Flex Takeoffs Margin Question
RL,
Two operators.
One uses TOGA every takeoff.
The other makes sensible use of reduced Thrust TO.
Which will have more engine failures?
Two operators.
One uses TOGA every takeoff.
The other makes sensible use of reduced Thrust TO.
Which will have more engine failures?
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Wiz,
I wondering, wouldn't it be more reasonable to ask which one spends more on engine maintenance? Would one really expect more engine failures operating engines nearer to but within their limits with appropriate maintenance?
I wondering, wouldn't it be more reasonable to ask which one spends more on engine maintenance? Would one really expect more engine failures operating engines nearer to but within their limits with appropriate maintenance?
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Ok guys, lets put some facts in.
Copy Paste from a study (Yan Chenghong)
The significance of reduced thrust takeoff.
Prolong the life-circle of an engine by reduction T3.
As we all know,the longer the engine life is,the higher profit and the lower operation cost is.Turbine,as main part of an engine,is easy to be damaged for its bad working condition with high heat load,great centrifugal force and anomalistic pneumatic force. The great centrifugal force will wiredraw the blade. The anomalistic pneumatic force causes vibration and affixation stress to blade,then blade is easy to fatigue and rupture. The turbine inlet gas temperature (T3*) is an important factor of turbine power.Increasing T3* leads to increasing blade load and decreasing metal intensity.It is showed that the metal life has logarithm relation to its temperature. For example,a blade lose 35 percent of its life under the condition with 705 ℃ after operating 3,500 hours but 51 percent under the condition with 870℃ after operating 6.6 hours. The reduced T3* (about 30 to 50 ℃) when taking off with reduced thrust lengthens twice life of the heat section.
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Ok that was clear enough despite his english..
Laker Airways was the first airline using reduced thrust method in BAC-111's in RR Sprey engines. Rolce Royce had noticed that engines sent for overhaul by Laker airways were the best maintained of any BAC-111 operator.
Dont forget also, that lower takeoff thrust settings could permit a takeoff where with full thrust it wouldnt dispatched, with V1 limited by Vmcg, in short/wet runway. So you can increase your weight or if field limited reduce the ASDA simple by using reduced thrust.
Flex is, a great tool.
Copy Paste from a study (Yan Chenghong)
The significance of reduced thrust takeoff.
Prolong the life-circle of an engine by reduction T3.
As we all know,the longer the engine life is,the higher profit and the lower operation cost is.Turbine,as main part of an engine,is easy to be damaged for its bad working condition with high heat load,great centrifugal force and anomalistic pneumatic force. The great centrifugal force will wiredraw the blade. The anomalistic pneumatic force causes vibration and affixation stress to blade,then blade is easy to fatigue and rupture. The turbine inlet gas temperature (T3*) is an important factor of turbine power.Increasing T3* leads to increasing blade load and decreasing metal intensity.It is showed that the metal life has logarithm relation to its temperature. For example,a blade lose 35 percent of its life under the condition with 705 ℃ after operating 3,500 hours but 51 percent under the condition with 870℃ after operating 6.6 hours. The reduced T3* (about 30 to 50 ℃) when taking off with reduced thrust lengthens twice life of the heat section.
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Ok that was clear enough despite his english..
Laker Airways was the first airline using reduced thrust method in BAC-111's in RR Sprey engines. Rolce Royce had noticed that engines sent for overhaul by Laker airways were the best maintained of any BAC-111 operator.
Dont forget also, that lower takeoff thrust settings could permit a takeoff where with full thrust it wouldnt dispatched, with V1 limited by Vmcg, in short/wet runway. So you can increase your weight or if field limited reduce the ASDA simple by using reduced thrust.
Flex is, a great tool.
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runway behind is no benefit
I am not into FLEX as a matter of principle.......
In general in corporate it is available, and sometimes used, but the economics in my opinion do not justify it.
I prefer the shorter roll, on the typical corporate airports. I prefer to limit the bumping to the gear, as well as the passengers. I prefer air under the wings creating a margin of safety. I prefer the hills to be below me, and not exactly at my computed level, in that first turn.
I will not do flex, when there is a heavy infront, I want to well inflight before ant residual turbulance.
