Re: [Flightgear-devel] c172p pitch at cruise question
On Monday 08 December 2008, gerard robin wrote: On dimanche 07 décembre 2008, LeeE wrote: On Saturday 06 December 2008, gerard robin wrote: On dimanche 07 décembre 2008, gerard robin wrote: On samedi 06 décembre 2008, Martin Spott wrote: gerard robin wrote: With the c172p i have included the following: [...] To me that is perfect, [...] This is the sole point I'm talking about: Apparently, even though 'we' have original drawings of the entire airframe, still none of us has authoritative information at his hands how it is supposed to be properly positioned 'at level'. This is the issue which I'd was trying to sort out. Cheers, Martin. Yes it is a guess, how many models here are drawn with a guess ? not only the landing gear :) Giving it a pitch of -3 deg is not so bad. Or extend more the nose gear which will be ugly. AND The question isn't it , only: Which is the less stupid :) to keep the model floating above the ground when not in air ? or to modify the offset ? which won't shock anybody using that FG Reference Model. Easy to do, giving the possibility, latter on, to update, if somebody is able to bring the right blueprint of that Aircraft ( same model, same equipment.). cheers Once you've aligned the reference point between the 3d model and the FDM model you should never have to add offsets to the 3d model; if there's a discrepancy it means that something is wrong. The best way, for modellers, is to make the landing gear in it's maximum extended position - the position it would be in without any weight upon it - and use those coordinates for the gear contact points in the FDM. Then you vary the gear spring and compression rates in the FDM so that the aircraft sits on the ground at the right height and attitude, and then finally adjust the model's gear compression animation so that the two match. That is right but only theory. That means, too, that you include an animation compression extension of the gear (which is not the case with that c172p). With it , yes, = a drawing (blue print detailed) which gives you the right position of the gear when extended + = the know how about the right values of the landing gear ( damping_coeff , spring_coeff, pos min pos max, ) + = the right weight and force applied , on each contact point, we can do the perfect Aircraft, with a perfect FDM regarding the landing gear reactions. Unfortunately it is very rare to have all of these informations, and in many case we must be pragmatic, and the less stupid (if possible). I remember when i did the F-8E , i had some very high detailed drawing, but nothing else regarding the landing gear, but the usual position on ground. In order to get it, in a correct position when it is in air fully extended, and to get it, retracted correctly in the box without cheating , i had to calculate the size and the geometry of each components , it was a lot of work :( I had the same difficulties with an other aircraft done for a friend (SU-34). While it's usually impossible to get exact data on what the height and attitude on the ground should be, with reference to photographs etc. it should be possible to get it correct to within an inch for small aircraft, and perhaps several inches for large aircraft. One of the checks that every modeller should do is to check the gear compression under different loads. This will amount to testing different fuel and passenger loadings, including asymmetric loadings. Military aircraft can also be checked with different weapon loads. Regardless of aircraft type though, once you've got it right the gear will sit on the ground whatever the loading, even with asymmetric loading. LeeE Cheers All of FG is only theory - it all takes place in your computer:) The C172P FDM includes spring and compression rates, not only for the main and nose gear, but also for the tail skid. Although the main gear is fixed in position it flexes and both this, and the nose gear compression, need to be modelled/animated if the gear wheels are to stay on the surface of the ground and not sink through it on touch-down, or rise above it during the take-off roll as the wings start to generate lift. This isn't difficult to do and doesn't need exact drawings or data to achieve an acceptable result. A bit of thought about the landing gear design and reference to lots of photos will give you a very good idea of the limits to the flex and movement, or oleo compression, in landing gear. Too much flexure in the fixed C172P main gear and they will break, and the oleo damper arms limit the maximum extension in the nose strut. Once you've established plausible limits to the gear flexure/extension it's just a question of putting in the time and effort to narrow
Re: [Flightgear-devel] c172p pitch at cruise question
Hi, I had today a closer look into this issue. I got a drawing of the OM of a c172 which shows the the pitch angle with compressed nose gear. I tried to rotate the model but then I found something which shows me that the problem lies on the fdm: at cruise speed about 100kias I got a pitch about 0.3- 0.55 degres. Myself and some others in IRC-Chat noticed that the model is hardly to steer on the ground and lift of itself without touching the controls or the trim. I don't know, but could it be that the cg of the aircraft isn't right which makes all these? Attached the drawing from the OM. Cheers HHS attachment: C172N-Seitenansicht.png-- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
The JSBSim C172 FDM assumes the thrust line is the X axis. I'm not sure what the angle of incidence of the wing is, but it seems that at rest on the runway the pitch of the C172 should be 5 degrees, according to the picture you attached. Jon -Original Message- From: Heiko Schulz [mailto:[EMAIL PROTECTED] Sent: Monday, December 08, 2008 12:16 PM To: FlightGear developers discussions Subject: Re: [Flightgear-devel] c172p pitch at cruise question Hi, I had today a closer look into this issue. I got a drawing of the OM of a c172 which shows the the pitch angle with compressed nose gear. I tried to rotate the model but then I found something which shows me that the problem lies on the fdm: at cruise speed about 100kias I got a pitch about 0.3- 0.55 degres. Myself and some others in IRC-Chat noticed that the model is hardly to steer on the ground and lift of itself without touching the controls or the trim. I don't know, but could it be that the cg of the aircraft isn't right which makes all these? Attached the drawing from the OM. Cheers HHS -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
