Re: [Flightgear-users] Building Fences
Christian Mayer writes: Really? I can't think of a reason why modern OpenGL accellerators take longer to display transparnet textures than solid ones (except of a harmless hardware optimized blending function). ? Transparency require a frame buffer read, a multiply, and a frame buffer write. Opacity requires a frame buffer write. I've only done software renderers, but I know a little bit about some of the issues involved and there's quite a bit of cache contention that happens when you start doing read/modify/write cycles, beyond the fact that you have to do the read in the first place. We like to think that our modern video hardware is infinitely fast, but it ain't. I don't know whether FlightGear is doing any of this stuff but back on the main processor transparency also means that there's a whole level of occlusion culling that can't occur. Dan ___ Flightgear-users mailing list Flightgear-users@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-users 2f585eeea02e2c79d7b1d8c4963bae2d
[Flightgear-users] recommendation for joystick/pedals for fgfs/Linux?
Vassilii Khachaturov writes: I'm looking for a decent set of joystick and pedals to use with FG on a Linux x86 box. I grabbed an el-cheapo twist joystick, a hammer and pair of pliers, and a little bit of hardware and came up with: http://www.flutterby.com/archives/comments/8207.html It's non-centering, 'cause I built it as small helicopter controls, and I have to hold it roughly centered while I power up or the el-cheapo firmware gets confused, but it was a great getting started experience. When I've got a little time, I want to take a couple of Atmel chips and some old mechanical mice and see if I can build a 10 bit per channel high quality setup, but except for the notes there about pedal construction I'll keep pretty much the same mechanical aspects (may also end up building a throttle and thumb switches into the collective). When I get there, what I've got now works fairly well. Dan ___ Flightgear-users mailing list Flightgear-users@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-users 2f585eeea02e2c79d7b1d8c4963bae2d
RE: [Flightgear-users] So what do you fly?
Shelton D'Cruz writes: I would like to compile such a list so that newbies now exactly the status of each aircraft, however, others here don't think thats neccessary so I will give it a miss. If it's kept up-to-date, I'd love to see such a list, for two reasons: 1. I want to know if the missing things I'm seeing are flaws in my knowledge of aircraft and aviation, or in the model. 2. It might make a good list for volunteers to dive in on. Dan ___ Flightgear-users mailing list Flightgear-users@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-users 2f585eeea02e2c79d7b1d8c4963bae2d
RE: [Flightgear-users] Helicopters in Flight Gear
Bill Galbraith writes: A brief review: Helicopter controls (longitudinal cyclic, lateral cyclic, collective, and pedals) will all be trimmed at different locations for different conditions of airspeed, altitude, weight, center of gravity, and pilot weight. I think Andy Ross's comment probably showed me why, even though I've gotten pretty darned good with the helicopters in FlightGear, I'm having trouble keeping the airport in sight while hovering in X-Plane. The joystick I built has no centering (based on a conversation I read somewhere about smaller helicopters than you're modeling), and I'll bet that X-Plane is floating the joystick model to keep trim center at joystick center, and FlightGear isn't. Thus on my non-centering joystick I'm able to track trim center on FlightGear, but on X-Plane when I try to do that I'm chasing something that it's trying to move around. One can envision a screw driven by a stepper motor, with a V attached to block on the screw, held on with an electromagnet. I was actually thinking that you could drive the spring attachments with a stepper motor connected directly either with friction or a toothed track, and have the trim release button just remove power from the stepper motors (or, if the friction of the unpowered steppers is too high, lift them so they disengage), so that the spring attachments can slide freely. Yeah, not something you can do for a $100 joystick, unless you just so happen to have a couple of beefy stepper motors and a controller lying around [grin]. Once again I'm finding that I need to go explore a real aircraft... Thanks! ___ Flightgear-users mailing list Flightgear-users@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-users 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-users] Re: Helicopters in Flight Gear
Georg Vollnhals writes: If I understand the right way what he tries to do is calculating the forces and effects of the rotor by calculating it for every blade in discrete time-steps and from this calculation the resulting forces on the helicopter. I haven't downloaded the code yet, my day job is currently funded out of my pocket and I'd rather do something that takes different neurons at the end of the day, but it sounds like this is the way that X-Plane does it, and on modern hardware it doesn't seem that unreasonable. It's also going to be very useful to be calculting lift-drag information for varying sections when we start to get a realistic engine model, when we start to model flapping, and when we model mast tilt and the effects of forward motion. So I'm not going to call this too complex immediately. However, next up on my technical reading list is NACA Technical Note 4357, Lift and Profile-Dra Characteristics of an NACA 0012 Airfoil section as Derived From Measured Helicopter Rotor Hovering Performance, which seems to reduce a lot of stuff down to a simple table that could be interpolated on. I think the other must-read is NASA Contractor Report 177476, aka Minimum Complexity Helicopter Simulation Math Model. Both of these are freely distributed PDFs that I eventually tracked down on the net, but they were hard to find so if you don't have