why do commercial planes always have a pitch of around 2 ° (or more) while on cruising flight?

Answer 1

It's pretty well known that all airplanes WILL cruise with some sort of a positive AOA or (Deck Angle). But read below on some other things.

Well, there are several reasons that the angle of attack on an airplane are positive in flight. Reason #1 - Angle of Incidence (angle at which the wings are attached to the fuselage of an airplane) Reason #2 (Weight and C.G of the airplane) An airplane having a heavier weight rather than lighter weight will cruise slightly more nose up than a lighter airplane..more weight means more angle of attack to keep generating the lift needed to counteract the weight.

Center of Gravity - an airplane having a forward C.G will have more of a nose up tendency ( to all you know it all wannabe's, this IS correct) this tendency is the natural force a pilot or autopilot would have to put in to keep the nose level while in flight. If no force were applied with a forward C.G the nose would drop.

Configuration/Power/Speed: A combination of all of these can cause an airplane to cruise with a slight angle of attack above the horizon.

An airplane that normally cruises at .78 mach slows to .72 will result in the airplane needing to attain a higher angle of attack at the slower speed to maintain the altitude desired. This applies to the speed and power.

Now, finally..Configuration changes on an airplane will affect the nose up or down tendencies of an airplane.
Flaps: Raising the flaps reduces the effectiveness of the wings so there is a need to raise the nose to keep the lift that you had while the flaps were down.
Lowering the flaps will increase the surface area of the wing, thus reducing the need for having the nose raised (angle of attack increase) This is why we use flaps for landing..we can fly slower...steeper..without the disadvantage of higher stall speeds etc.

Now..I hope I confused you...I can type all night about this...but I am done..Hope this helps a little....I'm sure alot of people who have never been a CFI or a pro pilot will thumb this down for some reason...go for it...

Jonathan S
ATP-LRJET,HS-125
CFI/AGI

Answer 2

I'm assuming you mean the cabin floor.

It is the most efficient cruising attitude.

The fuselage creates lift just like the wings (although less efficiently) and the angle for the best lift to drag is round about 2 to 4 degrees.

They could design the fuselage to be perfectly level at cruise by mounting the wings at a greater angle to the fuselage (angle of incidence) but the plane would have a lower L/D ratio.

That being said, there is a certain design speed that this would be the most efficient (usually a medium cruise speed). If the plane is flown slower or faster, the fuselage would be at a higher or lower angle.

Then there was the L1011 where someone forgot to carry the one when they determined the wing angle of incidence because the fuselage always points way up in cruise.

Answer 3

What pitch are you refering to?

The angle of attack is the angle made from the whats called the chord of the wing and the direction of wind flowing over it. The chord would be an imaginary line that is drawn through the wing from the very front edge to the back edge. It might be hard to picture so check this out http://www.grc.nasa.gov/WWW/K-12/airplane/geom.html

This angle will be apparent throughout the flight. The higher the angle of attack the higher the pitch of the nose will be.

The deciding factors of what that angle will be during cruise is a direct result of how the airplane was enginered. The short answer would be to provide enough lift so that it equals the weight of the aircraft so it flys stable and doesn't gain or lose altitude.

To explain it further we would need to look into more complicated aerodynamics.

Answer 4

Never encountered that in the many flights I've taken. My understanding was the "level flight" was just that. :D

However, if they do, it would probably to be to add additional lift, and minimise the effect on the passengers and crew.

Answer 5

Capt J got it....just wanted to add that it varies slightly with aircraft type...
I fly helos mainly....but also type rated on Twin Otters and Dash8..and for the helos...we fly nose down!

Answer 6

im not sure about planes but i work on helicopters and the tranny in a helicopter sits on a 2 or 3 degree foward tilt for lift and manueverabilty

Answer 7

So as not to spill the hot coffee unto your lap.

Answer 8

to keep the air pushing up on the flaps at all times its the same reason a helicoptor leans forward to go forward rather than flying perfectly level

Answer 9

idk