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MIT and NASA Designing Silent Aircraft
Iddo Genuth writes "Researchers at the Massachusetts Institute of Technology Department of Aeronautics and Astronautics recently won a contract from the National Aeronautics and Space Administration to design quieter, more energy efficient, and more environmentally friendly commercial airplanes. The two-million-dollar contract from NASA is just an initial step in bringing green technologies to the sky."
"Silent" is a relative term, but the presumption is one that has noise levels approaching that of an automobile.
That simply is never going to happen. Moving air around to create thrust will always be noisy. Even if all engine noises are reduced to zero, the vibrations of the air moving at the extreme speeds we would expect will cause more than enough noise. The only way I can imagine to combat that fact would be to distribute the effect over very large areas... and even then, as the size of the air moving system approaches "too big to be practical" it would still likely be way to noisy.
Helicopter style systems would be more of the same.
They are going to go back to Roswell and Area-51 and figure out how the aliens did anti-gravity so we can have aircraft that fly with less thrust requirement.
CA is not "trying" pass a law that would make electric cars have noise generators (it doesn't even makes sense to talk about a state "trying" to pass a law: an interest group might lobby a state for a law, but that's not the state trying anything.)
California rejected (the legislature passed and the governor, citing that the issue was appropriately handled at the federal level, vetoed) a bill that would create a study to committee to determine what the sound requirements were for the safety of the blind around quite vehicles and to investigate means of meeting those requirements.
Presumably, the findings on this could have been used in the future to support legislative proposals for requirements, if both sound types levels which provided notable safety benefits and reasonable means of meeting those were determined; they just as easily could have provided fuel to support the argument that the necessary sound levels would have other adverse effect, be unreasonably expensive, etc., against such a future proposal.
It's true that in many places, in the East Coast and in California, advocates for the blind have lobbied for requirements for noise generators (not just study of the issue), but that's very different from any particular state passing (or even "trying to pass") a law requiring that.
The prop tips on these airplanes reach transonic speeds at full power
Prop designs are tailored for a specific aircraft design and engine combination. Part of the requirement for prop selection is to avoid supersonic or even transonic speeds, even while at full throttle. The reason being, efficiency significantly falls off once a prop begins to reach transonic speeds, let alone supersonic speeds. It is so important to avoid these speeds, well, you now know the origin of the scimitar shaped prop.
In short, if you are flying any Cessna 185, 206 or 207 which has a prop reaching transonic speeds, your prop needs to be replaced as it has been overhauled too many times.