AirTalk.org Aviation discussions newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Dutch Roll Goto page 1, 2, 3  Next          AirTalk.org Forum Index -> Aviators (General Discussions) View previous topic :: View next topic   Author Message SelwayKid Guest Posted: Sun May 02, 2004 8:54 pm    Post subject: Dutch Roll So what is your understanding of a Dutch Roll? It is interesting to me the various understandings of this manuever, how it is performed and its origins. I've got my own that I was taught by a CFI over 45 years ago and have taught to virtually every student I've had over the years, including helicopters. Ol Shy & Bashful CFI - Airplanes and Rotorcraft Helicopters, Instrument Rotorcraft and Airplanes, Multiengine, Gold Seal (1967) Back to top Bob Moore Guest Posted: Sun May 02, 2004 11:18 pm    Post subject: Re: Dutch Roll (SelwayKid) wrote Quote: So what is your understanding of a Dutch Roll? It is interesting to me the various understandings of this manuever, how it is performed and its origins. I've got my own that I was taught by a CFI over 45 years ago and have taught to virtually every student I've had over the years, including helicopters. Well....a Dutch Roll is probably not what you understand it to be, particularly if you have not flown swept-wing transport aircraft. The aileron/rudder drill sometimes taught to student pilots is not a Dutch Roll. Copied from the following web site: http://142.26.194.131/aerodynamics1/Stability/Page5.html Dutch Roll 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 with 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. Bob Moore ATP B-707 B-727 FI Airplanes/Instruments Back to top Todd Pattist Guest Posted: Mon May 03, 2004 3:04 pm    Post subject: Re: Dutch Roll Bob Moore <rmoore16 (AT) tampabay (DOT) rr.com> wrote: Quote: Well....a Dutch Roll is probably not what you understand it to be, particularly if you have not flown swept-wing transport aircraft. The term is correctly used for both the intentional flight maneuver that you think he's thinking of (alternating motion on the roll axis without corresponding yaw) and the dynamic instability problem you describe below. It's also properly used for the motion of a ship with a following sea. Todd Pattist (Remove DONTSPAMME from address to email reply.) ___ Make a commitment to learn something from every flight. Share what you learn. Back to top Greg Esres Guest Posted: Mon May 03, 2004 4:29 pm    Post subject: Re: Dutch Roll < Can you specify on what basis you determine that the term is used "correctly"? It's true that the piloting community uses "Dutch Roll" in the way the OP did, but the piloting community uses lots of words with implied meanings at odds with the aerodynamic literature. This usage interferes with their ability to gain a more sophisticated understanding later on, due, I suppose, to the law of primacy. I agree with Bob Moore (and Bill Kershner, et al) that Dutch Roll shouldn't be used in this context. Back to top Darrell Guest Posted: Mon May 03, 2004 4:45 pm    Post subject: Re: Dutch Roll Dutch roll is roll due to yaw in a swept wing aircraft. It is more pronounced than that experienced in a relatively straight wing aircraft. Also, since swept wing aircraft are more frequently flown at high altitudes where the air is thinner and mach transitions can occur it is generally considered only a swept wing phenomenon. see http://142.26.194.131/aerodynamics1/Stability/Page5.html -- B-58 Hustler History: http://members.cox.net/dschmidt1/ - "SelwayKid" <selwaykid (AT) yahoo (DOT) com> wrote Quote: So what is your understanding of a Dutch Roll? It is interesting to me the various understandings of this manuever, how it is performed and its origins. I've got my own that I was taught by a CFI over 45 years ago and have taught to virtually every student I've had over the years, including helicopters. Ol Shy & Bashful CFI - Airplanes and Rotorcraft Helicopters, Instrument Rotorcraft and Airplanes, Multiengine, Gold Seal (1967) Back to top Todd Pattist Guest Posted: Mon May 03, 2004 6:39 pm    Post subject: Re: Dutch Roll Greg Esres <nospam (AT) nospam (DOT) com> wrote: Quote: Can you specify on what basis you determine that the term is used "correctly"? Simply that it seems to be successfully used for both meanings without any real confusion I can detect. CFI's suggesting coordination exercises are using the OP's meaning and aerodynamicists are talking about the dynamic instability problem. I suspect the OP had never heard the aerodynamic definition, and the first reply he got assumed the same thing, so in this group, it's likely to have the coordination exercise definition. If you think it's "incorrect" while I think it's "correct" that's interesting, but I suspect it's too late to stop it from being used the way it is currently being used, even if we wanted to. Language has a tendency to go its own way and get labeled as correct or incorrect after the fact :-) BTW, do you think the coordination exercise label was initially adopted by someone who'd heard of the aerodynamic usage, but didn't understand it, or do