[Flightgear-devel] A load of YASim engine stuff
[This posting is directed primarily at YASim's daddy, Andy Ross, but I'll be interested in hearing from others as well.] 1. Engine Idle -- I've been spending a bit of time on the PA-28 model in YASim, and one problem is that the engine idles far too fast sitting still on the ground (around 1000 rpm, instead of 600-650 rpm). Is there any simple parameter I can tune to slow it down a bit? 2. Fuel and Oil Properties -- Secondly, I've added fuel and oil gauges to the PA28 cockpit, and it is seriously disconcerting every time I scan the panel and see the oil temperature, oil pressure, and fuel pressure all at 0 (in real life, that means imminent disaster). What do we need to do to get YASim to publish convincing values for these properties for piston engines? /engines/engine[*]/oil-pressure-psi /engines/engine[*]/oil-temperature-degf /engines/engine[*]/fuel-pressure-psi 3. Changing the Fuel Level -- Once YASim is running, it takes control of the /consumables/fuel/tank[*]/level-gal_us property (as well as the associated weight property) and will not accept changes. To simulate refueling, either in the ground or on the air, it would be nice to be able to change these values dynamically inside a FlightGear session. Thanks, and all the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] A load of YASim engine stuff
David Megginson wrote > [This posting is directed primarily at YASim's daddy, Andy > Ross, but I'll be > interested in hearing from others as well.] > > 1. Engine Idle > -- > > I've been spending a bit of time on the PA-28 model in YASim, and one > problem is that the engine idles far too fast sitting still > on the ground > (around 1000 rpm, instead of 600-650 rpm). Is there any > simple parameter I > can tune to slow it down a bit? > > 2. Fuel and Oil Properties > -- > > Secondly, I've added fuel and oil gauges to the PA28 cockpit, > and it is > seriously disconcerting every time I scan the panel and see the oil > temperature, oil pressure, and fuel pressure all at 0 (in > real life, that > means imminent disaster). What do we need to do to get YASim > to publish > convincing values for these properties for piston engines? > >/engines/engine[*]/oil-pressure-psi >/engines/engine[*]/oil-temperature-degf >/engines/engine[*]/fuel-pressure-psi > > 3. Changing the Fuel Level > -- > > Once YASim is running, it takes control of the > /consumables/fuel/tank[*]/level-gal_us property (as well as > the associated > weight property) and will not accept changes. To simulate > refueling, either > in the ground or on the air, it would be nice to be able to > change these > values dynamically inside a FlightGear session. > We discussed changing fuel levels some little while ago in the context of drop tanks. I too would like to do at least this for the Hunter model, but in lbs please NOT US gals. The other engine stuff would be nice to have as well. If Andy could find the time I certainly would be most grateful. Regards Vivian Meazza ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] A load of YASim engine stuff
David Megginson wrote: > I've been spending a bit of time on the PA-28 model in YASim, and > one problem is that the engine idles far too fast sitting still on > the ground (around 1000 rpm, instead of 600-650 rpm). Is there any > simple parameter I can tune to slow it down a bit? Not really. The propeller torque near zero airspeed is just too low right now. I'm really happy with the way the existing propeller model works under normal cases; it works backwards from an efficiency curve to come up with a model that produces good physics for simple inputs without going wacky in some important regime. It's not good with edge cases, though. One option would be to port another engine/propeller model onto the existing yasim::Thruster interface. This might not follow the "solution from known performance" idiom, but for the case of a single aircraft can probably be tuned to work better. Short term, we could try to hack in a "idle speed" or "minimum torque coefficient" or somesuch too, although even that is probably going to be difficult. > What do we need to do to get YASim to publish convincing values for > these properties for piston engines? > /engines/engine[*]/oil-pressure-psi > /engines/engine[*]/oil-temperature-degf > /engines/engine[*]/fuel-pressure-psi I'm not quite sure what convincing values for these properties would be. The pressures are pump-driven and are, or should be, static under normal conditions, right? The oil temperature can probably be driven by a low-pass-filtered output power. Maybe a tiny bit of YASim-specific Nasal glue is what's required here. > Once YASim is running, it takes control of the > /consumables/fuel/tank[*]/level-gal_us property (as well as the > associated weight property) and will not accept changes. To > simulate refueling, either in the ground or on the air, it would be > nice to be able to change these values dynamically inside a > FlightGear session. This one is much easier to fix. I proposed a Nasal-driven fuel system a few months back, and still have half-finished YASim support