them I'll see about putting them somewhere that people can get to them. As I've said before, last time I looked seriously at aerodynamics modeling was two and a half decades ago when I was 12 years old, but a lot of it, especially when dummied up from tables for a simulator, isn't that complex. What's hard is that we're trying to approximate realism, and as such are more interested in a feel. I've sat in the middle back seat of an A*Star once, with a pilot who probably had a thousand hours under his belt. No matter what I code up, even if it's a full on fluid dynamics simulation of what's going on, I'm not going to know if it's right or wrong because right or wrong isn't whether it models the physics correctly, it's whether it feels like flying a real helicopter. Dan ___ Flightgear-users mailing list Flightgear-users@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-users 2f585eeea02e2c79d7b1d8c4963bae2d
[Flightgear-users] Re: Helicopters in Flight Gear
Melchior FRANZ writes: There is no ground effect currently in place at all. I've been looking at the math to model downwash, and I think there may be some relatively easy kludges to slap into place to both handle ground effect, and maybe even VRS. Oh for unlimited time to work on this stuff, I've got some good ideas to do blade lift modeling, but the last thing I want to do after a day of programming is program more. I can't make any promises as to time, but I'll take gradual steps towards getting a copy of the code on my machine and diddling with it. Is there a real helicopter pilot on the list who'd be interested in taking my changes and saying yes, this is realistic or not on anything I've ever flown? On another front: I spent a little time today with the Bell/Textron drawings and Blender, and I'm starting to see a 206 take shape on my screen. Despite my years in graphics (several renderers, both real-time and not, and experience with writing animation systems), I've never done modeling before, and I may be being too conservative on polygons. And I was so happy to get a basic fuselage together that I was getting really optimistic, now I'm down to the nitty gritty of two-sided doors. And aaargh I wish Blender would just let me say match the normal for the vertex on this object to the one for the vertex on that one... You do texture by poly color, and so far I'm just doing a white fuselage. Should I bother to put UV coordinates on things, or is trying to texture these aircraft just too heavyweight for now? If I get a little better at modeling, maybe I'll try to include one of the stock paint schemes in the model, at the expense of polys. Can I just make the doors double-sided for now, or should I model both an interior and exteror? I guess the downside is that the interior of the doors ends up the same color as the exterior, right? Is it reasonable to end up with two blades by just willy nilly deleting from your blade model, or is there a hidden gotcha intere? Aaaand, talk to me about shadows... Thanks! Dan ___ Flightgear-users mailing list Flightgear-users@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-users 2f585eeea02e2c79d7b1d8c4963bae2d
[Flightgear-users] Re: Helicopters in Flight Gear
Melchior FRANZ writes: http://baron.flightgear.org/pipermail/flightgear-devel/2003-October/021940.html Thanks. I think I'd seen that message before, but figured it was two years old and something must have happened since then. Having read through that full thread, I'm now thinking that maybe the better thing for me to do would be to buy X-Plane (or, choke, MSFS) for something to fly in the mean-time, and start trying to understand helicopter aerodynamics and eventually, when life slows down enough that I feel like coding in my spare time and I know quite a bit more about helicopters than I do now, writing another helicopter flight model from scratch. In digging through those messages, it seems like an awful lot still datesback to when the flight model was an integer/fixed-point i386 based platform, and some of the issues with my expectations of helicopter flight versus what's actually happening look like they come from limitations of that model, and not just 'cause I don't have a clue (although that is true generally). But at least it explains why I've had *zero* luck trying to autorotate... Dan ___ Flightgear-users mailing list Flightgear-users@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-users 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-users] Helicopters in Flight Gear
Arnt Karlsen writes: ..free in n the GPL kinda way is why Microsoft is running scared throwing millions to people like Ralph Yarro and Darl McBride for litigating us, details at http://groklaw.net/ . Oh, I'm a firm believer in both GPL software and as a license for many of my personal efforts. I've given time and money to various open source projects, have worked with open source developers as contractors to make sure that their software contains the features I needed, run GNU/Linux on several machines, try to not run proprietary software if there's a remotely capable open source alternative, and evangelize whenever I can. I have Mac, XP and Linux in my house, and for personal projects the Linux machines get used most often. But I know that unless I'm willing to either write the code or pay someone to write it for me, it's unreasonable for me to expect that those features will magically appear. And it's why, as a function of using FlightGear, I'm trying to teach myself enough Blender (one of the projects I gave money to to get GPLed) to fill in some of the missing pieces. ObFlightGear: I used the import AC3D feature of Blender today to load in the Bo105 and see how it's constructed. It was eye opening, I now need to go through the Bell 206 XML to see what model parts are being used, and to see if some of the attributes can be used to select things which change aspects of the outside of the helicopter geometry, such as the high versus low skid gear (floats should be just something I can invis). And I didn't immediately see if the Bo105 had mast tilt the way that the 206 does. Dan ___ Flightgear-users mailing list Flightgear-users@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-users 2f585eeea02e2c79d7b1d8c4963bae2d
