On Fri, 29 Oct 2004 08:23:18 +0200, Bruce Greeff wrote:

John Giddy wrote:
On Thu, 28 Oct 2004 08:07:07 +0200, Bruce Greeff wrote:


John Giddy wrote:

On 28 Oct 2004 02:44:06 GMT, Jim Vincent wrote:



Jim,
Why does the elevator have more translation on a T-Tail than on a
conventional one please ? (I presume you are referring to translation
in a direction normal to the tailplane surface)
Bemused John G.

John,

If the stab is mounted at the fuselage, if there is roll, the stab only
experiences a rotation around the center of the stab.

If the stab is T, then not only is it rotating, it is also moving in a circle
with a diameter of the rudder fin. Does that make sense?

Also, with a T, if you go full rudder in one direction then another, the fin
adds the inertia of the stab mounted at the top of the rudder...a torsion from
yaw too!



Jim Vincent
N483SZ



OK Jim,
I agree. I was thinking of normal elevator operation, and movement in
the pitch direction, which is the same for both arrangements.
Cheers, John G.

The one that tends to break them is the torque resulting from rapid translation
acceleration. With a T-tail the moment of inertia is far greater, so when you
ground loop, or perform a flick maneuver the lateral acceleration of the
elevator imposes large loads on the structure.

Agreed, except that it is not just the elevator. It is the whole
tailplane.
Cheers, John G.
I stand corrected - Cirrus drivers sometimes forget that there are sailplanes
that have fixed horisontal stabilisers... ;-)

That thought had crossed my mind, but I resisted the chance to point
it out :-)
Cheers, John G. (Std Cirrus Ser: 6720