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Murmur

Flying on rails?

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In another thread, tf51 posted this RL video of an A330 landing:

 

www.youtube.com/watch?v=3hn7Rmgmi_4

 

It made me notice something interesting: if you look at the video, you'll see that the flight is very (for lack of a better word) "slippery": there are continuous and smooth movements around the three axes, very noticeable. Now compare that to this video (of tf51 himself) with the 757 in X-Plane:

 

www.youtube.com/watch?v=mf0MFG60cP4&feature=player_detailpage#t=120s

 

And another video with X-Plane:

 

www.youtube.com/watch?v=5XUS6YJH5Ss&feature=player_detailpage#t=37s

 

To me, it seems that the continuous, slippery, smooth movements are very similar to the real life video.

Now watch these videos of PMDG 737 in FSX:

 

www.youtube.com/watch?v=rD4KQrrfATs

 

www.youtube.com/watch?v=E_P0CSjzuQw

 

www.youtube.com/watch?v=smaQkElAkls&feature=player_detailpage#t=105s

 

My impression is that in these cases, the flight dynamics seems much more stable than in the real life video. I think this is what people refer when saying FSX gives the impression of "flying on rails".

 

PLEASE NOTE: THIS IS NOT TO SAY THAT X-PLANE FLIGHT MODEL IS PERFECT OF FLAWLESS. As we know from the many discussions in this forum, it is full of imperfections and can be improved in a lot of things. For example, a lot of people find the X-Plane flight model too "twitchy". This is not what I'm contesting in this post. I'm just referring to, and trying to explain, the "flying on rails" issue that sometimes comes up when comparing FSX and X-Plane flight models. I'm not talking about the other issues X-Plane flight model may have.

 

Marco

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Interesting. I can only imagine how complicated it is to model a fluid dynamic like air in such a perfect manner to be able to get that in the sim. I guess until we have a large volume of air flowing out of our computer cases and over a real wing, stationary simulating with 0's and 1's will have to do. :lol:

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I think the term "flying on rails" is a bunch of baloney, but then I've said it many times before. As to the A330 landing, you'll notice that the weather isn't exactly a clear day. There is some obvious turbulence, though not dramatic. I have my own videos of my real life landings with hardly any yaw or roll, and just a smooth constant descent to the runway. So many of my real life GA flights have ranged from perfectly smooth, and nearly no sense of movement, to very harsh, turbulent, and uncomfortable. I've also lived across the street from the airport for 14 years, and watched many, many landings.

 

That's why "flying on rails" to me.....................is auto-pilot, and only auto-pilot. No FSX airplanes will remain on heading & altitude for long. They haven't done that since FS98. FSX just defaults to a smoother non-turbulent flight. It's actually what I prefer, unless it's real weather & I expect movement. Fake monitor "bounce" just doesn't thrill me much. It some times irratates me to the point of suspending the flight, and going to read a forum or something. In real life, we go out of our way to plan cross country flights , at least getting there...............to be earlier in the day when winds are calm. It's also usually calmer in the evenings & cooler months.

 

L.Adamson

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"Flying on rails" isn't a flight model problem, it's an atmosphere model problem.

 

Do the same flights with a bit of turbulence or wind gusting cranked in and see the difference.

 

Hook

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You can check out all my videos in a wide variety of conditions on youtube in mostly a Baron-just search geofa(ignore the iphone ones). There is very little motion-other than the cameraman-then pilots are paidthe big bucks to be smooth... :lol:

 

Also seems to be confusion over "Stable" and "turbulence".

 

Turbulence can and will bounce a plane around.

 

Stability is the plane with out pilot input trying to get back to the original trimmed condition.

 

e.g. if you are trimmed at 3000 ft. and a gust of turbulence picks your nose up and tosses you to the left slightly-you should return to the original trimmed condition (I think they specify something like 6 oscilations on pitch), original airspeed etc. if the plane has good stability, which most manufactured light GA aircraft do.

 

In the videos you will see the nose get disturbed-but it always comes back to the original trimmed place-sometimes with a little help of the pilot-very little.

The nose does not rock from one 30 degree bank to another , or climb 1000 fpm and then immediately start down 1000 fpm or even worse just go off in a steep bank or steep climb on its own.

 

So do the following test-trim the sim plane (if you can) for hands off flight and let go of the controls. In calm air it should remain there for quite a while and any momentary disturbance should self correct without pilot input. After a momentary disturbance does the sim plane try to come back to the original trimmed condition (positive stability)-does it remain on the new path (neutral) or worst-does everything continue to get worse.

