Re: [Flightgear-devel] FDMs and external atmosphere
Andy Ross writes: > Look at the wind over ground at the current location. Calculate > the up- or down-slope of the ground in that direction. Figure out > an up or downdraft based on the amount of air that must be > vertically displaced. I thought of looking at the surface normal, but we'd have to sample over a wider area to know if we're looking at a ridge or just a little bump. All the best, David -- David Megginson, [EMAIL PROTECTED], http://www.megginson.com/ ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] FDMs and external atmosphere
David Megginson wrote: > Ralph Jones writes: > > It would, indeed, be nice to have a vertical velocity model for simulating > > soaring flight. I'm still trying to run down stability derivatives for my > > sailplane! > > It will be easy to allow you to specify up- or down-drafts for > specific areas; it will be much harder to have FlightGear figure them > out itself, but it might still be doable. Doing this "right", of course, is a job for 2000 CPU supercomputers. But it might be OK for use to cheat a little. How about this: Look at the wind over ground at the current location. Calculate the up- or down-slope of the ground in that direction. Figure out an up or downdraft based on the amount of air that must be vertically displaced. Look at the amount of sunlight falling on the ground, maybe combined with an albedo value based on the terrain type and a cloud layer effect for shadow. This gives you a heat flux. Combine that with the air temperature on the ground to figure out how much air needs to be flowing upward to carry this heat away (this is going to require some hand waving about the uplift velocity as a function of temperature difference). This number should add to the turbulence as well. This won't take into account a whole range of second-order effects, like nearby mountain ridges, etc... But it might match reasonably well to a sailplane pilots intuition about where the updrafts "should" be. Not being a sailplane pilot, I couldn't say. :) Andy -- Andrew J. RossNextBus Information Systems Senior Software Engineer Emeryville, CA [EMAIL PROTECTED] http://www.nextbus.com "Men go crazy in conflagrations. They only get better one by one." - Sting (misquoted) ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] FDMs and external atmosphere
Ralph Jones writes: > It would, indeed, be nice to have a vertical velocity model for simulating > soaring flight. I'm still trying to run down stability derivatives for my > sailplane! It will be easy to allow you to specify up- or down-drafts for specific areas; it will be much harder to have FlightGear figure them out itself, but it might still be doable. All the best, David -- David Megginson, [EMAIL PROTECTED], http://www.megginson.com/ ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] FDMs and external atmosphere
At 07:36 AM 5/15/2002 -0400, you wrote: >Jon Berndt writes: > > > Yes. We've got hooks in JSBSim to add in the effects of turbulence, but > > the math model driver for turbulence can be complicated. It's being worked > > on, albeit slowly. > >When you're ready, let me know, and I'll add a normalized turbulence value >(0:1) to FGEnvironment. Ditto for YASim (i.e. I'll add it as soon as >*any* FDM supports turbulence). > >By the way, one of my more immediate goals is adding variable winds as >a complement to gusting winds. I might also add variability for >up/down drafts. It would, indeed, be nice to have a vertical velocity model for simulating soaring flight. I'm still trying to run down stability derivatives for my sailplane! rj ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] FDMs and external atmosphere
Jon Berndt writes: > Yes. We've got hooks in JSBSim to add in the effects of turbulence, but > the math model driver for turbulence can be complicated. It's being worked > on, albeit slowly. When you're ready, let me know, and I'll add a normalized turbulence value (0:1) to FGEnvironment. Ditto for YASim (i.e. I'll add it as soon as *any* FDM supports turbulence). By the way, one of my more immediate goals is adding variable winds as a complement to gusting winds. I might also add variability for up/down drafts. All the best, David -- David Megginson, [EMAIL PROTECTED], http://www.megginson.com/ ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] FDMs and external atmosphere
Simon Fowler writes: > Are there any plans for adding support for the interesting bits of > weather to this model? (ie, storms, realistic winds that actually > relate to the rest of the weather model, etc) We cannot do fully realistic winds, at least not with the amount of computing power available to us today. FGEnvironment does support gusting winds, not just in theory but in practice (i.e. they bounce the plane around and knock it off course) -- that's something we didn't have before. > There seemed to be support for them in the CM weather stuff, and it > seems a little redundant to be adding a new, less capable model when > there's one already there . . . WeatherCM currently has a bitbucket to hold the bounds of a thunderstorm and a random calculation for lightning probability, but that's only a tiny step -- most of the actual work of modelling thunderstorms (and other weather phenomena) needs to be done for either weather subsystem. All the best, David -- David Megginson, [EMAIL PROTECTED], http://www.megginson.com/ ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] FDMs and external atmosphere
