After a couple of simpler designs,we decided to tackle a .60/.90 size Edge 540. Using Winfoil we lofted a set of ribs using a NACA 0014 at the root and a NACA 1016 at the tip.

This set off a discussion whether it sould be the other way around or should I stick with a constant airfoil.

My thoughts were that the thicker airfoil at the tip would be less prone to stall than the root. Also it is more construction friendly.

Anybody have any thoughts on the subject.

Bert

Well, with the cambered airfoil at the tip, your adding an effective angle of attack (due to the camber) to an effective angle of attack (due to the location at the tip).

Basically, your adding wash-in... which will make the wing more prone to tip stalls. The thickness helps, but is definitely negated by the other factors I mentioned.

Personally, I would go the other way around and use a cambered section at the root and a symmetrical section at the tip. In this way, you can lower your wing incidence at the root and have an "airfoiled" wash-out (that is, non-geometric).

Whatever looks good to you, go for it. The Reynolds number at which it will operate , and the abundance pf power it will likely have, it really doesn't amount to a hill of beans. Just think, the SPAD folk out there use whatever airfoil results from wrapping a sheet of coroplast around a yardstick, and they perform about as well as the more "scientifically" designed models.

The technical answer is the thicker rib at the tip will in fact change the lift distribution to move the initial stall pattern inboard a bit. Unless tip stall is a serious problem with the basic design, you probably won't notice any difference. What is often blamed on tip stall is a lack of coordination in slow flight. (Reducing tip stall will make snap maneuvers more difficult.)

A more modern profile with the thick point moved forward might be worth considering, if you're into serious active aerobatics.
Look at what the full-scale Edge/Extra/Sukhoi uses.. fat part ab 20-25% instead of the NACA 30%.
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Tipstalls aren't the bugaboo they're claimed. Actually required for decent snapping manuvers.
Knowing when and how to do a tipstall, or not do one makes the pilot.

Sorry guys but I made a typo in my original posting. The tip airfoil is a NACA 0016 and NOT the 1016 that I had originally posted. Root chord is 15.75" and tip chord is 8.5". Does this make any difference?

Thanks for the input so far.

Bert

It will make a difference, although little one, but for aerobatic models it's not a big deal.....Tip stall problems are more serious in slow flying, underpowered models (like most trainers or "heavy lifters") that when the plane stalls, you don't have much engine power or control authority to recover, and the plane must recover for itself. Now in an aerobatic plane, just add full power (assuming it has adequate power for aerobatics) and it recovers right away....In 3D flying, like on a harrier, the wing is fully stalled, and yet the plane still flies just on the prop thrust. No matter if the tip stalls first, the plane still flies and is controlable......

So i think the addtional hassle is just not needed.

My 2 cents......