Why Does the Plane Fly Angled Up?

When I am on a Boeing 747 on a flight from L.A. to Taiwan or on a flight back, it feels like I am walking slightly uphill as I am walking down the aisle towards the front of the plane. And when I see a 747 flying, on a TV show or a movie, it does look like it is angled up slightly when in level flight. Why doesn't it fly completely level?



Many thanks.

C.L.Why Does the Plane Fly Angled Up?The lift of a plane has to be equal to its weight.

The lift is equal to the product of the dynamic pressure (proportional to the square of the speed) times the wing area times the lift coefficient.

The lift coefficient is a function of the angle of attack.

So, the wing has to be at an angle, the heavier the plane, or the slower it flies, the greater the angle needed.

So why is the angle of the wing not set at a given angle high enough so that the fuselage is more level in cruise? Two reason for that.

One is that a fuselage at an angle also gives a bit of lift, for not much of an increase in drag. Might as well make good use of it. Second is that, in order to allow takeoff and landings at lower speeds, wings are equipped with flaps that, among other effects, change the resulting camber of the wing to such a degree that the effective angle of attack is increased for a given geometric angle of attack. Having too much of such a setting would make the airplane land with the nose down, which is not advisable (a plane is meant to have the main gear touch down first). This also allows the airplane to have less lift on ground--up to the point of maybe having a slight nose down attitude in some cases--which is desirable (less lift on the ground means less drag to slow down the acceleration during take-off, and more weight on wheel on rejected take-off and landing for better brake effectiveness).Why Does the Plane Fly Angled Up?Naturally when any airplane that is loaded like a 747 or any other heavy jet would be. The airplane will cruise at a few degrees up "deck angle" otherwise known as Angle of Attack. Usually no more than 4-6 degrees depending on weight. This occurs because the load on the wings is greater at heavy weights (nose up) lower load on the wings with lighter weights(nose a little lower..maybe even level). If you were in the cockpit during a long flight you would notice that the more fuel is burned the lower the "deck angle" will be.

Hope this helps a little...



Jonathan S

ATP

CFI/AGIWhy Does the Plane Fly Angled Up?In addition to "Vincent G", I want to add that (in my experience via MS-FlightSim), keeping AoA (Angle-of-Attack) as low as possible but absolutely above Zero-degrees (Level) helps to keep fuel burn to a minimum. This is usually achieved via pitch-trimming. I normally (and very gently) trim my virtual Lear-45 %26amp; B734 pitch-trimmed to about 1-2 degrees AoA. I also do notice that as I use up my fuel, my AoA reduces, so I subtly adjust it so the auto-altitude hold doesn't have a hard time maintaining my chosen height. I also think there is a critical AoA which an airfoil must be at in order to produce the right kind of lift.