Debunkers dot Org

A Tradition of Looking Behind the Curtain
It is currently Wed Jun 28, 2017 3:45 am

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 7 posts ] 
Author Message
 Post subject: Circular Runways
PostPosted: Wed Mar 29, 2017 4:21 pm 
Offline

Joined: Fri Apr 04, 2008 10:47 am
Posts: 342
I debated where to put this, but it's definitely got a whiff of the "woo" about it.

Popular Mechanics article about circular runways for commercial airports
Quote:
The traditional runway—a long concrete stripe across the landscape—has some problems. A big one is crosswinds. If the wind blows hard and perpendicular to the direction of the runway, planes face harrowing takeoffs and landings. If the winds are bad enough, airports must close certain runways and reroute air traffic, sending a chain reaction of delays through the system.

But if a runway were circular, then a plane theoretically could take off in whatever direction was most favorable. And multiple planes could use the Endless Runway simultaneously.

1. I can see the advantage of always being able to takeoff / land into a headwind. But since the headwind is tangent to the circle at one point, I don’t see how multiple planes can use it simultaneously. (The source website says something about using more of the track in low wind conditions).

2. The track is 6.2 miles (32,700 ft) long. According to Google (the ultimate source of all knowledge) the minimum takeoff distance for a Boeing 737 is about 5300 ft, so from start to takeoff, the plane would be covering about 60 degrees. Bigger aircraft like a 777 would be closer to 90 degrees.

3. More fun with a 737:
Takeoff speed = 150 mph (220 ft/s)
Radius of the circle the plane would be traveling on = 5200 ft
Centripetal acceleration at the point of takeoff (v^2/r) = 9.3 ft/s^2

What provides the centripetal force to keep the plane moving in a circle? Supposedly the track is sloped, but my (increasingly dubious) calculations show it’d have to have a 15 degree slope to do that.

Some of the turning acceleration has to be provided by the plane, either the landing gear (I doubt it’d designed for that) or varying the engine thrust. Same thing with landing -- differential thrust reversers?

Yeah, more than a whiff of woo.


Top
 Profile  
 
 Post subject: Re: Circular Runways
PostPosted: Wed Mar 29, 2017 5:28 pm 
Offline
User avatar

Joined: Fri Apr 04, 2008 10:48 am
Posts: 4260
Location: Broomfield, Colorado
I remember reading something similar years ago, but in that case the plane didn't move through a circular arc; instead the airport was an enormous concrete circle, thus allowing takeoff and landing in any direction (i.e., aircraft took off and landed perpendicular to the circumference). Not so much woo - which always connotes magical thinking to me - but innumeracy, a lack of understanding of costs and benefits and engineering. You see this quite a bit with things related to airplanes - a recurring one is the whole jetliner parachute.


Top
 Profile  
 
 Post subject: Re: Circular Runways
PostPosted: Wed Mar 29, 2017 6:03 pm 
Offline
User avatar

Joined: Fri Apr 04, 2008 10:52 am
Posts: 1398
Location: California-prev Texas Montreal Virginia
It is quite exciting to land a small plane on a narrow runway with a 25 mph crosswind when your maximum sideslip only gives you a 24 mph sideways speed.


Top
 Profile  
 
 Post subject: Re: Circular Runways
PostPosted: Wed Mar 29, 2017 7:12 pm 
Offline

Joined: Fri Apr 04, 2008 11:51 am
Posts: 628
They could always take a cue from the original Battlestar Galactica and make a really giant tube they can shoot the airplanes out of.


Top
 Profile  
 
 Post subject: Re: Circular Runways
PostPosted: Thu Mar 30, 2017 9:10 am 
Offline
User avatar

Joined: Fri Apr 04, 2008 12:06 pm
Posts: 1625
Location: South Carolina
I don't like flying, I don't like modern planes. I do like the idea of shooting planes out of tubes a la Battlestar Galactica, but didn't Bugs Bunny do it first?

On all of this turning on a huge circle, would there be too sharp of a turn when the circle is that big? How would this pipedream of a runway affect houses nearby when planes take off in (and, I assume, land from) any direction?

_________________
Y gwir yn erbyn y byd.

(BTW, I'm on Facebook, so friend me, already - since it's just us here, the name is Ceridwen Keeley.)


Top
 Profile  
 
 Post subject: Re: Circular Runways
PostPosted: Tue Apr 04, 2017 11:22 pm 
Offline
User avatar

Joined: Fri Apr 04, 2008 12:20 pm
Posts: 840
Location: Tantalizingly close to Colorado
Ahh, airliner parachutes. One of the first debunkers topics I recall reading about.

Denver airport is pretty close to the plain circle concept. Two pairs of runways pinwheeled around the terminal...kind of looks like a swastika. I'm guessing they chose the orientation such that the least common wind direction is 45 degrees to the runways, or the most common wind direction is parallel to one set. No real need for infinite direction, so no real need for the expense of paving an entire circle.


Top
 Profile  
 
 Post subject: Re: Circular Runways
PostPosted: Wed Apr 05, 2017 12:03 am 
Offline
User avatar

Joined: Fri Apr 04, 2008 10:52 am
Posts: 1398
Location: California-prev Texas Montreal Virginia
A near infinite circular runway can be found beneath an aircraft carrier.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 7 posts ] 

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Americanized by Xaphos © 2007, 2008 phpBB.fr