Circular Runways [video]
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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.
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.
a secondary point: checkout any landing strip https://i.imgur.com/n99YiM5.png
a plane can't pinpoint the landing to absolute precision, even on autopilot. the dark patch should give you an idea on how much ahead/behind a large plane may land under real world condition - all the test they give in the papers are using small planes or even fighters, those can manage precise landing, a 737 not so much
the plane will have to follow the turn until it touches down, and as it follows the turn it'll change it's direction relative to crosswind, with all the implication it entails. few degrees on landing are already enough to need a significant correction.
Edit 5 optimal banking changes with speed and all plane takeoff and land differently. More to the point while accellerating for takeoff the plane will literally go everywhere but in the runway direction
http://www.airliners.net/forum/viewtopic.php?t=1357935#p1941...
radius is 3500m velocity is 82m/s
82^2/3500 ~ 1.92
atan(1.92/9.81) ~ 0.19 or 10 degrees of bank.
Where have I gone wrong?
Um, yeah, not so much. The concept may have problems, but that's not how it'll be debunked.
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.
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.
[1] http://paleofuture.gizmodo.com/these-circular-runways-were-d...
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.
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.
You do need a very big cable though. Think miles.
There are actually many promising technologies to get mass into space with much lower marginal cost. I think the problem is that they all have high capital costs and no one wants to take the risk on a new technology.
In my design I have the ship tethered by a cable and a pipe that's delivering the fuel.
A better idea is the launch loop, but again you have to deal with cable weight and tensile strength.
In my design the vehicle would feed its rockets from an onboard fuel tank which would be constantly replenished from the pipe/tether. At detachment time it would still have a full tank to manage drag, getting up to final speed, and circularizing the orbit.
The main limitations are surviving the hypersonic launch and short trip through the atmosphere, and you still need a second stage to get into a stable orbit. Your launch vehicle would basically be an upwards-travelling meteor.
Considerably more viable on the moon; lunar escape velocity is "only" 2.38km/s and there's no atmosphere. There's lots of 70s moonbase concept art depicting the use of rail launchers to return mined material to earth. Although I'm not sure it would be economically viable even if the moon were made of solid platinum.
https://www.kickstarter.com/projects/391496725/the-slingatro...
It didn't get backing but was a fun idea!