Taking off...how much throttle ?
Discussion
Can anyone tell me how much throttle is used when a regular type passenger aircraft ie 737/757 etc fully laden with people and cargo takes off ? are pilots using 100% throttle/power available or do they keep some in reserve ? i presume runway length and maybe wind can affect this but was thinking in general terms.
Unless necessary, jets like the 737 don't typically use 100%. As you said, weight, runway length, centre of gravity etc come in to play. In the cockpit is a Flight Management computer, which will assimilate the data and tell you what thrust setting to use. IIRC, high 80s into the 90s (percent).
Once above a certain height, which depends on the company's operating procedures, the pilots will reduce throttle to what's known as 'max continuous'; the highest throttle setting which can be used for extensive periods of time.
Once above a certain height, which depends on the company's operating procedures, the pilots will reduce throttle to what's known as 'max continuous'; the highest throttle setting which can be used for extensive periods of time.
Take-off power required is calculated and EPR (engine pressure ratio) dialled into the engines. There are also engine (thrust) de-rate selections that can be made. The idea is that only the required thrust is used in order to prolong engine life etc. The hotter the turbine stages run at, the shorter the service interval. Over several hundred take-offs per year this makes a difference.
Modern turbine engines have FADEC (Full Authority Digital Engine Control) which has a protection envelope meaning that you can't cook the turbine stages by overtemping them, even if you shove the levers all the way forward. Slightly older turbine engines have to be looked after a little more, and if the levers are pushed all the way forward it's only a matter of time before the turbine comes out the back as a molten orange splurge.
Modern turbine engines have FADEC (Full Authority Digital Engine Control) which has a protection envelope meaning that you can't cook the turbine stages by overtemping them, even if you shove the levers all the way forward. Slightly older turbine engines have to be looked after a little more, and if the levers are pushed all the way forward it's only a matter of time before the turbine comes out the back as a molten orange splurge.
All of the above accurate.
De rating to increase engine life however requires STRICT cockpit management skills and CRM. A Middle Eastern carrier's crew allegedly got the input to the FCMS (?) both wrong and also not crossed checked properly resulting in a A340-500 (a considerably large aircraft) failing to take of when expected resulting in as close to a fireball with a fully laden aircraft as you would wish to be.
http://www.atsb.gov.au/publications/investigation_...
De rating to increase engine life however requires STRICT cockpit management skills and CRM. A Middle Eastern carrier's crew allegedly got the input to the FCMS (?) both wrong and also not crossed checked properly resulting in a A340-500 (a considerably large aircraft) failing to take of when expected resulting in as close to a fireball with a fully laden aircraft as you would wish to be.
http://www.atsb.gov.au/publications/investigation_...
We don't (Boeing & Airbus) use Max Continuous Power unless we're single engine.
Normally we'll take off at either Full Thrust or (as mentioned before) de-rated or Flex Settings.
After a certain height, we'll accelerate at climb power which is a lower thrust setting than that used for take-off.
Normally we'll take off at either Full Thrust or (as mentioned before) de-rated or Flex Settings.
After a certain height, we'll accelerate at climb power which is a lower thrust setting than that used for take-off.
Pretty much every air carrier uses some kind of reduced thrust settings for take-off to increase engine life and reduce maintenance costs. Like Papoo says, it's usually an N1 (that's the large fan at the front of a high-bypass jet engine) percentage of mid 80s to low 90s.
You should understand though, that 90% N1 is 90% of the maximum RPM of the N1 spool, and not 90% of the power available. This is because turbines don't produce power in a liner fashion.
Anyways, we use what are called 'flex' power settings for take-off, and they are aimed at being 85% N1 (and never lower than 85% N1), and then increased from there depending on many factors. In certain circumstances (windshear forecasts, using anti-ice on take-off, etc) we only use full N1, which is about 90%.
In addition, airplanes that use reduced thrust on take-off usually have a system which automatically increases power on the operating engine if it detects an engine failure as an added safety margin.
Also max continuous is generally a power setting used for single engine operations to get the most power out of the engine safely for an extended period of time, but disregarding any maintenance considerations.
You should understand though, that 90% N1 is 90% of the maximum RPM of the N1 spool, and not 90% of the power available. This is because turbines don't produce power in a liner fashion.
Anyways, we use what are called 'flex' power settings for take-off, and they are aimed at being 85% N1 (and never lower than 85% N1), and then increased from there depending on many factors. In certain circumstances (windshear forecasts, using anti-ice on take-off, etc) we only use full N1, which is about 90%.
