Re: [Flightgear-devel] dc3-yasim model: engines?
Another issue is that, on landing with the dc3-yasim at a rather high speed (so that the angle of attack is near 0), the tail instantly falls onto the runway, but the aircraft nevertheless doesn't take off again, although the angle of attack just increased rapidly. Although I haven't ever been in a real-world taildragger, I don't think this is normal behaviour. I assume you're doing this with flaps ? That will increase your angle of attack compared to what you're seeing in an over-nose view. I don't know whether YASim models ground effect; if it does, the tailplane becomes more effective in ground effect and sucks the tail downwards. That'll exacerbate the torque of the forward gear mounting position. When I land the plane, I routinely get many bounces (I'm not very good at landing taildraggers). Are you absolutely sure you're seeing zero? Is it possible you're just not hearing the tire squeal sound being played? The sound code has gone through some changes lately and I've seen some sounds being missed, I think. It's just occurred to me that the taildrop of the landing may be increasing the AOA enough to put him on the back side of the lift curve in any case. I know a couple of DC3 pilots; when you feel the model is as good as you can make it, I'll ask them to take it for a spin and give you a critique. ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] dc3-yasim model: engines?
Andy Ross writes: What I think you're seeing is the feature that *everyone* who tries the DC-3 discovers: the DC-3 is a taildragger, and is really, really, really (!) hard to handle on the ground. I've had zillions of complaints about this, and have investigated every one thoroughly. Really, there's nothing unphysical going on. The instability is an actual feature of the real aircraft. Andy -- can you actually manage the DC-3 in a ground roll and takeoff? I have not been able to do so for a long time -- it always ends up spinning like a top. If you can do it, perhaps it would help if you posted a step-by-step. (3) YASim doesn't model prop wash, so rudder authority is lower at slow speeds than it should be. On the contrary, the slightest rudder input at slow speed starts the plane spinning right now. (4) You don't have toe brakes. At slow speeds, the only useful way to control yaw is with differential braking. Flapping the rudder is exactly like swinging open your car door -- it's a poor way to turn. I have toe brakes, but you shouldn't be using brakes in the takeoff roll anyway. (5) Really taildragger pilots are much better than sim jockeys. True enough. At our flight club, we have someone who does dual taildragger training in his Chipmunk, and apparently it takes most private pilots about 4-5 hours to get the hang of it. Note, however, that FlightGear users are trying this with perfectly calm winds, eliminating the hardest part of ground handling for the DC-3. This isn't a matter of having trouble taxiing, etc. -- basically, with the DC-3 moving fairly slowly (i.e. 20kt), a very slight (i.e. 5%) rudder deflection starts it spinning very rapidly as if it's on a turn-table and nothing less than full opposing toe brake can stop it (nearly tipping over in the process). I know that ground loops are a danger with taildraggers, but this seems excessive. Send us an XML file with what you'd like logged, and maybe we can get to the bottom of this. I've missed the DC-3 the past few months, since this problem started. 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] dc3-yasim model: engines?
Alex Perry wrote: I don't know whether YASim models ground effect; if it does, the tailplane becomes more effective in ground effect and sucks the tail downwards. That'll exacerbate the torque of the forward gear mounting position. Oooh! Good point. YASim does indeed model ground effect (kinda naively, but it's there), so this should really be happening. Cool. :) It's just occurred to me that the taildrop of the landing may be increasing the AOA enough to put him on the back side of the lift curve in any case. Also possible, although as I remember the DC-3 sits on its gear at significantly less than the stall angle, so it should still see increasing lift all the way to tailwheel touchdown. I know a couple of DC3 pilots; when you feel the model is as good as you can make it, I'll ask them to take it for a spin and give you a critique. That would be pretty cool. Some stuff, like the toe brake issue, is going to be pretty much unfixable except by those with special hardware. But certainly prop wash should be modelled before calling this thing done. Also, some of the statistics like the stall AoA and engine power/RPM settings are still guesses; it would be nice to come up with better numbers. 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] dc3-yasim model: engines?