Would it be fair to say that a derated engine core, benefits less from a FLEX take off, and thus negated the standard arguements.
I did a flex about two years ago, at Stansted......
glf
In general in corporate it is available, and sometimes used, but the economics in my opinion do not justify it.
I prefer the shorter roll, on the typical corporate airports. I prefer to limit the bumping to the gear, as well as the passengers. I prefer air under the wings creating a margin of safety. I prefer the hills to be below me, and not exactly at my computed level, in that first turn.
I will not do flex, when there is a heavy infront, I want to well inflight before ant residual turbulance.
Would it be fair to say that a derated engine core, benefits less from a FLEX take off, and thus negated the standard arguements.
I did a flex about two years ago, at Stansted......
glf
And, in the corporate world, that may be reasonable.
The savings in maintenance in an Airline, with hundreds of aircraft doing hundreds of takeoffs a year are enormous.
PLUS there is a decrease in the incidence of failures through the use of reduced thrust.
The savings in maintenance in an Airline, with hundreds of aircraft doing hundreds of takeoffs a year are enormous.
PLUS there is a decrease in the incidence of failures through the use of reduced thrust.
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It's been said here, but I think need repeating. There is a built in margin here that makes an assumed temp. t/o safe in most conditions. Let's say it's 15 c outside and we are using an assumed temp of 50 c. With the exact numbers and speeds we are using we could take off at 50 c., but we're using those numbers at 15 c. the huge increase in performance due to the cooler temp. is in our back pocket. We are way exceeding the performance we would achieve if it actually was 50 c.
Last edited by 5LY; 19th Dec 2011 at 17:47.
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With respect to the 2nd segment numbers I think the point of Mutt's chart is that it takes a lower rate of climb to acheive the 2.4% gradient. In other words if you are climb limited you have only to make 387 ft/m to meet the 2.4% requirement where if the temp. was actually 40, and your TAS was higher, you'd have to acheive a higher rate of climb.
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Look at the difference in TAS.......
Mutt
Mutt
The aircraft achieves rated-thrust AFM performance at 40C; and using this same thrust on a 15C day, it also makes rated performance but at a TAS (inertial speed) 6 or 7 kt slower. Thus less runway is used, and less ROC is required to make the climb gradient.
As I've said before, I'm perfectly happy with RainingLogic bending his throttles day after day, because that's how my employer makes money on spare parts sales, and that means a better pension and dividends for me. But he can't expect his ideas to gain traction in an industry that makes MANY more takeoffs, and sails or fails on takeoff-related costs.
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Pretty funny..airline pilot logic...you set for 40c, but if it's colder...It's a win!
So if it's 30c, you set Flex to 50c, it's a win!...and if it's 50c, you set to 70c! It's a win!
Hey I have an idea. If you have 50 pax, you can plan for 100 pax..it's a win!
Here's another one..plan to run out of fuel over the ocean but carry enough fuel to make it...it's a win!
Or, throw your charts out the window half way to Hawaii, but have a secret set under the seat, so when you get to Hilo...viola, charts! It's a win!
So if it's 30c, you set Flex to 50c, it's a win!...and if it's 50c, you set to 70c! It's a win!
Hey I have an idea. If you have 50 pax, you can plan for 100 pax..it's a win!
Here's another one..plan to run out of fuel over the ocean but carry enough fuel to make it...it's a win!
Or, throw your charts out the window half way to Hawaii, but have a secret set under the seat, so when you get to Hilo...viola, charts! It's a win!
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As I've said before, I'm perfectly happy with RainingLogic bending his throttles day after day, because that's how my employer makes money on spare parts sales, and that means a better pension and dividends for me
flexing is not an option in real life but company procedure whenever possible with pilots decision not to do when he believes he has reasons for it.
but when you make a full thrust takeoff on a situation when flex takeoff would be every day business you may have to explain why you decided to do this.
best regards
So tell me Raining Logic,
Are you prepared to take off at Max takeoff weight?
Wouldn't it be safer if you just alwys insisted on being 20% under?
Why not always err on the side of saftey?
Are you prepared to take off at Max takeoff weight?
Wouldn't it be safer if you just alwys insisted on being 20% under?
Why not always err on the side of saftey?
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Why not always err on the side of saftey?
