Author Topic: Circular runways are the answer! ?  (Read 9508 times)

Re: Circular runways are the answer! ?
« Reply #25 on: 16 March, 2017, 05:12:02 pm »
Takeoff velocity of commercial jets is around 150 knots (77 m/s) and the radius of the circular runway is 1750m. According to https://mathtab.com/app_id=75 the required banking angle (assuming zero lateral friction) seems to be 0.33 degrees which is about 0.6%. Seeing as that is less than the normal 1% drainage crossfall, I wouldn't be too concerned about the banking. Feel free to point out where I've dropped a decimal.

That calculator is incorrect as it's lost the g term.

tan-1( 82 * 82 / ( 1750 * 9.8) ) = 21.68 degrees
"Yes please" said Squirrel "biscuits are our favourite things."

LittleWheelsandBig

  • Whimsy Rider
Re: Circular runways are the answer! ?
« Reply #26 on: 16 March, 2017, 05:58:48 pm »
Well, that changes things a bit  ;D
Wheel meet again, don't know where, don't know when...

mattc

  • n.b. have grown beard since photo taken
    • Didcot Audaxes
Re: Circular runways are the answer! ?
« Reply #27 on: 16 March, 2017, 06:12:01 pm »
Well, that changes things a bit  ;D
Indeed !!!

The animation that I saw on [some website] did make it look like closer to 21' than 1'.   The pilot looked completely in control!
Has never ridden RAAM
---------
No.11  Because of the great host of those who dislike the least appearance of "swank " when they travel the roads and lanes. - From Kuklos' 39 Articles

caerau

  • SR x 3 - PBP fail but 1090 km - hey - not too bad
Re: Circular runways are the answer! ?
« Reply #28 on: 16 March, 2017, 06:14:06 pm »
I reckon an ellipse would be better.  That way you could have departure at one focal point and arrivals at the other.  :-D


Or perhaps a figure of eight.... hmmm


(Yes I just want it to look like a giant Scalextric)


It's a reverse Elvis thing.

Jaded

  • The Codfather
  • Formerly known as Jaded
Re: Circular runways are the answer! ?
« Reply #29 on: 16 March, 2017, 06:25:53 pm »
Surely a simple Mobius Strip would eliminate the possibility of crashes, with landing on one side and taking off on the other.
It is simpler than it looks.

caerau

  • SR x 3 - PBP fail but 1090 km - hey - not too bad
Re: Circular runways are the answer! ?
« Reply #30 on: 16 March, 2017, 06:26:53 pm »
Well indeed and I am embarrassed to have not thought of that.


I'll have a Klein bottle for my in-light champagne too :-)




[edit] except of course Mobius strips don't have another side ;)
It's a reverse Elvis thing.

hellymedic

  • Just do it!
Re: Circular runways are the answer! ?
« Reply #31 on: 16 March, 2017, 07:03:58 pm »
Wouldn't a circular runway make it more likely for an approaching plane to land off the runway if there were any glitch on the approach?

A landing that is not quite at the scheduled spot on a die straight runway and a low angle of approach causes few issues but this might be anther matter ona round runway.

I think my mind prefers straight lines!

Re: Circular runways are the answer! ?
« Reply #32 on: 16 March, 2017, 07:04:21 pm »
Takeoff velocity of commercial jets is around 150 knots (77 m/s) and the radius of the circular runway is 1750m. According to https://mathtab.com/app_id=75 the required banking angle (assuming zero lateral friction) seems to be 0.33 degrees which is about 0.6%. Seeing as that is less than the normal 1% drainage crossfall, I wouldn't be too concerned about the banking. Feel free to point out where I've dropped a decimal.

That calculator is incorrect as it's lost the g term.

tan-1( 82 * 82 / ( 1750 * 9.8) ) = 21.68 degrees

I think that it is incorrect because the answer is in radians and it hasn't been converted into degrees.

20 ish degrees sounds about right. I make it that it needs 6% more speed than on the flat (is that where the 82 m/s came from?) and 20° wouldn't make a plane fall over if it stopped on the banking.
Quote from: Kim
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Re: Circular runways are the answer! ?
« Reply #33 on: 16 March, 2017, 07:09:03 pm »
Wouldn't a circular runway make it more likely for an approaching plane to land off the runway if there were any glitch on the approach?

A landing that is not quite at the scheduled spot on a die straight runway and a low angle of approach causes few issues but this might be anther matter ona round runway.

I think my mind prefers straight lines!

The idea is that the plane can slow to the right speed, and bank to match the runway so that it is circling above it, and then descend at any rate and still hit the runway. With a straight, limited length runway, the plane has to get the rate of descent correct to hit the runway.

Similarly, when taking off, a plane can take as long as it likes to get to speed, and if it looses power and needs to abort, it just stays on the same curvature, stays above the runway, and lands.
Quote from: Kim
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hellymedic

  • Just do it!
Re: Circular runways are the answer! ?
« Reply #34 on: 16 March, 2017, 08:07:59 pm »
[Luddite] I still think a straight runway is easier to approach.
'Lining up' is pretty basal mentally. Doing things on the skew isn't.