you think they developed independently? Quote: It's true that the piloting community uses "Dutch Roll" in the way the OP did, but the piloting community uses lots of words with implied meanings at odds with the aerodynamic literature. This usage interferes with their ability to gain a more sophisticated understanding later on, due, I suppose, to the law of primacy. I didn't have any problem when I first learned of another usage. I'd already learned the nautical usage, so the two aviation usages were just added into the mix. I believe int h law of primacy, but we're talking intellectual stuff here, not how to react when your wing falls off :-) Quote: I agree with Bob Moore (and Bill Kershner, et al) that Dutch Roll shouldn't be used in this context. Todd Pattist (Remove DONTSPAMME from address to email reply.) ___ Make a commitment to learn something from every flight. Share what you learn. Back to top Greg Esres Guest Posted: Mon May 03, 2004 7:29 pm    Post subject: Re: Dutch Roll << If you think it's "incorrect" while I think it's "correct" that's interesting, >> No, no, just "non-standard". "Correct" is a fuzzy term. ;-) < initially adopted by someone who'd heard of the aerodynamic usage, but didn't understand it, or do you think they developed independently? >> Hmmm....interesting question. Seems low probability they'd develop independently. The originator of the term might well have understood the stability use of the term, but since the motions bear a resemblence to each other, might have used it anyway. Actually, I had never heard of the term in a nautical sense (I'm not a boater.) Given that boating is older than aviating, seems more likely that the term was originally use to describe a motion without regard to its origin. (Or is the boating use a stability issue too?) But now that it exists as a stability issue in aviation, it seems prudent to use it only in that sense. I can't tell you how many hours of confusion it has caused me in the past when the author of an aerodynamics text used a word carelessly and sent me along dead-end trails. Possibly an analogy is the description of the 4 left-turning tendencies of an airplane. Collectively they're often called "torque", but only one is caused by the torque of the engine, and is also called torque. So is calling p-factor "torque" incorrect? Not, I suppose in the sense that it creates torque around the vertical axis, and the engine torque creates torque around the longitudinal axis. But this generated ambiguity in the word "torque" makes it a bit confusing to talk about the subject. Back to top Julian Scarfe Guest Posted: Mon May 03, 2004 8:06 pm    Post subject: Re: Dutch Roll "Todd Pattist" <tpattist (AT) DONTSPAMME (DOT) snet.net> wrote Quote: Language has a tendency to go its own way and get labeled as correct or incorrect after the fact I spent a while writing the physics bit of the New Penguin Dictionary of Science. The hardest part was knowing whether to be prescriptive (tell them what the usage *should* be) or descriptive (describe what the common usage *is*). It's a judgement call in almost every case -- for example, I had no qualms about defining "weight" quite carefully to distinguish it from "mass", even though many people say "weight" when they mean "mass". But should I really make a fuss about the difference between "spectrograph" and "spectrometer" when everyone uses the terms interchangeably? I guess "Dutch Roll" is pretty close to the line. Julian Back to top Todd Pattist Guest Posted: Mon May 03, 2004 8:53 pm    Post subject: Re: Dutch Roll "Julian Scarfe" <julian (AT) avbrief (DOT) com> wrote: Quote: I guess "Dutch Roll" is pretty close to the line. I encountered the term first in sailing. Then I ran into the term used for the aviation coordination exercise and I have to admit that it seemed odd as the motions weren't really all that similar. Then I ran into the technical aerodynamic usage, which describes a motion more similar to the nautical motion. I suppose if I'd encountered the technical aviation usage first, I might have felt the coordination usage was "wrong," but I've never looked at it like that. I've always seen it as the same adopted name for two distinct things. Todd Pattist (Remove DONTSPAMME from address to email reply.) ___ Make a commitment to learn something from every flight. Share what you learn. Back to top Cub Driver Guest Posted: Mon May 03, 2004 9:04 pm    Post subject: Re: Dutch Roll Quote: It's also properly used for the motion of a ship with a following sea. Actually, a ship with a following sea pitches up and down, and in the worst case is pooped. A ship with a sea off the stern wallows, but is still pitching. It's a corkscrew motion, say rolling to port while diving down, then rolling to starboard while climbing up. Very sick-making. I never though of either motion as a Dutch roll, and it is not really similar to Dutch roll in an aircraft. all the best -- Dan Ford email: [email]warbird (AT) mailblocks (DOT) com[/email] (put Cubdriver in subject line) The Warbird's Forum www.warbirdforum.com The Piper Cub Forum www.pipercubforum.com