Learning the Dutch-Roll
UNCOORDINATED FLIGHT---A NECESSARY SKILL
While the controversy continues over spin training, I feel that a much more practical and useful flight skill is being neglected. I write thus of the 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.
The basic Dutch-roll consists of rocking the wings with the ailerons smoothly through a series of 10, 20, or 30 degree banks while keeping the nose on a point or heading with the rudder. If done while the aircraft is climbing most of the rudder application will be more or less right rudder with an occasional tap of left rudder. This does not detract from the value of the exercise.
To the student pilot, to whom the coordinated use of rudder and aileron has become a sacred ritual, the contradictory control pressures required for the Dutch-roll ranks as sheer heresy. The control pressures required equate with patting the head while rubbing the stomach. The skill acquisition compares with that of roller skating. It is best not to intellectualize it. Just do it until all by itself it seems to fall into place. Remember when you learned to skate?
Just as the four basics are skills essential in normal flight situations, so is the Dutch-roll an essential additional skill for successful crosswind landings and use of the rudder. In the off chance that the reader may be unacquainted I will endeavor to describe the maneuver and suggest an instructional sequence.
The Dutch-roll can be flown level, climb, or descent. You select a point or heading and try to keep on that heading. Beginners seem to do the series of banks too quickly. This increases the yaw effect and makes necessary abrupt usage of the rudder. At a slower pace the rudder use can be better anticipated. If the nose swings the rudder is being misused. Start over. The nose should not move during the banks. Maintain a constant airspeed. The rudder must be applied or relaxed sometimes in anticipation and at other times in conjunction with the ailerons.
A suggested instructional or practice sequence would be to use the climb time from pattern altitude to cruise altitude. This time is often under utilized and the Dutch-roll serves to clear the flight route. The student can begin with a series of rhythmical 10 degree wing movements while the instructor applies rudder to maintain heading. It is vital that airspeed be maintained relatively constant so that rudder application and effect will also be constant. Then the roles can be reversed between student and instructor. The third step would be the student performing both functions with the instructor monitoring. If, for any reason, banks and nose movements become erratic--start over. See, just as in roller skating. It seems to be best to initiate the first banking of the wings to the left followed quickly with a solid application of right rudder before the nose has a chance to swing.
The left turning-factors of the climb is a constant that requires right rudder. The banking causes yaw which is a variable depending on amount and quickness. When the bank begins toward the right the rudder pressure is gradually relaxed but not removed because of the left turning-factor and adverse yaw in climb. The banking movements must be continuously smooth and rhythmical, as in waltz time. All efforts to control heading must be done with rudder while the banks are maintained in rhythm. Rudder amounts and timing of release or application is done in anticipation of heading changes.
The student will experience extreme frustration with this exercise in the beginning. As the student becomes visually aware of the nose on the horizon and how rudder is a control he will improve. It is vital that expectations of proficiency be planned over at least five flights. If air sickness is a problem, approach the exercise in gradually extended time periods from twenty seconds to three minutes. The most common difficulties seem to be making the banks too quickly and of unequal angle, holding the yoke tightly, not making airspeed adjustments, not recognizing heading changes, belated rudder applications, and attempting to salvage a blown exercise. If the nose begins to wander, start over.
Even though we are in uncoordinated flight there is still a required coordination between foot and hand, rudder, aileron, and airspeed. Coordination, even in uncoordinated flight, is a basic skill required for slips and crosswind landings.
Now what do we get from this. We get a pilot who can enter final for a crosswind landing with one half of a Dutchroll and the visual coordination skills required to maintain runway alignment, the nose position and the airspeed. The pilot can do this with those Dutch-roll skills that enable him to anticipate rather than react. He is ahead of the plane, not behind. If, because of wind velocity and direction or control problems, the half Dutchroll cannot be held on final--GO-AROUND.
Why the Dutch Roll
There are two ways, actually three ways, to perform crosswind landings. The oldest method required that the aircraft fly the whole final in a wind correcting crab until in the flare. At the flare the nose would be rudder aligned with the centerline and a wing dropped into the wind for touchdown. Exquisite timing made this work very well. Anything less would (could) put damaging side loads on the landing gear.
The FAA preferred crosswind landing uses a cross controlled approach in which the nose is aligned with the centerline while a wing is lowered into the wind to correct for any crosswind. On the entire approach, flare, touchdown and rollout the nose is kept straight and the yoke into the wind. The third way is a combination of the two with the wing low initiated before the flare.
