80 minutes of fuel for that plane must be very expensive. Is it possibly to fly that plane, at say 200 knots ground speed, and save on fuel? Or are they stuck at their speed they filed in the flight plan, to keep traffic separation?
We landed a few minutes after 6am, and by the time I got through immigration and customs and rode home during the morning rush hour on the tube it would have been 8 or 8:30am.
Super frustrating that the last mile took 3 hours to complete!
That's also why flying low is really bad for fuel consumption, you're going to have to decrease thrust and you'll be aerodynamically less efficient at the same time.
In general turbine engines are limited mostly by the temperature at the first stage of turbine blades after the combustion stage. It's hard to get reliable instrumentation in this zone so a proxy temperature is often taken from a later stage.
In older airliners there was a table of max ITT values varying with altitude and outside air temperature. In modern FADEC engines the computer does the same calculations. It's not unusual for smaller jets to be set at their max continuous thrust setting shortly after takeoff and be left there until the beginning of the descent. Modern airliners will be flying a cost optimised Mach number.
That Mach number is entered on their flight plan and is used as a basis for ensuring they are separated from other flights on the north Atlantic tracks so they wouldn't be able to change it readily.
The interesting part of all of this is that they would have been assigned an altitude for the crossing, at high altitudes maximum speeds drop (because flutter margins are proportional to velocity rather than effective pressure) but stall speeds increase so the range of viable flying speeds is actually quite limited at cruise altitudes. They probably couldn't have slowed down if they wanted too.
So if you are shooting for miles per pound of fuel, there is a best. You will lose total trip fuel if you throttle up and go faster and you will lose total trip fuel if you throttle down and go slower.
I've only had some college physics and no aeronautical engineering so I could be way off. Of course there are other factors like the amount of lift per unit of velocity and so on...
But you measure speed in this context relative to the air, not the ground.
The fact that the plane is now moving across land much much quicker due to winds aloft is completely irrelevant from an aerodynamics perspective.
The plane doesn’t even “know” that it’s getting there sooner.
This is true of form drag. Airplanes are also subject to a somewhat counterintuitive induced drag that is inversely proportional to airspeed. The minimum total drag is therefore somewhere between a slow speed and a fast speed.
There are three optimal speeds depending on what you're trying to optimize. Maximum range (distance per unit of fuel) is best glide speed, which would be a painfully slow way to get somewhere. Maximum endurance (time per unit of fuel) is roughly max endurance divided by 1.316—even slower. "Optimum cruise," or Carson's speed (max speed per unit of fuel) is roughly max endurance times 1.316.
I'm pretty sure best glide speed times 1.3 can be achieved with less than 90% thrust from the engines of a typical commercial airliner.
https://www.wired.com/2012/10/can-we-build-a-more-efficient-...
It’s still less efficient, but some of that squaring works to your advantage.
I've experienced this in the US and Canada too, but it doesn't seem to be a problem at Heathrow in my experience. LHR is slot constrained, but not gate constrained. Worst case, you end up on a remote stand with a bus ride in to the terminal.
Landings before 6am are allowed, but are limited in numbers.
But with planes it doesn't work that way - everything is relative to the air outside, not the ground. With good tailwind you still have to go with your cruising speed relative to the tailwind. Your ground speed will be insane. The opposite is with headwind.
For example, if you maintain the same attitude, but decrease thrust so that your forward airspeed drops, and you begin descending... your angle of attack increases, despite the aircraft not actually rotating.
Why? When you start descending, the air below now seems to be "coming up at you"- you go from
---> (===
7 (===
/
/
Now consider how roll, yaw, and crosswinds affect this- as the AoA becomes variable across the wing...
You can stall in a nose down attitude if you're descending fast, the air comes from "below" and you try to pull out ift the dive thereby increasing the angle at which the air meets the wing. All the while your nose is still pointing below the horizon.
But also, it is sometimes useless at telling you about the conditions inside the plane too. If you're rolling and yawing at the same time (known as a coordinated turn), the water in the glass will stay level (relative to the bottom of the glass), and the glass will not slide along its surface, even in a 20 degree bank.
Of course, that doesn’t help you at all during dynamic or unusual situations.
https://www.heathrow.com/content/dam/heathrow/web/common/doc... "Schedule 5"
When an airplane is in a body of air which is moving across the ground, the airplane moves within that body of air with no knowledge that it is in a strong wind. Airspeed is unaffected, except for gusts or shear events. The airplane maintains it's normal airspeed within that body of air, even though that body of air is moving very quickly in relation to the ground.
This is evident in all phases of flight. For example, landing into a strong headwind does not change the approach speed required or the thrust required to obtain that approach speed. The only allowance is for gusty conditions, during which a gust will momentarily affect airspeed due to the inertia of the airplane. The heavier the airplane, the more time it takes a gust or shift to defeat the airplanes inertia.
The former doesn't make any sense, but the latter is what the GP was saying.
The poster I replied to was implying that due to the strong tailwind, they had to maintain an increased airspeed. That is incorrect. The airplane has no idea it is in a tailwind, and airspeed will be unchanged.
I think calling it a "common misconception" is also assuming a lot.
No, he wasn't. He explicitly said the opposite:
"higher ground speed to keep the same relative air speed."
The original was "relative air speed", which I would simply take as the way a person not familiar with aviation terminology would say "airspeed"--speed relative to the air.
This is further compounded when they say “they need to go faster”, as though the pilot needs to push the throttle harder. In actuality, the pilot doesn’t do anything differently to maintain their normal cruising speed.
The correct phrasing would have been the relative air speed and high wind speed combined, to result in a higher ground speed.
It was a great documentary I think a math program it wasn't all about the Heathrow system.
This isn't the show but it seems to explain the system: https://www.nats.aero/news/nats-trialling-use-artificial-int...
Source: I was on a Norwegian flight at exactly the same time and the pilot explained this logic to us and also mentioned that we were on pace to break this record. Unfortunately, the pilot couldn't land in the wind conditions and we had to divert. Good thing we had that extra fuel too as the diversion was to Copenhagen which is quite far.
They would have to fuel the flight light, which I doubt would ever happen because what if the atmospheric conditions changed on the way?
When you cross the Atlantic you're usually in sequence on a track. Slowing down one flight slows down all the flights behind it.
(Just checked and the flight in question was indeed on a track.)
On a personal note, you get so little sleep on a redeye flight as it is, I'd have been a bit miffed wake up so soon!