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Rudder turns in an airliner...

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Rudder turns in an airliner...

Old 8th May 2015, 08:59
  #21 (permalink)  
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Join Date: Aug 2011
Location: Portugal
Age: 55
Posts: 41
Interesting observation Chu Chu, thx!, but actually in the situation I tested in the sim, the 4 engines were shutoff, thus creating only a lot of yaw and roll inertia... and drag too :-)

Last edited by jcomm; 8th May 2015 at 10:37.
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Old 8th May 2015, 12:06
  #22 (permalink)  
Join Date: Nov 2010
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Quote by vilas: "The engines may surge and stall. It's futile discussion."

It's t'other way round. The airflow through the engine will be disrupted in severe side slip causing compressor stall closely followed by a surge, or multiple surges.
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Old 8th May 2015, 14:54
  #23 (permalink)  
Join Date: Jan 2006
Location: US
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"Boeing recommends landing in strong crosswinds with crab- basically landing sideways then correcting after main gear touchdown."

Boeing recommends side slips for crosswind landings except for the highest crosswinds. Beyond X kts(typically 30(+/-) kts XW) Boeing says additional crosswind should be corrected by landing in a crab. So in a 35 kt XW the majority of the crosswind will be corrected by the side slip and only a couple of knots will be corrected by the crab at touchdown.
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Old 8th May 2015, 15:57
  #24 (permalink)  
Join Date: Sep 1999
Location: USA
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jcomm - I hope you get your answer sometime despite all the irrelevance here.

From where I sit, I ask where your normal axis stability factors came from as it would appear the directional moment from yaw is too low while the moment from the rudder deflection is too high, and I question the value of any spoiler yaw factor used. Wings level with full rudder would require a large spoiler deployment producing a significant degrading yaw rate.

As misd said a while back, any resulting turn rate would be extremely slow and I suspect you would hit the ground well before completing a 360.
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Old 8th May 2015, 16:06
  #25 (permalink)  
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Join Date: Aug 2011
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thx for your comment, and yes, that's exactly how I see it and the flaw in the mentioned simulation model of the 744.

I have no air or stability data for that model - I am a simple user - but I questioned the accuracy of the flight dynamics as they are right now because I also think that...

1) The rate would be marginal

2) The loss of altitude huge!

among other factors...
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Old 8th May 2015, 22:21
  #26 (permalink)  
Join Date: Feb 2004
Location: Australia
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As far as blow back valves are concerned I have never heard of them being fitted to 747 rudder hydraulics
From the Boeing maintenence training notes:

"The [rudder]Actuators are snubbed at the end of the stroke and contain Load Limiting Relief Valves set at 2800 psi."

Regarding the rudder ratio system, the actuator has an AC electric servo. If main bus power is lost, the actuator will remain in the last commanded position. If power was lost at high speed, it would be interesting to see how much control you would have at lower speeds with crosswind landings.
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Old 9th May 2015, 01:50
  #27 (permalink)  
Join Date: May 2000
Location: Seattle
Posts: 3,134
The QRH limits landings to 10 kt with a dual rudder ratio failure in the high-speed mode, so authority is reduced by 2/3 or more.
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