Hey pplpeter:
First … welcome to the forum, and congratulations on working toward your PPL. You’ve received some good information from 18-Wheeler regarding aircraft pressurization and the weights of the B747 – of course, aircraft weights can vary greatly depending on the operation and the model of the aircraft being discussed.
Now, about the rudder. Every airplane needs something to keep it “coordinated” during a turn. Your instructor can explain the term “coordinated,” if you need some additional information. Most aircraft use the rudder to supply the necessary forces to keep the turn coordinated. Jets are no different in what they need – it’s just that some jets get what they need from different sources, but, actually, a yaw damper isn’t the source of this input. Some jet aircraft that use three separate autopilot axes can use the rudder axis to support this need, but that is usually insufficient for all cases. The controls that primarily allow jet pilots to make coordinated turns without using much, if any, rudder input (which is a tremendous training error in my not-so-humble opinion) are what is known as “roll control spoilers.” These are flat panels on the top surface of the wing that deploy with the input of aileron. The panels on the downside wing lift up into the airflow during a turn and “spoil” the lift produced by that wing, thereby assisting in the downward movement of that wing. This is in addition to the upward extension of the aileron on the same wing which causes the same thing. These extended spoiler panels also create some “form drag” on that wing, causing the whole wing to be moved rearward in relation to the opposite wing. This is essentially the same thing that rudder input would provide. Normally, the spoilers begin to rise with something like 5 to 6 degrees of aileron control movement and they can lift to a position of approximately 30 degrees relative to the wing surface. If you’ve flown on a commercial airline or have seen videos out the passenger window during final approach, you have probably seen those panels lifting and lowering at irregular intervals during the approach. That is directly the result of the pilot’s use of the aileron controls. Each time the panels rise, the pilot is asking for that wing to move down a bit … the higher the panel rises, the more the pilot is asking for a downward movement of the wing. The interesting point is that with each spoiler panel extension, there is a form drag component generated that has the same effect on the aircraft as rudder displacement toward that same side.
That may be all the information you need … but, if you’d like more … just ask.