Realstic Stopping?

[WestAir 2,530]

Autobrake aside, on the 737 (the real bird) will using reversers/spoilers with max manual braking reduce stopping distance compared to using only max manual braking? I always thought that, while the brakes are the primary speed-reduction tool used during landing, that spoilers/reversers were considered secondary speed-reduction tools that affected stopping distance when the same amount of brake pressure is used.I guess this is why I only fly small 4-seat planes. Bigger planes are too complex. :(

[VIPERGTSR01 22]

Autobrake aside, on the 737 (the real bird) will using reversers/spoilers with max manual braking reduce stopping distance compared to using only max manual braking? I always thought that, while the brakes are the primary speed-reduction tool used during landing, that spoilers/reversers were considered secondary speed-reduction tools that affected stopping distance when the same amount of brake pressure is used.I guess this is why I only fly small 4-seat planes. Bigger planes are too complex. :(

Manual braking allows you to use the brakes to full effect if you wish (even damage them), yes using spoilers and thrust reverse will shorten the stopping distance while manual braking.

[Efussander 0]

Autobrake aside, on the 737 (the real bird) will using reversers/spoilers with max manual braking reduce stopping distance compared to using only max manual braking? I always thought that, while the brakes are the primary speed-reduction tool used during landing, that spoilers/reversers were considered secondary speed-reduction tools that affected stopping distance when the same amount of brake pressure is used.I guess this is why I only fly small 4-seat planes. Bigger planes are too complex. :(

Also keep in mind that spoiler/speedbrakes are not like a drag chute on the ground. Their purpose isn't necessarily to slow you down. (although the effect of drag on the spoilers does slow you somewhat) What they are really doing that makes them effective is 1st) initially spoiling lift; 2nd) transferring the (energy/force/inertia ?) to the wheels for better braking. Wheels that have solid contact with the ground and that are heavy (weight of the plane supported by wheels, not wings) will have better braking effectiveness than wheels that are barely touching the ground, and that are light because the wings are still supporting the plane somewhat.Hope that makes sense.

[badderjet 181]

Autobrake aside, on the 737 (the real bird) will using reversers/spoilers with max manual braking reduce stopping distance compared to using only max manual braking? I always thought that, while the brakes are the primary speed-reduction tool used during landing, that spoilers/reversers were considered secondary speed-reduction tools that affected stopping distance when the same amount of brake pressure is used.

Given the conditions you propose, yes, when comparing with the same brake px stopping distance will differ once you kick in the revs and bring up the speedbrakes. The more 'complicated' thing for many to understand is that a certain A/BRK setting in fact retains a fixed decel rate, NOT a fixed brake pressure, so what the speedbrakes and revs do there is simply take some pressure off of the wheel brakes. Decel rate and hence distance remain the same. Or put in other words, don't use revs and speedbrakes and the wheel brakes will have to do all the work alone. It's really just some sort of sharing the load, so to speak. And thus preserving some brake life.

[WestAir 2,530]

Given the conditions you propose, yes, when comparing with the same brake px stopping distance will differ once you kick in the revs and bring up the speedbrakes. The more 'complicated' thing for many to understand is that a certain A/BRK setting in fact retains a fixed decel rate, NOT a fixed brake pressure, so what the speedbrakes and revs do there is simply take some pressure off of the wheel brakes. Decel rate and hence distance remain the same. Or put in other words, don't use revs and speedbrakes and the wheel brakes will have to do all the work alone. It's really just some sort of sharing the load, so to speak. And thus preserving some brake life.

Thank's guys - the above few comments cleared that up nicely. I always figured the autobrakes worked by using a pre-set pressure of braking: Light, medium, heavy, max - I didn't know they actually tried to adhere to a pre-set deceleration rate instead.It all makes sense now.

[antic81 57]

Also keep in mind that spoiler/speedbrakes are not like a drag chute on the ground. Their purpose isn't necessarily to slow you down. (although the effect of drag on the spoilers does slow you somewhat) What they are really doing that makes them effective is 1st) initially spoiling lift; 2nd) transferring the (energy/force/inertia ?) to the wheels for better braking. Wheels that have solid contact with the ground and that are heavy (weight of the plane supported by wheels, not wings) will have better braking effectiveness than wheels that are barely touching the ground, and that are light because the wings are still supporting the plane somewhat.Hope that makes sense.

