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Latest Rutan Design Looks to Make the Impossible Possible
By Randy Dufault
July 22, 2015 - After working at airports most of his life, legendary aviation innovator and designer Burt Rutan wanted an airplane that could go many places, but not be limited by the need for a runway.
The result of his desire is his 46th aircraft design, the SkiGull.
The SkiGull is a trimaran-hulled, amphibious airplane designed to land on water, snow, ice, and other unimproved surfaces–without having to bring the craft into a shop and physically change its configuration.
Rutan presented the design and reported on the project’s progress at a forum Wednesday afternoon at EAA AirVenture Oshkosh 2015.
According to Rutan the SkiGull seeks to solve all the shortcomings, and optimize the performance, of a light seaplane.
“So we are trying to develop to an impossible specification,” he said.
Rutan believes there are four significant shortcomings to common seaplanes: shock absorption, the major configuration changes required to operate off of various kinds of surfaces, the fact that seaplanes are noisy, slow, short-ranged, and inefficient, and the fact that the corrosive effects of salt water limit where the planes can go.
The SkiGull addresses all four problems with a number of innovative solutions.
First, and foremost, the design includes two skis that retract and extend from the tri-hull’s outboard sponsons. In the water the skis allow the craft to take off with substantially less effort than is required for a traditional seaplane. A pneumatic extension and retraction system also provides shock absorption on the water, a feature Rutan says is missing from all current seaplane designs, and is necessary for safe and smooth operations on calm-wind glassy water, and on very choppy water.
Small wheels on the skis allow for operation on traditional runways.
Range and efficiency are addressed with Rutan’s experience designing craft like the Voyager and the GlobalFlyer, both of which flew around the world unrefueled and nonstop. The SkiGull’s wing bears a strong resemblance to both long-duration designs and Rutan envisions trips from California to Hawaii in the craft.
Noise is addressed with a quiet engine and a properly designed propeller.
A modern, composite airframe, which is assembled without the use of metal fasteners, solves the salt water corrosion problem. All the metal parts of the plane are easily replaced should corrosion become an issue.
Designing the craft was a new challenge for Rutan.
“Aerodynamics is easy,” Rutan said. “Believe me, after designing 45 aircraft, the aerodynamic part is easy…you can do it on a calculator.”
However, he found hydrodynamics much more difficult and discovered that the sort of numerical processing that works for airplanes, starts to break down in the water.
Rutan’s solution, and the solution for many boat designers, is to build a test article, run it through the water, collect data and see how it performs. Results of those tests showed that the takeoff ski-extension speed he calculated was way off; the calculated takeoff distance was actually longer than what testing demonstrated.
The aircraft is substantially complete and Rutan had a goal of bringing it to AirVenture 2015. But addressing some of the typical challenges associated with a new design, and the need for a structured flight test program, just would not allow the trip to happen.
He did commit to bringing it next year.