Pete=0AYou are right about the flettner strips, they bite through the bound
ary layer and stop trim hunting hunting. The mass balance is there to balan
ce the weight of the elevator.=0AGraham=0A=0A=0A=0A=0A_____________________
___________=0AFrom: Peter Zutrauen <peterz@zutrasoft.com>=0ATo: europa-list
@matronics.com=0ASent: Wednesday, 12 May, 2010 14:22:36=0ASubject: Re: Euro
pa-List: Re: Effects of Flaps and Ailerons on Pitch Trim=0A=0AHi Frans,=0A
=0AI understand your thesis (thanks again! :-).=0A=0AYour thesis assumes th
at the tailplane is aerodynamically balanced wrt to the torque-tube positio
n, and the only aerodynamic component which is stabilizing it and keeping i
t from flutter is the anti-servo tab. =0A=0AI question this, as the fulcru
m is ahead of the center of the tailplane. Maybe my skepticism is unwarrant
ed? Is the fulcrum in the center of the tailplane aerodynamically? Without
the anti-servo tab, would the tailplane flutter by design? I doubt this i
s the case, as (I believe) the flettner strips were added to eliminate the
'dead zone' of the anti-servo tab (bringing it out of the boundary layer) t
o eliminate a trim-hunting issue, not flutter (someone with some historical
knowledge please do chime in!).=0A=0AI would expect/hope that the tailplan
e would remain aerodynamically stable without the anti-servo tab, and that
the tab is there only to provide for progressive stick forces, and trim.=0A
=0AThe "still curious",=0APete :-)=0A=0A=0A=0AOn Wed, May 12, 2010 at 8:54
AM, Frans Veldman <frans@privatepilots.nl> wrote:=0A=0A>--> Europa-List mes
sage posted by: Frans Veldman <frans@privatepilots.nl>=0A>=0A>=0A>>On 05/12
/2010 01:03 PM, Peter Zutrauen wrote:=0A>=0A>>> As the tailplane is a symme
trical airfoil, my confused mind asserts=0A>>> that in cruise (since the h
orizontal stab by definition must be=0A>>> providing a downward force) your
tailplane must have been at a negative=0A>>> angle of attack, and since th
e combination anti-servo/trim tab was in a=0A>>> neutral position then I wo
uld have expected a steady stick force would=0A>>> have needed to be applie
d....=0A>=0A>This is an *anti servo trim tab*, if it is not in line with th
e=0A>>tailplane, it puts a force on the tailplane so that the tailplane=0A>
>rotates until it is in line with the anti servo trim tab again.=0A>>You ca
n easily see what I mean by exercising the trim in whatever=0A>>position, a
nd then carefully with your hands on the anti servo tab, try=0A>>to push it
in line with the tailplane again. You will see that the=0A>>tailplane rota
tes during this process, and that you will always end up=0A>>with the anti
servo tab in line with the tailplane.=0A>>This is true for *any* speed, *an
y* CG, etc, except when the pilot=0A>>exercises some force on the stick. An
y force on the stick gets into the=0A>>equation and disturbes this balance.
=0A>>If you trim for a specific speed, all you do is put the stick in a=0A>
>specific position, and then with the trim button, line up the anti servo
=0A>>tab with the tailplane, to keep the tailplane at its new position. You
=0A>>will always end up with the anti servo tab in the same relative positi
on=0A>>of the tailplane.=0A>=0A>>The real confusion is that there are peopl
e flying around with the anti=0A>>servo tab not in line with the tailplane.
This means they are either=0A>>pulling or pushing slightly on the stick, o
r that the tailplane is not=0A>>balanced out properly.=0A>=0A>>About the la
tter: I disconnected everything from the tailplane when=0A>>balancing it ou
t. If you leave the stick connected, you won't get a=0A>>proper balance and
the anti servo tab will not find its equilibrium in=0A>>line with the tail
plane.=0A>=0A>>Next time we do this, I will vary the speed, trim for each s
peed, and=0A>>make a picture again. I would be really surprised if at any s
peed the=0A>>anti servo tab will not remain in its same relative position t
o the=0A>>tailplane. (Of course at every speed, the whole stack of tailplan
e plus=0A>>anti servo tab will rotate to a specific position... but with th
e anti=0A>>servo tab always in line with the tailplane. This is what you do
if you=0A>>trim: lining the anti servo tab up with the tailplane in its ne
w position).=0A>=0A>>Now, for your questions (although they don't matter):
=0A>=0A>=0A>>> - were you in stead-state constant-altitude cruise?=0A>=0A>Y
ep. (We were in close formation so we wouldn't dare to fly anything=0A>>tha
n a very stabilized attitude).=0A>=0A>=0A>>> - where was your trim set at?
=0A>=0A>At 1/3 from the nose down limit.=0A>=0A>=0A>>> - was your stick for
ce = 0?=0A>=0A>Of course 0.=0A>=0A>=0A>>> - what was your cruise speed?
=0A>=0A>About 110 Knots.=0A>=0A>=0A>>> - what was your weight and balance (
with fuel at that point in time)?=0A>=0A>Two adults, about 20Kg of bagage,
and about 40 liters of fuel.=0A>=0A>>Frans=0A>=0A>>========
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