In addition, airplanes that use reduced thrust on take-off usually have a system which automatically increases power on the operating engine if it detects an engine failure as an added safety margin.
Papoo said:
Unless necessary, jets like the 737 don't typically use 100%. As you said, weight, runway length, centre of gravity etc come in to play. In the cockpit is a Flight Management computer, which will assimilate the data and tell you what thrust setting to use. IIRC, high 80s into the 90s (percent).
Once above a certain height, which depends on the company's operating procedures, the pilots will reduce throttle to what's known as 'max continuous'; the highest throttle setting which can be used for extensive periods of time.
When using reduced thrust on take-off, setting climb power is actually an increase in power for many airplanes. For instance, 'flex' take-off thrust is 85.3%, and then for climb it's bumped up to 88.5%. Although, with a normal take-off setting climb power is always lower. Once above a certain height, which depends on the company's operating procedures, the pilots will reduce throttle to what's known as 'max continuous'; the highest throttle setting which can be used for extensive periods of time.
Also max continuous is generally a power setting used for single engine operations to get the most power out of the engine safely for an extended period of time, but disregarding any maintenance considerations.
CelicaGT said:
Pretty much every air carrier uses some kind of reduced thrust settings for take-off to increase engine life and reduce maintenance costs. Like Papoo says, it's usually an N1 (that's the large fan at the front of a high-bypass jet engine) percentage of mid 80s to low 90s.
You should understand though, that 90% N1 is 90% of the maximum RPM of the N1 spool, and not 90% of the power available. This is because turbines don't produce power in a liner fashion.
Anyways, we use what are called 'flex' power settings for take-off, and they are aimed at being 85% N1 (and never lower than 85% N1), and then increased from there depending on many factors. In certain circumstances (windshear forecasts, using anti-ice on take-off, etc) we only use full N1, which is about 90%.
In addition, airplanes that use reduced thrust on take-off usually have a system which automatically increases power on the operating engine if it detects an engine failure as an added safety margin.
Also max continuous is generally a power setting used for single engine operations to get the most power out of the engine safely for an extended period of time, but disregarding any maintenance considerations.
Thanks for that, I have always wondered why the fans made more rattle when the ac into climb, flex, now I know. You should understand though, that 90% N1 is 90% of the maximum RPM of the N1 spool, and not 90% of the power available. This is because turbines don't produce power in a liner fashion.
Anyways, we use what are called 'flex' power settings for take-off, and they are aimed at being 85% N1 (and never lower than 85% N1), and then increased from there depending on many factors. In certain circumstances (windshear forecasts, using anti-ice on take-off, etc) we only use full N1, which is about 90%.
In addition, airplanes that use reduced thrust on take-off usually have a system which automatically increases power on the operating engine if it detects an engine failure as an added safety margin.
Papoo said:
Unless necessary, jets like the 737 don't typically use 100%. As you said, weight, runway length, centre of gravity etc come in to play. In the cockpit is a Flight Management computer, which will assimilate the data and tell you what thrust setting to use. IIRC, high 80s into the 90s (percent).
Once above a certain height, which depends on the company's operating procedures, the pilots will reduce throttle to what's known as 'max continuous'; the highest throttle setting which can be used for extensive periods of time.
When using reduced thrust on take-off, setting climb power is actually an increase in power for many airplanes. For instance, 'flex' take-off thrust is 85.3%, and then for climb it's bumped up to 88.5%. Although, with a normal take-off setting climb power is always lower. Once above a certain height, which depends on the company's operating procedures, the pilots will reduce throttle to what's known as 'max continuous'; the highest throttle setting which can be used for extensive periods of time.
Also max continuous is generally a power setting used for single engine operations to get the most power out of the engine safely for an extended period of time, but disregarding any maintenance considerations.
Cheers
RDE said:
Flying the Big Jets by Stanley Stewart is a good read if you're interested in this sort of thing. It doesn't go into as much depth as some of the professionals responding on here but it seems a good overview of operating a modern aircraft.
Would the aircrew on here agree?
Yes, I'd also recommend Stewart's book if you want a general idea of what's involved in flying an airliner. Not to be confused with 'Handling the Big Jets' which will assault you with fold-out hydraulic system schematics, AC constant speed drive units and critical Mach numbers.Would the aircrew on here agree?
Stewart also wrote 'Emergency: Crisis on the Flight Deck' which has some very readable examples of what happens down the front when it all goes tits-up.
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