Practically every aspect of a model plane design is a compromise, nnowhere more common than in strength vs weight. Same is true of full scale. I try to build for light weight with adequate strength for good performance.

However, I gained a little perspective on this topic at a recent club weight-lifting event. The object was to lift more weight than the other guys, flying one full minute, taking off and landing in one piece, with power limited to stock two-cycle engine of no more than .46 displacement. The winner was a very ingenious 17' polyhedral wingspan, glider type wing, on a v-tail boom fuselage made from a composite surf-fishing rod blank, powered with an OS 46 FX turning through a 5:1 belt-driven gear reduction to swing a 26X10 prop. The plane itself weighed 23 pounds, before any payload was added. It flew slow, but steady, sorta like an albatross, if you've ever seen an albatross in the air. I couldn't stay for the very end, but they were up to 3009 grams at the time I left--that's close to seven pounds of payload on a 23 pound plane, so the OS .46 was flying 30 pounds around the field.

The other contestants had smaller planes, one of which was not way different looking from a standard 40-size trainer with maybe a little more wing area than typical, scratch design but conventional kind of airframe. I had the opportunity to heft this bird with its payload, and it was heavier than any Thanksgiving turkey I ever lifted. This plane was in second place when I left, and not far at all behind the albatross, in the neighborhood of 3000 grams payload as well. So what I learned from this was that a standard size model and standard size power will fly at two or three or even four times the five-pound weight we would aim for on a .40-.50 size engine. It won't loop, and it won't roll unless you start five hundred feet high, but it will fly.

The other end of perspective comes from watching a Yellow Sukhoi fly. I don't know its exact weight, but it was definitely light (and strong) for its size. I was amazed how it floated like a feather in low-speed maneuvers. So that showed me the benefits of light weight.

I am a sport flyer, out for a good time, not looking to win any trophies. So while I am not reckless about adding weight, it doesn't bother me to add a little weight when I think the added strength will pay off. My planes are usually within 10% of what might be considered light for their size, and there are no maneuvers of which I'm capable that they will not do, and in decent form depending on who's flying. If I think a particular model is more sluggish than I would like, I have no qualms about swapping in a bigger engine.

So on my Stinger as mentioned above, the stock design imho is clearly defective. The fix I came up with was carbon fiber reinforcement, at negligible added weight; plus 1/16" hard balsa sheeting on both sides of fuselage, certainly less than an ounce of added weight; and finally wrapping the fuselage in 2 oz fiberglass and painting instead of covering. The glass/epoxy/paint vs monokote covering maybe cost me another couple ounces. On the strength side, I have a very solid fuse, stress distributed via the balsa sheeting and fiberglass wrapping, and I can get a better looking fuse by painting vs covering. On a .60 size plane (powered with a .75), I think I'm way ahead of the stock kit.

All this extra fussing does take extra time, but to me that's the attraction of kit-building and bashing vs ARFing or bowing down to the original design. When I crash through my own stupidity, I accept it and build again. But when a plane fails in "normal" usage because of less than adequate strength in the design or manufacture, it takes me a long time before the urge to kill goes away.