RE: [Flightgear-devel] [OT] Commercial Ticket..
David M. wrote: I tried to fix this problem in JSBSim a year or two ago, and I seem to recall that no one on the flight model list could quite figure out how to code it back then. I also took a stab at YASim, and failed just as miserably. Neither model is set up to have the propeller driving the engine rather than the engine driving the prop. The rule of thumb for pilots is that a windmilling propeller creates as much drag as a disc of the same size, but that's too vague for modelling (plus, it doesn't handle the partial-windmilling situation). What we need to figure out is how much drag we get from the propeller turning the crankshaft, compressing the cylinders, and spinning the accessory drives (vacuum pump, alternator, etc.). Curt wrote: It very well could be a model setup issue at which point it's probably beyond my ability to debug, but with the JSBSim c310, I took off, climbed to a comfortable altitude and speed, and chopped the throttle on my right engine. Then I slowly pitched up to bleed off speed little by little. As the speed bled off, I held my heading with rudder and kept the wings level with aileron. From the readme: Minimum single-engine control speed (Vmca): 75 KIAS However, I was able to fly right through this until I got the stall horn, (about 60 kts?) and all the time, the rudder had plenty of effectiveness to hold heading. In the real thing (assuming the README is correct) at about 75 knots the rudder loses enough effectiveness to hold heading against the one good engine at full throttle and you begin an uncontrollable yaw. This doesn't happen right now in the JSBSim C310 anyway. As for the -310, I think we may have fixed both the propeller model and the stability issue. If someone wants to try out the C-310 doing the same test that Curt did above, I'd be interested to hear the results. I'll get to it sooner or later, but if someone else wants to grab the aircraft from JSBSim CVS and get the modified FGPropeller.cpp from JSBSim CVS, go ahead. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
David Megginson wrote: When you shut down the engine in YASim, the propeller does not windmill -- it just slowly spins down and stops. Probably because of the internal engine friction, I was looking at the propeller only. What's the right windmilling RPM? I can tune, but need numbers. :) Andy ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
Andy Ross wrote: Probably because of the internal engine friction, I was looking at the propeller only. What's the right windmilling RPM? I can tune, but need numbers. :) The higher the airspeed, the higher the windmilling RPM. Using my very weak math and physics skills, a fixed 60-inch-pitch prop is going to want to spin about 1215 rpm at 60 kt, 1620 rpm at 80 kt, 2025 rpm at 100 kt, and about 2430 rpm at 120 kt, but obviously, in every case, it's going to be slowed down by the engine and accessories. I don't know any general rule, but when I'm approaching at 70 kcas and 1500 rpm (which is about neutral thrust), then I cut the engine to idle on short final, my RPM drops to around 1100-1200 rpm (still at 70 kt) and the plane starts to sink like a rock. On the ground, standing still, my idle RPM is only around 500-600 rpm. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
Well Done! All the best, Matt. On 16:11 Wed 04 Feb , Ryan Larson wrote: I just got back from taking my Commercial Pilot, Airplane Multiengine Land checkride, and I am happy to say that I passed! Doing a single engine ILS down to minimums is lots of fun! I took the test in a Piper Aztec (PA23-250). The hardest part of the checkride was trying to get the aircraft back into the hanger without hitting anything. The area in front of the hanger was shear ice. As for the written test, I got a 92. Ryan ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
There's also various scenarios of asymetric thrust - two running engines but one running roughly or not developing as much power for a plethora of possible reasons. These incidents have killed many pilots on take off as they think they have plenty of power, and they do, but the situation easily gets out of hand and shortens the flight :-) All the best, Matt On 20:57 Wed 04 Feb , Jon Berndt wrote: Aha! OK, I would call that engine-out experience. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
Andy Ross wrote: That's no doubt true, but hopefully it's more a lack of tuning than it is a fundamental flaw. For the specific case of YASim: the asymmetric thrust effects should be more or less correct as-is, because it applies the force at the location of the engine. The blue line speed is almost certainly wrong, but should be relatively easy to find by tuning the rudder effectiveness only. The thrust from the good engine is only half the asymmetry -- the other half is the drag from the windmilling engine (until the pilot feathers the propeller). All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] [OT] Commercial Ticket..