Kim

  • Timelord
    • Fediverse
Re: Circular runways are the answer! ?
« Reply #35 on: 16 March, 2017, 09:29:18 pm »
The idea is that the plane can slow to the right speed, and bank to match the runway so that it is circling above it, and then descend at any rate and still hit the runway. With a straight, limited length runway, the plane has to get the rate of descent correct to hit the runway.

Similarly, when taking off, a plane can take as long as it likes to get to speed, and if it looses power and needs to abort, it just stays on the same curvature, stays above the runway, and lands.

I can't work out if that's genius or insanity.

Probably both.  See also: Helicopters.

Feanor

  • It's mostly downhill from here.
Re: Circular runways are the answer! ?
« Reply #36 on: 16 March, 2017, 09:43:27 pm »
So in this giant bowl, there's gonna have to be a Fucking Big drain at the bottom, to stop it filling up like , well, a bowl.
I'm imagining an airline pilot who's accidentally dropped the keys out of the window, and they've tinkled down the bowl and plopped down the grating.
And now we have The Dude , with the shirt and epaulettes and everything, grubbing around on the ground with his sleeve rolled up and groping around in the drain for the keys to the 787 :-)


PaulF

  • "World's Scariest Barman"
  • It's only impossible if you stop to think about it
Re: Circular runways are the answer! ?
« Reply #37 on: 16 March, 2017, 09:45:31 pm »
The circular runway ignores the fact that at Heathrow and most other airports aircraft land using the Instrument Landing System (ILS) which, in simple terms, projects a radio beam along the descent "path" to the landing point. The plane locks onto this and the autopilot flies the plane down the path to the landing point. A circular runway would require multiple sets of ILS transmitters on the ground, one for each approach path

Kim

  • Timelord
    • Fediverse
Re: Circular runways are the answer! ?
« Reply #38 on: 16 March, 2017, 09:46:35 pm »
A circular runway would require multiple sets of ILS transmitters on the ground, one for each approach path

TBH, that sounds like the easy bit.

Feanor

  • It's mostly downhill from here.
Re: Circular runways are the answer! ?
« Reply #39 on: 16 March, 2017, 09:52:42 pm »
AIUI,  ILS brings you to the touchdown point, not beyond.
It does not guide you along the runway, whatever shape, afterwards.
But I may be wrong.

Re: Circular runways are the answer! ?
« Reply #40 on: 17 March, 2017, 12:16:34 am »
Takeoff velocity of commercial jets is around 150 knots (77 m/s) and the radius of the circular runway is 1750m. According to https://mathtab.com/app_id=75 the required banking angle (assuming zero lateral friction) seems to be 0.33 degrees which is about 0.6%. Seeing as that is less than the normal 1% drainage crossfall, I wouldn't be too concerned about the banking. Feel free to point out where I've dropped a decimal.

That calculator is incorrect as it's lost the g term.

tan-1( 82 * 82 / ( 1750 * 9.8) ) = 21.68 degrees

I think that it is incorrect because the answer is in radians and it hasn't been converted into degrees.

Not sure what you mean.

0.33 radians is 18.9 degrees. It's not a units conversion issue.

The answer from the mathtab calculator was wrong simply because the formula the calculator used was incorrect.

20 ish degrees sounds about right. I make it that it needs 6% more speed than on the flat (is that where the 82 m/s came from?) and 20° wouldn't make a plane fall over if it stopped on the banking.

The 82m/s is a direct conversion of the typical landing airspeed of a common aircraft of 160 knots (82m/s = 159.3952kt).

Plugging that into the formula with a track of a radius of 1750m gives a required banking angle of 21.68o so that the centripetal forces balance out the horizontal component of the (normal reaction to the) gravitational force, i.e. you only have to steer straight on if you're going 82m/s on such a track (radius 1750m) with such a banking angle.
"Yes please" said Squirrel "biscuits are our favourite things."

Re: Circular runways are the answer! ?
« Reply #41 on: 17 March, 2017, 10:04:48 am »
Further up the thread, someone had quoted 150 kt as the landing speed. The slope of 20° means that the lift needed goes up by about 13%, so the speed goes up by 6%, which would take 150 kt up to 160 kt.

I only know the landing speeds from this thread. Either 150 kt or 160 kt look equally likely to me.
Quote from: Kim
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Cudzoziemiec

  • Ride adventurously and stop for a brew.
Re: Circular runways are the answer! ?
« Reply #42 on: 17 March, 2017, 10:25:39 am »
Surely a simple Mobius Strip would eliminate the possibility of crashes, with landing on one side and taking off on the other.
:D ;D :D ;D
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TimC

  • Old blerk sometimes onabike.
Re: Circular runways are the answer! ?
« Reply #43 on: 17 March, 2017, 10:33:32 am »
Seems mad to me, but I await TimC's sage words

It's bollocks. Won't happen. Dreamt up by someone for whom flying is a theoretical, not a practical, issue.

