> About the FDM for the Heli, I would not mind having the > opinion of a real Heli pilot (hopefully there is one on this > list ?). The only reference point I have, is a few weeks > flying the Bell 206 in Microsoft flight simulator, and that > was 5 years ago, but in Fligh Gear, I feel that two things > are "wrong".
I'm not a trainer helicopter pilot, but an Aero engineer that has done several helicopter simulators. Maybe I can shed a little light on the subject. > > 1) If I climb to say 2,000 feet then set collective pitch to > 0%, and maintain a constant and very high speed of say 120 or > 140 knots, it nonetheless takes litterally several minutes > before I reach the ground, almost feeling like I didn't > zeroed the collective pitch at all. Feels really weird. This doesn't sound right. Are you sure the collective is set to 0%, and not just bottomed out on control? With zero colelctive, you should assume the flight profile of a homesick brick... Oh, sorry. In clearer terms, yes, you should fall out of the sky. > 2) If I climb to say 2,000 feet again, then turn the engine > off, I instantly lose control big time, going all over the > place, instead of entering "auto-rotation" (sorry for the > French word, don't know how it's called in English) and let > me land smoothly. You don't 'enter auto-rotation' just because you lose power. I haven't flown or looked at this model at all, but in a helicopter with irreverisble controls, if you shut off all power, yes, you are going to lose control, because there is nothing to move the swashplates, the control surfaces per sea. If the hydraulic system isn't modeled correctly, and power to the swashplates depends only on the engiens running, then turning off engines loses hydraulic pressure, and thus control. So, don't look at how the actual aircraft is designed to see what the proper response is in the simulation. You have to look at the simulation to see if that particular malfunction is modeled correctly. Autorotation is more a maneuver than a state. Losing engines in forward flight, as the air flows through the blades, aerodynamic drag causes the blades to spin, which creates some lift. In a hover, the first thing upon engine loss is to push the nose over and gain airspeed, and thus lift. That's why "low and slow" (hover near the ground) is so dangerous. If you lose an engine, you can't recover and get into an autorotation. In an auto-rotation, you regulating the lift produced by controlling the rotor speed. Pulling up on the collective, you decrease your rate of descent, but you also slow ther rotors down, and therefore decrease your lift and increase your sink rate. As you approach the ground, you pull up on the collective which produces more lift, thereby cushioning the landing. You have to pull collective at the right time. Too soon, and you've bleed all the speed from the rotors and you are still off the ground. Too late, and you hit the ground too hard. I heard it described once as "An autorotation is something to keep the pilot busy while he is crashing". > The bo105 looks about the same size/kind of heli as the Bell > 206, so I was expecting the heli in FG to behave in the same > way as the Bell 206 in MS Flight Simulator. Size has nothing to do with it. It's the simulation model that's important. I hope this helps, and yes, I look forward to someday in the future being able to contribute to the JSBSim helicopter modeling efforts, to make that FDM more complete. I have other stuff on the plate right now, though.... Good Luck, Bill _______________________________________________ Flightgear-users mailing list [email protected] http://mail.flightgear.org/mailman/listinfo/flightgear-users 2f585eeea02e2c79d7b1d8c4963bae2d
