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737 or other jets full rudder deflection.

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737 or other jets full rudder deflection.

Old 12th Feb 2012, 15:31
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737 or other jets full rudder deflection.

The only internal indication of rudder panel deflection is pedal position, which always accurately reflects control surface deflection. Total authority of the control surface is modulated in relation to aircraft IAS using “blowdown”, ie a constant pressure is applied to the surface by the actuator, and the movement of the panel reduces accordingly as the dynamic pressure on it increases. For this reason maximum rudder pedal movement is reduced with increasing airspeed. Maximum rudder panel deflection is approximately +/-15 degrees on the ground, reducing to around +/-8 degrees at a typical cruise altitude.

Seeing as I can't realistically try a full rudder deflection in flight, does any one know what the feel is of full rudder deflection. In other words, do you feel a hard stop or just increased resistance untill you can't move the pedal anymore.
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Old 14th Feb 2012, 03:17
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Well....

Well....

First, I'm thinking the sim should provide a close feel.

Second, it's been proven that Boeing is full of XXXX with regard to
this statement. USAir 427 in Pittsburgh is proof of that. Further, it
was proven in a laboratory what happened to flight 427. The rudder
went full one dirction, but the rudder pedals went the opposite.

Fly safe,

PantLoad
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Old 14th Feb 2012, 08:07
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I would imagine the 737 is like most other jets in that you can apply full rudder pedal until the stop throughout the flight envelope. The internal computers then limit the amount of actual rudder deflection according to IAS. The feel will be the same at VMO as it will be on the ground.
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Old 14th Feb 2012, 08:11
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Total authority of the control surface is modulated in relation to aircraft IAS using “blowdown”, ie a constant pressure is applied to the surface by the actuator, and the movement of the panel reduces accordingly as the dynamic pressure on it increases. For this reason maximum rudder pedal movement is reduced with increasing airspeed. Maximum rudder panel deflection is approximately +/-15 degrees on the ground, reducing to around +/-8 degrees at a typical cruise altitude.
The rudder bars operate the rudder PCU via cables, through the Rudder Feel and Centering Unit, which uses a set of inner and outer springs to produce feel in the rudder pedals. The tension on the springs is adjusted by aircraft speed, so the rudder pedals are thus harder to push at speed, with the stiffness increasing with the amount of deflection.

Originally Posted by Jonty
I would imagine the 737 is like most other jets ... The internal computers then limit...
No computers on a 737 rudder flight control system! It's all springs, cables, cams and hydraulics Good ol' engineering! (There is an elevator feel computer.)

Other jets are different - on the BAe146 for instance (from old memory), the rudder circuit had a "q pot" with a stepped plunger. As speed increased the plunger would move out of the q pot, and each step would block the movement of the rudder by an increasing amount. The rudder pedal movement would thus feel the same in effort, but be blocked by the q pot to progressively smaller deflections.

The airbus series use software to limit rudder movement in flight.

Last edited by Checkboard; 14th Feb 2012 at 08:22.
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Old 14th Feb 2012, 08:18
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The rudder bars operate the rudder PCU via cables, through the Rudder Feel and Centering Unit, which uses a set of inner and outer springs to produce feel in the rudder pedals. The tension on the springs is adjusted by aircraft speed, so the rudder pedals are thus harder to push at speed, with the stiffness increasing with the amount of deflection.
Its like stepping back in time!
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Old 14th Feb 2012, 11:02
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The B737-300 flight simulator I instruct on has a malfunction button whereupon full hard over rudder pedal is applied in an instant. It is dramatic and as expected the aircraft yaws then rolls sharply accompanied by the inevitable spiral dive.

Instant hard over aileron stops the yaw and roll and the aircraft is controllable at its crossover speed. Unless the pilot reacts instantly with full opposite aileron, the aircraft will crash. Most pilots in the simulator lose control immediately unless they have been previously briefed on how to recover. Which of course they would have.
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Old 15th Feb 2012, 04:02
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Originally Posted by Checkboard
The rudder bars operate the rudder PCU via cables, through the Rudder Feel and Centering Unit, which uses a set of inner and outer springs to produce feel in the rudder pedals. The tension on the springs is adjusted by aircraft speed, so the rudder pedals are thus harder to push at speed, with the stiffness increasing with the amount of deflection.
It sounds like there is no actual stop in flight. Or at least in high speed flight as you cannot deflect the rudder pedal as much at this point. But, can a stronger legged person deflect the pedal further than a weaker person. And if so, is there a point where the rudder itself will not deflect any further due to airflow over it and therefore, you are just compressing the spring in the feel and centering unit with no actual increased rudder deflection?

