sudden
Posts: 3934
Joined: Fri Jul 13, 2001 5:20 pm

Pitch During Cruise.

Fri Jun 07, 2002 11:51 pm

The 737 is built so during cruise it has a positive pitch of 3-4 degrees.
For what reason is this, and what is the positive outcome of it?
Any other airliner that have this as well?
When in doubt, flat out!
 
Lubicon
Posts: 201
Joined: Sat Oct 14, 2000 5:13 am

RE: Pitch During Cruise.

Sat Jun 08, 2002 12:38 am

I believe most jet airlines cruise with a slight nose up pitch although I don't know why.
 
FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: Pitch During Cruise.

Sat Jun 08, 2002 1:32 am

The pitch is just a matter of definition. They could just as well have defined the pitch reference line to have the aircraft flying at 0 degrees pitch in cruise - or at -20 degrees pitch for that matter - without changing the actual attitude of the aircraft. The design attitude is of course whatever gives the best fuel efficiency, if the designers got it right. And yes, there are planes out there where they didn't.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
barney captain
Posts: 1399
Joined: Tue Nov 06, 2001 5:47 pm

RE: Pitch During Cruise.

Sat Jun 08, 2002 1:53 am

I'm not sure I follow FredT's explanation but here's my understanding. The positive pitch has to do with providing a positive angle of attack. It is accurate to state that the engineers determine the most economical cruise Mach, which generally gives @ 3 degree's of nose up attitude. I know on the 737, the faster you go beyond econ cruise, the pitch up gradually reduces as speed increases. When I've had the -300 beyond @ .78, the pitch has dropped to @1.5 degrees.
Southeast Of Disorder
 
wilcharl
Posts: 1153
Joined: Sun Jun 25, 2000 11:19 am

RE: Pitch During Cruise.

Sat Jun 08, 2002 2:45 am

any idea what the pitch attitude of the L-1011 was? I was recently on an MD-11 on a long pond crossing and it too seemed to have a noticible nose high pitch attitude
 
XFSUgimpLB41X
Posts: 3960
Joined: Fri Aug 25, 2000 1:18 am

RE: Pitch During Cruise.

Sat Jun 08, 2002 3:15 am

DC-10 is positive 4 pitch up during normal cruise.
Chicks dig winglets.
 
Panman
Posts: 603
Joined: Mon Aug 09, 1999 8:25 pm

RE: Pitch During Cruise.

Sat Jun 08, 2002 6:18 pm

Theory of flight:

Optimum angle of attack of an aerofoil is 3-4 degrees.

The wings are set at an angle of incidence (angle in respect of the longitudinal axis of the aircraft) that gives their optimum angle (or near to) during cruise. If the wings had a 0 degree angle of incidence the angle the aircraft would have to take in cruise would be steeper.

PanmAN
 
cosync
Posts: 635
Joined: Sat Nov 17, 2001 7:53 pm

RE: Pitch During Cruise.

Sat Jun 08, 2002 10:37 pm

i dont understand one thing.
hwo can u all be so sure about saying that the plane is always at a specific pitch at depends on tehe Indicated Airspeed. u can have 0 angle of attack. just by going a little faster.
i think
 
Rick767
Posts: 2613
Joined: Sun Jan 30, 2000 8:11 pm

RE: Pitch During Cruise.

Sat Jun 08, 2002 11:48 pm

Cosync,

Yes that is correct, by increasing IAS the pitch will decrease and vice-versa. What is being said here is that for the normal and economical cruise speed range on most jets the typical pitch is +2 to +5 degrees, depending on the aircraft.

It is also worth noting that there is a slight reduction in pitch attitude as the flight progresses since the weight of the aircraft reduces and therefore less lift force from the wings is required to provide level flight.

This is more noticeable on long flights.

But even if you put the 757/767 up to Mmo in the cruise, the pitch attitude will not drop to 0 degrees, maybe just a tad under +2 degrees.

Hope this made sense?!

Rick.
I used to love the smell of Jet-A in the morning...
 
Guest

RE: Pitch During Cruise.

Sun Jun 09, 2002 12:09 am

Here's a bit o'trivia...

The tip tanks on the early Learjets were mounted parallel with the fuselage. When the aircraft was in cruising flight the tip tanks were angled at about +3 degrees to the relative wind. After the first several aircraft were delivered, the angle of incidence of the tanks were reduced by 3 degrees so that they would be more aerodynamic in cruise flight.

Early Lear


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Late Lear


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Photo © Colin Parker



See, I did learn something when I got my type-rating.

Jetguy
 
sudden
Posts: 3934
Joined: Fri Jul 13, 2001 5:20 pm

RE: Pitch During Cruise.

Mon Jun 10, 2002 6:26 pm

Thank you all for the nice and detailed replys!
When in doubt, flat out!

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