[Flightgear-users] Helicopters in Flight Gear
This message should probably only be written after I've spent some extensive time digging through the source code, and it should probably go to the flightgear-dev of flightgear-flightmodel, but I've got a whole bunch of conflicting and not terribly well thought out questions running through my head, and I'm looking for the next steps (which may include X-Plane or MSFS, although I'd love to find a way to channel some energy back into this project). I've built myself some helicopter controls[1] and have been trying to fly the Bo105 with some success. I've been in a real helicopter once, for a tourist flight from the back seat, so I'm trying to figure out what should be happening from written descriptions. The first thing I'd like to find are some less capable helicopters. I've only really played heavily with the Bo105, but the power to weight ratio seems to let me fill all the seats with full sized passengers, take on a full load of fuel, and hover from good ol' Runway 29 on KSFO up to a few thousand feet AGL... I've only started to look at some of the issues of helicopter simulation, and I haven't been anywhere near the stick on a real one, but much of the reading I'm doing talks about the challenge of getting out of ground effect (admittedly some of those tales have been about overloaded takeoffs from Vietnam LZs in Huey model Ds[2]), and I'd like to experience the challenge of short field take-offs and landings with something that can't hover out of ground effect. So, is anyone working on new helicopters? If I'm willing to ignore the visuals, is there an easy place to start to plug in numbers like airfoil curves, rotor sizes, engine power, and information about fixed surfaces, or is that sort of thing better done by someone who knows what should happen? Does anyone know if the ground effect effects currently in place are moderately realistic? Since I'm taking on helicopters, I'm also interested in low level scenery. Is the San Francisco Bay Area the only place that's fleshed out? Is there a current simple guide for how to build models and scenery like that for an area, perhaps with some sample buildings or aircraft for Blender so that I could use them to get my units and axes right? How about helping the simulator with collision detection and level of detail or visibility frustums? Aaaand, are there general guidelines for aircraft and scenery construction? Ideas on poly counts and such? If I sat down with Blender and the drawings from the Bell website[3] and turned out a 206 to put an airframe on the flight model that's currently in FlightGear is there anything I should know? (And I suppose I should probably see what Bell's model licensing terms are...). Thanks for any encouragement or leads! Dan [1] http://www.flutterby.com/archives/comments/8207.html [2] http://www.vietnammoments.com/ [3] http://www.bellhelicopter.textron.com/en/aircraft/commercial/prodSpecs206B-3.cfm ___ Flightgear-users mailing list Flightgear-users@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-users 2f585eeea02e2c79d7b1d8c4963bae2d
RE: [Flightgear-users] Helicopters in Flight Gear
Bill Galbraith writes: Helicopter simulation in FlightGear, or any other 'simple' simulation program, is difficult. [grin] Understatement. Yeah, when I was a kid I used to build models and read through aeronautics books. Then I discovered computers, and those neurons went unused for two and a half decades, but when I rediscovered helicopters and FlightGear and started thinking this flight model might be open to improvement I looked at simple solutions, found a couple of NACA lift/drag curves for airfoils oft-used in helicopters (NACA0012 was the first one that came up multiple times), began to work out the geometry and the simpler bits of the math, and started to come up against the swept wing issues... And then decided that maybe a better start would be to figure out how to use Blender and donate a JetRanger model to the cause... With a joystick that is spring-centered, there would be only one condition where the controls would be centered. I tried to fly with a standard spring-loaded twist joystick for about 15 minutes, quit and immediately started cutting lumber for real controls. My current controls are a non-centering full-length cyclic, pedals (which need their sensitivity upped just a little), and a collective that needs a little less drag. Better balancing on the counter-spring for that is scheduled for this weekend, and realizing that hovering really required using the collective pretty much constantly improved my abilities dramatically. One of the questions I've got is: I've tried to work through the linkages that'd make up helicopter controls, and every way I come up with there's some force feedback. Am I hallucinating, or is it subtle enough or played out in such a way that it's just better to build controls which don't have springs? I can't commit to any schedule for completion, but there are enough people pressing for it now that I need to get off my butt and just do it. Keep your eyes open for an announcement in the coming weeks. I'm in heads-down mode for a 3d animation software startup, so I'm loathe to commit to writing code (and totally understand the unwillingness to commit to a free project, and I've still got quite a bit of playing with the Bo105 before I've flown that out), but if you want a second set of eyes from someone who at least has been through the 3d graphics end of the pipeline pretty heavily, and 25 years ago (when I was 12) knew what a Reynolds number was, give a holler. Dan ___ Flightgear-users mailing list Flightgear-users@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-users 2f585eeea02e2c79d7b1d8c4963bae2d
