I am currently working on mating two planes together and I the original plane had a flat horizontal stab. The elevator we will be using is airfoiled and i am wondering what the advantages/disadvantages are. Will it change where the cg needs to be? Incidence of the stab? It is a fully symetrical airfoil on the stab. In case this matters it will be going on a 60" 3d profile

same same same imo.

only change i see is more stability and pitch authority.

I seriously doubt you'll notice anything at all. If there is any difference it'll be so slight as to be unnoticable.

Structural strength is the biggest advantage for airfoiled stabs on models. Since you can make the main spar thicker, you get a stiffer structure which can help in preventing flutter for larger/faster models. For large models, it is usually lighter to have a built up stab as well.

Being full symmetrical ,seems to me it would not make any difference. If it was semi symmetrical [lifting] it would have some effect I think. I have a set of plans for a tri pacer that has a semi symmetrical stab on it. I am not sure what the full scale had. I have a Sterling tri pacer, that has a full semmetrical stab on it[crashed on the first flight]!

yes- as with most model and full scale airfoils - the primary requirement is that it hold it's shape and not break
after that - all the rest of it is simply shaping it for best efficiency at a given speed and load .

Efficiency is the main aerodynamic difference between a flat and a symetrical foil. It will not make a difference in the CG. If your wing airfoil is symetrical then I would say that you can keep the same incidence and it should be fine.

hi there from Toledo

If enhanced pitch authority is what you need go for a full flying horizontal stabilizer like used on many gliders, full scale and models, as well as many airliners. You will need servos with very repeatable centering and fine trim adjustment capability from your TX and turnbuckles in your linkage to really dial in the trim.

ciao -rjf

By efficiency I assume you all are meaning drag. A symmetrical airfoil horizontal stab should exhibit less drag than a plank.

And it looks so much cooler!

atually -- those flat plank setups with guy wires do perform a service -- they place more drag at the rear of the model--which for some models is a welcome addition.

If the stab is flat bottomed then it is much like the Telemaster line and it MAY affect the flying characteristics similarly. A Telemaster lifts its tail almost immediately on takeoff and you usually get the best results landing on the wheels, not a three point.

Take it for what it's worth but the manufacturer of the Telemaster indicates that the CG is further back than normal as a result of the stab configuration.

yeh-- actually the lightly loaded wing flies at a very flat angle -with fuselage more or less horizontal - not much if any angle of attack noticable - the so called lifting stab MAY correct somewhat for the tendency of flat bottomed shaped s to zoom as speed increases--- little if any
In flight if you could actually measure it -- the flat bottom of the wing may actually measure as pointing slightly downward- looking like a negative angle of attack-

I read on this forum that an Airfoiled stab slows downlines somewhat.I dont know,I want to believe that too.
I agree with the the looks though,if you got a 25% or bigger,sport scale plane,and the full size is airfoiled,then your model should be too

the idea was to decrease as much drag as possible and yet have a structurally sound elev/stab
the old downline ideas are 99.9% whimsey

A flat stab IS a symetrical stab.
The only thing gained is lighter tail section, and therefore more authority because of overall reduced total weight, lower moment arm...
OK, there are other gains, such as structural integrity...

Stan Douglass hit it on the head.
Less drag on larger models.
A 60" span is a considerable sized plane. Flat stab would work just fine. Built-up stab, (symetrical), would reduce overall weight, but if you need to add weight in the tail to counteract it, then the advantage would be lost.
Reality, I think it won't matter enough to get your shorts wrung out on this.
Just remember that aerodynamics is NOT proprtionate to scale. Smaller planes can get away with so much more deviation than larger planes, as Mr. Hanson has said in so many other posts.
60" is near the limit though where I would start to consider built-up stabs.
(My personal opinion)

Bob

Keep in mind that making an airfoiled stab doesn't always increase the weight of that structure enough to matter. And it often doesn't increase the weight enough that you could tell unless you had a decently accurate scale.

It's not like thicker stabs automatically make tail heavy models. Sometimes we're talking less than a ounce . Sometimes the weight increase in percentage isn't even over a couple percent. Using heavier covering can add more weight than going to a different structure does.

Sometimes it's not the difference, but the amount of difference.

An airfoiled surface has a more effective "flap" than a flat surface.
On teeny planes it machs nichts, but as they get larger, the lesser deflection of the flap to get the needed response is more efficient.

I used a Clark Y to get a low stall speed, on all the horizontal control surfaces and a Symetrical vertical surface. Worked for me.

on that size I don't think you are going to notice, but conventionally... it will increase pitch stiffness, stability, and reduce drag. As for the "flap effect", they are pretty much the same, when you go to 3D a plane, the R# are so low that fuse shape and wing position have as much to do with how well it files, as the tail airfoil does.

Best of luck!