DYNAMIC SOARING

 The latest and fastest development in RC!

 

Dynamic Soaring increases an aircraft’s airspeed by exploiting differences in velocity of two adjacent air masses. Most pilots will tell you that Dynamic Soaring is all about speed --- raw, heart-thumping, near-to-the-deck speed. The stronger the wind, the faster the plane can go. Typically Dynamic Soaring or “DS” requires a combination of specific terrain, weather conditions, experience and enough nerve to carve precious gliders through extreme wind shears at unbelievable speeds a few feet above the ground. When a hill or ridge has wind flowing up one side nearly perpendicular to the slope face, a reverse eddy develops on the leeward side. A hill with both an upwind, (front) side and a steep downwind (backside) side as well is ideal for Dynamic Soaring, the steep drop of the slope on the back of the hill causes the wind to separate from the hill, leaving a zone of still air. This reverse eddy or spinning vortex of air underneath the wind flowing over the ridge is much like an eddy seen behind a rock in a flowing stream. The area that separates the normal flow and reverse flow is called a shear and typically is turbulent air. This separation is what makes Dynamic Soaring possible.

 

To initiate Dynamic Soaring the aircraft would normally be made to gain altitude on the front side of the hill and when sufficiently high turned down wind to cross the ridge and dived towards the back side of the hill. As the craft gets near the leeward side it will pass though wind shear that separates the normal flow from leeward or still air behind the ridge. When the plane crosses this shear its airspeed is almost instantly increased.  The model must then be pulled up to avoid the ground, turned back and up toward the ridge and then again near the top of the ridge made to cross another shear as it passes through to the front side air. Each time the plane completes a full circuit it crosses the shear twice and gains airspeed with each crossing.  After a few laps speeds in excess of 250mph and up to a maximum speed of 513mph have been achieved.

 

The difference between slope soaring and Dynamic Soaring: Aircraft that are soaring or gliding use rising air to maintain or gain energy by either increasing their altitude or air speed. Dynamic Soaring increases the aircrafts speed by exploiting differences in air mass velocities. The most obvious difference to the spectator (and even more so to the pilot) is that the glider is flown on the back-side of the hill! Conventional lift is generated by a slope and wind blowing up the slope or thermals generated by differences in temperature. With Dynamic Soaring, differences in velocity between air masses can provide energy capture much higher than that available from slope soaring! It's up to the pilots skill and the model to make the most of this energy through interpretation of wind, terrain and invisible forces to achieve the such incredible speeds.

 

Dynamic soaring models: Extremely high speed DS'ng requires extremely strong gliders to stand up to the massive forces at 300mph or faster speeds. Aircraft performance is influenced significantly both by aeroelastic phenomena, arising from the interaction of elastic, inertial and aerodynamic forces resulting from maneuvers and gust/turbulence encounters while crossing shears.  This type of high speed flying subjects airframes to enormous loads and it is not uncommon for the planes to have spectacular failures in flight.  One of the parameters given to DS aircraft is “puff speed”. This is the speed at which the forces on the airframe become more than the plane can handle and the plane instantly disintegrates in the air. Another source of failure is what some of the pilots call dirt diving! Since maximum speeds are attained by crossing air masses with the largest difference in velocity the pilot who desires higher speed will fly as close to the ridge as possible. Its close to the ridge where the shear is thinnest and the crossing time the shortest... When planes hit the ground at 300mph or faster loud explosions and carbon confetti clouds are generated with multi thousand dollar machines!

 

High-speed flutter of either the wing or tail surfaces as the plane encounters turbulence at the boundary, is probably the most common cause of mid-air destruction. By far most planes are lost when the pilot makes a small control error and the plane piles  into the ground. Dynamic Soaring takes place low near the ground, things happen very fast and a small mistake can lead to instant catastrophic crashes. Typically these high speed crashes don't leave anything that looks like a model airplane and the pilot is lucky to get back a servo or a battery.

 

Starter Planes: Almost any plane except perhaps a balsa wood light-weight floater will do. Foam wings or planks are excellent places to start and are made of extremely durable EPP, (Expanded polypropylene).  Flying wings and planks such as Combat wings, JW's, WingWarriers, Bats, Zagi, Boomerang, Rebels all work well, although they have a lower top speed than stiffer carbon wings. They do have one huge advantage for the beginner, they bounce, i.e. they survive the inevitable crashes a lot better. Check out the RCSpeeds foam list for a complete list of foam planes and the speeds they fly.

 

Mid Range Planes: Generally, the faster and better penetrating a plane is (more efficient, less drag), the better Dynamic Soaring it will do. Heavier wing-loading helps retain energy and speed. Acrobatic and mid range speed(150/200mph) Dynamic Soaring can be done with well built carbon F3F planes, 80" and 60" planes.  Some of the best F3F DS planes are the NYX F3F, Stratos DS and the CrossFire. The Opus MCT is an extremely popular 80" 200-300 mph mid range plane and when modified has reached speeds of over 340 mph. A few 60" great mid range planes such as the Dynamic 60, Kinetic-60", Carbon Bird, Blast 54 and the Mach Dart/Sloper and have achieved speeds of over 300mph. The JW, Reaper and the Gulp all occupy spots near or at the top of the foam list and are excellent planes that, when built well, have no problem flying in the low 200mph range.

 

Big Dog Planes: RCSpeeds has a list of the twenty fastest planes in the world and they can all be seen on the fastest 20 list. These planes are already flying at speeds at or near 400mph!  The Big Dog list consists of the twenty fastest pilots we have to date.  Check it out to see what the fastest pilots in the world are flying.

For a scientific explanation download Dr. Philip Richardson’s High-Speed Dynamic Soaring paper! (Soaring Digest April 2012)    Dr. Philip Richardson a senior scientist from Woods Hole Oceanographic Institution presents the key parameters of dynamic soaring that allow high speeds to be achieved, how the flight may be optimized for fast speeds, and the maximum airspeeds that can be achieved with realistic winds.

Happy landings!

 

 

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