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wongben4

dutch roll

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Hi, could somebody explain what is Dutch Roll? I have read a lot of materials but none of them can give me a clear explaination.thanksbenPS 2nd Question:what is the max bank angle with 1 engine failure for a 744. I tried to shut-off engine number 4 and then made a right turn with 30 degree of bank, and I ended up losing control of the aircraft. (The aircraft kept banking over 30 degree to the right even I had my yoke fully turned to the left and the aircraft pitched down with rapidly increasing airspeed, and it looked like a sprial dive)thanks

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Dutch roll is a phenomena that is primarily a swept wing problem with directional instability. Dutch roll originates when a swept wing (some straight wing as well) aircraft starts to oscilate about its vertical axis. what happens is that the aircraft starts a slow side to side oscilation on the vertical axis. Someting like short little taps on the rudder in opposing directions and given enough time will end up in a dutch roll. What happens during this is when the yawing action on the vertical axis starts, the wing that is moving forward (left yaw, right wing forward) the right wing lifts and causes a roll to the left. Due to the lateral stability of the aircraft the wings right themselves but in the process a right yaw is developed which causes the left wing to lift, but a bit more than the previous diversion. Left unchecked, this will lead to a Duth Roll in which the aircraft is actually rolled inverted without input from the pilots. This is why a Yaw Damper is installed and if it is unserviceable, speed and altitude restrictions are imposed. I have been in a sim ride (B727) when the instructor failed the yaw dampers and told the crew to see if they could control it at cruise speed. It took less than 10 oscilations before we were inverted as the late reactions of the crew intensified the Dutch Roll phenomena.Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.sstsim.com/images/team/JR.jpg

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Imagine you're straight and level in cruise, and let the nose of the airplane point to the horizon. You'd expect the point on the horizon to be stationary, as long as your attitude remained fixed. However, now imagine your aircraft moves back and forth, left to right, but the pitch remains constant. Now the point on the horizon moves back and forth... are you with me? Okay, let's add aerodymanics to the scenario and what happens as the airplane yaw's back and forth is one wing is moving faster into the relative wind than the other and as a result the plane will start to bank. The dynamics work out that the banking and yawing are tied to each other, and the point on the horizon will be scribbing a figure eight on it's side. This is dutch roll. 2d Question is not in my realm... I only fly twins; however, even in a twin I would never exceed 15-deg with an engine out. The rudder can only give you so much.


Dan Downs KCRP

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hi, thanks for your answer. Now, I realize that dutch roll is the roll causes by yaw, is it correct?ben

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hi Dan, would you mind which twin are u flying? I want to get a twin rating but I don't have any low wing complex aircraft(variable pitch, retractable LDG GEAR) experience, my question is it is better for me to get a low wing complex aircraft check out first before starting the twin lesson. thanksben

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That's basically correct and left unchecked will cause most airliners to roll inverted.The 744 has two yaw dampers and only one can be inoperative for dispatch.Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.sstsim.com/images/team/JR.jpg

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Most of my time is in a C414 Chancellor. I earned my MEL in a Senaca, which is pretty close to an Arrow. I personally don't think high/low wing is much of an issue except here under the So Texas sun, but I do highly recommend some complex time so you're comfortable with variable pitch controls. There's a lot to learn in a twin, mostly about single engine flying (ironically) and it's best to have the MP-RPM levers already figured out in something that's a little easier on the budget.


Dan Downs KCRP

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Yeah, loss of the yaw damper was a serious emergency in highly swept wing aircraft like the 727, and required an immediate emergency descent to a lower altitude where the pilots can slow down to alleviate the condition...


Ryan Maziarz
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thx dan. It is very expensive to get a ME rating, especially my flight school has raised the rental price due to the increasing fuel price. For my flight school, 245CAD per hr for the seminole, plus 55CAD per hr for instructor ... and it takes around 11 to 13 hours...ben

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Gidday ben,It looks like the first question has been answered well but not the second.It really depends on what regime of flight you are in that determines what angle of bank is appropriate. You did not state what regime you were in when the eng failed. If you were in the cruise or descent then 30 degrees would be fine and in some cases even required. However shortly after TO or in the climb then 15 degrees should be the maximum considered. The reason that you probably entered a spiral dive, despite the application of full aileron in the opposite direction, is that you did not apply sufficient rudder. With any eng failure you must apply opposite rudder to the failed eng. CheersSteve


Cheers

Steve Hall

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Adding to your response Steve.It does sound like the original poster flew the aircraft outside the safe envelope with a failed engine. Whether it be a bank angle/speed issue or lack of rudder input.The 744 is very good at single engine out manouvering but some limits are imposed as to bank angle a airspeed. Here is a short quote for the Boeing 744 FCTM regardin single engine out operations:****************************************Limit bank angle to 15

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Hi all, thank for your answer and I finally understand what is going wrong..********************************************Limit bank angle to 15

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Ben now you know why the guys get the coin up front...although that is changing fast as the bean counters take over the world. Maybe your scenario will reflect the real world in the not too distant future. Hope not.CheersSteve


Cheers

Steve Hall

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>Hi all,> thank for your answer and I finally understand what is going>wrong..>********************************************>Limit bank angle to 15


Cheers,
Victor M. Lima
 

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Hi Victor, Thanks for pointing it out. I didn't realize what is wrong until I read your post for several times, and I thought 'rubber' and "rudder" are the same. However, thanks for pointing it out and I welcome any comment or correction for my english. I am a native english speaker and I want to learn and improve my english by all mean, therefore, if you see any mistake (sentence structure, grammar, please corrent me and I appreciate it very much. In fact, reading the posts on the forum is helping me a lot, like you used the word 'slick', I didn't know what it mean so I open my dictionary and find the meaning and learned one more word.Thanks ben

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