Viva Bush! blog www.vivabush.org Back to top Allen Guest Posted: Mon May 03, 2004 9:26 pm    Post subject: Re: Dutch Roll "Cub Driver" <warbird (AT) mailblocks (DOT) com> wrote Quote: It's also properly used for the motion of a ship with a following sea. Actually, a ship with a following sea pitches up and down, and in the worst case is pooped. A ship with a sea off the stern wallows, but is still pitching. It's a corkscrew motion, say rolling to port while diving down, then rolling to starboard while climbing up. Very sick-making. Whoa there Dan, you're beginning to sound a little like Douglas Eagleson! Allen Back to top Bob Moore Guest Posted: Mon May 03, 2004 9:38 pm    Post subject: Re: Dutch Roll Todd Pattist wrote Quote: The term is correctly used for both the intentional flight maneuver that you think he's thinking of (alternating motion on the roll axis without corresponding yaw) and the dynamic instability problem you describe below. Neither of my three Flight Instruction manuals, Jeppesen, FAA, and Kershner make any mention of a "Dutch Roll" co-ordination maneuver. From http://www.mountainflying.com/adverse2.htm Adverse Yaw - 2 TRAINING MANEUVER (This is sometimes improperly called a "Dutch roll") A training maneuver, called the training roll or coordination roll, is often introduced early during primary flight training to teach the pilot to cope with adverse yaw. It is mostly forgotten after the private certificate is obtained. Many instructors consider the training roll maneuver to be of greater importance in teaching some one to fly than chandelles, lazy eights, or other commercial pilot maneuvers. A pilot getting into a different airplane can determine the amount of rudder that is required for proper coordination with the ailerons by using this maneuver. ------------------------------------------------------------------- From William Kershner's "The Flight Instructor's Manual" And, for Pete's sake, don't call this maneuver a "Dutch roll." Dutch roll, a stability and control term, is a condition of a coupling of lateral-directional oscillations with the nose yawing as the airplane rolls from bank to bank; the object here is to keep the nose on the point." -------------------------------------------------------------------- Bob Moore Back to top Cub Driver Guest Posted: Tue May 04, 2004 9:49 am    Post subject: Re: Dutch Roll I just asked my daughter the blue-water sailor about this. She never heard of Dutch roll, but thought it perhaps came from the motion of a round-bottomed boat popular when the Dutch ruled the ocean waves (think Henry Hudson). She confirmed that a boat can oscillate off a set heading in certain combinations of wind and wave. Sometimes, she said, it might be impossible to steer 210 without moving the wheel constantly. But if you change to 212, you can hold the course just fine. She called the motion fishtailing :) On Mon, 03 May 2004 17:04:16 -0400, Cub Driver <warbird (AT) mailblocks (DOT) com> wrote: Quote: It's also properly used for the motion of a ship with a following sea. Actually, a ship with a following sea pitches up and down, and in the worst case is pooped. A ship with a sea off the stern wallows, but is still pitching. It's a corkscrew motion, say rolling to port while diving down, then rolling to starboard while climbing up. Very sick-making. I never though of either motion as a Dutch roll, and it is not really similar to Dutch roll in an aircraft. all the best -- Dan Ford email: [email]warbird (AT) mailblocks (DOT) com[/email] (put Cubdriver in subject line) The Warbird's Forum www.warbirdforum.com The Piper Cub Forum www.pipercubforum.com Viva Bush! blog www.vivabush.org all the best -- Dan Ford email: [email]warbird (AT) mailblocks (DOT) com[/email] (put Cubdriver in subject line) The Warbird's Forum www.warbirdforum.com The Piper Cub Forum www.pipercubforum.com Viva Bush! blog www.vivabush.org Back to top Todd Pattist Guest Posted: Tue May 04, 2004 12:51 pm    Post subject: Re: Dutch Roll Cub Driver <warbird (AT) mailblocks (DOT) com> wrote: Quote: I just asked my daughter the blue-water sailor about this. She never heard of Dutch roll, but thought it perhaps came from the motion of a round-bottomed boat popular when the Dutch ruled the ocean waves (think Henry Hudson). Yes, that's the origin. The Dutch had a need for large cargo and shallow draft, so Dutch-built ships tended to perform a pronounced pitch-yaw-roll motion in following seas. It's the origin of the "Dutch Roll" label used in aerodynamics. Todd Pattist (Remove DONTSPAMME from address to email reply.) ___ Make a commitment to learn something from every flight. Share what you learn. Back to top Gene Nygaard Guest Posted: Tue May 04, 2004 1:11 pm    Post subject: Re: Dutch Roll "Julian Scarfe" <julian (AT) avbrief (DOT) com> wrote Quote: "Todd Pattist" <tpattist (AT) DONTSPAMME (DOT) snet.net> wrote in message news:av0d90duvp0f1gnqt21q3ieeaskh3stmhf (AT) 4ax (DOT) com... Language has a tendency to go its own way and get labeled as correct or incorrect after the fact :-) I spent a while writing the physics bit of the New