you will find will be postings from the ever-increasing band of followers that this revolutionary form of slope soaring is ensnaring across the globe.</blockquote>
<blockquote>There are also a number of commercially available videos that demonstrate the awesome power of Dynamic Soaring. Probably the best of the bunch is 'Lift Ticket' from <a href="http://www.reeseproductions.com">Reese Productions</a></blockquote>
<blockquote>The best bit of advice that I can give you here is that when you first decide to drop into the void on the 'Dark Side' of the hill, tell the wife or girl friend that you will be home late. If you are successful, you won't want to stop!</blockquote>
<blockquote>"Do not underestimate the power of the Dark Side!"...Darth Vader.</blockquote>
<p align="center"><a href="/articles/liftzone/2002/oct/darkside/ade.jpg"><img src="http://static.rcgroups.com/articles/liftzone/2002/oct/darkside/ade_t.jpg" border="2"></a></p>
<blockquote>Here is another picture of me with a now dead model, a home brew 60" made by a friend of mine. This is what the model looked like after suffering tail flutter while DS'ing at 'Whump Crump', the local name for the White Sheet DS spot. That's the back of the hill behind him. The front is just as steep. 'Whump Crump' comes from the noise the model makes as it crosses the boundary layer.</blockquote>
<p align="center"><a href="/articles/liftzone/2002/oct/darkside/alexds.jpg"><img src="http://static.rcgroups.com/articles/liftzone/2002/oct/darkside/alexds_t.jpg" border="2"></a></p>
<blockquote>Alex McMeekin wraps up his Aeromod Aldij on the backside of Whump Crump. The turbulent air was gusting to over 50mph.</blockquote>
<p align="center"><a href="/articles/liftzone/2002/oct/darkside/jw.jpg"><img src="http://static.rcgroups.com/articles/liftzone/2002/oct/darkside/jw_t.jpg" border="2"></a></p>
<blockquote>The JW is a purpose made foamie DS model from Bowman Hobbies in the USA. Joe Wurts designed the aerofoil specifically for Dynamic Soaring. This MkII version belongs to the author. 'Dorothy' is a reference to the Tornado in the Wizard of Oz that carried her over the rainbow.</blockquote>
<p align="center"><a href="/articles/liftzone/2002/oct/darkside/blackhill.jpg"><img src="http://static.rcgroups.com/articles/liftzone/2002/oct/darkside/blackhill_t.jpg" border="2"></a></p>
<blockquote>This is Black Hill in South Wales (UK). This is an excellent site, apart from the walk up! It really shows the sort of sites where we fly DS. To the left is the normal slope, and to the right is the DS side. Great thing about these sites is that you can fly them the other way round too!</blockquote>
<blockquote>The following is a link to a video taken at La Muela in Spain by Kev Knewton. It shows Alex McMeekin winding up his Acacia F3F on the backside. The slope lift is behind the cameraman, Watch for the wing bend on this all molded 2.8meter span F3F model and the understandably language of the spectators! It needs the whole 6.8mb to keep the quality to a reasonable level. <a href="http://www.btinternet.com/~adrian.law/DS/video/DS.avi">http://www.btinternet.com/~adrian.law/DS/video/DS.avi</a></blockquote>
<blockquote>That's it from me for this month. If you don't know anybody doing DS that can help you get started, then the next issue is for you. I will help you find your own DS site and give you some pointers on what to look out for, and what to do and what to not do.</blockquote>
<blockquote>Welcome to the world of Dynamic Soaring (DS), a relatively new and exciting part of slope flying. Before I start, I had better introduce myself. I am based in the UK in a city called Southampton on the south coast. I mainly fly Slope/DS, and my model collection currently consists of an Acacia and a foamy. The Acacia is an F3F model and details can be found on <a href="http://www.f3x.com">F3X.com</a> (USA) and <a href="http://www.soarhigh.co.uk/">Soarhigh Models</a> (UK). The foamy is currently a rare bird called a Duck. It is a 60-inch span "plank" flying wing using an airfoil section designed by Joe Wurts. The Duck doubles as a great foamy DS model and is also competitive in the UK EPP60 man on man pylon league.</blockquote>
<p align="center"><a href="/articles/liftzone/2002/oct/darkside/acacia.jpg"><img src="http://static.rcgroups.com/articles/liftzone/2002/oct/darkside/acacia_t.jpg" border="2"></a></p>