The thrust from the good engine is only half the asymmetry -- the other half is the drag from the windmilling engine (until the pilot feathers the propeller). Good point. That's something that's also not too hard to fix. I could not (yet) find my NACA report on the light twin, but here are some interesting numbers: Cn_beta for some aircraft (per rad): Navion: 0.071 (Raymer ?) C-172p (JSBSim, from Raymer): -0.349 -0.0205 0 0 0.349 0.0205 This is roughly 0.06. Cherokee (McCormick): 0.067 C-310 (JSBSim): 0.1444 This is twice as high as the other aircraft. It could be due in some measure to a larger vertical tail, but I wonder if perhaps this value is too high? When coupled with the correction of drag due to prop, then I suspect we'll be a lot closer. Thanks for pointing this out, and I am going to submit this to our bug tracker so it doesn't get lost. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
Jon Berndt wrote: How do we not work well in this case? Do you notice a specific inadequacy? Yes -- neither JSBSim nor YASim does a good job generating drag for a windmilling prop. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
Jon Berndt wrote: The thrust from the good engine is only half the asymmetry -- the other half is the drag from the windmilling engine (until the pilot feathers the propeller). Good point. That's something that's also not too hard to fix. I could not (yet) find my NACA report on the light twin, but here are some interesting numbers: Is this the one: http://www.dfrc.nasa.gov/DTRS/1972/ LONGITUDINAL AERODYNAMIC CHARACTERISTICS OF LIGHT, TWIN-ENGINE, PROPELLER-DRIVEN AIRPLANES http://www.dfrc.nasa.gov/DTRS/1972/PDF/H-646.pdf Erik ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
Jon Berndt wrote: Good point. That's something that's also not too hard to fix. I tried to fix this problem in JSBSim a year or two ago, and I seem to recall that no one on the flight model list could quite figure out how to code it back then. I also took a stab at YSBSim, and failed just as miserably. Neither model is set up to have the propeller driving the engine rather than the engine driving the prop. The rule of thumb for pilots is that a windmilling propeller creates as much drag as a disc of the same size, but that's too vague for modelling (plus, it doesn't handle the partial-windmilling situation). What we need to figure out is how much drag we get from the propeller turning the crankshaft, compressing the cylinders, and spinning the accessory drives (vacuum pump, alternator, etc.). I could not (yet) find my NACA report on the light twin, but here are some interesting numbers: Cn_beta for some aircraft (per rad): Navion: 0.071 (Raymer ?) C-172p (JSBSim, from Raymer): -0.349 -0.0205 0 0 0.349 0.0205 This is roughly 0.06. Cherokee (McCormick): 0.067 C-310 (JSBSim): 0.1444 This is twice as high as the other aircraft. It could be due in some measure to a larger vertical tail, but I wonder if perhaps this value is too high? When coupled with the correction of drag due to prop, then I suspect we'll be a lot closer. Twins and taildraggers need a lot of rudder authority; tricycle-gear singles, not so much. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
On 2/5/04 at 2:36 AM David Luff wrote: On 2/4/04 at 8:24 PM Curtis L. Olson wrote: Also, speaking of FDM's. The current JSBSim C172 in cvs seems to have an engine that can break 3000 rpm in level cruise (150-160kts). That's clearly way too high for C172. I'm guessing from the engine rpm's that this is an engine or prop modeling problem??? It seemed to go up in power after the last JSBSim sync, but I couldn't see anything obvious changed. However, maxHP is set to 160HP in the spec file, but to 200HP in the constructor, so my suspiscion (sp?) is that somehow the 160 value isn't getting picked up anymore. This is indeed what is happening. Changing line 89 in FGPiston.cpp from MaxHP = 200; to MaxHP = 160; will cure it as a temporary measure. I guess someone who knows JSBSim well needs to look at why the config file value isn't getting picked up anyone. Cheers - Dave ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
David Luff wrote: I guess someone who knows JSBSim well needs to look at why the config file value isn't getting picked up anyone. I guess it would be a good idea to initialize the various variable *before* the get initialized by the configuration file ... Erik ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
David Luff wrote: I guess someone who knows JSBSim well needs to look at why the config file value isn't getting picked up anyone. Done. Erik ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] [OT] Commercial Ticket..
