
Circular Runways [video] - cadab
http://www.bbc.com/news/magazine-39284294
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lisper
Wow, there are so many reasons this is a terrible idea.

1\. It doesn't actually solve the problem it sets out to solve (crosswind
landings). To the contrary, a circular runway _guarantees_ that if you have
any wind at all then you _will_ have a crosswind at some point in the landing.
Not only that, but the apparent wind direction will be constantly shifting
during the landing, making the landing even more difficult than a normal
crosswind landing.

2\. Flying in a circle at a low airspeed and at low altitude is absolutely the
single most dangerous thing you can do in an airplane. When you are flying in
a circle, the outboard wing is moving faster than the inboard wing, and so if
you are flying close to stall speed the inboard wing will stall first,
resulting in a spin. It is possible to recover from a spin but you have to
descend in order to do it. If the spin starts at low altitude there is nowhere
to descend to, so you will crash. Spins on approach to landing are one of the
leading causes of fatal crashes in small general aviation aircraft.

3\. Airport approach and departure procedures are designed around the fact
that runways are aligned in particular directions.

~~~
bitmapbrother
The circular runway is banked so I would assume crosswinds aren't as
devastating due to this banking. However, I am curious as to why you so
adamantly believe that circular banked runways guarantee crosswinds. Is this
based on scientific research that have proven this or is this just a guess?

~~~
lisper
> I would assume crosswinds aren't as devastating due to this banking.

You would assume incorrectly. The bank is mostly irrelevant. Crosswinds happen
when the direction of motion of the plane is anything other than directly in
to the wind. If you're turning, your heading is continually changing, and so
the relative wind direction will be continually changing, and so you will
necessarily have a crosswind component _everywhere_ except at the one point
when you are heading directly into the wind. Even worse, the crosswind
component will be continually changing as you turn. This is even worse than it
seems. Landing in a crosswind involves a maneuver called "cross-control" where
you roll the plane into the wind with the ailerons while simultaneously apply
opposite rudder to arrest the resulting turn. It's one of the hardest things
to do in an airplane. Getting it right is tricky even when the runway is
straight and level and the wind is steady. Trying to do it on a curved banked
runway, where the wind is necessary continually shifting as you turn, would be
a total nightmare.

> However, I am curious as to why you so adamantly believe that circular
> banked runways guarantee crosswinds. Is this based on scientific research
> that have proven this or is this just a guess?

I'm a pilot with over twenty years of experience. But you don't have to be a
pilot to see the folly of circular runways. It's simple common sense: if
you're turning, you can't be heading directly into the wind the whole time.

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yock
Non-pilot aviation fanatic here. It seems like adding a bank angle to final
approach would increase the risk of stall-spin accidents on landing.

~~~
bitmapbrother
Adding a banking in airports that experience the side effects of cold weather
could also be very problematic.

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Nrsolis
Yeah. Not so much.

[http://www.airliners.net/forum/viewtopic.php?t=1357935#p1941...](http://www.airliners.net/forum/viewtopic.php?t=1357935#p19415407)

~~~
Applejinx
Well that's interesting. They seem to be arguing that the bank angle is super
high, causing the planes to pull massive Gs just to land or take off, and
that's terrible.

Even if it's true all that means is,

(a) planes achieving takeoff instantly have better than stall speed in the
open air and can safely get up and away from the city,

(b) planes landing can come in at any angle, have infinite space to negotiate
a decent landing and no specific window to hit as far as retaining enough
runway, plus the landing speed is significantly higher than stall speed in
free air. That directly improves the controllability of the aircraft.

The guy's right, this would work just fine. Even without a bank and increased
G forces, it's not a bad idea, but when you include the reality of the banking
increasing takeoff/landing speed over normal stall speed, it becomes a slam
dunk. Very good idea anywhere you can afford to build three or more runways in
your airport.

~~~
yock
Regarding a, how do you figure stall speed is higher? Stall-spin accidents
occur precisely because aircraft are in a bank near the ground. They're more
common on landing than takeoff because procedure often dictates flying the
runway heading until having sufficient speed and altitude to recover.

Regarding b, wind direction is still important. Your airspeed would be
constantly in flux when negotiating a landing at a bank since your angle to
the wind is constantly changing. This is especially perilous at low speed near
the ground due to the risk of spinning.

There may absolutely be benefits to a circular runway, but I see a lot of
increased risk around inducing low altitude spins.

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saycheese
Appears to be an idea that's been around before [1] - might be interesting to
build a smaller scale one that's explicitly for drone swarms.

[1] [http://paleofuture.gizmodo.com/these-circular-runways-
were-d...](http://paleofuture.gizmodo.com/these-circular-runways-were-
designed-to-catapult-planes-1679960133)

~~~
dingaling
Re: drones, Flight Refueling in the UK had a target-practice UAV called
Falconet in the 1980s that launched from a circular runway.

It rested on a dolly secured by a cable to the central post and whirled around
until take-off.

I think a couple of installations were built but most customers chose a more
conventional rocket-boosted dolly for straight runways.

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cadab
The projects site: [http://www.endlessrunway-
project.eu/](http://www.endlessrunway-project.eu/)

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mrfusion
Wouldn't a "P" shape make the most sense? That way you don't have to worry
about the banking angle during touch down.

~~~
nayuki
Even better would be a ρ (rho) shape!

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jason_wang
How would a circular runway affect inbound emergency aircrafts?

My intuition tells me that a straight runway would be less burdensome on the
flight crew. You set up for your approach then you can go back to dealing with
the issues at hand.

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nthcolumn
Okay only slightly related, I had an idea a long while ago for putting
satellites into orbit where you just fling them? I didn't think it good for
humans because of the G but for stuff. The win being that the power required
is all on earth and you don't have to carry fuel with the payload. You could
spin them up on a centrifuge and then let go at just the right time (and
angle). I was going to mention it to Elon one day...

~~~
ChuckMcM
that works well on the moon because there isn't an atmosphere to speak of but
on the earth trying to accellerate to 26km/hr at sea level is both very energy
intensive, and the vehicle experiences intense heating due to the atmosphere.
Atmospheric drag makes this idea impractical for pretty much anything.

~~~
ChuckMcM
as was pointed out offline, that is 26000 km/hr

~~~
nthcolumn
Yeow. Only good for rocks then.

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hirundo
How the heck can you camber the runway at the right angle to work for both a
Boeing 747 landing at 160mph and a Cessna Skyhawk landing at 60mph?

~~~
jason_wang
Most commercial aviation airports (Class-B and Class C) separate commercial
and general aviation traffic. The landing speed difference along (let along
the camber as you suggested) make it impossible to stagger 7x7 traffic with
general aviation traffic.

