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Discussion
99dndd said:
How far away does an airport need to be from a city before you call advertising standards?
Belfast International's bad enough but "Paris" Beauvais?!
Belfast International is only 15 miles distant from Belfast City Centre, which I think is acceptable.Belfast International's bad enough but "Paris" Beauvais?!
Ryanair used to advertise Vienna as a destination, however the flights landed in Bratislava, 40 miles away in neighbouring Slovakia.
OldGermanHeaps said:
JuniorD said:
Belfast International is only 15 miles distant from Belfast City Centre, which I think is acceptable.
Ryanair used to advertise Vienna as a destination, however the flights landed in Bratislava, 40 miles away in neighbouring Slovakia.
This means nothing to me.Ryanair used to advertise Vienna as a destination, however the flights landed in Bratislava, 40 miles away in neighbouring Slovakia.
Pac-Man, if you mean ‘once at cruising altitude, do you have to make control inputs to follow the curvature of the earth’, the answer is no. A ship floating on the ocean does not have to do this either. We are just further up and supported by a different fluid.
If you’re asking about during the climb, the ship comparison doesn’t work quite so well. It is simple enough to say that we are not going anywhere near fast enough for the shape of the earth to matter. A satellite in orbit is maintaining the same distance from the surface of the earth as it travels, but even the nearest of those is going at something like forty times the speed of a commercial airliner. Anyway, a comparison between orbital mechanics and aerodynamics sounds like a massive can of worms to open that I’m not clever enough for, so I think I’ll stop there.
If you’re asking about during the climb, the ship comparison doesn’t work quite so well. It is simple enough to say that we are not going anywhere near fast enough for the shape of the earth to matter. A satellite in orbit is maintaining the same distance from the surface of the earth as it travels, but even the nearest of those is going at something like forty times the speed of a commercial airliner. Anyway, a comparison between orbital mechanics and aerodynamics sounds like a massive can of worms to open that I’m not clever enough for, so I think I’ll stop there.
Edited by Prawo Jazdy on Friday 26th January 23:01
Pacman1978 said:
After taking off and climbing to the desired cruise altitude (sorry if incorrect terms used) how is the curvature of the earth dealt with?
Thank you
Actually, that's a pretty good question.Thank you
In terms of altitude, it's easiest to think of the aircraft actually flying through air of a certain ambient air pressure.
As you'll know, air pressure decreases with altitude, which is how altimeters work. So in essence, an aircraft level at 37,000 feet is actually flying at a height that 'feels like' 37,000. The actual height above the earths surface is largely academic - as the other aircraft are doing the same thing, referencing the same datum.
If the ambient air pressure increases or decreases, the aircraft will actually climb or descend to maintain it's 37,000 foot altimeter reading. But, no dramas, as the other aircraft in the area are all doing the same thing.
In terms of lateral tracking, then as mentioned, great circles come into it. A great circle is the shortest point to point on a sphere, which is what airlines try to fly for efficiency. To illustrate, try this ok for size:
A great circle is a line that goes all the way around the earth. The equator is one. So are lines of longitude.
The equator is a great circle - so if you flew to it and took up an easterly track, 090 degrees, and let go of the controls, the North Pole will be always straight off to your left.
Here's an example of what's not a great circle:
If you went to a higher latitude, say 85 degrees north, and took up that same track of 090 degrees and let go of the controls, initially the North Pole is straight off to your left, but before long, it is moving behind you and your true track would start to change.
To keep the North Pole straight off to the left and maintaining your 090 track, you'd have to keep turning a little bit left every now and then.
Taken to the extreme - if there was a big fence post sticking out from the North Pole, and it was a couple of hundred yards off to your left. If you wanted to fly track 090 you'd be flying very tight circles around it!
All that garbling on illustrates that when flying our great circle routes, the aircrafts true track will change. The rate of change is dependent on how far north you are.
To fly a great circle is difficult* because as said your true heading is continuously changing (unless going north or following the equator, and even then your magnetic heading is changing). This is why waypoints are used - points along the great circle route where once (hopefully) reached you can check your heading and correct if necessary. To calculate the great circle (geodesic - shorted distance between two points) on a sphere is relatively simple. To calculate the geodesic on an spheroid (the Earth is an oblate spheroid with polar axis 13 miles shorter than the equatorial) is more involved, but easily done by computer. GPS systems use a spheroid model of the Earth called WGS 84. To calculate the geodesic on an ellipsoid is very difficult. Luckily the WGS 84 model of the Earth is sufficient for navigation within +/- 1 metre.
Navigation without sight of land used to be by compass, clock, position of the sun, and by the stars. Navigation of ships before John Harrison's clock had to be by latitude alone as there was no way to say how far around the Earth (longitude) one was, so ships used to sail north/south until a certain latitude was reached and then sail east/west along a parallel at constant latitude.
*ETA: In principle, it's very easy - just keep your wings level, but unless you are flying something like Concorde you will probably have some pretty severe winds to contend with.
Navigation without sight of land used to be by compass, clock, position of the sun, and by the stars. Navigation of ships before John Harrison's clock had to be by latitude alone as there was no way to say how far around the Earth (longitude) one was, so ships used to sail north/south until a certain latitude was reached and then sail east/west along a parallel at constant latitude.
*ETA: In principle, it's very easy - just keep your wings level, but unless you are flying something like Concorde you will probably have some pretty severe winds to contend with.
Edited by V8LM on Saturday 27th January 09:47
dazwalsh said:
OP, your thoughts on the US A320 that went swimming in the hudson, did the aircraft systems or the pilot save those people?
Not sure you can separate the two. From the systems corner, you can certainly argue that despite the loss of power (in a fly-by-wire aircraft), the crew still had an aircraft that enabled them to communicate with the ground, and more importantly, still have control of.
From the pilot's perspective, once it was determined that they weren't gonna get the engines running again, and they weren't in gliding distance to a suitable airport, the decision making was relatively simple: 'land' in a built up area, or ditch in an open section of water. Either's not a great choice, but without wanting to trivialise the decision, it's a bit of a no-brainer to know that it would be counter-intuitive to go for the built-up area. Bear in mind, despite the bad luck they had in hitting a flock of Canadian Geese, and losing both engines, there was a lot of good luck that day - clear skies, flat water and boats in close proximity to assist with rescue. I shudder to think the outcome of this incident had it been a foggy day in New York!
The ditching checklist that the other pilot was running through is a long checklist, and it's more or less written based on losing all engines mid-Atlantic, and therefore time permits to run through each item. I was flying A320's at the time, and the aircraft has a 'DITCHING' push-button, which essentially closes all inlet valves on the underside of the aircraft to slow down the flooding process, due to it's position in the checklist, the crew never got that far and the aircraft ditched without closing the valves. You could therefore criticise the systems, or the procedures, that meant that in this example, the aircraft wasn't correctly configured for ditching. However, the aircraft structure remained intact on contact with the water, and still remained afloat for enough time for everyone to get out, so certainly a tick for the 'design' element.
All in all, (IMO!) it was a combination of everything that saved all on board - aircraft design, weather, pilot decision making, time of day, cabin crew co-ordination, passenger co-operation and proximity of rescue facilities.
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