Different landing distance with/without rev thrust
Thread Starter
Joined: Apr 2008
Posts: 247
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From: Test
Different landing distance with/without rev thrust
Hi,
This is a performance question. I've looked up FCOM 1 for the different landing distance based on landing with/without reverse thrust.
My thought is the rate of deceleration after landing is the same with or without reverse thrust with the use of Autobrakes.
If so, why does FCOM directs me to add an adjustment to the landing distance with autobrake 1, No Reverser on a dry runway and also on a Good Braking Action runway with varying autobrakes settings with No Reverser? The rate of deceleration should be the same and if so, shouldn't the landing distance be the same too?
Thanks for the enlightenment.
This is a performance question. I've looked up FCOM 1 for the different landing distance based on landing with/without reverse thrust.
My thought is the rate of deceleration after landing is the same with or without reverse thrust with the use of Autobrakes.
If so, why does FCOM directs me to add an adjustment to the landing distance with autobrake 1, No Reverser on a dry runway and also on a Good Braking Action runway with varying autobrakes settings with No Reverser? The rate of deceleration should be the same and if so, shouldn't the landing distance be the same too?
Thanks for the enlightenment.
Joined: Jan 2008
Posts: 1,269
Likes: 79
From: Denver
I would think: Friction of the tires on the runway is proportional to normal force (the weight of the plane pressing down on them). At the beginning of the landing run, there is still substantial lift from at least part of the wing, even with spoilers deployed, reducing the effective weight on the wheels, and thus the friction available for braking.
Therefore, a rate-based autobrake system just won't have enough braking to work with, until the plane slows enough and puts enough weight on the wheels. Reverse gets you down to a speed where the brakes become fully effective, in less time and thus in less distance.
At which point the autobraking will give a constant rate of deceleration (if so designed), based on the combination of reverse thrust (if used) and friction braking.
Therefore, a rate-based autobrake system just won't have enough braking to work with, until the plane slows enough and puts enough weight on the wheels. Reverse gets you down to a speed where the brakes become fully effective, in less time and thus in less distance.
At which point the autobraking will give a constant rate of deceleration (if so designed), based on the combination of reverse thrust (if used) and friction braking.
Joined: Sep 2002
Posts: 2,188
Likes: 6
From: La Belle Province
Autobrakes can give you less braking than is available by the conditions of the day, it can't give you more. If you are in a state where the max available braking action is less than that which the autbrakes is trying to achieve, then you will be limited by the conditions. In which circumstances changing the conditions - by, for example, using TRs - should change your stopping performance.
Joined: Aug 2013
Posts: 30
Likes: 0
From: PA
Thread Starter
Joined: Apr 2008
Posts: 247
Likes: 0
From: Test
I would think: Friction of the tires on the runway is proportional to normal force (the weight of the plane pressing down on them). At the beginning of the landing run, there is still substantial lift from at least part of the wing, even with spoilers deployed, reducing the effective weight on the wheels, and thus the friction available for braking.
Therefore, a rate-based autobrake system just won't have enough braking to work with, until the plane slows enough and puts enough weight on the wheels. Reverse gets you down to a speed where the brakes become fully effective, in less time and thus in less distance.
At which point the autobraking will give a constant rate of deceleration (if so designed), based on the combination of reverse thrust (if used) and friction braking.
Therefore, a rate-based autobrake system just won't have enough braking to work with, until the plane slows enough and puts enough weight on the wheels. Reverse gets you down to a speed where the brakes become fully effective, in less time and thus in less distance.
At which point the autobraking will give a constant rate of deceleration (if so designed), based on the combination of reverse thrust (if used) and friction braking.
Thanks for all the replies above.
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