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Thread: Bad take-off computation.

  1. #41
    Senior Member Evan's Avatar
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    Quote Originally Posted by Gabriel View Post
    But it did happen. Of course, because the 747 was cargo and only crew died, and the 737 was a small plane killing a limited number of passengers (plus singe digit on the ground), and the A340 was just a near miss where luck was the main factor in not having 350 bodies, these were minor incidents and not total air disasters, so nothing happened here, keep moving, and wait until it happens again, this time preferably with a A380 in high density config. Tick, tock, tick, tock.....
    Exactly.

    Quote Originally Posted by Schwartz
    The reason there is no cognitive dissonance here is that when it happens, it will clearly be the "Pilots' fault". That myth can persist because of the infrequent nature of the problem. Such a system won't help them sell more planes. It will only cost money, and since the actual accident rate is so low, they won't see the ROI because it's a pilot problem.
    How does that work with GPWS (and more expensive TAWS and EGPWS), TCAS and other VERY rarely needed systems?

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    Senior Member 3WE's Avatar
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    Quote Originally Posted by Evan View Post
    In other words, the will is not there...
    But it's such a minor effort. How can there be any objection?
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

  3. #43
    Senior Member TeeVee's Avatar
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    how bout this: full power EVERY takeoff. oh wait, that would use fuel which costs money and is worth more than life itself.....

    but 1 thing's for damn sure, this type of thing would NEVER happen again.

  4. #44
    Senior Member Gabriel's Avatar
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    Quote Originally Posted by TeeVee View Post
    how bout this: full power EVERY takeoff. oh wait, that would use fuel which costs money and is worth more than life itself.....

    but 1 thing's for damn sure, this type of thing would NEVER happen again.
    It will avoid the cases where the thrust setting was incorrectly calculated or set, which are probably most cases, but will not avoid all the cases of wrong take-off execution vs calculation: wrong RWY, wrong intersection, wrong weight entered (and the airplane is too heavy for the available runway even with max power), engine instrument/sensors issues, head/tailwind component much more unfavorable than used to compute the take-off, etc...

    Also, it will not only increase the fuel burn, but the wear and tear of the engines, and very likely will result in an increase of engine failures during take-off since high power settings increase the stress and likelihood of failure.

    Finally, if only for the fuel burn and increased engine wear, TOPMS will be much cheaper for the airlines than an "all TO max power" policy.

    --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
    --- Defend what you say with arguments, not by imposing your credentials ---

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    Quote Originally Posted by TeeVee View Post
    how bout this: full power EVERY takeoff. oh wait, that would use fuel which costs money and is worth more than life itself.....

    but 1 thing's for damn sure, this type of thing would NEVER happen again.

    Light or empty airplane, full thrust is NOT your friend!

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    Quote Originally Posted by TeeVee View Post
    how bout this: full power EVERY takeoff. oh wait, that would use fuel which costs money and is worth more than life itself.....

    but 1 thing's for damn sure, this type of thing would NEVER happen again.
    I have some suggestions on how to improve legal practices as well. Interested?

  7. #47
    Senior Member Gabriel's Avatar
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    Quote Originally Posted by BoeingBobby View Post
    Light or empty airplane, full thrust is NOT your friend!
    But can be a LOT of fun!!! I am just having the mental image of an empty 747 with barely the needed furl to relocate to a nearby airport, with a V1 in the low 100s, half the mass compared to the MTOW, accelerating at more than 10 kts per second, in the air in about 10 seconds and 2000 ft, and climbing with a deck angle of 25 to 30 deg at some 8000 fpm!!! (And TeeVee enjoying it from 3A, since he flies first class)
    (numbers are made up, but I would not be surprised if they are not way off)

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    Quote Originally Posted by Gabriel View Post
    But can be a LOT of fun!!! I am just having the mental image of an empty 747 with barely the needed furl to relocate to a nearby airport, with a V1 in the low 100s, half the mass compared to the MTOW, accelerating at more than 10 kts per second, in the air in about 10 seconds and 2000 ft, and climbing with a deck angle of 25 to 30 deg at some 8000 fpm!!! (And TeeVee enjoying it from 3A, since he flies first class)
    (numbers are made up, but I would not be surprised if they are not way off)
    Gabe & TeeVee, Look up VMCG. It can be a fun demonstration in the simulator!

  9. #49
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    Quote Originally Posted by ATLcrew View Post
    I have some suggestions on how to improve legal practices as well. Interested?

    Now that was funny! I miss our German friend, wonder where he went?

