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Guest Ron Freimuth

Flight model adjustments: Hz, slipstream, props.

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(sent to tell_fs@microsoft.com)1) The frequency of the FM seems too low;it is very noticeable when performing highly dynamic maneuvers (acrobatics and such) and it could be the cause of strange behaviours (instabilities, a/c's climbing with no thrust);2) The effect of prop slipstream on tail surfaces and possibly wings seems to be not modeled;it could make a lot more realistic:ground handling and take off roll of taildraggers;low-speed acrobatic maneuvers of unlimited acrobatics a/c's (like Extra300, Su31, etc.);One Engine Inoperative operations in twins;3) The modeling of props and rotors is very poor;very very noticeable (and unrealistic) during copters autorotations and after an engine quits. Props and rotors do no react correctly to airstream, especially after they come to an halt in mid-air.Thank you,Marco

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>(sent to tell_fs@microsoft.com)>>1) The frequency of the FM seems too low;>>it is very noticeable when performing highly dynamic maneuvers>(acrobatics and such) and it could be the cause of strange>behaviours (instabilities, a/c's climbing with no thrust);>>2) The effect of prop slipstream on tail surfaces and possibly>wings seems to be not modeled;>>it could make a lot more realistic:>ground handling and take off roll of taildraggers;>low-speed acrobatic maneuvers of unlimited acrobatics a/c's>(like Extra300, Su31, etc.);>One Engine Inoperative operations in twins;>>3) The modeling of props and rotors is very poor;>>very very noticeable (and unrealistic) during copters>autorotations and after an engine quits. Props and rotors do>no react correctly to airstream, especially after they come to>an halt in mid-air.>>Thank you,>>Marco>You share the same opinion as me and perhaps many other simmers!Someone will correct me if I heard wrong, but I thought that there were rumors that all the dynamics of the aircraft, wind, spins plus other significant items were all going to be addressed in FSX. If this really is the case, we are in for a real treat! :9 Regards,Mark.

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It would be nice to have a flight dynamics SDK, with a choice of models such as JSBSim, YASim or LaRCsim that FlightGear offers.This will allow the FS team to concentrate on what it does best - recreating the immersive experience of flying - and leave the task of flight dynamics to others just like any other add on.--M

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>1) The frequency of the FM seems too low;>>it is very noticeable when performing highly dynamic maneuvers>(acrobatics and such) and it could be the cause of strange>behaviours (instabilities, a/c's climbing with no thrust);>Behavior: A/c climbing with no thrust and instabilities.possible cause: Wrong Moment of Inertia of the aircraft Axys (Pitch, Roll and yaw) and/or wrong values under .air files (dihedral, pitch damping, etc...)USUALLY, the flight dynamic engineer in MSFS world use a Roskan formula for calculation of the moment of inertia in the axys, with engine position (tail, underwing, trijet (such as 727), Trijet with underwing mounted and fin engines and etc...), empty operational weight, and a lot of work, test flys, etc...BUT, there is something that always make me crazy. When I simulate a engine lost after V1 (twin jet aircrafts), the plane has a behavior to roll over the vertical axys, due assimetrical thrust due engine lost (as you noticed in case 2).maybe a good .air documentation can fix those "bugs" in the FSX?>2) The effect of prop slipstream on tail surfaces and possibly>wings seems to be not modeled;>>it could make a lot more realistic:>ground handling and take off roll of taildraggers;>low-speed acrobatic maneuvers of unlimited acrobatics a/c's>(like Extra300, Su31, etc.);>One Engine Inoperative operations in twins;>can be the same problem of wrong parameters in .air file. not sure, but the solution can be the same that I gave in case 1.but the leak information that we (flight dynamics engineers for msfs) have, some papers from the microsoft don

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"...like this from AIAA made at 2003, and only in 2005 the developers had knowledge of the existence of this document."Zyskowski's paper was read at the AIAA conference in 2003 and published in the conference proceedings in the same year. Hardly a secret document!

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I hear that Matthias Lieberecht (www.baepanelproject.com) has had some serious issues modelling turboprops and constant speed propellors owing to the FS engine. I'll post more info as I get it or you can read up on his forums about it (see the JS31/41 panel articles).

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>"...like this from AIAA made at 2003, and only in 2005 the>developers had knowledge of the existence of this document.">>Zyskowski's paper was read at the AIAA conference in 2003 and >published in the conference proceedings in the same year.>Hardly a secret document!and for some unknow reasons, just went in the "public knowledge" in fall 2005...and there is a lot of points in the paper of Zyskowski that don

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To be more specific, Matthias was trying to model a single shaft turboprop of the Jetstream 31, and having problems with the propeller pitch. The panel is quite a sophisiticated piece of kit, hence dummy engines and what not in the quote below."As soon as I increase the RPM lever of the dummy engines (3 and 4) to 97% N1 (RPM position flight), the propeller pitch of those engines increases too and forces the aircraft to move no matter which position the power lever has. I've programmed a separate gauge which forces the pitch to stay zero, but the Flight Simulator completely ignores this. It was not possible to seperate the pitch from the throttle and to bypass the FS gov control. Seems to be a lot preventing a single shaft TP engine [being modelled accurately]"

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>>"...like this from AIAA made at 2003, and only in 2005 the>>developers had knowledge of the existence of this document.">>>>Zyskowski's paper was read at the AIAA conference in 2003 and>>published in the conference proceedings in the same year.>>Hardly a secret document!>and for some unknow reasons, just went in the "public>knowledge" in fall 2005... Essentially a secret as far as FS FM developers go. I have the AIAA paper on JSBSim, it was announced in their emailer. But, without general access to the AIAA 'Flight Simulation' papers, non of 'us' knew about the MS paper until a few months ago.>and there is a lot of points in the paper of Zyskowski that>don

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