Whee, here we go again. :) David Megginson wrote: Andy -- can you actually manage the DC-3 in a ground roll and takeoff? I have not been able to do so for a long time -- it always ends up spinning like a top. If you can do it, perhaps it would help if you posted a step-by-step. First off, you need fine control over differential braking. I do this with a mapping from /controls/rudder to the mainwheel brakes. I know you hate this idea, but if you're not doing it, I simply don't see how you can ever get off the ground. The DC-3 (the real world plane -- forget YASim for a moment) simply cannot be controlled on the ground without the use of the toe brakes. Period. If the simulator pilot cannot use them, the simulated plane cannot be controlled. Really, this is the truth. I promise. What happens (again, in the real plane) is that the mainwheels are forward of the CG. This means that any side force due to not quite moving straight causes the nose to yaw *away* from the direction of travel. This is not the way that tricycle gear planes work, and it requires constant, small and immediate (!) adjustments to prevent divergence. At low speeds, this is simply impossible without braking control. BTW, the most recent aircraft descriptions that were posted contains the brake mapping (I forgot to remove it), if anyone wants to try that. (3) YASim doesn't model prop wash, so rudder authority is lower at slow speeds than it should be. On the contrary, the slightest rudder input at slow speed starts the plane spinning right now. This is simply not so, it just looks that way. Here's the proof: (1) Hard-wire the rudder control to zero. Either take the control-input section out of the YASim file, or the joystick mapping out of your preferences. Just make sure that there is no rudder input to YASim at all. (2) Try to take off. You will still be spinning like a top. What you are seeing is not rudder force. It is *gear* force, acting on a point forward of the CG. It only looks like rudder force because you're not used to dealing with an aircraft that is directionally unstable on the ground -- your immediate assumption when something weird happens with yaw is that the yaw control is to blame. Therein lies the essence of the problem: RUDDER IS NOT THE YAW CONTROL AT LOW SPEEDS IN A TAIL DRAGGER. :) 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] dc3-yasim model: engines?
Andy Ross wrote: Whee, here we go again. :) David Megginson wrote: Andy -- can you actually manage the DC-3 in a ground roll and takeoff? I have not been able to do so for a long time -- it always ends up spinning like a top. If you can do it, perhaps it would help if you posted a step-by-step. First off, you need fine control over differential braking. I do this with a mapping from /controls/rudder to the mainwheel brakes. I know you hate this idea, but if you're not doing it, I simply don't see how you can ever get off the ground. The DC-3 (the real world plane -- forget YASim for a moment) simply cannot be controlled on the ground without the use of the toe brakes. Period. If the simulator pilot cannot use them, the simulated plane cannot be controlled. Really, this is the truth. I promise. I think you can find all about the DC3 here: http://www.douglasdc3.com/dc3throt/dc3throt.htm Erik ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
[Flightgear-devel] DC-3 takeoff roll: partial solution
Here's a lot of information on taxiing the DC-3: http://www.douglasdc3.com/dc3taxi/dc3taxi.htm The most important point is that the DC-3 tailwheel must be locked for takeoff and landing (i.e. it doesn't caster freely). Also of note: 1. According to the author, at least, differential braking is bad form while taxiing the DC-3; you should use differential power instead except for very tight turns. 2. Maintaining a straight heading is hard during the early part of the takeoff roll, but the text describes S-curves rather than violent spinning as the problem for inexperienced pilots. Locking the tailwheel should help a lot, but we'll also have to make sure that the tailwheel has the right amount of authority. By the time the tailwheel starts to lift, I'd expect that the rudder should be becoming more effective. 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] DC-3 takeoff roll: partial solution
David Megginson wrote: 1. According to the author, at least, differential braking is bad form while taxiing the DC-3; you should use differential power instead except for very tight turns. I'll buy that. But working dual throttles during the takeoff and landing rolls can't possibly be a good idea, right? In that regime, you're still stuck with rudder and braking only. During the landing roll (with no significant prop wash), you're stuck with braking only. 2. Maintaining a straight heading is hard during the early part of the takeoff roll, but the text describes S-curves rather than violent spinning as the problem for inexperienced pilots. Is that with or without braking being applied? I can confirm that I execute lots of S curves during takeoff in the DC-3 when using the brakes method. It only spins violently when you try to correct yaw divergence with a flapping