No, not a reference to Star Wars but to the phenomenon of Dynamic Soaring or DS as it is better known. 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 flight between air moving at differing velocities over the sea. The concept is really quite simple but practically impossible for model sailplanes to emulate.

It is widely acknowledged that the first person to recognise a similar phenomenon whilst flying a model glider, was the American Joe Wurts who has won just about every model gliding championships there is to win. Joe recognised the phenomenon in 1995 during a foamie 'combat' session at Parker Mountain in California. Parker is 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. The engineer in him began to theorise the reasons behind this, and subsequently experiment to derive Dynamic Soaring as we know it today. The acceleration in flight of model gliders on the opposite side of a hill to the 'front-side' lift, by extracting energy from two adjacent air masses moving at different velocities.

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 frontside 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!

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. Whilst the theory does suggest that speeds approaching 300mph are possible they are in practice never likely to be attained. So, do you fancy a go?

It is essential that you approach your first foray into DS with the correct mind set 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.

I have often found that the best form of learning is watching others and then doing it yourself. If you can find someone local to you to go and watch dynamic soaring, your learning curve will be much, much steeper.
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 moulded model travelling 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!
Before I go on to describe what is happening during DS, I feel that some kind of health warning is appropriate.

DS will change your life! It is extremely addictive. You will never ever look at your favourite 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 in like minded company. But worse of all, flying around on the front of the hill, which until now was perhaps your favourite pastime, will become just something to pass the time with while you're waiting for the wind to turn onto your local DS site. You have been warned. Now, read on if you dare!

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 more 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 hill top twice in each circuit.

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.

If we assume a wind speed of 10mph, and ignore 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 windspeed) 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.

Now if the model makes a 180 degree turn in the 'dead air' on the back of the hill and again crosses the shear boundary on its way back out towards the front of the hill, its airspeed where it crosses this boundary will immediately rise to 50mph (40mph groundspeed plus 10mph windspeed - now a head wind).
If the model now immediately turns back 180 degrees to the downwind direction where it began, its ground speed will be :

50mph airspeed + 10mph windspeed = 60mph

A gain of 20 mph in a single 360 degree turn! Now imagine this with a wind speed of 50mph!

Obviously it is not quite so simple as there are factors which affect the net speed gain per circuit. Not least the drag of the model, the size of the circuit and the interference from the pilots thumbs.

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 if your DS is successful, the relationship between the speed of the model is directly proportional to the grin on the pilots face and the net fun had during the day!

DS can have a serious side too. I have recently read of DS techniques being used to fly out slots in thermal comps or build up speed to gain altitude during slope cross country events. I do believe in each case the pilots actions were frowned upon by both the organisers and their fellow competitors. Perhaps if they'd thought of it too it wouldn't have been so bad eh?

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.

www.dynamic-soaring.co.uk

Adrian Laws' website will pretty much lead you everywhere you need to go. It is dedicated to the UK DS scene. Site listings, Chat rooms, Forums, techniques, the lot are here. Ade too is extremely enthusiastic, and along with his hard core cluster of DS mates, are experimenting all the time. If you also get onto your favourite internet search engine and look up Dynamic Soaring, sure you'll turn up the Albatross stuff but most of what you find will be postings from the ever increasing band of followers that this revolutionary form of slope soaring is ensnaring across the globe. There are also a number of commercially available videos which demonstrate the awesome power of Dynamic Soaring and probably the best of the bunch is 'Lift Ticket' from www.reeseproductions.com

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/girl friend etc. that you will be home late because if you are successful, you won't want to stop!

"Do not underestimate the power of the Dark Side!".....Darth Vader.

Andy Ellison.