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The linked samara decelerator








The principle of the linked samara is simple: latch a load to a long rope fixed to a tough little glider. The glider flies in a circle above the load and brakes its fall like a parachute would. The glider is much littler than a parachute, yet by circling above the load it covers a virtual ring-shaped surface equivalent to the surface of a parachute. Flying at high speed, forced into a circle by the rope, the glider exerts a huge lift force.





Formerly I called this device "rotating parachute". I was advised by Yuri Mosseev that this term is already widely used for another device: a conventional tissue parachute with large cutouts that make it rotate slowly while falling. So I choose another name. Images of a rotating parachute shape can be viewed through links on this page: http://www.mtu-net.ru/mosseev/pl/paralab.htm


Maybe the linked samara system has some advantages on a parachute:


And surely some disadvantages:

The linked samara must be compared to a samara tree seed with its propeller blade. Yet with some advantages:

Here are the rules to follow to build a linked samara. I found them out while trying to make it work, by making bad prototypes and trying to understand how to enhance them. Most trials were awful. It took me three months to get results because my first approach was nearly the opposite of the right solution. These rules are a first base, for sure they will have to be changed further to get best performances. I do not give mathematical formula to calculate sizes because I don't know them. I suppose the formula for conventional planes and the laws of mechanics will do the job.





An important menace for some applications is that the rope could wrap around the glider body and blockade it into a dead position. The only possible solution is to make the glider be a convex shape. Either by giving it the shape of a flying wing, like a bird, or by using thin cables between the wing ends and the nose and tail, and between the vertical tail and the nose.

This is a photograph of my best prototype. It is miniaturized that much because it had to go into full rotation while being dropped from just 6 meters height.


balsa glider



In order to make tests, you can buy a little balsa or plastic glider in a toy or model store for a few $ and latch two thin nylon wires to it.

Best way to make tests without having to climb to some height to drop the device and go back down each time is to latch the rope to a rod and run with it. You can also use a long rod and turn it around you. Once the rotation goes on you will feel the brake force, like if a parachute was latched to the rod.

Just like a plane, a linked samara can seem to work yet have a poor yield. If it rotates slowly and has an absolute trajectory resembling the path of a corkscrew, it will have few brake capabilities. The rotation must be fast in order to create a complete ring-shaped virtual brake surface. The glider should be more rotating than falling. To achieve this some tuning will be necessary.

Maybe a ladder of gliders would be fun:


ladder


Many variants are possible, using several gliders. Gliders can be linked through several ropes and rotate in concentric cones... They can be latched to the extremities of a large load and tune the attitude of the load... they can be latched together by horizontal wires and become closer to the petals of a rotating parachute... All ways to have the wires mangle and crash the whole. Yet an interesting possibility is to have the glider turn neither around a vertical axis nor an oblique axis but straight around a horizontal axis, flying below and above the load each revolution. This creates a virtual balloon around the load. For example a long thin wing can be latched along a rocket booster. To brake the fall it will be released and turn around the horizontal booster. A tissue wing in a spiral around the load would be charming... I once hoped that the reciprocal rotation of the load would allow to decrease the impact speed but this seems difficult to tune.

Maybe a linked meta-samara is possible: the glider would turn in a circle but this circle would turn in bigger circle, producing a cycloid. Maybe a simpler approach would be to have the glider flow in a spiral; with a radius continuously increasing and decreasing, in order to sweep over a broader surface.

ATAIR Aerospace seems to have achieved an interesting design: http://www.atair.com/parachutes/heli-chute/

A link: http://home.att.net/~dannysoar2/Whirlygig.htm


I whish to thank Yuri Mosseev and Didier Bizzarri for their advice and data.



Eric Brasseur  -  May 12 2000  till  December 1 2010
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