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Thread: Dutch Rolls

  1. #11

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    Thanks again Wes, Retro Acro, Bill and Dr. Rob. It is starting to sink in. One of these days (finances permitting) I would like to learn more acro. In the mean time, I have to be satisfied with flying a C-150 and learning to do that as well as I can. You guys are great to share your knowledge and experience with me and I appreciate it.

  2. #12

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    Wes, my acro card says rolls, as that is all I want to do down low, except steep turns which aren't really acro. But there are many pilots who do much more than rolls down low as part of their act, it is not limited soley by the plane. I have even seen a spin done starting at about 1000 feet in a light warbird, but not what I want to do. Some heavier high performance warbirds are specifically prohibited from "flick manuevers", ie snap rolls. I have many times seen Bud Granley do a snap roll on takeoff in his Harvard, also seen him do a verticle roll in an SNJ at 10,000 feet density alititude, and a vertical 8 in a P-51, as well as Elliot Cross fly down the flight line inverted in a P-51 at Oshkosh, at about 150 feet.

  3. #13
    Eric Page's Avatar
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    Dutch Roll on Wikipedia (explanations of both the aerodynamic tendency and the pilot training exercise that share the name)
    Eric Page
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  4. #14
    RetroAcro's Avatar
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    Somorris, the nose-on-point (on heading) Dutch roll (ball will not be centered) actually has a lot in common with the aerobatic competition roll, in that the airplane must roll without causing the CG of the airplane to deviate from a straight flight path, as Wes mentions. That's a fancy way of saying that the airplane must not curve upward, downward, or turn while the airplane is rolling. If rolling from straight and level, the airplane must not climb or descend while rolling.

    I also think the term "coordination" may have different connotations for different folks. "Coordination" for some might always mean "ball in center". Others may simply apply the definition of the term with respect to the movement of the aileron and rudder: "to act together in a smooth concerted way". You can "coordinate" rudder with the aileron without the ball being in the center. Though in the world of primary flight training, this would mean "uncoordinated". As with the nose-on-point Dutch roll, the competition roll requires the rudder to be smoothly coordinated, just not in a way that puts the ball in the center.

    Let's say you do a straight-and-level competition roll (360 degrees of roll) slowly, in order to make all the individual stick and rudder movements stand out better. Training with a CFI, Dutch rolls are likely done with no more than 60 degrees of bank in order to remain legally "non-aerobatic". Let's say you roll left to 60 degrees of bank and then roll to 60 degrees of bank to the right, then back to level with zero altitude deviation or turning. Guess what, you have just performed the exact control inputs required for the first and last 60 degrees of a full 360 degree level competition roll. For the folks who have only been trained to "coordinate" the rudder in the "ball in center" fashion, this type of Dutch roll is a good exercise as an initial aerobatic training exercise to get the student to understand that the rudder must be used independently from the aileron (cross controlled) in order to roll the airplane without deviation from altitude and heading.

    So wing wags in competition are nothing but a Dutch roll...but typically with the bank only occuring in one direction, though some folks go once in the opposite direction, which produces a full Dutch roll cycle that non-aerobatic folks may fly. The only difference in competition is that we're typically diving to some degree during this process, but it's still Dutch roll. For the primary flight training student, this type of Dutch roll is fairly pointless. At this stage, the ball-in-center Dutch roll is a much more valuable exercise for teaching and practicing normal rudder use, which in the non-aerobatic world is generally only used to cancel adverse yaw from the ailerons. But of course, this produces slight s-turns, since the airplane will start to turn as bank is introduced, unless the airplane is cross-controlled with opposite rudder (to counteract the turning tendency of the banked wing), which puts the ball off center.
    Last edited by RetroAcro; 07-09-2012 at 11:03 AM.

  5. #15

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    Uh, I think that if you go do a Dutch Roll, you will find that the fuselage, and hence the CG, displaces left and right as you go from bank to bank with the nose on a point. A little, but very little, like what happens in a falling leaf. If I was sitting on the judges line and saw that it would be at least a 1 point deduction......

    Best of luck,

    Wes
    N78PS
    IAC National Judge

  6. #16

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    I think I am beginning to understand what you are saying, RetroAcro. Basically, when I am doing Dutch Rolls in a C-150, even though I am holding the nose on a point (or at least that is the way it looks to me), I am actually making very small left and right turns that are basically not noticeable to me, but would result in deductions if you were being judged at an aerobatic competition like you guys are.

  7. #17
    RetroAcro's Avatar
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    Quote Originally Posted by WLIU View Post
    Uh, I think that if you go do a Dutch Roll, you will find that the fuselage, and hence the CG, displaces left and right as you go from bank to bank with the nose on a point. A little, but very little, like what happens in a falling leaf. If I was sitting on the judges line and saw that it would be at least a 1 point deduction......

    Best of luck,

    Wes
    N78PS
    IAC National Judge
    Wes, I think the problem with talking about this is that "Dutch roll" means different things to different people. Two interpretations - 1) rolling the airplane back and forth as a ball-in-center rudder coordination exercise and, 2) Rolling the airplane back and forth with the nose on a point without regard to ball-in-center coordination. To me, "nose on a point" means that the airplane's heading does not change, and the flight path of the airplane stays straight...same as a competition roll. Of course with the competition roll, we call it "roll around a point", since it's a full 360 degree roll instead of the shallower back and forth banks of the "Dutch roll". This requires cross-controlling at times, and does not keep the ball in the center.

