What is the reasoning behind tapering the flap and elevator to 1/8" over say 3/16" or 1/4"?  Is this a case of "looks about right" and so it works?

James

Also,

It's easier to get square rods or dowels in those sizes.

Jim Pollock   

It is all about lift distribution along the plane of the wing. As you move toward the tip of the wing you have more lift. Ideally you want an even lift distribution. Equal Elliptical lift balanced along the wingspan gives you the least resistance with maximum effect witch in effect will minimize the loss of speed during maneuvers.  The flaps is the same, you try to balance it so as it deflects it maintains the wing lift balance. Elliptical wings in general have the best lift distribution.
This works if you do not have enough power. But fortunately we have more than enough so it becomes more of a, it looks good, that a pure design like a performance glider where every little bit helps. For example Windy has square shape flaps on a bunch of his ships and they fly good despite they are a flat sheet and it does not taper at all.


Serge you are right I was thinking of elliptical distribution and I typed something else instead.

It is all about lift distribution along the plane of the wing. As you move toward the tip of the wing you have more lift. Ideally you want an even lift distribution. Equal lift balanced along the wingspan gives you the least resistance with maximum effect witch in effect will minimize the loss of speed during maneuvers. ...Windy has square shape flaps on a bunch of his ships and they fly good despite they are a flat sheet and it does not taper at all.

Possibly we have semantics problem here, but I'm pretty confused by this wording and have to disagree with it.

First, I'll start with the flap part, since that is the topic of this thread. We have discussed this several places before - perhaps even in this thread, so I'll just say that these planes don't just fly well "despite" the flat-sheet flaps, but probably because of them (and any other good design strategies). NACA research, Al Rabe's experiments as documented in at least one of his articles, and my XFOIL plots indicate that flat-sheet flaps give the best performance for sealed hinges (non-Fowler type flaps) and even aid performance as stationary flaps on otherwise flapless wings, like the "Flite Streak's".

*Secondly, the most efficient wing for any given total lift, span, and speed is one with elliptical lift distribution. That means that the lift drops off elliptically toward the tip. Such a lift distribution gives constant downwash along the span, but not constant lift or "more" lift toward the tip. Theoretically - in a perhaps over-simplified way - an elliptical wing would have this lift distribution. However, since there are increased losses near and toward the tip, straight tapered wings come fairly close to elliptical distributions of lift. Again in simplified theory, lift at any tip is zero. The Spitfire is a good example of how much faith classical designers put in the elliptical shape, aligning the chords close to their aero centers to minimize twisting torques and probably to give some advantages in control deflection drag. One nice thing for stunt models is that for an elliptical wing has its a.c. much further inboard than normally tapered wings (at 42% vs 47% of the half span) - again theoretically. This diminishes susceptibility to side gusts or gust biased airspeed along the span. Again, this is because lift diminishes toward tips. This is what gives least loss of speed in maneuvers too.

'hope I did not misrepresent what was meant in the quote, but I certainly disagree with what was actually said.

* Edit: The exceptions to this are tips where vortices are split or minimized by sweep, which do indeed allow greater lift nearer the main area's extremities, but again the elliptical wings with straight trailing edges win over swept tips. These are still works in progress - see other threads - but perhaps this was the focus of the previous post??.

SK

Leave it to Howard,  thinking outside the box.  Why isn't he still using the idea?

...the elliptical wings with straight trailing edges win over swept tips.

In stunt? 

I'm a bit confused by the statement that there is more lift at the tip ?
I'm wondering how you might be seeing or thinking this ?