Braking deceleration of Airbus A320
 

Hi, I have an assignment in which I need to find the time and distance it takes for an A320 to brake from 30 knots to a full stop.

To do so I need to know the braking deceleration during taxi.

I have only been able to find the deceleration values for autobrake i.e.

LO - 2m/s2
MED - 3m/s2
MAX - 6m/s2

Am I right to say that autobrakes are off during taxi? What are the deceleration values of manual braking during taxi?

Thanks in advance.

We'll leave this query here for the time being. If it doesn't get much in the way of useful responses, we might look at moving it to Questions.

A difficult question as, for maximum braking, you would put everyone through the next seatback and for the range from nil to max braking is pretty broad.

Possibly you might do better with your assignment running the sums for the autobrake settings and qualifying your answers by reference to those values as examples within the available range. The other problem with the question is that, while the autobrake generally is set up to maintain a constant decel until the aircraft is stopped, the human pilot will modulate brake pressure throughout the stop with an associated varying decel.

Something of a strange assignment iat!!

Taxying out - after a certain stage Autobrake MAX will be selected for the RTO case but it is not available until 72kts IRS GS.

Taxying in - the PF will have disconnected Autobrake in order to be able to taxi in - otherwise it will bring you to a halt on the RW!!

I am not aware of how you would calculate the decel rate from 30kts to a standstill with max manual braking in an A320. Experience tells me that it would be almost instantaneous as JT suggests. - an unpopular move!!

I would be interested to know the context of the task you have been set.

Cheers

Mcdhu

Yes, the auto brakes are off during taxi. Otherwise, they would be constantly slowing down the A/C, negating the objective of taxying.

Towards the end of the landing roll, the ABRK would be disengaged by the pilot at low speed, in order to prevent a locked wheel situation once the anti-skid (a.k.a ABS) deactivates (technical low-speed threshold for that). Actually 30 knots is about the right moment, after which you'd assume normal pedal braking.

The answer to your question is pretty useless: the distance depends on how hard you press on the brake pedals, and what is the surface friction available. If I pressed the pedals to the metal, the brakes lock giving max effectiveness on a dry surface, and we'd skid to a stop inside 30 meters. Possibly even sooner - and trash all the 4 tyres.

You can use max for landing, it is just not recommended.
And it cannot be armed in flight (any more).

The same distance it takes a a truck to slow from 30mph...;)

+10 :ok: And if the professor gives you A on that one, you know you chose the school right! https://www.albany.edu/faculty/miesi...sess/hell.html

Try pressing max on your next landing.
I said, it cannot be armed in flight.

Why not use the appropriate equations of motion or a calculator such as Equations of Motion Calculator and simply insert your initial speed (30 kts), final speed (0) and choose sample deceleration rates (say 2 m/sec/sec.)? e.g. Answer = 59.55m, 7.7 secs.
At 6 m/sec/sec Ans = 19.8m, 2.6 secs etc.

In any academic assessment, exam or assignment, it is important to ask yourself "What am I being asked to demonstrate that I have learnt here?"

Is this a basic physics unit which teaches you to calculate time and distance to decelerate to a standstill from a known velocity given a known acceleration?
Or is it a unit which teaches you to track down typical performance parameters such as the likely deceleration of an A320 at taxiing speeds?
Or is it perhaps intended simply to get you to calculate an estimate (with no fixed "correct answer") to make sure that you thoroughly grasp and remember how much space is required to stop?

Once you've answered this, you can then set about providing the type of answer required.