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So, an extension of the Piccadilly Line, with room for wings? |
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"Welcome to Leicester Square International Airport". |
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//I propose the *outwards* runway is built
underground // |
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I have to say, [po], that that is actually a brilliant
idea. So I will. It is a brilliant idea. I take back
all those things I said about you, especially on that
radio interview and the report in the national
press. |
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For one thing, putting outbound runways
underneath the existing ones would double the
airport's capacity with no increase in footprint. |
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For another, it is the taking off that is noisy, not
the landing so much - so this would cut noise
pollution immensely. |
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And for yet another thing, the underground runway
would be weatherproof. |
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Even without massive excavations, this could be
done by building a huge boxed-in structure on top
of the existing runways, and banking up the earth
on either side. The roof now becomes the landing
runway, and the old runway, now enclosed, is used
for the take-offs. |
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The unfamiliar object I am now offering you is a
croissant. [+]. |
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I think an underground airport is a brilliant and
truly visionary idea - coming up with such an idea is
a true mark of genius. |
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I think there are going to be some critical air flow requirements, but I'll wait for somebody who can do maths to address that. |
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And if you could solve those, then why wouldn't landing work as well? You'd just need some funnelly options on the approach. |
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// why wouldn't landing work as well? // |
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3. Rejected landing/go-around. |
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[MB]'s suggestion of building up around the existing runway would work - but not with earth revetments. Some WW2 Japanese carriers built on repurposed cruiser hulls could launch aircraft direct from the hangar, below the main flight deck. |
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The "top" deck would need to be quite high to allow larger aircraft to fully rotate before takeoff. |
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Fire supression systems could be integrated into the structure. |
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Snow/ice clearance on the landing area could be an issue. |
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Awesome [+] I agree, it's not just for takeoffs. I could see landings working. This would allow double-decker airports too. |
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I think asking a pilot to land into a tunnel is
unreasonable. |
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Does it ever happen that, after rotation, a plane
takes off sooner than expected? I can see that being
bad. |
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On reaching the calculated Vr, the procedure is to pull back gently on the yoke to raise the nose. "Gently" is considered important by a significant proportion* of pilots. The aircraft should continue to gain forward speed, and the noise of the landing gear should diminish, then cease. Attitude is maintained until V2 is exceeded, after which it can be adjusted for best rate of climb, or to conform with local regulations, usually concerning noise abatement. |
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It's the failure to lift off after rotation that's a cause for greater concern. |
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*i.e. those that are still alive. |
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//Attitude is maintained// presumably an optimistic
one. |
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More in hope than expectation... |
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// the aircraft resembled a ping pong ball // |
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So, a thin-walled fragile plastic container, filled of air ? Just like the 787, then ... |
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The objective of rotation is to change the angle of incidence of the airfoil with respect to the airflow. If the plane just runs up a ramp, the airflow will still be "head on". |
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The "ski-jump" idea only works for Sea Harriers because they have vectored thrust. On a conventional airframe, the thrust is fixed to be more or less in line with the weight/drag metacenter, to give inherent stability. |
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//Snow/ice clearance on the landing area could be an issue.
— 8th of 7 // |
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Excess heat from the lower structure could be made to keep the upper runways steaming even in arctic storms. In fact there is a pressurized ammonia closed-loop system which will do this without pumps just by laying the. initial piping below the grounds' frost-line, so tapping into waste heat should just increase heat transfer. |
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// the ramp assists in rotation // |
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The ramp will convert some horizontal momentum into vertical momentum. But it isn't "rotation". It isn't changing the angle of attack of the airfoil with respect to the airflow. |
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But it does change the direction of motion of the airplane,
which, when it leaves the runway, will, I think, cause
increased AoA as the airplane starts to be a bit more
successfully pulled down by gravity, flattening its
trajectory. |
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Indeed ... co-incidentally, at one of the worst possible moments to have to trade airspeed for lift. But don't let that stop you trying it, please ... just let us know where and when, so we can set up the video cameras. |
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//The "ski-jump" idea only works for Sea Harriers
because they have vectored thrust.// |
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Nope. The Admiral Kuznetsov, of recent news
prominence has a ski-jump deck and launches regular
aircraft like the Su-33 |
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//The ramp will convert some horizontal momentum
into vertical momentum. But it isn't "rotation". It isn't
changing the angle of attack of the airfoil with respect
to the airflow// |
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That's complex. As soon as the aircraft leaves the ramp,
it is effectively "rotated" in that it has significant AoA
relative to the free air. It changes very quickly from ~2-
16 degrees. There's all sorts of complexity at the ramp
edge that is beyond my pay grade, so let's not go there.