 

Again, in turbulence you may have to help a little-but the trimmed condition is the "rock" the plane wants to come back to on its own.

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I'm not talking about stability or flight controls sensitivity. We know there are wide debates about those issues in the X-Plane flight model.

 

It's hard to explain... Here is another video from FSX, with high turbulence:

 

www.youtube.com/watch?v=MZ8-P0z41eI&feature=player_detailpage#t=210s

 

In this video there are ample movements of the aircraft, neverthless, my visual impression is that the... movements... the dynamic feeling, of the aircraft in the RL video look more similar to the X-Plane videos than the FSX videos. Again, hard to explain, maybe it's just me...

 

Again, this is not to say that X-Plane FM is more realistic, given the other issues widely discussed (controls sensibility, lack of damping etc.) the final result may very well be that it is less realistic. I'm just talking about this specific, particular aspect, that I notice when comparing RL and flight sim videos, and also when flying in X-P and FSX. As said, maybe it's just me and others don't see it.

 

Marco

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Dutch rolls in the air are very well done in xplane-perhaps that is what you are speaking of? Eg the dihedral of the wing ( and swept back in airliners) begins a series of Dutch rolls that gradually brings the aircraft back to its stable condition. I would agree xplane simulates this much better than FSX.

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Dutch rolls in the air are very well done in xplane-perhaps that is what you are speaking of? Eg the dihedral of the wing ( and swept back in airliners) begins a series of Dutch rolls that gradually brings the aircraft back to its stable condition. I would agree xplane simulates this much better than FSX.

 

And, if it's the dutch rolls..............then my little RV with it's shorter vertical tail would also do them, if started by turbulence. Since there are no back seats, it doesn't annoy passengers in the back, as that's where you'd feel it the most. However, it's short lived, and not the way of normal flight. What it comes down to, is the tail doesn't have to be jerking around, the fuselage doesn't have to be rolling and pitching to give an impression of operating in air. I'm very aware that some do believe that there is always these kind of movements, since the plane isn't sitting on solid ground. While in reality, flight may be smoother with less sense of movement .....than rail, car, or boat.

 

L.Adamson

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I think this is getting into the territory of "feeling". What "feels right" in a desktop sim is highly subjective. Some people seem to want their planes to fly hands-off from coast to coast (O.K., slight exaggeration) while others don't mind having to make small adjustments throughout the flight to keep their plane straight and level. It seems the only real blanket solution is to learn Plane Maker and tweak an aircraft to one's personal taste.

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I just want them to control and fly in somewhat a realistic fashion otherwise a desktop sim has no use for me for ifr proficiency-which a desktop sim is very useful for.

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in somewhat a realistic fashion

 

Which brings us right back to the problem of subjectivity. As the saying goes, one man's trash is another man's treasure.

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Also seems to be confusion over "Stable" and "turbulence".

 

Turbulence can and will bounce a plane around.

 

Stability is the plane with out pilot input trying to get back to the original trimmed condition.

 

There's enough "Real World" pilots indicating that there is some issue with the "Stability" of the aircraft (defaults?) in Xplane 10. That's NOT something that is subjective like feel, the aircraft are either stable, or their not. If Geof, and the other RW pilots say their "unstable", when compared to the real aircraft they have flown, then their unstable. Seems pretty simple to me. Question is, will the developers admit there is an issue, and do something about it. I don't know what needs to be done, but there is an issue. Work with these RW pilots, and together come up with a "fix". It's counterproductive to continually argue about something, that through consensus has been proven.

 

If it means the end user has to go into Plane Maker and make adjustments, so be it, just come up with something (?), and let us know. To continue to deny the issue is there, or try to talk around it serves nobody, do something about it, or tell us how to do it ourselves.

 

Glen

 

It's like a burner on a stove. When it's red, I don't need to feel it to know it's hot. I can, through past experience and learning, know that I shouldn't touch it.

 

Well, when Geof is flying a plane in Xplane he doesn't have to "feel" that something isn't right, he just knows from the behaviour of the aircraft that it's not flying the way it should, not like his real world experience has taught him. Nothing to do with feel, his senses tell him things are not the same, or as they should be, it's just not quite right.

 

Got it now?

 

P.S. I trust Geof's judgement, here's never given me or anyone reason not too. I think he's like the rest of us, and after the best / most realistic flight experience he can get on a computer, and nothing more.

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Well, when Geof is flying a plane in Xplane he doesn't have to "feel" that something isn't right, he just knows from the behaviour of the aircraft that it's not flying the way it should, not like his real world experience has taught him. Nothing to do with feel, his senses tell him things are not he same, or as they should be.

