What makes the airplane turn?

jtk15sc15 has the idea. The horizontal component of lift is the "force" that turns an aircraft. It is created by the deflections of the ailerons (Banking the airplane) Note:(there are a few airplanes that use spoilers in lieu of ailerons) (The rudder is used for coordinating the turn by countering the adverse yaw caused by the rolling moment

Yes, it's the ailerons that turn the plane, and the rudders are used to counteract adverse yaw (drag) from the uplifted wing since it is generating more lift than the lower (banked) wing. The rudders keep the nose where you want it - turning in the direction you banked and want the aircraft to turn. Simply stepping on the rudder will cause the plane to skid, not really turn how you'd want it to. It's an invitation to a spin. *edit* IF you want to just step on the rudders, and you have enough airspeed, and you get enough rolling motion on the upward wing, and you haven't already gone into a stall or spin, and you have a lot of time and room to make a large inaccurate turn, THEN you might get the aircraft turned, but it will be a very uncoordinated, inefficient turn. NOT the way you ever want to do it, and in reality, it's not considered a way to turn an aircraft for the purposes of this question. IF you've lost your aileron function, then maybe you want to try it with enough airspeed. But this question is assuming a normally operating airplane. It has nothing to do with the flaps.

the book answer "the horizontal component of lift" a straight and level airplane has all the lift directed below it perpendicular to its flight path. as it rolls, some of that lift is directed downwards (obviously or the plane would descend) and some of it sideways. Like a triangle with two components and a hypotenuse

An airplane turns when one wing is induced to fly slower therefore create less lift than the other. This can be done in a few ways but the most common and effective way is the use ailerons to raise one wing above the other. For many complex aerodynamic reasons I am too tired to go in to now the lower wing is induced to fly slower than the upper wing. This creates drag on one side effecting a turn in that direction. Think of driving your car and somehow apply the brakes on the left wheels only. As they are now turning more slowly than the right wheels you better believe your car will be forced to the left. One function of the rudder is to keep aileron turns coordinated or push the rear to the left as the front is forced right and Viceversa. Moving on anyone with at least a PPL has practiced rudder turns. Rudder deflections alone can and will change an aircraft's direction by pushing the tail one way or the other. However this method alone is not as effective and not very comfortable as far as aircraft stability is concerned. Also in multi-engine aircraft as a last resort asymmetric thrust can be used to make one wing fly faster than the other and induce a turn or at least counteract other forces causing an unwanted turn. Just ask captain Al Haines! All those for real here will know who and what I mean. Hope this helps. Goodnight.

Wow there's a lot of answers here. But none of them seem to complete the answer that I was taught by multiple class 1 instructors, a transport examiner, and my own studying as a flight instructor. Okay, as everyone is pointing out, banking the airplane into the turn is correct. However, horizontal force alone is not turning the aircraft... otherwise a canard-based aircraft would never turn! Throw a dart sideways, and it will right itself to fly straight. An airplane follows the exact same principle. Banking the airplane causes the horizontal force, creating horizontal direction through the air. The air hits the side of the aircraft fuselage, and rudder, causing it to 'right itself' or orient itself into the new direction of flight. Can I prove it? Absolutely. Bank the aircraft, and don't allow the aircraft to orient itself into the direction of the airflow by applying opposite rudder. Now the aircraft will not turn, but still fly partially sideways. (this cross-control is also known as a 'slip'). Of all the answers posted, no one mentioned this last detail which actually creates the turn...

the rudder does make the plane turn, but not by itself. In order to safely turn a plane, you must roll, pitch up, and yaw all at the same time. This maintians altitude and allows for the palen to handle g-forces better.

Im no expert but I was told (or read somewhere) that the flaps on the wings help aircraft to turn. If you've ever looked at a wing while it's turning depending on which way the flaps turn up or down it turns the plane to the left or right. I thinks it's the flaps check out this article. http://en.wikipedia.org/wiki/Banked_turn

The aircraft turns when it is banked to one side. For example, if the pilot rolls the aircraft slightly so that the right wing drops and the left wing rises, the aircraft is banking to the right, and this will cause it to turn to the right. Normally, when the aircraft is upright and level, all of the lift generated by the wings pushes straight upwards. When the plane banks, however, part of the lift from the wings pushes sideways, and this causes the airplane to turn. Whenever an airplane is banking, it's turning, and whenever it's turning, it's banking. In a bank, since part of the lift from the wings is pushing the aircraft sideways into a turn, there is less lift to support the aircraft. This means that an airplane will naturally tend to descend slightly as it enters a turn, and climb slightly as it rolls back to straight flight with wings straight and level. Pilots normally compensate for this by increasing power or pulling back slightly on the yoke, both of which increase lift. Rudder isn't used to turn, but it is used to keep the turn coordinated. When a plane banks, it tends to twist a bit in the opposite direction of the bank. The rudder is used to counteract this tendency and keep the bank and the turn smooth. So using the rudder makes a turn more elegant, but it doesn't actually produce the turn—that is done by banking the airplane. For example, If a pilot (one who doesn't have an instrument rating) gets stuck in fog and cannot see where he is going, a top priority for him will be to keep the wings level, because as long as the wings are level, he's not turning. If the wings are not level, he's banking, and therefore he is turning. So even though he cannot see where he is going, he can be sure that he's flying straight ahead as long as he keeps those wings level.

Well sonny. You thought wrong. Establishing a bank (and in doing so, displacing some of the lift component horizontally, as well as inducing centripetal force) causes an aircraft to turn. The rudder only keeps the turn coordinated, preventing a slip or skid. Try to turn a 2 wheel bicycle at riding speed without banking. It cannot be done.