ozark1
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Reverse Thrust Vs. Braking

Fri Jun 12, 2015 11:14 pm

Last night, on an A319, we braked very hard on landing. So hard many loose items flew to the front. On MD80's I have had mainly reverse thrust on landing, but braking at times. Basically some of both on all equipment I have flown. What are the reasons to use RT vs braking? I would assume RT uses more fuel? Most of the time, when braking is used instead of RT, it has been hard braking. Just curious. Thanks for any info.
 
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Starlionblue
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RE: Reverse Thrust Vs. Braking

Fri Jun 12, 2015 11:58 pm

Quoting ozark1 (Thread starter):
Last night, on an A319, we braked very hard on landing. So hard many loose items flew to the front. On MD80's I have had mainly reverse thrust on landing, but braking at times. Basically some of both on all equipment I have flown. What are the reasons to use RT vs braking? I would assume RT uses more fuel? Most of the time, when braking is used instead of RT, it has been hard braking. Just curious. Thanks for any info.

It's not really either or. Wheels brakes have many times the braking power of reverse thrust. While those landings in the MD80 used reverse thrust, most of the stopping power still came from brakes.

Three considerations:
- Reverse is noisy, meaning it is discouraged at many airports with noise restrictions.
- Steel brakes need periodic replacement depending on the amount of force applied, while newer carbon brakes are replaced after a set number of applications regardless of braking force.
- Reverse thrust effectiveness decreases as speed decreases.

With some exceptions, landing distance calculations do not consider reverse thrust at all. It is purely a bonus.
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tb727
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 1:50 am

Quoting ozark1 (Thread starter):
Last night, on an A319

Just curious, where at?
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bueb0g
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 2:47 am

Quoting ozark1 (Thread starter):
Last night, on an A319, we braked very hard on landing. So hard many loose items flew to the front. On MD80's I have had mainly reverse thrust on landing, but braking at times. Basically some of both on all equipment I have flown. What are the reasons to use RT vs braking? I would assume RT uses more fuel? Most of the time, when braking is used instead of RT, it has been hard braking. Just curious. Thanks for any info.

As already stated, most of the braking power on an airliner is delivered by the wheel brakes. Indeed, if you consider that for most landings, autobrakes are used and on newer aircraft autobrakes command a decel rate rather than specifically a given brake pressure, reversers have no effect on the braking distance. Therefore, on most landings, only idle reverse is selected.

However they become far more useful on contaminated surfaces.

So to answer your question, brakes are used nearly all the time, and what you have perceived as brakes vs reverse thrust is far more likely to be differing levels of brake application, both also using reverse. They are used together; and if a pilot is braking very hard, it's quite likely that max reverse is being used as well.
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nema
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 7:34 am

I also find sometimes the reversers are not used. Can you remember the time when just before landing, an announcement would be made warning you of the sudden noise caused by using reverse thrust? It seemed to be used on all landings in those days. That announcement isnt made these days and reverse thrust when used isnt as loud as it used to be.
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Max Q
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 8:00 am

Quoting bueb0g (Reply 3):
reversers have no effect on the braking distance.

This is not correct, you are right in stating that autobrakes command a specific deceleration rate, however if the commanded rate is more than the anti-skid system can achieve as on a contaminated runway then reverse will 'help' to achieve that rate.


Autobrakes are not magic, they can only achieve the desired deceleration rate if the runway condition allows.
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Tristarsteve
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 12:05 pm

Quoting Starlionblue (Reply 1):
Steel brakes need periodic replacement depending on the amount of force applied, while newer carbon brakes are replaced after a set number of applications regardless of braking force.

Which carbon brakes are these?
We have carbon brakes on B767 A320 and B777. They all have wear pins that are checked and the brakes replaced before the pin goes flush. They look identical to the B757 and B734 steel brakes that have the same pin and limitation.
Which carbon brakes are changed after set nbr cycles?

We use thrust reverse on every landing. But rarely above idle. the reverser is deployed to reverse idle in case it is required, the braking is with the brakes.
 
bueb0g
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 12:22 pm

Quoting Max Q (Reply 5):
This is not correct, you are right in stating that autobrakes command a specific deceleration rate, however if the commanded rate is more than the anti-skid system can achieve as on a contaminated runway then reverse will 'help' to achieve that rate.

Which is why I noted the caveat of contaminated surfaces, but point taken.

