Peter Zutrauen <peterz@zutrasoft.com> wrote:
>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. "
|