It's no secret that Cessna is working on a new piston single. Cessna boss Jack Pelton told single-engine dealers last fall that a new airplane was coming. Jack and I even discussed potential new designs at length several months ago. Jack bought the martinis that I drank, and I think he listened, but by the end of the evening I was suggesting, as I remember it, a biplane pusher configuration made from injection molded plastic, so I'm sure he gave up by then.
What Cessna hasn't revealed, in bars or otherwise, are any details of what a new piston single may look like. There have been hints that a new airplane would not replace any of the three models-the 172, 182 and 206-currently in production. Jack did tell me that preliminary work had begun in Cessna's engineering lab, but whatever timetable or other targets exist for the project remain a company secret.
So, with no facts other than confirmation that Cessna is working on a new piston single, we are all free to speculate and offer more suggestions that Jack and his team can ignore.
The first and most obvious design choice in this case is should the new Cessna have a high or low wing. Low-wing airplanes seem to have won that war a long time ago with nearly all high-performance singles having wings on the bottom. But, Cessna has built more airplanes than every other general aviation manufacturer put together, and all the Cessna singles that I can think of, except for a few crop dusters, have the wings on the top. A high-wing design is as powerful a trademark of a Cessna airplane as the name itself. However, given the dominance of low-wing singles, it would seem that the choice is a slam dunk with no advantages left for the high-wing airplane. But that's not true.
One of the most important assets of a high-wing design is the efficiency of the structure, particularly with a strut-braced wing. By efficiency, I mean the weight of the airframe. With the wing at the top the greatest loads are passed into a central frame, which conveniently falls in the right place to be the forward cabin door frame, which needs to be a reinforced structure in any case. Those wing loads are transmitted down the door frame to the bottom of the fuselage where the strut is attached. Positive wing loads are applied in tension to the strut, and airplane building materials have much greater strength in tension than compression so the strut is strong, but light. The strong main door frame is also useful for absorbing landing gear loads that are not transmitted to the wing spar as they are on most low-wing airplanes.
I would be surprised if a new Cessna single had wing struts, but a cantilevered high wing can also be built very light. If you don't believe me compare the empty weight of a Cessna 210 to singles of similar size from other manufacturers and you'll see that the 210 wins every time. Actually, every Cessna model I can think of has had the lightest empty weight in its category over the years, and the high wing is part of that weight control.
The high wing can also be more aerodynamically efficient in terms of drag. Airflow over the top of any wing is more complicated to manage than air passing beneath the wing. But in a low-wing airplane, the fuselage is smack in the middle of the upper wing surface, forcing airflow over the wing to diverge from a steady path toward the trailing edge. Aerodynamicists have become adept at minimizing drag caused by the presence of a fuselage on top of a wing, and you can see their work in the very complicated shapes of fillets and fairings of recent designs, but the high wing avoids many of those complications and can be inherently lower in drag.