> Are there any plans for adding support for the interesting bits of > weather to this model? (ie, storms, realistic winds that actually > relate to the rest of the weather model, etc) Yes. We've got hooks in JSBSim to add in the effects of turbulence, but the math model driver for turbulence can be complicated. It's being worked on, albeit slowly. Jon smime.p7s Description: application/pkcs7-signature
Re: [Flightgear-devel] FDMs and external atmosphere
On Wed, May 15, 2002 at 06:24:55AM -0400, David Megginson wrote: > Now that the environment subsystem can manage its own atmosphere model > (at least up to 60,000 ft or so), I've added an option to use that > model instead of the built-in model in each FDM (the default is still > to let the FDM manage the atmosphere). If you run with > > fgfs --prop:/environment/params/control-fdm-atmosphere > > JSBSim and YASim will bypass their own atmosphere models use the > values from the environment subsystem. > > Currently, YASim seems to be working fine with this after a few lines > of code changes, but JSBSim is not. JSBSim has built-in support for > an external atmosphere, and the values seem to be getting through OK > (after removing some spurious set_* methods), but the trimming routine > gets caught in a loop. I'd be very grateful if Tony and others could > look at this and figure out what the problem might be. > > Why use an external atmosphere model at all? Of course we want to be > able to control the atmosphere rather than always flying at the > equivalent of 15 degC temperature, 28.5 inHG, and 0.00237 slugs/ft^3 > density at sea level. We could do that by providing the sea-level > defaults and letting the FDM's atmosphere models calculate the values > at altitude (it would also require a few lines of code change), but > unfortunately, the FDMs are not the only subsystems that need > atmosphere information -- we also need it for the some of the > instruments, for the engine model (which might not always be > built-into the FDM), for cabin pressurisation, and for weather reports > like the ATIS, for icing, and who knows what else. > Are there any plans for adding support for the interesting bits of weather to this model? (ie, storms, realistic winds that actually relate to the rest of the weather model, etc) There seemed to be support for them in the CM weather stuff, and it seems a little redundant to be adding a new, less capable model when there's one already there . . . Simon -- PGP public key Id 0x144A991C, or ftp://bg77.anu.edu.au/pub/himi/himi.asc (crappy) Homepage: http://bg77.anu.edu.au doe #237 (see http://www.lemuria.org/DeCSS) My DeCSS mirror: ftp://bg77.anu.edu.au/pub/mirrors/css/ msg06064/pgp0.pgp Description: PGP signature
[Flightgear-devel] FDMs and external atmosphere
Now that the environment subsystem can manage its own atmosphere model (at least up to 60,000 ft or so), I've added an option to use that model instead of the built-in model in each FDM (the default is still to let the FDM manage the atmosphere). If you run with fgfs --prop:/environment/params/control-fdm-atmosphere JSBSim and YASim will bypass their own atmosphere models use the values from the environment subsystem. Currently, YASim seems to be working fine with this after a few lines of code changes, but JSBSim is not. JSBSim has built-in support for an external atmosphere, and the values seem to be getting through OK (after removing some spurious set_* methods), but the trimming routine gets caught in a loop. I'd be very grateful if Tony and others could look at this and figure out what the problem might be. Why use an external atmosphere model at all? Of course we want to be able to control the atmosphere rather than always flying at the equivalent of 15 degC temperature, 28.5 inHG, and 0.00237 slugs/ft^3 density at sea level. We could do that by providing the sea-level defaults and letting the FDM's atmosphere models calculate the values at altitude (it would also require a few lines of code change), but unfortunately, the FDMs are not the only subsystems that need atmosphere information -- we also need it for the some of the instruments, for the engine model (which might not always be built-into the FDM), for cabin pressurisation, and for weather reports like the ATIS, for icing, and who knows what else. All the best, David -- David Megginson, [EMAIL PROTECTED], http://www.megginson.com/ ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