rudder. Just to clarify what I said earlier: the reason that it looks like a rudder problem is that turning the plane a little bit with the rudder is possible. But once it is pointed little bit away from the velocity vector, it begins turning *farther* away very rapidly. If you don't correct this immediately, the aircraft will rapidly be so far out of whack that the rudder is incapable of correcting the yaw. Thus, what started out as a tiny rudder input diverges into a ground loop. But it's caused by a *lack* of rudder authority to correct the problem, not by too much authority causing it. Does that make more sense? Also, recognize that implementing prop wash would have the effect of increasing rudder authority during the takeoff (but not landing) roll, which will also help. Locking the tailwheel should help a lot, but we'll also have to make sure that the tailwheel has the right amount of authority. Hey, now that's really good information. This would *definitely* help with directional stability. You can lock the tailwheel by simply removing the castering=1 bit from the gear definition. This could be pretty easily made settable at runtime via a property. You don't have to worry about the skidding authority of the wheel -- skidding friction (to first order, anyway, for tires that aren't melting) is the same for wheels of all shapes and sizes. I really should read through this site more carefully. It's got lots of good stuff. The fantastic quote in question is: CAUTION: THE TAIL WHEEL LOCK MUST BE LOCKED DURING TAKE OFF AND LANDING. Sounds like good advice to me. I'm not at home right now; can someone remove the castering setting from the dc3.xml file and try it? If this is the solution, then I'll add a property-based control for castering tonight. 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] DC-3 takeoff roll: partial solution
Andy, CAUTION: THE TAIL WHEEL LOCK MUST BE LOCKED DURING TAKE OFF AND LANDING. Sounds like good advice to me. I'm not at home right now; can someone remove the castering setting from the dc3.xml file and try it? If this is the solution, then I'll add a property-based control for castering tonight. Works, but isn't perfect. At least I can take off now, but if I try to use only one engine, the aircraft soon pitches up and crashes with the front wheels still on the ground, the tail stuck on the tarmac. Two engines work fine, though. Andras === Major Andras e-mail: [EMAIL PROTECTED] www:http://andras.webhop.org/ === ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] dc3-yasim model: engines?
On Wed, 22 May 2002 21:49:44 +0200, Erik Hofman [EMAIL PROTECTED] wrote in message [EMAIL PROTECTED]: Andy Ross wrote: Whee, here we go again. :) David Megginson wrote: Andy -- can you actually manage the DC-3 in a ground roll and takeoff?I have not been able to do so for a long time -- it always ends upspinning like a top. If you can do it, perhaps it would help if youposted a step-by-step. First off, you need fine control over differential braking. I do this with a mapping from /controls/rudder to the mainwheel brakes. I know you hate this idea, but if you're not doing it, I simply don't see how you can ever get off the ground. The DC-3 (the real world plane -- forget YASim for a moment) simply cannot be controlled on the ground without the use of the toe brakes. Period. If the simulator pilot cannot use them, the simulated plane cannot be controlled. Really, this is the truth. I promise. ..or, a tail wheel lock. Code and try it. ;-) ..also, some have steered tailwheels, some are springloaded, and, some of these again can be locked straight, and released to free-swivel too. ;-) ..I believe the RL DC-3's used tail wheel locking, the RL AT-6 Texan, P-51, P-47 and many more, also use(d) them. ..the idea behind tail wheel lock is to keep the plane straight down the runway during takeoff, until you have enough airspeed to lift the tail. On landing, you want the tailwheel locked to avoid groundlooping, until you are turning off the runway onto some taxiway or some such. ..differential braking with a locked tail wheel will be far less dramatic, as they in RL rely on differential friction and tire hysteris, to turn the plane. Somewhat slowly. ;-) ..most taildraggers can be planted tailwheel-first, to prevent bounces, again easier in RL with a locked tailwheel. (One pointers are more intimidating to do in RL taildraggers, as most use speedometers rather than AOA instrumentation, as in you're _close_ to a stall on approach and without exact knowledge.) I think you can find all about the DC3 here: http://www.douglasdc3.com/dc3throt/dc3throt.htm Erik -- ..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] DC-3 takeoff roll: partial solution
Andy, I just made two recordings of flights with the DC3, but can't play them back because fgfs segfaults. I can put them on the web if that helps (maybe even to debug the segfault...). Andras === Major Andras e-mail: [EMAIL PROTECTED] www:http://andras.webhop.org/ === ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
[Flightgear-devel] Re: New YASim files for base package
