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frans(at)privatepilots.nl
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 Posted: Sat May 15, 2010 12:44 am Post subject: Effects of Flaps and Ailerons on Pitch Trim |
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On 05/14/2010 07:21 PM, Raimo Toivio wrote:
| Quote: | When trimming that means we are in fact in-lining tailplanes with
trimtabs to a certain desired position!
|
Well, I hoped to see a lightbulb switching on, but you lit the whole
X-mas tree!
We had a good laugh over here. 
| Quote: | One interesting point also: obviously all the tailplanes which have been
built perfectly, are perfectly also aerodynamically balanced.
Like Frans´s Europa´s tailplanes.
|
This is a compliment to the factory as I got the "accelerated kit" with
the tailplanes built by the factory.
Then again, I don't think you need to have perfectly aerodynamically
balanced tailplanes.
Now we agree about the function of the anti servo tabs, we can go back
to my previous statement about the mass balance weight.
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.
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!
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.
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.
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.
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. 
| Quote: | 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.  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.
| Quote: | Would be nice to meet you in Texel next autumn.
|
Nice to hear that you are coming! We might also show up in Popham next
month.
| Quote: | I give you some extra present: have you earlier seen a Duck on the wing
behind a running star engine?
|
Nice picture!
Frans
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raimo.toivio(at)rwm.fi
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| Posted: Thu May 20, 2010 2:15 pm Post subject: Effects of Flaps and Ailerons on Pitch Trim |
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Frans
and all those million people who might be
interested about this topic and follow it:
--------------------------------------------------
From: "Frans Veldman" <frans(at)privatepilots.nl>
Sent: Saturday, May 15, 2010 11:43 AM
To: <europa-list(at)matronics.com>
Subject: Re: Re: Effects of Flaps and
Ailerons on Pitch Trim
| Quote: | 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.
| Quote: | 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".
| Quote: | 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.
| Quote: |
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.)
| Quote: |
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!).
| Quote: |
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 McAllister´s )
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!).
| Quote: |
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!
***
| Quote: | > 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. XXXX´strip) 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
| Quote: | 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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josok-e
Joined: 29 Jan 2010
Posts: 16
Location: Ivalo Finland
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| Posted: Fri May 21, 2010 7:49 am Post subject: Re: Effects of Flaps and Ailerons on Pitch Trim |
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First: Any plane can only be trimmed for one speed. Any change of speed will require adjustment of trim.
Second: We have anti-TRIM-tabs. Mind the trim part of the description. Without deflection, the plane has to be at the designed zero trim speed. Any other speed will require trim, in other words: deflection.
Third: If the anti-trim-tabs could or would be level, zero, at any speed, you would not need them. It would be quite stupid to invent and add them in the first place.
Frans, in your unique case you could save a lot of complicated, potentially dangerous, heavy metal and remove all that stuff. Just fix your trim tabs to neutral for ever.
All readers: This is not a seriously intended and potentially dangerous advice. Please discard the idea, i shall not be held responsible!
Regards,,
Jos
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JonSmith
Joined: 21 May 2010
Posts: 110
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| Posted: Sun May 23, 2010 12:34 am Post subject: Re: Effects of Flaps and Ailerons on Pitch Trim |
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Hi Jos,
I am very sorry but I have to disagree with nearly everything in your recent posting! Your points are relevant to a "conventional" fixed tailplane with separate elevators and trim tab, but not to the Europa tail which is a masterpiece of design!
The thing is - your comments about "needing trim tab deflection" apply to a conventional elevator - which is in effect a trailing control surface or tab itself. This conventional elevator will always need to be "held" against a restoring force from the airflow and the trim tab deflection provides this "holding force", or trim as we call it.
The Europa tail principle is different however. The job that the horizontal tail surface does is the same on ALL conventional fixed wing aircraft (Europa, C-150, Piper Cub, whatever) - it provides a small downforce to balance the nose down pitch effect generated by the wing. It will always be a downforce needed from the tail because the C of G is always forward of the Point or Centre of the Lifting force generated by the wing. It is only a small downforce needed from the tail because of the distance the tailplane is from the wing - you have a long spanner!! As the Europa has a symmetrical section tailplane then this downforce has to be generated by a slightly negative angle of attack of the Relative Airflow to the tailplane. (Look at the line drawings of the aircraft - the tailplane's incidence in the neutral position is slightly negative to the fuselage waterline/ reference line - the wing's incidence of course is 2.5 deg positive). The downforce can be varied by the pilot adjusting the angle of the tailplane with the stick (control) or by changes to the Relative Airflow by say a gust (the starting point of the aircraft's natural longitudinal stability).
Now the clever bit regarding the Europa! The tailplane is "AERODYNAMICALLY BALANCED" which means that the tailplane can provide this "lift" force (downforce) BUT REGARDLESS OF THE PRODUCTION OF THIS DOWNFORCE AND THE AMOUNT OF IT THE TAILPLANE(OR ELEVATOR CONTROL) WILL NOT BE DEFLECTED AWAY FROM IT'S CURRENT POSITION EVEN WHEN THE GENERATED DOWNFORCE CHANGES BY CHANGING RELATIVE AIRFLOW.
THE TAILPLANE WILL NOT BE DEFLECTED BY THE RELATIVE AIRFLOW, EVEN IF THIS AIRFLOW CHANGES IN DIRECTION OR SPEED RELATIVE TO THE TAILPLANE. This is due to this very clever aerodynamic balance. Basically any "rotating" force on the tailplane created by the airflows's angle of attack will be the same behind the pivot (torque tube) as that created in front of it. In other words the slight negative angle of attack causes the airflow to "push down" on the tailplane from above with an equal average force behind the torque tube as in front of it. This is true regardless of speed and the angle of the airflow and so the tailplane will never be deflected by just the airflow even if the airflow changes. This is very hard to visualise because of course the surface area of tailplane behind the torque tube is very much greater than in front of it - but THE SHAPE or cross section of the tailplane is also very different fore and aft of the torque tube and due to the beautiful design this AERODYNAMIC BALANCE IS THERE!!
Now then - TRIM TABS!! The job of the tabs on the Europa is to hold the tailplane in the position that the pilot wants it to stay in! THE TAILPLANE WILL STAY IN IT'S CURRENT POSITION ONLY WHEN THE TRIM TABS ARE FLUSH WITH THE TAILPLANE SURFACE. IF THE TABS ARE NOT FLUSH THEN THEY WILL BE CREATING A ROTATING FORCE ON THE TAILPLANE THAT WILL WANT TO MOVE IT FROM IT'S CURRENT POSITION TO ACHIEVE THE TABS-FLUSH STATE AGAIN. If the tailplane moves out of the chosen trimmed position - maybe the pilot inadvertantly moves the stick - then because of the clever linkage design, the tabs move from their flush position in the same direction. (Tailplane trailing edge moves up - tabs move up). The tabs thus provide an aerodynamic "restoring force" to put the tailplane back where it was - in other words it's original trimmed position with the tabs flush again! The trim switch/ control on the Europa merely resets or adjusts the tailplane position where the tabs are flush with the surface. The required tailplane position simply depends on how much downforce you want it to make which depends entirely on what you are doing with the aircraft!
So, the functions of the tabs are:
1/ To hold the tailplane in the chosen position (tabs flush when achieved) and provide a restoring force to the tailplane if it is moved away from it's chosen trimmed position - this is known as "feel" that is provided to the pilot through the stick - the further you move the stick away from the chosen trimmed position (without re-trimming) the greater the tab deflection and thus the greater this restoring force will "feel". If there were no tabs then the tailplane would just stay wherever the pilot put it, regardless of speed/ airflow etc - but there would be no "feel" to the elevator at all (zero feel).
2/ To be pilot-adjustable so that you can reset the trimmed (tabs flush) tailplane position as required during flight.
Note that none of this theory specific to the Europa tailplane control is connected to the aircraft's longitudinal stability theory - that is a different subject and has no relevance specifically to balanced tailplanes or otherwise. Longitudinal stability theory is the same on all conventional fixed wing aircraft regardless of tailplane design.