<p><big>Exactly what is DS?</p></big>
<blockquote>Andy Ellison wrote the following. I couldn't have done it better so why try!</blockquote>
<blockquote>Dynamic soaring is not a new concept by any stretch of the imagination. DS has long been associated with Albatross flight. They and other seabirds, as masters of the air, extract energy from the wind gradient by alternating climbing and diving, upwind and downwind, between air moving at differing velocities over the sea. The concept is really quite simple, but practically impossible for model sailplanes to emulate.</blockquote>
<blockquote>It is widely acknowledged that the first person to recognize a similar phenomenon while flying a model glider was the American Joe Wurts who has won just about every model gliding championships there is to win. Joe recognized the phenomenon in 1995 during a foamie 'combat' session at Parker Mountain in California. Parker Mountain has a ridge with a rounded, but narrow top. Pilots had long since known about the turbulent backside air and knew to keep well away during landing. Joe Wurts however noticed that when his combat wing was knocked down the back of the hill, he turned it around and flew it out again with more energy than it had when it entered.
</blockquote>
<blockquote>The engineer in him began to theorize the reasons behind this, and subsequently experimented to derive Dynamic Soaring as we know it today. Dynamic Soaring is the acceleration in flight of model gliders on the side of a hill opposite to the 'front-side' lift, by extracting energy from two adjacent air masses moving at different velocities.</blockquote>
<blockquote>Basically, Dynamic Soaring is fast, very fast. In fact, it is possible to soar a glider so fast that it will far exceed the speeds that you may be able to achieve flying on the front side of the hill. It is true that sometimes this can cause the models or equipment within to fail, but if you approach DS sensibly with the right equipment, suitable site, and correct frame of mind, then it should be no more dangerous than any other form of 'conventional' high energy model glider flying. Please however always show consideration towards the other slope users and the wishes of your fellow fliers. DS is known to exploit weaknesses in your model and installation so extra care must be taken. Metal geared servos and total elimination of control surface slop would be the norm as would be better control over spectators because believe me, you will get some!
</blockquote>
<blockquote>To give you some idea of what is possible during DS, it is worth noting that the fastest speed actually recorded by radar gun during DS to date is 186mph. This of course is with a specially prepared model under appropriate controls at a recent Dynamic Soaring Festival in the USA. While the theory does suggest that speeds approaching 300mph are possible, it is not likely that they will be attained.</blockquote>
<p><big>So, do you fancy a go?</p></big>
<blockquote>It is essential that you approach your first foray into DS with the correct mindset and the correct model for the job. Foamies are very good for your first flights behind the hill, and some like the JW pictured are even purpose built for the job. At all times though, safety must come first. Lookouts should always be posted in areas known for public access. Local club rules must be followed, and other pilots must be made aware of your presence, as you will probably be flying on a different part of the hill to them.</blockquote>
<blockquote>I have often found that the best form of learning is watching others and then doing it yourself. Unless you can find someone local to you to go and watch dynamic soaring, your learning curve will be much, much steeper.</blockquote>
<blockquote>Aside from the speed, the one thing that hits you when you first see someone DS'ing a model is the noise that it makes as it moves around the circuit. Sound is very important to the prospective DS pilot anyway, but the sheer noise made by a hollow molded model traveling at speeds between 100 and 200mph is simply awesome. Couple this with the hollow "Whuumpp!" as the model crosses the boundary layer between the two air masses and you can get a sound that you can physically feel in your chest!</blockquote>
<blockquote>Before I go on to describe what is happening during DS, I feel that some kind of health warning is appropriate.</blockquote>
