Designing the Perfect Airport Runway

Designing the Perfect Airport Runway

This episode of Real Engineering is brought
to you by Brilliant, a problem solving website that teaches you to think like an engineer. Last year there were over 4 billion passengers
in airlines around the world, a figure that grew from about 2.5 billion just 10 years
earlier. The airline industry is big business with
a total revenue of 834 billion dollars expected in 2018. [1] With this kind of money for taking governments
and private companies want to get their share by designing an airport that can facilitate
AND encourage air traffic to pass through it. But if we take a look at the footprints of
some of the busiest airports in the world, there are some patterns, but nothing immediately
jumps as the go to design for air traffic. So let’s demystify some of this mysterious
world of aviation and figure out how to optimally design an airport. In the early days of aviation runways we often
nothing more than a cleared field. The Wright Brothers choose Kitty Hawk, an
isolated strip of beach, because it had plenty of space and more importantly strong winds
to help get their planes off the ground. Today, that practice isn’t all that different. Airports are some of the largest plots of
land allocated for a single use in any city, and wind still dictates their design. Once again, taking a look at runways around
the world, you may not see a pattern at first, but if you overlay the prevailing winds in
their area the pattern becomes clear. [2] Most airports in the Northern Hemisphere,
are alined east to west, which coincides with the most consistent wind directions. Inspect at any airport and it’s likely they
have followed this design principle. This is done to take advantage of the wind,
just as the Wright brothers did all that time ago, because a head on wind adds lift reducing
the power required for take-off, and reduces landing speed. It also maximises the operational hours of
the airport in windy conditions. The alternative is landing with heavy crosswinds,
which is not particularly fun for the passengers or easy for the pilot, if the pilot can land
at all. The crosswinds a plane can tolerate differ
with plane design, with planes with larger vertical surfaces like winglets and vertical
stabilizers being more susceptible to crosswinds pushing them off course. A typical plane like a Boeing 737, the most
common airliner on the planet, can tolerate a crosswind of about 60 km/h [3] with a dry
runway and 55 on wet. Anything exceeding that and planes need to
hold until winds calm down, or divert to an alternative airport. Tailwinds are even less tolerable with winds
from 18-25 km/h making it too dangerous to land at any, but the longest runways. Some Airports, like London City Airport, have
to enforce their own crosswind tolerances below plane tolerances, as their runways are
narrower than average. Fortunately tailwinds are easy to counteract
by landing in the opposite direction. NATs, formerly known as ‘National Air Traffic
Services’ , illustrated how these shifting winds affect air traffic with UK Air Traffic
data from February 14th 2014. On that day winds of up to 110 km/h were recorded,
making it impossible for aircraft to land all over the UK, causing towering holding
stacks to open over London airspace, with the lower aircraft waiting for a break in
the wind to land. Yellow flight paths here are delayed planes,
which were approaching two hours, red flight paths are diverted planes. This is an extreme case, but this incident
cost these airports and airlines massive amounts of money. Designers of airports will analyse decades
of wind data to minimise any possible operational shutdowns like this. [4] This is our first design principle to maximise
traffic, to simply minimise shutdowns due to wind. Now that we have chosen our runway direction,
let’s pick a location in our city to place our airport. With this wind alignment in mind, let’s
say East to West for this example, most city airports will attempt to place the airport
on the Northern or Southern edge of the city, so low flying aircraft coming in to land don’t
have to fly over the city. This is the case for most airports. But Heathrow airport is a special little butterfly
located smack in the middle of London. This is fantastic for accessibility with London
city centre only a short train ride away, but it creates problems of its own. The first is noise. In the 1950s the owners of Heathrow signed
an agreement with the residents of Cranford to not allow planes to take off to the east,
which is often needed as the wind blows from the East about 30% of the time in London. This was done to reduce noise over the most
populated area neighbouring Heathrow. This agreement is no longer in place, but
it still affects how Heathrow operates. It runs a policy of runway alternation. From 6 am to 3 pm, planes will land on the
Northern runway and take-off from the Southern Runway. Then the moment the clock strikes 3 they switch,
with planes taking off from the Northern runway and landing on the South. This order also flips every second week. All of this is done to give the residents
