# Relative Motion

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Question for the PC gurus -- there is, and always has been, a problem with relative motion/perspective of speed in FS2002, and many other sims. As you approach the runway for landing, on very short final, and particularly as you cross the threshold, the sensation of relative speed as sensed by how fast you are passing over the ground is very variable, ranging from pretty good (say, in smaller planes such as the Baron, and particularly good in add-ons like Marchetti), to very poor, and this is particularly noticeable in heavy iron. The bigger the plane, the slower the relative speed. This can be proven, if you track the time to cover a certain distance --e.g. if you're landing with 130 KIAS, your actual speed as determined by distance (feet of runway) covered and the time to cover it is usually NOT equal to KIAS/MPH, but much slower. This shouldn't be the case, of course, and motion as perceived in a twin Beech should be pretty similar to motion as perceived in a heavy jet, give or take a little for perspective sitting higher up in the latter. The best sim I've seen portray this perspective is x-plane, where I've almost broken into a sweat on crosswind landings because of fast, accurate relative motion of the runway passing under you. Can this be improved in FS2002?? Which parameters govern that particular aspect of the sim?? Any help would be appreciated. The frustration (being a pilot) is flying great sims like these, only to land in relative slow motion -- really takes away from the experience. Thanks. Greg.

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I once approached the problem mathematically. There is definitely nothing wrong with how fast airplane moves above ground, the only problem is "perceived" speed by pilot on short final. To make it realistic a proper zoom must be set. Theoretically the correct zoom may vary depending on the panel. I made once rigorous calculations only for the 767 panel (767PIC) and came up with 0.71. But I suspect this zoom will also work with other "heavy" aircraft and possibly for smaller airplanes too. If your zoom is too 'long' then indeed you don't get correct speed sensation. If it is too 'wide' there may be too much speed. But regardless of the zoom - the airplane still moves (tracks) along the ground according to its speed - I see nothing wrong here in FS.Michael J.[link:hifi.avsim.net/activesky]http://hifi.avsim.net/activesky/images/wxrebeta.jpg

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In the larger plane you are further from the ground (landing/takeoff)so it should appear slower. If thi is a nonlinear perception it would explain the difference between GA and jets. Exageration of this is the very slow visual progress along the ground when at 35,000ft.Dick

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Very good point about nonlinearity.Your approach speed in a 767 is roughly 40% higher than in a Baron yet you are seated a lot higher than 40%.Michael J.

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I use different combinations of moving my eye-point within the virtual cockpits by using "active camera" and the mouse wheel. I set myself back a bit farther than a seat would be in real life, but then this allows much more peripheral vision from the sides.That way.................. I too have had many eye popping/sweat landings with a real sensation of speed, within the bounds of FS2002!!Below is a pic of pulling the eye point back in the default Cessna. It work's because I get that "jump for joy" feeling in front of a P/C! Sometimes, I'll even do a replay, and look out the side or corner windows. They sensation of speed buildup seems very real as the runway approaches. Same for takeoffs.L.Adamson

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Excellent points, thanks for the feedback. I realize the point about perspective sitting higher up in a heavy jet, see my post. However, if you count runway stripes(and I can't remember the number of feet they are apart/long)to get distance, and time traversing of those stripes, then the speed usually does NOT come out to KIAS or MPH (converted).This is particularly obvious in take-off in a heavy jet -- KIAS may be 80, and runway stripes are passing at the rate you would see then at 20-30MPH. And even though the SENSATION of speed is different sitting up high in the heavy, you should still pass runway stripes (cover distance) at the same rate as in a small light aircraft if you're going the same speed. This has not been my experience in most sims, and definitely not what I see in real flight. Greg.

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>speed usually does NOT come out to KIAS or MPH >(converted).This is particularly obvious in take-off in a >heavy jet -- KIAS may be 80, and runway stripes are passing >at the rate you would see then at 20-30MPH. Again, you are suggesting the whole aircraft is moving with slower speed than the indicated speed (on the ground). I have no clue how you measure this but I suggest you recheck your calculations (or the way you measure it).Michael J.

