Evan767
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Using Rudders In Flight

Sat Jun 10, 2006 9:30 am

I was just thinking of this because I have tried it out on my flight simulator many times. Particularly on a jet, what happens if you put in full right or left rudder. Would it turn in to deadly results? I tried it on flight simulator and the aircraft turned way to the right and then right back to the left. In a real aircraft would it simply go into a roll and eventually crash?

I have been on a few flights where I feel the pilot is putting on too much rudder for comfort on short finals. We make a kind of turn to the left or right and I feel as though we might just drop straight down.

Also, I believe there might be a button on autopilot that prevents this. Yaw director or something like that? And if you activate it it prevents the aircraft from using rudder in flight. Do pilots use that? If they don't, what will actually happen if you put full rudder in in the middle of cruise?
The proper term is "on final" not "on finals" bud...
 
vikkyvik
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RE: Using Rudders In Flight

Sat Jun 10, 2006 10:18 am

Not a pilot, so can't answer some of your questions, but here's a couple threads about the Yaw Damper:

Yaw Damper... What Exactly Is It?

Yaw Damper

That's all I got.

~Vik
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
777wt
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RE: Using Rudders In Flight

Sat Jun 10, 2006 1:57 pm

There's rudder limiters in most jet aircrafts that limits the amount of rudder travel, increases the foot pressure required to turn the rudder as the speed increases.

AA #587 crash was related or resulted from the rudder foces being too high for it's phase of flight.
 
bri2k1
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RE: Using Rudders In Flight

Sat Jun 10, 2006 6:23 pm

Quoting Evan767 (Thread starter):
I have been on a few flights where I feel the pilot is putting on too much rudder for comfort on short finals. We make a kind of turn to the left or right and I feel as though we might just drop straight down.

This is an interesting statement. Why do you think it was too much rudder? After the first such experience, when you didn't drop straight down, was your thinking changed any? I guarantee even if the pilot had used "too much" rudder, you would not drop straight down. Read about the Gimli Glider and the forward slip to a landing.

Believe it or not, there are differences between flying MS Flight Simulator and a real plane. The more complex the plane, the more differences.

Quoting 777WT (Reply 2):
AA #587 crash was related or resulted from the rudder foces being too high for it's phase of flight.

Did you read the report? It, like the amount of rudder used during the landing phase, has been discussed here ad nauseum, so I won't repeat it. I'll just say you might consider re-reading it if that's all you got from it.
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Tristarsteve
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RE: Using Rudders In Flight

Sat Jun 10, 2006 10:20 pm

Airliners are usually flown on autopilot. Most autopilots have no connection to the rudder. The yaw damper is a separate entity which controls the rudder to counteract Dutch yaw. Some autopilots act on the rudder, but only during the flare to kick off drift.
All high speed airliners have some system to inhibit rudder movement at higher speeds. The rudder may move +- 30deg on the ground but only +-5deg at speed. Enough for an engine out case.
Except for landing and take off and engine out, the rudder is not used.
 
SlamClick
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RE: Using Rudders In Flight

Sat Jun 10, 2006 10:44 pm

When hand-flying a sweptwing jet the rudder pedals are just a convenient place to rest your feet. Most, maybe all of them have full-time active yaw dampers and you just let that unit apply any rudder that might be needed.

For a pilot to apply a bunch of rudder can get you into a condition called Dutch roll. The simple explanation is that you rudder in some yaw. That has the effect of making the outside wing 'longer' as seen by the oncoming airflow. (Because it is, in effect less swept, and the inside wing is more swept as measured from the actual direction of travel.) This makes the outside wing tend to rise. If you counter this with rudder you will quickly find yourself a half-cycle out of phase and the Dutch roll getting worse.

Getting out of it is easy. Neutralize the rudder pedals and if a wing starts to rise, slap it down with a quick shot of aileron. Might take a couple of cycles and it is over.

Twin jets have enough rudder surface area and enough rudder 'throw' that is the deflection to either side from centerline, to overcome one engine dead and the other at TOGA thrust at fairly low speeds. At the far end of the scale this would be far too much rudder, so we have rudder limiters. These are generally starting to come in by the time we get our flaps up.

At high mach number full rudder deflection would simply snap the tail off the airplane.

Rudder pedals are footrests in normal flight.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
Evan767
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RE: Using Rudders In Flight

Sun Jun 11, 2006 11:25 pm

Quoting Bri2k1 (Reply 3):
This is an interesting statement. Why do you think it was too much rudder? After the first such experience, when you didn't drop straight down, was your thinking changed any? I guarantee even if the pilot had used "too much" rudder, you would not drop straight down. Read about the Gimli Glider and the forward slip to a landing.

