[Closed] After the travelator question, circular runways?

why wouldn't it work (assuming the plane stays level)

Did he mention 'Centrifugal' forces!!???

Well, one difficulty is that the inner wing will be going slower than the outer wing and so generate less left, which will make take off a bit more difficult. I'm not saying it is insurmountable, after all helicopters manage something far more complex. But varying headwind etc. would make things a bit harder

Also given that the circular runway is equivalent to 3 runways in length, it would take up a large area, comparatively.

Presumably there would be a small straight section attached, like the 100m bit on an olympic track.

I think the main problem would be landing, you'd have to come in pretty fast and then sharply decelerate while turning in order to avoid going off the edge. I'm not saying it's inevitable there'd be an accident but the added risk of one would put airport designers off. Of course they could always add a circular one as a takeoff runway at an airport that already has a straight one to land on.

Oh, and relevant [url= http://xkcd.com/123/ ]xkcd.[/url]

I'd worry about strain through landing gear from centripetal forces.

Although these are meant to be banked.

I'd be more concerned with a constantly changing angle of cross wind.

Also given that the circular runway is equivalent to 3 runways in length, it would take up a large area, comparatively.

I don't see that - if a runway has length L, you're getting 3 runways worth in a circle of diam 95% of the Length of a single runway. Circ = pi x D = 3L, D = 3L/pi = 0.95L

To have 3 runways in a traditional configuration side by side, using a quick google of a few major airports with multiple runways indicates needing about 1/2 a runway length separation, so 3 runways is a square of LxL which is clearly more than a circle of diam 0.95L

I think it would work, but not without redesigning planes to work with it.
The stresses and strains on the landing gear/air frame would be very different from those experienced during a conventional straight take-off or landing.

Also given that the circular runway is equivalent to 3 runways in length, it would take up a large area, comparatively.

I don't see that - if a runway has length L, you're getting 3 runways worth in a circle of diam 95% of the Length of a single runway. Circ = pi x D = 3L, D = 3L/pi = 0.95L

To have 3 runways in a traditional configuration side by side, using a quick google of a few major airports with multiple runways indicates needing about 1/2 a runway length separation, so 3 runways is a square of LxL which is clearly more than a circle of diam 0.95L

Isn't the original post you quoted just a simplification of the phrase "the circular runway is equivalent to pi runways in length"?

just googled the min runway for a 747 and with all conditions favourable, seems like about 1.25 miles - so a full runway has to be about 2-2.5 at a guess?

Making the circular runway 7 miles around give or take.

Although that's clearly a curve it's not anything like a 'sharp' curve, particularly when banked as well.

Same goes for lift on take off, the comparative difference in airspeed from inner to outer tip of a wingspan on a circular runway wouldn't be significant.

[url= http://www.endlessrunway-project.eu/ ]more details [/url]

[url= http://www.endlessrunway-project.eu/downloads/d1.2-the-endless-runway-background-v3.pdf ]history of the idea [/url]

[url= http://www.endlessrunway-project.eu/downloads/d1.3-concept-v2.pdf ]concept doc[/url]

[url= http://www.endlessrunway-project.eu/downloads/d4.3-simulation-modelling-and-analyses-v2.pdf ]Simulation Modelling and Analyses[/url]

Isn't the original post you quoted just a simplification of the phrase "the circular runway is equivalent to pi runways in length"?

No.

The original post said that the circular runway was 3x the length of a normal one, which is a selection made presumably by the designers for some reason. I then just solved that equation to find the equiv diameter, it's coincidence that pi is close to 3.

If the designers had made it 2.5x the length or 4x the length then it would have been different.

[quote=theotherjonv ]just googled the min runway for a 747 and with all conditions favourable, seems like about 1.25 miles - so a full runway has to be about 2-2.5 at a guess?It's a circle - you can go round more than once. 😆

The figure given on the video is for a diameter of 3.5km

I'd be more concerned with a constantly changing angle of cross wind.

I don't think that the plane will be doing full laps at increasing speed until it takes off in a spiral, as the circumference is the equivalent of 3 runways you would have the ability to always take off into a headwind (as per the video)

diameter of 3.5km

a full runway has to be about 2-2.5mile

So the circle is 3.5km/2.17miles and the straight runway is 2.5miles/4km.

Now, about the saving of space made?

Seems like a solution looking for a problem.

Would the coriolis effect result in clockwise runways in the northern hemisphere and anti-clockwise in the southern, or vise versa?

The figure given on the video is for a diameter of 3.5km

Ties in perfectly with my approximation of a runway being 2-2.5 miles in length (3.2-4.0km) and hence the diam being 0.95x that = 3.0-3.8km

So the circle is 3.5km/2.17miles and the straight runway is 2.5miles/4km.

Now, about the saving of space made?

