Airfoiled Empennage... absolutely necessary?
 

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

RE: Airfoiled Empennage... absolutely necessary?
 

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.

RE: Airfoiled Empennage... absolutely necessary?
 

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........

RE: Airfoiled Empennage... absolutely necessary?
 

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

RE: Airfoiled Empennage... absolutely necessary?
 

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

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

RE: Airfoiled Empennage... absolutely necessary?
 

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.

RE: Airfoiled Empennage... absolutely necessary?
 

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