for it sitting in my build tree. The basic idea is that YASim merely exports an ever-increasing "consumed fuel" number for each engine. The Nasal code then poll this at some sane frequency (maybe 3 Hz), inspects configuration, subtracts the fuel from the appropriate tanks, sets engine out-of-fuel flags, and finally resets the consumed fuel numbers to zero. YASim then just reads the fuel quantities for mass calculation only. The best part is that this can be done portably. The consumed fuel properties will be missing for non-YASim aircraft and the script can simply disable itself. And for the future, arbitrarily complicated fuel flow schemes can be implemented entirely in Nasal with no FDM support needed. I'll try to get this working tonight. Andy ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] A load of YASim engine stuff
Andy Ross said: > > What do we need to do to get YASim to publish convincing values for > > these properties for piston engines? > > /engines/engine[*]/oil-pressure-psi > > /engines/engine[*]/oil-temperature-degf > > /engines/engine[*]/fuel-pressure-psi > > I'm not quite sure what convincing values for these properties would > be. The pressures are pump-driven and are, or should be, static under > normal conditions, right? The oil temperature can probably be driven > by a low-pass-filtered output power. Maybe a tiny bit of > YASim-specific Nasal glue is what's required here. > If you had an oil-pressure-psi-idle and oil-pressure-psi-maxrpm property you could then interpolate something reasonable. Oil-temperature could be hacked up from a normal maximum and some combination of rpm, time and outside temp. I'm not sure about fuel-pressure. Is that usually constant until the pump fails? Best, Jim ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] A load of YASim engine stuff
Andy Ross > David Megginson wrote: > > I've been spending a bit of time on the PA-28 model in > YASim, and one > > problem is that the engine idles far too fast sitting still on the > > ground (around 1000 rpm, instead of 600-650 rpm). Is there > any simple > > parameter I can tune to slow it down a bit? > > Not really. The propeller torque near zero airspeed is just > too low right now. I'm really happy with the way the > existing propeller model works under normal cases; it works > backwards from an efficiency curve to come up with a model > that produces good physics for simple inputs without going > wacky in some important regime. It's not good with edge > cases, though. > > One option would be to port another engine/propeller model > onto the existing yasim::Thruster interface. This might not > follow the "solution from known performance" idiom, but for > the case of a single aircraft can probably be tuned to work better. > > Short term, we could try to hack in a "idle speed" or > "minimum torque coefficient" or somesuch too, although even > that is probably going to be difficult. > > > What do we need to do to get YASim to publish convincing values for > > these properties for piston engines? > > /engines/engine[*]/oil-pressure-psi > > /engines/engine[*]/oil-temperature-degf > > /engines/engine[*]/fuel-pressure-psi > > I'm not quite sure what convincing values for these > properties would be. The pressures are pump-driven and are, > or should be, static under normal conditions, right? The oil > temperature can probably be driven by a low-pass-filtered > output power. Maybe a tiny bit of YASim-specific Nasal glue > is what's required here. So far as oil-pressure-psi is concerned a normalised number increasing with rpm should do the trick - we can then set max/min values. Oil temperature h - a function of OAT and rpm and any movable cowling - too engine specific - too difficult? > > Once YASim is running, it takes control of the > > /consumables/fuel/tank[*]/level-gal_us property (as well as the > > associated weight property) and will not accept changes. > To simulate > > refueling, either in the ground or on the air, it would be > nice to be > > able to change these values dynamically inside a FlightGear session. > > This one is much easier to fix. I proposed a Nasal-driven > fuel system a few months back, and still have half-finished > YASim support for it sitting in my build tree. The basic > idea is that YASim merely exports an ever-increasing > "consumed fuel" number for each engine. The Nasal code then > poll this at some sane frequency (maybe 3 Hz), inspects > configuration, subtracts the fuel from the appropriate tanks, > sets engine out-of-fuel flags, and finally resets the > consumed fuel numbers to zero. YASim then just reads the > fuel quantities for mass calculation only. > > The best part is that this can be done portably. The > consumed fuel properties will be missing for non-YASim > aircraft and the script can simply disable itself. And for > the future, arbitrarily complicated fuel flow schemes can be > implemented entirely in Nasal with no FDM support needed. That's very sophisticated. All I need is the ability to set fuel values, but this would be very interesting. > I'll try to get this working tonight. Thank you Regards Vivian Meazza ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] A load of YASim engine stuff
