I know how to compute aspect ratio but what i'm not sure on is what exactly the range for a pa cl airplane should be. Is 4.9 too low ? also is the acceptable range different for models with a straight leading edge ? as opposed to tapered ?

Jim,  the taper of the wing doesn't have much to do with aspect ratio.  A big difference occurs when the chord of the wing gets down in the 4 inch range and the thin layer of air on the wing surface(boundary layer) goes from partially turbulent to laminar(smooth) flow.  The scientific term that applies for this is called Reynolds number.  One formula for it is V*l*777=Rn.  Velocity in mph  l(length) of the wing chord in inches, and 777 is a constant that makes the units come out right(thanks Wild Bill).  A typical stunt plane flies at a Rn of around 500,000, which is smack dab in the middle of the transition from laminar to turbulent.  Free flight planes, especially indoor models, operate under 100,000 and are extremely affected by wing chord.  Full scale planes operate in the millions so the boundary layer is usually mostly turbulent.  Going as low as 5 inches or so in chord at the tip still keeps the Reynolds number well above where it might cause problems.

This phenomenon explains why almost all planes seem to fly "better" the faster they go.  As long as the lines hold and the controls are designed to work at higher speeds the plane hangs out on the end of the lines better, doesn't get bothered as much by the wind, flys smoother, and is easier to control smoothly and precisely.(Assuming your reflexes are up to the task).  It's another reason many people have gone to larger planes.  They just work better.

Jim,

Your numbers work.

A few other thoughts:

The tips are seldom as effective as the main wing area, particularly if they have a 'pleasing' shape in the plan view (looking straight down on the wing.) If they are rounded or tapered down as seen from the front or rear, they also act less like the main airfoil area. Tip effectiveness drops due to "tip vortices" - spiralling air trailing off the tips. The air "below" the wing also flows out towards the tips - higher pressure seeking lower pressure. The air "above" the wing produces most of the lift by being at lower pressure, further drawing the higher pressure air from "under" the wing to wrap over the tips. ("Above" and "below" refer to the direction of lift at any given moment. Towards the "pilot's head" in upright or inside maneuvering, and away from it in inverted and outside maneuvering...)

You could choose to start with a tapered "planform." The average of the tip and root chord lengths is the average geometric chord for the wing - it's that simple.

Wing sweepback (or -forward) is another thing you can play with. Aerodynamic sweep relates to the quarter chord (25% back from the LE) of the wing. Flite Streaks and Ringmasters have slight forward sweep. The LE is straight, and the TE slants forward... A P-51 Mustang wing has just about zero sweep at the quarter chord: the LE slants back about 1/3d as much as the TE slants forward... It's just a tad more complicated to find the quarter chord for a tapered wing, but it should be close enough to find the average chord (average of tip and root chords) and 'place' its quarter chord on the line drawn from 1/4 of the root chord to 1/4 of the tip chord.

CG also relates to the Mean (average) Aerodynamic Chord, not the root chord unless the wing is rectangular, like your example. (Aerodynamic chord is not exactly the geometric average chord, except for rectangular planforms. Still, it will be close...)

And finally: there are two ways to figure the Aspect Ratio. Simplest, for rectangular planforms, is Span divided by Chord.

But if you have an elliptical or tapered wing, what then? Can you figure out the area? If so, and you know the span, you can find the Aspect Ratio.

AR = b/c (span is usually labeled 'b', maybe from 'breadth' of the wing? chord is 'c'.)

Algebra lets us multiply both sides of an equation by the same value without changing the result, right? So, let's multiply both sides of that AR equation by (b/b)...

(b/b)*AR = (b/b)*(b/c),

On the left side, b/b = 1, so it cancels out, leaving AR unchanged.

On the right side, we don't do that, instead we see that the expression (b*b) / (b*c) uses the two things we DO know: span (b) and area (b*c). (Area is often represented by 'S', from working Surface?).

So, we wind up with AR = b^2/S.

This probably doesn't do much for your initial question, but it might help you see that it isn't hard to get a bit fancier, when and as you want to.

This is some information I can sink my teeth into---- Thanks Y'all. You have helped ME more than you know.     FRED