mike526mp

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anyone have any input on if it's worth the extra effort to use an airfoil for the horizontal stab for an aerobatic (not 3d) airplane/

thanks in advance

Chad Veich

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I'm no expert but my opinion is that it is worth the effort. Not only for the enhanced aerodynamic properties but also because a properly constructed airfoiled stab is much more rigid and less prone to flexing and/or flutter. Just my .02 cents of course.

BMatthews

Yes and no. For starters using an elevator means that the horizontal surface is actually a camber changing airfoil either way. When displaced the elevtor acts as a flap that induces both camber and a change in the angle of incidence all at the same time.

On a finer level using a built up airfoil with a rounded nose and front zone means that the air MAY tend to stay attached better to the convex side for a given amount of elevator travel. Will it be worth it? That depends on how radical you want the airfoil to look, where the hinge line is located and how much elevator angle you will use. But generally it's safe to say that even a thicker airfoil will be operating in a stalled state if you use more than about 20 degrees of elevator travel.

One place where a thick and stall resistant airfoil is MUCH better than a flat plate is when you use a full flying stabilator. In that case a thick airfoil will greatly help in avoiding a stalled condition and result in greater pitching torque for a given angle of deflection where the surface isn't stalled.


Having said all this much depends on the size of the model. If we're talking about small flat foamies with at least a small portion that is fixed I'd say don't bother. If we're talking about a new world class competition precision aerobatic model then I'd say that choosing the right airfoil and how it's used would make a big difference in a style of flying where a couple of points can be the difference between a spot on the podium or not. For general sport flying? I'd say that most folks would not see a difference one way or the other depending on the model. And a thick airfoiled stab would only be an overall net gain provided it can ge built to the same or lighter weight than the flat plate.

Now if I were a betting man and were looking at building something in the next little while where the model was larger and I wanted to get the very most pitching torque from my model's horizontal tail I think I"d be interested in trying this idea out. Is such an idea needed? Not really. There's LOTS of models flying very nicely with regular flat stablizers. All that happens is that the elevator nees to deflect a bit more to create the force needed to pitch the model hard enough. And truth be told even a flat stabilizer will produce more than enough pitching torque to push most wings to a stall during a loop. And once that happens you've got all you can handle.

Where an airfoiled stab proves to be an advantage is in models where speed is a primary concern. For such models a proper airfoil will produce a little less drag than a flat plate with rounded leading edge. On a basic stunt sporty model I'd go with which ever you can do that is lighter and still be strong enough. For most of us that are not afraid of the bit of extra work this means that an airfoiled stab is worth the time because it can be made built up to be stronger and stiffer and lighter all at the same time than a simple flat plate stabilizer. But the primary advantage comes from structural and weight considerations rather than any big aerodynamic advantage. Although there will be SOME aerodynamic advantage over a simple flat plate.

mike526mp

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Thanks for the advice, speed is not a consideration, handling quality is of my only concern.  Of course this is not at all scientific, but the models I have flown that have an airfoil horizontal stab have for the most part seemed to be, how can I say, softer and more predictable around neutral, where the slab horizontal models seemed to have a point around neutral that and small change would make a much more rapid change in pitch.  Am I just imaging that?   

speedracerntrixie

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I have been flying 40% IMAC airplanes atarting in 1997. All had airfoiled tails. IMAC popularity has dropped off in my area quit alot in the past couple years so I now fly smaller models but compete more then just IMAC now. My current airplane of choice in a 33% LAser with a flat tail. Yes, the setup is different. I too feel that the elevators have more power around nuetral. I have also notived that I need less overall travel. Snaps were a real issue until I dialed the elevator down to about 8 degrees. Do I feel a performance loss with a flat tail? Absolutly not. The model is lighter ( 15.25 lbs) Just as strong with .070 CF tail braces. Do I feel slightly out of vouge? Maybe a little....................until the flying starts

mike526mp

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thanks all for the input