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Two proposals to explore Dynamic Soaring
Dynamic soaring works only when the glider is passing through a path of
changing wind velocity. In this way the glider can gain or loose energy independent of it's own kinetic and potential energy (as in a shear or wind gradient). For example on final approach into a 15 knot headwind, we increase our approach speed because we know as we descend through the wind shear, we will loose airspeed (energy) and might have to put the nose down (giving up our potential energy to get kinetic) to keep the glider flying. Indeed, if we think we are going to be short, we "dive under the wind" and then bleed off our speed in the weaker headwind closer to the ground. This is Dynamic soaring that we all have done. In order to continuously extract energy from wind gradients or shears in a closed loop path, our upwind path must be different than our downwind. For example, of the Albatross was able to "hang a 180" and fly back along the exact same path to it's starting point, it would loose exactly the same amount of energy it had gained. It claims it's free energy from "the area inside the loop" of it's flight path that contains a gradient. From a practical perspective, wind gradients are hard to see/feel unless we have some topology like the ground or a hill for reference, and even then we are only inferring the boundaries and makeup of the shear, rather than measuring it directly like airspeed. So even if the theory works, how do we practice? for example, no matter how sensitive our backside may be, finding and centering lift is a whole lot harder without a vario. Proposal #1 As pilots that want to take advantage of dynamic soaring, we need an instrument that can measure the rate at which the glider is gaining or loosing energy independent of the normal Newtonian exchanges of kinetic, potential and frictional (drag) forces. Such an instrument could be created based on predicted v.s. actual airspeed. It is possible to accurately model the dynamic flight parameters of a given glider such as velocity, rate of sink, angle of attack, etc. in still air. If we pull back on the stick, increasing the angle of attack by 2 degrees, we can predict what the airspeed will be in 1 second, 5 seconds, 20 seconds, etc. Now imagine we pull up into a wind shear. Two seconds later, our airspeed is actually three knots higher than our model predicts. We are gaining energy! The needle (and tone) in our new instrument starts to rise. If the airspeed was five knots higher, the needle (tone) would rise even further. It shows us the rate of energy absorption through airspeed. Similarly it would show loss, just like a vario. Of course we could locate convergence lines with this instrument as well. Who knows, we might even get thermal information from the ability to detect horizontal gusts. Proposal #2 While it is possible to design and build this new instrument, and just how to do it will make an interesting discussion in itself, it will take some time to perfect it and get it into production. In the mean time, we want to learn how to use it before we have it. Just like the albatross has several different techniques for taking advantage of the same surface shear conditions, there are probably many new ways that have not been discovered at "full" scale to soar dynamically. What is the best way to fly in wind gradients that run side to side, rather than top to bottom? What is the best way to dynamically soar orthogonal to the wind direction? While our instrument is difficult to build in the real world, it's a snap to create in a flight simulator where the glider is already fully modeled. Lets build a virtual instrument and experiment by flying in virtual shear using one of the excellent glider flight simulators on the market. Anyone have an in with the programmers? Food for a winter discussion, Matt Herron (jr) |
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