around Heathrow some relief from the constant blaring of jet engines over their homes. Not an ideal situation when trying to run
a busy airport. [5] Parallel runways like this are great for traffic,
as two planes can land and take-off simultaneously. Once again maximising traffic. You can see two planes landing at the same
time at Heathrow, typically between 6 am and 7 am when departures are quiet, but you do
need space between the runways The FAA specifies that parallel runways with centrelines spaced
760 to 1300 metres apart must use staggered approaches, meaning planes cannot land side
by side Runways with centre lines spaced between 1300 metres and 2700 metres can land simultaneously
with air traffic control monitoring. Seeing a flight land alongside your own is
a pretty common sight at LAX for this reason with it’s runway pairs 1.4 kilometres apart, and even though Gatwick Airport has two runways
it operates as a single use runway as they are too close to each other to work simultaneously. The alternative to parallel runways are intersecting
runways, and while these are more space efficient, and can provide alternative approaches with
a shift wind patterns, they come with their own risks and require careful monitoring by
air traffic control to prevent crashes. In general a single runway operating both
take-offs and landings can achieve a similar throughput of aircraft if wind conditions
are favourable. [6] So when looking to increase air traffic volumes,
placing additional parallel runways at least 1.3 kilometres apart is best. This is where Heathrow runs into its next
design issue. It’s location has made it near impossible
to expand. Heathrow is now operating at 98% capacity,
and being the UK’s hub international airport increasing capacity is a major concern. So where can we place another runway? Let’s see. Hmmm nope, no, nope, definitely not, that
won’t work…..or will it. Amazingly this was the proposal set forth
earlier this year that will require a village to be bulldozed and a tunnel dug to reconnect
the M25. This will cost 3.3 billion dollars for compulsory
land purchases alone, with a further 18.4 billion for the expansion itself, though the
British Government has promised this bill will be entirely privately funded. [7] Under its current format, Heathrow is constrained
to about 480,000 flights a year, but they have managed to continually grow passenger
numbers by increasing the numbers of large long haul flights passing through it, but
this is not an option for all airports, as their runways are too short. Take Dublin airport as an example, it currently
operates two intersecting runways. One 2623 metres long and another 2072 metres
long. To see why this is a problem let’s analyse
runway length requirements. Basic runway length is determined by airplane
performance, and to calculate it we analyse the critical moments in an aeroplanes take-off
sequence. A plane hits 6 critical speeds during take-off. The first is the stall speed, this is the
minimum speed at which a plane will remain airborne. This is not used as the take-off speed, as
any decrease in speed due to fluctuations in wind or orientation of the plane will cause
the plane to fall. The next critical speed is the minimum control
speed, this applies to multi-engined aircraft only. If a multi-engined aircraft loses an engine,
the uneven thrust between the wings will cause the plane to turn, this is called yaw in aviation. To counteract this the rudder will be deflected
to provide the opposite yawing moment. The rudder needs air passing over it to work,
and thus the minimum control velocity is the velocity at which the rudder can provide enough
of a yawing moment to keep the plane straight in the event of an engine failure. The next speed a pilot needs to worry about
is V1. V1 is a line in the sand for pilots making
a decision whether to abort a take-off. If something happens before V1, like an engine
failure, the pilot must abort the take-off. If it happens above V1, they must continue
with the take-off, as it would be unsafe to stop. This is the most important speed for runway
designers. At this speed the plane will need enough distance
on the runway to safely bring the plane to a stop, which is exactly the same as the distance
needed to reach V1. The resulting total runway length is thus
called the balanced field length. Back to that in a moment. The 4th critical speed is Vr, or the rotation
speed, this is the point the plane can begin to lift its nose up and begin it’s ascent. The next speed, which results in some of the
coolest testing videos, is the minimum unstick speed, Vmu, this is the speed the plane can
take-off at its maximum pitch, which is actually the point where the tail skid hits the ground. This is a video of a test pilot testing this
speed. Since this would be incredibly uncomfortable,
the actual take off-speed is at least 10% higher than the minimum unstick speed. At this point no part of the plane is touching
the ground, and it is officially airborne. It must then accelerate to it’s climb speed