What the ramp does do is change the thrust vector to
have an "up" component. Because of the deck shape,
the drag component is directly opposite to this aligned
along the aircraft's longitudinal axis, the least draggy
way of doing it. The change in AoA is achieved by rolling
wheels along a pretty smooth surface, but you're right,
there is no increase in AoA while the aircraft is on the
ramp. |
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Contrast this to a conventional take off. Rotation is
achieved by pulling back on the stick, the elevators are
now producing enough negative lift to oppose the
weight of the front of the aircraft and create a moment
around the undercarriage. While this is happening, you
can effectively subtract the elevator lift from the wing
lift. So at the beginning of rotation you have lower net
lift and a whole lot of extra drag from the elevator
deflection. Now, the aircraft will take off because this
is temporary, once the AoA increases the lift from the
wing increases dramatically (and the pilot will take off
some elevator). At this point there is a major difference
between conventional and ski-jump vectors. The ski-
jump has lift and drag exactly opposite, the
conventional aircraft gains a vector. The drag is now of
the aircraft at 10 degrees or so, which is much more
draggy. |
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The ramp effectively get's the plane the first few feet in
the air with no increase in drag. |
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I think one argument against a ramp would be that a
late abort would be expensive. |
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Now, regarding the main idea, it's ideal. Apart from the
significant drawbacks. |
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While you may be able to take off from the lower
runway at the same time as another aircraft lands
above, what happens if the landing aircraft needs to go
around? Now you have two aircraft taking off into
roughly the same airspace. You could do opposite
directions, but then you have aircraft taking off into a
descending stream of aircraft and the wind will be non
optimal for one of them. |
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Taking off out of a tunnel has a lot of problems at the
transition too. Nearly all the instruments are going to
be messed up by a sudden change in temperature,
pressure and wind direction, you could have a fairly
open-sided structure at the business end to combat
those issues though. |
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The aircraft in the tunnel will be hidden from ATC
unless you build in a system to complement the existing
ones to give a comprehensive overview. |
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The proposed extra runway is supposed to be parallel
and north of the existing ones. I'm not sure that's super
smart, they could build one on a NE/SW axis over the
SW road/T4 area. It wouldn't increase capacity as
much, you'd have to stagger TO/Landings as the paths
potentially cross, but you'd have more area to move
around on and it aligns with the other major wind axis.
So you'd gain reliability. |
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How is this great idea different to that of the equally great [hippo] one in the link? |
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Ground effects of trying to float inside a tunnel could get
interesting and partially self-defeating. |
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If there could be a very large turbofan at the slow end of
the runway sucking air through, the plane could have a nice
headwind all of the time. |
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[bs0u0155], re simultaneous take-offs and landings.
I was thinking the same thing; while (in theory) you could, you wouldn't want to. But you could do taxiing etc on one while the other gets used, to speed up aircraft movements. Definitely top for landings only, bottom for take-offs only. |
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Ahh, one problem I just though of: if a landing "overshoots" the end of the runway (while wheels are on the ground)... You would want 1km or so of "emergency" strip past the end of "normal usage" runway. |
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Do planes need more space to take off or to land? I'd
assumed they need more space to take off (since
they can only accelerate as fast as the engines will
go, but can presumably brake a bit harder), but then
again a mis-judged landing may start further down
the runway, whereas the starting point for a take-off
is pretty well under the pilot's control. |
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Take off is normally 20-50% longer than landing for garden
variety commercial jets. |
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There's a lot of variables in there. They account for engine
failure at the worst possible time at max weight, for
example. Braking distances normally assume no thrust
reverse is in place and a tire or two missing. |
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//Take off is normally 20-50% longer than landing for
garden variety commercial jets. // Blimey - I
never realized they could operate from such a small
space. |
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Bravo, po, sorry I was late to the party. I think your idea is
visionary, and way beyond the current trends in thinking.
