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
Maybe the linked samara system has some advantages on a parachute:
- A big problem with parachutes arises once the load is on
the ground and there is a lot of wind. The parachute will be
pushed by the wind and will pull the load on the ground. The
linked samara avoids this: once the load lands the glider
can do nothing else but land too or smash to the ground. It can by
no way be pushed by the wind.
- The little surface of the glider, the fact it can be
transparent, the high speed of the glider and the single rope,
allows for stealth capabilities.
- The lift capability can be tuned by changing the rope
length. This changes the diameter of the virtual lift surface. Also the
flight attitude of the glider can be changed, using ailerons and tail.
This allows for example to adapt to the decreasing speed of a Mars
- The glider and the rope can be made to withstand higher or
lower temperatures than a tissue parachute and can be stored
for a longer time under difficult conditions like moist.
- It makes the Rogalo delta wing even more interesting for
spacecraft recovery because a rather little delta wing can be
used as rotating glider. A part of the external structure of
the spacecraft can be released and serve as glider, saving more
weight than a conventional parachute and perhaps being even
- It is a simple landing or safety system for planes. The
load the plane carries just has to be dropable and latched to a
long thin wire. The plane body itself then becomes the glider
of the linked samara. No need for a parachute, the plane structure
itself is the parachute.
- The glider can be easy to manufacture and low-cost. A few
wooden pieces of good quality, correctly latched together, will
do the job. Mac Gyver can assemble one in a few minutes to
escape a mad plane.
- The system can make sideways movements. Indeed if the glider has
ailerons it can make the virtual lift surface to rotate sideways like a
helicopter propeller does. This could be interesting for a Mars lander,
to cope with sideways wind, avoid dangerous zone or aim desired zones.
(This can be done with a parachute too, using a parafoil or releasing
some parachute ropes on one side of the parachutes just before
landing.) A silly way to compensate for sideways wind is to make use of
the horizontal rotation of the load inherent to this system. The load
is released just when its speed vector is aligned with the wind speed
vector yet in the opposite direction.
- Like a parafoil, the linked samara can be powered and
allow to rise in the air and fly:
- By using a motor and a propeller on the load, just like a
powered parafoil. This needs some flight control ailerons on the
glider, to orient it like the blades of an autogyre.
- By using a motor and a propeller on the glider itself,
making a powered plane of it. A sophisticated version of this can be
used for the take-off of a conventional plane: the plane takes off
easily without its load yet is latched to it by the rope. It
turns around the load and rises in the air, till the load is
pulled into the air too. The rope is hailed by either the
load or the plane till the load joins with the plane and the
plane goes into a straight flight. This is quite complicated
yet it can be the only way to launch on the spot a heavy plane
with almost no infrastructure and making not too much noise.
- By pulling and releasing the rope alternatively, while
changing the glider incidence.
- Pulling on a long rope, with an
electric motor using a one-shot high current battery, can be
useful to make the landing smooth. (This is true for
conventional parachutes too and could be more interesting than
JATO rockets.) A very long and thin rope is used. When the surface is
near, the electric motor is switched on. The load will experience a
huge pull force while the distance between the load and the glider
shortens. Till it stands still a few meters above the ground. To
compensate for the rotation inherent to this device the glider can make
a steep turn and bring the load to complete immobility above the
- Devices working on the principle of the linked samara
can be interesting. For example a kite that rises in the
air and go into rotation around an oblique virtual line
(without touching the ground) or sweeps
horizontally. It can be used as a huge virtual sail for boats,
high in the air where the wind speed is higher or the
wind direction is different. Or produce energy for example
by pulling back and forth on the rope.
And surely some disadvantages:
- The load is brought into rotation too. This is no problem
for furniture but it makes the use of such a parachute
difficult for humans. I bet some sportsmen will try it out but
I doubt it could become of common use. A very long rope is a
solution to decrease the angle. Aerodynamic brakes along the rope can
help. One interesting possibility is
to use a glider a little bigger than a man and jump with the
body latched to the glider. This allows to fly at high speed a
long while and make acrobatics. To land, just release the
glider and let the rope roll out. A way to recycle your old
- Several conventional parachutes can be dropped at the some
time with almost no risk they hamper each other. Yet
two linked samaras that meet in the air will twist their wires and
fall to the ground.
- A conventional parachute is far easier to fold and put
into a small volume. A bendable glider can be conceived, or
even a tissue glider resembling a little parafoil, yet this will be
difficult. For some applications like droppings from the rear
of a carrier plane, the glider can be placed above the
rectangular load and can have the same surface as the load.
Only the vertical tail surface will have to fold in order to reduce the
height or in order to be able to stack several flat loads each
latched to its glider (the rope can be placed inside a box or
be lousily fixed above the load).
- The opening of a conventional parachute can be very
quick. This is not the case of the linked samara because
it takes a while before the glider goes to full rotation speed.
The linked samara must be compared to a samara tree seed
with its propeller blade. Yet with some advantages:
- The surface of the glider wing is more effective than the
surface of the samara seed blade because it is located
further from the
load and sweeps over a much wider virtual surface.
- By using a bearing on the rope the load can be allowed not
- Latch the load to the rope is easier than to a blade.
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.
- The glider must be of conventional shape. Roughly, it
needs to be able to fly by itself. Yet it does not have to be a
very stable glider since it is guided by the rope. The weight
at the front and the vertical tail surface at the rear are both
very important. Yet the weight does not need to be the optimal
weight for a normal straight flight: it can be a little too
heavy or a little too lightweight. Better a little too heavy
than a little too lightweight, tough.
- The rope must be latched to the belly of the glider at the
place of the center of gravity. Better a little to the rear of
the center of gravity (probably because this forces the wing
to a higher incidence).
- A second little rope must be attached to the middle of one
wing and to the main rope a further away down from the glider.
This second piece of rope must pull down the glider wing
towards an angle of about
30° with the horizon when the main rope falls vertically. This
is necessary to force the glider to turn while flying above the
load. Once the rotation is launched the little rope is of no
more use because the angle between the glider wing and the rope
will be less than 60°. The little rope will hang lousily.
(Except when a very long main rope is used for stability and the
glider turns by itself instead of being forced by the main
rope and the load.) (The problem that arises when the glider is latched
the middle of each wing and the main rope is short is that once the
rotation is launched and the glider is forced strongly outwards,
its outer wing is forced lower than the inner. The glider then
plunges its nose towards the ground and exerts few lift. The
braking of the fall is weak and the whole could perhaps even
accelerate to a high fall speed.)
- The rope must be as thin as possible. The side surface of
the rope brakes the glider. Best is to use a steel cable. For
little prototypes I use 0.07 millimeter diameter nylon fishing
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.
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:
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
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
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
May 12 2000 till December 1 2010