Variances: A perfectly constructed and balanced tailplane will always have it's tabs flush with the tailplane in steady correctly trimmed flight, regardless of speed and attitude. Variation in build MAY affect this perfect state. If the aerodynamic balance of the tailplane is not quite perfect (not quite the perfect tailplane profile section) then the balance of forces (created fore and aft of the torque tube) might not be quite perfectly equal with the trim tabs flush and so a slight tab deflection in the appropriate direction will be permanently needed in steady trimmed flight to balance the forces up again. Not a problem, just very slightly less efficient due to the slight increase in drag caused by the permanently deflected tabs. Also if the counterweight (mass balance weight) in the fuselage is not perfectly correct then this too will create an unwanted rotating force on the tailplane that would require an (unwanted and continuous) tab deflection to counter/ balance out this unwanted force. Also, if the pilot flies "out of trim" for some reason then a tab deflection will be required in the appropriate direction to oppose the pilot's push or pull force on the tailplane. This one can easily be corrected though!!!
The only real way to tell if your tailplane system is absolutely perfect in balance (aerodynamically as well as in weight) is to trim the aircraft perfectly in steady flight (any steady speed) and get a mate to come up behind you and take a close up photo of your tabs. In a perfect set up they will be flush with the tailplane!!!!
Cheers, Jon
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G-TERN
Classic Mono |
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raimo.toivio(at)rwm.fi
Guest
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| Posted: Mon May 24, 2010 5:39 am Post subject: Effects of Flaps and Ailerons on Pitch Trim |
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Hi Jon
Thanks for an exellent settlement!
| Quote: |
Variances: A perfectly constructed and balanced
tailplane will always have it's tabs flush with
the tailplane in steady correctly trimmed
flight, regardless of speed and attitude.
Variation in build MAY affect this perfect
state. If the aerodynamic balance of the
tailplane is not quite perfect (not quite the
perfect tailplane profile section) then the
balance of forces (created fore and aft of the
torque tube) might not be quite perfectly equal
with the trim tabs flush and so a slight tab
deflection in the appropriate direction will be
permanently needed in steady trimmed flight to
balance the forces up again> --------
G-TERN
Classic Mono
|
I assumed earlier all the factory build NG
tailplanes are perfect but builder-built foam
structures are seldom ideal.
How is that - do there exist any Europas with foam
tailplanes flying with trimmed trimtabs perfectly
in-lined with tailplanes?
Was not that interesting: many people have built
ja flied with success their Europas and still they
could not understand it is principles how it
works?
Jos, welcome to D.D. Club there are many
members already...
Terveisin, Raimo Toivio
Europa XS Mono OH-XRT #417
37500 Lempäälä
p +358-3-3753 777
f +358-3-3753 100
toivio(at)fly.to
www.rwm.fi
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josok-e
Joined: 29 Jan 2010
Posts: 16
Location: Ivalo Finland
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| Posted: Mon May 24, 2010 1:42 pm Post subject: Re: Effects of Flaps and Ailerons on Pitch Trim |
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(at)Jon:
Of course the Europa tailplanes are fully balanced aerodynamically, so are conventional tailplanes. I can't think of tailplanes with an aerodynamical design providing lift. This aerodynamical balance has nothing to do with the discussion here. The anti-TRIM-tabs on the Europa will deflect the whole tailplane, if not neutral, the trimtabs on a conventional elevator will deflect the elevator if not neutral. Why this varying deflection is needed has been mentioned in this thread before and i will not start repeating facts. If you really think the Europa does not need trim, well, fix the tabs And eat a few burgers extra, because it will be a muscle exercise. And, oh, the ANTI part of the equasion is to add resistance to the feel an the stick, to prevent pilots from breaking things. How that works has also been excellently explained previously.
I am very sorry to read that you disagree of most of my simple message, and in a very long message fail to tell me why.
Regards,
Jos Okhuijsen.
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grahamsingleton(at)btinte
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| Posted: Mon May 24, 2010 3:24 pm Post subject: Effects of Flaps and Ailerons on Pitch Trim |
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Jos
I tend to agree with you. In most of the envelope the tailplane has to provide lift, usually down force. In fact the pivot on the Europa is not quite at the aerodynamic centre. I don't remember the reasons but are concerned with short period oscillation. (not flutter)
There will have to be a slight tab deflection to apply the load required by the pilot, ie speed control. In particular flaps down the a/c of the wing moves significantly so a big trim force is required.
So, I personally haven't the mental energy to work out why the tab may not be in line, I just accept what the stick load tells me. Just try taking off with trim set wrong, my goodness do you need to push on the stick!
Graham
From: josok-e <josok-e(at)ukolo.fi>
To: europa-list(at)matronics.com
Sent: Monday, 24 May, 2010 22:42:31
Subject: Re: Effects of Flaps and Ailerons on Pitch Trim
--> Europa-List message posted by: "josok-e" <josok-e(at)ukolo.fi (josok-e(at)ukolo.fi)>
(at)Jon:
Of course the Europa tailplanes are fully balanced aerodynamically, so are conventional tailplanes. I can't think of tailplanes with an aerodynamical design providing lift. This aerodynamical balance has nothing to do with the discussion here. The anti-TRIM-tabs on the Europa will deflect the whole tailplane, if not neutral, the trimtabs on a conventional elevator will deflect the elevator if not neutral. Why this varying deflection is needed has been mentioned in this thread before and i will not start repeating facts. If you really think the Europa does not need trim, well, fix the tabs And eat a few burgers extra, because it will be a muscle exercise. And, oh, the ANTI part of the equasion is to add resistance to the feel an the stick, to prevent pilots from breaking things. How that works has also been excellently explained previously.
I am very sorry to read that you disagree of most of my simple message, and in a very long message fail to tell me why.
Regards,
Jos Okhuijsen.
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JonSmith
Joined: 21 May 2010
Posts: 110
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| Posted: Tue May 25, 2010 11:59 am Post subject: Re: Effects of Flaps and Ailerons on Pitch Trim |
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Hi Jos & Graham, My theory about the tailplane was based on the principle of a FULLY aerodynamically balanced "all moving" tailplane, this being the perfect situation for efficiency. (Jos - MY interpretation of "aerodynamically balanced" being specifically related to an "all moving" tailplane that is not deflected at all from it's current position by it's relative airflow, including any changes to that airflow, ie the center or point of the lifting force (downforce) generated by the tailplane acts through the pivot (torque tube))
However, IF Graham's info about the C of L being deliberately designed to be NOT quite acting through the pivot (due to this short period oscillation - whatever that is!) is true, and I am very pleased and interested to bow to his most extensive experience of the Europa development and learn about this, then this means that the Europa tailplane is not quite perfectly aerodynamically balanced. Thus, unless the Angle of Attack of the tailplane is at any time zero (most unlikely) then a small tab deflection in the relevant direction would be required to counter the rotating force created on the tailplane by the airflow. (I would class this as another "unwanted" rotational force as in my previous text under variances!). This rotating force - and the corresponding amount of tab deflection required to offset it to maintain trimmed flight would vary slightly depending on the relative airflow to the tailplane and the corresponding amount of lift (downforce) being generated. This aerodynamic imbalance of the tailplane must I feel only be slight - the whole downforce generated by the tail is fairly small and is needed just to balance the wing's own imbalance of forces.
(Question - WHY then are some people's tabs completely flush in steady trimmed flight.....?!)
This aside though, I still fully stand by my comments of how the tailplane, especially the tabs work in principle. The tabs, when trimmed by the pilot correctly, hold the tailplane in the desired position as set by the elevator control. The tabs would ideally be flush (fully aerodynamically balanced tailplane) but will have a permanent, slightly variable deflection if Graham's info on the tailplane not being fully aerodynamically balanced is true (as I'm sure it is..!)
Jos - of course the trim control is necessary - vital in fact to keep the elevator control where the pilot wants it and to provide "feel" or "weight" (the anti-trim part as you call it) to the stick to stop the pilot "breaking things" as you most eloquently put it! But I think that without trim tabs fitted the elevator control would be VERY LIGHT to move (not heavy) throughout the entire range, dangerously so without extreme care. A perfectly aerodynamically balanced (all moving!) tailplane without trim tabs fitted would be completely without weight or feel at all throughout the entire elevator range (most undesirable). The trim tabs we have are very powerful being so far from the torque tube and if set even slightly out of the correct trimmed position would make the stick very heavy to hold in position. This of course is not force generated by the tailplane itself, rather the (rotating) force being applied to the tailplane by the incorrectly set trim (tabs).
Best Regards, Jon
(Sorry about the length again!)
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raimo.toivio(at)rwm.fi
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| Posted: Tue May 25, 2010 12:51 pm Post subject: Effects of Flaps and Ailerons on Pitch Trim |
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This is what I think this topic shortly:
1) we could fix permanently the tabs and stop
trimming but then we have to
accept we loose also anti-servo-function which is
necessary to generate some pilot´s stick forces.