You beat me to it.Spoilers are a must in wet or contaminated runway conditions because the wheels need to be in solid contact with the ground, not aquaplaning, there is an equation that you use to work out the speed the wheel brakes start to become effective on a wet runway (9 x the square root of the tire pressure in psi)There have been more than one incidents in the past of runway overruns due to spoilers not deploying properly on touchdown - another reason that landing an ultra smooth "greaser" on a wet surface is not recommended, also why there is the call on touchdown of spoilers deployed.Cheers,

[Guest]

no, when using the autobrake function the braking is modulated to stop you in X distance (where X is a constant defined from lots of parameters, such as speed, aircraft weight, elevation, weather, runway surface etc) REGARDLESS of whether you are using spoilers or reversers. So you will always see the same stopping distance in the same conditions with reversers or not. The system will reduce or apply brake pressure as necessary dependent on drag being provided by other devices, to even out the stopping distance. As RSR pointed out, with spoilers and reverse the brakes don't have to work so hard to stop in that distance X so they ease off as required to save wear and tear and overheating.If you are not using autobrakes and plan on using manual braking it is a different story and you are going to have to work out how much brake pressure you want to apply.This modulated braking with the autobrakes is PRECISELY how the real 737 works. It is also the first time I have seen this achieved properly in a sim. How many other sims have this level of complexity in braking to take into account spoilers/reversers? Every other sim I have seen just applies a fixed brake pressure for each notch of autobrake. Not realistic at all!all the bestJR

Hi JR,yes the way you described it makes sense.I like you, please post more often here.thxMark Fosseth

[Jack_C 1]

Just did my autobrake 2 landing and am very pleased. I used the real numbers and actual aircraft weight. From my numbers I should stop at ~7000 feet. The AB2 stopped it at 6600 feet. To me that is very accurate. The thing I didnt account for are atmospheric conditions. If I used the atmospheric conditions that were on the flight plan instead of a standard day that 6600 may very well have been 7000 feet. But from that test, I can say it exceeded my expectations. Great job guys!JackColwill

[michal 44]

Jack, thanks for your very informative posts. But to me much more important are take off numbers - to have a realistic spread between sea-level cold conditions and high altitude hot days. This spread can be phenomenally large in real world. But I guess you already alluded above that you were satisfied with takeoffs.

[Jack_C 1]

Hey Michael. If I have time I will give ya some take off reports too, ok?JackColwill

[michal 44]

Hey Michael. If I have time I will give ya some take off reports too, ok?

No rush. Thanks.

[Flyer01 0]

Autobrake aside, on the 737 (the real bird) will using reversers/spoilers with max manual braking reduce stopping distance compared to using only max manual braking? I always thought that, while the brakes are the primary speed-reduction tool used during landing, that spoilers/reversers were considered secondary speed-reduction tools that affected stopping distance when the same amount of brake pressure is used.I guess this is why I only fly small 4-seat planes. Bigger planes are too complex. :(

Kenneth,As both an Aeronautical Science & Aviation Business Major and a Private Pilot, I really, really, really hope you were experiencing a temporary brain fart when you asked that question. :( Brian O'Donnell

[WestAir 2,530]

Kenneth,As both an Aeronautical Science & Aviation Business Major and a Private Pilot, I really, really, really hope you were experiencing a temporary brain fart when you asked that question. :( Brian O'Donnell

Brian,Don't worry, my signature is inaccurate. It should say: Private Pilot, Instrument Rating, Commercial/Multi in progress. :( All joking aside, yeah, Roberts comment on the AutoBrake system threw me off; For a second I thought he was saying "Don't worry, the Spoilers/Reversers won't ever affect your stopping distance!" | Obviously I experienced a brain stall, as opposed to just a brain fart. :(

[Jack_C 1]