V2, which it must achieve with a minimum clearance of 10 metres from any obstacle. With all this in mind we can begin designing
our runway length. Planes are typically designed to use standard
runway lengths, and not the other way around, but these speeds can vary between different
aircraft, so let’s start our calculation with the world’s largest plane the Airbus
a380. Here we will be assuming a maximum take-off
weight at sea-level with the international standard atmosphere model for weather conditions,
and no wind. A typical decision speed of a fully laden
a380 is about 280 km/h, or about 78 metres per second. This, along with other critical speeds, do
vary with flight conditions and will vary for the runway itself. The pilots have a flight computer to output
the relevant critical speeds for this reason, and gives them an appropriate thrust percentage
to provide the acceleration needed. This is just an example. Assuming an average acceleration of about
2 metres per second squared we can calculate the distance needed to reach v1 by employing
one of the fundamental kinematics equations every high school student learned in physics,
specifically this one. Initial velocity is zero and we can rearrange
the equation to find distance. Applying our variables and we get a distance
of 1521 metres to reach v1. In the event of an aborted take-off the plane
will need an equal distance to bring the plane to a stop, this is called the balanced field
length. Which is simply double this distance at 3042
metres. Again this value varies wildly and v1 is dictated
by the runway available, not just the plane performance. This graph provided by airbus, shows the various
runway lengths needed for the a380 at various take off weights and altitudes, and agrees
roughly with our calculation [8] So, as you can see, Dublin Airport’s runways
are too short to accommodate fully laden planes like this. Large long haul planes can and do land here
when needed, but cannot take-off with a full tank of fuel and passengers on board, which
prevents any large long haul carriers from operating from Dublin. Thus a new runway is being built to run parallel
to the existing longer runway to the South, but even this may be too short. As winds and weather will increase the runway
distance needed, on top of this Dublin airport is 75 metres above sea level, which would
add about 2% to runway length requirements, as the thinner air reduces the lift provided
by the wings, and thus increases the take-off speeds. The longest runway in the world in Tibet at
an elevation of 4334 metres or 14,219 feet is 5.5 kilometres long for this reason. The temperature of the air at the airport
also has a significant effect on runway length requirements, with an additional 1% of runway
length required for every 1 degree celsius over the standard atmosphere measurement we
used earlier at 15 degrees celsius. Once again this is a result of reduced air
density reducing lift capabilities. Last year this actually resulted in flights
being delayed and cancelled out of Phoenix Arizona when temperatures rocketed to 49 degrees
celsius. Clearly, designing airports is a tricky and
expensive business. If money and space wasn’t an issue the ideal
design would simply be multiple parallel runways spaced about 1.3 kilometres apart. The busiest airport in the world the Atlanta
International Airport runs 5 parallel runways.Beijing comes next, running 3 parallel runways each
far enough apart to run simultaneous operations, and long enough to accomodate any plane. Dubai Airport coming 3rd with it’s two parallel
runnings each over 4000 metres long due to the heat of Dubai, allowing it to be one of
the world’s most important stop over points for long haul carriers. This pattern reoccurs all over the world. International airports with parallel runways
long enough to accomodate large planes are consistently the busiest, but with limited
space available some alternative designs have been proposed to increase capacity, like this
circular runway design. Which would not only be a nightmare for air
traffic control trying to direct airplanes AND make it even more difficult for a pilot
to land and take-off, but would also only be useful in calm weather with no wind dictating
take-off direction. These are the kinds of issues that are only
found when engineers carefully analyze a problem. Without paying close attention to detail,
it’s easy to fall into the trap of thinking a design that looks promising on the surface
will work. And if you want to improve your own analytical
skills, a great place to start would be this course on logical thinking on Brilliant. Logic is the foundation of all problem solving
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and combining it to come to a new unique conclusion. Training our logical thinking encourages people
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of logic to understand fun riddles. These may initially sound complicated and
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100 thoughts on “Designing the Perfect Airport Runway

