Thrust line: a no-thought experiment.

On Nov 14, 6:00*pm, Alan Baker wrote:

I can't help noticing you've somehow missed the cutsie reply when I
provided an actual reference that shows that your entire notion is
bull****...

http://www.av8n.com/how/htm/4forces.html

Interesting that the above article does not address thrust acting
through centre of mass. Not once. Thrust opposes drag, and acts on
mass only during acceleration or deceleration. The thrust line does
not *have* to be aligned anywhere near the CG.
Too much of this discussion has ignored the stabilizer. There's a
thing called decalage, which is the difference in angles of incidence
between the wing and the stab/elevator. The stab is usually angled
down a degree or two relative to the wing's chord line and has the
effect of stabilizing the rotational couple imparted by the CG being
ahead of the CP. This downward alignment also has the necessary effect
of lifting the nose when power is applied so that the nose will fall
into a glide all by itself if the power fails or is reduced. This
aspect of the airplane is mandated by design standards, and is the
reason lifting tails were abandoned early in WWI.
(In lifting-tail airplanes a power reduction would lead to a pitch-
up and stall, and usually an unrecoverable spin. And it still happens
once n a while when some dude overloads his airplane with all that
beer in the back, CG way aft of the limit, and has to hold the yoke
forward to keep the nose from pitching up. Death often follows,
especially on approach when power is low and the tail can't be lifted
anymore.)
So thrust lines that aren't or can't be aligned near the CG are
not a big deal. The stab incidence is adjusted so that the desired
pitching occurs. Just look at the Lake amphibians, with their very
high thrust lines; The decalage is quite pronounced, and even at that
there's some odd behavior when the throttle is opened. But it still
glides like it should when the power's taken off.
http://www.seaplanes.org/graphics/members/la4200.jpg
Note that the thrust is pointed right at the stab to help control
pitching; it's not pointed through the CG at all. THAT would be
impossible.
See the decalage he http://mars.ark.com/~dcf/takeoff2.jpg
And he http://www.seabee.info/images/teal/N6595K-03-640.jpg

Now look at the decalage on various "ordinary" airplanes that have
their props on the nose, and see that there's very little compared to
those amphibians.

Decalage: http://en.wikipedia.org/wiki/Decalage

Dan