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Post by Tom Goodrick on Dec 29, 2010 14:59:50 GMT -5
The flap effect on takeoff performance is something I had no idea of although as I think about it, I should anticipate that sort of thing due to flap moments. But I would have no way of telling if that makes a burden on the pilot unless someone like you tells me about it. We could fix that in a day or two, based on our performance as a "team" in the past.
Of course there are many things like that pilots with experience in the aircraft could bring out if they worked with FD developers.
As for the relation between pitch adjustment by stick or by trim, there is certainly a difference there between RW flying and FS flying because only in FS flying does the stick remain fixed unless you adjust it. In RW you have to hold the wheel anytime the forces are unbalanced so you naturally adjust the pitch some with the wheel toward the direction of change needed while keeping the plane steady enough to please the passengers. In FS I often move the stick substantially only twice to initiate pitch changes - (1) rotation for takeoff and (2) rotation for a landing flare. Of course when flying manually I make slight adjustments for airspeed changes, flap extension or retraction, and during turns. Also there is the occasional need to damp a phugoid when climbing a jet or to smooth out configuration and speed changes during a descent. There is a close similarity to "trimming out stick forces" when flying in FS: after a configuration change or a change from level to climb or decent you move the stick first to control the airspeed and then adjust the trim so you can remove your hand from the stick with no disruption.
Also, I just realized this thread is in the FSX section. All my experience is with FS9. I am not at all familiar with FSX and do not expect to become familiar with it. FS9 is plenty good enough for me. My gauges and FD files are only developed for use in FS9.
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Post by bkimoun on Dec 30, 2010 5:17:18 GMT -5
The trim in FS is sufficient to enable realistic control of flight of a wide range of aircraft. I fly everything from slow piston singles to multi-engine jets. I use the autopilot for the main portion of any flight after the takeoff and before beginning the approach. I have onlyt flown slow piston singles in real life so I cannot speak for the realism of more advanced aircraft. But from what I have read of pilot reports for more advanced aircraft, the process is similar to what I do in FS. The way the trim works in FS is fine in my opinion. I use the digital trim indicator as described above. I always set a takeoff trim value appropriate to the aircraft. I put that info into a checklist for each aircraft. After lift off I transition to climb with manual trim adjustment. My only stick input is at rotation. From climb until the autopilot can be engaged in climb, I manage speed and climb rate with pitch trim and power adjustment. The autopilot simply adjusts the trim to achieve the specified climb rate (given manual adjustment of power) until the specified altitude is reached. Then I adjust power for cruise. Following descent near the destination airport, I keep the autopilot on until vectored to the final approach. Then I switch to manual where I primarily adjust power and trim. It is good that the transition from autopilot to manual trim control is very smooth. I am not convinced that the equations you presented show all the terms used in the sim. I don't know who developed AFSD or how thoroughly they disassembled the sim code. I know they got no help from Microsoft. I am not even sure Microsoft understands their own code. They certainly do not understand conventional aeronautical engineering or they would not have removed the wing incidence variable when they developed FS9. But I don't think the downlift on the tail is a big deal, if, indeed, they do not account for it. It could be in the code that AFSD did not see. There are serious simulations of particular aircraft used in flight schools. They cost several thousand $$ per aircraft. If you are so concerned about this, you should use those sims. I am sure they would model the exact trim tab geometry. Hi Tom ! I agree with you that MSFS simulates satisfactorily flying aircrafts but we must agree that it sacrifies somehow some details that may be seen by some simmers as important, like the trimming process for instance. The details ignored by FS (or missing) become bothering once they become visible and especially if we have some knowledge about aircraft aerodynamics. When I used FS for the first time I couldn't notice anything wrong and the game seemed to me perfect. But later on, I started to make some experiments to see how aerodynamics is emplemented throught FS. And the first thing I could discover is that angle of attack does not change if we play with the cg location, while weight is kept constant.At the beginning, I used simply AoA and cg monitoring in my investigation. After that, I tried the AFSD tool. This is then how I came up with the conclusion that trim does not work perfectly in MSFS.
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Post by Tom Goodrick on Dec 30, 2010 8:12:52 GMT -5
If you agree with my calculations involving the King Air 350, then it seems that to be correct, FS should change the angle of attack 0.009 degrees when the weight is shifted.
You get upset over that? How about the fact you can land yawed 40 degrees to the runway with no consequence because some nut at Microsoft couldn't figure out how to calculate lateral friction on the wheels?
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Post by Tom Goodrick on Jan 1, 2011 21:16:21 GMT -5
While working with some FD problems today I happened to spot some parameters that are relevant to this discussion about lift from the tail components involved in stability. In section 1100, primary aerodynamics, in the sub-section on Lift, I found these parameters: CL_de which gives lift per elevator deflection and CL_dh which gives lift per angle of attack of the horizontal stabilizer. There were several others such as lift per rate of change of pitch and of angle of attack.
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Post by bkimoun on Jan 3, 2011 4:29:36 GMT -5
Hi! Moreover, in MSFS the XYZ axes pass through the visual center of the aircraft model and not through the aircraft cg like in real world. This difference means that all moments in MSFS are computed with respect to the visual center and not with respect to cg. Then again another complicated issue. Back now to trim issue: Tom, may be MSFS deals differently with the types of joysticks used, and thus trims differently depending on the joystick type usde? Because, I think the centering of a spring controlled joystick must be different from that of a force feedback joystick. For the first case, a joystick released at trim, means no spring resistance and a joystick at null position (rest position) corresponding then to a zero deflection of elevator. While for the second case (force feedback), the no resistance position (trim) of joystick corresponds to a given position (not necessarilly zero position) within the range of movement of the joystickstick permitting then a certain elevator deflection at trim.
