I was reading about the development of the new LSA RV-12 from Van's aircraft. Van's extended the chord of the aileron's by attaching an extension to the trailing edge of the ailerons (it is likely that the production version of the plane will not have this attachment). Somebody, not connected to Van's, said that the reason for the extension was to reduce the responsiveness of the ailerons, in other words, to reduce the roll rate. Does this make sense? Why would increasing the chord make the roll rate lower?

No it dosn't make sense. It would seem to me that it would increase the roll rate.given the same deflection. The same effect as a larger rudder has.

Makes no sense to me either. Some of the facts may be missing on this story.

Making the ailerons wider with an extension will mean that the effective angle of attack and camber value change for a given angle of surface deflection will be more And more angle/camber means more lift.

Unless it's a case of a trailing edge extension making it harder to move the stick so the pilot gets less deflection for the same input effort and hence a lower roll rate for a given amount of control FORCE as opposed to control deflection.

Those extentions are anti-servo tabs. The ailerons were probably too sensitive so they simply added some tabs instead of redesigning the controls.

So they are set up to move compared to the aileron but the opposite way compared to servo tabs? Oh yeah! That would do it!

The tabs don't move, they just add some aerodynamic stabillity and make the surface more difficult to deflect. A true anti-servo tab would move in the same direction as the surface and be a lot more effective.

I've never heard the term "anti servo tabs", where did it come from and what is the definition? I have heard of "boost tabs", the extensions which move in the opposite direction to the surface movement. In fact I often use them on 1/4 scale as it lets a weaker servo do a giant job. Just don't over do the size, limit them to 10% or less of the moveable area.

Never heard of "anti-servo tabs" either. Anybody got a reference?

Boost tabs are used in full scale and work great to reduce the pilot's work. We use them to reduce the servo load. Larger models can use smaller servos or get rid of multiple servos on one surface or simply lessen the battery drain.

Anti-servo tabs, as I remember from my A/C engineering apprentice days, work in the opposite sense to `servo tabs' in that the do not assist the pilot to move the surface, but actually add to the pilots load. They are/were used on occasion when the control surface load would actually decrease, either as the surface moved further from the neutral position, or when (perhaps) as the a/c slowed from cruise to landing speed and the aileron or elevator loads would reduce to the point where the pilot could easily overcontrol, or the surface could move to the extreme position rather than tend to hunt to the neutral position, reverse loading, as it were. There were/are occasions in the full size world when such things happened. These day, with synthetic feedback, FBW technology etc the pilot no longer has direct control over the moveable bits of the a/c, so has no idea of the actual size or direction of the surface loads he imposes to fly the things. He has a computer which applies a load to his flight controls. Bit like us modellers, I guess, in that the servo gives no feedback to the transmitter of any flight loads from the surface being controlled, we just have a spring under the stick.
Evan, W.B #12.

The stabilator was designed with the anti-servo tab which helps with centering feel, along with a counter balance weight. Pretty much like Piper have done for decades. Van's LSA design has a smaller, shorter horizontal tail so it will fit on a trailer for towing without removing the tail. The wings do remove and are fitted with flaperons

Van's has had some difficulty in achiving the required stall speed with the prototype wing, flaperons extentions may have been an experiment to increase area.

The Cherokee 140 for example, has an anti-servo tab along the entire trailing edge of the stabilator.

We call them anti-balance tabs in the UK. Typically fitted to aircraft with all-moving surfaces, such as the PA 28, Evans VP-1, TB20 (IIRC) Grummans ?

Anyway, the purpose is to oppose the pilot's input, giving some weight to the controls and, I would guess, providing negative feedback to the control surface. I suppose that a surface which has one of these fitted, would be very resistant to flutter, since every deflection is automatically and instantly opposed by the anti-balance tab. You can never find an aerodynamicist when you need one, can you?

Interesting idea.....sort of an aerodynamic gyroscore. It sounds like it would resist unwanted movements and give a more locked in feel. Anyone have a sketch??

MattK

http://en.wikipedia.org/wiki/Anti-servo_tab