Frans
and all those million people who might be
interested about this topic and follow it:
--------------------------------------------------
From: "Frans Veldman" <frans@privatepilots.nl>
Sent: Saturday, May 15, 2010 11:43 AM
Subject: Re: Europa-List: Re: Effects of Flaps and
Ailerons on Pitch Trim
> This is a compliment to the factory as I got the
> "accelerated kit" with
> the tailplanes built by the factory.
Yes, I called them NG (next generation) tailplanes
without bluefoam structure inside.
> The balance of the tailplane and anti servo tabs
> is not purely
> aerodynamic, it is the result of all forces
> acting upon the system:
>
> 1) If the pilot pulls or pushes on the stick,
> the tailplane will rotate,
> the anti servo tabs rotate even further, and
> this imbalance is countered
> against the force the pilot is exercising. This
> means we have a stable
> position here with the anti servo tabs pushing
> the system some way, and
> the pilot pushing it the other way. The trim
> tabs stay deflected then,
> because they provide the counter force to null
> out the pilots unconsious
> input.
>
> 2) If the tailplane is not weight balanced
> correctly, it has a tendency
> to rotate by itself, and the anti servo tabs
> need to balance this
> tendency out. Again we get a situation where
> weight is trying to get the
> tailplane rotating this way, and the anti servo
> tabs trying to undo
> this. There is a balance, but this balance is
> not with the anti servo
> tabs lined out behind the tailplane.
Frans, may I add a third influence in your list?
How about that, could we consider also it (please
notice, this is *not* a statement):
3) The friction in the pitch system. I remember
some builders had some difficulties with
unnecessary friction with the roll/pitch control
system in the cockpit modul (that was not a NG
cockpit modul!).
Anyway, if there is more or less too much friction
in the pitch /tailplane control, I assume that is
a force which will also keep the trim tabs
deflected and pilot thinks "this plane is well
trimmed" and it is not!
This is quoted from Sport Aviation, vol 59 No 5
May 2010, page 53 /Ravin 500 (an experimental from
South-Africa which is a look-a-like Piper
Comanche):
" Starting at 195 mph, the airplane will maintain
any speed between 195 and 220 mph hands free,
because friction holds the elevator at the
deflection required. But, keep in mind friction
causes a band of hands-free trim speeds. So, the
25-mph trim speed band could span 195 to 220 mph
or 170 to 195 or anything between, like 181 to
206. "
Interesting: "band of trim speeds".
> So, in both situations, you won't get the anti
> servo tabs to line up
> with the tailplane.
>
> What can go wrong:
> 1) The pilot. When I was learning to fly, the
> instructor had a habit of
> ripping my hands of the yoke, which immediately
> revealed whether I had
> trimmed the airplane incorrectly. Often I was
> sure I had trimmed
> correctly, but apparently it is easy to
> unconciously exercise a force
> upon the yoke or stick. So as a student I
> quickly developed the habit to
> "let go of the stick" after trimming to make
> sure it is really trimmed
> and get the tension of my muscles out of the
> equation.
> Maybe everyone does this, maybe not. Anyway,
> keep this in mind: with the
> Europa design you can possible gain a few knots
> by making sure the
> tailplane is perfectly trimmed for the intended
> speed: let go of that stick!
My habit: when levelled and cruising - I do not
touch the stick at all. When necessary, I only use
my panel attached low speed (adjustable) trimming
ability to control and maintain the desired
altitude.
In the rough air, I of course keep the stick
between my thumb and a fore finger.
>
> 2) The mass balance weight. As said before, I
> got through the hassle to
> disconnect the pitch tube to really balance out
> the tailplane. Still
> then, it is difficult to balance it with the
> frictions and inertia
> involved. When I thought by moving the trailing
> edge of the tailplane up
> and down that the system was in balance, I
> double checked with an
> elastic band... and discovered that humans are
> not able to compare a
> lifting force against a pushing force very well.
> So, tape an elastic band to the trailing edge,
> put a mark somewhere, and
> start pulling the trailing edge up or down.
> Measure the distance between
> the mark and the trailing edge with a ruler,
> exactly at the moment the
> tailplane actually starts moving. Do this also
> the other way. Goal is to
> have the trailing edge moving with the same
> stretch of the elastic band
> pulling up and pulling down.
Well Frans, that was nice.
I left those rubber bands for boys with model
aeroplanes and did it with electric lightfish
scale until I was happy enough. You know, fighting
against grams and redoing it many many times.
Btw I used same equipment (as per manual!) to
calibrate the spring force in the trimming motor
system.
