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Guest Ron Freimuth

To Microsoft : Please Give Us A Realistic Rudder!

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This is basically a one item wish-list for FS2004 which I thought I would post online so other people can comment. It is regarding the way the rudder functions in MSFS.My first flight simulator was FS2000, which I bought about 2 years ago. At the time, I had never had the opportunity to fly at the controls of a real aircraft. Even so, based on my limited understanding of aerodynamics, I had an expectation that the rudder could be used for limited directional control. After using FS2000 for awhile though, I found out that this was not the case. As anyone who has every used the simulator has I'm sure observed, applying rudder does indeed swing the nose of the aircraft right or left (yaw), but as soon as you release control pressure, the nose "snaps-back" almost to it's original heading. Based on this, I "learnt" that the only effective way to make heading changes was banking the aircraft with the ailerons. So, for example, on an approach, I was constantly banking one way, then the other, trying to get the aircraft lined up with the runway. The only reason for using the rudder, I concluded, was for making coordinated turns. Then, about a year ago, I had the wonderful privilege of taking about 12 hours of flight instruction in a Cessna 150. DID I EVER HAVE A LOT OF UN-LEARNING TO DO!!! I can clearly remember my first couple of approaches. "Knowing" that the rudder was completely useless, I began banking anxiously first one way, then the other, trying to line up with the runway. It only took a short while before the instructor started yelling at me, "Would you knock it off with the ailerons! Use the rudder!" "What good is that going to do!", I'm thinking, but I dutifully obey, and much to my amazement, the nose of the aircraft smoothly swings over, I release rudder pressure, and there's NO SNAP-BACK!!! I was absolutely amazed!!. After that, I had no trouble at all lining up for approaches. As my time and experience increased, I found that the rudder on a C150 is in fact a very accurate and easy way to make minor course corrections. The ailerons, on the other hand, are for major heading changes (10 degrees or more). It makes perfect sense when you think about it from an aerodynamics point of view. Say, for example, that you apply right rudder. This will cause the nose of the aircraft to yaw to the right, which will expose the entire left side of the aircraft to the oncoming airstream. The whole aircraft has now become a rudder, deflecting air off to the left, which by Newtons laws of motion will cause an equal and opposite reaction in the other direction, pushing the aircraft to the right, thus changing it's heading. The whole "snap-back" effect just doesn't make any sense.To put it another way, in straight and level flight, the sides of the airplane are at zero angle-of-attack (AOA), but when you yaw the plane to the right, you now have a positive AOA, and the whole airplane has become an vertical airfoil generating lift towards the right. How can that NOT change your course heading?So, Microsoft, for FS2004, please do some work on the rudder, and make this program one step closer to "As Real As It Gets!"Russel Dirks

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I agree. The rudders in FS2K2 and previous versions is the worse I've experienced in a sim and I'm a RL pilot. I normally fly airliners in FS and the rudders react like some spastic, A-type personality pumped up on caffiene, crack and steriods....and thats with huge null zones, 10-20% sensitivity, curved axes' in my Cougar eqm't and deadening statments in the software. FS wants to be linear and thats, that. I hope MS makes a rudder revamp a high priority in the next release. Actually I wish MS would dump the table physics all together and adopt the dynamic physics most top Combat sims use, i.e. IL-2, Falcon 4, Flanker etc..."FS Combat Sim is not one of them." I'd also like to see MS imploy a "save axis contol settings to the aircraft" rather than "one setting fits all". FS, as real as it gets? Well it's as real as it gets for MS-FS anyway. Time for them to move up a notch.

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There are some areas in the .air file of interest, that can reduce the "snap" effect. Sadly, they are not well documented. But one can play with them (under Aired, they are found in the Primary Aerodynamics section, and they are the entries related to yaw). I've been able to tweak some flight models to the point where a "normal" amount of rudder is required to keep them on the centerline in a crosswind takeoff and landing.Still, try as I might, I've never been able to get the rudder to react as well as the real thing. I had a little stick time in a 140 and a 172, and I well remember being coaxed to use the rudder for minor course corrections. Tonight I'll play with the 172 a bit.... Much of my FDE work is in the ultralight arena. It's been some months since I played around with this, and then it was because a specific U/L would be all over the place taking off in a 2mph crosswind....-John