  1. You may have noticed little numbers popping onto screen throughout the video. These are referring to references in the description of the video. This was inspired by my friend, Simon Clark. Specifically this video: Props go to him for the clever technique.

  2. Why don’t pilots use WASD controls?

    I think implementing WASD controls on planes will make it so gamers can become pilots

  3. Hello, I'm really interested in how you got your wind distribution maps. I've love to use them for my projects. Would you be able to tell me the source? Thanks!

  4. I think you dismissed circular runways too quickly. On the contrary, air traffic control could choose any segment of the circle and essentially eliminate crosswinds. Also, runway length and all associated calculations could be dismissed.

  5. If parallel is better then why does Denver (KDEN) have runways going North/South and East/West? They have plenty of room to add parallels too.

  6. Real Engineering: “Seeing a flight land beside you is a common sight at LAX”

    SFO: Am I a joke to you?

  7. Take a look at Kingsford Smith International in Sydney, Australia for an example. 3 things about it,
    1. The airport must close Entirely from 11pm – 6am due to the position of the airport being so close to suburbs of Sydney. The only exception is emergency aircraft, otherwise, the airport is closed to All aviation all night long.
    2. There is only 1 runway (out of 3) that is long enough for the largest of aircrafts to land on it.
    3. There is no possible way to expand the airport due to its position being so close to residential areas. There was a proposed idea to build a second airport opposite the current one but it got scrapped a while ago.

  8. The Airbus may be big, but it's most likely not the biggest
    One of the biggest planes, if not the biggest, is the Antonov AN-225

  9. Strange that you didnt mention anything about radars, in video which is about perfect airport. Radars are one of the most important things in the subject. One of the most important ones to have, especially on busy airport is ground and waether radars. So you can see where the planes are even in heavy fog or other extreme weather. While weather radar are to detect those crosswinds you mentioned, which are very important to detect. In order to takeoff or land safely. Other important radars are ESR (En Route Surveillane Radar), TAR (Terminal Area Radar) and PAR (Precision Approach Radar). Also, if i recall correctly you didnt mention anything about calculating take off weight. Which also affect on V1 speed. Calculating that wrong can also lead to crash as have happened few times. And too far away locationed weather radar was the reason to one close call crash where crosswind was way more powerful which the plane were controllable. Missing an ground radar was one reason what led to deadliest aviation crash in history. Which also was affected by misscommunication and missunderstandings aswell.

  10. The engineers working on airport design are horrible. Make a hexagram landing strip aligned to the prevailing winds of the location. This gives you the best possible take off and landing pads in all conditions, temperatures and wind conditions. It's not rocket science. Idiots.

  11. Some of the busiest airport in the world: Heathrow… yeah, Atlanta….yeah, Dublin….No Dublin is nowhere near one of the worlds busiest

  12. How about a runway that looks like a swatsika? Please don't understand that wrong, but wouldn't that be pretty optimal and space efficient? Or is there an flaw that i didn't see when i just thought about it?

  13. Heathrow is at the very edge of Greater London, not in the centre of London. Originally part of Middlesex, and even then at the edge furthest away from London.

  14. Yeager airport in Charleston WV is a nightmare to land on. It’s on top of a mountain and you feel like you’re gonna go flying off every time you land. Luckily they mainly fly out Boeing 717s and MD-80s

  15. Balanced field length is when the accelerate stop and accelerate go distances are the same distance … not exactly what is said in the video (or maybe I misunderstood the explanation in the video). Otherwise I love this channel and the video is great.

  16. 13:30
    Some four year old child designing a runway: 'This circle runway will be great! I can't see any problems at all! '
    Real Engineering: 'These are the kinds of issues only found when engineers carefully analyse problems…'
    Real Engineering viewer: 🤔🤔🤔 seems legit.