I thought it was too much rudder because it just gave me this feeling like we would just drop straight down. The aircraft was an MD-88. My thinking still wasn't changed any after the first experience. When the pilot still puts on a bit of rudder on final I still get that weird feeling as though we might lose all our speed and drop straight down.
The proper term is "on final" not "on finals" bud...
 
bri2k1
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RE: Using Rudders In Flight

Sun Jun 11, 2006 11:32 pm

Quoting Evan767 (Reply 6):

Well, what else can I say? Maybe you'll continue learning about aerodynamics and see why that can't happen. Or, maybe you'll get lucky and be right someday.
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SlamClick
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RE: Using Rudders In Flight

Mon Jun 12, 2006 12:06 am

Quoting Evan767 (Thread starter):
In a real aircraft would it simply go into a roll and eventually crash?

Some airlines operating 737s have put 'rudder hardover' training into their simulator syllabus. At a speed somewhere around 220 knots or so, (I dont' remember the actual number) one student (PNF) pushes one rudder pedal or the other to the mechanical stops and holds it there. The other student, flying, then deals with the unwanted input. He is then instructed to begin slowing the plane toward 'crossover speed' which is a (weight/configuration dependant and unpublished) speed below which the roll control can no longer compensate for the rudder input. The plane will then begin to roll and will eventually become uncontrollable - unless speed can be gained above crossover speed and still have space to clear the terrain.

As the plane begins to roll if the nose can be lowered and perhaps power applied the plane will accelerate above crossover speed and can be flown normally again.

One of the things a student must overcome is any reluctance to add power. The reason this can be an issue is that the maneuver feels like a VMC demonstration in which you would NOT want to add power. We sometimes want to do what our muscle memory tells us to do.

* * *


As to your MD-80 ride, I think you just experienced a well-known MD-80 characteristic. The cabin is so ridiculously long that the airplane looks and feels unstable on all approaches in any wind or thermals. It rocks back and forth in all three axes. A 737-100 might oscillate just as much but the shorter tube hides it. When the MadDog was a new airplane we used to watch every approach because of the seemingly large pitch and yaw excursions.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
2H4
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RE: Using Rudders In Flight

Mon Jun 12, 2006 12:30 am




Quoting SlamClick (Reply 8):
one student (PNF) pushes one rudder pedal or the other to the mechanical stops and holds it there.

One of the sims I flew allowed the instructor to induce a rudder hardover from his station. He could also alternate between hardovers to the left and hardovers to the right, making life rather interesting for the PF....

I would love to see a chart of crossover speeds for various aircraft types, weights, and configurations. It would be interesting to compare and contrast crossover characteristics from type to type.




2H4


Intentionally Left Blank
 
SlamClick
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RE: Using Rudders In Flight

Mon Jun 12, 2006 12:34 am

Quoting 2H4 (Reply 9):
I would love to see a chart of crossover speeds for various aircraft types, weights, and configurations. It would be interesting to compare and contrast crossover characteristics from type to type.

Just as VMC varies on light twins. I suppose that rigging, actual CG and a host of other issues affect it in varying degrees. One twin I flew seemed to have a VMC that varied inversely with pilot experience. It killed two of the best friends I'll ever have.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
art
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RE: Using Rudders In Flight

Mon Jun 12, 2006 5:25 am

It sounds like the rudder is not normally used in flight on an airliner. Do airliners never sideslip?
 
bri2k1
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RE: Using Rudders In Flight

Mon Jun 12, 2006 5:38 am

There are dozens of threads on this site about crosswind landings in airliners which will provide plenty of detail. The short answer is that yes, they do slip to land in crosswinds, but usually much later in the landing approach than small planes.
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pilotaydin
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RE: Using Rudders In Flight

Mon Jun 12, 2006 5:52 am

Quoting SlamClick (Reply 8):
Some airlines operating 737s have put 'rudder hardover' training into their simulator syllabus

we recently did that in the -400 sim. It was wild  Smile reconstructing the UsAir 737 accident on some ways

the rudder deflects FULL into L or R direction, the recovery seems illogical at first, you DIVE the plane while retarding the throttle on the opposite side while advancing the throttle on the rudder side, with the increase in speed from the dive you gain aileron effectiveness and try to fly the plane with the assymetrical thrust, it takes some getting used to

but RPR installed the risks reduce, but all in all i hate any issues related with flight controls, ill take an engine fire over a flight control issue anyday... shivers...
The only time there is too much fuel onboard, is when you're on fire!
 
saab2000
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RE: Using Rudders In Flight

Mon Jun 12, 2006 5:53 am

Quoting Art (Reply 11):
It sounds like the rudder is not normally used in flight on an airliner. Do airliners never sideslip?

