Announcement

Collapse
No announcement yet.

Bad take-off computation.

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #46
    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?

    Comment


    • #47
      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)

      --- 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 ---

      Comment


      • #48
        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!

        Comment


        • #49
          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?

          Comment


          • #50
            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...

            Comment


            • #51
              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.

              Comment


              • #52
                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 ---

                Comment


                • #53
                  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.

                  Comment


                  • #54
                    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.
                    The German long haul is alive, 65 years and still kicking.
                    The Gold Member in the 747 club, 50 years since the first LH 747.
                    And constantly advanced, 744 and 748 /w upper and lower EICAS.
                    This is Lohausen International airport speaking, echo delta delta lima.

                    Comment


                    • #55
                      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!

                      Comment


                      • #56
                        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!

                        Comment


                        • #57
                          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.
                          The German long haul is alive, 65 years and still kicking.
                          The Gold Member in the 747 club, 50 years since the first LH 747.
                          And constantly advanced, 744 and 748 /w upper and lower EICAS.
                          This is Lohausen International airport speaking, echo delta delta lima.

                          Comment


                          • #58
                            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 ---

                            Comment


                            • #59
                              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.

                              Comment


                              • #60
                                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.

                                Comment

                                Working...
                                X