David Luff wrote: I guess someone who knows JSBSim well needs to look at why the config file value isn't getting picked up anyone. Done. Erik smacks forehead Thanks, Erik! Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
David Megginson wrote: I tried to fix this problem in JSBSim a year or two ago, and I seem to recall that no one on the flight model list could quite figure out how to code it back then. I also took a stab at YSBSim, and failed just as miserably. Neither model is set up to have the propeller driving the engine rather than the engine driving the prop. I just hacked up a test rig for the propeller code. Feeding it numbers from the Cub's propeller (my guess for the best tested of the YASim propellers), and using 40 KTAS @ 4000 MSL as a base environment, I came up with the following: Windmill (i.e. zero torque) speed is 450 RPM. Windmill drag at that speed is 47N, about 10.5 pounds of force, or about 5 equivalent horsepower at that airspeed. The rule of thumb for pilots is that a windmilling propeller creates as much drag as a disc of the same size, but that's too vague for modelling What's the drag of a 0.63 square meter (area of a 0.9m disc) flat plate at 40 knots? I wouldn't be shocked if it was in the realm of 10 lbs or so. A pickup truck (about as close to a flat plate as you can get, heh) at the same speed has perhaps 10x the surface area and requires just about 50 HP of engine power to cruise. Certainly we're within the right order of magnitude, anyway. Andy ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
Andy Ross wrote: Windmill (i.e. zero torque) speed is 450 RPM. Windmill drag at that speed is 47N, about 10.5 pounds of force, or about 5 equivalent horsepower at that airspeed. When you shut down the engine in YASim, the propeller does not windmill -- it just slowly spins down and stops. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
David Megginson wrote: Andy Ross wrote: Windmill (i.e. zero torque) speed is 450 RPM. Windmill drag at that speed is 47N, about 10.5 pounds of force, or about 5 equivalent horsepower at that airspeed. When you shut down the engine in YASim, the propeller does not windmill -- it just slowly spins down and stops. I see the same thing in the JSBSim c172, except that it spins down rather quickly and stops. Regards, Curt. -- Curtis Olson Intelligent Vehicles Lab FlightGear Project Twin Cities[EMAIL PROTECTED] [EMAIL PROTECTED] Minnesota http://www.menet.umn.edu/~curt http://www.flightgear.org ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
Curtis L. Olson wrote: I see the same thing in the JSBSim c172, except that it spins down rather quickly and stops. I've never shut down an engine in flight in real life, but from reports I've heard, you have to bring a 172 almost to the stall to stop the propeller from windmilling; once stopped, however, it will stay stopped at a more reasonable speed. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
On 2/5/04 at 7:10 PM David Megginson wrote: Curtis L. Olson wrote: I see the same thing in the JSBSim c172, except that it spins down rather quickly and stops. I've never shut down an engine in flight in real life, but from reports I've heard, you have to bring a 172 almost to the stall to stop the propeller from windmilling; once stopped, however, it will stay stopped at a more reasonable speed. JSBSim - very crude currently - hardwired -1.5 HP resistive power when engine cutoff but still windmilling. This is probably on the very low side - would expect at least 5% of max engine power to be used overcoming friction OTOH, so possibly prop code not windmilling propellor enough? LaRCsim - uses published friction model, but can't remember offhand if rubbing friction only or rubbing + pumping. Assumes fully warm oil I think. Should port it to JSBSim. Note that both the above only cut in when engine cut since power correlation used is for shaft power - by definition it gives zero at (running) idle. Need to check the whole windmilling thing re prop and engine. Closing the throttle should increase pumping losses and help to stop the engine - is this standard procedure for a definately dead one? Cheers - Dave ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
Ryan Larson wrote: I just got back from taking my Commercial Pilot, Airplane Multiengine Land checkride, and I am happy to say that I passed! Doing a single engine ILS down to minimums is lots of fun! I took the test in a Piper Aztec (PA23-250). Congrats! On a related note, I'd like to figure out how to make FlightGear more useful for ME practice -- I don't think either of the main FDM's does a very good job on single-engine, but I don't have any real experience to compare them with. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] [OT] Commercial Ticket..