[Edited 2015-06-13 05:23:45]
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zeke
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 12:38 pm

Quoting ozark1 (Thread starter):

Last night, on an A319, we braked very hard on landing.

Probably not at the lowest autobrake setting.

Quoting bueb0g (Reply 7):
Which is why I noted the caveat of contaminated surfaces, but point taken.

To be pedantic, autobrakes can have a short time delay before they start after touchdown, reverse maybe the only stopping mechanism for a short period of time. This is dependant on the autobrake setting/system, and the time required for the reverse to deploy which varies between engines. Normally reverse is cancelled or reduced to idle at lower speeds.
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Starlionblue
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 12:58 pm

Quoting Tristarsteve (Reply 6):
Quoting Starlionblue (Reply 1):
Steel brakes need periodic replacement depending on the amount of force applied, while newer carbon brakes are replaced after a set number of applications regardless of braking force.

Which carbon brakes are these?
We have carbon brakes on B767 A320 and B777. They all have wear pins that are checked and the brakes replaced before the pin goes flush. They look identical to the B757 and B734 steel brakes that have the same pin and limitation.
Which carbon brakes are changed after set nbr cycles?

Information on this site. I stand corrected.
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Tristarsteve
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 1:25 pm

Quoting Starlionblue (Reply 9):
Information on this site. I stand corrected.

No worries. I wondered if there was some new fangled system that I hadn't encountered
 
ZBBYLW
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 1:49 pm

It depends on many many factors.

Reverse is done usually at idle reverse. The point is if you need it it's there.

On the airbus there is essentially 4 brake settings. Off, low, med and Max. Max is only used for take off in the event of an RTO.

Many factors will decide whether you leave the brakes off or use low and medium. Generally most approaches are flown with auto brake either off or in low. Med is only used if the runway is quite short, contaminated or if you want to get off the runway in a hurry (LGA or other higher intensity runway operation airports).

Low is a nice smoother deceleration, how ever takes 4 seconds to engage and keeps you on the runway for a while.

Off seems to work best provided that you have practice in using the brakes smoothly and evenly (can heat up one side more than the other if not smooth).
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longhauler
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 1:54 pm

Quoting zeke (Reply 8):
autobrakes can have a short time delay before they start after touchdown, reverse maybe the only stopping mechanism for a short period of time.

It's been a few years since I flew the A320, but if I recall, it is 1 second delay on Med, and 4 seconds on Low. During that time, as you state, reverse is very effective.

Quoting ozark1 (Thread starter):
I would assume RT uses more fuel? Most of the time, when braking is used instead of RT, it has been hard braking.

Where I fly, the brakes are "leased" on some aircraft and costs the same whether used or not. For that reason, we are encouraged (when conditions permit) to use idle reverse and make up the difference with braking. Braking is almost always more effective than reverse, so it make feel harder.

But it comes down to pilot technique .... pass the first high speed turnoff for the second and it is a much smoother experience for the passengers.
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CALTECH
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 3:38 pm

Quoting ozark1 (Thread starter):
Last night, on an A319, we braked very hard on landing. So hard many loose items flew to the front. On MD80's I have had mainly reverse thrust on landing, but braking at times. Basically some of both on all equipment I have flown. What are the reasons to use RT vs braking? I would assume RT uses more fuel? Most of the time, when braking is used instead of RT, it has been hard braking. Just curious. Thanks for any info.

Auto brake logic A319/320
The auto brake logic is located in the BSCU on the control and monitoring boards of the SYS 1 and SYS 2.
The signals below are sent to the logic circuits of the auto brake:

• 3 signals that the AUTO BRK LO/MED and MAX on the center instrument panel supply:

2 deceleration rates, LOW = 1.7 m/square second and MED = 3 m/square second (2 m/square second in MED limited) , and a MAX = 10 m/square second (higher than the maximum possible deceleration of the aircraft)
There is a LOW type 2 mode = 2 m/square second depending of the aircraft pin programming.

• 3 signals which tell that the ground spoilers are extended.
Two of them must be present to permit the automatic braking.

Quoting zeke (Reply 8):
To be pedantic, autobrakes can have a short time delay before they start after touchdown, reverse maybe the only stopping mechanism for a short period of time.

Looks like it can be immediate for MAX Autobrakes, in a RTO setting, to 4 seconds in LOW or MED mode.

