Design Improvements for the Zenith 601 HDS: Wing Root Fairings

Wing Root Fairings

Wing root fairings have substantially improved low-speed and high-load flying characteristics. The design process and results are described in Finding Hidden Drag .

The basic idea is as follows. If the fuselage expands and contracts over the wings, as it does for the 601 HDS, then this increases drag and reduces lift, particularly for large payloads or high angles of attack. The negative effects can be mitigated by a fairing that simulates a constant width fuselage. The fairings significantly improve climb rate, ceiling, stall speed, sink rate at low speeds, optimum glide ratio, minimum power to stay aloft, and stability of the plane when CG is close to the rear limit. Generally, the required angle of attack in level flight is significantly reduced at or below cruise power settings. This manifests itself by a much lower nose, particularly at gross weight.

The design of the fairing is not difficult. One draws on the fuselage the points of attachment of the fairing in a reasonable curve. On the wing, one draws a straight line that is at 90 deg with the spar and that just touches the fuselage at its widest point. Now one connects the line on the wing with the curve on the fuselage, thus getting a surface. The fairing must have that surface.

For creation of the fairing, one protects the wing and fuselage with masking tape, then establishes the fairing surface using plaster. Once the plaster is cured and dried, one lays the fiberglass. When the resin has set, the fairing is removed, trimmed, and the fairing surface is finished using light-weight filler. Of course, the plaster and masking tape are removed as well. The finished fairing is riveted to sidewall and wing surface, and then painted. Overall, one should aim for very lightweight fairings that together do not exceed 4 lbs when painted. The photos show the shape chosen by us.

Next are two views of the left-hand-side fairing from below. The first picture shows how the fairing is attached to the fuselage and leading edge in front. The second picture shows the attachment in back. The latter attachment is only to the fuselage and not to the trailing edge portion of the wing.

Finally, some pictures with paperstrip showing size in inches.

First, four pictures taken near the leading edge, at midsection, at aft part of wing, and near the trailing edge.

Second, two pictures below the wing, near the leading edge.

Third, one picture below the wing, near the trailing edge.