Andy Ross wrote: I'm not quite sure what convincing values for these properties would be. The pressures are pump-driven and are, or should be, static under normal conditions, right? Not quite. First, I think that the main pumps run off the accessory drive (I'll have to check), so they will be affected by the crankshaft speed. Second, and more importantly, fuel pressure changes as you move the mixture. I could probably calibrate these off the fuel and oil flow, though I'd have to do some more research (in real life, I think that some fuel pressure gauges are actually calibrated as fuel flow gauges). The oil temperature can probably be driven by a low-pass-filtered output power. Maybe a tiny bit of YASim-specific Nasal glue is what's required here. Oil temperature depends on outside air temperature and calibrated airspeed as well. For bigger engines with cowl flaps, you also have to take those into account. An engine will get very hot in a steep, slow power climb; on a cold winter day, it's a real challenge just to get the engine warm enough to evaporate any water out of the system. The best part is that this can be done portably. The consumed fuel properties will be missing for non-YASim aircraft and the script can simply disable itself. And for the future, arbitrarily complicated fuel flow schemes can be implemented entirely in Nasal with no FDM support needed. That's a good idea. Most low-wing planes, like the Piper Cherokee, do not have a "both" fuel selector setting -- the engine is always drawing from a single tank (left or right main, in my case; also left or right tip for fancier planes). It's pretty unrealistic to see both fuel needles moving down together. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] A load of YASim engine stuff
Jim Wilson wrote: If you had an oil-pressure-psi-idle and oil-pressure-psi-maxrpm property you could then interpolate something reasonable. Oil-temperature could be hacked up from a normal maximum and some combination of rpm, time and outside temp. I'm not sure about fuel-pressure. Is that usually constant until the pump fails? It varies with throttle and mixture. At 75% power, mine indicates about 5 psi running lean of peak or about 7 psi running rich of peak. I don't remember what it indicates in a full-rich, full-power climb. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] A load of YASim engine stuff
On Tue, 02 Mar 2004 18:53:34 -0500, David Megginson <[EMAIL PROTECTED]> wrote: It varies with throttle and mixture. At 75% power, mine indicates about 5 psi running lean of peak or about 7 psi running rich of peak. I don't remember what it indicates in a full-rich, full-power climb. Is it usual to make the approach or initial climb-out with the mixture set full rich and prop fine in your aircraft? I'm just wondering because it's part of the downwind and pre-take off checks for the aircraft I fly (although I skip over the prop check because it's not CS). All the best, Matt --- # Begin Script to show all SCO IP in linux #!/bin/bash # End Script to show all SCO IP in linux ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] A load of YASim engine stuff
Matthew Law wrote: Is it usual to make the approach or initial climb-out with the mixture set full rich and prop fine in your aircraft? I'm just wondering because it's part of the downwind and pre-take off checks for the aircraft I fly (although I skip over the prop check because it's not CS). Like the Archer, the Warrior has a fixed-pitch prop. You have to go up to the Archer (or the now-discontinued Pathfinder) to get a CS prop on a PA-28. For constant-speed props, there are a lot of people who argue that, while you should take off at max RPM, climb-out with the prop at maximum RPM is not that great an idea, while approach at max RPM is downright moronic (it just makes a lot of noise and pisses off the general public, who then proceed to try to close the airport). I highly recommend that you spend a few evenings reading John Deakin's engine articles (start from the oldest ones at the bottom): http://www.avweb.com/news/columns/182146-1.html For the record, I fly lean of peak, wide-open throttle regularly in cruise -- my engine runs cooler, I burn a lot less gas to produce the same power (about 8.5 gph instead of 10 gph), my spark plugs don't foul, and the risk of CO poisoning virtually vanishes, so there's not much to dislike about it. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] A load of YASim engine stuff
David Megginson wrote: Like the Archer, the Warrior has a fixed-pitch prop. You have to go up to the Archer (or the now-discontinued Pathfinder) to get a CS prop on a PA-28. For "go up to the Archer", read "go up to the Arrow". All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] A load of YASim engine stuff