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After switching back and forth between FS2002 & X-Plane using 737's, I found that X-Plane really did appear faster than the default FS2002 setup. It really is just a matter of zoom adjustments as someone else suggested. While heading down the "wide" International airport runway in FS2002, start hitting the "-" key to quickly change zoom levels. The perception of speed will dramatically change and look just like X-Plane. Start hitting the "+" key and everything appears to slow to a crawl................because your really looking at runway striping much farther down the runway. X-Plane just appears to default to a different zoom level.L.Adamson

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Michael J. -- try this -- On a precision approach runway, the runway aiming point markings are 1000 feet from the threshold. If you over-fly the runway just above the ground at, say, 80-90 KIAS, time how long it takes you to cover that 1000 feet. Or, see how long it takes to over-fly a designated runway of known length (reported in the airport info), and time that. Then convert these to groundspeed, and then KIAS -- my point is that the TIME it takes to cover the ground at low altitudes (where you can measure something visually) and particularly at low airspeeds (motion problem doesn't exist at higher speeds), when calculated with distance travelled and then converted to KIAS isn't correct in many instances. Not trying to kill this, but the visual impression of relative ground "covered" in the flare and approach are NOT the same as in actual flight. I've landed at KORD in heavy jets (both real, professionally simulated, and FS2002 simulated), and in our PC sims it can take 3-4 seconds to pass over an intersecting runway (perpendicular, 90 degree intersection)-- at 130KIAS, converted to groundspeed, that should equate to a runway width of between 550-770 feet!! Not accurate. Try taking off in a 747 -- hold take-off speed to something short of Vr,say 100 KIAS, and look outside -- airspeed indicator will say 100 KIAS, and runway is going by like you're driving a car down your sidestreet. Greg.

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Another factor added to the perceiption of speed is the apparent level of detail in the texture, that fools our brains. You can try both with and whitout detail textures and see the difference when landing. This little "noise pattern overlay" on the texture makes the textures looks like they were finer, with more details, and this helps a lot. At least, to my eyes!

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>that 1000 feet. Or, see how long it takes to over-fly a >designated runway of known length Greg,This is exactly what I did. I used 13R at JFK (long runway) and rather than overfly I simply did high-speed taxing (at 93 kts). When I measured the taxi time and compared with precomputed time based on the known runway length I was within 5% error - very good result relative to crudness of the test.A couple of remarks based on my math/physics background. When you feel something is off, first define exactly what you want to measure and compare and then come up with a repeatable method to measure it in such a way as to minimize influence of other factors. Michael J.

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>Try taking off in a 747 -- hold >take-off speed to something short of Vr,say 100 KIAS, and >look outside -- airspeed indicator will say 100 KIAS, and >runway is going by like you're driving a car down your >sidestreet. Greg. Why argue ??..............I told you what to do. Reply #7. Use the minus key to change the outside field of vision. Then you can use ctrl enter or ctrl backspace to resize the cockpit. Then you'll get your feeling of speed!!L.Adamson

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I think one of the biggest contributors to reduced percention of speed is having no peripheral vision in an FS. We have almost 180 degrees of peripheral vision, and seeing objects or patterns 'whizzing by' out of the corners of your eye triggers something in your brain to to make you think you are going fast.

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When I first tried FS2002 I was also "annoyed" by the impression that somehow FS2002 gives a very slow perception of speed over ground, when flying low and relatively slow. Adjusting the zoom factor did make a difference, but the effect was still there.I therefore did some tests, but instead of using runway lengths etc., I used exact Lat/Lon coordinates and compared elapsed time vs distance covered while flying low speed/low altitude. The FS2002 engine came out "spot on" when it comes to the mathematical aspect of this motion, so we cannot blame the mathematics used.Thus, I cannot agree with Gunfighter's suggestion that the motion is actually slower than real. But as I said I fully agree with him that the perception of motion is wrong.It is solely a visual problem, and I believe the zoom is not the answer, just a part cure.Stamatis

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>It is solely a visual problem, and I believe the zoom >is not the answer, just a part cure. well, I am strong believer in numbers. If outside dimensions are done right, if Newtonian equations of motions are obeyed, if perspective from the cockpit is correct (zoom factor) then I have no idea what else could be done. If this is not enough then perhaps people should start looking at secondary factors like fidelity of ground textures, lack of peripheral vision or focusing eyes in the wrong place (this last one I correct using the Fresnel lens with great results).There are many real-life jet pilots (specially on the 767PIC forum) and while examining the fidelity of this simulation from different angles I never heard them complain about skewed sense of motion. I spent a few moments (flying and landing !) in a full motion KC-135 simulator and don't recall the sense of motion being vastly different from what I get in FS2002.Michael J.