I have never seen a diagram of how the rudder feel and centering unit works. If anyone has a link, it would be appreciated.
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Old 15th Feb 2012, 12:23
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What if a pilot hits full rudder deflection in cruise by mistake?

Thats one of the reasons i never let a cabin crew occupy a flight deck seat inflight!!
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Old 15th Feb 2012, 20:43
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Airliners have phase out on the rudder. Meaning less max deflection at higher airspeeds. Pedal travel also reduces and pedal force somewhat
on older models.

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Old 15th Feb 2012, 21:04
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First, I'm thinking the sim should provide a close feel

That would be your first error. All depends on how the sim is set up and tweaked.

For instance, going back 10 years or more, the FAA dictated that US AOC operators of the 737 had to have sims with the latest rudder model to cover the hardover problems in vogue at the time, as I recall.

At the time I was instructing on a 732 which had the upgrade installed to cover its US customers. Before mod, the rudder response was a bit like a slap in the face with a wet fish. Afterwards, totally impressive.

As I was the slowest fellow to step back I ended up being conscripted to fly the before and after demo checks that the particular operator wanted to see so I had a pretty close up and personal view of the detailed differences.

Trust a sim to represent the aircraft ? In the middle of the routine envelope, sure ... around the edges, it depends on this and that ...
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Old 16th Feb 2012, 16:19
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Originally Posted by icaro_2992
What if a pilot hits full rudder deflection in cruise by mistake?

Thats one of the reasons i never let a cabin crew occupy a flight deck seat inflight!!
In principle, if it's done precisely once, and the recovery is done in a suitably benign fashion, and assuming all the sums were added up correctly during design and development, and any repairs or mods have been done to the right standard, then the various important bits of the airframe will stay attached.

All bets are off if the recovery is in any way hamfisted (which, given the hamfistedness of applying the input to start with, is a condition you might consider a bit optimistic....)

The structure is protected either through the natural hinge moment limiting (if the PCUs are weak enough, then you can't apply enough rudder to break anything) or through active control limiting (either through a relatively 'dumb' travel limiter or through fancier FBW-type limiting) and whatever the rudder is that CAn be input, the relevant FAR25/CS25 design case requires adequate structural strength for.

In cases where the stop (either a positive stop, through an RTL or similar or an 'effective' stop through hinge moment limiting) is not provided actually at the pedals, then there will be some amount of squishyness at the pedals - although the rudder itself wont move further, increasing pilot force will deflect/distort system components. Usually the greatly increased force per pedal deflection that comes into play is pretty apparent to a pilot, but it depends on the amount of lead in the boot.
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Old 28th Mar 2012, 07:55
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Rudder pedal movement is limited in flight by mechanical stops,effort simulators or software programs,depending on the aircraft type.
Each of the different systems is design to limit the rudder movement as the speed increases,for obvious reasons. No system, mechanical or software ,is totally error proof ,fact demonstrated by Boeing or Airbus alike...
An unintended application of rudder in flight will be instantly recognized by the pilot ,due to sudden reaction of the plane. (I've seen it once,with a tall cpt,that tried to stretch his legs,slipping one foot on the rudder for a second.)
Intentionally applying the rudder is made when inducing dutch roll, it is done progressive ,and not to the limit. It will be quite impressive.
The main risk,is with quick opposite application,that will most sure result in rudder failure,no matter the aircraft type.
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Old 29th Mar 2012, 01:00
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Originally Posted by alexban
Rudder pedal movement is limited in flight by mechanical stops,effort simulators or software programs,depending on the aircraft type.
Are you sure about that for the 737-200. It seems to me like it is just reduced maximum deflection based on aerodynamic force acting on the rudder.
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Old 29th Mar 2012, 22:02
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Full Rudder

For JammedStab (and not the first time, I think)