The Dutch roll is the basic training maneuver that prepared the pilot to enter into the wing-low/nose-straight by 'doing what it takes' without conscious intellectual involvement. My best analogy is the art of roller skating.
The actual Dutch roll is a process of using uncoordinated applications of rudder and aileron in such a manner as to fly a specific heading without change while at the same time making the aileron changes necessary to offset any existing crosswind and it's variations.
Simply put, you practice rocking the aircraft wing down to wing down the same amount to each side while using the rudder to prevent ANY yaw. If yaw occurs, start over. I usually do this exercise in climb beginning with the second lesson for 2 to 4 minutes at a time. In five lessons a student suddenly has it fall into place. Just like roller skating. A pilot usually takes only two sessions. Being done in a climb forces the student to apply the right rudder far differently than the left.
Crosswind Landing
Everything you need to do in a crosswind is in your imagination. The use of rudders in a crosswind just involves doing what it takes. You make the airplane do what it is supposed to do. What you experience is more what you think has happened and what actually did happen. Imagine what is supposed to happen and then make it happen.
As a student working on crosswind landings, or any landings for that matter, you must be asking yourself an infinite variety of questions about the process. High, low; close, far; fast, slow; up, down, in, out; it doesn't matter you must never focus on one item, the whole process must be put together to make the landing. As in a poker game, each landing is a new hand that must be bet and played with the cards you are given
The necessity for a stabilized approach even applies to crosswind landings. You should hold the crossed controls throughout the final approach. The crabbing approach, which requires a sudden application of rudder and aileron during the flare, seems to pose an unnecessary risk at touchdown.
The problem of crosswind instruction is not with students; it is with instructors. All to often I take my students up in a moderate 15-knot 60- degree crosswind for an hour. We are lonely. The FBOs with their cadre of young instructors have flight restrictions to protect their equipment. How is a student to learn to cope with the adversity of a crosswind if the opportunity of exposure is denied? A crosswind is a learning opportunity. An event to be challenged, studied, and conquered. If the student should discover that he is incapable of handling a specific wind, then that, too, is a valuable lesson. We must learn our limits, how better to learn them under experienced instruction?
I have had occasion, of late, to fly with several mid-time pilots who show weaknesses while making crosswind landings. On each occasion, my first query is as to whether or not they have been taught Dutch rolls. They may have heard of the Dutch roll or may even be able to describe it. None of these pilots admit having had instruction, proficiency, or awareness of the Dutch roll relationship to cross wind landings. Proficiency in the Dutch roll takes the mystery out of how much rudder and aileron to apply for a crosswind landing. Become sensitive to signs that will give wind direction and velocity. Check the windsock on final.
There are two distinct cross wind landing patterns for a given wind. Left or right patterns in less than 90 degree crosswind affects the amount of turn required to hold runway heading on takeoff, the turn and heading to maintain crosswind track, as well as the amount of turn required for downwind and base legs. The pilot must learn to take into consideration the velocity of the crosswind as it influences the ground track of the traffic pattern. The 90-degree crosswind does not affect track on crosswind or base except in terms of speed.
In a crosswind landing this runway alignment is doubly important. Each turn from base to final, left or right will require a completely different rudder/wing low technique in a crosswind. This can best be practiced where parallel runways exist or where left/right patterns can be flown to the same runway. When practicing crosswind landings it is very important that both left and right patterns be flown to teach planning of the crosswind, downwind, and base legs as well as turning to final with the proper wing low/rudder position. The initial practice of runway alignment can be done in calm to slight crosswind conditions. Later practice should be done in increasingly strong crosswinds even to the point of requesting a crosswind runway not currently in use.
Aircraft that are certified under FAR Part 23.233 requires the aircraft to be safe for operations in 90-degree winds up to 0.2 Vso. Vso is the slowest speed an aircraft is controllable in landing configuration, at approach speed, no brakes and no special pilot skills. For a 60-knot speed with the C-150 this equates at 12 kts. These are minimums. This means that anything beyond a 12-kt. 90-degree crosswind exceeds the design expectations for an average pilot. If during the certification trials of a given aircraft, only ten-knot winds were available then that is the limit of the demonstrated crosswind component. This does not appear to be a very realistic criteria.