Operation
(a) LOW mode
1 This mode is used at landing.
2 The selector valve is energized by the extension command of the ground spoilers.
3 Braking is applied when the ground-spoilers extension signals are present (speed of the main gear wheel > 80 kts).
The braking has a delay of 4 seconds. It is then progressively applied.
4 The pressure supplied by the 4 servovalves gradually increases, t = 3 s approx.
The programmed deceleration is reached progressively.
5 The control circuit sends identical commands to the 4 servovalves.
6 The BSCU uses the deceleration from the ADIRs and limits or increases the braking order to make it reach the selected deceleration rate.

(b) MED mode
1 This mode is used at landing.
2 The selector valve is energized by the extension command of the ground spoilers.
3 Braking is applied when the ground-spoilers extension signals are present (speed of the main gear wheel > 80 kts).
The braking has two phases:
• phase 1: the MED limited deceleration is progressively applied without delay until the A/C attitude is less than 1 degree or T= 4 seconds.
The pressure supplied by the 4 servovalves gradually increases,
The programmed deceleration (2 m/square second) is reached progressively.
• phase 2: when the A/C attitude is less than 1 degree or T= 4 seconds, the MED deceleration is then progressively applied.
The pressure supplied by the 4 servovalves gradually increases,
The programmed deceleration (3 m/square second) is reached progressively.
4 The control circuit sends identical commands to the 4 servovalves.
5 The BSCU uses the deceleration from the ADIRs and limits or increases the braking order to make it reach the selected deceleration rate.

(c) MAX mode
1 This mode is selected before take-off in case of rejected take-off (at least 2 out 3 spoilers must be out).
2 The command for the ground spoiler extension controls:
• the energization of the selector valve,
• the immediate delivery of a maximum pressure to the four brakes (with antiskid protection).
3 The programmed deceleration rate is such as the full pressure is applied on the four brakes.
A small differential braking is not permitted.
The auto brake system is disengaged:
• when you push again the mode-selection pushbutton switch already selected.
• when you put the landing-gear control lever in the UP position
There is no AUTO BRK indication on the ECAM.
The automatic braking is only re-initiated after the selection of a new deceleration rate. This occurs if the signal for the extension of the ground spoilers is still generated.
The automatic braking is totally and immediately cut off as soon as a ground spoilers-retraction signal is applied (this signal possibly results from a go-around command).
The braking is inhibited but the system stays armed.
The automatic braking is re-initiated as soon as there is a new mode selection (LO or MED mode).
(d) In the MAX mode, the load required at the pedal to cut off the automatic braking is greater than that in the LO or MED mode.
Travel of the two brake pedals: 7.5 degrees in LO and MED mode.
Travel of one brake pedal: 10.8 degrees in LO and MED mode.
The pilot can disengage the AUTO BRAKE when he pushes only one pedal.


Quoting Starlionblue (Reply 1):
while newer carbon brakes are replaced after a set number of applications regardless of braking force.
Quoting Starlionblue (Reply 9):
Information on this site. I stand corrected.

Starlionblue,you are correct in that Carbon Brake wear does depend on how many applications are performed, in a way, but like Tristarsteve said, carbon brakes are just like steel brakes with wear pins determining when they are replaced. Think that Carbon Brakes last about twice as long as steel brakes in normal service, Hard to see when they get changed with all the MODs and Checks going on.

From a Maintenance and Engineering Bulletin,

Steel Brakes
• Steel brakes are relatively inexpensive
• Much larger mass of steel is required than carbon
to absorb the same energy
• Steel brake wear is dependent primarily on energy
added
• Less severe aplication longer life
• Steel brake wear increases significantly as brake
temps become elevated.

Carbon Brakes
• Carbon brakes immune to “welding”
• Much lighter than steel brakes
• Carbon brakes can withstand much higher operating
temperatures
• Initial cost and overhaul cost is much higher than steel
• Carbon brake wear is dependent primarily on number
of applications

• Fewer applications longer life
•Excellent wear characteristics at high temps
• Carbon brakes much less susceptible to fade
• Carbon brakes more forgiving in terms of
residual energy

Primary benefit of Carbon Brakes is the weight savings.

Most effective cooling is still achieved with Inflight gear extended cooling.

Weight savings on a B-737 with carbon brakes is about 700 Lbs.