On a related note, I'd like to figure out how to make FlightGear more useful for ME practice -- I don't think either of the main FDM's does a very good job on single-engine, but I don't have any real experience to compare them with. ?? This is confusing on several fronts. You don't have any single engine experience? Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
On 2/4/04 at 8:24 PM Curtis L. Olson wrote: Also, speaking of FDM's. The current JSBSim C172 in cvs seems to have an engine that can break 3000 rpm in level cruise (150-160kts). That's clearly way too high for C172. I'm guessing from the engine rpm's that this is an engine or prop modeling problem??? It seemed to go up in power after the last JSBSim sync, but I couldn't see anything obvious changed. However, maxHP is set to 160HP in the spec file, but to 200HP in the constructor, so my suspiscion (sp?) is that somehow the 160 value isn't getting picked up anymore. Just a hunch... Cheers - Dave ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
Jon Berndt wrote: for ME practice -- I don't think either of the main FDM's does a very good job on single-engine, but I don't have any real experience to compare them with. ?? This is confusing on several fronts. You don't have any single engine experience? Not in the context of ME (multi-engine) flying. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
Jon Berndt wrote: On a related note, I'd like to figure out how to make FlightGear more useful for ME practice -- I don't think either of the main FDM's does a very good job on single-engine, but I don't have any real experience to compare them with. ?? This is confusing on several fronts. You don't have any single engine experience? Hi Jon, I think what David meant was that for multi-engine practice, it's not really all that interesting to practice with both engines all the time. The real fun comes from practicing with only one engine running, or practicing when one engine dies at the worst possible moments. Sometimes the most optimistic objective is to hit the ground right side up. There are some real world effects that are important for training which I don't think we model well on existing twins. The main one that comes to mind is that with an engine out there is a minimum speed you must maintain, or else the torque of the good engine will overcome the ability of the rudder to hold heading and you end up spiraling until you can get the nose down enough to pick up some speed. Not fun if you don't have any altitude to trade at the moment. Also, speaking of FDM's. The current JSBSim C172 in cvs seems to have an engine that can break 3000 rpm in level cruise (150-160kts). That's clearly way too high for C172. I'm guessing from the engine rpm's that this is an engine or prop modeling problem??? Regards, Curt. -- Curtis Olson Intelligent Vehicles Lab FlightGear Project Twin Cities[EMAIL PROTECTED] [EMAIL PROTECTED] Minnesota http://www.menet.umn.edu/~curt http://www.flightgear.org ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] [OT] Commercial Ticket..
The main one that comes to mind is that with an engine out there is a minimum speed you must maintain, or else the torque of the good engine will overcome the ability of the rudder to hold heading and you end up spiraling until you can get the nose down enough to pick up some speed. Not fun if you don't have any altitude to trade at the moment. How do we not work well in this case? Do you notice a specific inadequacy? Also, speaking of FDM's. The current JSBSim C172 in cvs seems to have an engine that can break 3000 rpm in level cruise (150-160kts). That's clearly way too high for C172. I'm guessing from the engine rpm's that this is an engine or prop modeling problem??? That's strange. I know it was correct at one point. I haven't done anything to that as far as I remember. We'll look into it. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] [OT] Commercial Ticket..