Yes. When landing in a crosswind an airliner will sideslip as a result of rudder pressure to keep the nose lined up with the runway centerline.
smrtrthnu
 
pilotpip
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RE: Using Rudders In Flight

Mon Jun 12, 2006 3:26 pm

Quoting Evan767 (Reply 6):

I thought it was too much rudder because it just gave me this feeling like we would just drop straight down. The aircraft was an MD-88. My thinking still wasn't changed any after the first experience. When the pilot still puts on a bit of rudder on final I still get that weird feeling as though we might lose all our speed and drop straight down.

The MD-80 and DC-9 have a pitot tube on the tail, this pitot is linked to a cam which limits rudder travel based on speed. At approach speeds, the pilots will have full rudder authority. Depending upon the crosswind, you may want this.

Side slips are not only needed, they may be manditory. And yes, you may feel the airplane "drop" as some lift is lost and there is now more drag. However, you shouldn't feel that this is unsafe. In fact, quite the opposite. I think you'd rather have the discomfort of a slip than the alternative of having the airplane fly all the way down in a nice coordinated state until it goes right off the side of the runway because the pilot did not add appropriate crosswind correction. Or have the gear shear off from the loads associated with landing the airplane crabbed.
DMI
 
bri2k1
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RE: Using Rudders In Flight

Mon Jun 12, 2006 3:28 pm

Pilotpip, are you type rated on the MD-80? I ask because it has relatively short landing gear for its relatively long length, and I wonder what the maximum recommended touchdown crab angle might be. I am not rated on the MD-80, but anyone who knows the answer, please let me know. Aside from sitting in row 32, I have never felt especially uncofortable on this type.
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pilotpip
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RE: Using Rudders In Flight

Mon Jun 12, 2006 6:04 pm

No I'm not. One thing I know about the 80 is that when doing an autoland it switches from a crab to a sideslip relatively early on in the approach whereas Boeing aircraft do it much later. I was told this by a retired TWA captain. One of the advantages to short gear is that it should be stronger.

One airplane that has trouble with sideslipping is the 737. the engines sit low to the ground and there isn't much room for slipping in so it seems that pilots typically crab and straighten out really quick. I know a couple in here have flow the 737 so I'm sure they can chime in on this.
DMI
 
pilotaydin
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RE: Using Rudders In Flight

Mon Jun 12, 2006 6:08 pm

Quoting Pilotpip (Reply 17):
One airplane that has trouble with sideslipping is the 737

so true, if you bank more than 7 degrees, you can strike the engine....so we're dancing at the controls in gusts and cross winds....

the other day i was sweating coming into Vienna, for runway 34, winds from 280 at 24 gusting 29
The only time there is too much fuel onboard, is when you're on fire!
 
tu204
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RE: Using Rudders In Flight

Wed Jun 14, 2006 4:01 am

Well, on the Tu-204 the plane won't allow you to use it. It will let you make a minor deflection, thats about it. If you were to fully deflect the rudder in flight at cruise speed there would be some structural damage to the rudder and the stabiliser itself. No guarantee that the rudder will remain on the aircraft.
I do not dream about movie stars, they must dream about me for I am real and they are not. - Alexander Popov
 
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litz
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RE: Using Rudders In Flight

Wed Jun 14, 2006 10:54 pm

Quoting Art (Reply 11):
It sounds like the rudder is not normally used in flight on an airliner. Do airliners never sideslip?

I'm sure there's a bit of that if you have to switch runways at the last minute, but one of the more infamous uses of sideslip was the Gimli Glider; the piilot of that plane sideslipped to lose altitude when they were on final for their powerless landing @ Gimli.

There are situations where you might want to intentionally use a good bit of rudder, say an engine out situation where you are compensating for loss of thrust.

There's a good picture of a UA 747 that emergency landed @ ATL; it ferried to its MX base on 3 engines; the takeoff roll had quite a bit of rudder to it to compensate for the off-axis thrust.

- litz
 
cptspeaking
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RE: Using Rudders In Flight

Thu Jun 15, 2006 2:15 pm

Quoting TristarSteve (Reply 4):
Except for landing and take off and engine out, the rudder is not used.