Aww, Boeing has some good stuff on carbon brakes, could've saved some typing,...
http://www.boeing.com/commercial/aer...ticles/qtr_03_09/article_05_1.html
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flylku
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 4:59 pm

Quoting zeke (Reply 8):
autobrakes can have a short time delay before they start after touchdown

So is braking initiated automatically or does the pilot initiate braking but the rate is pre-selected regardless of the pressure applied by the pilot. If it is the former, how is autobraking disengage for reasons other than TOGO?
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Tristarsteve
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 5:36 pm

Quoting flylku (Reply 14):
So is braking initiated automatically or does the pilot initiate braking

The pilot selects autobrake before landing.
Read CALTECHs post above.
When autobrake is selected, braking starts automatically on landing if the right conditions are met, like, weight on wheels, spoilers out, wheel speed,
Braking stops when the pilot selects autobrake off, or he touches the brake pedals.
 
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 5:53 pm

Quoting ZBBYLW (Reply 11):

Reverse is done usually at idle reverse.

Only on some carriers. WN requires a minimum of reverse thrust at the 3rd detent on touchdown.
 
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DocLightning
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 6:15 pm

Quoting Starlionblue (Reply 9):
Information on this site. I stand corrected.

And to some degree, it strained my credulity. I also heard that carbon brakes wear by the number of times they are applied and not by the forces applied.

Quoting CALTECH (Reply 13):
• Carbon brake wear is dependent primarily on number
of applications

This makes no physical sense. The way I think about these things is to take it to a mathematical limit. So you're telling me that if the lightly-loaded aircraft is taxiing at 5 knots and the brakes are applied, that wears them as much as an overweight, overspeed landing? What possible material made of protons, neutrons, and electrons could have such properties?

It may be that carbon brakes are strong enough and inexpensive enough that it makes more sense to use them as the sole braking mechanism as compared to the additional wear and tear on the engines and reverser mechanisms (although we'll see if RR's new Ultrafan with variable pitch blades changes that), but the idea that they wear a fixed amount per application makes no sense.
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CALTECH
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 6:37 pm

Quoting DocLightning (Reply 17):
This makes no physical sense. The way I think about these things is to take it to a mathematical limit. So you're telling me that if the lightly-loaded aircraft is taxiing at 5 knots and the brakes are applied, that wears them as much as an overweight, overspeed landing? What possible material made of protons, neutrons, and electrons could have such properties?

It may be that carbon brakes are strong enough and inexpensive enough that it makes more sense to use them as the sole braking mechanism as compared to the additional wear and tear on the engines and reverser mechanisms (although we'll see if RR's new Ultrafan with variable pitch blades changes that), but the idea that they wear a fixed amount per application makes no sense.

Not me. Boeing, manufacturers of carbon brakes do. It takes some new thinking. And it does make sense.

"Carbon Brake Wear

Type I. This type of wear happens at low energy conditions, such as aircraft taxiing, or when low pressure is applied during braking. At these conditions, a particulate and powdery wear type debris is formed. These worn particles create abrasive wear which is the most damaging mode in terms of brake wear - liken it to applying a sand paper over the brakes. The particles are mostly formed by the carbon matrix, not carbon fibres.

Type II. This type of wear is at high energy conditions, such as in aircraft landing, or when high pressure is applied during braking. The difference in these conditions is that a smooth friction film is formed on the brakes which serves as a solid self-lubricant. This film protects the brakes, therefore the brakes will wear less. But then, the braking efficiency suffers, meaning that the friction coefficient is lower for brakes that have formed such a film.

High braking pressure with Carbon Brakes leads to lower brake wear, but only up to a limit. The lower brake wear is due to the formation of the silicon film at high energy braking which serves as a lubricant and protector of the ceramic/carbon brake material. The formation mechanism of the film is the subject of scientific debates, but it's known that it does not form at low energy braking, and it is destroyed at extremely high energy braking."
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flylku
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 10:15 pm

Quoting CALTECH (Reply 13):
Weight savings on a B-737 with carbon brakes is about 700 Lbs.

What is the $ cost differential between carbon and steel breaks. 700 lbs is a lot of fuel over thousands of cycles (or do carbon brakes last for thousands of cycles?).
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larshjort
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 10:48 pm

Quoting DocLightning (Reply 17):
This makes no physical sense. The way I think about these things is to take it to a mathematical limit. So you're telling me that if the lightly-loaded aircraft is taxiing at 5 knots and the brakes are applied, that wears them as much as an overweight, overspeed landing? What possible material made of protons, neutrons, and electrons could have such properties?

