At 02:47 PM 5/22/2002 -0700, you wrote: >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? [snip]
Differential braking should be kept to a minimum in any airplane, for two reasons: (1) An airplane is a really lousy automobile. It has about as little undercarriage as it can get away with (one has only to look at pictures of an airplane and a truck scaled to the same size to realize this), and every brake application is hard on its pitiful little brakes. (2) Differential braking tends to scrub rubber off some very expensive tires. So differential power becomes the steering method of choice in airplanes that have it available. Light taildraggers generally have steerable tailwheels, and being single-engined, they always have some prop blast over the tail; consequently they're not very hard to steer in the takeoff roll. Larger taildraggers don't have steerable tailwheels because the steering forces would require powered controls which were not in use when they were designed. In the Gooney Bird one must line up on the runway, lock the tailwheel, and hold the wheel firmly back until there is full tail surface control. Prior to that point, you aren't really steering a heading: you're just holding yaw rate to a minimum. The airplane will turn somewhat in a crosswind; this can be dealt with to some extent by judiciously positioning and aiming the airplane before starting the roll. The divergence you mention is present in a real taildragger; it's just a basic instability in the yaw axis resulting from most of the weight being supported in front of the cg. When the fuselage is misaligned with the direction of motion, the side force on the wheels is destabilizing. I don't know exactly how the tailwheel lock is implemented in the DC-3; in the AT-6, the last couple of inches of aft stick travel center and lock the wheel. It's an ideal arrangement, because if you don't have the stick back the tailwheel won't do you any good anyway. rj _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
