Dynamic Soaring ('DS')
Dynamic Soaring, often abbreviated to DS in the radio control world, broke into the rc gliding scene in the late 1990s and is an adrenalin-packed experience for anyone looking for a rush that conventional slope soaring can't always provide!
The fundamental thrill of DS is speed - if you thought that rc jets were fast, take a look at some experienced radio control glider pilots performing Dynamic Soaring and you'll be somewhat impressed, and very surprised.
In fact, about the only limitation of DS is the strength of the glider's airframe, as well as the pilot's nerves! The speed and forces that act on the glider during a good DS flight can be phenomenal - many wings have folded and airframes have failed as a result of 'over-DSing'!
Principles of Dynamic Soaring
Believe it or not the world's largest seabird, the Wandering Albatross, is way ahead of us rc pilots. They sussed out Dynamic Soaring long before we did and it's how they soar over thousands of square miles of open ocean while using very little energy indeed.
In a nutshell, energy can be drawn from differing zones of wind speed. The principle involves some basic laws of physics, kinetic energy and a few more subjects that you probably didn't pay attention to at school.
Conventional slope soaring with an rc glider makes use of air that is being forced upwards as it approaches an area of higher ground i.e. a hillside or cliff face. The upward push of air ('ridge lift') keeps the glider aloft and the pilot needs to keep the glider flying around the top face of the slope to get maximum lift.
But Dynamic Soaring involves flying the glider on the back side ('leeward' side) of the hill as shown in the badly scaled illustration below...
Ideally DS is done on the leeward side of a ridge although a normal hillside that is experiencing the wind blowing off the top is acceptable - just launching isn't as easy. For Dynamic Soaring from a ridge, as in the picture above, the glider is launched into the ridge lift (area 'A') as if conventional slope soaring and then flown round to the leeward side.
The wind blowing off the top of the ridge continues in an approximate straight line away from the ridge (area 'B') and the area below the ridge top (area 'C') is sheltered and so the air is relatively still, or very slow moving.
The difference between the two areas of fast moving air and still air creates a definite boundary layer and finding this layer is crucial to successful Dynamic Soaring.
Once flown to the leeward side of the ridge, the glider picks up speed because it now has a tailwind. Flying the glider downward towards the still air below the boundary layer accelerates it further because now gravity is kicking in, increasing its air and ground speed (imagine freewheeling on your bike, down a hill with a tail wind helping you along...you move fast!). When the glider crosses the boundary, there is very little drag from the still air to slow it down (no head wind to speak of).
The glider is then pulled out of the dive and flown back up the slope, back across the boundary layer and into the wind blowing off the top of the ridge - not directly into it, but more 'side-on' to keep the resistance minimal. Now the glider experiences an increase in lift and energy as the wind increases the airflow over the wings.
The pilot then makes a quick turn to fly the glider downwind again, and repeats the same circuit. The turn downwind needs to be made quickly so that the glider doesn't lose any airspeed as a result of being flown into the wind.
Every time this circular flight path is followed the glider picks up more speed - a small amount each time. So, the more the glider is flown in this way, the faster it will get until either something snaps or the pilot can't cope any longer!
The realities of DS
Probably the hardest part is finding a suitable slope that generates the perfect DS conditions. A ridge is the best option and preferably one with a nice 'bowl' on its leeward side.
The photo below shows an effective DS site local to me, it's not perfect but the sharp ridge that the road follows provides an excellent cut-off point for a boundary layer to form.
The first time I tried my hand at Dynamic Soaring it scared the jeebees out of me! My little glider did stand up to it, but wasn't pushed as hard as it might have been. Don't be fooled, DS is fast! You need to have the right kind of glider and the right frame of mind. Your reactions have to be pretty good, and you need to be able to keep hold of the transmitter when your hands start shaking!
But it's a lot of fun, and addictive too if you find the right combination of glider and slope.
If you have access to a RealFlight rc simulator you can try some virtual Dynamic Soaring on there... load the Sierra Nevada DS Ridgeline and the Shuriken 60" Sloper for some high speed action!
Above: virtual DS on the RealFlight G4.5
(picture modified to show the path of the glider)
If you are looking for some high-speed, adrenalin packed rc flying why not give Dynamic Soaring a go?!
And if you're doubting the high speed claims of Dynamic Soaring, just watch Spencer Lisenby get a world record of 392 mph (since broken and now currently [Feb 2011] at 468mph!)...
Now that's fast - more than Mach 0.5! With an rc glider!!
Discuss Dynamic Soaring in the forum.
Related pages
Slope flying - on the windward side of the slope.
Launching RC gliders - the main launching methods.
RC gliders - a general overview of rc gliders.
Thermal soaring - using the sun's heat to keep airborne.
G4 rc flight simulator - offers a DS slope and choice of gliders for virtual soaring.
