On Jun 24, 6:32 am, Gig 601Xl Builder
wrote:

Jay, he's full of crap. The Horz Stab has four attach points. It doesn't
move at all unless you count the fact that the entire airplane moves
when you move it.

I am indeed full of crap sometimes, but not this time. The four attach
points that Dr. Einstein here was referring to are the exact parts
that moved slightly when I pulled on the stabilizer tip.

Here's a graphic visual example for the mechanically challenged:

Imagine that the four stabilizer mounting tabs on top of the fuselage
were all 12 inches tall, instead of the one or two inches tall that
they actually are... So the horizontal tail would be mounted a foot
above the top of the fuselage.

Under this example, when you tried to move one stabilizer tip forward
and the other one aft, it would move easily, and the four foot-long
imaginary mounting tabs would all move back and forth a little as you
twist the tail left and right (looking from above).

In order to prevent this type of movement, you would have to rivet
sheets of aluminum between these tall stabilizer supports to make the
system "torsionally stable". You would be riveting "shear webs"
between the stab supports, to oppose the shearing (and then twisting)
relative motion.

Now of course the mounting tabs are not a foot tall, so you cannot
swing the stabilizer tip fore and aft with one finger like you could
if it was a foot tall. But the stabilizer mounting tabs ARE an inch or
two above the fuselage, and this distance is NOT braced in shear or
twisting. So you CAN move it fore and aft a little, and when you do
this you CAN see the mounting tabs move relative to each other a
little.

Ladies and Gentlemen, you CANNOT move the stabilizer back and forth
this way on an undamaged Cessna, Taylorcraft, Champ, or Beech. You
cannot do it on a Luscombe, you cannot do it on an undamaged Piper
Cherokee, and you cannot do it on a Maule and you cannot do it on a
Grumman Yankee. I can go on if I have not made the point clearly
enough.

The stabilizer mounting system on the 601 and possibly the 701 is in
my opinion not rigid enough. The tabs are not braced against shearing
or twisting. There is no reason you should be able to move the
stabilizer back and forth on a standard configuration light aircraft
like that. When you move it like this, you are slightly bending the
stabilizer mounting tabs (and the attach structure on the fuselage)
back and forth a little bit each time.