I've been poking around reading thousands of posts here in the pattern forum lately to help me break into pattern. First I need a plane. I'm seriously considering the new GP Venus II but noticed that the elev/stab/rudder are not airfoiled, but rather flat. Is this a big deal in flying precision? As a beginner to pattern, will this not be noticeable? Or should I stick to a plane with an airfoiled empennage such as the Epsilon 60?

I may be approaching this entire pattern thing a bit too particular or detailed (or obsessive), but I want to do it the best, or most correct way possible.

Thanks.
Bob

This is a pretty aerodynamics question...

It is a fact that an airfoiled wing section can provide "greater lift" than a flat one (CL grows with airfoil thickness). For a stab this means IMHO that an airfoiled one can yeald a bit more pitch-"stable" airplane, in the sense that when the stab is seeing an AoA (for example, after a wind gust or so) it has a greater tendency to the equilibrium. Furthermore, another difference can be during snap rolls, spins - i.e. when the stab flies at high AoA - for the same reasons.

That said, it must be said also that in pattern planes the tail moment has a so great moment arm that small forces are needed to control pitch axis...

Moral of the story, IMHO: hard to tell the difference. For a beginner, I think that no difference could be noticed.

Thickness for thickness, airfoiled stab will be stiffer.
To put it another way, an airfoiled stab with a typical high-point thickness of around 1"
will be lighter than a 1" flat plate.
On the other hand , an airfoiled stab with a very thin T/E will not provide much (needed) drag, and could well be a bit too abrupt in response.
As usual, it's never quite as clear cut as first it seems........

Since I'm one of the "old" guys I'll tell you what Jim KIrkland wrote in an article in Model Airplane News
many years ago about trimming a pattern airplane after he won the AMA nationals. He apparently did a
lot of experimenting and found a flat stab has a dead spot right around neutral and the airfoiled stab has
a much smoother response. The shape apparently has little to do with how it reacts so he used a diamond
shaped stab on his Intruder which is much easier to build than a rounded airfoil.

tommy s

Tommy, very interesting! A diamond shaped stab???

Is it possible to read the article you are referring to?

I wish I could find a copy, it was probably the best, most detailed article ever written about trimming a model to fly
correctly, before the days of computer radios. I don't know the exact dates but it was a short time after he won the
US Nationals with his Intruder, sometime in the 70's.

tommy s

PS: Dick Hanson probably knows as much about this as anybody, maybe he can help you with details.

A taper at the last part of the control surface will help prevent flutter.