The "Dutch Roll?"

[BoDEAN]

Can anyone provide some tips or techniques on doing these? Have a checkout tomorrow and the guy hits this pretty hard.

 

[firstthird]

And here I thought that 'dutch roll' was an adverse flight regime that swept wing jets are partial to, thus the installation of yaw dampers to damp out the dutch roll tendency.

 

[KeroseneSnorter]

I suck at dutch rolls.....how about a nice muffin?

 

[midlifeflyer]

Here's a description of the maneuver from my personal FAQ. See if it helps.

The "Dutch Roll" is a maneuver used to visually develop aileron-rudder coordination. The idea is to use "hand-eye-foot" coordination to keep the nose of the airplane from moving while rocking the wings back and forth.

Like other maneuvers with a heading component (slow flight, stalls), start by pointing the nose of the airplane on some distant object as a visual heading reference.

Begin to rock the wings s-l-o-w-l-y back and forth with the aileron. Use rudder to keep the nose on target.

If there was no rudder used at all, you know what would happen. On a right roll, adverse yaw would initially cause the nose to drift left. Eventually the nose would follow the bank and the airplane would turn. So you need right (coordinated) rudder initially to keep the nose from drifting, and then left (uncoordinated) rudder to keep the airplane from turning. You can start with shallow 10º banks and move up to 20 or 30.

The maneuver can be done in level flight, but it can be a really good exercise to do while climbing to altitude on the way to the practice area.

It ain't easy. Students need to be patient. Most common error is doing them too quickly. It should be slow like a Waltz, not quick like a Swing.

 

[firstthird]

that's why I like this board, learn something everyday. and some of it is even useful (unlike airline X is doomed unless it buys emb-190's, DOOMED I say). Didn't mean to be too much of a smart aleck with my earlier response but not having done this particular maneuver in Navy training, never heard of it. Sounds like a good one for people that get airsick easy.

 

[avbug]

It's a good rudder-aileron coordination exercise. With a primary student, it's one I use later. I like to have the student practice slicing the nose back and forth using rudder only, while keeping the wings level. Then keeping the wings level, raise the nose above the horizon, slice left, lower it to the horizon, then slice right to complete a box. Then the other way. Circles or triangles with the nose are easy for the student to understand and do, and are good coordination exercises as well as confidence building maneuvers.

The dutch roll can be accomplished by keeping the nose on the horizon on a particular point and rolling back and forth. One may do the same using the heading bug or a particular heading, to integrate instrument use. One may also then require the student to roll left and right keepign the ball in the center. Moving from a dutch roll to a "coordinated" roll, and then back to dutch rolls again provides a good contrast and can accelerate the student's grasp of control useage.

A good exercise later, is to fly down the runway keeping heading, but touching one gear and then the other on each side of the centerline. Then fly down the runway with the wheels off the ground, using rudder to drift to one side of the runway and then the other while keepign the wings level. This provides a graphic visual feedback for the student regarding the reaction of the airplane to the control inputs, and can greatly improve the student's understanding of the aircraft control. With a little exposure, it also pays dividends to the student in control in gusty conditions, landing on narrow runways or emergency strips, etc.

 

[midlifeflyer]

Didn't mean to be too much of a smart aleck with my earlier response

You weren't. You described what dutch roll tendency is. I'm not sure how the very different coordination exercise got the same name.

 

[avbug]

The name is a racial slur, in the same way we speak of a polish fire drill. It's a dutch roll.

Dutch roll is an uncoupled aerodynamic response to aileron input, or upset about the vertical axis, between the vertical and lateral axes. The maneuver is a mexican hat dance, a polish fire drill, a dutch roll.

Capice?

 

[bobbysamd]

Dutch rolls

Are we sure they aren't a kind of bread that is eaten in Delft?

Really, dutch rolls are a great coordination exercise. They are great for making every training minute count. Instead of just having your students fly straight and level to and from the practice area (and assuming they have no trouble holding straight and level), have them do dutch rolls.

 

[Flyingdutchman]

Re: Dutch rolls

Are we sure they aren't a kind of bread that is eaten in Delft?

----

Bobbysamd,

Have you ever been to Delft??

g'day

 

[TonyC]

Not being quite satisfied with the explanations given so far, I took some time to research the matter myself. After all, my Dutch Roll training focused on how to get OUT of them.

