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Tower Fans for Liftoff

For use when extreme heat might delay flights due to altered liftoff conditions
 
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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?
21 Quest, Oct 28 2013

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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.
jurist, Oct 28 2013
  

       We used to have to lighten the load for takeoff at certain times at Duke Field, FL.
21 Quest, Oct 28 2013
  

       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.
Voice, Oct 29 2013
  

       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.
ytk, Oct 29 2013
  

       Will this not just create a large area jet wash over the runway, right in the ground effect ?
  

       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.
  

       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.
  

       We consider steam catapults a better option.
8th of 7, Oct 29 2013
  

       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.
Vernon, Oct 29 2013
  

       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.
21 Quest, Oct 29 2013
  

       All things being equal, mechanically introducing density would be a drag.
4whom, Oct 29 2013
  

       I like [Vernon]'s solution though. Doesn't have to be liquid air though. Sublimating solids would work, dense gasses would work....
4whom, Oct 29 2013
  

       ... as long as they don't displace oxygen, which would be a problem for the aircraft engines.
lurch, Oct 29 2013
  

       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.
4whom, Oct 29 2013
  

       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.
scad mientist, Oct 29 2013
  

       How much benefit would be gained simply by painting the runway white so it does't get as hot?
scad mientist, Oct 29 2013
  

       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.
21 Quest, Oct 29 2013
  

       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.
  

       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.
8th of 7, Oct 29 2013
  

       An alternative way to cool the runway would be to install a cool water circulation manifold beneath it.
21 Quest, Oct 29 2013
  

       Or make it out of ice.
the porpoise, Oct 29 2013
  

       Perhaps some industrial grade coolth projector?
  

       A series of large parabolic reflectors around Pluto ready to beam down cool onto the runways,
not_morrison_rm, Oct 29 2013
  

       [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.
Vernon, Oct 29 2013
  

       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.
lurch, Oct 29 2013
  

       How about just douse the runway with water? And there could be spritzers spritzing merrily. Planes are fine with being spritzed.
bungston, Oct 30 2013
  

       //But tarmac is surprisingly reflective; from altitude all runways tend to appear pale grey- brown in strong light, irrespective of their construction material.//
  

       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.
  

       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.
spidermother, Oct 31 2013
  

       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).
not_morrison_rm, Oct 31 2013
  
      
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