On 04/13/2010 01:19 AM, Peter Zutrauen wrote:
> that was my understanding as well - but when trimmed for cruise,
> wouldn't the anti-servo/trim-tab be required to portrude *downwards* to
> drive the trailing edge of the tailplane *up*
Read again what you just said. If the trailing edge of the tailplane
moves up, the trim tab moves up even more. It *always* goes back to the
same stabile position, regardless of trim setting. The only difference
is that this stabile position is achieven by a different tailplane
incidence. This is how it works: you trim it down, it drives the
tailplane up, this will take the trim tab up even more, counteracting
what you just did... and the nett effect is that the tailplane's
trailing edge has moved up. This is how a anti-servo tab works.
> to result in the
> equivalent of pulling back on the stick,
Pulling back on the stick is not the equivalent. If you pull on the
stick, the trim tab won't revert to its stabile aerodynamic position...
and that is why you need to keep pulling on the stick, to counteract the
forces on the trim tab.
> to have the tailplane produce
> the required downward force on the tail?
Actually, it is not a trim tab, but an anti-servo trim tab. It works
differently.
> All the pics I've seen show the trimtab portruding *up*, ie, trim
> foward stick..... no?
The *only* conclusion you can draw from the trimtab protruding up, is
that its stabile position is upwards relative to the tailplane. This
will remain the same for all trim settings. If you change the trim, the
only nett effect is that the tailplane will move to a different
incidence... but the trim tab will remain at the same position. Play
with it on the ground, until you see what's happening.
Frans
|