(Lifting and pushing - how about pushing and
pulling when the entire plane is in the vertical
position. OK - that was not in this world.)
>
> If you are flying around with the anti servo
> tabs deflected upwards, it
> could mean the mass balance weights are a tad
> too heavy, or the pilot is
> unconsiously pulling on the stick. The weight of
> the pilot's arm is
> enough to disturb the delicate balance.
Or + there is some friction and they just happen
to be so or the tailplanes are not "perfectly
aerodynamically balanced" = they are not NG
tailplanes = the builder has made them by
her/himself from foam or the combinaton of at
least those mentioned four factors.
Maybe there are even more factors (which will
cause The Symptom "deflected trim tabs when
trimmed" (that is: pilot thinks I am trimmed!).
>
> If you are sure both of these are really ok,
> then there is a last
> resort: You could connect a spring or bungee to
> the pitch push rod, and
> "preload" it in the correct direction. This is
> however where my
> understanding of the system ends: I'm not sure
> if this could induce
> flutter. Then again, it is not different than a
> pilot unconsiously
> pushing or pulling on the stick, and the system
> seems to cope with that
> very well. This corrective bungee gets into the
> equation and can get the
> balance so that the anti servo tabs line up
> behind the tailplane, and
> this could gain you a few knots.
OK. If there is no pilot hand in the system and
they really *are* perfectly balanced by weight,
what is still left:
Unbalancing by aerodynamically and those possible
friction forces.
Just now - please correct me and I am sure you
will do it if necessary - by preloading (with a
spring or bungee) the system you can take out only
unbalancing which is by aerodynamic.
Please remember - no pilot hand and no errors in
balancing by weight. So, almost all the "foam
tailplane Europas" ( except Mr Paul McAllisters )
will need a bungee or spring to the system
because they cannot be "perfect" because of the
builder variations (and a poor manual when
designing the shape of the tailplanes!).
>
> I had it all worked out, assuming that ALL
> Europa's had this deflected
> trim tab defect... and then discovered that my
> Europa doesn't need it at
> all. :-)
>
That is no wonder: you have made it (and bought NG
tail planes).
***
An idea: how to fly formation with some Europa
with "the deflected trim tabs syndrom" with normal
cruising speed. With an advice and instructions by
radio the Europa pilot will trim, keep levelled
same time AND push or pull the stick until they
are in-lined. Heureka we have found the necessary
force for trim tabs & tailplanes in-lining . Add
the spring or bungee with that force and you have
gained some knots, congratulations!
***
>> Frans - next time I will consider a bit more
>> before I think you are wrong.
>> You are wrong probably very seldom, I assume.
>
> Well, I wouldn't guarantee that. In fact, I just
> keep my mouth shut if I
> do not have a strong feeling that I'm right. ;-)
That is a *good* lesson for me. But, actually I
was sure!!!
Infact - Frans - I almost asked you "why in the
hell we have that trimming ability at all if they
are always in-lined with tailplanes"!
It was absolutely "The New World" to understand
the meaning of the "Aerodynamically Balanced".
As you well remember - me and *some* other boys
---From Z (this is for You Mr. XXXXstrip) and from
other countries - I was sure there will be forces
without any extra forces by
anti-deflections-ability.
That means (if it would be so) Europa could be
flyable without tabs at all.
But I assume it is not (without
anti-servo-system).
I wrote I do not like this!
In the other hand: if the pilot happen to
understand what means sudden feeling "I have not
at all pitch forces" (=that is I have maybe lost
my tabs or anti-servo-function-ability or I have
not at all a pitch control via stick).
1) if the tabs or the anti-servo-function has
gone, you have still a pitch control but no forces
at all in the stick. Take it very easy. Could I
fly in that case? Must be awful!
2) if the control tube has disconnected (and you
still have tailplanes) pilot can control pitch by
operational trim tabs. Landing, well...maybe
possible to walk away from crashed plane, is it?
As I wrote - I will respect and check my trim tabs
more than carefully. I really did not know they
have so important role in that Europa came.
Quite a lot of other
> people had the same knowledge about the
> tailplane, but most of them
> didn't bother to convince the rest of us. I was
> prepared to leave it as
> well, but your Donald Duck thing was just too
> provocative. ;-)
OK, so that (DD) was worth of it. Please remember
there are many people just monitoring this list.
Maybe this discussion gave the light for some
other people also. I think DD was not alone!
Frans, thank you once more (and please comment!).
Raimo aka DD
OH-XRT Europa #417 (with the foam tailplanes and
trim tabs (just slightly) deflected) !!!
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