It may be that carbon brakes are strong enough and inexpensive enough that it makes more sense to use them as the sole braking mechanism as compared to the additional wear and tear on the engines and reverser mechanisms (although we'll see if RR's new Ultrafan with variable pitch blades changes that), but the idea that they wear a fixed amount per application makes no sense.

Carbon brakes is best at thier optimal working temperature which above 3-400 degrees celsius. Below that temperature the Wear rate is very high. The amount of energy absorbed by the brakes also have an anfluency on the Wear but the number of brake applications is the most importent.

Airbus has also made a nice document with nice Graphs from the brake manufacturers.
http://code7700.com/pdfs/carbon_brakes_airbus.pdf

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zeke
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RE: Reverse Thrust Vs. Braking

Sat Jun 13, 2015 11:23 pm

Quoting Tristarsteve (Reply 15):
Braking stops when the pilot selects autobrake off, or he touches the brake pedals.

Pressing brake pedals is the normal way.

Quoting CALTECH (Reply 18):
Boeing, manufacturers of carbon brakes do.

Dont think so, they buy them from suppliers.
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CALTECH
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RE: Reverse Thrust Vs. Braking

Sun Jun 14, 2015 4:44 am

Quoting DocLightning (Reply 17):
So you're telling me that if the lightly-loaded aircraft is taxiing at 5 knots and the brakes are applied, that wears them as much as an overweight, overspeed landing? What possible material made of protons, neutrons, and electrons could have such properties?
Quoting CALTECH (Reply 18):
Not me. Boeing, manufacturers of carbon brakes do. It takes some new thinking. And it does make sense.
Quoting zeke (Reply 21):
Dont think so, they buy them from suppliers.

You took it out of context. Boeing and Carbon Brake Manufacturers state what DocLightning questioned.

http://www.boeing.com/commercial/aer...icles/qtr_03_09/pdfs/AERO_Q309.pdf
"Carbon brake wear is primarily dependent
on the total number of brake applications —
one firm brake application causes less wear
than several light applications.
Maximum
carbon brake life can be achieved during
taxi by using a small number of long,
moderately firm brake applications instead
of numerous light brake applications."

Airbus too.

http://code7700.com/pdfs/carbon_brakes_airbus.pdf

Boeing some more

http://www.smartcockpit.com/docs/Taxing_with_Carbon_brakes.pdf

Do you think it was stated that Boeing makes carbon brakes ? That is not what that post meant.........
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Max Q
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RE: Reverse Thrust Vs. Braking

Sun Jun 14, 2015 6:48 am

On the 75/67 you can also disengage the autobrakes by retracting the speedbrakes, in fact just a very small forward movement of the speed brake handle will disengage them and usually more smoothly than with the brake pedals or just
turning the switch off.
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BravoOne
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RE: Reverse Thrust Vs. Braking

Sun Jun 14, 2015 4:57 pm

Just a point of interest to the MD 11 followers. The #2 engine will deploy the reversers along with 1 & 3, but it will not develop reverse thrust until the NW is on the ground. This is a function of the FADEC. The DC10 does all three engines at once. Don't know about the MD 10 but I would imagine it is like the DC 10. There is also a two stage spoiler deployment on the MD 11 that is triggered by the NW touchdown.

For the 1st couple of years the center MLG ABS was deactivated on the MD 11 due to mechanical issues.

[Edited 2015-06-14 09:58:18]
 
ozark1
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RE: Reverse Thrust Vs. Braking

Sun Jun 14, 2015 5:31 pm

Quoting tb727 (Reply 2):
Just curious, where at?

It was at SAT
 
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CALTECH
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RE: Reverse Thrust Vs. Braking

Mon Jun 15, 2015 1:05 am

Quoting flylku (Reply 19):
What is the $ cost differential between carbon and steel breaks. 700 lbs is a lot of fuel over thousands of cycles (or do carbon brakes last for thousands of cycles?).

