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Russian Tu-154 'Disappears From Radar' Near Sochi

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  • #16
    Originally posted by 3WE View Post
    Did he mention AA-191, or PSA-182, or some other incident with a 727 that lost a flap?...can't seem to remember that third one...something involving a takeoff over run.

    Those planes didn't do so good with asymmetrical flaps, although I recall hearing that had the AA-191 folks improvised and deviated from procedure and nosed over for more speed, the plane was 'supposedly' controllable.
    Here are some you've never heard about:

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    • #17
      I get the distinct impression the Tu-154 is a bit more dangerous in roll than the average swept wing airliner. The limited FCOM I have read tells us that at speeds up to V3 (flap retraction) the roll alarm will sound at angles exceeding 15° and that angles exceeding 25° are forbidden. There is also a pilot-selectable wing-leveler function that might be there to compensate for neutral or negative spiral stability. Hmmmm...
      Attached Files

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      • #18
        Originally posted by Evan View Post
        Based on the frequency of flap asymmetry incidents and the uneventful landing vs the hull-loss rate and the splits flaps procedures I am familiar with, a flaps 15 asymmetry will not overwhelm aileron authority with sufficient airspeed if dealt with at a reasonable bank angle.
        What incident are you familiar with where there was an asymmetry of 15 degrees? Don't confuse that with an asymmetry (of perhaps 1 degree) at 15 degrees.

        What about roll-rate? I have the impression that anhedral will have a greater roll-rate and that is why certain fighters use it
        Roll rate is not affected by dihedral or anhedral... as long as the sideslip angle remains zero (coordinated flight). There is no rolling moment caused by bank itself, no matter the design of the plane. In other words, unlike directional and longitudinal static stability, roll static stability is always neutral.

        --- 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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        • #19
          Originally posted by 3WE View Post
          Did he mention AA-191, or PSA-182, or some other incident with a 727 that lost a flap?...can't seem to remember that third one...something involving a takeoff over run.
          Aerosucre!!!

          I recall hearing that had the AA-191 folks improvised and deviated from procedure and nosed over for more speed, the plane was 'supposedly' controllable.
          In fact, they had no big issue keeping control... until they decided to slow down to V2... what is what they were expected to do after losing an engine during the take-off (according with the procedures current at that time).

          --- 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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          • #20
            Against my better judgement, I'm going to attempt a summary statement; however, I doubt Evan will ease up on his need to confirm that asymmetrical flaps are ok and that, if it applies to the crash here, then it's the pilots fault for ignoring a procedure.

            Here we go:
            If a plane crashes after take off and there are indications of asymmetrical flaps, the asymmetrical flaps are a good candidate to be a major contributing cause to the crash.

            Ag-Logic/Broad, Sweeping, Fundamental Statement: These are big powerful lifting surfaces (that are generally bigger than ailerons and spoilers- hint hint) that do amazing things to lift, stall speeds and drag...it's generally good for them to be fairly closely balanced.
            Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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            • #21
              Originally posted by 3WE View Post
              Ag-Logic/broad, Sweeping, Fundamental statement: These are big powerful lifting surfaces (that are generally bigger than ailerons and spoilers- hint hint) that do amazing things to lift, stall speeds and drag...it's generally good for them to be fairly closely balanced.
              You have two powered ailerons positioned further out from the CoG working against one set of flaps, possibly at the 15° setting**. Yet the entire accident sequence took 10 seconds. The link I posted includes flap asymmetries of at least 10° (many are not stated) that resulted in stablization, a checklist procedure and a safe landing. I can concede that the Tu-154 is a different kind of bird (although, as Gabriel has pointed out, that 35° wing sweep probably results in a slightly dihedral aircraft with at some neutral static spiral stability). But there has to be something more to it. Most likely a delayed or incorrect pilot response due to a lack of situational awareness.

              **Could also have been at 28°

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              • #22
                Originally posted by Evan View Post
                Based on the frequency of flap asymmetry incidents and the uneventful landing vs the hull-loss rate and the splits flaps procedures I am familiar with, a flaps 15 asymmetry will not overwhelm aileron authority with sufficient airspeed if dealt with at a reasonable bank angle

                They are saying the flight lasted a total of 70 seconds (I suppose that should include the 10 secs of loss of control and crashing). Highest altitude was 250m (850 ft), and the speed was 194-199 knots. Too slow and definitely too low?

                One problem with the Tu-154 is weak pitch control at low speeds, especially during landing. And then the tendency to pitch-up at high AoA (unprovoked according to some sources) and enter a flat spin after stalling. Don't know how it relates with the anhedral wings or lateral stability.


                At the same time, there is this incredible incident:

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                • #23
                  Side comment:

                  Originally posted by Evan View Post
                  ... static spiral stability...
                  That is something new for me...

                  --- 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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                  • #24
                    Originally posted by Black Ram View Post
                    One problem with the Tu-154 is weak pitch control at low speeds, especially during landing. And then the tendency to pitch-up at high AoA (unprovoked according to some sources) and enter a flat spin after stalling.
                    My gosh!!! If that's one problem I wonder how three problems would look like in this plane!!!!

                    --- 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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                    • #25
                      Originally posted by Black Ram View Post
                      At the same time, there is this incredible inaccident :

                      http://www.baaa-acro.com/2006/archiv...bishkek-manas/
                      Wow!!!

                      --- 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


                      • #26
                        Originally posted by Gabriel View Post
                        Side comment:



                        That is something new for me...
                        make that: static lateral stability

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