 

Which is still a subjective evaluation. The other problem, which has been discussed at length in the other thread, is that flying a desktop sim lacks many of the sensations you experience while flying a real plane, so you can't take as much advantage of your instincts. That is to say you fly a desktop sim differently than you fly a real airplane. This, I suspect, also has a dramatic impact on the "feel" of a particular plane.

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I find that XPlane does a decent job on some well modeled planes. I have a couple of hundred hrs in RL, so something to compare it to. But after trying a handful of planes in Xplane and A LOT in FSX, my only conclusion that if the model is done right- it will fly right. FSX never really feels Great but all are more or less consistent.

 

Ixeg demonstrator can fly the 737 very accurately as seen in demo videos. His landing is top notch, yet the plane slips and slides just enough.

 

I especially like the feeling of correcting yaw in some XP planes, although its a bit too sensative. FSX just doens't seem to feel right in any plane.

 

I agree that it is very subjective.

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Which is still a subjective evaluation. The other problem, which has been discussed at length in the other thread, is that flying a desktop sim lacks many of the sensations you experience while flying a real plane, so you can't take as much advantage of your instincts. That is to say you fly a desktop sim differently than you fly a real airplane. This, I suspect, also has a dramatic impact on the "feel" of a particular plane.

 

I guess I can accept that reasoning, but when you get enough people / pilots telling you that something is amiss, are they all wrong? If it was only one or two people, then yes, it could just be subjective, but when there are multiple people saying the same thing, it's no longer subjective, more like fact?

 

Glen

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I have posted over and over simple flight tests that the FAA requires for stability in rw aircraft that can not be passed in this sim. This is not subjective, but clearly demonstratable. Never being able to admit there is this easily demonstratable flaw and not trying to work towards a solution is unfathomable to me, but as greater numbers ( if they do) start to flock to this sim it needs to be improved/fixed. How about we work for a fix and leave subjective defense behind?

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There are many things that happen when flying in an aircraft, all taken in through multiple senses. Smell and feel in the seat and yoke are out due to the interaction with the computer, but when you go from 100% throttle firewalled with an aircraft trimmed well and stable, then drop the throttle to 50% and add a notch of flaps, when you're familiar with an aircraft, you can feel with your eyes how the aircraft reacts. The altimeter climbs, nose drops then climbs as the various parts of the aircraft react to the lift/thrust configuration changes. You know when it's right, it does all the things you look for. A yoke not tied to the actual ailerons or hydraulics in an aircraft but instead have a centering spring will always feel differently, but moving them to a position at a certain rate will yield a specific roll rate or pitch rate.

 

These are not things that can be numbered, only "felt" by observation and your knowledge of the real aircraft in those situations. Patterns are great as you've done countless numbers of them in varying circumstances, but there are things that are the same in each one of them. Those are what you look for the sim to do, and if it does what you're looking for, it's successful in recreating the feel of flight when the response is the same in sim as in real flight.

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I guess I can accept that reasoning, but when you get enough people / pilots telling you that something is amiss, are they all wrong?

 

I suppose it depends on what they think is wrong and why they think it's wrong.

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I suppose it depends on what they think is wrong and why they think it's wrong.

 

They've already explained all the issues, with various real world examples. I don't know why were still talking about this, thought they would have moved onto "fixing" the issues by now. The "fixing" will be a benefit too all, this bickering is just a waste of time, every bodies time.

 

Address this issue, fix what's not right, put it to rest. Then move on to the next one. That's progress, moving forward, better for everyone involved.

 

Glen

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Wrong:

 

1) A Baron, Bonanza, most Piper and Cessna's do not need aileron/rudder trim to trim for level flight. In fact most of these aircraft do not have aileron/rudder trim controls.

 

2) Once trimmed an aircraft should not be immediately leaving a trimmed condition-banking 45 degrees within a couple seconds or in a climb 1000 fpm or above and never returning to the initial trimmed position is not right and is negative stability. Positive stability means an airplane will develop forces or moments which tend to restore it to its original position-this does not happen.

 

Fact:

 

1) This has nothing to do with control feel, and requirements are clearly stated in Far's part 23 as to what is required for aircraft performance. This is not subjective stuff but can be easily measured. I have repeatedly stated tests one can do-they literally take a minute or two.

 

2) We have been told that a well designed aircraft by a master Xplane guru should be perfectly flyable without the use of pitch stability augmentation and all the other stability items in that menu-yet it seems these must be utilized to make an xplane aircraft fly in a somewhat realistic way.

 

3) I have never mentioned "control feel" however what fvapres states above is completely correct. As proof, why would a simmer buy different fs aircraft if in some way the difference of handling of the aircraft were not simulated? It can be done, even with our primitive spring controlled controllers.

