shiv wrote:The simple question is in a turn to the left (for example) does the pilot use his rudder at all? If he uses his rudder does he deflect the rudder to the left or right?
If the plane is turning left, it is already banked to the left. If the rudder is moved to the left the nose will go down (yaw to left) as the tail goes up. If the rudder is turned right, the nose will tend to point up as the plane is yawed to the right. Raman says the plane that is turning to the left will have a natural tendency to yaw to the right (towards the "high wing"because of differential lift). Does this require rudder correction? If so in which direction? Raman made no statement about what direction the rudder is deflected. Counter intuitively it appears that for a left turn the rudder must be deflected to the right to keep the nose up, or else the nose will tend to go down because of "lift" from the tailplane.
I understand that it is all in 3-D but I am doing my best to explain 3-D in words because what has been written does not fit in with what I have observed or what you are saying. Obviously "nose up and nose down" take on new meanings when a plane is banked say 45 degrees. Nose up and nose down while a plane is banking demand some yaw unlike level flight where nose up and nose down means pitch alone.
Shiv ji, I completely understand the difficulty of explaining 3D stuff in words. Hence I believe a lot of things are getting mixed up here.
It all started with Shalav saying that rudder has only yaw effect and no rolling effect - he was wrong there. Using the rudder alone for yaw will induce roll as others and I explained, which if uncorrected will lead to a zero lift condition, where the plane will nose dive.
Now lets move on to the ailerons.
Shalav also had got it wrong as to what the ailerons do to induce the bank, maintain the bank and then reverse the bank. In all modern planes, AFAIK ailerons are used to induce the bank as the moment is much higher and hence the response is much more niftier. However, Shalav went on to say that the plane has a tendency to pitch down (which is what Raman ji corrected). When a plane uses ailerons to bank, it has a tendency to turn towards the outward wing. which in this banked position actually leads to positive AoA (3D again). It is somewhat like the nose is not aligned in the direction of the planes turn. But then once the banking is achieved the ailerons are leveled this differential dissipates to a lower extent. However even with the ailerons leveled there is still some lift and drag differential. This is because the planes outer wings covers a circumference of a bigger radius. This makes the airspeed higher over the outward wing. This means that the outward wing (even with leveled ailerons) creates more lift and more induced drag. So the plane would continue to roll and skid (albeit by a much lesser extent than when the ailerons were deflected). This can be corrected in many ways. The designer has the all the control surfaces to play with to negate this differential and hence make the nose point in the direction of the turn. He can use the rudder, or the ailerons or a combination of both.
So to answer your question, what happens if I created a bank with ailerons (almost always) while turning left. Obviously the roll is counter clockwise. While the banking is being achieved, and once the required banking is achieved, reverse yaw will make the nose turn towards it right(clockwise). In a 45 degree bank, this reverse yaw would mean that the nose would get misaligned to the right and up. As a correction the rudder might be used (deflected left) to make the nose yaw to the left (an anti clockwise moment). Hence the nose will be pushed left and down. Generally the amount of deflection of the rudder is a function of the deflection of the ailerons which is very simple to understand.
Albeit there are other ways like using the ailerons themselves to negate the differential. So once the banking angle is reached, even when turning left, one would deflect the ailerons (ever so slightly) to create a clockwise roll moment to negate this unintended roll and yaw. Another method which is almost never used is providing more power to the outer engine. This is sluggish and maintenance prone. Probably Gilles can clarify if using differential power from engines is even in the manuals if the hydraulics fail.
Now for creating a pure yaw effect in a left turn, the rudder would be turned left. This would create a parasitic anticlockwise roll moment. The ailerons could be used to counter this roll moment. So left aileron would be down (ever so lightly) and the right aileron would be up (ever so lightly). Again the deflection of the ailerons would be a function of the deflection of the rudder.
Sorry for going OT. I hope the moderators don't mind a discussion on aerodynamics on this page.