As in my other post, you have 3 usable runways in a circle - to get 3 runways side by side I reckon you'd need a square (allowing for half a runway's length in separation, a figure plucked purely from google earthing a few multirunway airports)

Square with side = L vs circle of diam 0.95L You do the math(s)

[edit] and to answer my own question

The original post said that the circular runway was 3x the length of a normal one, which is a selection made presumably by the designers for some reason.

my assumption would be this is the sort of diameter they need to make the usable bit of runway (the bit where the plane's at speed as opposed to initial acceleration / deceleration / taxiing) 'straight enough' that the effect of the curvature vs side stresses on landing gear, etc is 'negligable' (maybe not negligable but 'overcomeable')

What if the runway was rotating, like a record player?

I think it would work, but not without redesigning planes to work with it.
The stresses and strains on the landing gear/air frame would be very different from those experienced during a conventional straight take-off or landing.

Would a headwind landing on a gentle curve be more violent than landing on a straight runway in a crosswind?

[quote=miketually ]
Would a headwind landing on a gentle curve be more violent than landing on a straight runway in a crosswind?

Just put a high fence round it.

In fact, build the angle up a bit more so that it's more like a wall of death.

[quote=scotroutes ]Would the coriolis effect result in clockwise runways in the northern hemisphere and anti-clockwise in the southern, or vise versa?

😆

Not actually a lot wrong with the idea that I can see. In a totally windless world it might be better to have straight runways, but this appears to be a way of avoiding crosswind problems, in which case all the supposed disadvantages (which are in reality fairly minor given the radius of the proposed circle) are massively outweighed by the huge advantage of not having a crosswind landing (which results in issues like massively increased stresses on landing gear and airframe 😉 )

In fact the biggest issues I can see are the increased precision required in picking a touchdown point, and the lack of a single approach flightpath (with associated beacons). Both issues which might have been a problem 20 or 30 years ago, but rather less likely to be with computer control.

Circular runways have been around for decades, have a look at control line model racing. The dogfights are the best, racing to cut the streamer from your oppo.

And a Lancaster

[quote=midlifecrashes ]Circular runways have been around for decades, have a look at control line model racing.

Is control line still a thing? I can kind of get the combat as there's clearly a lot of skill involved there, but flying a Lanc around in circles appears to be dead boring. I can understand how it came about, but given how cheap and widespread radio gear is now why don't people just fit that and give themselves a more interesting flight envelope?

Or is it just old codgers (even more so than model aircraft is in general) who've always done it, and therefore going to die out at some point?

Yes, I think it's very much a niche thing now. I only knew of it as my mate has his old plane mounted on the wall as decoration, from pre RC days(ok pre 1970s RC affordability). Also you can set up a flying ring in places where RC wouldn't be practical or legal.

given that this thread is full of plane geeks..

why can't big planes use a similar method of acceleration\deceleration as aircraft carriers? Obviously, you couldn't do it on the same scale, but surely some form of ground based engine (treadmill? jk) would reduce the amount of runway needed, and you'd also be able to recover the energy used in slowing down planes which are landing (which must be fairly significant), so you can use it for helping those taking off again (I'm imagining a big KERs system)..?

why can't big planes use a similar method of acceleration\deceleration as aircraft carriers?

(IANA... no, wait, I actually did a degree in this, let's see what I can remember....) Cats and traps are brutal on the airframe and require a fair amount of modification and strengthening. I'd hazard a guess that the fuel losses carting all that extra weight to the other side of the world would significantly outweigh the benefits, even before you get into the problems of shortened airframe life, g limits on the passengers/luggage/drinks cabinet and the problems of building larger catapults (US aircraft carrier ones basically run off the nuclear reactor).

which results in issues like massively increased stresses on landing gear and airframe

Not really. The maximum load rating of the gear is vastly in excess of the force required to make the tyre slide, so it's a non-event.

Ideally the aircraft is de-crabbed in the flare but manufacturers are relaxed about drift at touchdown. Landing gear and airframe damage is pretty much exclusive to hard touchdowns, or touchdowns on the nose gear.

I think the circular runway will never happen. Which is good, because landing in a straight line on a flat runway is hard enough.

I think the circular runway will never happen. Which is good, because landing in a straight line on a flat runway is hard enough.

I'm far from an expert, but I can't help think that this might fly (ho ho) in perfect conditions. But I've seen plenty of videos of large aircraft making frankly heroic landings in adverse conditions (there was one from Storm Doris very recently) which makes me very very worried that this sort of thing could add a complication which would make the difference between "featured on YouTube" and going down in history as a catastrophic disaster.

The whole point though Cougar is that in adverse conditions rather than landing in a crosswind (which is what you see in the videos) they land into a headwind which should make it far less dramatic.

I'd worry about strain through landing gear from centripetal forces

If you bank the runway like a Nascar track, at a specific speed, the planes will follow the curve without any steering input. By varying the banking, you can allow for the acceleration/deceleration of takeoff and landing. Would ruin the crosswind thing though.

Think Millbrook rather than Nascar - banking is constant around the track, but varies as you go up and down it. So you land on the outside where banking is steepest, then move down as you slow down.

Think Millbrook rather than Nascar

Of course. Now I see why you earn the big bucks.

Test it out wih some drones