Saw a price just under $40K for a steel B-737 brake, overhaul at about $10K. Imagine Carbon Brakes are probably about twice as much, if not more. Hard to find the buy price of a carbon brake.

http://www.aviationpros.com/article/...erican-airlines-wheel-brake-center

"Brakes and critical steps
However, every overhauled brake does get relined. In fact each steel brake contains approximately 140 of pads on five stators in assembly with four rotors, a pressure plate, and torque tube at an estimated overhaul cost of around $10,000 per brake. In comparison, a carbon brake (where each stator and rotor is individually machined from a carbon disc) can carry a full-stack cost of up to $50,000; they’re used in certain applications where the significant weight reduction and increased service life produce cost-justifiable long-range efficiencies."
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Max Q
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RE: Reverse Thrust Vs. Braking

Mon Jun 15, 2015 11:27 am

Quoting BravoOne (Reply 24):
Just a point of interest to the MD 11 followers. The #2 engine will deploy the reversers along with 1 & 3, but it will not develop reverse thrust until the NW is on the ground. This is a function of the FADEC.

Because of pitch up with # 2 Reverse ?
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longhauler
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RE: Reverse Thrust Vs. Braking

Mon Jun 15, 2015 2:21 pm

Quoting BravoOne (Reply 24):
The #2 engine will deploy the reversers along with 1 & 3, but it will not develop reverse thrust until the NW is on the ground.

We had something similar on some of our B737-200s. There was a squat switch on the nose-wheel that locked out T/R until activated.

They all didn't have it, but I had heard it was to reduce (eliminate) the possibility of scraping the buckets until the nose was down.
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BoeingGuy
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RE: Reverse Thrust Vs. Braking

Mon Jun 15, 2015 5:15 pm

Quoting Max Q (Reply 23):
On the 75/67 you can also disengage the autobrakes by retracting the speedbrakes, in fact just a very small forward movement of the speed brake handle will disengage them and usually more smoothly than with the brake pedals or just
turning the switch off.

I'm pretty sure this is true off all Boeing models. If you do this during landing the switch will snap to DISARM. If during an RTO the switch will stay in RTO.
 
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CALTECH
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RE: Reverse Thrust Vs. Braking

Tue Jun 16, 2015 2:43 pm

Quoting Max Q (Reply 23):
On the 75/67 you can also disengage the autobrakes by retracting the speedbrakes, in fact just a very small forward movement of the speed brake handle will disengage them and usually more smoothly than with the brake pedals or just
turning the switch off.

Running into a lot of 757 crews on RON aircraft that do not know how to put the airplane on Ground Service Power from the cockpit. They keep going back to the flight attendant 1L station and hitting the button there.

Showed a few of them how to do it from the cockpit and they were surprised that it could be done. It looks like these crews are new to the 757.
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RE: Reverse Thrust Vs. Braking

Wed Jun 17, 2015 11:32 am

Quoting CALTECH (Reply 30):

Can this also be done on the 73 from the cockpit? Because I keep going back to the galley to do this.

Airbuster
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Tristarsteve
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RE: Reverse Thrust Vs. Braking

Wed Jun 17, 2015 8:29 pm

Quoting CALTECH (Reply 30):
Running into a lot of 757 crews on RON aircraft that do not know how to put the airplane on Ground Service Power from the cockpit. They keep going back to the flight attendant 1L station and hitting the button there.

Well I used to work B757 and never knew that. How do you select Ground Service in the Flight deck?
You can also tell me how to do it on B737 B767 B777 and B744 and A320 A330. Because I go out into the galley on all these to select ground service.
 
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CALTECH
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RE: Reverse Thrust Vs. Braking

Tue Jun 23, 2015 12:16 am

Quoting airbuster (Reply 31):
Can this also be done on the 73 from the cockpit? Because I keep going back to the galley to do this.
Quoting Tristarsteve (Reply 32):
Well I used to work B757 and never knew that. How do you select Ground Service in the Flight deck?
You can also tell me how to do it on B737 B767 B777 and B744 and A320 A330. Because I go out into the galley on all these to select ground service.

Doesn't work on the 737, believe it works on the 767, does work on the 757.......all aircraft should have this feature.......

Battery switch on, External Power Available but not on, run throttles forward to the stops, then back to idle, Grd Service Power is now on, then you can turn off the battery. Saves the battery if external power drops off, and keeps the lights on for the cleaning crew. All from the cockpit.
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a3xx900
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RE: Reverse Thrust Vs. Braking

Wed Aug 05, 2015 3:02 pm

It is a known fact that modern brakes are more effective than steel brakes. Many airlines don't use reverse unless necessary due to weather/runway conditions.
Since modern carbon brakes are so effective and spooling up the engines is simply more expensive (wear and tear...), there was a discussion if reverse mechanism should be added to the A380 at all. As kind of a compromise they decided to put reversers in the inner engines only  
Can't quote a source but I remember that from the time the A380 was new...
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Western727
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RE: Reverse Thrust Vs. Braking

Wed Aug 05, 2015 3:20 pm

Quoting ualbq200 (Reply 16):
WN requires a minimum of reverse thrust at the 3rd detent on touchdown.