As to what happens when full rudder is applied ….. well it happened.
Many years ago on a 757, and before corrective mods, a slow leaking L HYD required the system to be off-loaded until required for landing (Flaps, Gear & N/W Steering). I off-loaded the system in accordance with the QRH and the aircraft banked about 40 degrees but kept going straight ahead, just. This was instantaneous and verging on the violent. Switching on the L HYD again restored equilibrium.
It was extremely alarming and initially puzzling. However, the (then normal) progressive amount of rudder trim required on our fleet as we climbed into colder air, meant that in the cruise it was normal to have several divisions of trim applied. Turning off the L HYD also turns off the RUDDER RATIO. Boeing’s analysis showed that the amount of actual rudder displacement with full pedal deflection decreases with an increase of speed by a maximum multitude of 15 from Vmca to Mmo.
So now I know. I am glad they made it strong!
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Old 29th Mar 2012, 22:33
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So then....does this mean that on a 737-200, you can deflect the pedal to a mechanical stop for the actual pedal at high speed, but the rudder does not go to full deflection. Actually, I already know the rudder itself does not go to full deflection, but what about the rudder pedal? Does it always go to the same full deflection with the same required force?
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Old 30th Mar 2012, 09:16
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Originally Posted by JammedStab
But, can a stronger legged person deflect the pedal further than a weaker person. And if so, is there a point where the rudder itself will not deflect any further due to airflow over it and therefore, you are just compressing the spring in the feel and centering unit with no actual increased rudder deflection?
I know nothing about the B737 except your underlined paragraph in your first post and generic aircraft systems knowledge, but based on that the answer is no, a strong legged person will not be able to push the pedal further or get more rudder deflection.

The rudder is hydraulically actuated so the max pressure to move the rudder is whatever the hydraulic pressure is, this has nothing to do with how hard you can push on the pedals. According to your blurb the rudder pedal position accurately reflects the rudder deflection so the available pedal movement reduces as you get faster and the available rudder deflection reduces. Whether this feels like a hard mechanical stop or a little softer, I don't know.

So then....does this mean that on a 737-200, you can deflect the pedal to a mechanical stop for the actual pedal at high speed, but the rudder does not go to full deflection.
According to your own underlined paragraph; no, the rudder pedal deflection is proportional to the rudder deflection.
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Old 30th Mar 2012, 17:29
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Originally Posted by AerocatS2A
I know nothing about the B737 except your underlined paragraph in your first post and generic aircraft systems knowledge, but based on that the answer is no, a strong legged person will not be able to push the pedal further or get more rudder deflection.

The rudder is hydraulically actuated so the max pressure to move the rudder is whatever the hydraulic pressure is, this has nothing to do with how hard you can push on the pedals. According to your blurb the rudder pedal position accurately reflects the rudder deflection so the available pedal movement reduces as you get faster and the available rudder deflection reduces. Whether this feels like a hard mechanical stop or a little softer, I don't know.


According to your own underlined paragraph; no, the rudder pedal deflection is proportional to the rudder deflection.
Makes sense to me. I just wasn't sure anymore because Alexban said....

"Rudder pedal movement is limited in flight by mechanical stops,effort simulators or software programs,depending on the aircraft type."


I would assume then that this statement is not applicable to all jet transports.
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Old 9th Sep 2023, 00:36
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USAF F/E on C141A

I hope to God this situation has been remedied years ago . The US Air pilots were highly qualified aviators,caught up in enigma. A C-141A experienced a simulator upset, known as the only supersonic C141A in the C-141 accident database. A shorted diode in the Yaw Dampener test circuit caused the rudder to fully deflect at FL 410 over Vancouver, Canada enroute to Alaska Read the report .
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Old 9th Sep 2023, 11:20
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Do you have a link to the report?
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Old 9th Sep 2023, 12:01
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Originally Posted by SJR71
I hope to God this situation has been remedied years ago . The US Air pilots were highly qualified aviators,caught up in enigma. A C-141A experienced a simulator upset, known as the only supersonic C141A in the C-141 accident database. A shorted diode in the Yaw Dampener test circuit caused the rudder to fully deflect at FL 410 over Vancouver, Canada enroute to Alaska Read the report .

Does the report really refer to "yaw dampener" and not "yaw damper"?
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