NOTAM : That ol' rudder problem (why and how)

[Guest Vangelis]

Gents,There have been reports of wierd behaviour of the aircraft when rudder is applied. The reports were valid under a specific set of circumstances. The problem has been identified and fixed for an upcoming (within a fee days) mini-update. Here follows a small technical "briefing" for this issue.In practice this anomalous behaviour required the following :(1a) Significant amount of rudder(1b) Aileron the other way (i.e cross-controls)(1c) Sustained application of cross controls for over 5 seconds (i.e.combination of (1)+(2))Behaviour :(2a) If attitude (pitch) was maintained above a very narrow FS defined limit zone the plane accelerated unreasonably.(2b) If attitude was below a certain (minute) threshold the plane decelerated rapidly.Reasons for non-identification of this issue :(3a) Application of quick corrections to maintain attitude (primarily pitch and secondarily bank) the plane behaved normal, and/or(3b) Quick release of cross-controls(3c) This behaviour becomes apparent through **sustained** application of a fundamentally wrong procedure to fly an airliner class jet (as opposed to a single engine prop trainer). Rudder is primarily used at about 50ft to align the aircrat heading with runway and that's that ! (Whoever disagrees earns a free ticket for row 23 in a empty plane for a trully unforgettable special flight -- barf bag(s) come also absolutely free)Reason of occurence :MSFS goes crazy and calculates a huge negative or positive drag ! Negative is correct (see attachment)Remarks :(4a) An essential characteristic of 737's i.e. rudder induced considerable and sharp rolling motion is moderated (MSFS cannot take all of it).(4b) Problem is fixed(4c) An easy platform to cut teeth on cross controls in an airliner class jet (never said that, see item (3c) above !).Many Regards,Vangelis Vaos===================================== Evangelos M. Vaos Precision Manuals Development Group www.precisionmanuals.com=====================================

[teropa 4]

Van,Just one comment regarding the sustained cross-control situation being wrong in a transport category aircraft.In a x-wind situation, when you start to kick the crab away, simultaneous application of opposite aileron is always needed to counter the rolling momentum initiated by the rudder. It is not uncommon to stay in that crossed-controls situation for 5 seconds or more. Even in the most perfect situation (with a firm, non-greaser landing) you would hold the controls crossed for 3-4 seconds, at minimum. Thus, I feel it is well within reason to address this issue, just as you have done :).Terops. forward slips are not forbidden in a 737NG. Not thought of as one of the "best" procedures to resolve a hot and high -situation, but commonly used anyway. That is when you definitely have the controls crossed for 5 seconds or more.

[Guest cordelia]

Excellent NewsThe best is gonna be better!Steve

[rsrandazzo 6,353]

Tero-You might be misundertanding the specific scenario: Vangelis is referring to FULL control deflection for sustained periods.... i.e. control inputs clearly beyond the normal operating range for the aircraft....Imagine what conditions would require full application of rudder in close proximity to the ground.... I can't think of any that would require that it be HELD at full deflection- but that is the region where Vangelis discovered we were sending data to the FS flight model that it could not interpret correctly.... and the result was as described...

[Guest MSMITH6]

Robert-I haven't noticed this issue personally, but after reading the threads, how is all this related to those having problems manually landing in a crosswind? I doubt they were using full rudder deflection. PMDG's post seems to imply that this is an issue ONLY with full rudder deflection and a cross control situation. So, I'm confused as to how that would fit with the manual crosswind landing issue.Think I'll try one to see how it goes on my system.Thanks,

[teropa 4]

Robert,A very good point. I misunderstood it.The only thing that comes into mind would be a sudden engine failure just before decrabbing the aicraft in a strong crosswind :). Not very likely though... hehehcheersTero

[Guest mikepettit]

As soon as I load the PMDG737 the rudder seems to be a problem. Before engine start if I apply rudder it will move in the correct direction and then immediately flip back to neutral. This is without any other control inputs.I can get a temporary fix by unplugging the rudder pedals (CH) and immediately plugging it back in. Great product apart from this rudder problem. Can't wait for the fix and just hoping it cures my problem.

[Guest Vangelis]

No Mike,This is probably not an NG problem. Not even an FS probrem. Probably the infamous WinXP "USB gets suddenly de-calibrated" problem. I have the same pedals. Usually no trouble. Most times mis-aligned to the left. Sometimes go absolutely nuts. By un-plugging and re-plugging in the USB you "wake" the port up. This probably is your (and used to be mine) user specific setup problem. The auto system is disconnected from the rudder on the ground.By the way try the CH control manager from the CH site. Worked wonders with both the yoke and the pedals (never used and no need to use FSUIPC for calibration after that).Regards,Vangelis===================================== Evangelos M. Vaos Precision Manuals Develpment Group www.precisionmanuals.com=====================================

[speedbird068 0]

Also check to be sure your hydraulic power is on. I get that when there is no hyraulic power on (I don't have CH Pedals).Murrell

[qnh 70]

Also check your USB ports in device manager - turn power management off!ScottYBTL

[Guest jcomm]

Vangelis,good to know you identified the problem! Now, just for the sake of curiosity, could you ekaborate a little more on how you plan to solve the problem? You say this has it's origin somewhere in MSFS's AIR file intrincacies... and the attached file produced using AFSD really shows the undefined values for the drag entries, but... how are you going to fix it? Will it be done by reducing rudder authority? Will it be somewhere in the max deflection of the rudder/aileron? Or... will you give a touch to the stability derivates?Any enlightnement really appreciated!!!!

[SQUAWKIDENT 3]

Looking forward to the "fix"I think I speak for many customers by hoping that it will be offered for download on more than one server this time to avoid the "SU2" fun we all had a few weeks back:-)RegardsAdam MoorePMDG Boeing 737NG Registered User

[Guest Vangelis]

JC,Haha -- trade secrets. Hardly. AFSD is correct. Herve has done a wonderful job. Yes everything is in section #1101 of air files -- nothing to do with aircraft.cfg files and all that. All I can say is that it was pretty simple in the end. Just cut down the yaw-induced roll (but not the speed of yawing motion). One of the last 4 parameters in this section is pretty critical. You will open the air file and you'll figure it out no doubt...By the way saw a hacked air file for this plane...Oh well !Anyhow, the real big surpise is that FS really screws up this one, no ? Could not believe negative drag. Sometimes I really miss Fly! in this department. Stability derivatives are **derived/post-calculated** quantities not primary design variables. Instead of stability derivatives and all that rubbish one could do proper aircraft design based on lift/drag/moment curves for wing elements. In the present case given that most air file parameters are "good" guesses as to what they do and the absence of any documentation, FDE people have a really nice wonderful time.Regards,Vangelis

[Guest jcomm]

Vangelis,thanks for the prompt and informative reply!!!I am sure the modifications will feel good and contribute to make this aircraft an even better product!!!

[Guest esperienza]

Hello everyone, I was just about to open a similar topic but reading your comments became a little reluctant.The way I experience the problem may be perhaps slightly different;on final approach to LOWI, below 50 feet I tried to get allined with the runway using rudder input but noticed massive adverse yaw which caused the aircraft to be out of control and due to low altitude I finally opted for the missed approach procedure.I'm no expert but the reaction I've experienced, I presume and forgive my ignorance in regard if I'm wrong that this is unrealistic behaviour.Are the above problems somehow related to the problem I've experienced?PS. Thanks to PMDG for considering a fix for the above in their next mini-patch, that's what I call customer service!!!Cheers,David