Why is that the case? Granted, I've noticed in a few years of flying many dozens of times on WN (after years of preference for other carriers) that reverse seems to be used more liberally by WN crews compared to crews from other carriers in the United States.
Jack @ AUS
 
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RE: Reverse Thrust Vs. Braking

Wed Aug 05, 2015 5:31 pm

Quoting a3xx900 (Reply 34):
Since modern carbon brakes are so effective and spooling up the engines is simply more expensive (wear and tear...), there was a discussion if reverse mechanism should be added to the A380 at all. As kind of a compromise they decided to put reversers in the inner engines only
Can't quote a source but I remember that from the time the A380 was new...

I thought they only put reverse thrust on the inboard engines due to FOD concerns due to the wingspan.

The KC-46 won't have thrust reversers as it currently stands.

My understanding is that most airline policies is to at least select reverse idle. That way they are already deployed in case of emergency and they need full reverse.
 
Western727
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RE: Reverse Thrust Vs. Braking

Wed Aug 05, 2015 5:53 pm

Quoting BoeingGuy (Reply 36):
The KC-46 won't have thrust reversers as it currently stands.

Intrigued by this, I found some more info and learned that the KC-135R/T do not have them, either, apparently for maintenance and weight considerations. I suppose that means that landing on highly-contaminated runways isn't generally a concern for tankers, then?
Jack @ AUS
 
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RE: Reverse Thrust Vs. Braking

Wed Aug 05, 2015 8:00 pm

Quoting Western727 (Reply 37):
Intrigued by this, I found some more info and learned that the KC-135R/T do not have them, either, apparently for maintenance and weight considerations. I suppose that means that landing on highly-contaminated runways isn't generally a concern for tankers, then?

Not my authority to speak on this topic.  
 
tommy1808
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RE: Reverse Thrust Vs. Braking

Wed Aug 05, 2015 9:39 pm

Quoting Western727 (Reply 37):
I suppose that means that landing on highly-contaminated runways isn't generally a concern for tankers, then?

they should also usually land very light.

Quoting Western727 (Reply 35):
Why is that the case? Granted, I've noticed in a few years of flying many dozens of times on WN (after years of preference for other carriers) that reverse seems to be used more liberally by WN crews compared to crews from other carriers in the United States.

I am wondering if that is allowed everywhere they fly, with no "reversers only idle, unless required" for noise abatement.

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JAGflyer
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RE: Reverse Thrust Vs. Braking

Thu Aug 06, 2015 4:23 pm

Quoting Western727 (Reply 35):

They don't want any repeats of this unfortunate incident...

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musang
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RE: Reverse Thrust Vs. Braking

Sat Aug 08, 2015 10:13 am

Quoting zeke (Reply 8):
To be pedantic, autobrakes can have a short time delay before they start after touchdown, reverse maybe the only stopping mechanism for a short period of time.

Another viewpoint -

Hard to imagine the T/Rs being even deployed before the A/B has kicked in, never mind being the only stopping mechanism. I'm on 737s. On touchdown the criteria are met for A/B almost instantly. With T/Rs, pull the levers to the detent, wait for the interlocks to release, then pull back into reverse then wait a while for the engines to spool up from about 32% Flight idle to about 75 or 85 for what our company calls Normal or Full reverse respectively. All that takes a good few seconds, and on a heavy braking short landing run, by the time the reverse has spooled up you've dissipated so much speed that reverse is a waste of time and you're immediately asking for reverse idle.

Reverse is most effective at high speeds, its effectiveness dropping exponentially as speed reduces. Wheel braking effectiveness increases as speed reduces, there being more weight on the wheels so less chance of locking a wheel

Quoting ZBBYLW (Reply 11):
Reverse is done usually at idle reverse.

Likely on an route network with noise sensitive airports. Like for example Heathrow, where I observe many arrivals don't use reverse above idle, at which level it negates the residual thrust of the un-reversed hot stream, which is significant since the engine will still be at Flight Idle rather than Ground Idle (31% vs. 21% for the 737s I drive)

My operation is short haul around Europe. Idle deployment is mandatory as mentioned in an earlier post, and we probably use "normal" reverse in 90% of landings. Rare to need full reverse, and the times we restrict it to idle are (a) landing at anti-social hours when the aircraft's not going out again (i.e. we would need to limit brake heating) and (b) runways where the exit is at the far end. I can think of a couple where one might land with idle reverse and no auto brake.

