
Engineer defends concept circular runway idea - 2manyredirects
http://www.bbc.co.uk/news/magazine-39643292
======
esemor
As an airline pilot flying Boeing 757 and 767 I think this concept is really
cool but it does overlook some fundamental principles of the unreliability of
weather in order to be practical.

This week I have landed in variable winds gusting up to 45 knots and then
every inch of wingtip clerance counts, a drawback of this design.

What if the aircraft makes a long landing (floats) and suddely faces a
different wind component that subjects it to a tailwind.

Also, the full circle would only be useable on zero wind days which makes me
wonder about the economical reality of having a large part of the pavement be
unusable most days.

~~~
rpmcmurphy
I am also a pilot. I'll add to this by explaining a couple of basic principles
in flying aircraft.

The #1 reason this is a very bad idea is it is not compatible with flying
what's called a stabilized approach, which is fundamental to safe landings.
What this means simply is you fly your last (final) leg of approach on a
straight line aligned with the centerline at a shallow glide angle. The moment
before touch down you reduce engine power and flare (bring the nose up) and
stall the wings just above the runway. If you are flying into a crosswind, you
crab (fly with the nose angled into the wind to stay on centerline), then kick
out of the crab angle just prior to touchdown (you control the rudder with
foot pedals). A banked circular runway is totally incompatible with this. If
you misjudge your approach a bit and land long, you miss the runway. You have
to go from wings level to a banked turn at exactly the right moment. Lots of
potential for things to go wrong. It's just a bad, unsafe idea.

Another reason this is bad, higher landing speeds. If you are flying in a
banked turn, your wing will stall at a higher airspeed. Heavy aircraft already
land fast, and anything that adds to that creates problems, wear on tires and
brakes, etc.

These people also seem to be unfamiliar with basic geometry. A "circle-ish"
runway configuration would do the job while retaining long straight runways.
For example, just arrange eight runways in an octagon configuration, with the
airport terminal etc in the center. If you have enough land area to work with,
this is easy. The problem, of course, is that land in large metro areas is
expensive, so you end up with compromises such as intersecting runways as you
see at airports like San Francisco (SFO).

So while this may be fun as a flight simulator challenge, it is a bad, unsafe
idea for the real world.

~~~
tropo
I don't think you need to "go from wings level to a banked turn at exactly the
right moment" for this. There are two ways to make it work.

As proposed, the runway is banked. You bank your aircraft well above the
runway surface. You fly above the runway, possibly following it as your
holding pattern prior to landing. You can keep going around, banked already.
When it is your time to land, you continue around in that bank and descend to
the runway.

Alternately, it could be unbanked with straight landings. This makes the
circle considerably thicker. Landing is quite normal, aside from the runway
markings.

BTW, your "kick out of the crab angle just prior to touchdown" method may be
standard, but it is pretty bad. The B-52 gets this right, with 4 pairs of
wheels that touch the ground at the same time and are all capable of being
rotated.

~~~
rpmcmurphy
The whole point of a stabilized approach is to avoid unnecessary maneuvers in
the final moments of flight, and to simplify decision making. Your approach is
a straight in powered glide. If you like where you end up, you cut power,
flare and land. If you don't like the situation, you apply full power and
climb straight ahead, then turn according to the rejected landing procedure
for the runway or ATC instructions.

What you describe needlessly adds complication to the approach, which adds
risk, which will certainly result in accidents and fatalities. It's just a bad
idea, and there is a reason airport designers never considered this (it is not
as if the idea of banked curved roadways is new).

Sorry as a pilot, I can say this is not just a bad idea, it is a lethally bad
idea. A fun simulator challenge, but not something that will work in the real
world. If you are doubtful, I would suggest you try circling around a point in
IFR conditions within 50' lateral tolerance above a circular runway. Be sure
to add zero visibility and a 10-20 knot cross wind to simulate doing so in the
clouds above the runway as you descend.

~~~
dragonwriter
> Be sure to add zero visibility and a 10-20 knot cross wind to simulate doing
> so in the clouds above the runway as you descend.

With a circular approach to a circular runway, aren't all winds cross winds
(and, also, headwinds _and_ tailwinds)?

~~~
rpmcmurphy
That was a trick suggestion. Also while dealing with flying the airplane, also
be sure to keep track of whether the landing pattern is clockwise, or counter-
clockwise, or was it clockwise, and which heading you are currently on and how
that relates to your rejected landing turn in case you need it, which you
probably will. I don't see what could possibly go wrong.

All I'll say is if I was the head of the programming committee for the air
transport association conference, I would invite the designer to keynote, as
comic relief.

~~~
tropo
I don't see why a human has to do this.

Even if they do, I don't see why it can't be done with an awareness system
like the F-35 helmet. That would let you see the outline of the runway through
arbitrary fog.

There is no special "rejected landing turn". You rise up just a bit, keep
following the runway, and retry when you wish.

~~~
htwillie
> I don't see why a human has to do this.

Because a human driving the plane has a vested interest in surviving the
landing.

A person who writes buggy landing software, or an operator "piloting" it from
the ground can get another job if they fail.

~~~
burfog
The Romans would put civil engineers underneath newly-built bridges, then
march the army over. Very few low-quality bridges were built, and nobody built
more than one low-quality bridge.

This sort of thing works for planes too.

------
2manyredirects
> If someone one hundred years ago would have said that we would be
> transporting as many passengers in aircraft as we would in trains, people
> may have thought , "a steam engine would never fit in an aircraft made of
> wood and ropes".

