Festo is known as a top-notch automation hardware manufacturer, but apparently their research division is capable of making very artistic, bio-inspired robots as well. This post specifically examines their robotic dirigible and submersible manta rays, both of which harbor a life-like gracefulness. I encourage you to check out the videos below; the technical specifications are provided for good measure.
In this case, I think the videos are the most compelling.
The dirigible is my personal favorite, as it conjures images of light-weight aerial manta rays serenely swimming in an alien sky (a notion befitting a scene in sci-fi master Arthur C. Clarke's Rama series). Regardless, both look very graceful.
Festo Air_Ray Dirigible (from the Festo website):
Air_ray, modelled on the manta ray, is a remote-controlled hybrid construction consisting of a helium-filled ballonet and a beating wing drive. Its light design makes it possible for it to “swim” in the sea of air, boosted by helium, in a similar way to the manta ray in water.
Propulsion is achieved by a beating wing drive. The servo drive-controlled wing, which can move up and down, utilises the Fin Ray Effect® and is based on alternate pulling and pushing flanks connected via frames. When pressure is exerted on one flank, the geometrical structure curves automatically against the direction of the influencing force. A servo drive pulls the two flanks alternately in the longitudinal direction, thus moving the wing up and down.
The dirigible manta ray has a 4.2 meter wingspan and a mass of 1.6kg. You can find some other detailed specs here (in German, sorry).
Festo Aqua_Ray Submersible (from the Festo website):
Aqua_ray is a remote-controlled fish driven by water hydraulics, the shape and movements of which have been based on the model of a manta ray.
The central drive and control unit of Aqua_ray takes the form of a Festo Fluidic Muscle. This is combined with the Fin Ray Effect®, a design based on the functional anatomy of a fish’s fin that makes it possible to imitate the fin drive of the natural role model almost perfectly.
As the Aqua_ray can be manoeuvred extremely well, and can be operated both as a hydrostatic glider and with an active wing beat, substantial energy savings can be achieved. Thanks to its shape and method of movement, the Aqua_ray can be used in wide ranging areas of oceanography, without disrupting the natural environment.
You can find detailed specs here (this one is in English).