In article
,
JohnO wrote:

On Oct 29, 11:46*am, Alan Baker wrote:
In article ,
*"Gregory Hall" wrote:



"Bryan Martin" wrote in message
...
That could only happen if the plane was loaded with the CG way aft of
the limit. Otherwise, the plane would pitch DOWN if the stabilizer
stalled because the stabilizer normally produces a down force to keep
the nose up.

If it worked that way it would be a built-in safety factor helping to
forestall a stall of the main wing. But suppose the motor died and the
aircraft was then a glider. One must glide nose down. The horizontal
stabilizer forcing the nose down would then cause the pilot to pull back
on
the stick to counteract the forces for aft. If the stabilizer stalled in
this attitude the nose is supposed to pitch down but would it? The tail
might just continue to drop provided the main wing still gets traction???
CG
is dependent upon both lifting both control surfaces as well as weight
distribution.

Sorry. But centre of *mass* (to use the correct term) is not in any way
dependent on the lift from anything.

The centre of mass is a parameter than is completely fixed by the
distribution of the mass of the aircraft's components. Whether any
surface is providing lift will not change it.

So as long as the main wing is located aft of the centre of mass, the
aircraft will pitch *down* when lift from the tail plane is lost.

Period.
snip

It's kinda simple. Assuming the main wheels are under the wing and the
a/c still rests on those and the nose wheel then wings are aft of the
cg and the horizontal stabilisers are there for down force to keep the
nose up. Not sure what Gregory is banging on about here.

Well, it's not quite *that* simple. There's no rule that the wheels need
to be directly under the centre of lift of the wing, but yeah...
....basically that's it.

I have no idea how anyone can get the wrong headed idea that the centre
of mass of a rigid body can move around.

--
Alan Baker
Vancouver, British Columbia
http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg