Glenn,
that makes sense.
That is why when flying faster pilot have to push stick forward to keep
altude.
Tailplane=B4s trailing edge is moving then down and tailplane=B4s
negative AoA goes slightly smaller.
Tab=B4s anti-servo function moves tabs even more down to generate (more)
force to the pilot=B4s hand. To eliminate that force pilot trims "nose
down" = trim tabs move a little upp to keep tailplane=B4s trailing
edges down = where they should be to keep to maintain level flight.
Without anti-servo function I assume there would be still pitch forces
but only about 1/3-1/2 (look at the torque tube position in relation
with tailplanes)?
When cruis=EDng levelled and with power lever in it=B4s fore position,
XRT needs almost full nose down trimming.
Raimo OH-XRT
----- Original Message -----
From: glenn crowder
To: europa-list@matronics.com
Sent: Tuesday, April 13, 2010 6:54 AM
Subject: RE: Europa-List: Effects of Flaps and Ailerons on Pitch Trim
OK Pete - the tailplane is ALWAYS pushing down at all airspeeds but at
higher airspeeds the wing is at a very low angle of attack. As the
airspeed goes up, the
aerodynamic forces on all control surfaces (ailerons, rudder,
tailplane) go up by the
SQUARE of airspeed. This is why you cannot give full control
deflection at VNE, the
control surfaces will depart the aircraft. So when the wing goes to a
very low angle
of attack, the tail must also. The tail is still flying at a negative
angle of attack but
it is very small. However this small negative angle of attack is
generating a lot of
positive CM because of the high airspeed. To get this slightly
negative angle of attack
at a high airspeed requires a lot of force and this is generated by
the UP position of
the trimtab forcing the trailing edge of the tailplane DOWN. The trim
tab controls the
angle of attack of the tail (always negative but less negative at high
speed), the
anti servo system keeps the tail at the set angle of attack. Other
factors come into
play here such as the angle of relative airflow from the wing
downwash. The tail
may look as though it has a positive angle of attack but because of
the wing downwash, the relative airflow is actually hitting it from
above This angle becomes less at high speeds but the forces go up with
the square of airspeed.
at high speeds
-------------------------------------------------------------------------
-----
Date: Mon, 12 Apr 2010 19:19:06 -0400
Subject: Re: Europa-List: Effects of Flaps and Ailerons on Pitch Trim
From: peterz@zutrasoft.com
To: europa-list@matronics.com
Hi Glenn,
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* to result in the
equivalent of pulling back on the stick, to have the tailplane produce
the required downward force on the tail?
All the pics I've seen show the trimtab portruding *up*, ie, trim =
foward stick..... no?
Still confused,
Pete
A239
On Mon, Apr 12, 2010 at 2:41 PM, Glenn Crowder <gcrowder2@hotmail.com>
wrote:
<gcrowder2@hotmail.com>
The airfoil of the wing of any aircraft with a non symmetrical
section will produce a negative pitching moment (-cm) around the
aerodynamic center of the wing. This means that without the tailplane
producing an equal but opposite moment the acft will pitch over into a
vertical dive. The all flying tailplane on the Europa has no fixed
angle of incidence so to produce an opposing positive torque moment to
the wings negative one the trim tab must be held out of plane. At
higher speeds then the tailplane must provide greater downforce then
requiring even more trim tab offset. We have to pay a small drag
penalty to achieve a level trim condition in cruise flight. This
penalty can be reduced somewhat by loading the acft towards the aft cg
limits requiring less trim tab offset reducing the downforce the
tailplane must produce to maintain level flight.
The tailless flying wing derives it's pitch stability due to the
outer portions of the wing being reflexed up to produce that necessary
positive pitching moment but also introduces that small drag penalty
again. There is no free lunch in aerodynamics! Every desireable
aerodynamic quality (like pitch stability) has a price that must be
paid.
Glenn
Fred Klein <fklein@orcasonline.com> wrote:
>
>On Apr 12, 2010, at 6:24 AM, david miller wrote:
>
>> I think that for most efficient flight the incidence of the wing
and
>> tail should be such that at cruise there is no up or down trim on
>> the elevator or all flying tail.
>
>Fascinating discussion...as a non-aerodynamicist, I can't resist
the
>temptation to add a comment...
>
>I've always understood that the elevator or an all-flying tail
>(horizontal tail plane) has a "job"...namely, to exert a force,
either
>up or down, in order to balance the lift of the wing and stabilize
the
>flight path of a normally configured aircraft (i.e., not a canard
>type). To do this "job" requires "work"; the tail plane is never
>neutral. And w/ our Europae...with it's trim tabs acting in
>opposition to the all-flying tail plane thru a direct mechanical
>connection...whenever the tail plane is doing its job (at whatever
>angle of incidence), the trim tabs will be doing their job as well
>(that of counterbalancing forces on the tailplane), and will
>necessarily be raised or lowered w/ reference to the tailplane.
>
>Of course if this explanation is correct, one might ponder the
>aerodynamics of my tail-less biplane...pix below.
>
>Fred
>
>
>
>
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