Seahawk (oz14017)

About this Plan

Seahawk. Radio control sport floatplane model. Wingspan 64 in, wing area 655 sq in, for OS Max .46 SF engine.

Quote: "Fly off land or water. Seahawk, by Andy Lennon.

The Seahawk is an older big brother of the Swift (which, as of this writing, late May '92, is being very successfully flight-tested). There is a distinct family resemblance.

The Seahawk may be easily and quickly converted from tricycle landing gear to central and wing-tip floats for water flying. The low-wing configuration permits this change. The horizontal tail is in a conventional location.

Seahawk Features: The wing incorporates the NASA safe wing modification (Model Airplane News, June 1990) and features Youngman flaps. These are similar to Fowler flaps, but are actuated by two pairs of arms for each flap. They increase the wing's area by 102 square inches and have a coefficient of lift maximum of 2.60 for the area of the wing that is flapped. The basic airfoil section of the Eppler 197, which I'm using on the Swift, has a maximum coefficient of lift of 1.17.

The Youngman flap was a British development and was used on the Fairey Firefly and Gannet, both British naval aircraft. Extension of the Seahawk's big, slotted flaps requires a powerful servo. The Futaba servo S131S with 69.5 ounce/inches of torque proved adequate, provided the model was slowed down at low rpm and in a slight climb. It has since been replaced by a Futaba S 125 sail servo of 129 ounce/inches of torque.

Flaps extended, landing speeds are in the low 20s in mph. One very pleasing characteristic is that the model noses down gently on flap extension. The nose-down pitch of the deployed flaps must exceed the nose-up pitch generated by the increase in the angle of downwash impacting on the horizontal tail.

This model's structure is based on the principles outlined in the recent articles on stressed-skin design (see the September and October '92 issues of Model Airplane News).

The design of the central and wing-tip floats are detailed in RCM articles on hull and float design, (February, March and April 1991). The central float is based on the short after-body hull, with a stem-post angle of 8 degrees. Its beam is 6 inches at its widest point.

Construction: This isn't a beginner's model. For a reasonably experienced modeler, the drawings and photographs provide ample detail for 'kitting' the various metal, plastic, plywood and balsa sheet, strip and block parts.

The following focuses on assembly procedures and sequence. For example, the 1/8-inch brass tube on the elevator's 3/32-inch wire horn should be slipped onto the wire before making the second bend, for obvious reasons. Let's start with assembly of the component parts of the Youngman flaps.

Start by assembling four sets of ply arms and flap ribs as shown in the drawings and in Photo 1. Four sets of support ribs are needed. Photos 2 and 3 illustrate how the arms and supports function as the flaps extend. Photo 4 shows the jig for these assemblies..."

Supplementary file notes

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