people are anxious about pollution, noise, wildlife issues, destroying cute little villages etc and I have much sympathy for all that.
I propose the *outwards* runway is built underground and aeroplanes emerge from the tunnel in true Thunderbirds style.
I don't think it would work for planes landing at Heathrow but its a start.-- po, Oct 26 2016 Underground_20airport [hippo, Oct 26 2016] Ski Jump Take Off Vectors http://www.scienced...i/S1000936112000155 [bs0u0155, Oct 27 2016] King's Cross Airport https://www.ianvisi...ings-cross-airport/ [Dub, Nov 12 2016] So, an extension of the Piccadilly Line, with room for wings?
"Welcome to Leicester Square International Airport".-- pertinax, Oct 26 2016 //I propose the *outwards* runway is built underground //
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.
For one thing, putting outbound runways underneath the existing ones would double the airport's capacity with no increase in footprint.
For another, it is the taking off that is noisy, not the landing so much - so this would cut noise pollution immensely.
And for yet another thing, the underground runway would be weatherproof.
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.
The unfamiliar object I am now offering you is a croissant. [+].-- MaxwellBuchanan, Oct 26 2016 I think an underground airport is a brilliant and truly visionary idea - coming up with such an idea is a true mark of genius.-- hippo, Oct 26 2016 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.
And if you could solve those, then why wouldn't landing work as well? You'd just need some funnelly options on the approach.-- normzone, Oct 26 2016 [+] for the idea.
// why wouldn't landing work as well? //
1. Flarepath visibility
2. Wave-off
3. Rejected landing/go-around.
[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.
The "top" deck would need to be quite high to allow larger aircraft to fully rotate before takeoff.
Fire supression systems could be integrated into the structure.
Snow/ice clearance on the landing area could be an issue.-- 8th of 7, Oct 26 2016 Awesome [+] I agree, it's not just for takeoffs. I could see landings working. This would allow double-decker airports too.-- ixnaum, Oct 26 2016 I think asking a pilot to land into a tunnel is unreasonable.
Does it ever happen that, after rotation, a plane takes off sooner than expected? I can see that being bad.-- MaxwellBuchanan, Oct 26 2016 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.
It's the failure to lift off after rotation that's a cause for greater concern.
*i.e. those that are still alive.-- 8th of 7, Oct 26 2016 //Attitude is maintained// presumably an optimistic one.-- MaxwellBuchanan, Oct 26 2016 More in hope than expectation...-- 8th of 7, Oct 26 2016 // the aircraft resembled a ping pong ball //
So, a thin-walled fragile plastic container, filled of air ? Just like the 787, then ...-- 8th of 7, Oct 26 2016 Yes, it is.
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".
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.-- 8th of 7, Oct 26 2016 //Snow/ice clearance on the landing area could be an issue.— 8th of 7 //
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.
ps. I like this idea.-- 2 fries shy of a happy meal, Oct 26 2016 // the ramp assists in rotation //
No. <sigh>
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.-- 8th of 7, Oct 27 2016 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.-- notexactly, Oct 27 2016 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.-- 8th of 7, Oct 27 2016 //The "ski-jump" idea only works for Sea Harriers because they have vectored thrust.//
Nope. The Admiral Kuznetsov, of recent news prominence has a ski-jump deck and launches regular aircraft like the Su-33
//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//
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.
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.
The ramp effectively get's the plane the first few feet in the air with no increase in drag.-- bs0u0155, Oct 27 2016 I think one argument against a ramp would be that a late abort would be expensive.-- MaxwellBuchanan, Oct 27 2016 Now, regarding the main idea, it's ideal. Apart from the significant drawbacks.
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.
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.
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.
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.-- bs0u0155, Oct 27 2016 How is this great idea different to that of the equally great [hippo] one in the link?-- xenzag, Oct 27 2016 Ground effects of trying to float inside a tunnel could get interesting and partially self-defeating.
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.-- RayfordSteele, Oct 27 2016 [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.
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.-- neutrinos_shadow, Oct 27 2016 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.-- MaxwellBuchanan, Oct 27 2016 Take off is normally 20-50% longer than landing for garden variety commercial jets.
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.-- bs0u0155, Oct 27 2016 //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.-- MaxwellBuchanan, Oct 27 2016 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.-- blissmiss, Oct 27 2016 I believe the reference is your garden. Apparently the A380 can't reliably get airborne without risking a dunking in the innermost moat.-- bs0u0155, Oct 27 2016 Oh wait, maybe I read that comment somewhere and thought it was new.-- blissmiss, Oct 27 2016 Blissy, wot?-- po, Oct 27 2016 //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.-- MaxwellBuchanan, Oct 27 2016 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.-- MaxwellBuchanan, Oct 27 2016 //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?//
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.-- AusCan531, Oct 27 2016 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?-- blissmiss, Oct 27 2016 Yes. The merest mention of Thunderbirds is enough for me.-- DenholmRicshaw, Oct 27 2016 // Does it ever happen that, after rotation, a plane takes off sooner than expected? // [MB]
Ummm... yeah. KLM at Tenerife.-- lurch, Oct 27 2016 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".-- hippo, Oct 28 2016 Ah, a tunnel filled with fire retardant covered cardboard boxes. The stacking robots are going to have to be much faster .... much faster indeed.-- wjt, Oct 28 2016 On a roundabout. Zebedee would be proud.-- wjt, Oct 28 2016 MFD? No, hislovelyhippo's is generic and wonderful, mine is specific to taking off at Heathrow.-- po, Oct 28 2016 //mine is specific to taking off at Heathrow// Never say anything like that in a patent. Heathrow is merely "a preferred embodiment".
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.-- MaxwellBuchanan, Oct 28 2016 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.-- normzone, Oct 29 2016 // the required 5.5° glidepath of EGLC. //
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.
// Most aircraft operating from LCY can land in a surprisingly short space and take off similarly. //
Well, if they want to do it more than once, yes. A C-130 would be favourite.-- 8th of 7, Oct 29 2016 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.-- 8th of 7, Oct 29 2016 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-- Dub, Nov 12 2016 // in a reclining seat and by a system of tubes, pulleys and levers? //
No, that's just you channeling Wallace and Gromit again.
// Will there be bendy trees //
Too polluted for trees. Too polluted for cockroaches, and that's saying something.
// and swimming pools which slide out of the way? //
No, just an expanse of brown, smelly Thames mud.-- 8th of 7, Nov 12 2016 [8th] not understanding Brit humour as always. Probably the cabbage diet he maintains or something.-- po, Nov 13 2016 [@8th] {One more level of indirection required.}-- Dub, Nov 13 2016 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.
All of this would take up less horizontal space than a runway.-- not_morrison_rm, Nov 13 2016 // [@8th] {One more level of indirection required.}// Like this? Or maybe &(// [@8th] {One more level of indirection required.}//)-- pertinax, Nov 15 2016 Don't forget to
#include <EOSSACR.H>-- 8th of 7, Nov 15 2016 random, halfbakery