Deceleration A320 during RTO

[Flight777]

Hello,

I'm a student at the Hogeschool van Amsterdam (Univerisity of Amsterdam) Aviation Studies.
Our current project is about A320 braking, but I have a problem with the following:

I need to determine the average deceleration of an A320 during RTO. I already know that the auto-brakes are in max mode and give maximum braking pressure.

My way of approaching this problem was to determine the kinetic energy of the A320 during V1 and then calculate how much energy the brakes can absorb per second and then somehow calculate this to a average decelleration. But I can't find any info on that last part (so the formula for the amount of energy the brakes can absorb) so could anyone help me with this? Or if you know an easier way, please inform me! Because I'm getting an headache from this problem :P

Thank you in advance!

P.s. Sorry for the bad English

[PhilM]

I think the autobrake system will try to brake the aircraft with a deceleraion of 6m/s² if I recall.

[subsonic69]

max mode is actually not defined in m/s2( well maybe in our manuals ) but to give you an idea.

deceleration rate is 2 m/s2 in low, 3 m/s2 in medium or a 0.27G decel in max.

i think you shouldn't go calculating the amount of energy the brakes use in comparison with the deceleration rate since its not only the brakes that is utilized on the Airbus 320 auto brake system (most modern airliners too) even the spoilers have a role in it, thus giving you an erroneous result which would probably mean that (if your instructor notices) you will be repeating your calculations.:}

hope this helps:ok:

[Flight777]

Thanks for your replies. What I understand from the TTM (which is the only manual I have) the 0.27g is not the deceleration but then the DECEL lights comes on, for LO and MED mode this is when 80% of the deceleration is aquired.

And I know the ground spoilers, thrust reversers etc give also a deceleration. But I just have to know the approx deceleration during RTO so it does not have to be so very precise :)

But I don't know if the 6m/s^2 is on average?

Maybe it is easy to tell the whole assignment. I finally need to calculate the forces that act on each main bar/strut of the main landing gear during an RTO. So I need to know the deceleration and use F=ma but I also need to take friction into account etc

[subsonic69]

That is true... but there is no actual value for deceleration in the MAX mode only that once ground spoiler is sequenced for deployment then maximum braking pressure will then go to your brakes hence MAX.. I guess its safe to use the 6 m/s2 since its approximate only or you can go ahead with your calculations. :ok:

[Fargoo]

The BSCU commands a 6m/s/s decelleration rate but it's a moot point as the aircraft can never achieve this rate of decelleration (in normal circumstances).

[subsonic69]

fargoo is correct. i just found this out a while ago ..

2 deceleration rates (LOW = 1.7 m/square second and MED = 3 m/square second) and a MAX = 6 m/square second (higher than the maximum possible deceleration of the aircraft)

[Flight777]

Ok so what is a realistic deceleration rate to calculate with?

[superliner]

If you know the distance covered from the point me application of brakes till it comes to a full stop, and the velocity (V1?) cant we use a = v*v/2*d ?

[Flight777]

I don't have to use a specific distance etc. I just need to know the average decelleration of an A320 during normal circumstances in MAX Mode.

But thanks for your thoughts! :ok:

[BoeingDriver99]

Just reviving this thread because of a certain unmentionable incident somewhere.... The A320 AMM states the autobrake will aim for 10m/s/s in the case of MAX/RTO. And the DECEL light will come on at 0.27g which if we assume is 80% of the required rate, then max rate is 0.3375g. That works out at 3.31m/s/s. Well short of 10 but that's a target to aim for and anti-skid/tires will be the limiting factor.

The 737 aims for 14/ft/s/s which is 4.27m/s/s using MAX, not RTO

https://www.convertworld.com/en/acceleration/g-unit.html
Landing Gear (http://www.b737.org.uk/landinggear.htm#Autobrakes)