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Interesting in theory but I believe you are way off the mark here. If you had an instructor that told you to use the rudder to line yourself up for approach then I would seriously consider finding another instructor. What makes an airplane turn is the horizontal component of lift....banking the airplane. The rudder is used for two things only....countering adverse yaw when applying aileron or keeping the nose on a specific heading when making cross controlled approaches or slips. Trying to use the rudder only to align yourself with the runway only results in a skidding approach. Yes, the plane will eventually skid around to the new course but it is very inefficient and takes longer than a coordinated turn. The proper method is to use coordinated rudder and aileron. If you are overshooting back and forth then you are using too much aileron. Another concern is that when in the pattern you should keep that ball centered...unless you are slipping in a crosswind. A coordinated stall on approach is almost a nonevent, except for the mess that might result in your breaches! :-) However, an uncoordinated stall could very well result in a spin. At pattern altitudes, you are not likely to survive. I lost three good friends last month to this very thing. The one flying had been a pilot since 1952 and was one of the most experience pilots I knew. The other two with him were also extremely experienced. I'm not an instructor, and certainly no expert, but I am an instrument rated pilot presently working on my commercial ticket.A really good book that you might want to read is "Stick and Rudder" by Wolfgang Langewitz (I think I got his name correct, not real sure).Happy flying!David

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>I agree. The rudders in FS2K2 and previous versions is the >worse I've experienced in a sim and I'm a RL pilot. I'll add a bit of comment here. One area where the rudder control in FS2002 "shines" is during the takeoff roll and climb. With a set of rudder pedals, the feel of pushing to the right & against a "force" is quite good. It stays this way through the climb. Most other sims with exception to IL-2 seem to get wishy washy when on the roll. You might be applying right rudder pedal, then all of the sudden the plane drifts off to the right as if there is no force trying to pull it to the left. And then there is even simulations that require no rudder when on the roll with single engine aircraft.In my experience with MSFS products, FS2K pulled too much right when applying power. FS2002 smoothed this out. The re-worked default Cessna 182 by RealAir Simulations has a real close rudder effect during roll and climb. In fact, it's one of the best I've run into during the last year and a half of FS2002.L.Adamson

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I was taught myself to use rudder for a couple degrees of heading change if needed, instead of applying a bank. Schools of different thought here.Another time that I found rudder useful was during the "dog fight" training I had with "AirCombat USA" in their Marchetti 260's. We'd get the opponent within the general area of the crosshairs, and then apply small amounts of rudder/yaw to get the other aircraft centered in the crosshair. Rudder is also the effective way to lead the opponent with your gunsight if needed.L.Adamson

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Another time that I found rudder useful was during the "dog fight" training I had with "AirCombat USA" in their Marchetti 260's.Agreed about the rudders! Almost useless.. Coincidently, the Marchetti 260 from RealAir Simulations is about the only add-on plane that does a pretty good job of canceling out the "snap back".

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In talking "snap back" here, a couple of items come into play. For instance, what's the amount of dihedral of the specific aircraft's wings; and the effect of this dihedral putting the plane into a slight bank when using rudder only? And then............... what is the effect of this banking, or righting itself when rudder is released?It is a fact that diheadral effects the flight dynamics of rudder use. As an example, early radio control aircraft had just one channel & it was usually used for rudder. The aircraft had lot's of dihedral built into the wings to initiate a bank and turn from rudder only. Many aerobatic planes will have NO dihedral so that rudder doesn't start a rolling effect. I've also flown an ultra-light that required leading with the rudder because the ailerons had more of a banking effect than actual turning.A few months ago, I purposely banked harder than normal with ailerons in both directions on a 172SP to compare effects to flight simulation. But un-fortunately, I didn't experiment with the rudder. What I'd like to ask,..... is who has been up recently and with what aircraft to make direct comparisons to real and the sim. Also, I feel it's important to use rudder pedals in the sim. I find little realism in using keyboards, twist grips, or rocker switches. The pedals seem to create a "feel" to opposing forces that I don't get with other devices.Notice, I'm not saying one way or the other on the exact reaction, because I need to experiment first..L.Adamson

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A 172SP in real life will "snap back" if you fully release rudder pressure from when you apply max pressure on the rudder (eg in a forward slip). The student should be taught to slowly release the rudder pressure (I'm sure this is what you were doing in the 150 so as to not make it snap back).As far as using rudder to maintain a localizer, you should only use the rudder to make small corrections in heading (if you want to use the rudder to turn the airplane). This would seem to make sense on an approach however the "book" technique would be to use the ailerons and small heading changes. Please note that all the rudders do is cause the airplane to roll slightly which causes the turn (NOT the rudder turning it).As with many things in flying, "technique" is usually whatever works best.