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Post by Tom Goodrick on Jan 3, 2011 11:04:19 GMT -5
Now you are bordering on the absurd. The CG of any aircraft moves in flight for a variety of reasons (normally fuel burn). Are you going to move the axes as fuel burns? The real world does not run XYZ axes through the CG. They set an arbitrary center for their axis system. Different companies use different definitions. In the case of MSFS they provide an offset in X that enables us to match a real aircraft's coordinate system relative to the CG. I have done that in two cases (Learjet 45 and CitationJet1).
I use a gauge that reads and displays the CG on every aircraft I fly. I have studied what happens to it. I am quite sure the sim code computes MOI's in flight properly. I have experienced MOI changes in FS with loading changes and with fuel burn.
I don't use a force-controlled joystick and have not investigated their effects. No one has ever reported such problems.
It is becoming clear to me that you are engaged in nothing more than a slander campaign against the Microsoft Flight Simulators. There is little benefit in continuing this discussion. If you do not stop, you may be banned from this Forum. I could counter your arguments both in theory and in examples where real aircraft performance is demonstrated very closely in FS. But, indeed, that is what the bulk of my writing in this Forum has been about.
You should confine your studies to the expensive airline-quality simulators. I'll bet you can find some shortcommings with them too, especially the "full motion simulators" where the net acceleration integral is zero in all directions (because they never leave the building).
This sim is not perfect. But, on the whole, it does a pretty good job for the money.
Good day to you.
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Post by Tom Goodrick on Jan 3, 2011 11:16:14 GMT -5
On 12/29/10 I wrote: "The flap effect on takeoff performance is something I had no idea of although as I think about it, I should anticipate that sort of thing due to flap moments."
I should clarify that. I normally spend more effort looking at the effect of flap pitching moment on approach and landing where it predominates. Many variables relate to the takeoff rotation including the main wheel position relative to the empty CG. This is often left to the developer as a variable to be used to get the basic CG into proper position. Also it should be noted that the wheel position used in sim computations is seldom the same as that shown in the geometric model. This is where problems can develope.
Lou, if you spot a problem with takeoff rotation on any of the aircraft I have worked on, please bring it to my attention. I will fix it. I can help with other aircraft in that regard or in other regards if you identify a problem to me. Most of the time, if I pay any attention to the effect of flaps on takeoff, it is only to the flap setting normally used. I often look at that with regard to departure stall handliing.
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Post by louross on Jan 3, 2011 16:59:33 GMT -5
The T.O. flap situation is not a big deal to me. It would take a lot of time, which I'd rather not do. Actually, I spend more time in transport cat jets than anything else, second is time spent in airline piston planes, then the "commuter" type stuff.
I'd like to point out the follwing and see what you think. This concerns the 727, of which Dreamfleet wins hands-down over the other programs in FS for FDE's. This is the real a/c: 1) PAX loading does not affect CG. Although I have more time in the DF727 than any other a/c in FS, I don't pay much attention to the CG, as long as the loading program (provided by DF) is within limits. Therefore, without running a check, I don't know how this point is handled in FS (by DF).
2) RW T.O.: If you rotate after Vr, you will run off the end of the runway because the plane is accelerating so fast that by the time the nose comes up you've run out of runway.
3) RW T.O.: If you rotate before Vr, you will be lucky to get off because the early rotation causes so much drag that the a/c cannot accelerate to lift-off speed. If the runway is long enough to accelerate, you'll probably climb 500-1000 agl in about 30-40 miles. This was "demonstrated" by an unfortunate crew departing the N-S runway at Denver Stapleton.
4) X-Wind T.O.: In a strong cross-wind, it is very possible that the center engine will not produce thrust until you've accelerated to at least 100kts or so due to the "S-tube" inlet. According to a current 727 pilot this has been coorected by managing the power differently during the T.O. run. lr.
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Post by bkimoun on Jan 4, 2011 5:42:19 GMT -5
Now you are bordering on the absurd. The CG of any aircraft moves in flight for a variety of reasons (normally fuel burn). Are you going to move the axes as fuel burns? The real world does not run XYZ axes through the CG. They set an arbitrary center for their axis system. Different companies use different definitions. In the case of MSFS they provide an offset in X that enables us to match a real aircraft's coordinate system relative to the CG. I have done that in two cases (Learjet 45 and CitationJet1). I use a gauge that reads and displays the CG on every aircraft I fly. I have studied what happens to it. I am quite sure the sim code computes MOI's in flight properly. I have experienced MOI changes in FS with loading changes and with fuel burn. I don't use a force-controlled joystick and have not investigated their effects. No one has ever reported such problems. It is becoming clear to me that you are engaged in nothing more than a slander campaign against the Microsoft Flight Simulators. There is little benefit in continuing this discussion. If you do not stop, you may be banned from this Forum. I could counter your arguments both in theory and in examples where real aircraft performance is demonstrated very closely in FS. But, indeed, that is what the bulk of my writing in this Forum has been about. You should confine your studies to the expensive airline-quality simulators. I'll bet you can find some shortcommings with them too, especially the "full motion simulators" where the net acceleration integral is zero in all directions (because they never leave the building). This sim is not perfect. But, on the whole, it does a pretty good job for the money. Good day to you. Sorry Tom if you find my questions bothering. I however agree 100% with you that MSFS simulates flying fine, and honestly I don't have any particular interest in talking publically about what does not seem to me as realistic in this flightsimulator. But, Tom, is it really a good thing or not to go thoroughly in how realistic is MSFS, and how it implements aerodynamics? I like the game and find it intersting but would like to learn and understand theory at the same time. None can disagree, MSFS is a good simulator to teach and popularize flying, but can also be a teaching mean for those who search to learn and understand real aerodynamics like me.
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