Jon S. Berndt wrote: The JSBSim C172 FDM assumes the thrust line is the X axis. I'm not sure what the angle of incidence of the wing is, but it seems that at rest on the runway the pitch of the C172 should be 5 degrees, according to the picture you attached. Jon But as others have pointed out, this attitude should be determined by the modeling of the main gear flex and nose strut compression. The 3D model should be such such that when the FDM calls for 0 degrees pitch, the 3D model does not need any pitch rotation. If the modeller tries to achieve the attitude that a taxiing AC would have (e.g. 5 degrees pitch) in blender or ac3d, then the AC will have that 5 degrees pitch when the FDM is calling for 0 degrees. Dave P. -Original Message- From: Heiko Schulz [mailto:[EMAIL PROTECTED] Sent: Monday, December 08, 2008 12:16 PM To: FlightGear developers discussions Subject: Re: [Flightgear-devel] c172p pitch at cruise question Hi, I had today a closer look into this issue. I got a drawing of the OM of a c172 which shows the the pitch angle with compressed nose gear. I tried to rotate the model but then I found something which shows me that the problem lies on the fdm: at cruise speed about 100kias I got a pitch about 0.3- 0.55 degres. Myself and some others in IRC-Chat noticed that the model is hardly to steer on the ground and lift of itself without touching the controls or the trim. I don't know, but could it be that the cg of the aircraft isn't right which makes all these? Attached the drawing from the OM. Cheers HHS -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
Yes! -Original Message- From: dave perry [mailto:[EMAIL PROTECTED] Sent: Monday, December 08, 2008 6:21 PM To: FlightGear developers discussions Subject: Re: [Flightgear-devel] c172p pitch at cruise question Jon S. Berndt wrote: The JSBSim C172 FDM assumes the thrust line is the X axis. I'm not sure what the angle of incidence of the wing is, but it seems that at rest on the runway the pitch of the C172 should be 5 degrees, according to the picture you attached. Jon But as others have pointed out, this attitude should be determined by the modeling of the main gear flex and nose strut compression. The 3D model should be such such that when the FDM calls for 0 degrees pitch, the 3D model does not need any pitch rotation. If the modeller tries to achieve the attitude that a taxiing AC would have (e.g. 5 degrees pitch) in blender or ac3d, then the AC will have that 5 degrees pitch when the FDM is calling for 0 degrees. Dave P. -Original Message- From: Heiko Schulz [mailto:[EMAIL PROTECTED] Sent: Monday, December 08, 2008 12:16 PM To: FlightGear developers discussions Subject: Re: [Flightgear-devel] c172p pitch at cruise question Hi, I had today a closer look into this issue. I got a drawing of the OM of a c172 which shows the the pitch angle with compressed nose gear. I tried to rotate the model but then I found something which shows me that the problem lies on the fdm: at cruise speed about 100kias I got a pitch about 0.3- 0.55 degres. Myself and some others in IRC-Chat noticed that the model is hardly to steer on the ground and lift of itself without touching the controls or the trim. I don't know, but could it be that the cg of the aircraft isn't right which makes all these? Attached the drawing from the OM. Cheers HHS --- --- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix .com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
[Flightgear-devel] C172P pitch at cruise
I agree with what Jon has said--the pitch angle with the aircraft on the ground should be 5 degrees. If this is modeled, I don't think there's any other significant issue. With regards to the pitch angle at cruise, I simply cannot see how you'd ever model that exactly. First of all, it is dependent upon several things: Airspeed, density altitude, aircraft loading and the general rigging of the aircraft, just to name a few. I have flown two nearly identical aircraft (both 172's) and can tell you that they each fly slightly differently--and the picture out the window is not exactly the same in both aircraft. Certainly the horizon intersects the side of the cowling (from the pilot's perspective) at about the same spot, but it isn't exact. And without looking at the XML properties for the 172P I cannot say; but where is the CG located for the current emulation? Is the aircraft modeled at maximum gross weight, or with only the pilot--and how heavy is the pilot? I am not trying to say that the picture out the window changes drastically with variations in loading, but it certainly *does* change somewhat. But more importantly however is that the control force required to maintain flight stability changes, as does the trim requiring to relieve those control forces. But if the emulation can be loaded in similar fashion to the real aircraft, with similar results (airspeed and power settings), then I submit that it's probably as close as you're ever going to get. The point here is that I do not believe there is any ONE right answer. If the emulation flies like the actual aircraft, then all is good. For example, if full throttle in the emulation gives the same approximate airspeed as in the real aircraft (about 115-120 knots, if memory serves); if a power setting of about 1900-2000rpm allows one to maintain an altitude of about 1500-2000 feet MSL at 90 knots; and if 1500-1600 RPM allows me to fly a 3-degree glideslope at about 90 knots with 10 degrees of flaps...then all is good. How much better can it get? (Having said this, I do think that the default 172P model in FG needs property value tweaks to increase realism; but that cannot be done to an accurate degree until a proper set of 3-axis flight controls are configured to the emulation. A joystick is simply not accurate enough to make the kinds of hair-splitting determinations we're talking about here, IMHO.) Incidentally, I did make contact with a friend that is sending me a copy of the entire set of drawings included in the 172P service manual. If they are of value and are of good quality, I will gladly scan them and post them for review. TB -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] C172P pitch at cruise
Tom Betka wrote: Incidentally, I did make contact with a friend that is sending me a copy of the entire set of drawings included in the 172P service manual. If they are of value and are of good quality, I will gladly scan them and post them for review. Thanks for filling the gap, Martin. -- Unix _IS_ user friendly - it's just selective about who its friends are ! -- -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
John Denker wrote: On 12/06/2008 04:02 PM, Martin Spott wrote: In a case like this one I prefer the 'pragmatic' approach of reading a manual (if available), determining what its authors consider as being at level (if they do in some way) and finally to evaluate if we're able to make use of it. It doesn't serve anyone if you define your own fancy idea of the term at level if you don't get any reference for it, Sometimes facts are facts, whether or not they appear in an authoritative reference manual. True. I've been proposing to check wether the maintenance manual would provide some insight. I don't claim this to be the best way to get our hands onto the relevant numbers, but I think it's worth a try. On the other hand, if you have real facts to offer, I'm all ears - it really makes me wonder why you insist on going with the facts even though you were unable to provide any, Martin. -- Unix _IS_ user friendly - it's just selective about who its friends are ! -- -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