Oscar's dad

  • aka Septimus Fitzwilliam Beauregard Partridge
Re: Circular runways are the answer! ?
« Reply #44 on: 17 March, 2017, 10:34:51 am »
Seems mad to me, but I await TimC's sage words

It's bollocks. Won't happen. Dreamt up by someone for whom flying is a theoretical, not a practical, issue.

Well there we are then, discussion over  ;D

Just as a matter of interest, why is it bollocks?

clarion

  • Tyke
Re: Circular runways are the answer! ?
« Reply #45 on: 17 March, 2017, 10:42:07 am »
Jeez, OD, how many reasons do you need?  There must be Fahzands of 'em!

I think this thread (and the idea) should now be placed carefully in the round file.
Getting there...

TimC

  • Old blerk sometimes onabike.
Re: Circular runways are the answer! ?
« Reply #46 on: 17 March, 2017, 10:50:01 am »
The issues of aligning an aircraft with a curved, banked runway are very difficult. That's for a single aircraft with no additional traffic. Add a strong wind, and the difficulties of putting the aircraft on the ground at a predictable, consistently-achievable position, become severe. Yes, an extremely skilled, specially trained test pilot could achieve it, but it makes landing very much more difficult than it is now.

To exceed the benefits of a current dual-runway setup, this consistency must be achieved with an arrival rate of <40 seconds per movement, while simultaneously allowing departures at a similar rate. Those arrivals and departure need to follow set paths. That's fairly easy to achieve when the landing/take-off direction is constant and unmoving, but different landing and take-off performance coupled with variably-skilled pilots means that -particularly for take-off, the vector of each aircraft will be different. Equally, the amount of runway allocated for each movement must be sufficient to allow for all eventualities. The 2.5 mile length of Heathrow's runways does not include the extra ~half a mile or so of 'clearway', which is the fudge factor for upsets like the BA 777 a few years ago. However, the problem of providing a curvature and banking that the average pilot could cope with would, in my opinion, require a 'runway' of several miles diameter - using much more space than any current UK airport.

Re: Circular runways are the answer! ?
« Reply #47 on: 17 March, 2017, 10:51:17 am »
Takeoff velocity of commercial jets is around 150 knots (77 m/s) and the radius of the circular runway is 1750m. According to https://mathtab.com/app_id=75 the required banking angle (assuming zero lateral friction) seems to be 0.33 degrees which is about 0.6%. Seeing as that is less than the normal 1% drainage crossfall, I wouldn't be too concerned about the banking. Feel free to point out where I've dropped a decimal.

That calculator is incorrect as it's lost the g term.

tan-1( 82 * 82 / ( 1750 * 9.8) ) = 21.68 degrees

I think that it is incorrect because the answer is in radians and it hasn't been converted into degrees.

Not sure what you mean.

0.33 radians is 18.9 degrees. It's not a units conversion issue.

The answer from the mathtab calculator was wrong simply because the formula the calculator used was incorrect.

Note quite.  There were two mistakes, hence the confusion.  In the nasty jpegged formula which was visible, the "g" was missing.  in the tab to the left with the two-line calculation code, the "g" was included, but atan was used directly without the operator seemingly understanding that computer code trig functions always uses radians, not degrees.  The result of the calculation then had the word "degrees" next to it on screen. 

So at least three basic faults which shouldn't normally be made by a technically competent person on that page.  Given that the author was someone with the same user id as the website, I would make a mental note to write it off for future use.

Oscar's dad

  • aka Septimus Fitzwilliam Beauregard Partridge
Re: Circular runways are the answer! ?
« Reply #48 on: 17 March, 2017, 10:59:33 am »
The issues of aligning an aircraft with a curved, banked runway are very difficult. That's for a single aircraft with no additional traffic. Add a strong wind, and the difficulties of putting the aircraft on the ground at a predictable, consistently-achievable position, become severe. Yes, an extremely skilled, specially trained test pilot could achieve it, but it makes landing very much more difficult than it is now.

To exceed the benefits of a current dual-runway setup, this consistency must be achieved with an arrival rate of <40 seconds per movement, while simultaneously allowing departures at a similar rate. Those arrivals and departure need to follow set paths. That's fairly easy to achieve when the landing/take-off direction is constant and unmoving, but different landing and take-off performance coupled with variably-skilled pilots means that -particularly for take-off, the vector of each aircraft will be different. Equally, the amount of runway allocated for each movement must be sufficient to allow for all eventualities. The 2.5 mile length of Heathrow's runways does not include the extra ~half a mile or so of 'clearway', which is the fudge factor for upsets like the BA 777 a few years ago. However, the problem of providing a curvature and banking that the average pilot could cope with would, in my opinion, require a 'runway' of several miles diameter - using much more space than any current UK airport.

Oh dear, I hope the Dutch chap who is promoting the idea never reads Tim's post!

Jaded

  • The Codfather
  • Formerly known as Jaded
Re: Circular runways are the answer! ?
« Reply #49 on: 17 March, 2017, 11:02:43 am »
He has nice simulators though.
It is simpler than it looks.