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I flew the Lago Quicksilver tonight (part of their UL collection). I had no problem using the rudder for small course corrections, experiencing a little snap back only when there was a significant bank. The Lago Quicksilver also has dihedral effect modeled quite well. As noted in the other reply, gradual release of the rudder in this example allowed me to maintain the heading the aircraft took after rudder was applied. I think much has to do with the flight model, especially in the .air file entries I mentioned in my post above... Flying the default 172 is a completely different experience...definite snap after rudder was released, even if released gradually. In my FDE work, one parameter that made a huge difference in the .air file was the "Yaw moment-Sideslip" entry in the Primary Aerodynamics record. A very high number can really aggravate the snap effect. The 172's default entry is 270, and lowering it to 30 makes a big difference/improvement.... Lago's entry is 13 for the Quicksilver.... Also, the aircraft is much easier to slip and/or ground taxi in crosswinds when this entry is lower.-John

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Just bumping this thread to see if anyone's tried the Aired .air file edits I suggested.....

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Great topic about one of the most difficult and important areas of flight simulation. As a real life pilot, I would like very much to see more realism in the simulation of roll/yaw couplings. I agree with FlyingRhino on several points. The important one is to stay coordinated on approach. Being low and slow and overbanking to minimize the overshoot while turning base to final is a frequent source of accidents, deadly ones. Statistics show the same thing tends to happen a lot during IFR circling approaches.In fact, the nature of roll and yaw and their interactivity is complex because many different forces with opposing non-linear effects interact (a physicist's delight!). A good detailed discussion including wingsweep effects is given in the excellent book:"The Illustrated Guide to Aerodynamics" H.C. Smith, Mc Graw Hill, 1992Jump to pages 172 and following if in a hurry. This reading is a must for anyone interested in aerodynamics and aircraft design. It is easier to read than of Raymer's monumental book.Anyway, if banking and letting the yoke go back to neutral, the airplane will keep banking because, at least in first approximation, there is no restoring moment. With rudder applied continuously, the yaw will increase resulting in spiral divergence (dangerous). If rudder is applied and then abruptly released, induced roll ensues, but it is out of phase with the yaw, producing a damped oscillatory motion called dutch roll. I remember this to be real bad when flying the Cessna 310 which has tip tanks and a rather small vertical stabilizer.The thing to remember on the subject is that several distinct effects cause coupling between roll and yaw forces and it is impossible to isolate one from the other, whether in the real airplane or in the simulator.With Fs2k2, I never had that feeling of "real" when applying control inputs with rudder and/or ailerons on final with a crosswind. I must admit that Fly!II gave the closest feel with some of their aircrafts.Here is a challenge for a brave and patient sim pilot: optimize the airfile under "primary flight dynamics". There are so many roll/yaw parameters to vary that it may well be possible to get closer...Or, since we do not have the equations of motion and the models from MS, use a statistical or Monte Carlo method with the airfile parameters?Charles

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OMG.. i just finished a flight,,, i was gonna post tha same thing....i agree once you let go of the rudder it jsut returns back to the normal position making it more diff to line up with the runway....Hope in FS2004 there is more realisctic Rudder...and other stuff...Javier CamposAvA-LaX/AAL251OAK ARTCC/VATSIM

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>With Fs2k2, I never had that feeling of "real" when applying >control inputs with rudder and/or ailerons on final with a >crosswind. I must admit that Fly!II gave the closest feel >with some of their aircrafts. >But.................. Have you tried Rob Young's Marchetti SF260 for FS2002? While his flight dynamics were king for the FLY series, I believe he's outdid them with the Marchetti. The effect of rudder, ailerons, and especially slips are simply wonderful!!I was trying out a few flight comparisons in FLYII last evening because of this initial post/replies, and realized just how far flight dynamics have come with the SF260. I personally think they're much better than say the FLYII Flyhawk's..L.Adamson