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"There are many real-life jet pilots (specially on the 767PIC forum) and while examining the fidelity of this simulation from different angles I never heard them complain about skewed sense of motion. "With all the respect to these pilots, I will not agree simply because they say so, I have a pair of eyes myself :-)I am lucky enough to be in the cockpit jump seat during every single flight I have taken this year, and after I noticed this, I paid extra attention to "visualize" motion looking out of the windshield while at less than 2000 feet during approaches, and then comparing this with my own sim, virtually hours later. I still maintain there is something funny with the speed perception at low altitudes/low airspeeds.Now, just the same as I do not have to be convinced by the 767PIC pilots, same gfoes for everyone else of course, nobody needs to agree with me just because I say so :-)After all, I just said I was impressed with the accuracy of the FS2K2 numbers, so I can't explain what is causing this to me. It may be just me, but then how come so many others mention it too?"If this is not enough then perhaps people should start looking at secondary factors like fidelity of ground textures, lack of peripheral vision or focusing eyes in the wrong place (this last one I correct using the Fresnel lens with great results)."Hmmm... Maybe the relative size of nearby objects, like trees houses, etc? If these are wrong, then surely the perception of speed passing them by will be also wrong?Anyway, it is no longer important for me, I guess I have gotten used to it. It is only while jumpseating in the cockpit that I sometimes get reminded of this.Stamatis

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Oh, and another thing I forgot to ask:If one zooms out to 0.70, then surely speed perception will be further reduced, not increased, since you are moving the ground and all the objects on it further away from you, no?Stamatis

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>further away from you, no? >No, the wider the zoom the faster the speed and likewise the longer the zoom the slower the speed. If you have a zoom equipped camera you can see it for yourself (or use FS2002 .. ;-) ) Michael J.

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.... because zoom compresses distances in front of you.Michael J.

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Hi again Michael,".... because zoom compresses distances in front of you"when you zoom in it sure does, not when you zoom OUT, which a factor of 0.71 does!If you advised using a Zoom of >1, then I'd agree that it compresses distances in front of me, but when I use a wide-angle setting of 0.70, surely it has the opposite effect?Stamatis

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>If you advised using a Zoom of >1, then I'd agree that it >compresses distances in front of me,More zoom IN = More compressed distances = stronger perception of slower speed.If neither experiment nor math can convince you - not sure what to add to this subject. You just have to work it out on your own.Take care.Michael J.

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No problem Michael, thanks for your ideas anyway!Stamatis

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Thanks for all the great, thoughtful, ideas. For whatever it's worth, there is a video of heavy jet approach I downloaded from AVSIM called kmdwmovie.zip. See if the perception from the cockpit is what you typically see in a sim. Granted, don't know the approach speed, but it's going to be somewhere around what most heavies would use. My opinion is that the approach over the numbers seems much faster than we would see in the sim -- maybe not for you. Greg.

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>My opinion is that the approach over the numbers seems much >faster than we would see in the sim -- maybe not for you. Greg,You have fallen into your own trap - this movie is from within the FS2002 sim (not the real world). I mean - just look at the scenery. So .. is 'his' FS2002 faster than yours ? :-lol :-hahMichael J.[link:jdtllc.com]http://jdtllc.com/images/RCsupporter.jpg

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Michael -- couple of points. First, I wasn't aware I was setting a trap -- the question I raised was sincere and legitimate, not baiting anyone or any idea. I guess it's all in the perceiver (no pun). I have plenty of time in both military and GA aircraft, and for me the perception of motion is slow in the sims, period.I don't give a rip if the math works or not -- Wasn't criticizing the sim, and others seemed to agree. Second, the problem may very well be PC's -- my system is older, and the video(on my screen)looked pretty real, and I thought illustrated a point. Guess I really got burned there, huh? Score one for you. Finally, your accusatory attitude is something I got real tired of in these forums well over a year ago when I stopped following. Your "laughing face" is typical of what was a pervasive juvenile mentality. Looks like nothing has changed, and I havn't missed anything.

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