Penguin Dictionary of Science. The hardest part was knowing whether to be prescriptive (tell them what the usage *should* be) or descriptive (describe what the common usage *is*). It's a judgement call in almost every case -- for example, I had no qualms about defining "weight" quite carefully to distinguish it from "mass", even though many people say "weight" when they mean "mass". You are confused if you think you made a correct "should be" call on this. When we say our bag of sugar has, as it might be labeled in the U.S., a "net weight" of 10 lb (4.54 kg), where the pound is of course a unit of mass officially defined as 4.5359237 kg, that is absoloutely correct and proper, well justified in linguistics, in history, and in the law. That's the original meaning of the word "weight," which entered the English language meaning the quantity measured with a balance, used to measure goods sold by weight in commerce. We measures mass, as that term is used in physics jargon today, with a balance--not the force due to gravity. Of course, they couldn't have called this "weight" by today's physics term, because "mass" didn't have that meaning until half a millennium or thereabouts after "weight" had this meaning. In other words, it isn't a case of us saying the wrong thing. We mean to say "weight"; we mean "weight" in a quite legitimate and proper meaning of the word; it just happens to be the same quantity that physicists happen to call "mass" in their jargon--but we don't normally "mean" something different from what we "say." You can argue that we should give up this word, to which we have a prior claim by about 800 years, if you want to. But if you are too stupid to realize that these are indeed *different meanings* in the first place, then you will never expend the effort that would be needed to accomplish this change. Furthermore, if you hope to accomplish this change, you had darned sure better offer us a verb as well as a noun, something we can utter in public without embarrassing ourselves. Currently, there is a difference between the use of the noun "weight" with different meanings each used fairly consistently in different contexts, and the verb "to weight" which is correctly used in any context to mean "to determine the mass of" or "to have a mass of" as well as the "to exert a force due to gravity of." That verb and noun distinction is expressed fairly clearly in The National Standard of Canada, CAN/CSA-Z234.1-89 Canadian Metric Practice Guide, January 1989: 5.7.3 Considerable confusion exists in the use of the term "weight." In commercial and everyday use, the term "weight" nearly always means mass. In science and technology, "weight" has primarily meant a force due to gravity. In scientific and technical work, the term "weight" should be replaced by the term "mass" or "force," depending on the application. 5.7.4 The use of the verb "to weigh" meaning "to determine the mass of," e.g., "I weighed this object and determined its mass to be 5 kg," is correct. <end quote> More on the noun usage: NPL FAQ http://www.npl.co.uk/force/faqs/forcemassdiffs.html Weight In the trading of goods, weight is taken to mean the same as mass, and is measured in kilograms. Scientifically however, it is normal to state that the weight of a body is the gravitational force acting on it and hence it should be measured in newtons, and this force depends on the local acceleration due to gravity. To add to the confusion, a weight (or weightpiece) is a calibrated mass normally made from a dense metal, and weighing is generally defined as a process for determining the mass of an object. So, unfortunately, weight has three meanings and care should always be taken to appreciate which one is meant in a particular context. <end quote> NIST Guide for the Use of the International System of Units (SI) http://physics.nist.gov/Pubs/SP811/ Thus the SI unit of the quantity weight used in this sense is the kilogram (kg) and the verb "to weigh" means "to determine the mass of" or "to have a mass of". Examples: the child's weight is 23 kg the briefcase weighs 6 kg Net wt. 227 g Gene Nygaard Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         AirTalk.org Forum Index -> Aviators (General Discussions) All times are GMT Goto page 1, 2, 3  Next Page 1 of 3   Jump to: Select a forum Aviation----------------alt.aviationAviation safety EnhancementPlanes, gliders and flying in AustraliaAviation et pilotage (Français)rec.aviationAviation (Aerobatics)Hot air, gas balloons and airshipsHang-gliding, paragliding, foot-launched flightAircraft Design & BuildingInstrument Flight RulesAviation (Classifieds)Military AircraftNaval AviationAviation (Miscellaneous Topics)Owning AirplanesAviators (General Discussions)Aviation related productsAircraft RestorationHelicopters and rotary wing aircraftsFlight SimulationSailplanesAviation (Students)Light aircraftFlying related activities in the UK Airports----------------alt.airportsEdinburgh Airport Glasgow Airport Humberside Airport Luton Airport Aberdeen Airport Glasgow Prestwick Airport  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.