Wind Tunnel Testing: During 1987 -1991, Seair conducted exploratory wind tunnel tests on 1/20 scale models of several wing, body, tail, and endplate combinations. This testing was accomplished in a small research tunnel at Aeronautical Testing Services of Arlington, Washington. Data from these tests were used to develop practical aerodynamic prediction methods, identify viable configuration options, and to help understand various ground effect phenomena. Wind tunnel tests helped determine several viable tail and endplate shapes from more than a dozen options. Wing pressure measurements were used to assess the influence of several airfoil section shapes and flaps on takeoff lift and cruise height stability. The wind tunnel program employed several measurement methods to gather a range of data:

• Longitudinal force and moment data
• Off-surface and downstream wake survey
• Flow visualization (tufts)
• Wing and ground plane pressures
• Free-to-trim pitch-heave dynamics

Some the data obtained over eight tunnel entries was the first of its kind collected on WIG's anywhere (and some may still be unique in 2001). Pressures measured on the ground-plane under a WIG wing with endplates graphically showed why the ride of some WIG's has been described as feeling like that of a large luxury car with soft suspension. A hovercraft must support itself on a short cushion of air bounded by the skirt around its hull, and a hydrofoil is supported only at its ends on stiff struts. In contrast, the experimental data showed that a WIG's supporting cushion extends well forward and aft of the wing. Its total pressure "footprint" on the water (or in this case on the tunnel ground-plane) is three to four times the length of the wing chord. The length of the WIG's air cushion acts as the aerodynamic equivalent of a long wheelbase that smoothes out the bumps when the craft is "platforming" over a choppy surface. Just as the craft exerts a force on the water surface well out in front of the wing, oncoming waves feed a pressure force back to the wing of the craft allowing it's motion a slight "lead" on the shape of the surface when "contouring" at an angle to long swells.

Model Scale Flight Testing:

From 1987-1996 Seair Craft Inc. conducted extensive outdoor testing with 1/5 and 1/4 scale powered models, and two small hand-launched gliders. Hull planing characteristics were studied with towed and radio controlled models.

Just as the wind tunnel models provided insight into the aerodynamic lift and pitch stability, the first generations of towed-hull and R/C model tests provided an understanding of the hydrodynamics. We found that traditional seaplane float and boat hull design guidelines could be used to build WIG endplates and hulls that had good "boating" characteristics, but these were not necessarily compatible with the aerodynamic requirements. Conversely, the lowest drag and highest lift aerodynamic shapes had very poor hydrodynamics. These were difficult to get over the "hump" and onto plane, to unstuck from the water, and could have bad "slamming" characteristics in choppy water.

When properly executed, the reverse-delta planform of Lippisch type WIG's has been shown to offer good height and pitch stability, but the arrangement is inherently larger in width x length for a given square footage of lifting surface. Besides being difficult to build compactly, the wing geometry is potentially more difficult and costly to build than a rectangular planform. The simple tandem rectangular wing arrangement favored by Jorg is perhaps the most straight-forward and results in very fast cruise speeds over smooth waters. We were concerned that the tandem wing craft did not seem to be very robust in stability or takeoff performance when in choppy waters or gusty winds.

We initially investigated single-piece rectangular wings with simple trailing edge flaps and flat-bottomed or S-shaped airfoils. First results were disappointing. After performing computational fluid dynamics (CFD) on nearly 50 airfoil modifications, we arrived at a family of custom hybrid airfoils and wing planforms that provided reasonable pitch stability, lift, unstick from the water, when combined with a specially designed center hull and sponson/endplates. We settled on
a preferred general arrangement formula consisting of a mid-mount low aspect ratio main wing, coupled with a high-mounted, moderately tapered horizontal tail surface of high aspect ratio. The horizontal tail is supported and stiffened by twin vertical fins (in the case of single engined craft) or a single centerline tail behind side-mounted twin engines. Although most testing was conducted with open props, the preferred design employs shrouded props or ducted fans. The resulting combination enables takeoffs without the use of auxiliary engines or PAR devices at static thrust-to-weight ratios or less the 1:4. The horsepower to weight ratios are comparable to efficient PAR WIGS. This makes the complexity of powered lift or hovercraft type air cushions unnecessary (unless amphibious capability is desired).

Material on this website is copyrighted ©2000 by C.P.Nelson, Seair Craft Inc.