(Autobrake is not mandatory in our organisation. Common sense is allowed to prevail and its a whole other debate!)

Regards - musang
 
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zeke
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RE: Reverse Thrust Vs. Braking

Sat Aug 08, 2015 3:40 pm

Quoting musang (Reply 41):
On touchdown the criteria are met for A/B almost instantly.

On the Airbus with low autobrake there is a 4 second delay after ground spoilers are deployed before autobrake starts so the crew can perform a rejected landing if necessary, medium autobrake its 2 seconds.

Also on the Airbus autobrake commands a deceleration rate, not a brake pressure, so while the autobrake is engaged assuming a runway that is not contaminated the deceleration rate is the same without without using reverse. Using full reverse, the autobrake will use less brake to achieve the same deceleration rate.

Wheel brake effectiveness increases as weight is increased on the wheel.
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musang
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RE: Reverse Thrust Vs. Braking

Sun Aug 09, 2015 10:07 am

Interesting. On the 737 (classic, at least), A/B application begins when:-

1) both thrust levers retarded to idle, and

2) main wheels spin up.

No system-imposed delay.

If we decide to go around, advancing the thrust levers cancels A/B.

Your second para applies to the 737 in its entirety, and other modern Boeings too I think.

Regards - musang
 
Max Q
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RE: Reverse Thrust Vs. Braking

Mon Aug 10, 2015 4:26 am

Quoting musang (Reply 43):
Interesting. On the 737 (classic, at least), A/B application begins when:-

1) both thrust levers retarded to idle, and

2) main wheels spin up.

No system-imposed delay.

If we decide to go around, advancing the thrust levers cancels A/B.

Your second para applies to the 737 in its entirety, and other modern Boeings too I think.

Correct, building in a delay for brake application seems unecessary with this logic.
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Richards2K14
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RE: Reverse Thrust Vs. Braking

Mon Aug 10, 2015 11:58 am

I was spotting at MAN on Friday and noticed a lot of aircraft using full reverse or what sounded like it landing on 23R, but that was mainly during the busier early afternoon period when they were trying to exit at the first high speed taxiway. Ryanair still had their reversers open on the taxiway. A380 used the whole length of 23R landing in the evening, whilst other time I have seen it leave the runway earlier.
 
BoeingGuy
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RE: Reverse Thrust Vs. Braking

Mon Aug 10, 2015 3:51 pm

Quoting musang (Reply 43):
If we decide to go around, advancing the thrust levers cancels A/B.

Your second para applies to the 737 in its entirety, and other modern Boeings too I think.

The Autobrakes on all Boeing models will DISARM if you advance the throttles, manually step on the brakes, or retract the speedbrakes during roll out.
 
Leezyjet
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RE: Reverse Thrust Vs. Braking

Sun Aug 16, 2015 9:35 pm

Using the reverse also affects brake cooling times, which can be important if you are on a tight turn round, as if the brakes are too hot, then they may not work as expected on take off in the event of an RTO.
On the 737CL, landing close to max landing weight and using auto brake 3 only for example, can easily put you into the CAUTION zone on the brake cooling schedule, but using auto brake 3 and reverse usually requires around 19 minutes on the ground for brake cooling at the same weight, so it can make a big difference.
 
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lh346
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RE: Reverse Thrust Vs. Braking

Tue Aug 18, 2015 8:51 am

May I ask how much breaking force the front landing gear contributes?
Certainly there ought to be some kind of equipment installed up front to stop the wheels from spinning when the gear is cycled up (correct?).
 
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glen
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RE: Reverse Thrust Vs. Braking

Tue Aug 18, 2015 9:27 am

Quoting lh346 (Reply 48):
May I ask how much breaking force the front landing gear contributes?
Certainly there ought to be some kind of equipment installed up front to stop the wheels from spinning when the gear is cycled up (correct?).

The nose wheels are not equipped with brakes. They only stop spinning once they are in the wheel well by means of a kind of rubber band they are presses against.
As the gear retracts in the same plane like the rotating wheels, there are no gyroscopic forces like on the main gear and therefore no braking before retraction is necessary.
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