?? This is confusing on several fronts. You don't have any single engine experience? Not in the context of ME (multi-engine) flying. Aha! OK, I would call that engine-out experience. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
for ME practice -- I don't think either of the main FDM's does a very good job on single-engine, ... I think JSBSim does a good job of modeling single engine operation. The big problem is with these cheesy twist-grip rudder controls on the joysticks. They make the engine-out work harder than it has to be. As far as practicing goes (without rudder pedals), I think one is better off using auto-coordination to take care of the rudder, and forget even trying to use the twist-rudder. Dave -- David Culp davidculp2[at]comcast.net ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
Curtis L. Olson wrote: The real fun comes from practicing with only one engine running [...] There are some real world effects that are important for training which I don't think we model well on existing twins. The main one that comes to mind is that with an engine out there is a minimum speed you must maintain That's no doubt true, but hopefully it's more a lack of tuning than it is a fundamental flaw. For the specific case of YASim: the asymmetric thrust effects should be more or less correct as-is, because it applies the force at the location of the engine. The blue line speed is almost certainly wrong, but should be relatively easy to find by tuning the rudder effectiveness only. If anyone with ME experience wants to take a few hops in the DC-3 or (YASim) C310 and provide feedback, I'd be happy to try tuning the models. Andy ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
Andy Ross wrote: Curtis L. Olson wrote: The real fun comes from practicing with only one engine running [...] There are some real world effects that are important for training which I don't think we model well on existing twins. The main one that comes to mind is that with an engine out there is a minimum speed you must maintain That's no doubt true, but hopefully it's more a lack of tuning than it is a fundamental flaw. For the specific case of YASim: the asymmetric thrust effects should be more or less correct as-is, because it applies the force at the location of the engine. The blue line speed is almost certainly wrong, but should be relatively easy to find by tuning the rudder effectiveness only. If anyone with ME experience wants to take a few hops in the DC-3 or (YASim) C310 and provide feedback, I'd be happy to try tuning the models. It very well could be a model setup issue at which point it's probably beyond my ability to debug, but with the JSBSim c310, I took off, climbed to a comfortable altitude and speed, and chopped the throttle on my right engine. Then I slowly pitched up to bleed off speed little by little. As the speed bled off, I held my heading with rudder and kept the wings level with aileron. From the readme: Minimum single-engine control speed (Vmca): 75 KIAS However, I was able to fly right through this until I got the stall horn, (about 60 kts?) and all the time, the rudder had plenty of effectiveness to hold heading. In the real thing (assuming the README is correct) at about 75 knots the rudder loses enough effectiveness to hold heading against the one good engine at full throttle and you begin an uncontrollable yaw. This doesn't happen right now in the JSBSim C310 anyway. I'm sure this is just a matter of tweaking the configuration file. But this is an important behavior to have reasonably correct in small twins. I also tried this with the YASim C310. I see a definite yaw effect from the engine, but I think I am getting to the stall point there too before I'm getting to the point where the rudder looses effectiveness against the engine. At about 80 kts (yasim version) the rudder can't quite hold heading by itself, but I can add a bit of bank towards the good engine with ailerons and hold my heading until I stall. At the point of the stall in the real aicraft, the good engine would definitely dictate the direction of the spin. I find in the yasim model, the aircraft can stall/spin into the good engine about as easily as the other way. In both cases it's probably just the models that need tweaking, but in their current form, I don't think they are very useful for engine out training. -- Curtis Olson Intelligent Vehicles Lab FlightGear Project Twin Cities[EMAIL PROTECTED] [EMAIL PROTECTED] Minnesota http://www.menet.umn.edu/~curt http://www.flightgear.org ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
