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If an Airbus A380 lands with all brakes disbled, including reverse thrust, wheel brakes and any other measures it has to stop or slow down. Then how long would it take it to reach a complete stop.

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    $\begingroup$ How is a question that could literally be answered by providing an equation possibly be considered for closing as "primarily opinion-based"? $\endgroup$ – Daniele Procida Jun 9 at 11:09
  • $\begingroup$ If someone had a flight simulator, he could see how much does the speed decrease over a certain distance and then we could extrapolate when does it reach zero. $\endgroup$ – stackzebra Jun 9 at 13:23
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    $\begingroup$ Flaps, drooping ailerons, spoilers do contribute to slow down, so is it in clean configuration? Or not?Should it be in full configuration, what landing speed? Do you understand how unprecise is this question? Why not asking a question such as : To slow down what is the relative effectiveness of the brakes, ground spoilers, reversers ...compared to each other? $\endgroup$ – user40476 Jun 9 at 15:33
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    $\begingroup$ This sounds like a Blues Brothers quote: "OK, it's a hundred and six miles to Chicago, we're in an A380, we've got no brakes, no thrust reversers, it's dark, and we're wearing sunglasses". "Check". "Hit it!" $\endgroup$ – Bob Jarvis Jun 9 at 20:56
  • $\begingroup$ Into the EMAS, through the EMAS, through the fence, into the bay, out of the bay and into the nightclub district. At least they'll have margaritas... $\endgroup$ – Harper Jun 10 at 1:42
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This is a very hypothetical question. If the aircraft has no means to slow down it has to lose all kinetic energy through rolling friction and air resistance. Both of these are very small (and get smaller as the aircraft gets slower) and will not have too much effect on a heavy aircraft like the A380 with an enormous amount of kinetic energy. Therefore the aircraft will continue to roll way beyond any runway or proper landing surface.

For high speeds, the air resistance will have the bigger impact on slowing down the aircraft (air resistance is about proportional to the square of the true air speed). Once the aircraft gets slow, the air resistance gets very little and rolling friction (highly dependant on ground surface) will be the bigger force to slow down the aircraft.

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    $\begingroup$ I bet it stops a lot faster once it overruns the runway and the ground below its wheels gives way. $\endgroup$ – Joshua Jun 9 at 19:44
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It depends

In practice, it would keep on rolling (as TomMcW summarises it) "until it hits something". It will run into something before it stops of its own accord.

How far it would roll if there were nothing in the way depends on a lot of things, some of which are discussed below.

Real-life or idealised conditions?

Are you asking about an idealised perfectly smooth and level runway, in conditions of still air? Or are you asking about real-life conditions?

I'm assuming that your disabled measures include the flaps, so now the plane is coming in for an over-speed landing.

Real-life runways are not long enough; under most conditions your plane would run off the end, onto rougher terrain.

Also, real-life runways are also often inclined. Once something like an A340 is moving slowly, its enormous mass needs only the slightest encouragement to keep rolling indefinitely to overcome friction.

Perhaps the closest we can get to an idealised runway is a desert salt flat, but the weight of a landing airliner would probably be high enough to damage it substantially and have a very rough experience.

Then we have to decide: how much fuel, how many passengers (i.e. how much mass has to slow down)? What's the air density? Will the tyre fuses blow because of overheating due to the prolonged high-speed roll?

Too many variables

In short, too many variables, and adjusting just some of those within real-life limits could change the stopping distance by an order of magnitude.

Calculating with an idealised model

A different way of asking the question would be to agree on the weight of the plane at landing (passengers plus fuel).

Then, we decide that it is landing at its minimum possible speed without flaps (180 knots, perhaps).

Now we have its momentum.

It's going to land on a perfectly flat smooth runway, in still air, at STP (standard temperature and pressure: 0 degrees C, 1 atmosphere). The runway has no end.

At that speed, air resistance will help slow it down. An engineer will be able to calculate the aerodynamic drag under those conditions, but there'll be quite a bit at first, and it will drop off rapidly as the plane slows.

We'll assume the tyres miraculously remain inflated until the plane comes to a complete halt. An engineer, again, will be able to calculate the friction of the wheels and tyres.

Our engineer will be able to combine the drag and friction into a calculation that includes the initial mass and landing speed to give us a curve that finally reaches zero.

Under these perfect conditions, the plane will roll for many kilometres. The tail of the curve will be shallow and very long.

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    $\begingroup$ tl;dr: Until it hits something. $\endgroup$ – TomMcW Jun 9 at 14:35
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    $\begingroup$ Hmm. Why should the tires burst? Moving and load will rise their temperature, but not fast and much. The car tires for a Porsche or Ferrari of class (Y) can hold more than 300 km/h. Of course this is a huge plane, but we neither apply brakes or plan to turn around. $\endgroup$ – Peter Jun 9 at 16:05
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    $\begingroup$ Tyres burst all the time! $\endgroup$ – Daniele Procida Jun 9 at 16:16
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    $\begingroup$ I'd expect the tires to enjoy this trip - the roughest thing they experience is touchdown, and then it's a cool, gentle rollout with the kinetic energy providing them a cooling breeze, instead of being converted into heat in the brakes. If they survive touchdown, they should hold. $\endgroup$ – Saiboogu Jun 9 at 16:45
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    $\begingroup$ @DanieleProcida - that link shows around one tire incident per day, but there are around 100,000 scheduled flights worldwide each day (44,000 in the USA alone), so based on that, it seems that aircraft tires rarely burst. $\endgroup$ – Johnny Jun 10 at 6:18

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