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Guest kohenen

Yam Damper function

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Hi,During cruise at FL31000 using pmdg 747-400, With LNAV turned on, I shutdown the engine 3, 4 and turn off the yam damper function. My expectation is the plane will deviate from the original route and yam to right. But it doesn't, is it normal.Rgds,Thomas

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The yaw damper system is not designed to compensate for engine asymmetry, so it doesn't really matter if the YD is on or off.The YD system helps to co-ordinate turns, but it's authority is very limited (a few degrees either side of neutral). If LNAV is engaged, the autopilot will keep inputting a roll command until it points the aircraft in the right direction (to keep it on track). However, you really need to use rudder trim for engine asymmetry.With the YD system off, the aircraft will be very unstable. It may help to use the rudder pedals for turns.Note that the 777 has a rudder control system designed to handle asymmetry. AFAIK, this has nothing to do with the Yaw Damper system either.Cheers.Q>

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Sorry for the hijack but what is the magenta 'fl020 180-365kts' text on the right CRT? Regarding the engine out and rudder. I would also think that in the last situation there should be some rudder used at least. If you look at this picture on airliners.net you will see that #2 was shutdown and still there is a visible rudder deflection!http://www.airliners.net/open.file/0652327/M/FRED

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I think you are a little confused here guys...The 744 Autopilot only uses automatic rudder control below 1500' Radio Height. As far as I can see in your pics, 3 Autopilots are NOT engaged. 1 is engaged and 2 are armed (as you are above 1500').Autopilot rudder control is not used to maintain track. (A/P) rudder (yaw control) is only used below 1500' (and to varying degrees) to DE-crab the aircraft for touchdown.Only ROLL (i.e. ailerons and spoilers) is used to maintain track, however you will have discuss the angles of roll with the PMDG programmer (as I don't have any real world values handy).Hope this helps.Cheers.Q>

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"I would also think that in the last situation there should be some rudder used at least."No argument here. Rudder SHOULD be used. But what is causing the rudder deflection in the pic? Is the United Aircraft autolanding? Is the rudder input, autopilot induced? Rudder Trim induced? Rudder pedal induced?Re rudder trim.... During manual landings, (electric) Rudder Trim has to be reduced to zero before landing (ask the real world pilots at what height they do this), leaving the pilots to use the rudder pedals for touchdown.(re your hijack)... The magenta values are the recommended airspeeds for an engine relight at the altitude shown.Hope this helps.Cheers.Q>

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The engine out was on the Lufthansa 747 actually ;) Do that magenta text automatically appear if you shutdown an engine in flight or is there a pushbutton the press to make them appear?

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"automatic" (kinda)... needs the fuel cutoff levers in the cutoff position.Cheers.Q>

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Ref: http://en.wikipedia.org/wiki/Dutch_rollThe yaw damper authority is limited to that required to dampen longitudal oscillations (aka dutch roll), often severe enough on many swept wing designs to require stability augmentation.Some multi-engine designs have rudder assist that automatically kicks in during asymmetrical thrust (the new King Airs have this). I wonder if Boeing uses a feature like this?

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"I wonder if Boeing uses a feature like this?"The 777 does (see previous msg)Cheers.Q>P.S. (Edit) The 737, 744 and 767 doesn't

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Yes, there is too many Yams around. Honda dosen't get a look in any more............;-)

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Thread jack . . . Rudder for $100Topic:Useless rudder trivia! (or why the rudder is useless in normal ops). Anyone remember MSAS (modal stability augmentation system) on the old 742s? It drove the rudder to keep the fuselage from bending in flight, like the end of a spaghetti noodle! It wasn't a structural issue. The theory was the pax in the tail would get whipsawed into airsickness without it. This was before the 10 day DMI rule and we'd have the thing deferred for months on end. The company didn't have any spare MSAS accellerometers! Pax never complained and the system finally went away. Had a DC8 with a "yaw damp inop" writeup. The airplane had gone through a complete avionics upgrade / cockpit mod 8 years before. I saw an open on the yaw damp wires between the FFC and the rudder pack. Broken wires, I thought. Nope. The wires were capped and stowed, pretty (and well aged) as could be. The yaw damp had never been hooked up since the mod . . . 8 years before.I'd tell you more, but it'd just scare ya!

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:D and then you fly things like PA28's a lot, they can do with a freaken yaw damper!!!! ;) BE20's most prob as well!I think the big sticks just have sooo much aerodynamic stability from the long fuselage that it would not really make an impact unless someone go and stomp on the pedals a lot :) FRED

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"Pax never complained and the system finally went away."Well, it came back again... It's part of the Yaw Damper system on the 744.Cheers.Q>

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