On Wed, 2004-02-04 at 19:54, Curtis L. Olson wrote: Andy Ross wrote: Curtis L. Olson wrote: The real fun comes from practicing with only one engine running [...] There are some real world effects that are important for training which I don't think we model well on existing twins. The main one that comes to mind is that with an engine out there is a minimum speed you must maintain That's no doubt true, but hopefully it's more a lack of tuning than it is a fundamental flaw. For the specific case of YASim: the asymmetric thrust effects should be more or less correct as-is, because it applies the force at the location of the engine. The blue line speed is almost certainly wrong, but should be relatively easy to find by tuning the rudder effectiveness only. If anyone with ME experience wants to take a few hops in the DC-3 or (YASim) C310 and provide feedback, I'd be happy to try tuning the models. It very well could be a model setup issue at which point it's probably beyond my ability to debug, but with the JSBSim c310, I took off, climbed to a comfortable altitude and speed, and chopped the throttle on my right engine. Then I slowly pitched up to bleed off speed little by little. As the speed bled off, I held my heading with rudder and kept the wings level with aileron. From the readme: Minimum single-engine control speed (Vmca): 75 KIAS However, I was able to fly right through this until I got the stall horn, (about 60 kts?) and all the time, the rudder had plenty of effectiveness to hold heading. In the real thing (assuming the README is correct) at about 75 knots the rudder loses enough effectiveness to hold heading against the one good engine at full throttle and you begin an uncontrollable yaw. This doesn't happen right now in the JSBSim C310 anyway. It sounds like it's got too much rudder power or too much directional stability. It could be the propulsion, too, but if the performance is about right then it's probably the aero. I'm sure this is just a matter of tweaking the configuration file. But this is an important behavior to have reasonably correct in small twins. I also tried this with the YASim C310. I see a definite yaw effect from the engine, but I think I am getting to the stall point there too before I'm getting to the point where the rudder looses effectiveness against the engine. At about 80 kts (yasim version) the rudder can't quite hold heading by itself, but I can add a bit of bank towards the good engine with ailerons and hold my heading until I stall. At the point of the stall in the real aicraft, the good engine would definitely dictate the direction of the spin. I find in the yasim model, the aircraft can stall/spin into the good engine about as easily as the other way. In both cases it's probably just the models that need tweaking, but in their current form, I don't think they are very useful for engine out training. -- Tony Peden [EMAIL PROTECTED] ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
Curtis L. Olson wrote: It very well could be a model setup issue at which point it's probably beyond my ability to debug, but with the JSBSim c310, I took off, climbed to a comfortable altitude and speed, and chopped the throttle on my right engine. Then I slowly pitched up to bleed off speed little by little. As the speed bled off, I held my heading with rudder and kept the wings level with aileron. From the readme: Minimum single-engine control speed (Vmca): 75 KIAS However, I was able to fly right through this until I got the stall horn, (about 60 kts?) and all the time, the rudder had plenty of effectiveness to hold heading. In the real thing (assuming the README is correct) at about 75 knots the rudder loses enough effectiveness to hold heading against the one good engine at full throttle and you begin an uncontrollable yaw. This doesn't happen right now in the JSBSim C310 anyway. I'm sure this is just a matter of tweaking the configuration file. But this is an important behavior to have reasonably correct in small twins. I also tried this with the YASim C310. I see a definite yaw effect from the engine, but I think I am getting to the stall point there too before I'm getting to the point where the rudder looses effectiveness against the engine. At about 80 kts (yasim version) the rudder can't quite hold heading by itself, but I can add a bit of bank towards the good engine with ailerons and hold my heading until I stall. At the point of the stall in the real aicraft, the good engine would definitely dictate the direction of the spin. I find in the yasim model, the aircraft can stall/spin into the good engine about as easily as the other way. In both cases it's probably just the models that need tweaking, but in their current form, I don't think they are very useful for engine out training. Ok it seems we need a little definition of Vmc. To do a Vmc demo you configure the aircraft as follows. Altitude - 3500 MSL Gear and Flaps - UP Left engine - IDLE Right engine - Full Throttle Props - Full Forward Entry Speed - Blue line CG - farthest aft. Weight - Maximum 0 to 5 degrees of bank to the right. Execute manuver - pitch nose up to decrease airspeed by 1 kt / sec. discontinue when you encounter any of the following stall warning stall buffet lose of directional control These will give you the worst possible situation to deal with. Also remember that Vmc decreases as altitude increases in normally asperated twins. I will play around with the 310 tomorrow to see if I see any other issues. BTW, does FG currently simulate P-factor? This is very important in multi-engine aircraft because of the off-center nature of the thrust being created. This is why most US made ME aircraft consider the left engine to be the critical engine. Ryan ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] [OT] Commercial Ticket..
