Re: [Flightgear-devel] Helicopter: First Impressions
Hi Andy, Andy Ross wrote: Since the helicopter mechanism doesn't use the solver, you'll need to fudge a factor that makes sense. The actual number is going to depend in sensitive ways on the size and shape of the aircraft and will probably be impossible to guess in practice (this, after all, was the whole point behind writing the solver in the first place). But you'll probably get into the ballpark by picking coefficients that result from an airplane of a similar size. I am using this code instead the solver: applyDragFactor(Math::pow(15.7/1000, 1/SOLVE_TWEAK)); applyLiftRatio(Math::pow(104, 1/SOLVE_TWEAK)); setupState(0,0, _cruiseState); _model.setState(_cruiseState); _controls.reset(); _model.getBody()-reset(); I took the values from the c172. But maybe the stabs are not working because I use them in different conditions than in an airplane. I use them as a damper with nearly no airspeed, where the local wind is nearly parallel to the surface-normal (or with other words: 90 degree incidence). Maybe you can tell me, if they would produce forces in this circumstances. All the best, Maik ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Helicopter: First Impressions
Maik Justus wrote: I am using this code instead the solver: applyDragFactor(Math::pow(15.7/1000, 1/SOLVE_TWEAK)); applyLiftRatio(Math::pow(104, 1/SOLVE_TWEAK)); I took the values from the c172. Don't include the SOLVE_TWEAK bit. That exists to slow down the convergence of the solution and to prevent oscillation about the correct solution point (or at least to bludgeon the oscillation magnitude down to the point where it is small enough to not matter, heh). What you are doing is applying a one-time correction, not iteratively solving for a value. My suggestion would be to keep the lift ratio fixed at a reasonably sane number (maybe somewhat lower than 100 because helicopter surfaces are low-aspect wings and comparatively inneficient lift generators) and allow the user to set a drag magnitude in configuration. That said, my reading of the code above would indicate that you would have too *much* force generated because of the SOLVE_TWEAK computation, not too little. Dunno. But maybe the stabs are not working because I use them in different conditions than in an airplane. I use them as a damper with nearly no airspeed, where the local wind is nearly parallel to the surface-normal (or with other words: 90 degree incidence). Maybe you can tell me, if they would produce forces in this circumstances. This should work. This is one of YASim's strengths, actually. It produces reasonably sane output even for conditions like the 90° AoA you mention. You might want to make sure that the positioning and orientation of the surfaces is correct, I guess. Although I'd be suspicious that helicopter tails are effective at zero airspseed and near-zero rotation speed. These are big machines, and the tails are very small. :) Andy ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Helicopter: First Impressions
Hi Jim first: thanks to everyone who helped to put this code into the flightgear codebase. Jim Wilson schrieb: What I have noticed is that overspeed effects don't seem to show up (negative speed on the blades coming back should cause a stall) and if you get it up to far enough over 200 it seems as though it'll hold speed and altitude forever even with the collective all the way down. Best, Jim This is due to the not realistic simulated translational lift. I am searching for a more realistic formula for it. The exact simulation of this is very complicate (and at least I am not able to program this). The helicopter simulation is not finished yet. I will describe later, which functions/ effects are totally missing or simplified. @jim,curt: Maybe you can add also the bell206like.xml, ch47like.xml an as350like.xml to the cvs? I think it is interesting, how different they are. All the best, Maik ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Helicopter: First Impressions
Martin Spott writes: Very different here. The indicators on the HUD were moving and the heli flies very calm. Did you recompile the stuff from scratch ? That's worth a shot -- I'll try a make clean; make in SimGear and FlightGear. I'll just confirm that it is the bo105 that everyone else is finding so smooth -- I actually got motion sick last night from all the yaw osciallations. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Helicopter: First Impressions