In aviation maintenance, level is flat. When you weigh an aircraft to determine empty CG, for instance, it is placed on jacks and leveled--both along the X-axis and along the Y-axis as well. However when an aircraft such as the 172 is sitting (empty) on a ramp, the pitch attitude is determined in large part by the inflation of the oleo nose strut. With the proper oil quantity and nitrogen gas inflation, the strut will be extended by some distance. As the main gear legs are relatively rigid, it is therefore the nose strut that will determine the angle in question. In Aviation Maintenance school, we were taught that the proper distance is about a pack of cigarettes, which is about 3 inches give or take, and allows for a compromise of view over the nose during ground operations, and the avoidance of bottoming of the strut upon landing. However to some degree, there is a range of acceptable values--and one person's pack of cigarettes is another's cigar, I suppose. Never having been a smoker I simply measured it at about three inches, and this is the value I always tried to achieve. But I stress that this is only a guideline, as it is rare to achieve an *exact* degree of extension; simply due to the nature of the process. And as soon as the pilot/copilot/passengers get into the aircraft, this amount changes of course. That being said, I believe that I do have access to service manuals for the 172-series of aircraft. Although I don't work in the industry any longer, several friends do--and I could likely get the proper dimensions from one of them without any difficulty. I will make a couple phone calls and report back in a day or so. Given the limitations of setting the exact oleo strut inflation, I would simply recommend that the nose angle be computed and set based upon the dimensions given in the Cessna drawings, which *should* be available in the service manual. TB -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
On 12/07/2008 03:50 AM, Martin Spott wrote in part: it really makes me wonder why you insist on going with the facts What, me, facts? It's just one of my little quirks. it really makes me wonder why you insist on going with the facts even though you were unable to provide any, 1) First of all, that's not true. On 12/06/2008 05:55 PM, I provided an image that could provide factual answers to at least some of the questions that have come up in this thread. I asked whether it was the sort of information that was desired. If anybody wants to discuss what can and cannot be learned from such pictures, please let us know. 2) I'll make you a deal: I won't question your motives, if you will stop questioning mine. 3) But since you asked: Why should I spend my time and money gathering more facts, if you place zero value on the facts that I have already provided? 4) Why should I spend my time and money gathering more facts, when I asked what facts were wanted and got no reply, and indeed was told on 12/06/2008 04:02 PM that facts were of no interest unless they appeared in an authoritative reference manual. Apparently facts are more appreciated today, and I encourage that ... However .. The previous question remains: If somebody could say more precisely what facts are wanted, please let us know. It would greatly facilitate the task of gathering such facts. As previously mentioned, possibilities include: *) Pitch attitude in level flight at some specified indicated airspeed? *) Pitch attitude while parked, unoccupied? *) Pitch attitude while taxiing, occupied? *) Pitch attitude just prior to touchdown? *) Degree of landing gear extension/compression? *) Lift versus AoA? *) Drag versus AoA? *) Drag versus flaps? *) Incidence versus flaps? *) Trim versus flaps? *) Trim versus flaps*power? (!) *) et cetera? If nobody can say what facts are wanted, then maybe we need to take a step back and re-examine what problem(s) we are trying to solve, and why. -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
On Saturday 06 December 2008, gerard robin wrote: On dimanche 07 décembre 2008, gerard robin wrote: On samedi 06 décembre 2008, Martin Spott wrote: gerard robin wrote: With the c172p i have included the following: [...] To me that is perfect, [...] This is the sole point I'm talking about: Apparently, even though 'we' have original drawings of the entire airframe, still none of us has authoritative information at his hands how it is supposed to be properly positioned 'at level'. This is the issue which I'd was trying to sort out. Cheers, Martin. Yes it is a guess, how many models here are drawn with a guess ? not only the landing gear :) Giving it a pitch of -3 deg is not so bad. Or extend more the nose gear which will be ugly. AND The question isn't it , only: Which is the less stupid :) to keep the model floating above the ground when not in air ? or to modify the offset ? which won't shock anybody using that FG Reference Model. Easy to do, giving the possibility, latter on, to update, if somebody is able to bring the right blueprint of that Aircraft ( same model, same equipment.). cheers Once you've aligned the reference point between the 3d model and the FDM model you should never have to add offsets to the 3d model; if there's a discrepancy it means that something is wrong. The best way, for modellers, is to make the landing gear in it's maximum extended position - the position it would be in without any weight upon it - and use those coordinates for the gear contact points in the FDM. Then you vary the gear spring and compression rates in the FDM so that the aircraft sits on the ground at the right height and attitude, and then finally adjust the model's gear compression animation so that the two match. While it's usually impossible to get exact data on what the height and attitude on the ground should be, with reference to photographs etc. it should be possible to get it correct to within an inch for small aircraft, and perhaps several inches for large aircraft. One of the checks that every modeller should do is to check the gear compression under different loads. This will amount to testing different fuel and passenger loadings, including asymmetric loadings. Military aircraft can also be checked with different weapon loads. Regardless of aircraft type though, once you've got it right the gear will sit on the ground whatever the loading, even with asymmetric loading. LeeE -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
