Rudder trim equal to Fuel Flow ?
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Join Date: Nov 2001
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Rudder trim equal to Fuel Flow ?
I have 3 questions.
1)Which A/C require the rudder trim to be set to match FF times 2, and which require trim to equal FF. (course units vs PPH times 1000)
2) Is that related to how big those units are ?
3) Also, during Single engine ops, in a/c like say 757, 767, 737.., when flying manually....do you hold a small amount of bank toward the good engine, with the ball of the inclinometer slightly displaced toward the good one, or you just hold wings level, ball centered and accept the side slip ?
Thanks a lot guys !!!
[ 02 December 2001: Message edited by: Drag Bucket ]
[ 02 December 2001: Message edited by: Drag Bucket ]
1)Which A/C require the rudder trim to be set to match FF times 2, and which require trim to equal FF. (course units vs PPH times 1000)
2) Is that related to how big those units are ?
3) Also, during Single engine ops, in a/c like say 757, 767, 737.., when flying manually....do you hold a small amount of bank toward the good engine, with the ball of the inclinometer slightly displaced toward the good one, or you just hold wings level, ball centered and accept the side slip ?
Thanks a lot guys !!!
[ 02 December 2001: Message edited by: Drag Bucket ]
[ 02 December 2001: Message edited by: Drag Bucket ]
Join Date: May 2001
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Interesting point about the slip ball in SE work.
As I understand it the certification authorities allow up to 5 deg bank toward the live engine in addition to the rudder input. I think that this is because it allows further performance to be squeezed out of the a/c at low weight t/o where you may be near VMCA. You could be running out of rudder, but the bank allows you to maintain centreline tracking on climb out. I think it's 5deg because any more would raise spoilers and degrade lift.
The Airbus flight director and 'slip' indicator work together to achieve this.
The slip indicator becomes a 'beta target' when an EO is sensed, and if it is centred the a/c will still turn toward the dead engine (with wings level). The F/D commands a small (5deg) bank toward the live engine to correct this.
The resultant flight control inputs also correspond to a minimum drag config.
If you think about it, it's actually impossible to completely centre a normal slip indicator in assymetric flight on a twin (or more) type. If you do you'll probably have to apply cross control on aileron in order to track straight. Undesireable due to unecessary drag.
I'd need a diagram to explain that point more clearly, but think about the way the displaced thrust line acts relative to the yaw axis of the a/c. If you trim the rudder to allow the a/c to track straight there will still be a 'slip' indicated. Conversly if you 'dial out' the slip with the rudder trim you won't track straight without some bank.
I seem to recall the B737 manual states the same, and recommends allowing the ball to be slightly off centre (i.e. slipping) if the a/c is trimmed to track straight with wings level.
Clear as mud?
[ 03 December 2001: Message edited by: maxalt ]
As I understand it the certification authorities allow up to 5 deg bank toward the live engine in addition to the rudder input. I think that this is because it allows further performance to be squeezed out of the a/c at low weight t/o where you may be near VMCA. You could be running out of rudder, but the bank allows you to maintain centreline tracking on climb out. I think it's 5deg because any more would raise spoilers and degrade lift.
The Airbus flight director and 'slip' indicator work together to achieve this.
The slip indicator becomes a 'beta target' when an EO is sensed, and if it is centred the a/c will still turn toward the dead engine (with wings level). The F/D commands a small (5deg) bank toward the live engine to correct this.
The resultant flight control inputs also correspond to a minimum drag config.
If you think about it, it's actually impossible to completely centre a normal slip indicator in assymetric flight on a twin (or more) type. If you do you'll probably have to apply cross control on aileron in order to track straight. Undesireable due to unecessary drag.
I'd need a diagram to explain that point more clearly, but think about the way the displaced thrust line acts relative to the yaw axis of the a/c. If you trim the rudder to allow the a/c to track straight there will still be a 'slip' indicated. Conversly if you 'dial out' the slip with the rudder trim you won't track straight without some bank.
I seem to recall the B737 manual states the same, and recommends allowing the ball to be slightly off centre (i.e. slipping) if the a/c is trimmed to track straight with wings level.
Clear as mud?
[ 03 December 2001: Message edited by: maxalt ]
