I don't know what world of aeronautical engineering you live in but...
Strong and light is not an oxymoron. Carbon fiber, foam and Mylar has made this a falsehood. And, NEVER in the history of "real" airplane engineering has weight been added to make a design fly better other than gliders which is another realm completely from powered flight.
If you begin the design process by making light weight your priority then everything about the aircraft canl be engineered lighter. 30 years ago I built a 72" ws C-130 with retracts, flaps and operating cargo doors that weighed 3 lbs., (No carbon fiber then). It flew wonderfully but I used an airfoil that was suited to the reynolds numbers the model was flying in. It was powered by two Enya CX-11's with feathered 4 blade props outboard on ball bearing shafts.
If you're replicating an airplane research how it was engineered/built. Thousands of expensive man hours went into the design by engineers a lot smarter than most of us will ever be so don't reinvent the wheel. Simply scale down their engineering.
Most RC models are grossly overbuilt/overweight and overpowered to compensate for the basic bad engineering. As a result they've got to fly fast to stay in the air. Even a brick can fly if you put enough power in it and fly it fast enough. A good real world example of this is the F-4 Phantom.
The tensile/compressive strength of carbon fiber is astonomical. An 1/8" CF rod can support in excess of 2000 lbs.! And Mylar has a tensile/compressive strength that's quite near 6062 T6 aluminum. For modeling aluminum aircraft, mylar is already glossy smooth and far cheaper than balsa/glass/resin/filler/primer, yada, yada. The lighter the airframe, the lower power/wing loading, period. Lower power/wing loading equals tremendous weight savings throughout the whole airframe from the motor mounts to the landing gear.
To start the design process with old technologies/building techniques is to commit to a heavy, overbuilt, overpowered airframe because "we've always been built them that way". The assertion it will fly better, heavier is ludicrous. The Gossamer Condor (First man powered crossing of the English channel had a wingspan of 96' and weighed less than 50 lbs! Carbon fiber, foam ribs and mylar, not balsa and plywood. Progress only happens when you step out, way out, of the box of conventional thinking/engineering.
I suggest anyone designing RC aircraft do some researching of airfoils/reynolds nos. at UCIC Airfoil Data site. Find out what reynolds nos. your planned aircraft will fly in, use the appropriate airfoil and add lightness wherever possible with 21st century materials.
Never let anyone tell you an RC airplane will fly better, heavier. Lighter equals less kinetic energy which requires less force to control. (Read: smaller engines, servos, batteries, etc.) Whether an airplane is heavier or lighter won't compensate for inadequate piloting skills. Also, an aircraft that's not balanced correctly about all axis won't fly correctly.
My 2 cents and I'm sorry if I offended anyone but facts are facts.