Light Laminar Lifter
From Wise Nano
Light Laminar Lifter (LLL, pronounced "tri-ell") is an efficient, quiet, in-atmosphere lifting/propulsion system.
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Overview
Start with a horizontal "comb" array of long, closely spaced vertical slats, spaced in pairs like so (end view):
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Each slat is covered by a continuous belt running vertically up one side and down the other, so it covers the full width and height of the surface. The belts meet (touch) between the adjacent slats. The belts are driven so they move up where they touch, and down next to the gaps.
The slats and gaps are very small. The belts drag air downward through the gaps.
This Is Not An Airfoil.
Forget what you know about lift, vortices, Bernoulli, boundary flow, etc. The LLL has a Reynolds number less than 100. It is often said that small insects swim, rather than fly, through the air. The LLL climbs the air, like climbing a rope.
Technology assumptions
Nanoscale features (negligible cost-per-feature) Strong materials Small motors Efficient bearings
Dimensions and speeds
We want LLL to be able to climb at 10 m/s.
Slats will be 0.4 micron wide, 20 micron tall, with pairs spaced 10 micron apart. The belt will be 25 nm thick.
Low Reynolds number
The Reynolds number for flow through a tube is rho v r / eta. Near sea level, rho (density) is about 1 kg/m^3 (decreasing by half every 6,000 meters), and eta (viscosity) is about 1.7E-5 N-s/m^2. At 9 microns lattice spacing (r=4.5E-6), the Reynolds number is about 3.
Note that this calculation is wrong for at least two reasons: 1) The air is moving through a slit, not a round tube; 2) the walls of the cavity move along with the air. Both of these should improve the picture.
Low friction
Because the belt is moving at essentially the same speed as the air, there is no friction between the air and the belt inside the slat. The only friction is seen at the tops and bottoms of the slat, where air must be "gathered" to bypass the slat. At the leading edge, the belts sweep air away from the center, creating lower pressure; likewise, there's higher pressure at the trailing edge. This produces friction and contributes to force in the desired direction, but is probably minimal for thin slats (<0.5 micron) and laminar flow.
Worst case, the air is being compressed by 10% and then decompressed. But in fact, only a fraction of a micron of the belt is moving horizontally and tending to compress/decompress the air; what actually happens is that the air in the slots speeds up a bit relative to the motion of the slats through the air. In a larger system, this momentum increase would translate to thrust; here, I'm not sure what it does; I think it cancels out (recovering the energy somehow).
Slat design
The slat is filled with vacuum to minimize friction. It contains rollers to support the belt, and a frame to support the rollers and keep the slat rigid. The belt is a seamless cylinder with conical ends, completely enclosing the slat, and hermetically sealed. The slat design is reasonably dense; assuming conservatively that slats are as dense as solid diamond, the mass per square meter is equivalent to a 2 micron sheet, or 7 grams.
The belt is driven from outside, by another framework that contacts and supports the slats (through the belt) via powered roller bearings.
Sheet loading
So we have a sheet of material that can climb its way through the air at 10 m/s. If it is trying to hover or ascend, it will be pulled downward. According to this page, a loading of about 1 Newton (~1/10 kg) per square meter on a round parachute translates to a descent rate of about 1 m/s. So if sheet weight is 7% of payload, you burn ~10% extra fuel in "parachuting" while rising at ~9 m/s. This may be the main inefficiency!
