With the era of the seaplane long over, the past half-century has produced very few airplanes designed specifically for the water, and that makes the debut of the new Dornier Seastar especially noteworthy. It is a brand new seaplane that has already been certified and is scheduled to go into production next year. There is currently only one of these airplanes in existence and last month I had a chance to spend a day flying it.
While the Seastar is noteworthy for being new, it is also noteworthy for its ties to the past. It is basically a re-make of an old design that dates back to the earliest days of commercial aviation. In the early 1920's, the German company Dornier Flugzeugwerke began developing their signature seaplane design, a sponson-equipped monohull with inline engines on top of a strut-mounted parasol wing. Dornier made several variations of this basic design throughout the 20's and 30's, and these seaplanes were very successful in commercial service worldwide. In recent years, the Dornier family has decided to reintroduce this design with modern materials and turbine engines, which resulted in the Seastar, a ten-thousand pound, 1,300 horsepower amphibious seaplane.
Probably the Seastar's greatest innovation is its all-composite airframe, which is completely immune to salt-water corrosion. All of a sudden the biggest ongoing maintenance issue for a commercial seaplane is reduced to irrelevance. The considerable time and resources devoted to salt-water corrosion control on metal airplanes are not a factor for the Seastar. In the past, there has been some skepticism about the suitability of composite materials for seaplanes, but time seems to be delivering a favorable verdict on that. In recent years, composites have been gaining credibility for airframe and float construction, and if there was ever an airplane to really benefit from composites, it is a salt-water seaplane.
When it comes to flying the Seastar, it has a little different personality on the water than we are used to, which is largely due to its sponsons. We don't see sponsons very often anymore, they were common on old airplanes and I'm not sure why they went out of fashion because they work well. Sponsons serve two functions, first they keep the airplane upright in displacement, doing what is otherwise accomplished by wing floats, and second they provide extra surface area to aid the airplane's transition to the step, making it possible to begin planing at a lower speed and use less horsepower to get on the step.
Unlike the sponsons on the old Dorniers that have a uniform profile, the Seastar has a two-stage sponson, with a separate section devoted to each of the sponson's separate functions. The thick inboard section works to assist the airplane's transition to the step while the higher-riding, lower-profile outboard section merely serves to keep the airplane level in displacement. This refinement maximizes the efficiency of the sponson and keeps surface drag to a minimum.
The airplane gets on the step in the standard manner although the pitch changes are not as pronounced and the elevator inputs are not as critical. This is because the sponsons do some of the work of guiding the airplane onto the step. The airplane actually has two phases of being on the step, a low speed phase early in the takeoff when the airplane is planning with the assistance of the sponsons, and a high speed phase when the sponsons come out of the water and planning is transferred entirely to the main hull. The airplane transitions to the second stage of the step at about 50 knots, and at that point there is a subtle yet discernible reduction in drag as the sponsons are lifted out of the water. The airplane is very stable and handles well on the step, and the low-speed step range is particularly useful for tight maneuvering. When maneuvering in a low-speed step taxi, the Seastar can make extremely tight step turns, far outmaneuvering standard seaplanes that require higher waterspeeds to be on the step.
Sponson airplanes generally do well in rough water and I was anxious to see the limits of what the Seastar can handle. Unfortunately conditions didn't fully cooperate but I did find a large boat wake to land on, the kind that you would normally avoid, and I was impressed with how the Seastar did on that. The reverse thrust of the PT-6s is a great tool for rough water, on touchdown you can go hard into reverse to quickly dissipate the airplane's energy and minimize the beating. On takeoff, the sponsons help out in rough water by lifting the hull up on the waves and spreading out the impact. The airplane is generally very stable in pitch without any hint of porpoising tendency, and the aggressive pitch inputs that I've come to associate with hull airplanes in rough water were largely unnecessary. While I didn't see the exact limits of what it can handle, I saw enough to tell that it has good rough water characteristics, at least as good or better than comparable sized hull airplanes.
The parasol wing is another thing we don't see very often. Certainly raising the wing up on struts adds some drag but it also makes the wing more efficient. Compared to a standard twin where the fuselage and two engine nacelles subtract from the effective wing area, almost the entire Dornier wing is available to produce lift. Add the long-span flaps to this and you have a high-lift wing that is both appropriate for a seaplane and typical of the high-lift design philosophy of the 1920's. Also the engine placement above the wing removes the propellers from the spray zone and prop erosion isn't a problem in the Dornier.
One area where the Seastar truly distinguishes itself is its multiengine capabilities. Unlike many twin-engine seaplanes, it is a true multiengine airplane in the sense that it can have an engine failure at max gross weight with a minimum of inconvenience. It has a generous amount of horsepower to start with and the only adverse consequences of an engine failure in cruise seem to be a 40 knot loss of airspeed, so that by the time the checklists are all done, you find yourself flying the rest of the way to your destination at 120 knots. It didn't occur to me until after I had flown it, but I should have subjected it to the ultimate test and tried a single-engine takeoff. I suspect with 650 horsepower of one engine and the assistance of the sponsons it could probably do it. In any case, there is no doubt that it is a very capable turbine twin.
The airplane can be configured in different ways, and the part 135 version has 9 seats, a large cargo area and a door big enough that you can load a 55 gallon drum through it. All in all, I was very impressed with it. It appears to be a serious working airplane that would be well suited to scheduled commercial service in the Alaskan tradition of the Goose or PBY. It has a certain understated functional elegance that you'd expect from a design that has been in development throughout nearly the entire history of commercial aviation. I'll look forward to seeing it around.
A more detailed review of the Seaster will appear in an upcoming issue of Water Flying magazine.
Burke Mees flies commercially in Alaska.