Ever heard of a coordinated turn? I realize you don't need as much in a jet, mostly due to higher speeds and a greater arm on the input, but any airplane will always require input from all 3 controls to remain coordinated.

Quoting Pilotaydin (Reply 18):
the other day i was sweating coming into Vienna, for runway 34, winds from 280 at 24 gusting 29

ouch. Somebody on the CivAv forum the other day (obviously not a real pilot...) tried to tell me that NOBODY should be up flying when the wind was 20 gusting 25. I think it was in the discussion about the King Air crash in Tampa, FL when Tropical Storm Alberto was nearby...I'm sure you guys had plenty of fun putting that one down...60 degrees off the runway is rough at those wind speeds

Your CptSpeaking
...and don't call me Shirley!!
 
pilotaydin
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RE: Using Rudders In Flight

Thu Jun 15, 2006 4:53 pm

Quoting CptSpeaking (Reply 21):
I realize you don't need as much in a jet

well you do just as much...because there are spoilers which increase the yaw rate when you bank
The only time there is too much fuel onboard, is when you're on fire!
 
bri2k1
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RE: Using Rudders In Flight

Thu Jun 15, 2006 5:06 pm

Quoting CptSpeaking (Reply 21):
I realize you don't need as much in a jet



Quoting Pilotaydin (Reply 22):
well you do just as much

I interpreted the first quote to mean as much pedal deflection, with which I agree. You still need a coordinating yaw to go with a bank, but with swept wings, at speeds above the approach regime, no pedal input is required.
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pilotaydin
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RE: Using Rudders In Flight

Thu Jun 15, 2006 5:53 pm

Quoting Bri2k1 (Reply 23):
I interpreted the first quote to mean as much pedal deflection, with which I agree. You still need a coordinating yaw to go with a bank, but with swept wings, at speeds above the approach regime, no pedal input is required.

agreed sir  Smile
The only time there is too much fuel onboard, is when you're on fire!
 
SlamClick
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RE: Using Rudders In Flight

Thu Jun 15, 2006 11:48 pm

Quoting CptSpeaking (Reply 21):
I realize you don't need as much in a jet, mostly due to higher speeds and a greater arm on the input, but any airplane will always require input from all 3 controls to remain coordinated.

I believe it actually has more to do with swept-wing flight characteristics regardless of speed. However, read this:

Quoting SlamClick (Reply 5):
When hand-flying a sweptwing jet the rudder pedals are just a convenient place to rest your feet. Most, maybe all of them have full-time active yaw dampers and you just let that unit apply any rudder that might be needed.

As you suggest, there certainly will be some rudder used, but if the pilot does it with his feet it is going to get screwed up. Three results will follow, in this order:

1. Passengers heads swaying left at the forward end of the cabin and right at the rear end, then vice versa, rhythmically, the amplitude of the swaying proportional to their distance from the center of gravity.

2. Dutch roll.

3. Captain Click will plant his size-elevens on the pedals, immobilizing them, stop the Dutch roll with aileron, look over at the newhire first officer and say "Leave those damn pedals alone!" Then he will turn and look out his window and mutter: "We must be hiring over the phone again!"

Some really smart engineers and test pilots agreed on yaw damper design. I will not presume to debate their wisdom. I use it.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
PlainSmart
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RE: Using Rudders In Flight

Wed Jun 21, 2006 11:02 pm

Quoting TristarSteve (Reply 4):
Airliners are usually flown on autopilot.

I'm going to have to sort of disagree with you on that one.
 
Evan767
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RE: Using Rudders In Flight

Wed Jun 21, 2006 11:19 pm

Well, I just got back from Toronto yesterday. My route was RIC-ATL-YYZ-ATL-RIC. Every leg was on an MD-88. I did feel a little rudder here and there on approaches, but I was not as nervous as I used to be. The pilots on the ATL-RIC leg were pretty shaky on approach though with many turns to the left and then jolting to the right. That made me feel a bit sick but maybe it was because I was in 10C, right in the middle of the plane.
The proper term is "on final" not "on finals" bud...
 
2H4
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RE: Using Rudders In Flight

Wed Jun 21, 2006 11:28 pm




Quoting PlainSmart (Reply 26):
I'm going to have to sort of disagree with you on that one.

Could you produce some evidence to back your claim...that airliners are usually hand-flown...up?




2H4


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SlamClick
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RE: Using Rudders In Flight

Thu Jun 22, 2006 12:06 am

Quoting 2H4 (Reply 28):
...that airliners are usually hand-flown...

Or...in the case of rudder control...foot flown?
Happiness is not seeing another trite Ste. Maarten photo all week long.

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