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Guest ESSA82

MD-11 oscillation during approach

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Hi!First, I'd like to compliment the whole PMDG team for a wonderful add-on.However, I have a little issue with this lady.When approaching the runway with AP OFF, the pitching moments seems to have a life of its own.I have specially noticed that during 100ft RA the aircraft seems schizophrenic, believing it's an AIRBUS and lowers its nose by itself. This has happened several occasions with our without Active Sky enabled.So is the aircraft actually programmed to behave like this or can it be a controller issue (Saitek Pro Yoke)?Overall I experience the LSAS to behave very irrational and slow to adjust, despite using small movements on the yoke. This has lead to (contrary to what any instructor would tell you) me using the stabilizer trim to correct any G/S deviation, and not the elevator.If you want I can put a youtube with the PFD when this happens.RegardsNick

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Hi!First, I'd like to compliment the whole PMDG team for a wonderful add-on.However, I have a little issue with this lady.When approaching the runway with AP OFF, the pitching moments seems to have a life of its own.I have specially noticed that during 100ft RA the aircraft seems schizophrenic, believing it's an AIRBUS and lowers its nose by itself. This has happened several occasions with our without Active Sky enabled.So is the aircraft actually programmed to behave like this or can it be a controller issue (Saitek Pro Yoke)?Overall I experience the LSAS to behave very irrational and slow to adjust, despite using small movements on the yoke. This has lead to (contrary to what any instructor would tell you) me using the stabilizer trim to correct any G/S deviation, and not the elevator.If you want I can put a youtube with the PFD when this happens.RegardsNick
Actually...The MD-11 is well known to have pitch instability, due to the smaller tail on this plane (designed smaller in order to reduce drag during cruise). Sounds to me like PMDG has simply done a marvelous job with the flight model! :(There have been several documented incidents - and indeed accidents - where the MD-11's pitch instability has been cited as a contributing factor.Check out http://www.airlinesafety.com/faq/faq9.htm. Interesting stuff.

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Overcontrolling is a common problem with handflying and LSAS. The proper technique is to nudge her into the attitude you want and she will stay there for the most part. I have only handflown a couple of dozen approaches so have not experienced a problem with her.

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Oddly enough, with the right technique, I've found this aircraft to be quite stable during handflown approaches. The above technique seems to work the best, small corrections to the correct pitch attitude, with power controlling descent and airspeed. On the other hand, the real world MD-11 is most definitely known (as the above poster stated), for pitch sensitivity during approaches, specifically in highwind/gusty situations.Perhaps adjust the LSAS sensitivity in the PMDG menu.`LS

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Thanks for your replies people.But the aircraft lowered its nose while I had some yoke pressure to raise the nose, and what I got was the opposite effect.Obviously I'm blaming my control setup since the aircraft becomes MUCH more stable with LSAS disconnected.Oh well, I will test and report back if I have found a solution :)Cheers!Nick

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Maybe you have some joystick noise that's causing a problem with the LSAS. I find that it's an absolute dream to handfly, but if you start to overcontrol, the ride gets very rough very quickly. Make the inputs as small as possible and it'll appear like she's running on rails.Paul

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PIO: Pilot Induced Oscillations :( Not to suggest it's your flying Nick ;), but just let the aircraft settle first and use smooth control inputs. That is weird though that with the LSAS disconnected it seems to fly better for ya.Anyways, hopefully you get it figured out!Patrick

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Flew a dozen of patterns over ESSA yesterday and I can confirm it flies more smoothly now.I did a total re-calibration in FSUIPC, and for some reason the MD11 has settled down significantly.Now I can gently nudge the yoke in order to keep the attitude desired, and she is solid all the way down. :)Cheers!Nick

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Actually...The MD-11 is well known to have pitch instability, due to the smaller tail on this plane (designed smaller in order to reduce drag during cruise). Sounds to me like PMDG has simply done a marvelous job with the flight model! :(There have been several documented incidents - and indeed accidents - where the MD-11's pitch instability has been cited as a contributing factor.Check out http://www.airlinesafety.com/faq/faq9.htm. Interesting stuff.
This article has received a ton of, IMO, undue attention. Boser's far too opinionated in his "report" and draws many overly simplistic conclusions. It's written in the tone of an ambulance chaser, and he (and the media currently) love to point to the md-11's stabilizers, calling them "smaller than other airliners". The md-11's stabilizers are smaller than the dc-10's due to the longer lever arm and trim tanks located therein. His entire "relaxed (static) stability" argument is also erroneous, and modern airliners such as the 777 utilize this system for much better fuel burn. RSS uses computers & trim to give the impression of a neutral CG at the control station. Mr. Boser seems unaware of this fact when stating that the md-11 should have been designed with a stable CG "as are Boeing airliners". Unfortunately Mr. Boser's report is the same kind of sensationalism and circumstantial reporting that killed the dc-10 program. He cites accidents where pilot error were listed as the root cause but points to the airframe as the "real" cause... Obviously this struck a nerve with me, and I'm blasting him, not you MELKOR :( but I've never forgotten all the front-page "deathtrap" news on the dc-10's, nor the page 8 follow-ups essentially clearing the airframe later on. IMO no matter how good an aircraft is it can't overcome certain abuses caused by pilots or circumstances....Dan

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This article has received a ton of, IMO, undue attention. Boser's far too opinionated in his "report" and draws many overly simplistic conclusions. It's written in the tone of an ambulance chaser, and he (and the media currently) love to point to the md-11's stabilizers, calling them "smaller than other airliners". The md-11's stabilizers are smaller than the dc-10's due to the longer lever arm and trim tanks located therein. His entire "relaxed (static) stability" argument is also erroneous, and modern airliners such as the 777 utilize this system for much better fuel burn. RSS uses computers & trim to give the impression of a neutral CG at the control station. Mr. Boser seems unaware of this fact when stating that the md-11 should have been designed with a stable CG "as are Boeing airliners". Unfortunately Mr. Boser's report is the same kind of sensationalism and circumstantial reporting that killed the dc-10 program. He cites accidents where pilot error were listed as the root cause but points to the airframe as the "real" cause... Obviously this struck a nerve with me, and I'm not blasting him, not you MELKOR :( but I've never forgotten all the front-page "deathtrap" news on the dc-10's, nor the page 8 follow-ups essentially clearing the airframe later on. IMO no matter how good an aircraft is it can't overcome certain abuses caused by pilots or circumstances....Dan
I completely agree.

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