Antiservo Tab

[pilotman2105]

Looking for information about the antiservo tab on a Piper Arrow. If someone could give me some feedback, that would be great. My understanding of it so far is:

Antiservo tab deflects in the same direction as the stabilator/elevator, but deflects more than the stabilator/elevator. This is to increase the amount of control input required from the pilot. In other words, it makes it harder for the pilot to pull-up/push-down on the controls.

Furthermore, the antiservo tab is adjusted via the trim setting to provide "trim" for the aircraft. If the elevator were to remain at a constant position and nose up trim was added, the antiservo tab would move down, causing the stabilator/elevator to move up, increasing the tail down force and thus moving the nose up. Vice-versa for the other direction.

Am I on the right track?

 

[Mr. Irrelevant]

Sounds good to me......


Mr. I.

 

[labbats]

Anti-servo doesn't serve you in moving the yoke forward and back. It works against you.

A servo helps move the yoke forward and back, it serves you.

 

[Mmmmmm Burritos]

You're correct. There are three things that help to stabilize a stabilator.

1) Anti-servo tab which fights against overcontrolling the tail by giving feedback to the controls. The more you input, the more the tab deflects and the more feedback you will get.

2) Stabilator pivot point located about 1/3 back from the leading egde. If it were located further forward, you would have too much control authority and the plane will be very hard to control. If this point were located further back near the halfway point (or further), the stab will be very unbalanced especially in maneuvering flight. Imagine in a steep turn where all of a sudden the stab center of pressure moves forward of the hinge point of the stab, then BAM, the yoke moves full rearward just like that. So they put the pivot point forward to keep the center of pressure behind it. It's like the CG/CP correlation when speaking of airframe longitudinal stability. The CG needs to stay ahead of the CP to be stable.

3) Stabilator counterweight located forward of the leading edge, but hidden in the fuselage. This does basically the same thing as the pivot point. It also helps to quell any flutter at higher speeds, like any other flight controls counterweights. Arrows have counterweights on the ailerons, but Warriors don't. You can see the Warrior's ailerons fluttering a tiny bit at higher cruise speeds or when descending in the yellow arc.

 

[dmspilot00]

So, can you tell us the pros/cons of stabilators versus regular stabilizers and elevators or why a manufacturer would choose one over the other?

BTW Why would you be descending in the yellow arc? Sounds like a bad idea to me, considering the lower you go the rougher the air, usually.

 

[Mmmmmm Burritos]

Obviously it need be smooth air to be in the yellow arc, then it's no problem. A lot of high performance aircraft actually cruise just inside the yellow arc. I usually descend with cruise power set in and just drop the nose to meet whatever descent rate I want, normally 500-700fpm. It saves time using a powered descent.
A lot of descent performance charts assume you do this. Of course with a fixed-pitch prop, you will have to decrease power slightly as you speed up in the descent.

Anyway for the stabilator versus the elevator thing. I definitely know that stabilators are for low speed flying only. This is because they are more powerful than a traditional elevator at a certain airspeed with with a like size horizontal stabilizer/elevator.

I would also guess they are cheaper to build. One stabilator and one anti-servo tabe versus two horizontal stabilzers, two elevator and one elevator trim tab.