What Should Cessna Build Next?


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.

A high wing also delivers, in general, greater static stability, meaning the airplane tends to remain straight and level with less pilot input. Powerful static stability would be a bad thing in an aerobatic airplane or a fighter where maneuverability is itself a primary design goal. But in the kind of transportation flying most of us do, static stability reduces pilot workload, particularly when flying on instruments. Low-wing airplanes can enhance static stability by adding dihedral to the wing, and using other techniques, but the high-wing design comes by more of it naturally.

Landings can be more predictable, particularly short field landings, with a high-wing design because the ground effect cushion is less powerful. A low-wing airplane, particularly one with short landing gear, entraps a cushion of air between the wing and runway and can cause the airplane to float for considerable distances if approach speed and pilot technique are less than optimum.

A high wing also has some non-aerodynamic benefits such as keeping you dry when it rains; you can park your car under it in the T-hangar; the high wing can pass safely over a snow bank on a narrow taxiway; and you can get a better look down at the earth passing below you.

There are disadvantages to the high wing such as the need to climb up to add or check fuel and limitations on landing gear placement. With a carbureted engine, having the fuel up high eliminated the need for fuel pumps as gravity did the work, but with fuel-injected engines, as Cessna will certainly use in the new airplane, a pump is needed in any case. The landing gear complications of a high-wing design are restricted to retractable gear operation. No matter how you do it, the retracted gear goes into the fuselage taking up valuable space. The retractable gear on the singles Cessna has built in the past is just about as simple as a high-wing gear system can be, but still occupies fuselage space. The only way to get the gear out of the fuselage is to put pods on the outside like Lockheed did with the C-130, or Mitsubishi did with the MU-2s with the long body.

So, for all of these reasons-the most important being 80 years of tradition-I bet the new Cessna will be a high wing. But I don't think it will have wing struts or retractable landing gear.

How many seats do you want? Six is my guess. Nobody wants to be in any kind of vehicle where every seat is filled, at least not for very long. Think middle row of coach in an airliner. So when two couples fly, or a couple with two kids, the greatest luxury is having seats you don't use for people, which then become available for other stuff. And a six-seat cabin doesn't add much drag over a four-seater because the frontal area, which is unchanged, is a greater drag producer than the length of the fuselage. If you don't believe me fly a six-seat A36 Bonanza against the four-seat F33A. If you use your imagination you may find a knot or two speed edge for the shorter F33A, but no more than that.

Next question: Metal or plastic? The answer for Cessna should absolutely be aluminum. If it was starting from scratch a composite airframe could make sense, but with so many decades of experience in building metal airframes Cessna would be nuts to switch to composites. In piston singles the composites are working well for Cirrus, Columbia, Diamond and others, but so far those airplanes are not lighter than Cessna's metal airframes.

Finally, how much power should Cessna bolt on the nose? As much as Lycoming or Continental will deliver, I say. I would expect Cessna to stay with Lycoming given the common corporate parentage, but it has used many thousands of Continental engines over the years. Continental's cross flow cylinder head IO-550 series engines are producing prodigious amounts of power, well above the 310-horsepower rating and could churn out an easy 350 horsepower in a turbo version. Lycoming, I'm confident, can up the power ante, too. What we have seen conclusively from Cirrus and Columbia is that lots of power on an efficient fixed-gear airframe can produce cruise speeds that rival or exceed retractable gear singles, and that's what pilot's insurance companies want-fixed landing gear.

Bottom line, I expect the new Cessna to be a high-wing, fixed-gear single with six seats, more than 300 horsepower, at least 100 gallons of fuel capacity, complete dual bus electrical system, all-glass cockpit, some type of airframe ice protection, and a cruise speed of 180 or more knots. I expect the price to be very close to the high-performance four-seaters currently available. And I think Cessna will make its announcement later this year, by Oshkosh or sooner. What do you think the new Cessna single will look like?