Matthew Law wrote: Is it usual to make the approach or initial climb-out with the mixture set full rich and prop fine in your aircraft? I'm just wondering because it's part of the downwind and pre-take off checks for the aircraft I fly (although I skip over the prop check because it's not CS). For takeoff the mixture should be set for maximum power.. aka on a hot day or at high altitude, if you put the mixture full forward, you will actually decrease the amount of power available and increase your takeoff distance.. For landing it is advisable to make sure that your mixture is rich enough to do a go around with full power. Ryan ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] A load of YASim engine stuff
Ryan Larson wrote: For landing it is advisable to make sure that your mixture is rich enough to do a go around with full power. Unless you choose to do overshoots pushing forward both levers (or knobs, in a Cessna). I still go to full rich for descent and landing, but it certainly doesn't do my engine or plugs any good squirting all that extra, cold, unburned gas in suddenly, especially when the engine is already cooling fast from the reduced power. I don't want to change my procedure for normal flights, though, until I have a chance to do at least a few dozen practice overshoots with the new technique. Note that that's the same argument people use for setting high RPM on constant-speed propellers, but again, the alternative is to get used to pushing both (or all three) levers together for an overshoot. In a Cessna 172, you have to get used to pushing the carb heat back in anyway to avoid the risk of detonation on the full-rich climbout (Pipers don't generally use carb heat on approach), so it's not unprecedented. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] A load of YASim engine stuff
On Thursday 04 March 2004 01:16, Ryan Larson wrote: > Matthew Law wrote: > > Is it usual to make the approach or initial climb-out with the mixture > > set full rich and prop fine in your aircraft? I'm just wondering > > because it's part of the downwind and pre-take off checks for the > > aircraft I fly (although I skip over the prop check because it's not CS). > > For takeoff the mixture should be set for maximum power.. aka on a hot > day or at high altitude, if you put the mixture full forward, you will > actually decrease the amount of power available and increase your > takeoff distance.. > > For landing it is advisable to make sure that your mixture is rich > enough to do a go around with full power. > > Ryan I've got problems with the mixture on the Comper Swift, if anyone could have a look at it. The mixture needs to be set to about half of what I'd expect and the fuel consumption seems to be about double the figures I got for the engine. Other than that, the engine power and rpms are about right. I can't help thinking this might be due to the geared prop as the ratios seem close. LeeE ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] A load of YASim engine stuff
David Megginson writes: > For the record, I fly lean of peak, wide-open throttle regularly in cruise > -- my engine runs cooler, I burn a lot less gas to produce the same power > (about 8.5 gph instead of 10 gph), my spark plugs don't foul, and the risk > of CO poisoning virtually vanishes, so there's not much to dislike about it. > >From a non-pilot engineer's point of view this makes perfect sense. At wide-open >throttle you've reduced the pumping losses, and by running lean of peak you increase >the engine's thermal efficiency. The key is not to go so lean that combustion >becomes unstable. This is effectively how diesel engines are controlled (without the >lean combustion stability limits inherent in homogenous-charge gasoline engines), and >is one of the reasons why they are more efficient than their gasoline cousins. >Diesels are much more popular in private cars in Europe than in the States - my wife >drives a small, 1.4litre diesel hatchback, and this is regarded as perfectly normal. >Of course, it's possible that my perception of the States as diesel-hating gasoline >guzzlers is out of date by now! The reason for the lack of lean-burn cruise in most current automotive gasoline engines is entirely due to emissions regulations. Of the three main pollutants legislated against, two (unburned hydrocarbons [HC] and CO) must be oxidised (to H2O and CO2) and one (NOx) must be reduced (to N2). Running the engine at a stoichiometric (just the correct amount of oxygen for complete combustion) air-fuel ratio and using a 3-way catalyst allows an order of magnitude reduction of these pollutants post catalyst. Running lean and trying to reduce NOx in an oxygen rich exhaust stream has been likened to drying one's washing in a rainstorm. An effective lean NOx trap is one of the 'holy grails' of aftertreatment engineering, and would probably allow an immediate reduction of at least 10% in fuel consumption from new gasoline engines calibrated for lean cruise if available, and probably more in the future since lean-burn stability would inevitably receive more design focus. I'm not entirely sure what the current and future legislative landscape looks like as far as general aviation is concerned - are you likely to face emissions regulations in the near future? I'm pretty sure they're starting on the bikers now. Cheers - Dave ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
