Light dawns on marblehead!
Bruce, your post finally clicked with me and with what Ptulmer wrote originally. I dont have the experience or reference point for estimating a balsa airframe weight, but working backwards as you suggest makes it all clear.
I have 12 oz of gear, maybe less if I use a single aileron servo, Wing area is 319 so my airframe needs to be around 10 oz bare. This is encouraging! I have the fuse framed, with turtledeck and tailfeathers, less hatch, gear mount and cowl and am at 2.6 oz. The rest should make it come in around 4 oz (guess). Wing under 5 oz

Speaking of hi-jacking, I was not sure whether to post in scratch building or aerodynamics originally, Is this more of a scratch build thread now?

12 oz of gear sounds a bit much. You may want to look into buying some smaller servos and a smaller battery pack since those items are often the most weighty items.

10 oz for an airframe of that size is doable but it'll need to be built like an old timer using lots of sticks and air with lighter covering. If that doesn't fit in with the program then you need to reduce your gear allowance so more can transfer to the airframe.

And yeah, it's getting close to the time for a new thread about the structure in the Scratch Building area...

Do you migrate this thread or should I start one new?

before the thread moves -- the questions really do illuminate the problems a number of modelers see when attempting to scale to a given size
In this case ,a 300sq in model -
the radio for this can do the job at --2-3 ounces
the powerplant and battery at under 5 ozs
the total weight can easily be under 15 ounces and will fly reasonably up to 20 ozs if it is kept moving
our own experience at this size says " stay under 12 ozs".
Th airfoils needed are simply ones that will maintain shape - and for best results - just a rather flat plate. easy to do and I defy anyone to show any improvement in using any other shape for this kind of a project

Start a new one with the structural design work as it's topic. Different questions deserve different threads.

Scaled sown structure is not the real problem. as it is proportionately stronger than the original larger structure. Plus it may get beefed up a little, if sizes get too small for the builder's comfort. The real problem is scaling the weight of the non-structural components.

just pictures of the progress... 7.2oz airframe, 12 oz hardware, radio, motor, battery, 19.2oz total plus covering ?? Thinking about cutting lightening holes in the fuselage sides, maybe delete landing gear and run a little fiberglass up the bottom. I'll post flight pix and characteristics when available.

Looks great! I expect that wing planform to have somewhat abrupt stall characteristics but that's not a bad thing if you know it and the airplane isn't too heavy.

Thanks for the feedback. What is it about the wing that would indicate the stall characteristics?

The wing planform is approximately elliptical. Elliptical planforms tend to stall uniformly and simultaneously along the entire span, rather than from the root outward (for a constant-chord wing), unless the tips are washed out. If you intend to fly it inverted much, I would not twist the wings at all and just learn how the airplanes stalls. I practice stalls up high on the first flight of any new airplane before the first landing anyway.

I think that if the chord of the wing tip (including ailerons) is at least 70% of your root chord, your wing will probably not tip stall on you unless you do it on purpose with a snap roll maneuver.
In addition to wash out, you can also make the leading edge more rounded at the tips and leave it sharper at the root in order to force the stall to happen at the root first. You sometimes see this on full scale planes.

On many full-size aircraft, small strips of metal, with a triangular cross section, are riveted to the wing's leading edge somewhere close to the fuselage. They are actually quite small. They add just enough of a change in the leading edge contour to force airflow separation inboard and tame the stall characteristics. One light plane I recall had a piece that was about 1/2" wide, sticking forward about 1/4" and was about 6 inches from inboard to outboard ends. They were not symmetrically placed on the left and right wings...to account for differences caused by the propeller stream.

Many times, in full-size certificated aircraft, these add-ons are used to comply with spin-recovery regulations. Also, if the stall is too abrupt and sharp, forcing it earlier over part of the wing will 'soften' the feel. Even on full-sized aircraft, a bit of 'try and see' is used.

Hey BAX,
One of the most famous applications of that "stall inducing thingie" is to the Corsair. It's just as you said. It's rather small and was applied to only one wing. In the case of the Corsair, it was truly an "afterthought" kind of deal. They did it after the airplane was operational.

I just remembered a solution that has been used on the Spitfire and others: Square off the wing tips if it turns out to have stall characteristic that are too abrupt for you. It will change the planform in such a way that you may get a slightly more gradual stall, i.e. slightly root-first.

If your plane is light enough, you probably will not need stall strips or modified tips or anything anyway.

This is very interesting, I am chomping at the bit to get it done and in the air. Dang that working, eating, and sleeping business....