h a l f b a k e r yWhat's a nice idea like yours doing in a place like this?
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Huge fan towers mounted at the ends and sides of runways in
extremely hot locales to concentrate the air along the runway until it is
dense enough to achieve liftoff. Thoughts?
[link]
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That seems like a really interesting idea. I've been at Burbank, CA (BUR) when temperatures above 100 degrees F caused carriers to offload fuel so that they could takeoff with reduced weight, only to have to shuttle to another nearby airport to refuel at a lower temperature so that they could continue to fly across country. Your tower fans might have helped a lot of passengers maintain their travel schedule, while simultaneously saving the fuel expended in unnecessarily repeated takeoffs. |
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We used to have to lighten the load for takeoff at certain times
at Duke Field, FL. |
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For density the turbulence will destroy you. Rather
lay an extra several hundred meters of runway and
use the fans to create an artificial wind to let the
airplanes get high enough to be safe before the end
of the runway. |
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Even assuming this would work, you might get a few feet
off the ground, and then what? You're back to the same old
density air as you otherwise would have had, resulting in a
very short trip. It's the same basic problem as wind shear,
really. Just being able to get off the ground isn't enough if
you can't sustain lift. |
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Will this not just create a large area jet wash over the runway, right in the ground effect ?
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Bouncing the wake vortex of an airliner is an interesting experience, if you're ready for it. The idea proposes deliberately creating a huge multiple vortex, presuming something like an array of high-bypass turbofans are used.
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The Dyson "air multiplier" technology would offer a turbulence-free alternative but the structures would be very big, and vulnerable to weather when not required.
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We consider steam catapults a better option. |
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Maybe just release a cloud of evaporating liquid air
onto the surface of the runway, just before the
plane starts its acceleration run. The liquid air
should be injected from below-ground-level all along
the length of the runway. |
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I thought of that but the fans are just plane awesome, and the
resulting cloud might hamper visibility. I never said, by the way,
that the fans had to be blowing on full power. |
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All things being equal, mechanically introducing density
would be a drag. |
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I like [Vernon]'s solution though. Doesn't have to be liquid
air though. Sublimating solids would work, dense gasses
would work.... |
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... as long as they don't displace oxygen, which would
be a problem for the aircraft engines. |
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Quite right [lurch], but dense gasses could be mixed with
that in mind. And sublimation techniques are advanced
enough, thanks to DDS technology, to allow for oxygen to
be available. My worry with sublimation, apart from cost
and complexity (obviously), is temperature. |
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So use liquid oxygen. Cool the air AND give a little boost to the engines. But be sure to stand back. This could get messy. |
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How much benefit would be gained simply by painting the runway white so it does't get as hot? |
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Scad, the gout of flame from the Gas Turbine Compressor would
not mix well with a heavily oxygenated environment, and
visibility would be horrendous with a white runway under a
blazing sun. |
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Doesn't help that much. As airfields are large, flat areas and free from obstructions, the slightest breeze will move air in from surrounding areas. The hotter runway surface may generate a small amount of convection, drawing in air from the sides. But tarmac is surprisingly reflective; from altitude all runways tend to appear pale grey-brown in strong light, irrespective of their construction material.
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It's the scale of the problem that needs to be considered here. A typical runway is going to be not less than 2000m long, and 50m wide; 100,000 m2. With solar gain of 0.5kW/m2, not an unreasonable figure, that's 50MW. Given a heatpump efficiency of 2:1, you'll need 25MW of power just to stop the the runway surface getting any hotter ... if you want to significantly cool the runway and all the air in its immediate vicinity, the energy demand is orders of magnitude greater. |
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An alternative way to cool the runway would be to install a cool
water circulation manifold beneath it. |
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Perhaps some industrial grade coolth projector?
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A series of large parabolic reflectors around Pluto ready to beam down cool onto the runways, |
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[lurch], I specified liquid air specifically because it
has the same oxygen percentage as regular air. But
perhaps instead of being directly placed on the
runway, it might be passed through some heat-
exchangers on the way toward the runway. The hot
sun would supply the heat, and the formerly liquid air
would emerge not-as-dangerously cold, but still
plenty dense-enough to help planes get into the air. |
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Problem is, at a point just past where you're [cooling the air
| replacing the air with cooled air] the velocity necessary
for flight is the same. It's like [ytk] said, you need sustained
lift past the runway - you need more speed. Put the dense
cool air where the engines can ingest it and get better mass
flow - that makes more thrust, so your airplane will be
going faster by the time it gets to the end of the runway. |
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How about just douse the runway with water? And
there could be spritzers spritzing merrily. Planes are
fine with being spritzed. |
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//But tarmac is surprisingly reflective; from
altitude all runways tend to appear pale grey-
brown in strong light, irrespective of their
construction material.//
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Perhaps you need to recalibrate the cube's remote
sensing systems, or budge out to where you're
not having to look through so much of the sun's
corona.
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Listed albedo figures for tarmac are 0.04 to 0.12. It
may appear relatively bright because most of the
earth's surface - excluding particularly reflective
things, such as snow, beaches, and clouds - is also
towards the lower end of the albedo scale. |
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Once again, gravy would seem to do the trick, being much denser than air, so the airplane would gain more lift. I rest my case (full of shares in Bisto). |
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