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:
>
> 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
> >
> >
> >
> >
>
>
--
"A man is not old until his regrets take the place of his dreams. "
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