Tres bien. |
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I believe the reference is your garden. Apparently the A380
can't reliably get airborne without risking a dunking in the
innermost moat. |
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Oh wait, maybe I read that comment somewhere and thought
it was new. |
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//I believe the reference is your garden.// I don't
think you'd get many aircraft off the ground from my
garden. Croquet hoops, sundials, follies and
groundsmen would keep getting thrown up into the
engines. And in any event they'd never clear the
airship hanger on the near side of the ha-ha. At least
that's been my experience to date. |
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Actually, if you take [po]'s excellent idea to its
logical extreme, and add [pertinax]'s first anno, you
arrive at the possibility of a very-high-speed A380
stopping service that could run from beneath London
out to Heathrow, and thence to any destination other
than the one your baggage has gone to. |
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//While you may be able to take off from the lower runway
at the same time as another aircraft lands above, what
happens if the landing aircraft needs to go around?// |
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The runways don't have to be perfectly aligned. It would
cost a bit more space but the upper and lower runways
could be slightly offset to allow for this contingency. |
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Dear po, I was referring to my rather similar rendition of
[hippo]'s anno. Which leads one to the slightly similar idea
that he once posted. That is like yours. Do you get it now? |
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Yes. The merest mention of Thunderbirds is enough for me. |
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// Does it ever happen that, after rotation, a plane takes off sooner
than expected? // [MB] |
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Ummm... yeah. KLM at Tenerife. |
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Excellent questions, [xenzag] and [blissmiss]. It's
almost as if the author of this idea posted it
without first doing even the most cursory search for
e.g. "underground airport". |
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Ah, a tunnel filled with fire retardant covered cardboard boxes. The stacking robots are going to have to be much faster .... much faster indeed. |
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On a roundabout. Zebedee would be proud. |
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MFD? No, hislovelyhippo's is generic and wonderful, mine is specific
to taking off at Heathrow. |
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//mine is specific to taking off at Heathrow//
Never
say anything like that in a patent. Heathrow is
merely "a preferred embodiment". |
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Also, if you're going to build a tunnel with a
runway on top, make the runway magnetic. That
way planes can also take off upside down from the
underneathside of it. OK, we may have to start
building planes out of steel, but I'm sure that can
be done. |
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Having to cancel your landing and go round again is no big deal. Have the whole thing be a honeycomb - if you can't make your target runway tunnel the optional go round tunnels are available at all the usual angles. |
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// the required 5.5° glidepath of EGLC. // |
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The approach is a bitch ... not just the glideslope, the whole approach is cramped, low level, and happens very, very fast. We no like. Add in the swirling and buffeting from the numerous tall structures in the vicinity shedding wind vortices and the thought "Give up and go somewhere easier" soon occurs. |
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// Most aircraft operating from LCY can land in a surprisingly short space and take off similarly. // |
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Well, if they want to do it more than once, yes. A C-130 would be favourite. |
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With plenty of runway and no need to stop suddenly, they can drift down with engines at idle and hardly make a sound. It's when they're heavy, and the pilot pulls the props into Beta on touchdown, that it gets loud ... both outside and inside. Very loud. |
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FAB Idea! Will the pilots be transported to the waiting aircraft in a cool way? - say, like in a reclining seat and by a system of tubes, pulleys and levers? Will there be bendy trees and swimming pools which slide out of the way?
Virgil Out |
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// in a reclining seat and by a system of tubes, pulleys and levers? // |
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No, that's just you channeling Wallace and Gromit again. |
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// Will there be bendy trees // |
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Too polluted for trees. Too polluted for cockroaches, and that's saying something. |
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// and swimming pools which slide out of the way? // |
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No, just an expanse of brown, smelly Thames mud. |
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[8th] not understanding Brit humour as always. Probably the cabbage
diet he maintains or something. |
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[@8th] {One more level of indirection required.} |
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Err, if they went the WS-125 nuclear powered plane route, then... the plane lands on a spun-up wide but not long conveyor belt - which is a smidgeon below taking off speed - the passengers could using a sealed tunnel to get off, and the next lot could get on. |
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All of this would take up less horizontal space than a runway. |
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// [@8th] {One more level of indirection required.}// Like this? Or maybe
&(// [@8th] {One more level of indirection required.}//) |
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