Hi, I don't understand what going on here! First: I used the .pdf for the c172 which could be found some months ago on the official homepage of Cessna. Unfortunately they changed their hoempage, the PDF I used can't be found anymore. The PDF showed the aircraft on the ground, so I used that as first reference. But: I used the old Model by David Megginson for alignement which means, if there is a problem, then it has been since the first c172 was introduced to FGFS! The current c172p has the sme orientation like the old one- only the 3d-model changed so the problem is now visible. 1) First of all, that's not true. On 12/06/2008 05:55 PM, I provided an image that could provide factual answers to at least some of the questions that have come up in this thread. I asked whether it was the sort of information that was desired. If anybody wants to discuss what can and cannot be learned from such pictures, please let us know. The pic wasn't enough- we don't know if the aircraft is really flying with this orientation at cruise speed. 3) But since you asked: Why should I spend my time and money gathering more facts, if you place zero value on the facts that I have already provided? Like we said it before: we need some more informatons. This little pic wasn't enough. *) Pitch attitude in level flight at some specified indicated airspeed? *) Pitch attitude while parked, unoccupied? *) Pitch attitude while taxiing, occupied? *) Pitch attitude just prior to touchdown? *) Degree of landing gear extension/compression? *) Lift versus AoA? *) Drag versus AoA? *) Drag versus flaps? *) Incidence versus flaps? *) Trim versus flaps? *) Trim versus flaps*power? (!) *) et cetera? If nobody can say what facts are wanted, then maybe we need to take a step back and re-examine what problem(s) we are trying to solve, and why. Well, the problem was that it was said that the fdm of the c172p is totally wrong. And without any datas like the one above noone can verify if this is really the case. We have reports from real c172 pilots that thy don't see any issues! Cheers HHS -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
On dimanche 07 décembre 2008, LeeE wrote: On Saturday 06 December 2008, gerard robin wrote: On dimanche 07 décembre 2008, gerard robin wrote: On samedi 06 décembre 2008, Martin Spott wrote: gerard robin wrote: With the c172p i have included the following: [...] To me that is perfect, [...] This is the sole point I'm talking about: Apparently, even though 'we' have original drawings of the entire airframe, still none of us has authoritative information at his hands how it is supposed to be properly positioned 'at level'. This is the issue which I'd was trying to sort out. Cheers, Martin. Yes it is a guess, how many models here are drawn with a guess ? not only the landing gear :) Giving it a pitch of -3 deg is not so bad. Or extend more the nose gear which will be ugly. AND The question isn't it , only: Which is the less stupid :) to keep the model floating above the ground when not in air ? or to modify the offset ? which won't shock anybody using that FG Reference Model. Easy to do, giving the possibility, latter on, to update, if somebody is able to bring the right blueprint of that Aircraft ( same model, same equipment.). cheers Once you've aligned the reference point between the 3d model and the FDM model you should never have to add offsets to the 3d model; if there's a discrepancy it means that something is wrong. The best way, for modellers, is to make the landing gear in it's maximum extended position - the position it would be in without any weight upon it - and use those coordinates for the gear contact points in the FDM. Then you vary the gear spring and compression rates in the FDM so that the aircraft sits on the ground at the right height and attitude, and then finally adjust the model's gear compression animation so that the two match. That is right but only theory. That means, too, that you include an animation compression extension of the gear (which is not the case with that c172p). With it , yes, = a drawing (blue print detailed) which gives you the right position of the gear when extended + = the know how about the right values of the landing gear ( damping_coeff , spring_coeff, pos min pos max, ) + = the right weight and force applied , on each contact point, we can do the perfect Aircraft, with a perfect FDM regarding the landing gear reactions. Unfortunately it is very rare to have all of these informations, and in many case we must be pragmatic, and the less stupid (if possible). I remember when i did the F-8E , i had some very high detailed drawing, but nothing else regarding the landing gear, but the usual position on ground. In order to get it, in a correct position when it is in air fully extended, and to get it, retracted correctly in the box without cheating , i had to calculate the size and the geometry of each components , it was a lot of work :( I had the same difficulties with an other aircraft done for a friend (SU-34). While it's usually impossible to get exact data on what the height and attitude on the ground should be, with reference to photographs etc. it should be possible to get it correct to within an inch for small aircraft, and perhaps several inches for large aircraft. One of the checks that every modeller should do is to check the gear compression under different loads. This will amount to testing different fuel and passenger loadings, including asymmetric loadings. Military aircraft can also be checked with different weapon loads. Regardless of aircraft type though, once you've got it right the gear will sit on the ground whatever the loading, even with asymmetric loading. LeeE Cheers -- Gérard http://pagesperso-orange.fr/GRTux/ J'ai décidé d'être heureux parce que c'est bon pour la santé. Voltaire -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
On samedi 06 décembre 2008, Martin Spott wrote: Heiko Schulz wrote: Well- like I said it yet- OI used original drawings and they showed her on the ground. So the rotation is not much... Apparently the the term original drawings is not sufficently precise in this context. The POH for example has accurate drawings, but these imply a terrain slope of 5 degrees and the front gear fully extended to get the aircraft body into horizontal level Looks like you're in need of a copy of the maintenance manual. If there's no such thing available, I might ask at our local aircraft maintenance 'shop' to make a copy of the respective page(s). Cheers, Martin. It is not wrong to tune the 3D model with an offset during loading , which modify nothing regarding the FDM and gives a better visual when it is on ground. Mainly, because most of the original blue print are given with the aircraft on ground the gears compressed. So, it is not wrong to give some minor adjustment on the 3D model itself , the easiest being to use the offset ( instead of to modify the 3D model.ac ). With the c172p i have included the following: offsets pitch-deg-3/pitch-deg z-m-0.05/z-m /offsets To me that is perfect, may be more z-m -0.065 in order to show the tire compressed. The next update could be to include animations with the compression extension of the gears. :) Cheers -- Gérard http://pagesperso-orange.fr/GRTux/ J'ai décidé d'être heureux parce que c'est bon pour la santé. Voltaire -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
gerard robin wrote: With the c172p i have included the following: [...] To me that is perfect, [...] This is the sole point I'm talking about: Apparently, even though 'we' have original drawings of the entire airframe, still none of us has authoritative information at his hands how it is supposed to be properly positioned 'at level'. This is the issue which I'd was trying to sort out. Cheers, Martin. -- Unix _IS_ user friendly - it's just selective about who its friends are ! -- -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