    Keeping the ball in the center while rolling back and forth will cause the airplane to s-turn, the degree of which depending on bank angle, roll rate, and airspeed. Do this type of "Dutch roll" in a plane like a J-3 Cub and the nose will probably move (turn) 10-15 degrees to each side if you're banking 45-60 degrees each way. Due to the s-turning, I do not consider this is a "nose on point" dutch roll. Since I've never heard of, nor know of a third way to fly a dutch roll, I consider the ball-off-center, cross-controlled, constant heading/flight path, "nose on a point" dutch roll to be fundamentally the same as the way we roll the airplane in competition. Unless you're flying at zero G, it's impossible to roll the airplane back and forth with the ball in the center without also s-turning to a degree. To me, s-turning would produce "left and right of a point", not "on a point". But I guess as with anything in flying, interpretations can differ. If there are different ideas about what "nose on a point" means, then this whole "Dutch roll" stuff just got exponentially more confusing than it already was. :-)

    Eric
    Lowly IAC Regional Judge
    Last edited by RetroAcro; 07-09-2012 at 03:07 PM.

  8. #18

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    I recall that coordinating rudder and aileron to keep the ball in the middle you can keep the nose on the point while rolling from bank to bank in the "Dutch Roll" that is referred to when talking about airplane stability and long ago training standards. I think that the original poster flew that traditional method and I hesitate to put a competition acro spin on the old maneuver. Competition rolls that do not coordinate rudder with aileron are fine being called competition rolls and I doubt they would be much fun in a C-150. I like to ratchet my harness tight so that I don't bounce off the inside of the airplane while doing my wing wags. Can't do that in a Cessna.

    But my guess is that rather than talk in the abstract, we should all go fly and try what the original poster, and the Wiki article, describes. We are about flying right?

    And since you fessed up to being a Regional Judge, this is my opportunity to completely hijack this thread and encourage you to look at your IAC Judges credit log on the IAC web site's contest results page and lobby that you should upgrade to a National Judge. I received a very nice note from Ellyn Robinson, the 2012 Nationals Volunteer Coordinator and she is begging for judging help at this September's Nationals. If you have never been to Nationals it is a tremendous learning experience. Also, a National Judge is needed to certify new Regional Judges so if the contests that you go to are short of Judges, you can be part of the solution to that problem and nag you peers about going to Judges School. End of paid political announcement.

    Y'all have fun flying,

    Wes
    N78PS

  9. #19
    WeaverJ3Cub's Avatar
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    Quote Originally Posted by WLIU View Post
    I recall that coordinating rudder and aileron to keep the ball in the middle you can keep the nose on the point while rolling from bank to bank in the "Dutch Roll" that is referred to when talking about airplane stability and long ago training standards. I think that the original poster flew that traditional method and I hesitate to put a competition acro spin on the old maneuver. Competition rolls that do not coordinate rudder with aileron are fine being called competition rolls and I doubt they would be much fun in a C-150. I like to ratchet my harness tight so that I don't bounce off the inside of the airplane while doing my wing wags. Can't do that in a Cessna.
    This is a VERY interesting thread. I've learned a lot reading through it...

    Just my 2 cents.....I agree with the above. I did some dutch rolls in a Champ and a Cub, and they were coordinated (ball in the center) maneuvers and the nose stayed on a point. Now I didn't bank past 40 degrees or so, but I'm pretty sure the nose stayed on point.

    Either way, I'm taking your advice and trying some when I fly the Cub tomorrow. Then I won't have to rely on memory....

  10. #20
    RetroAcro's Avatar
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    Quote Originally Posted by WeaverJ3Cub View Post
    Just my 2 cents.....I agree with the above. I did some dutch rolls in a Champ and a Cub, and they were coordinated (ball in the center) maneuvers and the nose stayed on a point. Now I didn't bank past 40 degrees or so, but I'm pretty sure the nose stayed on point.
    I like a good discussion on flight dynamics. And I would be interested in the physics explanation of how you can roll the airplane back and forth, in level flight, with the ball in the center - without s-turning to a degree. I'm still assuming that when folks say "nose on a point", they mean the airplane is not turning at all, and that the flight path remains perfectly straight. If not, please let me know as it will save much miscommunication. :-)

    As long as you are banking the airplane under positive G with the ball in the center, the total lift vector of the airplane is produced solely by the wing, and will be perpendicular to the wing. This means that as soon as you start rolling off of a level attitude, that the airplane will start turning slightly, due to the developing lateral component of the lift vector due to the bank angle. If you are using shallow banks, and the airplane rolls fairly fast, and your airspeed is high, it could be that you are just not noticing the slight s-turning. But it would defy the laws of physics to fly the airplane at 1G, banking banking back and forth with the ball in the center, while keeping the airplane's heading and flight path constant. What your eyes interpret (or misinterpret) is different.

    The reason I consider the nose-on-point Dutch Roll to require the ball to be off center, is that as you bank the airplane under positive G, the only way to keep the nose from beginning to turn off heading is to reduce AoA slightly, and to apply opposite rudder. This keeps the total lift vector of the airplane (which now includes fuselage lift in addition to wing lift) perpendicular to the ground, which prevents turning off heading. Opposite rudder introduces a fuselage lift vector that opposes the direction of the wing lift vector, which prevents turning.

    I'll try go grab some video of these two different types of Dutch rolls in the Cub. Hopefully the visual difference will be clear. I've flown these two types and have definitely noticed s-turning while keeping the ball in the center, rolling the airplane back and forth.

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