dutch roll terminology

GeorgeC

GeorgeC

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GeorgeC
1. http://pilottraininguide.wordpress....nders-pilots-make-and-how-to-stay-avoid-them/ describes dutch rolls as a crossed-control maneuver.

2. http://www.mountainflying.com/Pages/mountain-flying/adverse-yaw.html describes dutch rolls as an exercise in coordinated flight, with the rudder leading the aileron to correct for adverse yaw.

3. of course, there is the textbook dynamics definition of a dutch roll, which is stated here for completeness.

With respect to flight training, which of 1 or 2 is correct? Or are both correct, with each teaching different lessons?

I ask because I did (1) during my primary training, but only recently did (2) after I was upbraided by a CFI ("That's not a dutch roll, you're just slipping! *This* is a dutch roll!").

Discuss(tm).
 
number 2 is what my instructor described to me as a dutch roll. lead with rudder before aileron.
 
Whether you lead with rudder or not depends on the aircraft. The other term for Dutch roll is Rolling on a Point. As I understand and teach it the idea is to bank left and right but reversing bank before a turn begins, while keeping the aircraft pointed at a fixed point, in other words not allowing for any yaw to develop. When you get good at it you get good at rolling into and out of turns with precise coordination.
 
Well technically Dutch roll is a phenomenon that occurs usually in swept wing aircraft due to an out of phase roll/yaw combination mostly due to where the swept wings are located.

The Dutch roll that we use to train students coordination is a coordinated "roll" hope that helps

Cheers


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patmike said:
lead with rudder before aileron.
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There is never a need to lead w/ the rudder in any airplane to control adverse yaw. All you're doing is skidding the airplane momentarily and unnecessarily before applying aileron. The rudder is perfectly capable of compensating for adverse yaw simultaneous with the aileron input, but it's up to the pilot to use the proper amount of rudder for a given amount of aileron.

'Lead with the rudder' is what some instructors tell their students who have lazy feet during training when they're too slow or too timid in their rudder use. It just gets them thinking about it more, not that it's necessary, or is good flying technique - it's not.

Won't get into the Dutch Roll discussion. :)
 
Two different usages:
  1. Aerodynamics: The tendency of an aircraft to roll when displaced in yaw.
  2. Flight training: The training maneuver in which the aircraft is rolled back and forth with aileron while the ball is kept centered and the nose is kept from yawing by rudder inputs.
 
Ron Levy said:
Flight training: The training maneuver in which the aircraft is rolled back and forth with aileron while the ball is kept centered and the nose is kept from yawing by rudder inputs.
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Yes, kept from adverse yawing, but not necessarily from changing its heading, since it's not possible to roll back and forth with the skid ball in the center without doing small turns in each direction.
 
RoscoeT said:
Yes, kept from adverse yawing, but not necessarily from changing its heading, since it's not possible to roll back and forth with the skid ball in the center without doing small turns in each direction.
Click to expand...
Good point -- how about "coordination is maintained" instead of "kept from yawing"?
 
Ron Levy said:
Good point -- how about "coordination is maintained" instead of "kept from yawing"?
Click to expand...

That's a good way to put it. I only brought it up because some people seem to be confused about Dutch rolls thinking that the nose can be "kept on a point" while keeping the ball in the center...it can't. Either the ball is centered and the plane is s-turning slightly, or the nose is kept on a point (plane does not turn) and the ball rolls back and forth (uncoordinated).
 
Actually, the nose can be kept apparently on a point (i.e., appearing to remain pointed at a point on the distant horizon) with the ball centered even though its heading changes slightly, due to the depressed angle of the sightline from the cockpit in relation to the axis of the propeller shaft.
 
Thanks!
 
Ron Levy said:
Actually, the nose can be kept apparently on a point (i.e., appearing to remain pointed at a point on the distant horizon) with the ball centered even though its heading changes slightly, due to the depressed angle of the sightline from the cockpit in relation to the axis of the propeller shaft.
Click to expand...