On 12/06/2008 03:25 PM, Martin Spott wrote: This is the sole point I'm talking about: Apparently, even though 'we' have original drawings of the entire airframe, still none of us has authoritative information at his hands how it is supposed to be properly positioned 'at level'. This is the issue which I'd was trying to sort out. As a step toward sorting it out, it would be nice to have a clearer idea what at level means. *) Level flight? -- At what airspeed? *) Parked on the ramp? -- Like this? http://upload.wikimedia.org/wikipedia/commons/a/ab/GDQG.jpg -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
On samedi 06 décembre 2008, Martin Spott wrote: gerard robin wrote: With the c172p i have included the following: [...] To me that is perfect, [...] This is the sole point I'm talking about: Apparently, even though 'we' have original drawings of the entire airframe, still none of us has authoritative information at his hands how it is supposed to be properly positioned 'at level'. This is the issue which I'd was trying to sort out. Cheers, Martin. Yes it is a guess, how many models here are drawn with a guess ? not only the landing gear :) Giving it a pitch of -3 deg is not so bad. Or extend more the nose gear which will be ugly. -- Gérard http://pagesperso-orange.fr/GRTux/ J'ai décidé d'être heureux parce que c'est bon pour la santé. Voltaire -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
On dimanche 07 décembre 2008, gerard robin wrote: On samedi 06 décembre 2008, Martin Spott wrote: gerard robin wrote: With the c172p i have included the following: [...] To me that is perfect, [...] This is the sole point I'm talking about: Apparently, even though 'we' have original drawings of the entire airframe, still none of us has authoritative information at his hands how it is supposed to be properly positioned 'at level'. This is the issue which I'd was trying to sort out. Cheers, Martin. Yes it is a guess, how many models here are drawn with a guess ? not only the landing gear :) Giving it a pitch of -3 deg is not so bad. Or extend more the nose gear which will be ugly. AND The question isn't it , only: Which is the less stupid :) to keep the model floating above the ground when not in air ? or to modify the offset ? which won't shock anybody using that FG Reference Model. Easy to do, giving the possibility, latter on, to update, if somebody is able to bring the right blueprint of that Aircraft ( same model, same equipment.). cheers -- Gérard http://pagesperso-orange.fr/GRTux/ J'ai décidé d'être heureux parce que c'est bon pour la santé. Voltaire -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
On 12/06/2008 04:02 PM, Martin Spott wrote: In a case like this one I prefer the 'pragmatic' approach of reading a manual (if available), determining what its authors consider as being at level (if they do in some way) and finally to evaluate if we're able to make use of it. It doesn't serve anyone if you define your own fancy idea of the term at level if you don't get any reference for it, Sometimes facts are facts, whether or not they appear in an authoritative reference manual. The only authoritative notion of level that I know of for the C172 is part of the empirical weight-and-balance measurement procedure. It has no specified relationship to the pitch attitude during parking, taxiing, or flying at any particular airspeed. If anybody knows of another authoritative, or even conventional, or even unambiguous notion of level pitch attitude, I'd be very interested to learn about it. As the saying goes: Q: How long does it take a student pilot to properly level off a C-172? A: About 35 hours. -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
dave perry wrote: Hi All, snip Would it not be more realistic to rotate the 3D model about -3 or -4 degrees about the ac3d z-axis. I did not make myself clear in the initial questiion. The video link only detracted from my point. The model in the .ac file is just a rigid body that gets displayed when the fdm says the pitch is zero degrees (or perhaps zero incidence). The fdm then rotates this rigid model for other flight conditions. So if the model starts 3 or 4 degrees too nose high for realistic cruise, it will remain 3 or 4 degrees too high in pitch for all other rotations from the fdm. In particular, it will be 3 or 4 degrees higher than a realistic stall at touch down, burying the tail cone in the runway. To make this clear, I opened the c172p.ac in ac3d, made a screen capture of the side view, then rotated the model by - 4 degrees and made a 2nd screen capture of the side view and then scaled and combined these into one small .png which is attached. My only point is that I think the rotated side view pitch (bottom image) looks like a c172p at cruise and the original side view (top image) looks like a c172p in level no flap slow flight. Compare the wing and horizontal stab incidence angles in the two images. In the rotated side view, the horizontal stab is at zero incidence while the non rotated side view shows a noticeable positive incidence for the horizontal stab which would normally require significant up elevator to maintain. Making this change will be a lot of work since the panel will be messed up. I know because I made a similar rigid rotation correction about a month after I first submitted the pa24-250. Dave P. inline: c172p-4deg-pitch.png-- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
... Making this change will be a lot of work since the panel will be messed up. I know because I made a similar rigid rotation correction about a month after I first submitted the pa24-250. Dave P. If this is really necessary, I wonder if is not enough to rotate the model in the model.xml? Well, the Model-How-To says something like that?! -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
On vendredi 05 décembre 2008, dave perry wrote: dave perry wrote: Hi All, snip Would it not be more realistic to rotate the 3D model about -3 or -4 degrees about the ac3d z-axis. I did not make myself clear in the initial questiion. The video link only detracted from my point. The model in the .ac file is just a rigid body that gets displayed when the fdm says the pitch is zero degrees (or perhaps zero incidence). The fdm then rotates this rigid model for other flight conditions. So if the model starts 3 or 4 degrees too nose high for realistic cruise, it will remain 3 or 4 degrees too high in pitch for all other rotations from the fdm. In particular, it will be 3 or 4 degrees higher than a realistic stall at touch down, burying the tail cone in the runway. To make this clear, I opened the c172p.ac in ac3d, made a screen capture of the side view, then rotated the model by - 4 degrees and made a 2nd screen capture of the side view and then scaled and combined these into one small .png which is attached. My only point is that I think the rotated side view pitch (bottom image) looks like a c172p at cruise and the original side view (top image) looks like a c172p in level no flap slow flight. Compare the wing and horizontal stab incidence angles in the two images. In the rotated side view, the horizontal stab is at zero incidence while the non rotated side view shows a noticeable positive incidence for the horizontal stab which would normally require significant up elevator to maintain. Making this change will be a lot of work since the panel will be messed up. I know because I made a similar rigid rotation correction about a month after I first submitted the pa24-250. No if that was necessary , their is nothing else than modification of the offset in the c172p.xml model. The panel should follow However i noticed that with the actual position the model has the nose gear up above the ground. An offset of -2 deg would be nice pathc172p.ac/path offsets pitch-deg-0/pitch-deg /offsets Dave P. -- Gérard http://pagesperso-orange.fr/GRTux/ J'ai décidé d'être heureux parce que c'est bon pour la santé. Voltaire -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
