Silent, Solid-State Propulsion for Advanced Air Mobility Vehicles
by Douglas Messier
Managing Editor
NASA is funding research into how to reduce noise levels produced by the next generation of vertical takeoff and landing (VTOL) air mobility vehicles.
The space agency is providing Steve Barrett of the Massachusetts Institute of Technology with a NASA Innovative Advance Concepts (NIAC) Phase I grant worth $175,000 to develop an electroaerodynamic (EAD) propulsion systems that would allow VTOL vehicles to fly much quieter.
“EAD produces thrust through collisional ion acceleration without any moving surfaces. As such, EAD thrusters are nearly silent, enabling missions that would not otherwise be possible due to community opposition to noise,” the proposal abstract said.
“Example missions enabled by silent EAD propulsion include those near noise-sensitive urban communities, or time-critical delivery missions at night (e.g. for critical medical supplies), when community opposition to noise is most severe. Novel multi-stage ducted (MSD) EAD thrusters, in which multiple EAD thruster stages are enclosed inside a duct, will be used to increase thrust enough to enable VTOL operations,” the document added.
The project abstract follows.
Silent, Solid-State Propulsion for Advanced Air Mobility Vehicles
Steven Barrett
Massachusetts Institute of Technology
NIAC Phase I
Amount: $175,000
Length: 9 months
Advanced air mobility (AAM) is an aviation ecosystem that envisions small, electric, vertical takeoff and landing (VTOL) aircraft operations in urban areas. Community opposition to noise is likely the biggest obstacle to the widespread adoption of AAM vehicles.
We propose to overcome this obstacle via designing electroaerodynamic (EAD) propulsion systems for AAM applications. EAD produces thrust through collisional ion acceleration without any moving surfaces. As such, EAD thrusters are nearly silent, enabling missions that would not otherwise be possible due to community opposition to noise.
Example missions enabled by silent EAD propulsion include those near noise-sensitive urban communities, or time-critical delivery missions at night (e.g. for critical medical supplies), when community opposition to noise is most severe. Novel multi-stage ducted (MSD) EAD thrusters, in which multiple EAD thruster stages are enclosed inside a duct, will be used to increase thrust enough to enable VTOL operations.
Under this effort, we will design a VTOL-capable, near-silent aircraft powered by MSD thrusters. The aircraft would enable package delivery missions in noise-sensitive areas or at night, where operations would otherwise not be allowed due to community opposition. This effort would be in support of the long term goals (1) to build and fly an MSD-powered aircraft, and (2) to assess the applicability of MSD thruster technology to other AAM use cases, including intra- and inter-city passenger transport.
7 responses to “Silent, Solid-State Propulsion for Advanced Air Mobility Vehicles”
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So . . . does this build on his Bose grant from 2017? Did he actually produce results, or did NASA just decide to give his idea another go?
https://news.mit.edu/2017/b…
This might be better for airships. A rigid frame is a rectenna…and pokes out for ion wind.
Airships are essentially big sails. Too much lateral force.
My thought was that this seems to be the sort of thing JP Aerospace was checking out for their lighter than air spaceship a couple of decades ago.
With new superconductor materials I suppose it is possible. I have seen some interesting cycloidal propulsion concepts so maybe this would work in combinations with this so it might not quite be silent but very quiet.
Similar work was being done in the mid-1960s, which stumbled because of high power consumption in simple *single* layer devices. There were photos of a “flying bedstead” that was indeed off the floor and overhead of the researchers, but with a power cord dangling below it, because batteries simply were too heavy. That power demand, in turn, was caused by the energy needed to ionize *enough* air molecules to successfully transfer momentum to a column of air that provided enough accelerated mass to provide adequate thrust.
I note the use of the term “multi-stage ducted EAD”. This *seems* to indicate the possibility of taking advantage of the inverse/square relationship of electrostatic fields, in which when opposite charges are three times as close, the force between them is 9 times greater. *If* this can be applied in both ionization and acceleration of the ionized air molecules, without causing too much higher drag and weight by the ducts themselves, it should reduce power consumption there.
The “multi-stage” improvement *may* come through lowering the total energy needed for a given number of air molecules to be accelerated. Nitrogen makes up 4/5ths of our atmosphere. The first ionization potential of the Nitrogen molecule is 1402kJ/mol, … which is quite a lot. *If*, however, these same ions are used in multiple layers of acceleration, in the ducts, so that a single ion collides with, and accelerates, a far larger number of non-ionized molecules, then the percentage of power needed for ionization, in the total power needed for flight, could drop dramatically.
Still, there is the weight, and the drag, caused by ducts. Weight may be helped by new materials, especially non-conductive ones. Dr. Julia Greer, at Caltech,
https://jrgreer.caltech.edu/
heads a group looking into high strength-low mass materials that are trusses with their smallest truss member size at the nm scale, far below the smallest size of flaws that detract from the theoretical strength of materials. These trusses are also so lightweight that, if they are “skinned” to exclude air, they can *float* in air. That may do well for ducts. The techniques for forming these trusses are *definitely*not* any sort of current industry standard today, however.
As to drag inside the ducts, that may at least be ameliorated by reducing duct diameter to a level smaller than the boundary layer of flowing air. If reducing diameter also helps with the inverse/square law of the electrostatic fields, that may be a double win.
We must await the results of Dr. Barret’s work with great interest!
I’m guessing this will win the “Product of the Year” award from Nude Sunbathing Voyeur Monthly.