Dutch Rolls

Hi guys.

On another forum board, a discussion has been underway about Dutch Rolls. I am not sure I am getting the correct answer so am coming to the experts.

I was taught to do Dutch rolls by holding the nose on a point, then banking left and right with no hesitation and keeping the nose on a point the whole time. The banks can be 45 or 60 degrees each way (or more or less depending on preference, I guess). The argument is whether or not the ball will stay centered during Dutch rolls done correctly. I went out yesterday (C-150) and tried it after I was told the ball should max out on each side of the cage by an aerobatic pilot that should know. My ball stayed in the center (more or less, since it was difficult to stay totally coordinated with the differenct rudder pressures required and I had to keep an eye out for traffic). Either I am doing something wrong, or the other pilot is telling me wrong, or we are not totally coordinated with each other. Can you guys help out with my understanding?

Note that I am not an aerobatic pilot, just an enthusiast that has had a very few hours in a Super Decathlon doing aileron rolls, a few loops, and falling leaf stalls. I want to do more, but as always, money is a factor.

Thanks for your help!

Stacey

Although I have a low level acro card for rolls, I have never done competitive acro, so someone may differ. But it seems to me that this is not a coordinated manuever, that the ball will move around. The object is to keep the nose straight in the center not the ball.

Hello,

There are two ways to fly this. If you apply coordinated rudder and aileron, I think that I recall that you can keep the ball in the center as you go back and forth from bank to bank.

What a aerobatic pilot is more likely to do is roll from knife edge to knife edge, holding altitude and heading. That requires opposite rudder to keep the nose up on the point. I will also note that many aerobatic airplanes have no ball to look at. A standard ball installation does not work inverted and when upright, a competent pilot should be able to feel the yaw without the use of a ball.

So your friend may not be flying the exact same maneuver you are flying. From your post I believe that you are flying a "Dutch Roll".

As an aside, is an "acro card for rolls" a warbird thing? When I let my ICAS membership expire you got an airshow competency card that was good down to a specified altitude through an ACE that had to be renewed each year and allowed you to fly any program that you wanted. The FAA stopped doing competency evaluations and handed it off to ICAS. If you did not renew each year it became a useless piece of paper.

Best of luck,

Wes
Pitts N78PS

Somorris: You are doing the maneuver exactly right. The purpose of Dutch rolls (sometimes call Coordination Exercise) is to teach a pilot to apply exactly the correct amount of rudder to compensate for adverse yaw caused by the ailerons when rolling into or out of a turn. If your coordination is good, you should be able to roll from level flight to 30 or 40 degrees of bank in one direction, reverse the roll to roll 30 - 40 degrees in the other direction, then reverse again back to level flight, keeping the nose on a point on the horizon, and keeping the ball in the middle throughout. The application of this is to learn to use the same control pressures to roll into a turn, neutralize rudder and aileron when reaching the desired bank angle, and adding a little back pressure to make a turn. When you reach the desired heading, apply top aileron and rudder to roll back to level flight. Rolling into a turn (every turn you make,) the heading should not change until the bank is established, and completing turn, the nose should stop on the horizon at the desired heading while the wings are rolling level (and the ball remains stationary through the entire maneuver.) Suggestion: Do two or three cycles each way, and then fly straight and level for a few seconds. If the nose (or the skid ball) starts moving around, it becomes increasingly hard to "catch up." Just stop and start over. Get good at this, and you'll amaze your friends at how good all your flying gets.

Dr. Rob
ATP, CFI, DPE (and a bunch more stuff)

P. S. Since the FAA, in its infinite wisdom, chose not to put this maneuver in the Practical Test Standards for any license or rating, it's not taught much any more. Most instructors just want to get the student through the checkride, so they don't throw in much in the way of extras. It was taught as a formal, testable maneuver, in the Army Aviation School in the 1960's.

Wes, my acro card was first issued by the FAA about 1987. Since then I have had a civilian evaulator issue the remewals. It used to be Carl Schmeider. I will treasure my most recent one as it was issued by Howard Pardue, done in Breckenridge.

I think all cards have an alitude limit, mine began I think at 800 ft and is now 500 ft. I don't need to do any acro, rolls or otherwise, at 100 feet.

Mine specifies the plane and type maneuver. I don't have any interest in doing vertical acro at 500 ft.Mine is rolls only. I am sure that many of the airshow folks and particularly acro only type planes have an unlimited type card.

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Originally Posted by Bill Greenwood

Although I have a low level acro card for rolls, I have never done competitive acro, so someone may differ. But it seems to me that this is not a coordinated manuever, that the ball will move around. The object is to keep the nose straight in the center not the ball.

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Originally Posted by Docrob

If your coordination is good, you should be able to roll from level flight to 30 or 40 degrees of bank in one direction, reverse the roll to roll 30 - 40 degrees in the other direction, then reverse again back to level flight, keeping the nose on a point on the horizon, and keeping the ball in the middle throughout.

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OP, seems the confusion persists. :-)

I think that "Docrob" covered the topic comprehensively. Keep doing what you are doing.

