Re: Nose high during cruise?

From:         STOCKER@alpha.salem.ge.com (David Stocker)
Organization: GE Drive Systems, Salem, VA, USA
Date:         10 Mar 94 02:39:57 PST
References:   1
Followups:    1
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In <airliners.1994.980@orchard.Chicago.COM> sdd@larc.nasa.gov writes:

> On many flights on jet airliners, I have noticed that during cruise the 
> aircraft appears to maintain a nose-up pitch angle.  This is not only 
> based on personal perception, but also the stewardesses say that the push 
> carts tend to move downhill (i.e. toward the rear of the aircraft).
> 
[snip snip]
>
> Why then do I notice this "uphill" effect?  Is the fuselage actually 
> pitched up slightly?  I have noticed this on many flights on jet 
> airliners, but have never noticed a "level / nose on the horizon" 
> attitude during a lengthy cruise. 
> 
I've noticed this too - I always assumed that the plane was
trimmed out to that attitude.  The lift produced by the wings
is a function of the airspeed and angle of the relative wind
over them, this must balance with the weight of the plane,
which is of course not all located at the CG but distributed
about.  While I suppose it is possible for everything to
balance in a perfectly level flight attitude, I would think
this is rarely the case.

When I am flying (not jetliners, mind you!), and I sense
that I am flying in a nose high attitude, I adjust the trim
(nose down) and power (up) accordingly.  But this makes the
plane less stable in pitch, and it becomes harder to hold
a fixed altitude.  Perhaps there is a stibility margin
involved with such a nose high attitude.  Of course this
is not as efficient (i.e. most any airplane that doesn't
have afterburners can get "behind the power curve" - it can
be in such a nose-high attitude that it will take full power
just to hold altitude, and climb is not possible without
bringing the nose DOWN) - but the added stability is desired.

David Stocker

stocker_dg@salem.ge.com         (PP-ASEL, CAP, EAA, AOPA)
GE Drive Systems, 1501 Roanoke Blvd, Salem, Virginia, USA
703-387-7844   GE Dial Comm: 278-7844  Fax:  703-387-7651