  10. #50
    Senior Member Evan's Avatar
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    Quote Originally Posted by TeeVee View Post
    how bout this: full power EVERY takeoff. oh wait, that would use fuel which costs money and is worth more than life itself.....

    but 1 thing's for damn sure, this type of thing would NEVER happen again.
    What BoeingBobby is referring to is that the yawing power of full take off thrust, if it suddenly becomes asymmetrical due to an engine failure, can overpower the control surfaces below a certain speed, known as VMCG. For example, because of the VMCG limitation, the V1 and VR speeds for a 747-400 are actually about 10kts lower with derated thrust (TO2 derate) that they are at full thrust. With full thrust, you must achieve a higher speed before taking off.

    Still, with full thrust you should get to that higher Vr sooner along the runway...

  11. #51
    Senior Member Evan's Avatar
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    Quote Originally Posted by Gabriel View Post
    But can be a LOT of fun!!! I am just having the mental image of an empty 747 with barely the needed furl to relocate to a nearby airport, with a V1 in the low 100s, half the mass compared to the MTOW, accelerating at more than 10 kts per second, in the air in about 10 seconds and 2000 ft, and climbing with a deck angle of 25 to 30 deg at some 8000 fpm!!! (And TeeVee enjoying it from 3A, since he flies first class)
    (numbers are made up, but I would not be surprised if they are not way off)
    At flaps 20 and full thrust you could get V1 just a tick above 100 at 230t. But you can't use full power below 230t. VMCG limited...

    But below that weight, you can still get that same V1 at 200t using TO2.

  12. #52
    Senior Member Gabriel's Avatar
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    Quote Originally Posted by Evan View Post
    At flaps 20 and full thrust you could get V1 just a tick above 100 at 230t. But you can't use full power below 230t. VMCG limited...

    But below that weight, you can still get that same V1 at 200t using TO2.
    There must me something more to this. Vmcg, the power of the asymmetric thrust, and the power of the rudder to compensate for that are all independent of the weight. V1 cannot be lower than Vmcg, Vr cannot be lower than V1, and I think it was Vmu the one that was limited by Vmca. So the bottom line would be that you cannot take off slower than a certain speed even if the plane could, but you would get to that certain speed more quickly.

    --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
    --- Defend what you say with arguments, not by imposing your credentials ---

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    Quote Originally Posted by ATLcrew View Post
    I have some suggestions on how to improve legal practices as well. Interested?
    Yes.
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

  14. #54
    Senior Member LH-B744's Avatar
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    Quote Originally Posted by BoeingBobby View Post
    Hey, I don't work there anymore! http://avherald.com/h?article=4accc5bc&opt=0
    Hm. I wouldn't call that a bad computation. Don't we all know our 747 by heart? Sometimes computers try to steal human knowledge, and I consciously avoided the word intelligence in this context.
    Thank God, knowledge is based on experience. And I am still convinced, after all these years, that experience over decades is something which computers will never own.

    2500 m - or 8,200 ft?! I know one 747 which is able to t/o at KGCN...
    But this field is 2743 m (8,999 ft) long. Which I assume as the lower limit for a B744 (without MTOW).

    In this case we talk about a B748F, which under certain circumstances behaves like my nickname. So, where was the human experience? Temporarily n/a?

    But today I've again learned something. Not all rwys on worldwide known airports are longer than the 23L on my home airport. Good to know.
    One evening, not long ago, I watched TV and I wondered what you will possibly do after you've lost one parent. Strange question, why did I wonder. You will possibly be annoyed because he will miss so many happenings which you liked to show him. But after you somehow have regained your countenance, you will also join again people who you don't know. Stay strong, Jimmy.

    Aviation enthusiast since more than 30 years.

  15. #55
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    Quote Originally Posted by Gabriel View Post
    There must me something more to this. Vmcg, the power of the asymmetric thrust, and the power of the rudder to compensate for that are all independent of the weight. V1 cannot be lower than Vmcg, Vr cannot be lower than V1, and I think it was Vmu the one that was limited by Vmca. So the bottom line would be that you cannot take off slower than a certain speed even if the plane could, but you would get to that certain speed more quickly.

    Empty airplane, full thrust applied, 80 knots I take # 1 or # 4 away from you, you are in the grass!

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    Quote Originally Posted by LH-B744 View Post
    Hm. I wouldn't call that a bad computation. Don't we all know our 747 by heart? Sometimes computers try to steal human knowledge, and I consciously avoided the word intelligence in this context.
    Thank God, knowledge is based on experience. And I am still convinced, after all these years, that experience over decades is something which computers will never own.