 

I can't remember but I joined xplane very early in either version 3 or 4 (maybe even 2). I and others including Larry have been asking these same questions since (just search the org). The addition of the stability sliders is welcome (though it seems looked as a "cheat" by some). After owning so many versions I'd like to see this issue addressed. The Carenado crew seems to have hit on something because they are closer-with the stability sliders all the way to the left.

 

Stability and trim are pretty much the basics of flying-period-all else comes from that.

 

From Wiki: " The use of trim tabs significantly reduces pilots' workload during continuous maneuvers (e.g.: sustained climb to altitude after takeoff or descent prior to landing), allowing them to focus their attention on other tasks such as traffic avoidance or communication with air traffic control."

 

As it stands now Chuck Yeager ability would be required to fly and the subsequent accident rate would make no one want to fly.

 

Yes I and others have tried to make these points many, many times. It would be welcome to move to the fix level but I have to say it is frustrating when the problems are clearly stated many, many times over many many years and one is met with astonishment, subjective when it is anything but, and then crawling back under a rock.

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I especially like the feeling of correcting yaw in some XP planes, although its a bit too sensative. FSX just doens't seem to feel right in any plane.

 

I agree that it is very subjective.

 

Yep, very subjective.

 

After numerous real life flights, involving mountainous terrain, I'd often come home & fire up the computer to re-create these flights. Since XP9 has some descent topigraphical terrain right out of the box, I'd use it, as well as FSX. For me, the RealAir Marchetti SF260 (FSX) always just seemed right, when going from my Van's RV6 to the desktop sim. It just "felt right"! With X-Plane, something seemed wrong, and I'd usually exit after five minutes. I do believe we now have the reason nailed, which is the subject of this thread.

 

L.Adamson

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I don't understand why this thread turned into the stability issue. That is already being discussed in another thread, and in the first post of this thread I even wrote (in capital letters) that I was _not_ referring to the other issues of X-Plane flight model (among them the stability issues) but _just_ to the specific things i mentioned when comparing the videos of RL, X-Plane, FSX.

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Are they not connected-the view out the window will be connected to what you are feeling in the cockpit? (however after making my nice comments at how xplane does this very well I confess to being suckered in by Mountains comments that dragged the other thread in-I apologize)

 

Despite my using videos to illustrate a point I am somewhat suspicious of them.

In almost all my videos my flying partner will try to make a 30 degree bank look like an 80 degree just for the fun of it, if you are holding the camera it is shaking all around due to the vibration of the aircraft that really might not be going on. In my kdkx landing which is one of my favorites-it looks like the trees on final are 1 ft. away-but they are further than that...

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Which is still a subjective evaluation. The other problem, which has been discussed at length in the other thread, is that flying a desktop sim lacks many of the sensations you experience while flying a real plane, so you can't take as much advantage of your instincts. That is to say you fly a desktop sim differently than you fly a real airplane. This, I suspect, also has a dramatic impact on the "feel" of a particular plane.

I think this is getting into the territory of "feeling". What "feels right" in a desktop sim is highly subjective. Some people seem to want their planes to fly hands-off from coast to coast (O.K., slight exaggeration) while others don't mind having to make small adjustments throughout the flight to keep their plane straight and level. It seems the only real blanket solution is to learn Plane Maker and tweak an aircraft to one's personal taste.

 

My "feeling", is that you don't exactly know what you're trying to say. This has nothing to do with hands off, or making small adustments. It's more like flying a plane cross country that's seriously out of rig. We know the "feel", and don't like it. I once flew a Cessna 172, in which a bird strike took nearly the whole front windscreen out. I ferried it back to it's FBO after the windscreen was replaced. It just always wanted to bank to the right. It was constant aileron & rudder for the 215 miles. And I didn't like that either. The XP problem isn't near that bad, but it's still annoying, and our "pilot" brains are certainly filling in some of the gaps, that many of you don't have sensations of.

 

I don't understand why this thread turned into the stability issue. That is already being discussed in another thread, and in the first post of this thread I even wrote (in capital letters) that I was _not_ referring to the other issues of X-Plane flight model (among them the stability issues) but _just_ to the specific things i mentioned when comparing the videos of RL, X-Plane, FSX.

 

Yep...................and now I'm even getting the threads mixed up!!!

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Maybe we can say that both sims have good enough flight modeling for a simulator. And it's just a matter of what payware developers do with the platform. For me I really like the way the tires touch the runway in XP when landing, it looks much more detailed, however I don't know if enough ground effect is modeled.

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