FPV 747-400X

[KCA9304 0]

Hi all,Didn't find much on the forum regarding FPV indications. (737 only)Vertical FPV indicates as should be.Have my doubts about the lateral indication.After some experiments, found that during turns, the lateral displacement is dependend on speed. same is true for the Track pointer on PFD heading scale.On this indicated displacement the effect of wind (if any) is "superimposed".My knowledge of FPV (please correct where wrong!) is that the lateral displacement is a function of real time drift.So (for me) during a NO-Wind condition, the indication has to stay just in the middle. During wings level AND also in a turn.With the upcoming MD-11, much more use will be made of FPA and Track, so a clear understanding of the (correct?)indications might help to enjoy that very different aircraft.Two example pics to show what the (present) 400X indicates.Can anyone clearify this?Regards,Harry

[Mats_J 2]

Harry,As far as I know the FPV (flight path vector) will point where the aircraft is heading (your track) and your aircraft symbol will point in the direction of the nose. Nothing more nothing less. Both vertical and lateral. The momentary track and your nose will not be aligned when turning thus the FPV and the aircraft symbol will not be aligned either.That is how I understand it. Cheers,

[KCA9304 0]

Hallo Mats,Thank you for your remarks on FPV.Q< As far as I know the FPV (flight path vector) will point where the aircraft is heading (your track) and your aircraft symbol will point in the direction of the nose. Nothing more nothing less. Both vertical and lateral. >QThis is also my understanding, and this definition is true during turns as well !!. No problem.QQFrom here our interpretation has a different "vector". Does not matter. My intention is NOT to point a finger at someone, but to add and seek information so the total product gets even more precision. In the 747-400 manuals the only reference to FPV is the button on the EFIS/MCP. For the future MD-11 the FPV is a much more integrated feature in her operation, so I imagine also more discriptive text will be incorporeted in the Flight Manuals.Back to the difference:To my knowledge the vertical and lateral signals to present the FPV come from the IRS directly. They are the momentary acceleration forces (relative to earth !!!) in the respective axes and are in no way processed to give a trend. ( The Trend Vector on the ND is quite a different calculation.) Regarding FPV we are not talking about airodynamic acceleration forces acting on the aircraft, but acceleration forces relative to earth!So in a coordinated turn, the momentary track AND the momentary heading are the same in a no-wind condition and the FPV should remain aligned with the nose.Only when there is wind or side-slip the track and heading will be different, but this is already progammed. (added to the caculation) Maybe some RW pilots are able to confirm correct FPV indication during turns. (Markus MD11 sim?)Regards,Harry

[Mats_J 2]

Harry,>From here our interpretation has a different "vector". :-)>To my knowledge the vertical and lateral signals to present>the FPV come from the IRS directly. They are the momentary>acceleration forces (relative to earth !!!) in the respective>axes and are in no way processed to give a trend. ( The Trend>Vector on the ND is quite a different calculation.) Regarding>FPV we are not talking about airodynamic acceleration forces>acting on the aircraft, but acceleration forces relative to>earth!I am not a real pilot but do have some knowledge about the aircraft. As far as I understand the FPV will indeed include any deviation due to external influences i.e. winds. I might be wriong however but it seems logical as at least I would like to know my true vector even if winds are present. Any wind will act on the aircraft as an acceleration force and will be picked up by the IRS.>So in a coordinated turn, the momentary track AND the>momentary heading are the same in a no-wind condition and the>FPV should remain aligned with the nose.>Only when there is wind or side-slip the track and heading>will be different, but this is already progammed. (added to>the caculation)I beg to differ here. If the vector and the nose were heading the same way you would not be turning. As far as I know this is basic physics. The vector will point slightly towards the centre of the turn to force the aircraft to actually turn. Interesting discussion never-the-less,

[KCA9304 0]

Mats,Some more, before RW pilots "tell the truth" :-)QQFully true again! And... this vector (due external influence) is already programmed correctly.QQ Here we are using "vector" for different forces acting on the aircraft during turn.1- Aerodynamic force pointing horizontally to the center of the turn as a component of the banked lift vector. This will make the a/c turn and change track and heading in the same amount over time. However, due to speed, because of the turn, the a/c mass "resists" this inward move by producing a horizontal force vector to the outside of the turn. (thats why we feel increased G during turns).In a coordinated and steady turn these horizontal forces are balanced and should not deflect the FPV.2- Accelleration force due to external influence, ie winds. This (resultant) horizontal force is used the same as in wings level flight to deflect the FPV indication of center accordingly.Regards,Harry

[Mats_J 2]

Harry,>1- Aerodynamic force pointing horizontally to the center of>the turn as a component of the banked lift vector. This will>make the a/c turn and change track and heading in the same>amount over time. True.>However, due to speed, because of the turn, the a/c mass>"resists" this inward move by producing a horizontal force>vector to the outside of the turn. (thats why we feel>increased G during turns).>In a coordinated and steady turn these horizontal forces are>balanced and should not deflect the FPV.Now this is where I think you are a victim of your perceptions. There cannot be balance of forces in a turn as a turn *is* acceleration and thus *must* have an inward radial force applied to it. (Here we are assuming uniform circular motion i.e. the tangential speed is constant.) This is the centripetal force and is produced as you rightly stated as a component of the lift vector.The outward 'force' you are feeling can be explained if we see the aircraft and you in an inertial frame referenced to the earth. In this frame the aircraft is accelerating (due to the lift vector component during the bank) and making a turn. You on the other hand would continue straight forward unless the friction and the normal force between you and the seat made you follow the aircraft. This is what is called the centrifugal force and is a common misnomer.Hence I still claim that the vector and the nose should not be pointing in the same direction.Now let the hounds lose! ;-)Cheers,