Hey guys. I will try to give you the skinny on the autobrake system.There are 5 modes of autobrake on the NG; 1,2,3,Max, and RTO. Here are the deceleration rates of each one.AB1- 4 feet/secondAB2- 5 feet/secondAB3- 7 feet/secondMAX- 14 feet/secondSo lets say were are landing and the only means of stopping is autobrakes, you can expect to decelerate at the above speeds. Now lets take into account reverse thrust. INITIALLY reverse thrust will decelerate you at a rate of 6 feet/second. As the plane slows down this value diminishes. Therefore, reverse thrust is only effective at higher speeds. SO lets say we are planning a AB1 landing. When we touch down, we apply max reverse, and he autobrake system says hmmmmmm we are decelerating at a rate of 6 feet/sec therefore I am not going to apply any hydraulic pressure to the brakes. As the planes slows, and as mentioned the reverse becomes less effective now only slowing the plane at 3 feet per second, the autobrake system says Hey I am supposed to be decelerating this plane at 4 feet/sec but it is only decelerating at 3 feet/sec so I better apply hydraulic pressure to the brakes. At this point it applies only enough pressure to boost the deceleration rate back up to 4 feet/sec so it needs to add enough to create an additional 1 foot/sec. So we got the reversers 3 feet/sec and the autobrakes 1 foot/sec to make 4 feet/sec. As we slow even more the reversers create less deceleration and in turn the autobrake system keeps boosting pressure to maintain the 4 feet/sec. The same goes for AB2 except now it just tries to maintain a deceleration rate of 5 feet per second.NOW AB3 and max are a bit different in the sense that autobrakes start applying pressure right away. So when using AB3, the autobrakes are looking for 7 feet/sec. So when you touch down and apply max reverse you get 6 feet/sec so the autobrake system needs to apply enough pressure to boost the decel rate up to 7 feet per second. So as you can see even with max reverse, the AB system needs to start working right away as opposed the AB1 and 2 it waits until the reverses diminish in effectivesness to fall below the AB1 (4 feet/sec) or AB2 (5 feet/ sec). In AB MAX it works he same as AB3 but just a higher decel rate.Now when RSR said reversers dont really decrease your stopping distance he was essentially correct. For AB3 and max he was exactly correct. Lets say you land without reverse on AB 3. When you touch down, the AB is looking for 7 feet per second. So it applies enough brake pressure to give you 7 feet/sec. WITH reverse the AB3 initially gives 1 foot/sec because the reversers give you 6 feet/sec BUT the net result is 7 feet/sec. But you can see initially the autobrakes dont have to work as hard and thats what RSR was referring to; its easier on the brakes. Now the only difference when using AB 1 and 2 you INITIALLY get 6 feet per second with reversers so this is where reversers will give you a shorter stopping distance than using without. BUT that 6 feet/sec diminishes quickly below the 4 or 5 feet/sec that AB1 and 2 is looking for. The end result of using max reverse thrust on AB1 or 2 is about a few hundred feet shorter stopping distance so not much at all.So I hope this helps you out.JackColwill

[Joel 10]

Hey guys. I will try to give you the skinny on the autobrake system.There are 5 modes of autobrake on the NG; 1,2,3,Max, and RTO. Here are the deceleration rates of each one.AB1- 4 feet/secondAB2- 5 feet/secondAB3- 7 feet/secondMAX- 14 feet/secondSo lets say were are landing and the only means of stopping is autobrakes, you can expect to decelerate at the above speeds. Now lets take into account reverse thrust. INITIALLY reverse thrust will decelerate you at a rate of 6 feet/second. As the plane slows down this value diminishes. Therefore, reverse thrust is only effective at higher speeds. SO lets say we are planning a AB1 landing. When we touch down, we apply max reverse, and he autobrake system says hmmmmmm we are decelerating at a rate of 6 feet/sec therefore I am not going to apply any hydraulic pressure to the brakes. As the planes slows, and as mentioned the reverse becomes less effective now only slowing the plane at 3 feet per second, the autobrake system says Hey I am supposed to be decelerating this plane at 4 feet/sec but it is only decelerating at 3 feet/sec so I better apply hydraulic pressure to the brakes. At this point it applies only enough pressure to boost the deceleration rate back up to 4 feet/sec so it needs to add enough to create an additional 1 foot/sec. So we got the reversers 3 feet/sec and the autobrakes 1 foot/sec to make 4 feet/sec. As we slow even more the reversers create less deceleration and in turn the autobrake system keeps boosting pressure to maintain the 4 feet/sec. The same goes for AB2 except now it just tries to maintain a deceleration rate of 5 feet per second.NOW AB3 and max are a bit different in the sense that autobrakes start applying pressure right away. So when using AB3, the autobrakes are looking for 7 feet/sec. So when you touch down and apply max reverse you get 6 feet/sec so the autobrake system needs to apply enough pressure to boost the decel rate up to 7 feet per second. So as you can see even with max reverse, the AB system needs to start working right away as opposed the AB1 and 2 it waits until the reverses diminish in effectivesness to fall below the AB1 (4 feet/sec) or AB2 (5 feet/ sec). In AB MAX it works he same as AB3 but just a higher decel rate.Now when RSR said reversers dont really decrease your stopping distance he was essentially correct. For AB3 and max he was exactly correct. Lets say you land without reverse on AB 3. When you touch down, the AB is looking for 7 feet per second. So it applies enough brake pressure to give you 7 feet/sec. WITH reverse the AB3 initially gives 1 foot/sec because the reversers give you 6 feet/sec BUT the net result is 7 feet/sec. But you can see initially the autobrakes dont have to work as hard and thats what RSR was referring to; its easier on the brakes. Now the only difference when using AB 1 and 2 you INITIALLY get 6 feet per second with reversers so this is where reversers will give you a shorter stopping distance than using without. BUT that 6 feet/sec diminishes quickly below the 4 or 5 feet/sec that AB1 and 2 is looking for. The end result of using max reverse thrust on AB1 or 2 is about a few hundred feet shorter stopping distance so not much at all.So I hope this helps you out.JackColwill

Fantastic explanation! Thank you very much.