  17. Actualy your wrong about the airbus a380 being the largest aircraft isnt antonov an 225 the biggest ang heaviest pane ever built.

  18. You kept showing recent footage from DCA, but never referenced it in the examples used…. it is also a very unique airport with slot controls, limited radius served, proximity to highly sensitive ARSA, and lots of political aspects… if I can ask, why did it not show up in your discussion ? Oh, and I've worked there for 25 years !

  19. Heathrow was originally built with 6 runways of equal length, laid out in the star of David design. This was due to all aircraft using it being prop driven. whilst 27R &27L have been extended to cope with jets, the original runways can be determined as some remain as taxiway. Before it was a civilian airport it was a large grassed field commandeered for WW2 use. The original design of the star of david layout ensured all wind conditions could be coped with.

  20. Man you missed out on the Adolfo Suarez Madrid Barajas Airport, it runs quad runwas of wich to main ones, 4500m each and for these one secondary runway 3500m, size-wise it is bigger than the 2nd largest you named… And its Ms of runway per passenger isn't that different 0.00012093379m/pas. against 0.00012059117m/pas. it isn't that different and I beleive "size does matter." I'd be pleased to know you at least considered the fact and didn't just go on google and type "biggest airports annual traffic" and that you used the 2017 results as the 2018 are preliminary and the 2019 aren't even out.

    Signed, a preocupied Subscriber.

    Thenk You

    P.D. PLs respond I am a bit worried…

    P.P.D. I have said Madrid barajas airport because I live in spain and noticed the Beijing airport isn't thet big, but I am sure there are others…

  21. I agree with you, but you forgot one thing. Performance factors.

    If you have wet runway you have to multiply distances by 1.15 for landing (LDA)

    And what is more important is the safety margins. If you fly with a plane where it is needed 1000 meters to stop and the runway available is 1300 meters you are NOT allowed to land, in this case minimum RWY distance for you to legally land must be 1420 meters. Same with T/O but you have to multiply by 1.25.

  22. I remember how popular the circular runway was for a long time. People were going “it’s the future” (cnn, Fox, etc) and no one even considered how much of a pain it would be. Thanks for not siding with designers. Engineer gang for life

  23. The best runway in the world is KSP's. You cannot land anything on it. Not because it's too short or surrounded with mountains… No, just because the physics make planes almost impossible to control !

  24. Circular runways. 13:25 “These are the kinds of issues that come about only after engineers carefully analyze the design”

    I don’t think it takes much thought to shoot that one down.

  25. This video is incorrectly named. It does not really address the perfect runway. It is focused on Heathrow Airport having outgrown its useful life in its current location. The airport closer to the "perfect runway" would be something like Dallas-Fort Worth, but there's no way to fit that airport anywhere near London. No disrespect intended to London – it's just got no space to put a new airport.

  26. I'm not even an engineer and I can think of several reasons why a circular runway would probably be a bad idea…..

  27. Eh, as soon as we get fusion reactors small enough to shove on an airliner, we'll just make them all VTOLs while we're at it.

  28. ahhhh 21bn dollar privately founded… come visit Berlins Ghost airport… we tried and failed… still not open and it wont be until 2021…

  29. This missed alot of basic information on runway design take off speed and distance. Like why it's common to see runways going in different directions or how wind speed affects take off speed and distance.

  30. Istanbul New Airport also will have 5 parallel runways once all the phasses completed. Right now, there are 2 parallel runways, which are 4100 m and 3600 m along.

  31. That circular run ray really scares me, the fact someone would come up with that idea means they have no knowledge of aircraft. And as a pilot myself that’d be a nightmare even in my bonanza

  32. Why most of runways I saw, were not flat? They were very wavy and I can't understand why; is there anyone who can help me? Here the wavy runways I saw:

    Thank you 😊

  33. Maybe stupid but since take off and landing are the most dangerous and fuel consumption moments, what about an arm or a launcher to litteraly take the plane ?







  35. The longest runway in the world is in China: Qamdo Bamda Airport in China has the longest paved runway in the world at 18,045 feet.

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