Flying with zero pitch forces by stick would be
nauseous and
dangerous.
2) trimming function is there just to zero trim
tabs´anti-servo
loads when tailplanes are in their desidered
position = when trimming pilot is in fact
in-lining the
tabs with the tailplanes to zero the stick forces.
Stick loads means the tabs must be deflected more
or less, no
stick loads means the tabs are in-lined with
tailplanes = the plane is trimmed.
3) if the trim tabs are slightly deflected when
the plane is trimmed and there are no stick
forces, it means some unperfection with
tailplanes´ shape (foam structure, no NG factory
made).
4) " aerodynamically balanced " tailplanes = the
forces which try to turn the tailplanes clockwise
are always equal with the forces which try to turn
them anticlockwise.
That is why they could float in any position any
time (without anti-servo function or pilot´s hand
which keeps the stick steady).
Frans, do you now have more photos with varying
speeds and CofGs ?
Raimo
--------------------------------------------------
From: "JonSmith" <jonsmitheuropa(at)tiscali.co.uk>
Sent: Tuesday, May 25, 2010 11:00 PM
To: <europa-list(at)matronics.com>
Subject: Re: Effects of Flaps and
Ailerons on Pitch Trim
| Quote: |
<jonsmitheuropa(at)tiscali.co.uk>
Hi Jos & Graham, My theory about the tailplane
was based on the principle of a FULLY
aerodynamically balanced "all moving" tailplane,
this being the perfect situation for efficiency.
(Jos - MY interpretation of "aerodynamically
balanced" being specifically related to an "all
moving" tailplane that is not deflected at all
from it's current position by it's relative
airflow, including any changes to that airflow,
ie the center or point of the lifting force
(downforce) generated by the tailplane acts
through the pivot (torque tube))
However, IF Graham's info about the C of L being
deliberately designed to be NOT quite acting
through the pivot (due to this short period
oscillation - whatever that is!) is true, and I
am very pleased and interested to bow to his
most extensive experience of the Europa
development and learn about this, then this
means that the Europa tailplane is not quite
perfectly aerodynamically balanced. Thus,
unless the Angle of Attack of the tailplane is
at any time zero (most unlikely) then a small
tab deflection in the relevant direction would
be required to counter the rotating force
created on the tailplane by the airflow. (I
would class this as another "unwanted"
rotational force as in my previous text under
variances!). This rotating force - and the
corresponding amount of tab deflection required
to offset it to maintain trimmed flight would
vary slightly depending on the relative airflow
to the tailplane and the corresponding amount of
lift (downforce) being generated. This!
aerodynamic imbalance of the tailplane must I
feel only be slight - the whole downforce
generated by the tail is fairly small and is
needed just to balance the wing's own imbalance
of forces.
(Question - WHY then are some people's tabs
completely flush in steady trimmed
flight.....?!)
This aside though, I still fully stand by my
comments of how the tailplane, especially the
tabs work in principle. The tabs, when trimmed
by the pilot correctly, hold the tailplane in
the desired position as set by the elevator
control. The tabs would ideally be flush (fully
aerodynamically balanced tailplane) but will
have a permanent, slightly variable deflection
if Graham's info on the tailplane not being
fully aerodynamically balanced is true (as I'm
sure it is..!)
Jos - of course the trim control is necessary -
vital in fact to keep the elevator control where
the pilot wants it and to provide "feel" or
"weight" (the anti-trim part as you call it) to
the stick to stop the pilot "breaking things" as
you most eloquently put it! But I think that
without trim tabs fitted the elevator control
would be VERY LIGHT to move (not heavy)
throughout the entire range, dangerously so
without extreme care. A perfectly
aerodynamically balanced (all moving!) tailplane
without trim tabs fitted would be completely
without weight or feel at all throughout the
entire elevator range (most undesirable). The
trim tabs we have are very powerful being so far
from the torque tube and if set even slightly
out of the correct trimmed position would make
the stick very heavy to hold in position. This
of course is not force generated by the
tailplane itself, rather the (rotating) force
being applied to the tailplane by the
incorrectly set trim (tabs).
Best Regards, Jon
(Sorry about the length again!)
--------
G-TERN
Classic Mono
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