As I understood it, a Dutch roll is a phenomenon, primarily of swept-wing aircraft, where oscillations of roll are out of phase with oscillations of yaw. In other words, it is yawing in one direction while rolling in the opposite, and not because you're controlling it that way. One of the reasons that it is emphasized in training is that left unchecked it can be lethal. Another is that the corrective action is not intuitive - - in fact it is exactly the opposite.

For a far better explanation, I offer this webpage:
Dutch Roll

For the connection-speed challenged (I feel for you, I used to be myself), I'll paste a couple of nuggets.

Dutch Roll - bill howell

Many swept wing aircraft suffer a dynamic instability problem known as Dutch Roll.

Dutch roll happens when the aircraft has relatively strong static lateral stability (usually due to the swept wings) and somewhat weak directional stability (relatively.) In a Dutch roll the aircraft begins to yaw due to a gust or other input. The yaw is slow damping out so the aircraft begins to roll before the yaw is stopped (due to the increased speed of the advancing wing and the increased lift due to the swept wing effect.)

By the time the yaw stops and begins to swing back toward zero slip the aircraft has developed a considerable roll rate and due to momentum plus the slip angle the aircraft continues to roll even once the nose has begun returning to the original slip angle.

Eventually the yaw overshoots the zero slip angle causing the wings to begin rolling back in the opposite direction.

The whole procedure repeats, sometimes with large motions, sometimes witch just a small churning motion. Like all dynamic stability problems, Dutch roll is much worse at high altitudes where the air is less dense.

Dutch roll is almost certain to happen in a jet aircraft if the Yaw dampener is turned off at high altitude. Therefore, the first thing to check if an aircraft begins to exhibit Dutch roll is that the Yaw Dampener is on. The pilot should then try to minimize the yawing oscillations by blocking the rudder pedals (i.e. hold the rudder pedals in the neutral position.) Next apply aileron (spoiler) control opposite to the roll. The best technique to use is short jabs of ailerons applied opposite to the roll. Try to give one quick jab on each cycle (i.e. turn the wheel toward the rising wing, then return it to neutral.) Finally accelerate to a higher speed, where directional stability will be better, or descend into more dense air, for the same reason.

This next guy says what I was thinking about the first several posts on this thread in a much more diplomatic way than I was prone to do.

Here's another example of terminology being used in error. I’d never thought this would need any discussion, however several computer forum exchanges within the past few months have delved into this subject and – in the words of one student of my acquaintance – “Wow, those guys must really be misinformed, huh?”



Before we get into a discussion of the “rolls” we’re talking about here, I should mention a couple “tongue-in-cheek” definitions of “rolls” and aerobatics from the CAF dictionary of the past (circa 1967); they just somehow seemed apropos to this subject. The “sweet roll” (as well as the “Puerto Rican sixteen”) found their way into that dictionary as maneuvers.



Anyhow, now back to the serious stuff. Over the years, I’ve seen this [the following] maneuver taught in two or three ways. And I’ve taught different ways of doing it – depending upon the objective. So I guess we have a consensus among flight instructors of the maneuver’s validity – but not of the terminology.



(1) One method would be while in straight and level flight to pick a point on the horizon and enter a turn away from it for some amount of turn and then, without stopping, reverse the turn to pass through the original point in the opposite direction, then again reverse the turn and so on, while all the time coordinating the flight controls (especially the rudder and ailerons). (2) Another variation or method used is to pick a straight road or a point on the horizon. Then precisely hold that point while initiating a bank (takes opposite rudder), then reverse the bank to an equal amount in the opposite direction. This is repeated over and over while using the flight controls to precisely maintain that point (especially the rudder and ailerons). This variation especially lends itself to getting the student ready for the aggressive use of the rudder in acrobatic flight.



Evidently – to a certain number of instructors – the above aileron/rudder coordination exercises (especially #2, the one that holds the reference point) that we all give our new students are called “dutch rolls”.



Well, we’ve got some news for you, chum! Those aren’t “dutch rolls”, they’re simply plain old garden variety “coordination exercises” or “coordination rolls”. And – undeniably – they’re extremely useful for teaching coordination or for quickly evaluating an aircraft’s handling qualities! I’ve used them from the very first time I took my first lesson in an Aeronca Champ right up until the present. When we were aviation cadets in “Bevo” Howard’s USAF T-6 school, we were taught them from the very first day of our flight training. BUT THOSE ARE NOT DUTCH ROLLS! You copy that? “Sorry Charlie” but no cigar, those are NOT dutch rolls! No big deal, you say? Well, OK, but you need to realize that when you use an incorrect term it’s teaching your student something completely wrong. It’s sort of like the media using the term “Piper Cub” for every airplane less than a medium sized jet. And – besides perpetrating a falsehood – it can later kill him/her! And if you don’t think or realize that a dutch roll can easily become lethal, look up the Braniff/Boeing 707 (N-7071) flight training accident involving the tossing of a couple of pylon mounted engines off the wings in the fall of 1959.

