The Cessna Cardinal is a good example of the unintended consequences of aircraft design. What should be so hard about designing a sleeker, strutless 172?
In the early 1960s the 172 was still selling well, but the (comparatively) sleek new Cherokee was proving to be a hit. Somewhere in Cessna upper management it was decided that the 1967 172H would be the last year for the "clunky" strutted design, to be replaced with a modern new Model "172J" for 1968. The thinking likely went something like this:
First requirement for the 172J: No wing struts, so the competitors can't mock our old-fashioned look in their ads. That means a carry-through spar structure in the upper cabin. That's heavier than a strutted construction going out the gate. So where do we put the spar? It has to be at or near the thickest part of the wing. The low-wing guys have it easy; they just run it under the seats. But put a strutless wing on a 172, and the maximum airfoil thickness, and thus the spar carry-through, is right where the pilot's head is. So we have to somehow move that spar aft, where the bulge in the cabin ceiling will be out of the way. How to do that?
First, we can use one of those NACA 6-series "laminar flow" airfoils, like the Cherokees, Comanches and Mooneys. The maximum thickness is further aft than on the 172's old reliable 2412. So the 172J won't have the same slow flight, stall and short-field qualities as the strutted model. But hey, all the competitors' ads say "laminar flow" is faster. But we know that though it reduces drag some on something like a P-51 or maybe even a Centurion, it doesn't make much of a difference on a typical low-power bugsmasher with imprecise production tolerances and oilcanning, lightweight skins. But it gives us the cabin packaging we need, so we use it.
Next we have to move that wing as far aft as we can, resulting in a forward CG of only 5% of mean aerodynamic chord, much further forward than a legacy 172. Our customers like big flaps, so we're gonna need a LOT of pitch authority to land tail-low with full flap and that forward CG. That means a long tail arm (more weight) and a stabilator (more weight and complexity, not to mention different handling qualities).
This thing is starting to take shape, and it looks slick. It's obviously going to be much different from the old 172, so the model number gets changed to 177.
Now with the wing (and fuel tanks) so low and so far aft, we can't count on gravity to deliver adequate fuel pressure to the engine in extreme nose-up attitudes. So add engine-driven and auxiliary electric fuel pumps and a header tank (more weight and complexity).
Flight tests show we need more lateral stability, so make the vertical tail taller (more weight).
The weight is adding up alarmingly, so we choose to go with thinner skins and lighter components in places. Still, it's about 150 pounds heavier than a 172H. And it's more expensive and labor-intensive to build than a 172. But 2,000 150 hp O-320-E2As have already been delivered from Lycoming, with an option for 2,000 more, so by cracky, we're gonna use 'em. To hedge our bet, though, we'll keep the strutted 172 line going and convert that old relic to the Lycoming engine, too.
And the rest is history.