On 10/17/03 at 9:24 AM David Megginson wrote: Martin Spott writes: Very different here. The indicators on the HUD were moving and the heli flies very calm. Did you recompile the stuff from scratch ? That's worth a shot -- I'll try a make clean; make in SimGear and FlightGear. I'll just confirm that it is the bo105 that everyone else is finding so smooth -- I actually got motion sick last night from all the yaw osciallations. FWIW, I got sudden yaw oscilations as you describe for no apparent reason as well. I've no idea how to fly a heli though!!! Cheers - Dave ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Helicopter: First Impressions
David Luff writes: FWIW, I got sudden yaw oscilations as you describe for no apparent reason as well. I've no idea how to fly a heli though!!! Nor do I, but I'd expect any strange oscillations to happen at very low or very high airspeed, not at a medium cruise speed. I just rebuilt everything from scratch, and it's still happening. Usually, I can stop it with only a tiny change in control position (often pitch), but then it will start again a while later. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Helicopter: First Impressions
Hello David, I will try to get the oscillations. Maybe I am able to change the bo105.xml to avoid them. Maik David Megginson schrieb: David Luff writes: FWIW, I got sudden yaw oscilations as you describe for no apparent reason as well. I've no idea how to fly a heli though!!! Nor do I, but I'd expect any strange oscillations to happen at very low or very high airspeed, not at a medium cruise speed. I just rebuilt everything from scratch, and it's still happening. Usually, I can stop it with only a tiny change in control position (often pitch), but then it will start again a while later. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Helicopter: First Impressions
On 10/17/03 at 1:11 PM David Megginson wrote: David Luff writes: FWIW, I got sudden yaw oscilations as you describe for no apparent reason as well. I've no idea how to fly a heli though!!! Nor do I, but I'd expect any strange oscillations to happen at very low or very high airspeed, not at a medium cruise speed. I just rebuilt everything from scratch, and it's still happening. Usually, I can stop it with only a tiny change in control position (often pitch), but then it will start again a while later. Yes, it definately felt like a simulation artifact, not a real-life phenonemon. Fantastic effort for a first cut at a heli model mind :-) Heli's always want to seem to do non-standard things such as check power lines below the normal arrival paths that'll be a pain to code ATC support for though!! Cheers - Dave ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Helicopter: First Impressions
Hi Maik Justus wrote: The helicopter simulation is not finished yet. I will describe later, which functions/ effects are totally missing or simplified. Here it is: Missing: -Downwash -Effect on stabs -Effect on rotor itself -Effect on ground (ground effect) -Engine (The needed power is calculated, but very simplified (i.e. a autorotation is not possible now) , but the rotor now accelerates in 5 sec and hold than the revolution for every circumstances) -Fuel consumption -Garbage collection to the source -Comments in the source Unrealistic: -Translational lift -Teetering (I am not sure, which effect the teetering has. If I try to calculate it, I get some discrepancies) -Lift and drag from the Rotor blades is very simplified. To use realistic values of a realistic airfoil should be not very complicate (and then the needed power would be realistic and autorotation should be possible) -The rotor is simulated at only 4 points. To use many points along the rotor blades is much better. And maybe much more, which I forgot to mention here ;-) The bo105.xml contain only more or less realistic rotors. The fuselage and the stabs are still missing. (the same for bell206like.xml, ch47like.xml and as350like.xml). (I am not sure if the stabs are working correct without the solver. I tried to use fixed values if you specify no wing and hstab, but maybe there is a bug. In the ch47like.xml the vstab seems to have no effect at all) All the best, Maik P.S.: I would be very thankful if someone would correct my english in the README.yasim ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Helicopter: First Impressions