OK, so he wasn't as diplomatic, but at least I don't have to take the heat for it!

[EDITED TO ADD THIS:]

OK, another nice site for you to peruse:

Centennial of Flight - Theories of Flight - - Essays - - Stablity II

Again, a nugget:

Dutch roll is a motion exhibiting characteristics of both directional divergence and spiral divergence. The lateral stability is strong, whereas the directional stability is weak. If a sideslip disturbance occurs, as the airplane yaws in one direction, the airplane rolls away in a countermotion. The airplane wags its tail from side to side.

Ventral fins, although primarily used to augment the vertical fin that may be in the wake of the wing at high angles of attack, are also beneficial in decreasing the lateral stability and increasing the directional stability to reduce the effects of Dutch roll.

(I'm still searching for the origin of the term.)

Cheers!

 

[TonyC]

The name is a racial slur, in the same way we speak of a polish fire drill. It's a dutch roll.

You may be on to something....

All things Dutch ?

From the page:

My list of English expressions featuring the Dutch. I collected this list from various dictionaries. Does the fact that most of these expressions are unfavourable say something about the English or about the Dutch?

 

[TonyC]

Apparently Bill Howell got his info from THIS site:

Lateral Stablity

which has an excellent discussion on stability and several animations to demonstrate the concepts. The Dutch Roll discussion is near the bottom of this page.

 

[TonyC]

Origin of "Dutch Roll"

Perhaps the skating technique is the origin??

The 'Dutch Roll'

In the Dutch language this is known as 'schoonrijden' which translates into graceful but controlled skating. It is beautiful and serene in its appearance. The purpose of the rolling is to place curved strokes on the ice by skating in turn on the outer edge of the runner blades only in a regular pace

 

[TonyC]

Origin of "Dutch Roll"

Or, perhaps:

Dutch Roll

I suppose that just as much of our aviation language originated from naval terms, the origin of the Dutch-roll could have come from the peculiar sideways shift of the stern of an apple-bowed caravel (Dutchman) when running before a following sea. As the stern was lifted by the oncoming wave it would swing to one side, the hull would roll as the swell passed, and the stern would swing back onto the course-line as the breaker moved under the bow and the hull rolled upright.

In an aircraft, especially those with V-tails, it is a tendency for the tail to wander off the line-of-flight far enough to generate a straightening force, but overshooting the correction only to repeat the excursion on the other side. If accompanied with a pitch variant, the tail may oscillate in a circle. The Dutch-roll in ship and aircraft is an undesirable characteristic.

 

[Wang Chung]

When I first did Dutch Rolls, the instructor told me how I could tell if I was doing the maneuver correctly - the advice stuck with me.

When you look out the side window, the wing should be moving straight up and down with reference to the horizon - with no aft/forward movement.

That made sense to me, and the maneuver became simple. After a couple rolls, you will find the stick/rudder dance pattern that will do the job.

 

[f18pugsley]

Tony C,

Your last explanation is the correct one for the origin of the term 'Dutch Roll'. All ships exhibit this tendency (makes for added challenge landing in heavy seas-the deck moves up, down, and side-side). Some ships do have dampers, however.

My understanding of the source is that since the dutch were one of the first western naval powers, the term is credited to them. Whether it comes from the type of ships they sailed or just the number of Dutch ships on the oceans then, I don't know.

 

[cubpilot]

Edited to correct some gramer.

Dutch Roll is the tendency, but the “erroneously” named coordination training-maneuver has been around for years. I think its time for diehards to recognize that too many people know of the training maneuver as dutch rolls to ignore. The term now has two very different meanings.

As a side point, the term coordinated flight has two meanings which are often more difficult to reconcile. One is the simultaneous use of flight controls (more than one) to achieve the desired result. The other is (simplified), the ball centered. The training maneuver dutch rolls are coordinated under the first definition and uncoordinated under the second.

 

[nosehair]

Well,...after all that, the only thing I'm sure of now is that I like my Dutch rolls to have love handles.

 

[mizzouguy]

I hate Dutch Rolls they always make me sick