Getting 1200lbs out of a 1050

[av8rps]

The easiest way to provide safety margin for more capacity is to make a strap from some flat 4130 that will run between the wing strut attach points on the bottom of the fuselage. Dean Wilson (original designer of our planes) suggested doing that on early Avid Flyers when they knew they were going to be flown heavy (typically on floats). A friend of mine years ago did it to his plane and after I saw it installed I could see how effective it would be.

When you think about excessive positive g-loads due to added weight on an airframe, as the wings get loaded and want to move upward, the wing strut attachment points on the fuselage is where most of that force is pulling. So if a failure were to happen there the strut would tear away from the fuselage, collapsing that wing (making for one very bad day ) but with that strap under the fuselage and attaching both struts together in effect, about the only thing that could happen then would be if the forces were so high that the strap would start to crush the bottom of the fuselage. But the struts would still be attached to the fuselage, so your wings wouldn't collapse. (You'd have one messed up Kitfox, but you'd have a much better probability of getting back on the ground than the alternative of trying to fly with just one wing ..)

In my opinion the most probable failure areas in order would be the strut attachment area on the fuselage, then the rod ends where the struts attach to the wing, and finally the wing strut itself (and then only if rusted excessively at the bottom). The least likely failure area would be the wing spar. There have been a bunch of 1050 912 powered Model 4's (weighing typically 800 empty) flown on amphibs for years with no issues, and they didn't even have the safety strap. The 1st company demo Kitfox amphib was a 1050.

The Model 4 is a pretty strong little airplane, so with that safety strap installed and some good common sense (like operating under max structural cruising speed in turbulence and doing all you can to keep operating weight's within a reasonable range), I personally wouldn't be afraid to operate a little heavy. But again, do what you can to minimize excessive stress to the airframe.

With all that said, I just told you what the factory never will because they can't. We live in a litigous society so it would hardly be in their best interest to promote flying their airplanes over the designed gross weight. And some here may disagree or even flame me for my opinion. But I've been flying these airframes for over 3 decades and can tell you I'm ok operating them 10-15% over. But again, when I need to do so I do all I can to minimize airframe stress. I hope this helps.