There are no powered spinning propellers in nature. When evolution has found an advantage to producing thrust in a fluid, it has done it mainly by flapping things back and forth. This new VTOL aircraft propulsion system aims to do the same with a series of flapping wings mounted in large ducts.
What's wrong with the prop-powered, drone-style VTOL flying car designs we're seeing all over the place? Ignoring the energy density issues that are holding the entire electric aviation industry back, multirotors are quite noisy, and they have basically no adequate safety systems in place if the power systems fail.
A somewhat mysterious startup called Volerian claims to have a solution for both these points, and it uses a very odd propulsion system we've never run across before.
The system places a large number of flapping wings inside a series of precisely shaped ducts. The wings are driven by cams on a rotating shaft, such that they flap back and forth quickly between the walls of these ducts, much like the tails of fish. A second fixed "stator" wing is mounted further down the ducts "to further increase efficiency," presumably by messing with the swirling pressure vortices created by the flapping wings.
The company claims its furious flappers not only make less noise than a comparable multirotor setup, but that the system is safer as well. In the event of power loss, the wings can be released to flutter against the airstream coming up through the bottom of the vents as the aircraft falls, acting a bit like a parachute. Not to mention, there's no rotating decapitators in the system to worry about.
Thus, Volerian is proposing a range of different aircraft based on this odd propulsion system. Point them forward, and you can build a conventional winged aeroplane. Point them upward – you'll need more, of course – and you've got a VTOL craft ready for use as a flying taxi, although it's not clear exactly how horizontal thrust control will be achieved in such cases.
The company, at this stage, has only shown a bunch of renders, as well as a single-wing demonstration rig that it rolled out at this year's Farnborough airshow. This rig, though running at a slow speed, demonstrated that these moving wings will be far from silent:
Volerian is dreaming big, though, planning a modular factory design that can be rolled out to multiple production partners. Slow down, guys, how about we get some scale models flying first to assuage our doubts about the propulsion system?
For example, it seems to be reliant on a heck of a lot of moving parts, any of which could be easily damaged by a bird strike, or anything else dropping through the top of the ducts. If something gets wedged in there, does it take out all the wings on the same cam?
Also, does it provide thrust that rises consistently with flapping speed, or does it, like fish tail flapping (which produces a similar "reverse Kármán vortex street" effect) have "a narrow range of frequencies of maximum amplification" in which it can efficiently produce thrust?
Furthermore, how does it handle high-speed incoming wind? And how would a VTOL craft be designed in order to balance itself in the air and provide forward, sideways and rotational motion?
Many questions remain to be answered before this design can be seen as anything but a set of CAD renders. Still, brand new propulsion systems certainly don't pop up every day, so the Volerian is certainly worthy of a good bit of chin-scratching.
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