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When the wings are level, the aircraft will not change heading immediately when yawed, but eventually it will. Because 1: along the fuselage the aircraft has the least air resistant, it means that the sideward motion-component will disappear first. 2: The only independent force comes from the motor (assuming level flight), which is pointing about the same direction as the fuselage. The fuselage is changing direction immediately when rudder is applied, and the heading is then altered gradually when the air resistant is

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One response and a General CommentChickenHawk said "... Please note that all the rudders do is cause the airplane to roll slightly which causes the turn (NOT the rudder turning it)."Well, I agree that the rudder will induce roll, which will cause the airplane to turn. But would it turn if you applied rudder but kept the wings level with opposite ailerons? I think it would. (Can't verify it though, as I'm not currently a real pilot. And please note, I'm not suggesting this is the proper way to turn!)My reasons are:1. As I mentioned in my first post, forcing the airplane into a yaw exposes one side of the fuselage to the oncoming slipstream. A C172 has a lot of flat surface on its side, probably about half as much as the wing, so surely this is going to cause side pressure.2. With the airplane in the yaw'ed position, the thrust from the propeller is no longer aligned with your direction of flight, but pointing slightly in the direction of your yaw. The lateral component of the thrust will pull you around in a turn.General CommentHere's an interesting thing to try: Do a low pass directly over the edge of a runway. As you cross the threshold, try various techniques to get over to the other side of the runway, and see how long it takes you. After you've done the pass, pause and do an instant replay, from top-down view. Note how long it takes for ANY lateral movement to begin (D1), and the total distance required to cross the runway (D2). Here are my results, crossing a 75ft wide runway flying a C172.Method  D1  D2Light rudder pressure (minimal roll)  1000ft  3000ftMedium rudder (induces roll)  800ft 1800ftHeavy rudder pressure, but keep wings level 1800ft  4000ftDo you think this is realistic? I don't. In general I think lateral movement should begin almost immediately, and based on my limited time in a real plane, I would guess you should be able to cross over to the other side of the runway in a couple hundred feet, although the third method might take a bit longer(?). Anybody care to go try this in a real plane? (Mind you don't try anything if it's dangerous, especially that third one)Russ

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I agree wih Charles brief sumation. >>I remember this to be real bad when flying the Cessna 310 which has tip tanks and a rather small vertical stabilizer.<< Yikes, unrelated, but I watched in horror, a lineman top off a Lear 35, RIGHT TANK FIRST! Damn near killed himself when the a/c began to lean (left strut nearly fully relaxed)....AGAINST the Fuel truck!He missed the hint something was wrong when he failed to notice himself stepping down one rung at a time on the step ladder as he happily pumped jet fuel into the tip tank. HAHA! "The trick to flying is cordinated rudder/aileron". I.e. Standard bank, rudder + aileron, establish the bank, neutralize the rudder, is basicly the way it goes. Use the slip indicator, aka Needle and ball to oppose any slipping. I also use the rudder quite often to make adjustments during IFR approaches. Also, contrary to popular belief, you can quite literally fly a race track pattern using only the rudders. I wouldn't recommend it to new pilots as it requires frequent trim and throttle adjustments, but it proves the theory that, "Yes, The rudders can and do something." During my instructor years, aside from students having difficulty landing/taking off, the other problem I had was convincing them to use the rudders. :-) Light aircraft tend to hide the need for them and so many fly off over the horizon never really using them (except for taxing around the airport or worse, understanding their "true" purpose.

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> Also, contrary to popular belief, you can >quite literally fly a race track pattern using only the >rudders. I wouldn't recommend it to new pilots as it >requires frequent trim and throttle adjustments, but it >proves the theory that, "Yes, The rudders can and do >something." Then the Dreamfleet ArcherII passed! :) I kept it in a nice racetrack pattern with rudder, from tower view, thanks to many past years of R/C aircraft racing. It did tend to climb when applying opposite rudder for the "straight away", which had to be quickly adjusted with forward pressure & trim. As to how much a real aircraft would tend to climb.........................I can't say. I just havn't done any rudder only real life race track patterns. But I'll make a note to try it.L.Adamson

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Many GA aircraft will snap back from being yawed in many situations. Also your statement about aerodynamics is a bit off. When you first yaw the aircraft left or right the flight path of the aircraft does not necessarily change(you are merely changing the direction the nose is pointing). The side of the aircraft now exposed to the relative wind them may demonstrate some keel and even some vane tendencies and help the aircraft point into the relative wind again. This would be a form of positive static stability (about the vertical axis of the aircraft). The aircraft does not