On vendredi 05 décembre 2008, gerard robin wrote: On vendredi 05 décembre 2008, dave perry wrote: dave perry wrote: Hi All, snip Would it not be more realistic to rotate the 3D model about -3 or -4 degrees about the ac3d z-axis. I did not make myself clear in the initial questiion. The video link only detracted from my point. The model in the .ac file is just a rigid body that gets displayed when the fdm says the pitch is zero degrees (or perhaps zero incidence). The fdm then rotates this rigid model for other flight conditions. So if the model starts 3 or 4 degrees too nose high for realistic cruise, it will remain 3 or 4 degrees too high in pitch for all other rotations from the fdm. In particular, it will be 3 or 4 degrees higher than a realistic stall at touch down, burying the tail cone in the runway. To make this clear, I opened the c172p.ac in ac3d, made a screen capture of the side view, then rotated the model by - 4 degrees and made a 2nd screen capture of the side view and then scaled and combined these into one small .png which is attached. My only point is that I think the rotated side view pitch (bottom image) looks like a c172p at cruise and the original side view (top image) looks like a c172p in level no flap slow flight. Compare the wing and horizontal stab incidence angles in the two images. In the rotated side view, the horizontal stab is at zero incidence while the non rotated side view shows a noticeable positive incidence for the horizontal stab which would normally require significant up elevator to maintain. Making this change will be a lot of work since the panel will be messed up. I know because I made a similar rigid rotation correction about a month after I first submitted the pa24-250. No if that was necessary , their is nothing else than modification of the offset in the c172p.xml model. The panel should follow However i noticed that with the actual position the model has the nose gear up above the ground. An offset of -2 deg would be nice pathc172p.ac/path offsets pitch-deg-0/pitch-deg /offsets oups err offsets pitch-deg-2.0/pitch-deg /offsets may be more Dave P. -- Gérard http://pagesperso-orange.fr/GRTux/ J'ai décidé d'être heureux parce que c'est bon pour la santé. Voltaire -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
However i noticed that with the actual position the model has the nose gear up above the ground. An offset of -2 deg would be nice pathc172p.ac/path offsets pitch-deg-0/pitch-deg /offsets Dave P. Cave: the nose gear animation (compression-gear) isn't right yet. But the offsets was that was I meant in the previous post! But we have to know how much the ac has to be rotatedI just try -3.5 but this seems a bit too much. Well- like I said it yet- OI used original drawings and they showed her on the ground. So the rotation is not much... Cheers HHS -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
We really want to make sure that the visual model is correctly aligned with the dynamics model. Then if the 3d model isn't sitting correctly at rest on the ground, it could be that the gear lengths aren't set properly in the 3d model compared to the dynamics model, or visa versa. If everything is self consistent, it should sit nicely on the runway. And then if the pitch angle is visually off in flight, it probably makes more sense to fix the flight dynamics configuration to achieve the correct cruise pitch instead of hastily rotating the visual model a few degrees to compensate for a flight dynamics deficiency, and also a mismatch in dynamic model gear length versus 3d model gear length. I'm not saying that is the problem, just that it seems more likely to me since we have a added a new 3d model to an existing flight dynamics configuration. Regards, Curt. On Thu, Dec 4, 2008 at 7:02 PM, gerard robin wrote: On vendredi 05 décembre 2008, gerard robin wrote: On vendredi 05 décembre 2008, dave perry wrote: dave perry wrote: Hi All, snip Would it not be more realistic to rotate the 3D model about -3 or -4 degrees about the ac3d z-axis. I did not make myself clear in the initial questiion. The video link only detracted from my point. The model in the .ac file is just a rigid body that gets displayed when the fdm says the pitch is zero degrees (or perhaps zero incidence). The fdm then rotates this rigid model for other flight conditions. So if the model starts 3 or 4 degrees too nose high for realistic cruise, it will remain 3 or 4 degrees too high in pitch for all other rotations from the fdm. In particular, it will be 3 or 4 degrees higher than a realistic stall at touch down, burying the tail cone in the runway. To make this clear, I opened the c172p.ac in ac3d, made a screen capture of the side view, then rotated the model by - 4 degrees and made a 2nd screen capture of the side view and then scaled and combined these into one small .png which is attached. My only point is that I think the rotated side view pitch (bottom image) looks like a c172p at cruise and the original side view (top image) looks like a c172p in level no flap slow flight. Compare the wing and horizontal stab incidence angles in the two images. In the rotated side view, the horizontal stab is at zero incidence while the non rotated side view shows a noticeable positive incidence for the horizontal stab which would normally require significant up elevator to maintain. Making this change will be a lot of work since the panel will be messed up. I know because I made a similar rigid rotation correction about a month after I first submitted the pa24-250. No if that was necessary , their is nothing else than modification of the offset in the c172p.xml model. The panel should follow However i noticed that with the actual position the model has the nose gear up above the ground. An offset of -2 deg would be nice pathc172p.ac/path offsets pitch-deg-0/pitch-deg /offsets oups err offsets pitch-deg-2.0/pitch-deg /offsets may be more Dave P. -- Gérard http://pagesperso-orange.fr/GRTux/ J'ai décidé d'être heureux parce que c'est bon pour la santé. Voltaire -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel -- Curtis Olson: http://baron.flightgear.org/~curt/ -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
