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VLA sensitivity to wakes

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  • Grey Area
    Punter
    • Apr 2004
    • 12157

    #21
    At least you can spell "investigative"........
    You can't fool owls.

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    • Bmused55
      Aaahh Emu!
      • Oct 2003
      • 11136

      #22
      what's that supposed to mean?
      Bmused55

      Keep thy airspeed up, less the earth come from below and smite thee.

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      • Grey Area
        Punter
        • Apr 2004
        • 12157

        #23
        Touchy!!!!

        Look at my spelling in posting #19.....
        You can't fool owls.

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        • Bmused55
          Aaahh Emu!
          • Oct 2003
          • 11136

          #24
          I see.

          I wasn't being touchy, genuinely had no idea what you were on about
          Bmused55

          Keep thy airspeed up, less the earth come from below and smite thee.

          My Blog
          My Designs

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          • chornedsnorkack
            Rank 5 Registered User
            • Jul 2005
            • 1108

            #25
            Originally posted by Whiskey Delta
            Large aircraft are still sensitive to wakes. I remember seeing a few pictures of 707's and DC-8's who had engines removed by the wakes of similar aircraft they were following. Sure, the dangers for a 747 are different than a C152 but there are still risks.

            Isn't only the 753 considered a Heavy aircraft? I believe I have also heard the Heavy callsign for 739's as well but I could be mistaken. I know there was an attempt to get the 737NG's recategorized as the wakes off their new wings packed quite a punch when compared to the previous 737's. I know the few times I've gotten rocked rather hard by a previous airplanes wake it was reported as a 738 or 739.
            Well, somehow the ordinary Heavies are thought to be less sensitive. Light aircraft are allowed to get 6 miles behind a Heavy, Medium aircraft are allowed to get closer inside the wake, to 5 miles, and Heavies are allowed to get to 4 miles behind another Heavy.

            Can it be proven by testing that all Heavies whether a 767-200 or 747-400 are safe to fly less than 5 miles behind another Heavy, like a 747-400?

            Exactly how many miles behind the 747-400 was the Airbus 300 when wrecked?

            Can it be argued that the VLA might be safe less than 4 miles behind a Heavy, the way it sounds accepted that Heavies are safe at less than 5-6 miles behind a Heavy?

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            • Schorsch
              Severely Transonic
              • Aug 2005
              • 3843

              #26
              Originally posted by Whiskey Delta
              It's always easier to blame the dead guy in order keep the living (persons/company) clear of the inevitable lawsuits. Plus, we've yet to see a dead pilot be able to speak on his own behalf. Instead, we have hundreds, if not thousands, of "experts" judging the actions of a few in perfect hindsight. Nothing like a board of suits spending years to judge an action that someone had only seconds to comprehend let alone react to.
              Sorry, I do not know the pilot (not even his name). I just draw my conclusions from the available information. I do not judge the pilot as an individuum, I just judged him as pilot. And in this function, he certainly did a fatal mistake and, as I said, that was partly contributed by AA training and A300-600 rudder control mechanism. Those "experts" actually are experts. The pilot misjudged? Why did he do it? Read the report!

              Originally posted by Bmused55
              I agree with you.
              This is why American Airlines are bitterly defending their pilot.
              Its because of all this, I reserve judgement on who or what was responsible.
              American law suit resulted in a 95%-share of "financial responsibility" for AA. Maybe all the high-paid lawyers did not get it right? Don't you think that if there was any possibility of blaming Airbus of the accident they would have tried it. After all, I in the first place blame AA and not the individual pilot for that accident.

              Originally posted by chornedsnorkack
              Exactly how many miles behind the 747-400 was the Airbus 300 when wrecked?
              Please, the aircraft wasn't wrecked by the vortex but by the pilot (or if somebody wants to believe by the faulty VTP, but definitly not the vortex). AA587 was about 120 seconds behind the Japan Airlines B747. Vortex decays with time, not distance. ICAO recommandations quoted are for approach/take-off. Seperation grows for cruise, although cruise vortex encounter is far less dangerous (and therefore normally not mentioned).
              Last edited by Schorsch; 31st December 2005, 01:23.
              Publicly, we say one thing... Actually, we do another.

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              • chornedsnorkack
                Rank 5 Registered User
                • Jul 2005
                • 1108

                #27
                Originally posted by Schorsch
                AA587 was about 120 seconds behind the Japan Airlines B747. Vortex decays with time, not distance. ICAO recommandations quoted are for approach/take-off. Seperation grows for cruise, although cruise vortex encounter is far less dangerous (and therefore normally not mentioned).
                Hm, that is strange. The ICAO recommended wake separations are 4 miles for a Heavy behind Heavy on approach/take-off, 5 miles for cruise - only 25 % bigger. For a Heavy behind Ai-380, it is 10 miles for approach/take-off, 15 miles for cruise - only 50 % bigger. Whereas the cruise speed, at about 0,85 Mach or 500 knots TAS, is at least 200 % greater than the speeds on approach/take-off (around 150 knots...). So a plane at a minimum safe distance behind a craft cruising ahead is leaving at most a half, and likely one-third, the time for wake decay that is allowed on approach/take-off.

                How do the separation requirements change from 4 miles takeoff limit to 5 miles cruise limit over the course of the climb?

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                • Schorsch
                  Severely Transonic
                  • Aug 2005
                  • 3843

                  #28
                  Originally posted by chornedsnorkack
                  Hm, that is strange. The ICAO recommended wake separations are 4 miles for a Heavy behind Heavy on approach/take-off, 5 miles for cruise - only 25 % bigger. For a Heavy behind Ai-380, it is 10 miles for approach/take-off, 15 miles for cruise - only 50 % bigger. Whereas the cruise speed, at about 0,85 Mach or 500 knots TAS, is at least 200 % greater than the speeds on approach/take-off (around 150 knots...). So a plane at a minimum safe distance behind a craft cruising ahead is leaving at most a half, and likely one-third, the time for wake decay that is allowed on approach/take-off.

                  How do the separation requirements change from 4 miles takeoff limit to 5 miles cruise limit over the course of the climb?
                  And that is reasonable, because wake intensity is not constant. It decreases with airspeed and configuration, so that the wake of a cruising aircraft is considerably lower amplitude than that of a approaching aircraft with similar weight. Same with sensitivity: At cruise speed a wake would induce lower forces than at approach or take-off speed (same vortex strength, same aircraft, same configuration). Additionally, any turbulence or even upset is far less dangerous in cruise as ground clearance is suffcient to counteract and small deviations from planned flight-path is less of concern.
                  Publicly, we say one thing... Actually, we do another.

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