Andy Ross [EMAIL PROTECTED] writes: The patch requires new aircraft descriptions. These are available at: http://plausible.org/yasim-aircraft-20020521.tar.gz is anybody able to fly the yasim planes with latest cvs and the above patch? i keep getting: YASim SOLUTION FAILURE: Solution failed to converge after 1 iterations for the a4, harrier, 747. --alex-- -- | I believe the moment is at hand when, by a paranoiac and active | | advance of the mind, it will be possible (simultaneously with | | automatism and other passive states) to systematize confusion | | and thus to help to discredit completely the world of reality. | ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Re: New YASim files for base package
Alex Romosan wrote: is anybody able to fly the yasim planes with latest cvs and the above patch? i keep getting: YASim SOLUTION FAILURE: Solution failed to converge after 1 iterations for the a4, harrier, 747. I appear to have goofed something up with the posted planes. Or perhaps missed a checkin. I promise to check tonight. Things have been a little busy lately. :) 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] DC-3 takeoff roll: partial solution
but if I try to use only one engine, the aircraft soon pitches up and crashes with the front wheels still on the ground, the tail stuck on the tarmac. Two engines work fine, though. But here you've lost me. Normally, the aircraft state with all three wheels on the ground is not called a crash. :) Sorry, sorry, that should have read tail stuck IN the ground. Attached screenshot taken within 3sec after releasing brakes, after this, the plane pitches up even more, and fgfs hangs, moaning about terrain intersections. Maybe it's the two fronts wheels taking off rather than the tailwheel being buried, but in any case airspeed builds up much too quickly. Sorry for the confusion. Andras === Major Andras e-mail: [EMAIL PROTECTED] www:http://andras.webhop.org/ === attachment: dc3-1engine.jpg
Re: [Flightgear-devel] DC-3 takeoff roll: partial solution
Major A wrote: Sorry, sorry, that should have read tail stuck IN the ground. Attached screenshot taken within 3sec after releasing brakes, after this, the plane pitches up even more, and fgfs hangs, moaning about terrain intersections. Maybe it's the two fronts wheels taking off rather than the tailwheel being buried, but in any case airspeed builds up much too quickly. One note is that the fact that the wheels are drawn inside the ground is probably a red herring. David's 3D model and the YASim geometry description of the DC-3 aren't in perfect agreement, so you can sometimes see this artifact. We need to clean this up at some point, but that's clearly not the bug you're seeing. Just to be clear: You started up the engines, firewalled the throttle, let the RPMs stablize, released the brakes, and the aircraft pitched *up*??? That's clearly unphysical. Clearly the only right thing here would be for the aircraft to accelerate slowly (the DC-3 gets about 0.3G of acceleration at the start of the run), and maybe ground loop. Under no circumstance should it be pitching until there is enough airflow over the horizontal stabilizer to lift the tail. This happens somewhere around 40kts or so, I think. Unfortunately, I've never seen anything like this behavior before. I'll try it this evening, but I'm pretty sure I would have noticed it before. Can anyone else reproduce this? Is there anything weird about your platform (other than the ugly window manager, that is)? The hanging of flight gear is just YASim detecting the crash and ceasing simulation. You should be able to recover by selecting File-Reset from the menu. 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] DC-3 takeoff roll: partial solution
You started up the engines, firewalled the throttle, let the RPMs stablize, released the brakes, and the aircraft pitched *up*??? That's clearly unphysical. Why ? The nose pitches down with power and brake application. So, releasing the brakes makes the nose pitch up. ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] DC-3 takeoff roll: partial solution
but if I try to use only one engine, the aircraft soon pitches up and crashes with the front wheels still on the ground, the tail stuck on the tarmac. Two engines work fine, though. But here you've lost me. Normally, the aircraft state with all three wheels on the ground is not called a crash. :) Sorry, sorry, that should have read tail stuck IN the ground. Attached screenshot taken within 3sec after releasing brakes. Sorry for the confusion. Andras === Major Andras e-mail: [EMAIL PROTECTED] www:http://andras.webhop.org/ === attachment: dc3-1engine.jpg
[Flightgear-devel] Couple links for visual designers
AVSim.com had a post today with a really good link to an aircraft resource page. It's here: http://www.aircraftresourcecenter.com/walk.htm That page has walk-around pics for many military aircraft from a host of countries. Great stuff for anyone working on 3D models or panels. AVSim also linked to a nice site with pretty detailed layouts of cockpit panels in several major airliners. It's here: http://www.meriweather.com/flightdeck.html Enjoy -- Cameron Moore __END__ ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