On vendredi 05 décembre 2008, gerard robin wrote: On vendredi 05 décembre 2008, gerard robin wrote: On vendredi 05 décembre 2008, gerard robin wrote: On vendredi 05 décembre 2008, dave perry wrote: dave perry wrote: Hi All, snip Would it not be more realistic to rotate the 3D model about -3 or -4 degrees about the ac3d z-axis. I did not make myself clear in the initial questiion. The video link only detracted from my point. The model in the .ac file is just a rigid body that gets displayed when the fdm says the pitch is zero degrees (or perhaps zero incidence). The fdm then rotates this rigid model for other flight conditions. So if the model starts 3 or 4 degrees too nose high for realistic cruise, it will remain 3 or 4 degrees too high in pitch for all other rotations from the fdm. In particular, it will be 3 or 4 degrees higher than a realistic stall at touch down, burying the tail cone in the runway. To make this clear, I opened the c172p.ac in ac3d, made a screen capture of the side view, then rotated the model by - 4 degrees and made a 2nd screen capture of the side view and then scaled and combined these into one small .png which is attached. My only point is that I think the rotated side view pitch (bottom image) looks like a c172p at cruise and the original side view (top image) looks like a c172p in level no flap slow flight. Compare the wing and horizontal stab incidence angles in the two images. In the rotated side view, the horizontal stab is at zero incidence while the non rotated side view shows a noticeable positive incidence for the horizontal stab which would normally require significant up elevator to maintain. Making this change will be a lot of work since the panel will be messed up. I know because I made a similar rigid rotation correction about a month after I first submitted the pa24-250. No if that was necessary , their is nothing else than modification of the offset in the c172p.xml model. The panel should follow However i noticed that with the actual position the model has the nose gear up above the ground. An offset of -2 deg would be nice pathc172p.ac/path offsets pitch-deg-0/pitch-deg /offsets oups err offsets pitch-deg-2.0/pitch-deg /offsets may be more Dave P. Just tried with -3 deg it is right sorry no snapshots. May be the pilot position must be upper , since it has moved and again before leaving may be z-m -0.05 /z-m -- Gérard http://pagesperso-orange.fr/GRTux/ J'ai décidé d'être heureux parce que c'est bon pour la santé. Voltaire -- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
On mardi 02 décembre 2008, Heiko Schulz wrote: The answer is that the flight dynamics is unrealistic, and has been for years. Redrawing the aircraft won't help much (if any). -- The lift curve is unrealistic, which explains the observations that started this thread. -- The drag curve is unrealistic, which explains the unrealistic climb performance and unrealistic short-field landing performance. -- The effect of flaps on incidence is unrealistic. -- The effect of flaps on drag is unrealistic. -- The effect of flaps on trim is unrealistic. -- The effect of engine power is unrealistic, especially the interaction between flaps and power. -- Et cetera. You get the idea. So if you know that all of the fdm is totally unrealistic, so you have real datas and wanna improve her? I'm a little surprised- I always heard that the c172p is one of our most realistic ones Me too, that is why, when i started the idea about a wrong the lift, i did not trust what i said :) -- Gérard http://pagesperso-orange.fr/GRTux/ J'ai décidé d'être heureux parce que c'est bon pour la santé. Voltaire - This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100url=/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
Dave, Heiko, Heiko Schulz wrote: Notice that in the video 1. the tail is higher in cruise than what we have in fgfs for the new model. 2. the nose wheel is below the main wheels in cruise. 3. in fgfs, the tail cone is presently below ground at touch down. [...] I wait for a comment from our c172 pilot Martin! Well, I didn't watch the video (Get the latest Flash player.), therefore I'll add just few little comments: - With a 'properly' (TM) inflated front wheel damper, the C172 has the tendency of having its tail surprisingly low when standing on the ground at a common configuration: Max fuel capacity, one pilot (of approx. 80 kg) and some utilities in the baggage compartment (a can of oil and such). This one has approx. 50% fuel, no pilot/passenger and just light baggage (additional to the 'utilities'): http://foxtrot.mgras.net/bitmap/EDDI/imm021.jpg - On a slow approach in a real C172 the tail also gets _very_ low above the ground. When watching students flying traffic circuits I noticed several of them getting close to a tail strike - the tiedown ears at a C172's tail sometimes feature noticeable scratches. - Just 10 kts of difference in airspeed (95 vs. 105) have a significant effect on the pitch (to my experience much more than with the DR400 for example), therefore telling from a single video sequence without further information might be misleading. Cheers, Martin. -- Unix _IS_ user friendly - it's just selective about who its friends are ! -- - This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100url=/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
On Tue, Dec 2, 2008 at 9:21 AM, Martin Spott wrote: - With a 'properly' (TM) inflated front wheel damper, the C172 has the tendency of having its tail surprisingly low when standing on the ground at a common configuration: Max fuel capacity, one pilot (of approx. 80 kg) and some utilities in the baggage compartment (a can of oil and such). This one has approx. 50% fuel, no pilot/passenger and just light baggage (additional to the 'utilities'): http://foxtrot.mgras.net/bitmap/EDDI/imm021.jpg - On a slow approach in a real C172 the tail also gets _very_ low above the ground. When watching students flying traffic circuits I noticed several of them getting close to a tail strike - the tiedown ears at a C172's tail sometimes feature noticeable scratches. - Just 10 kts of difference in airspeed (95 vs. 105) have a significant effect on the pitch (to my experience much more than with the DR400 for example), therefore telling from a single video sequence without further information might be misleading. I have some data from a real C172 (again noting that individual aircraft can differ quite a bit depending on weight, balance, and a variety of other factors.) level flight, 90 kts, flaps up ... pitch angle is between 0 and 1 degree. level flight, 60 kts, flaps 10 degrees ... pitch angle is about 6 degrees. level flight, 65 kts, flaps 30 degrees ... pitch angle is about -1 degree. Regards, Curt. -- Curtis Olson: http://baron.flightgear.org/~curt/ - This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100url=/___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