That's such an eloquent way of highlighting the need for conceptualisation in
engineering but also the struggle to convince others (investors perhaps) that
you're not a complete nutcase when you think outside the box.

~~~
avar
If you're struggling to convince others it's best to leave the Galileo fallacy
out of your arguments.

Just because something was thought to be ridiculous in the past and now we
know better, that doesn't mean that your seemingly ridiculous idea is just as
misunderstood and underestimated as that other idea was at the time.

------
jenhsun
Opposite Opinion: REALITY CHECK: CIRCULAR RUNWAYS
[http://theavion.com/reality-check-circular-
runways/](http://theavion.com/reality-check-circular-runways/)

~~~
EliRivers
Not to disagree with anyone, but just thinking out loud, some of those
arguments seem valid only because the current means of flying assumes straight
runways. Like the ones about how existing instrument systems and procedures,
made for straight runways, will be inapplicable to circular runways.

------
srigi
Under one of the original articles, in the comments section some military
pilot pointed that lateral forces on big airliner on this runway would break
the fuselage and gear of the plane. I'm disappointed that this argument wasn't
addressed in todays article.

~~~
nikcub
Given a radius of a curve and bank angle it is simple to calculate what the
minimum required speed is to have 0 lateral force

~~~
rpmcmurphy
If only airplanes all landed and took off at the same speed. Actual take off
and landing speeds will vary depending on the aircraft's characteristics,
fuel/passenger load, wind conditions, and density altitude (which varies
depending on temperature and humidity). So the idea that you could build a
runway with a bank angle that produces 0 lateral force for all aircraft is
just not possible. Sorry.

~~~
alejohausner
Why couldn't the runway adapt to these conditions? Why not arrange gigantic
superfast hydraulic jacks all along the track, to vary the runway's tilt,
according to the needs of the current aircraft? Oh and very flexible and
strong runway materials to handle the change in circumference. As long as
there were no power failures, this would be a piece of cake.

Frankly, the circular design isn't ambitious enough, as initially proposed.

~~~
htwillie
Yeah - make a huge rotating disc of a runway that rotates at a constant speed,
so the pilot can stick the landing at whatever radius has an angular velocity
equal to groundspeed.

Then slow down the disk enough to allow taxiing toward the center exit drain.

------
mrfusion
I'm thinking if we ever figure out a way to reduce airport foot prints it
could drastically drop housing costs. There are hundreds? Of acres of prime
urbanish land.

Look at Boston for example. I wonder if they take the opportunity cost of
having an airport there into the cost of flying? That land could be worth 100
billion??

~~~
matt4077
It's a drop in the bucket if you look at the percentage it would add to total
available land, and also considering that the ground isn't usually the most
expensive part of construction, and that most airports are outside the cities
they serve.

One interesting data point in that regard is Berlin's Tempelhof Airport (which
you might remember from Indiana Jones 3). It's extremely central because it
was one of the first commercial airports and was shut down a few years ago.

It's a park now and will probably remain–the plan to build even a few houses
was killed by a referendum. It's also a really fascinating place, because it
feels entirely unlike a normal park. There are very few trees, so it's much
more open. The runways remain unchanged, and it's quite an experience to jog
there, with all the history that place has seen always on your mind.
([https://www.google.de/maps/@52.4760745,13.3994616,3a,75y,279...](https://www.google.de/maps/@52.4760745,13.3994616,3a,75y,279.09h,101.14t/data=!3m8!1e1!3m6!1s-JSQQRTZZliQ%2FVgVCFvx_gYI%2FAAAAAAAABVs%2F5u0jXkkv8qQ3cr2XinPhV6iuJBez0G4vQCJkC!2e4!3e11!6s%2F%2Flh4.googleusercontent.com%2F-JSQQRTZZliQ%2FVgVCFvx_gYI%2FAAAAAAAABVs%2F5u0jXkkv8qQ3cr2XinPhV6iuJBez0G4vQCJkC%2Fw203-h100-k-no-
pi-0-ya110.74613-ro-0-fo100%2F!7i8704!8i4352?hl=en))

------
htwillie
For any given approach, with a circular runway there's exactly one point
tangent to the runway to land. Landing short or long isn't an option.

Things are conventional because they tend to work well. And part of working
well is being resilient to errors and non-optimal situations.

------
mrfusion
Im still suggesting my rho shape variant of this idea. You have a straight
runway with enough distance to land but then have the circle for slowing down
once landed.

~~~
Arizhel
That won't work. Normal small airports that only have one runway use the
runway in both directions, depending on wind direction. You never land with a
tailwind, and you never take off with one either. A rho shape wouldn't work
here because the circle is only at one end, preventing bidirectional use.

~~~
mrfusion
But for larger airports it would.

~~~
Arizhel
I don't see how. I don't see how this would result in better land utilization
at all. You could have a big circle around the airport (like in the original
circular runway idea), with a bunch of straight "stems" protruding in all
directions, which can then be chosen based on prevailing winds. Then airplanes
can land on these stems and then enter the circle after their speed has
greatly dropped, so it's really like a big circular taxiway of sorts. And
departing planes can accelerate in the circle some, then proceed onto the
appropriate stem and increase to take-off speed and take off. This might
actually increase throughput, I dunno. However the land usage would be
atrocious, because you probably aren't going to have any productive use of all
that land between the stems, and the overall area used when you account for
the maximum extent of the stems is going to be enormous. The traditional
layout of having a number of parallel runways really makes more sense as far
as land-use efficiency.

