Servotab antiservotab trim tab

[Raptor71]

Hi

I have some questions about the antiservotab and trim tab.
On pa44 we have an antiservo tab for the horizonal stabilator, i understand that the pilot via the control wheel acts on the control surface, in response the antiservotab goes in the same direction as the control surface does.

What does happen when yiu use the trim control?
Is there a separate cable connecting the trim wheel and the antiservotab that will make the antiservotab move into the right position to cancel efforts?

Thanks

[glendalegoon]

my understanding of the PA 44 or other stabilator pipers is that the servo tab moves the stabilator

and the ANTI SERVO TAB provides tactile feedback to the control yoke for the pilot to FEEL like it is an elevator and not an all moving stabilator.

[formulaben]

This (http://books.google.com/books?id=LIr3dZZPROgC&pg=SA5-PA11&lpg=SA5-PA11&dq=trim+tab+servo+antiservo&source=bl&ots=f3zvMBb2-c&sig=_FdCHprtStIXTmvLG0u2uHr4AZU&hl=en&sa=X&ei=Kj-aU9rqFIqxoQTNkIG4CQ&ved=0CC0Q6AEwAjgK#v=onepage&q=trim%20tab%20servo%20antiservo&f=false) may explain it.

[eckhard]

Raptor
Is there a separate cable connecting the trim wheel and the antiservotab that will make the antiservotab move into the right position to cancel efforts?

Yes.

If you watch the stabilator tab from the outside and a friend moves the trim wheel in the cockpit, you will see that the anti-servo tab moves in the required direction to act as a trim tab.

Different speed, power, flap position and CG conditions for the aircraft require different stabilator angles.

As the stabilator is a 'free-flying' surface, its aerodynamic qualities depend on the relationship between its hinge point and its centre of pressure.

The 'trimming' function of the tab sets the stabilator at the required angle to satisfy the aircraft conditions.

The 'anti-servo' function of the tab provides a correcting moment to keep the stabilator at the trimmed angle (Stick-free stability). It also provides force feedback to the pilot to improve handling qualities and prevent over-controlling.

Glendale

my understanding of the PA 44 or other stabilator pipers is that the servo tab moves the stabilator

and the ANTI SERVO TAB provides tactile feedback to the control yoke for the pilot to FEEL like it is an elevator and not an all moving stabilator.

The stabilator is moved directly by the control wheel fore/aft movement. The anti-servo tab is linked directly to the stabilator and is moved as a function of stabilator angle.

There is only one tab. The same tab can be moved independently of stabilator position by moving the trim wheel.

Example: (starting with neutral stabilator and neutral pitch trim)
1. Note the position of the leading edge of the stabilator against the fin and the deflection of the tab with respect to the trailing edge of the stabilator. Let's assume it starts streamlined (no deflection).
2. You pull back fully on the control wheel. Stabilator rotates fully leading-edge down. Tab moves up, acting as an anti-servo tab.
3. Holding the control wheel fully back, you then move the trim wheel fully in a 'nose up' sense. The tab will move downwards while the stabilator remains in its position.
4. You then push the control wheel forward, back to neutral. The stabilator rotates leading-edge up. The tab moves down, acting as an anti-servo tab but you notice that it results in a lower tab position than in 1.
5. You push fully forward on the control wheel. Stabilator rotates fully leading edge up. Tab moves down, acting as an anti-servo tab.
6. Holding the control wheel fully forward, you then move the trim wheel fully in a 'nose down' sense. The tab will move upwards while the stabilator remains in its position.
7. You then pull the control wheel, back to neutral. The stabilator rotates leading-edge up. The tab moves up, acting as an anti-servo tab but you notice that it results in a higher tab position than in 1.

Hope this helps.

Eckhard
(600 hrs instructing on PA-44)