On mardi 02 décembre 2008, dave perry wrote: Hi All, As we approach a new release, here is a suggestion that I think would increase the realism of our default AC. I really like the new c172p 3D model. But it seems to me that the model cruise pitch is too nose high. Here is an interesting video link of a real c172 in flight. http://www.youtube.com/watch?v=tg2zXfuywuc Notice that in the video 1. the tail is higher in cruise than what we have in fgfs for the new model. 2. the nose wheel is below the main wheels in cruise. 3. in fgfs, the tail cone is presently below ground at touch down. Would it not be more realistic to rotate the 3D model about -3 or -4 degrees about the ac3d z-axis. I hope these comments/suggestions are taken as constructive input. Thanks again for a much improved c172p 3D model. Regards, Dave P. That would involve a modification of the landing gear on the model. Or, ( i will get flame :) ) the lift on the model at cruise speed is wrong which wants more incidence.sorry it is late Cheers -- Gérard http://pagesperso-orange.fr/GRTux/ J'ai décidé d'être heureux parce que c'est bon pour la santé. Voltaire - This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100url=/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
Hi, Hi All, As we approach a new release, here is a suggestion that I think would increase the realism of our default AC. I really like the new c172p 3D model. But it seems to me that the model cruise pitch is too nose high. Here is an interesting video link of a real c172 in flight. http://www.youtube.com/watch?v=tg2zXfuywuc Nice video- but the view doesn't really shows the pitch of this aircraft. It is hardly noticable. Notice that in the video 1. the tail is higher in cruise than what we have in fgfs for the new model. 2. the nose wheel is below the main wheels in cruise. 3. in fgfs, the tail cone is presently below ground at touch down. Would it not be more realistic to rotate the 3D model about -3 or -4 degrees about the ac3d z-axis. I can't see any difference to our model. And it wouldn't be more realistic! I used original drawings by Cessna- the Cessna stands on the ground how it does to do. Only the compress animation of the frontgear isn't right yet. That's why it looks on the ground like the frontgear is lifted. In the moment the Aoa is at 112 kias around -0.36, pitch around -0.53 and the frontgear a bit lower than the maingear. Here is a pic showing it in flight: http://fgfs.i-net.hu/modules/xcgal/albums/userpics/10046/c172-pitch.jpg I didn't notice something with the cone at landing- landing speed should be around 55-60 kias. The only thing I aware of is the empty weight seems to be a bit low (1500 in fdm against 1642) I hope these comments/suggestions are taken as constructive input. Thanks again for a much improved c172p 3D model. Regards, Dave P. I wait for a comment from our c172 pilot Martin! Cheers HHS - This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100url=/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
Heiko Schulz wrote: I didn't notice something with the cone at landing- landing speed should be around 55-60 kias. The only thing I aware of is the empty weight seems to be a bit low (1500 in fdm against 1642) It does seem easy to sink the tail cone into the ground if you have much of a flare going on (just tried at K-SFO). In fact it's seemed easy to get it sitting stopped on the tail and needed a burst of power to shift it forward (although I was on Nimitz at that time, so perhaps helped). Perhaps weighted a bit aft c-of-g? But not having flown in a real 172 I can't comment if it's accurate, perhaps mr Cessna thought replacing tails would be good recurring income ;-) - This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100url=/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
One should look at the angle of attack value at cruise and see if it's as expected. The question seems to be whether the flight dynamics is wrong, or whether then aircraft is drawn right. JB -Original Message- From: James Sleeman [mailto:[EMAIL PROTECTED] Sent: Monday, December 01, 2008 7:48 PM To: FlightGear developers discussions Subject: Re: [Flightgear-devel] c172p pitch at cruise question Heiko Schulz wrote: I didn't notice something with the cone at landing- landing speed should be around 55-60 kias. The only thing I aware of is the empty weight seems to be a bit low (1500 in fdm against 1642) It does seem easy to sink the tail cone into the ground if you have much of a flare going on (just tried at K-SFO). In fact it's seemed easy to get it sitting stopped on the tail and needed a burst of power to shift it forward (although I was on Nimitz at that time, so perhaps helped). Perhaps weighted a bit aft c-of-g? But not having flown in a real 172 I can't comment if it's accurate, perhaps mr Cessna thought replacing tails would be good recurring income ;-) --- -- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100url=/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel - This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100url=/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
On 12/01/2008 07:52 PM, Jon S. Berndt wrote: One should look at the angle of attack value at cruise and see if it's as expected. True. The question seems to be whether the flight dynamics is wrong, or whether then aircraft is drawn right. Agreed, that's the right question. The answer is that the flight dynamics is unrealistic, and has been for years. Redrawing the aircraft won't help much (if any). -- The lift curve is unrealistic, which explains the observations that started this thread. -- The drag curve is unrealistic, which explains the unrealistic climb performance and unrealistic short-field landing performance. -- The effect of flaps on incidence is unrealistic. -- The effect of flaps on drag is unrealistic. -- The effect of flaps on trim is unrealistic. -- The effect of engine power is unrealistic, especially the interaction between flaps and power. -- Et cetera. You get the idea. - This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100url=/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
Re: [Flightgear-devel] c172p pitch at cruise question
Agreed, that's the right question. The answer is that the flight dynamics is unrealistic, and has been for years. Redrawing the aircraft won't help much (if any). -- The lift curve is unrealistic, which explains the observations that started this thread. -- The drag curve is unrealistic, which explains the unrealistic climb performance and unrealistic short-field landing performance. -- The effect of flaps on incidence is unrealistic. -- The effect of flaps on drag is unrealistic. -- The effect of flaps on trim is unrealistic. -- The effect of engine power is unrealistic, especially the interaction between flaps and power. -- Et cetera. You get the idea. I thought that one of the C172s had been extensively overhauled and improved in the past ... ? I've got a flight manual here. Maybe I can find time to take another look. We did have a C172 pilot a few years ago try it out and he thought it seemed pretty good. It can be tricky to make a comparison on feel, but there are some performance numbers that can be looked at. JB - This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100url=/ ___ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