Very interesting that "my acro card was first issued by the FAA about 1987. Since then I have had a civilian evaulator issue the renewals." I have to guess that the warbird community has gotten their implementation of the program tweaked a little. That group tends to do more traditional maneuvers given that their equipment is harder to keep in front of a crowd and is actually less aerobatic capable. I hang with the unlimited acro crowd so I have not seen an airshow competency card with a maneuver restriction. A Pitts/Laser/Extra/Edge flight program typically involves snaps, avalanches, and maybe tumbles in addition to vanilla loops and rolls. So no point in putting a restriction on the card.

On the topic of acro in Cessna 150's, the wonderful Amelia Reid used to do a show in an A-150 that you would not believe. Used every bit of performance that the airplane could give.

Fly safe,

Wes
N78PS

Wes, wing-wagging into the box is a dutch roll no? ...even if you only go to 45 degrees and not knife edge. Do this coordinated with the ball in the center and you will be off heading going into figure one, meaning the nose is going off heading (not on point during the process). This one requires opposite rudder to keep the nose on point, which makes the maneuver very uncoordinated.

Thanks guys, although I am still a little confused. I guess if you are flying competition, the wing wagging going into the box is an uncoordinated Dutch roll, although the original intent of a Dutch roll was a coordination exercise? The guy I was going back and forth with was an acro competitor, so I can at least now understand what he was getting at.

Thanks again!

Well competition rolls are NOT coordinated and are NOT "dutch rolls". A competition roll uses lots of opposite rudder and puts you against the down side of the airplane when on knife edge. A ball would be all the way out to the side a lot of the time. The goal is to keep the CG of the airplane travelling in a straight line while the airplane rolls. Since the airplane does not lift well as it passes through the knife edge points you have to sneak the nose up at the start and use lots of top rudder at each knife edge point.

A box entry wing wag can be one of the most violent rolling figures that you do. I put the nose down 45 degrees and slam the stick over as hard as I physically can. I am rapidly loosing altitude and building speed and my goal is to hit the airframe red line speed at the moment that I complete my third roll to 45 and back. The throttle is all the way in so speed builds and altitude goes away fast so I use all of my strength on the stick so that I do not waste altitude.

Your Dutch Rolls are relatively calm.

Stop by an aerobatic contest this summer and check out the flying. Some of it is pretty violent precision in the airplane. Some is very gracefull. Its a great challenge.

Have fun,

Wes
N78PS

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.

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.

Dutch Roll on Wikipedia (explanations of both the aerodynamic tendency and the pilot training exercise that share the name)

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.

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

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.

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Originally Posted by WLIU

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

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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

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

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Originally Posted by WLIU

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.

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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....

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Originally Posted by WeaverJ3Cub

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.

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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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Originally Posted by RetroAcro

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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I was just out in the Cub, and this was my experience.....

If I tried to keep the nose on a point (on a fixed point on the horizon) then it was not coordinated (ball-in-the-center). There's no turn coordinator in the plane, but it didn't feel coordinated to me. If I just tried to "keep the ball in the center" then yes, I made small s-turns as I went left and right. Seemed that the shallower the maximum bank, the less the nose moved, which I guess is no surprise. So....since seeing is believing....then I believe! :)

I haven't tried it again yet, but I did read a couple of noted authors on the subject yesterday. The late Bill Kershner said the ball would not be in the center in doing Dutch rolls. Bill Thomas said the Dutch roll is a coordination exercise and the airplane would stay on point and the ball centered. I think it has to get back to what RetroAcro said about the two different types of Dutch rolls. By the way, not in discussing Dutch rolls but in discussing turns, Rich Stowell in one of his books said to practice rolling into a turn with rudder and aileron with the nose on a point (he didn't say coordinated, but I interpreted it and practice it that way), then turn using the elevator to "pull the airplane around." I haven't checked, but I think that is what "Stick and Rudder" said also. It is still a little foggy!

For what its worth, a competition turn, as defined in the IAC judging criteria, requires that the airplane roll to at least 60 degrees of bank without changing heading, and once the bank has been established, the heading change is done. The heading change is stopped first and then the bank is rapidly brought to zero. Coordinating the entry of exit to the turn is a points deduction.

A typical general aviation turn coordinates rudder and aileron on both turn entry and turn exit.

Fly safe,

Wes
N78PS

So I went out this afternoon and flew "Dutch Rolls" trying to keep my rear end centered in the seat since my Pitts does not have a ball. Was surprised that I had to work at it, but I got the airplane to swing gently from side to side as I went from bank to bank, with the nose aimed at a far away point. Was harder than I expected and I see why you have a student do it. I had to apply the right amount of rudder, but not too much, to match the aileron as I rolled, to keep the nose pointed where I wanted. I have no doubt that my flight path was not a straight line, but a gentle "S".

Interesting change of pace from +6G -3G. Give it a fly.

Regards,

Wes
N78PS

Thanks Wes. That confirms my understanding that the nose does move slightly, although not a lot. It is harder to see when your flying is not as precise as a competition pilot has to be. Good information in this post and once again thank you for your (and others) help.