I guess it depends on your roll rate and the bank angle used. I used to do these in the Champ when first learning to fly and it rolled so slow that if you used 45 degree banks back and forth while keeping the ball centered, the nose would turn about 15 degrees in each direction for a 30 degree total displacement. No way I would consider that keeping the nose on an apparent point. But if you're rolling fast and using shallow banks, then I guess it's all perception...but the airplane is still turning to a degree if the ball is centered.
 
RoscoeT said:
I guess it depends on your roll rate and the bank angle used. I used to do these in the Champ when first learning to fly and it rolled so slow that if you used 45 degree banks back and forth while keeping the ball centered, the nose would turn about 15 degrees in each direction for a 30 degree total displacement. No way I would consider that keeping the nose on an apparent point. But if you're rolling fast and using shallow banks, then I guess it's all perception...but the airplane is still turning to a degree if the ball is centered.
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Typically we use about 15 degrees of bank or so when teaching this -- avoids bringing up the subject of what we had for breakfast -- again.
 
Ron Levy said:
Typically we use about 15 degrees of bank or so when teaching this -- avoids bringing up the subject of what we had for breakfast -- again.
Click to expand...

Backwards breakfast rarely tastes as good as it did the first time around:no:
 
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flyingmoose said:
Well technically Dutch roll is a phenomenon that occurs usually in swept wing aircraft due to an out of phase roll/yaw combination.
Click to expand...

This.

Swept wing yaws left.
Right wing advances.
Right wing creates lift+drag, raises and is drawn back.
Happens again with left wing in reverse.

This is my understanding of a "dutch roll".
 
lr60plt said:
This.

Swept wing yaws left.
Right wing advances.
Right wing creates lift+drag, raises and is drawn back.
Happens again with left wing in reverse.

This is my understanding of a "dutch roll".
Click to expand...

Yup in a nut shell. It gets aggrevated in a swept wing because of the location of the wings. Some airplanes use Yaw dampers to correct it
Sweptback.gif

This came from the turbine pilots manual.....
Dutch roll is caused by an aircraft’s tendency to sideslip slightly when the aircraft yaws. One wing yawing forward in this situation changes the effective span between left and right wings. The wing yawed forward momentarily creates more lift than the one of the other side. The result is that the forward wing rises and starts a rolling movement. The problem is aggravated by the fact that the forward wing, due to its increased lift, also has more drag, pulling that wing back once again and starting an oscillation in the other direction

Cheers
 
The 747-400 simulator is a ***** to land if you get it started in a crosswind too.

I learned that in a single attempt with heavy feet that Mr. Yaw Dampener was my friend.

And I also learned that the #1 engine nacelle will drag on the ground to remind you of the maximum left crosswind limitations. ;)

Next attempt with lighter pedal pressure and more consistent, yielded much better results. :)
 
Yeah, dragging an engine on the ground might give you a new nickname, like Sparky ...

I always heard jet jockeys don't need feet
 
^:rolleyes:
 
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Haha. I just enjoyed trying. A rare treat to go get to play with someone's multi-million dollar sim. I still owe a particular UA Captain a lot of beer or something. He makes this difficult by being on a low-carb diet all the time. ;)

Low speed outboard engine failures in the 747-400 at takeoff are amazing, too. Never realized how much leverage those outboard engines have until you lose one before the rudder is effective.

It's a stomp-on-the-brakes, shut it down now, and hope you don't have a slick runway or you are going into the grass, moment. Yee haw. Off-roading in an 18-wheeler. (Yeah, it has 18 wheels and the UA guy says he has used that line when people ask him what he does... "Drive an 18 wheeler.")

I went off into the grass at KHNL, for the record. Haha. Got it right the second time after he explained. If you're going to ground the airplane, might as well do it where there's a nice beach, I guess. ;)

We had a few of us noobs in there. My co-pilot was no help. Haha. Blame it on the co-pilot, right? :)
 
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