On Wed, 04 Feb 2004 21:54:41 -0600, Curtis L. Olson [EMAIL PROTECTED] wrote in message [EMAIL PROTECTED]: Andy Ross wrote: Curtis L. Olson wrote: The real fun comes from practicing with only one engine running [...] There are some real world effects that are important for training which I don't think we model well on existing twins. The main one that comes to mind is that with an engine out there is a minimum speed you must maintain That's no doubt true, but hopefully it's more a lack of tuning than it is a fundamental flaw. For the specific case of YASim: the asymmetric thrust effects should be more or less correct as-is, because it applies the force at the location of the engine. The blue line speed is almost certainly wrong, but should be relatively easy to find by tuning the rudder effectiveness only. If anyone with ME experience wants to take a few hops in the DC-3 or (YASim) C310 and provide feedback, I'd be happy to try tuning the models. It very well could be a model setup issue at which point it's probably beyond my ability to debug, but with the JSBSim c310, I took off, climbed to a comfortable altitude and speed, and chopped the throttle on my right engine. Then I slowly pitched up to bleed off speed little by little. As the speed bled off, I held my heading with rudder and kept the wings level with aileron. From the readme: Minimum single-engine control speed (Vmca): 75 KIAS ..with or without the 5-ish degree bank towards the good engine? However, I was able to fly right through this until I got the stall horn, (about 60 kts?) and all the time, the rudder had plenty of effectiveness to hold heading. In the real thing (assuming the README is correct) at about 75 knots the rudder loses enough effectiveness to hold heading against the one good engine at full throttle and you begin an uncontrollable yaw. This doesn't happen right now in the JSBSim C310 anyway. I'm sure this is just a matter of tweaking the configuration file. But this is an important behavior to have reasonably correct in small twins. I also tried this with the YASim C310. I see a definite yaw effect from the engine, but I think I am getting to the stall point there too before I'm getting to the point where the rudder looses effectiveness against the engine. At about 80 kts (yasim version) the rudder can't quite hold heading by itself, but I can add a bit of bank towards the good engine with ailerons and hold my heading until I stall. At the point of the stall in the real aicraft, the good engine would definitely dictate the direction of the spin. I find in the yasim model, the aircraft can stall/spin into the good engine about as easily as the other way. In both cases it's probably just the models that need tweaking, but in their current form, I don't think they are very useful for engine out training. -- ..med vennlig hilsen = with Kind Regards from Arnt... ;-) ...with a number of polar bear hunters in his ancestry... Scenarios always come in sets of three: best case, worst case, and just in case. ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] [OT] Commercial Ticket..
BTW, does FG currently simulate P-factor? JSBSim does, and IIRC YASim does as well. JSBSim does it with a tweak that offsets the point of force application. It could probably be done better if we set our minds to it, and it is a factor that needs to be set from testing and experience - i.e. it's not a completely physics-modeled quantity. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] [OT] Commercial Ticket..
I'm sure this is just a matter of tweaking the configuration file. But this is an important behavior to have reasonably correct in small twins. Yes, it would most certainly be a setup issue in the config file. I've got a book of aero data for a twin around here somewhere. I'll see if I can dig it up and compare values. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