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>The side of the aircraft now exposed to the relative wind >them may demonstrate some keel and even some vane tendencies >and help the aircraft point into the relative wind again. Not if you maintain rudder pressure, which is the situation I was talking about. >The aircraft does not

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I'm talking about sustained >rudder pressure. >The whole boat (side of the airplane, >get it?) has now become a rudder, held in that position by >the "little rudder" at the back. Due to the density of the >water, the boat will change direction. >>The same affect will happen with an airplane moving through >the air, except air is much thinner so the affect is much >less. >>Russ Big difference, though. A boat won't sink if you keep rudder pressure but an airplane will eventually spiral to its demise if you keep a lot of pressure applied because of the coupled roll resulting in an ever increasing spiraling skid. In fact it's a very similar situation to the loss of one engine on a twin where the line of thrust is suddenly offset laterally from the CG. Twin training is mostly about that: at high engine power setting if you loose one engine and delay any corrective action, the plane will quickly yaw towards the dead engine and at the same time roll over towards that same dead engine because of added lift on one wing. This usually result in deadly accidents because of the very quick and total loss of control. The remedy is a prompt application of a lot of rudder and some bank towards the good engine.In short, in real flying, do not attempt sustained firm rudder application. As I said above, roll and yaw are cross-coupled through more than one mechanism, which is why lateral stability is the result of a number of design trade-offs.Charles

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You are certainly correct that you can cause an aircraft to eventually turn if you use only rudder. The turn however will be a horribly uncoordinated skid and the same resultant aerodynamic effects I mentioned in my last post will still cause the nose of the aircraft to move back towards the relative wind if the rudder pressure is released. I tested this in a real 172N this morning by holding nearly full rudder for 30 seconds and releasing it (AKA a forward slip & by the way you need a fair amount of opposite aileron control to prevent loss of control of the aircraft). Your original post questioned why there is snap back effect and that the rudder in MSFS is not realistic. I find it to be fairly accurate for the GA aircraft I fly.Also your connection with a boat rudder and an aircraft rudder is not a 100% accurate. Yes a boat rudder works much like an aircraft rudder (Air & water are both fluids and the same dynamics apply). When you move the rudder on either craft you change the chord line of the vertical stabilizer on the aircraft or a portion of the keel/rudder in the case of the boat (boat keels and rudder designs are considerably more diverse than most aircraft so lets not go there right now). This change in chord line increases the angle of attack on one side or another of the keel stabilizer or keel/rudder. The resultant is that side begins to produce lift that moves the vertical stabilizer or the aft portion keel/rudder in that direction. The difference is that a boat is moving in effectively a two-dimensional plane and has a hull that is designed to take advantage of this force not resist it. We can also get into the different types of stability, buoyancy, etc which also separate how a boat differs from an aircraft.The basic point you have to recognize is that with most aircraft the inherent stability that is designed and built into each aircraft counters the same attempt to use rudder alone to turn the aircraft. Yes you apply a similar force using the rudder on a plane, but the aircrafts design & stability resists the turn. Sorry if my descriptions are bit off. It

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Well folks,I have been using MSFS since 1985. The improvements have been great over this period of time, no doubt.The key is Microsoft's philosphy about MSFS....Is it a Toy or a Simulator? Is it a Game or a Simulator?As soon as the line is drawn and more importantly understood by Microsoft, then "real development" can take place. Then they need to hire real "Flight Simulator" programmers and use the current game programmers to enhance the scenery, etc.Until then, for now, I believe Microsoft consideres MSFS just another game.FS 2004 wil be the real test.X-Plane is making a good run, but still lacks good ATC functionality and scenery. But my understanding is their flight dynamics are pretty close.Just my two cents worth...Barry

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> I tested >this in a real 172N this morning by holding nearly full >rudder for 30 seconds and releasing it (AKA a forward slip & >by the way you need a fair amount of opposite aileron >control to prevent loss of control of the aircraft). Your >original post questioned why there is snap back effect and >that the rudder in MSFS is not realistic. I find it to be >fairly accurate for the GA aircraft I fly. >I was hoping someone would do this.........thanks!I didn't yet get a chance too.L.Adamson

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