Unless I missed it, no one has talked about the glue used to hold fabric down. Stits (Polyfiber is new name) used to rate their glue as good up to 140 mph. So, because a Kitfox is built typically without stitching the fabric to the flying surfaces, I'm guessing the 135 to 145 number is mostly because of that, AND the simple fact that this airframe was tested to those speeds and proven safe.

And honestly, considering we started with an airframe originally designed for only 80 mph top speeds, 145 miles per hour is a huge increase over original design criteria. I doubt there are many airplanes that have increased there top speeds by 50 percent through just a few decades of evolution. 50 percent is a really big number in that regard. And it's even bigger when you consider the airplane is still a phenomenal STOL airplane.

And even if you rib stitch the wings and tail to alleviate the glue concern, the standard 32 ft Kitfox wing flex in turbulence at high speeds could easily induce flaperon flutter (ultimately leading to wing flutter). And then there's that tall vertical fin that moves a lot, so it should be made stronger and while you're at it add an aerodynamically balanced elevator and rudder. Unfortunately, that is a lot of re-engineering for such little gain of only 15 to 20 mph. Of course, re-designing a more rigid wing (and tail) is certainly doable, but I'm a bit concerned by the time you were done modifying a Kitfox for 160+ speeds, it wouldn't be right to even call it a Kitfox. It would almost be a whole new airplane.

The gang here knows that I am one of the guys that believes a modern Kitfox could fly a lot faster than it does with a few modifications. However, my "Fast" is a 140-145 cruise speed, not 160 mph.

I know this airframe can high cruise safely at 140+ mph if you clean it up more and add some more thrust. But I think unless you are willing to majorly redesign this airframe, it would be a better goal to keep high cruise goal to current VNE numbers. All of us that love Kitfoxes have enjoyed and benefitted from the designs great safety record.

With all that said, I really do think we can get our Kitfox cruise speed up while still retaining most of its STOL abilities. With all we have learned about these great little planes over the decades, I would suggest you just follow the basic concept of the original Speedster and maybe make a few more minor improvements from there. I think the company had it mostly figured out a long time ago with the Speedster concept, and I know that concept would work again if we took it even further.

Oh, and fwiw, a super cleaned up "Speedster" will be the best looking plane on the ramp, and will look like it goes at least 160 mph to onlookers...

....Only you have to know it's 15 mph less.