<blockquote>DS will change your life! It is extremely addictive. You will never ever look at your favorite slope sites in the same way again. Small mounds of grass, dams, banks of trees and even rooftops that you spy from your car window on the way to work will all become new slope soaring possibilities. You will develop a sudden urge to construct one of those foamie gliders that you previously abhorred. You will travel immense distances for a few laps on the backside of nationally known DS sites with like-minded company. But worse of all, flying around on the front of the hill, which until now was perhaps your favorite pastime, will become just something to pass the time while you're waiting for the wind to turn onto your local DS site. You have been warned. Now, read on if you dare!</blockquote>
<blockquote>DS differs from conventional soaring in that it doesn't use rising air to sustain flight. Energy is extracted from the air by flying in and out of air masses moving at different speeds. This is similar to the wind gradient exploited by the Albatrosses, but happens in a much smaller space. If you select the right kind of hill, the two different air masses are basically adjacent to each other, and the contrasting airspeeds between them are much greater. The best sites for good DS are sharp peaked ridges like Rushup Edge in the Peak District or Cat Bells in the Lake District. There are however many smaller hills and coastal sites that work perfectly well dotted around the country. Even small ditches on the edge of the slope like the Westbury White Horse or Minera in North Wales make small but adequate DS spots for EPP foamie models.
The following diagram gives a visual indication of what the air is doing over a typical DS hill. The path of the model takes the form of an inclined 'loop' and crosses the boundary or shear layer behind the hilltop twice in each circuit.</blockquote>
<p align="center"><a href="/articles/liftzone/2002/oct/darkside/julian.jpg"><img src="http://static.rcgroups.com/articles/liftzone/2002/oct/darkside/julian_t.jpg" border="2"></a></p>
<blockquote>I have come across many different explanations of the DS phenomena lately, but the easiest I have found to understand is this abridged one based on Joe Wurts' original musings.</blockquote>
<blockquote>Assuming a wind speed of 10mph and ignoring any losses from model drag, turning, etc, we can see that a model heading downwind over the top of the hill with an airspeed of 30mph and a ground-speed of 40mph (30mph airspeed plus the 10mph wind speed) crosses the shear boundary into the still air where immediately the airspeed becomes equal to the ground speed i.e. 40mph. You will notice the model wobble slightly as it accelerates.</blockquote>
<blockquote>Now, if the model makes a 180 degree turn in the dead air on the back of the hill and crosses the shear boundary on its way out towards the front of the hill, its airspeed will immediately rise to 50mph as it crosses the shear boundary (40mph ground speed plus 10mph wind speed which is now a head wind).</blockquote>
<blockquote>If the model now immediately turns back 180 degrees to the downwind direction where it began, its ground speed will be 50mph airspeed plus 10mph wind speed equaling 60mph. A gain of 20 mph in a single 360 degree turn! Now imagine this with a wind speed of 50mph!</blockquote>
<blockquote>Obviously it is not quite so simple, as there are factors which affect the net speed gain per circuit. The least of these are the drag of the model, the size of the circuit, and the interference from the pilots' thumbs.</blockquote>
<blockquote>Aside from the buzz to the pilot from flying an extremely fast model so close to the ground, there is definitely an art to flying proper DS. Mastering the perpetual energy increases and accelerating the model to a much higher velocity than it would normally see as its terminal velocity, in say a prolonged front side dive, is not at all easy to do. You will also find that if your DS is successful, the speed of the model is directly proportional to the grin on the pilot's face and the net fun had during the day!</blockquote>
<blockquote>DS can have a serious side too. I have recently read of DS techniques being used to fly out slots in thermal competitions or build up speed to gain altitude during slope cross-country events. I do believe in each case the pilot's actions were frowned upon by both the organizers and their fellow competitors. Perhaps if they'd thought of it too, it wouldn't have been so bad, eh?</blockquote>
