Thanks to both Frans & Bud for the detailed explanations!
Coo!l ... it's all so clear to me now :-)
My build goal with then to have a perfectly flettner'd tab to emulate
Frans's beautiful workmanship.
Cheers & thanks again!
Pete
A239
On Wed, May 12, 2010 at 10:35 AM, Bud Yerly <budyerly@msn.com> wrote:
> Good analysis Frans,
>
> If the tail plane is perfectly balanced and friction in the system nil, the
> trim tab is centered.
> A too heavy counter weight is offset by the trailing edge of the tab up. A
> difference in flettner strips can cause the same.
>
> Flutter is dependent on the center of mass and the aerodynamic center. A
> horizontal control surface, mechanically balanced, with a symmetrical
> airfoil surface with the aero center co-located with the center of mass
> tends to stay neutrally stable. Camber angle and or trim tabs change that
> of course.
>
> When the center of mass is behind the the center of pressure, the trailing
> edge goes down due to gravity, aerodynamic forces then try to lift the
> trailing edge and in some cases overshoot the center line, so gravity and
> the aero forces push the TE down, then it overshoots again and flutter
> occurs. This is especially a concern of a cambered aileron not mass
> balanced.
>
> I don't have time to go into the drawings, but a symmetrical airfoil
> contributes no moment to its normal force at low angles. That is, if it is
> perfectly balanced at its aerodynamic center, it will stay at its angle of
> attack unless acted on mechanically and requires no force (beyond mechanical
> friction in the mechanism) to move it. It will, by previous statement, also
> apply no counter force when moved (so no pilot feel). This is why we have
> the anti servo tab, to create feedback to the pilot. It also cleverly
> applies trim.
>
> If the flettner strips are not perfect, and or the mass balance is slightly
> off, your trim tab will show the effect of that. The asymmetric flettner
> strips of course act as a flap and become not an anti-servo tab, but a servo
> tab which drives the trim tab, which drives the tail.
>
> As for the unbalanced anti-servo tab. The tab itself does not contribute
> to flutter if it is *fixed*. If the tab is loose, the tail plane bushings
> or trim bushings are missing, loose, damaged or not installed, *flutter
> will occur. * This is why, I am such a zealot about stabilators, loose
> pins, and bearings. I would even prefer to try to mechanically balance the
> trim tab for the guy who mistakenly fails to hook up the trim tab pins to
> the trim bar.
>
> Hope that doesn't add to the confusion Pete.
>
> Bud Yerly
> Tech Support
>
>
> ----- Original Message -----
> *From:* Frans Veldman <frans@privatepilots.nl>
> *To:* europa-list@matronics.com
> *Sent:* Wednesday, May 12, 2010 9:52 AM
> *Subject:* Re: Europa-List: Re: Effects of Flaps and Ailerons on Pitch
> Trim
>
>
> On 05/12/2010 03:22 PM, Peter Zutrauen wrote:
>
> > Your thesis assumes that the tailplane is aerodynamically balanced wrt
> > to the torque-tube position, and the only aerodynamic component which is
> > stabilizing it and keeping it from flutter is the anti-servo tab.
>
> Stabilizing, but not necessarily keeping it from flutter. I think that
> the mass balance weight is to keep it from flutter, just as with the
> ailerons (that don't need to have a trim tab for that either).
>
> > I would expect/hope that the tailplane would remain aerodynamically
> > stable without the anti-servo tab, and that the tab is there only to
> > provide for progressive stick forces, and trim.
>
> This is how it works I believe. At least is seems so on the PH-DIY.
> p; Features Chat, http://www.matronnbsp; via the Web
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> _p; generous bsp; title
> http://www.matronics.com/contribution href="
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>
>
> *
>
> *
>
>
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