Hal V. Engel > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:flightgear- > [EMAIL PROTECTED] On Behalf Of > Sent: 20 April 2006 21:00 > To: [email protected] > Subject: Re: [Flightgear-users] Re: Rudder Trim > > On Thursday 20 April 2006 09:24, [EMAIL PROTECTED] wrote: > > On Tuesday 18 April 2006 23:00, barsalou wrote: > > > I have been trying to trim the rudder so that the plane doesn't go to > > > the left off the runway when trying to take off. > > > > > > Maybe this is normal airplane flight? > > > > > > > > > I have made attempts at setting the dead-band and other things, but > am > > > not succeeding. > > > > > > I realize I probably haven't given enough info here...please help me > > > how you can. > > > > > > Mike B. > > > > As others have pointed out the torque is normal but here is a little > more > > insight based on limited experience in real 172's. Which is probably > > relevant for all tricycle gear aircraft in flightgear. > > The torque is most pronounced at high RPM and low speed. At higher > speed > > the aircraft tail assembly, I think this is true for all aircrafts, act > > like a weather vane and help to point the nose into the relative wind, > > i.e. direction of flight. Also at low speed the rudder is not > effective > > since there is little wind over it and steering is done using the nose > > wheel. > > You are probably taking off the way I started with flightgear. Brakes > > locked at end of runway, some flaps, full throttle and release the > brakes. > > That's great for a soft runway and/or short field operation, or a 747, > > but makes the torque problem worse. The proper normal runway technique > in > > the 172 is NO FLAPS, release the brake and smoothly increase the > throttle > > to full power. > > In fact a flight instructor will tell you to increase the power slowly and > smoothly. Aircraft with constant speed props (not the 172) need time for > the > prop governor to react to the increase in throttle so taking 4 to 6 > seconds > to open the throttle is about right for most GA aircraft. The more > powerful > the aircraft the more slowly you should increase power during takeoff. > Not > holding the breaks while increasing the power applies only to single > engine > and other (near) center line thrust (CLT) aircraft for the most part. > > Non-CTL twins are different in that you do hold the breaks while (slowly > and > smoothly) opening the throttles. The reason for this is to allow the > engines > to settle at or near takeoff RPM before you begin the talkoff roll to > prevent > the engines from spooling up at differrent rates during takeoff which > would > result in asymmetric thrust. My experience with FlightGear is that both > engines spool up at exactly the same rate which is not realistic. But > this > may not be true for all multi-engine aircraft in FlightGear since of the > twins I have only tried the C310 and the DC3. > > > A slight nose down trim is also helpful in keeping the nose > > wheel on the runway and steering control until speed increases and the > > rudder is effective. Use the nose wheel to counter the torque, LEFT > PEDDLE, > > Mouse with left button down or the period key. If set for auto > > coordination once you use the left or tight arrow keys or mouse without > the > > left button down the wheel and rudder will jump to an almost centered > > position so be careful. During maximum climb and slow fight with high > > RPM's you still have to use the right peddle to counter the torque. > > Normally this would be handled by applying rudder trim rather than holding > pressure on the rudder pedals. But at least in 0.9.9 I have never been > able > to get the rudder trim to work. I need to try this with 0.9.10. > > > That's > > why the standard pattern at an airport is to the left so the torque is > > pulling the plane in the proper direction your not fighting it. > > My tail dragger experience is based solely on flightgear. Since the > > steering is done with the tail wheel and it's friction on the ground > tends > > to keep the tail from drifting as well, a nose up trim is desired. I > have > > found with high power aircraft, P51 especially, that take off flaps 10 > > degrees to increase lift, slow acceleration until the plane flies, not > > full throttle and steady nose up attitude to keep the tail wheel on the > > ground but not pitch the nose up too early. Allows you to fly the > plane > > with all three wheels coming off the ground at the same time and > maintain > > control. I'm sure that's not the real tail dragger technique but it > works > > in flightgear. > > My real world tail dragger experience is limited to a Super Decathlon > which > has more power (180 HP) than the J3 but not nearly as much as a P-51 or > Spitfire. In general most tail draggers are setup so that when all three > wheels are on the ground the plane is in about the same attitude as it > would > be when stalled. So taking off "with all three wheels coming off the > ground > at the same time" means you are taking off at a speed that is very close > to > stall. This is probably not a good idea. In fact the only real world > case > where this is done that I know of is with Reno unlimited race planes that > have had larger engines with bigger props installed that prevent the > aircraft > from taking off in the normal way without a prop strike. > > You should accelerate with the tail wheel down (hold some back pressure on > the > stick) until you are gong fast enough that the rudder has enough authority > and then bring the tail up slowly (2 to 3 seconds) until the aircraft is > level. Then continue accelerating while adding more power to rotation and > takeoff which should happen well above stall speed. You will also > accelerate faster once the tail is up since there will be less drag. >
This is all good stuff, but it is perhaps worth mentioning that not all aircraft have a rudder trim in real life - the c172 is one such, and therefore does not have one in FlightGear, which is why you can't make it work. Most others - Hunter, Spitfire do. Vivian ------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid0709&bid&3057&dat1642 _______________________________________________ Flightgear-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/flightgear-users