[Woo hoo! Check it out: two posts in two days! I'm back in the game! Amusingly, I'm also employed again. I wonder if there's a connection?] Maik Justus wrote: I am not sure if the stabs are working correct without the solver. I tried to use fixed values if you specify no wing and hstab, but maybe there is a bug. Your guess is correct. The force coefficients of all the Surface objects in YASim starts out as a unitless number related only to their shape and size. That is, they make sense relative to each other, but not in relation to outside issues like, heh, air flow. It's the job of the solver to scale them properly to produce the target performance. I guess the numbers you are seeing are too small by several orders of magnitude; at least this is preferable to the helicopter feeling many times *more* force than it should. :) Since the helicopter mechanism doesn't use the solver, you'll need to fudge a factor that makes sense. The actual number is going to depend in sensitive ways on the size and shape of the aircraft and will probably be impossible to guess in practice (this, after all, was the whole point behind writing the solver in the first place). But you'll probably get into the ballpark by picking coefficients that result from an airplane of a similar size. P.S.: I would be very thankful if someone would correct my english in the README.yasim Or mine, for that matter. :) Andy ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
[Flightgear-devel] Helicopter: First Impressions
I've been been playing with Maik's most excellent helicopter model, now in CVS: fgfs --aircraft=bo105 I can (just barely) fly it -- I'll try hooking up my rudder pedals to see if that makes it easier. One thing I don't understand is that I get a lot of small, rapid fishtail oscillations, even when the controls are perfectly still and the forward airspeed is 60 kt or higher (i.e. I'm nowhere near a hover). Is this a reflection of a real aerodynamic effect in heli's, or is it something we need to hunt down? Let's all give Maik a round of applause for this one. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Helicopter: First Impressions
David Megginson [EMAIL PROTECTED] said: I can (just barely) fly it -- I'll try hooking up my rudder pedals to see if that makes it easier. One thing I don't understand is that I get a lot of small, rapid fishtail oscillations, even when the controls are perfectly still and the forward airspeed is 60 kt or higher (i.e. I'm nowhere near a hover). Is this a reflection of a real aerodynamic effect in heli's, or is it something we need to hunt down? This isn't happening here. How are you controlling the antitorque (rudder)? Maybe the problem is in the control input? Best, Jim ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Helicopter: First Impressions
David Megginson [EMAIL PROTECTED] wrote: Let's all give Maik a round of applause for this one. Indeed ! I'd say: When dreams come true , Martin. -- Unix _IS_ user friendly - it's just selective about who its friends are ! -- ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Helicopter: First Impressions
Jim Wilson writes: This isn't happening here. How are you controlling the antitorque (rudder)? Maybe the problem is in the control input? I've tried it with two different controllers and seem the same effect -- furthermore, the control-position indicators on the HUD are not moving, suggesting that the flutter isn't coming from there. Are you sure that you don't see yaw flutter at all? Try cruising around for five minutes or so -- it always shows up for me. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Helicopter: First Impressions
David Megginson [EMAIL PROTECTED] said: Jim Wilson writes: This isn't happening here. How are you controlling the antitorque (rudder)? Maybe the problem is in the control input? I've tried it with two different controllers and seem the same effect -- furthermore, the control-position indicators on the HUD are not moving, suggesting that the flutter isn't coming from there. Are you sure that you don't see yaw flutter at all? Try cruising around for five minutes or so -- it always shows up for me. Not at all. I've probably got an hour or more on it. Just took it for from SFO to the golden gate and then back to try and land in the football stadium. The tail rotor animation is a little off center, but that's it. Maybe this is related to cpu speed somehow. What I have noticed is that overspeed effects don't seem to show up (negative speed on the blades coming back should cause a stall) and if you get it up to far enough over 200 it seems as though it'll hold speed and altitude forever even with the collective all the way down. Best, Jim ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] Helicopter: First Impressions
David Megginson [EMAIL PROTECTED] wrote: I've tried it with two different controllers and seem the same effect -- furthermore, the control-position indicators on the HUD are not moving, suggesting that the flutter isn't coming from there. Very different here. The indicators on the HUD were moving and the heli flies very calm. Did you recompile the stuff from scratch ? Martin. -- Unix _IS_ user friendly - it's just selective about who its friends are ! -- ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