<blockquote>An awful lot has been written elsewhere on how best to get started with dynamic soaring, and I'm afraid that space negates me saying too much here. However if you really are interested in a new and exiting challenge to try with your slope models, try looking here first. <a href="http://www.dynamic-soaring.co.uk">Dynamic Soaring</a>.</blockquote>
<blockquote>Adrian Laws' web site will pretty much lead you everywhere you need to go. It is dedicated to the UK DS scene. There is a lot of information here. Ade is extremely enthusiastic, and he and his hard core cluster of DS mates are experimenting all the time. If you get onto your favorite Internet search engine and look up Dynamic Soaring, I am sure you'll turn up the Albatross stuff. However, most of what you will find will be postings from the ever-increasing band of followers that this revolutionary form of slope soaring is ensnaring across the globe.</blockquote>
<blockquote>There are also a number of commercially available videos that demonstrate the awesome power of Dynamic Soaring. Probably the best of the bunch is 'Lift Ticket' from <a href="http://www.reeseproductions.com">Reese Productions</a></blockquote>
<blockquote>The best bit of advice that I can give you here is that when you first decide to drop into the void on the 'Dark Side' of the hill, tell the wife or girl friend that you will be home late. If you are successful, you won't want to stop!</blockquote>
<blockquote>"Do not underestimate the power of the Dark Side!"...Darth Vader.</blockquote>
<p align="center"><a href="/articles/liftzone/2002/oct/darkside/ade.jpg"><img src="http://static.rcgroups.com/articles/liftzone/2002/oct/darkside/ade_t.jpg" border="2"></a></p>
<blockquote>Here is another picture of me with a now dead model, a home brew 60" made by a friend of mine. This is what the model looked like after suffering tail flutter while DS'ing at 'Whump Crump', the local name for the White Sheet DS spot. That's the back of the hill behind him. The front is just as steep. 'Whump Crump' comes from the noise the model makes as it crosses the boundary layer.</blockquote>
<p align="center"><a href="/articles/liftzone/2002/oct/darkside/alexds.jpg"><img src="http://static.rcgroups.com/articles/liftzone/2002/oct/darkside/alexds_t.jpg" border="2"></a></p>
<blockquote>Alex McMeekin wraps up his Aeromod Aldij on the backside of Whump Crump. The turbulent air was gusting to over 50mph.</blockquote>
<p align="center"><a href="/articles/liftzone/2002/oct/darkside/jw.jpg"><img src="http://static.rcgroups.com/articles/liftzone/2002/oct/darkside/jw_t.jpg" border="2"></a></p>
<blockquote>The JW is a purpose made foamie DS model from Bowman Hobbies in the USA. Joe Wurts designed the aerofoil specifically for Dynamic Soaring. This MkII version belongs to the author. 'Dorothy' is a reference to the Tornado in the Wizard of Oz that carried her over the rainbow.</blockquote>
<p align="center"><a href="/articles/liftzone/2002/oct/darkside/blackhill.jpg"><img src="http://static.rcgroups.com/articles/liftzone/2002/oct/darkside/blackhill_t.jpg" border="2"></a></p>
<blockquote>This is Black Hill in South Wales (UK). This is an excellent site, apart from the walk up! It really shows the sort of sites where we fly DS. To the left is the normal slope, and to the right is the DS side. Great thing about these sites is that you can fly them the other way round too!</blockquote>
<blockquote>The following is a link to a video taken at La Muela in Spain by Kev Knewton. It shows Alex McMeekin winding up his Acacia F3F on the backside. The slope lift is behind the cameraman, Watch for the wing bend on this all molded 2.8meter span F3F model and the understandably language of the spectators! It needs the whole 6.8mb to keep the quality to a reasonable level. <a href="http://www.btinternet.com/~adrian.law/DS/video/DS.avi">http://www.btinternet.com/~adrian.law/DS/video/DS.avi</a></blockquote>
<blockquote>That's it from me for this month. If you don't know anybody doing DS that can help you get started, then the next issue is for you. I will help you find your own DS site and give you some pointers on what to look out for, and what to do and what to not do.</blockquote>