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Pitch During Cruise.

Sudden From Sweden, joined Jul 2001, 4127 posts, RR: 6
Posted (10 years 11 months 3 weeks 1 day 2 hours ago) and read 2480 times:

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!

10 replies: All unread, jump to last

Lubicon From Canada, joined Oct 2000, 197 posts, RR: 0
Reply 1, posted (10 years 11 months 3 weeks 1 day 2 hours ago) and read 2465 times:

I believe most jet airlines cruise with a slight nose up pitch although I don't know why.

FredT From United Kingdom, joined Feb 2002, 2184 posts, RR: 26
Reply 2, posted (10 years 11 months 3 weeks 1 day 1 hour ago) and read 2454 times:

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 From United States of America, joined Nov 2001, 749 posts, RR: 14
Reply 3, posted (10 years 11 months 3 weeks 1 day ago) and read 2453 times:

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.

...from the Banana Republic....

Wilcharl From United States of America, joined Jun 2000, 1158 posts, RR: 3
Reply 4, posted (10 years 11 months 3 weeks 1 day ago) and read 2437 times:

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 From United States of America, joined Aug 2000, 3956 posts, RR: 36
Reply 5, posted (10 years 11 months 3 weeks 23 hours ago) and read 2424 times:

DC-10 is positive 4 pitch up during normal cruise.

Chicks dig winglets.

Panman From Trinidad and Tobago, joined Aug 1999, 789 posts, RR: 0
Reply 6, posted (10 years 11 months 3 weeks 8 hours ago) and read 2349 times:

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 From Mexico, joined Nov 2001, 556 posts, RR: 0
Reply 7, posted (10 years 11 months 3 weeks 4 hours ago) and read 2330 times:

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 From United Kingdom, joined Jan 2000, 2662 posts, RR: 52
Reply 8, posted (10 years 11 months 3 weeks 2 hours ago) and read 2328 times:

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...

Jetguy From , joined Dec 1969, posts, RR:
Reply 9, posted (10 years 11 months 3 weeks 2 hours ago) and read 2321 times:

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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