    2500 m - or 8,200 ft?! I know one 747 which is able to t/o at KGCN...
    But this field is 2743 m (8,999 ft) long. Which I assume as the lower limit for a B744 (without MTOW).

    In this case we talk about a B748F, which under certain circumstances behaves like my nickname. So, where was the human experience? Temporarily n/a?

    But today I've again learned something. Not all rwys on worldwide known airports are longer than the 23L on my home airport. Good to know.
    There you are, we have missed you!

  17. #57
    Senior Member LH-B744's Avatar
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    Quote Originally Posted by BoeingBobby View Post
    There you are, we have missed you!
    Lol. You're kiddin me. What can I say now. I really would be curious to know at least all the details about you which since almost one decade each and every jetphotos member is able to learn about me. That especially concerns age.

    I often accept online friendships which contain the age. With only 1 exception! And I don't think that'll become more than only 1 exception...

    To be honest, I thought that you also were on the way to 1,000 posts. I wasn't aware that today almost 100 posts are between us. Come on, catch up again.
    One evening, not long ago, I watched TV and I wondered what you will possibly do after you've lost one parent. Strange question, why did I wonder. You will possibly be annoyed because he will miss so many happenings which you liked to show him. But after you somehow have regained your countenance, you will also join again people who you don't know. Stay strong, Jimmy.

    Aviation enthusiast since more than 30 years.

  18. #58
    Senior Member Gabriel's Avatar
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    Quote Originally Posted by BoeingBobby View Post
    Empty airplane, full thrust applied, 80 knots I take # 1 or # 4 away from you, you are in the grass!
    Believe it or not, ending up in the grass when aborting below V1 is within the certification standards. In some planes it is unavoidable. In the 747 you loose half of the thrust on one side. Imagine in a 777 loosing all the thrust on one side! In some planes at some slow speeds and wights it is unavoidable, and acceptable.

    I need to think a bit deeper to see why a plane under a certain weight will end up in the grass but not above that weight... The force of "full thrust", the distance from the CG, and hence the asymmetric moment, are all independent of the aircraft weight. The moment of inertia will, IN GENERAL (but not necessarily,) be higher at higher weights. The mass itself... I don't think it has a lot to do here...

    EDIT TO ADD: Not saying that there is not a thrust limitation below a certain weight. Just that the situation that justifies that limitation is probably a tad more complex than a linear "VMCG limit and you end on the grass".

    --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
    --- Defend what you say with arguments, not by imposing your credentials ---

  19. #59
    Senior Member 3WE's Avatar
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    Quote Originally Posted by Gabriel View Post
    EDIT TO ADD: Not saying that there is not a thrust limitation above a certain weight. Just that the situation that justifies that limitation is probably a tad more complex than a linear "VMCG limit and you end on the grass".
    Manure shoveling vs. aeroengineer moment: Weight on the nose wheel.

    Remember that MD-80 that laid into it a bit too hard as he turned onto the runway?
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

  20. #60
    Senior Member Evan's Avatar
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    Quote Originally Posted by Gabriel View Post
    Believe it or not, ending up in the grass when aborting below V1 is within the certification standards. In some planes it is unavoidable. In the 747 you loose half of the thrust on one side. Imagine in a 777 loosing all the thrust on one side! In some planes at some slow speeds and wights it is unavoidable, and acceptable.

    I need to think a bit deeper to see why a plane under a certain weight will end up in the grass but not above that weight... The force of "full thrust", the distance from the CG, and hence the asymmetric moment, are all independent of the aircraft weight. The moment of inertia will, IN GENERAL (but not necessarily,) be higher at higher weights. The mass itself... I don't think it has a lot to do here...

    EDIT TO ADD: Not saying that there is not a thrust limitation above a certain weight. Just that the situation that justifies that limitation is probably a tad more complex than a linear "VMCG limit and you end on the grass".
    You said it yourself: V1 cannot come before VMCG and V2 cannot come before V1. VMCG is only affected by two things: air density and thrust component, so weight doesn't move it (though it might affect the rate of the yawing moment - that's your department - uncontrollability is uncontrollability). But weight affects performance. So on a standard day using full thrust, when VMCG is coming at 133kts and your fast-accelerating empty 744 is reaching V1 at 103kts and VR of 116kts, it seems unwise. Derating to TO2 moves VMCG down to 122kts. Even then it seems unsafe to rotate before 127kts.

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