After Ben Ellison reviewed a Widgeon, Ben & Marty Ellison, & Ross Mahon designed the Gewduck around the Widgeon’s shortcomings and, one by one, eliminated them. They started designing the aircraft in 1990. The design involved a hired structural engineer and coaching from David Thurston, and the goal was an airplane that could carry 6 people and 300 lb of cargo.
Gweduck twin engine, six place, 600 hp amphibian. Construction is fibreglass, vinyl-ester resin and carbon fibre. All of the Gweduck’s akins are glass-foam-glass sandwiches of varying thicknesses. The fuselage sides and the wing skins are 3/8 in thick with the closed-cell, polyurethane Last-A-Foam (commonly used in the boating industry).
The landing gear borrows heavily on Grumman concepts with machined billet A-arms pulling the oleo struts up into the fuselage sides and the saled landing gear wells.
The fuselage basically uses three moulded parts: the sides, the aft bottom, and the forward bottom ahead of the step, which is ¾ inch thick. The entire hull is totally sealed.
The windshield is 3/8 in thik to transfer some of the bow loads up to the top of the hull.
The fuselage is designed to be hosed out with salt water to wash. There is no metal from shoulder-level down, and everything drains into the bilge and is pumped overboard.
The wing has two molded-sandwich skins, top and bottom, and the molded ribs are bonded to the lower skin while it’s still in the mold. The spar is two C-sections back-to back with carbon fibre caps. They bolt the C-sections together and insert 3/8 in aluminium plates between the webs where the wings bolt into the fuselage. Once the top skin is bonded on, the bolts joining the spar halves are superfluous.
The main spar is at 39% and ther is a front spar at 10% chord. The leading edge is non-structural for easy repair.
The airfoil is a 15% thick Ribblet, and the ailerons are linked to the flaps, so they go down 15 degrees as the externally hinged Fowler flaps come down 30 degrees.
All of the fuel is in the wings with none in the fuselage. The normal capacity is 200 USG but outboard auxiliary tanks increase the total capacity to 360 USG.
Engines: 2 x Lycoming IO-540, 300 hp
Prop: MTV-9, reversible
Wing span: 52 ft 6 in
Span floats down: 48 ft
Height: 10 ft 10 in
Empty weight: 4200 lb
MAUW: 6000 lb
Fuel cap: 200 USG + 180 USG aux
Cruise speed: 100 kt
Fuel burn econ cruise: 19.5 USG/hr
Power loading: 10 lb / sq.ft
Wing laoding: 20 lb/sq.ft