Phoenix Prototype

The Phoenix is an entry level craft designed to be quick to build and easy to fly for beginners. It is constructed from an EPS foam core with fiberglass skin, resulting in a strong but lightweight hull with ample built-in flotation. These pictures show the step by step construction of the craft, which we are in the process of testing and rolling out as a quick build kit. The foam hull components and duct will come precision CNC-cut, along with the engine reduction drive, controls, and many of the smaller components required for assembly. This craft is designed to perform well with the widely available Predator 13 HP engine as shown here, but can also accommodate up to a Briggs small block V-twin (23 HP), which is an easy drop-in replacement.

This is the underside of the hull after the three hull sections have been glue together. The pieces are glued together right-side up, with wax paper beneath the joints to catch any epoxy squeeze-out (visible here as yellow strips along the hull joints. In this picture, the outer skirt attach strips are also being test fit.
A router with a home made edge-following jig is used to route pockets for the inner and outer skirt attach strips. The pockets are 1/2″ deep and 3/4″ wide. For the inner attach strips, the outer edge of the pocket is 8″ from the outer edge of the hull. For the outer attach strips, the underside of the strip is 2.25″ from the bottom of the hull.
Pockets on the underside of the hull for the inner attach strips.
Ripping 1/2″ thick pieces from a 1×6 board using a circular saw and edge guide. Sometimes 3/4″ x 1/2″ rectangular strips can be found in the moulding sections of hardware stores, but are typically very expensive.
Test-fitting the outer skirt attach strips. Kerfs are cut every 1″ or so to allow the strip to bend.
A bead of Gorilla glue is laid in the skirt attach strip pockets, and the skirt attach strips are pressed into the pockets. They should be a snug press fit, but it might be necessary to weigh the outer attach strips down on the bends at the front of the craft if the pocket ends up loose.
The inner and outer skirt attach strips are used as a guide to cut the plough planes with a hot wire bow. Be conservative on the front and back edges of the cut where the inner attach strip stops and there’s nothing to guide the inside of the wire. Leave excess material here, and sand to clean corners later..
The plough plane corners are cleaned up with a belt sander.
Cutting the topside contours. Moulding boards are kerfed to bend over the topside profiles, and stuck to the hull with a very light coat of spray adhesive on the wood only (too much spray adhesive will attack the foam). A 1.5″ wide strip is placed just above the outer skirt attach strips, and a 3/4″ wide strip is placed so that the outer edge is about 1.5″ inches from the footwells.
This results in a nice topside contour. Imperfections can be cleaned up with a belt sander and light weight spackling compound. Carefully remove the guide strips when finished. Dimensions and placement of the guide strips can be modified to suit personal preference, but these sizes give a great result.
The bench section has been glued down, followed by the footwell 1/8″ plywood reinforcement, as well as the 1/8″ plywood bench top. The lift air holes are then cut out with a jigsaw according to the dimensions provided in the drawings.
On the underside of the craft, round the primary lift air hole edges to provide better airflow to the underside of the craft, as well as easier edges to fiberglass.
Fiberglass the underside of the craft. We used a single layer of 6 oz cloth.
Drape glass cloth into the lift air holes and be careful to seal the corners. This is a prime area for water to seep into the hull when off cushion if not sealed properly.
When glassing the outer edges, ensure that the glass over the outer skirt attach strips is thoroughly saturated. If the layup is dry here, delamination could occur at the edges. After the epoxy has cured, trim the cloth to the outer skirt attach strips using a sharp hobby knife.
Glue down the nosepiece with epoxy, and weigh down with weights or similar while curing.
The complete hull.
We sink 3/4″ dowels into the EPS hull to anchor handles later. We don’t recommend lifting the hull from these points, but they are strong enough to maneuver the hovercraft on cushion, and to pull the hovercraft onto a trailer.
The complete hull. Not all of the handle anchors have been added here, but we place handles on all four corners of the hull, as well as on the left and right outer edges of the cockpit and on the top of the nosepiece.
The nosepiece edges can be beveled or rounded over with a belt sander according to personal preference. Some rounding makes the topside fiberglass and paint preparation easier.
A piece of 3/8″ plywood is glued down to the front of the bench, and then a square cutout is created with a jigsaw to mount the electronic joystick (fly-by-wire option only).
CNC thrust duct sections are fiberglassed together along their outer edges to join the four thrust duct sections into one long section.
This is the completed CNC thrust duct section, ready to be bonded to the inner duct liner. The EPS easily bends into a 36.375″ inside radius
Joining two sections of 12″ wide 1/8″ bending plywood to make the inner thrust duct liner. A single layer of 9 oz glass cloth is used at the joint (it is critical that the INSIDE of the duct liner is fiberglass taped, not the outside, or the inner liner will not take a proper bend near the joint). The fiberglass tape is covered with wax paper, and then flat board and weights.
The thrust duct liner is shown glued into the external duct braces (see dimensions in drawings). This setup is sufficiently rigid without requiring brace fins or tubes later.
The CNC duct sections are epoxied to the inner duct liner A cam clamp with a board on the outside is used to apply extra pressure to the edges of the duct section.
The glued up thrust duct. The small gap at the bottom will be oriented facing the bottom of the hull, and will be mostly removed in preparation for bonding the thrust duct to the hull, so attention does not need to be directed to making this edge perfect.
A single layer of 9 oz flexible (2×2 twill) glass cloth is used to laminate the EPS foam to the inner plywood liner.
Outside view of the laminated duct. A fillet is added to the joints between the external braces and the inner plywood liner using epoxy with microsphere filler. This adds strength and results in a nicer finish than fiberglass tape.
Fan guard mounting tabs are cut from 1/8″ x 3/4″ aluminum flat bar. We will soon be CNC router cutting these parts.
3/4″ x 1/8″ slots are cut into the fiberglass leading edge of the duct at regular intervals using a sharp hobby knife. Foam is dug out to a depth of about 3/4″. These cavities are then partially filled with an epoxy/microsphere mixture, and the fan guard mounting tabs inserted.
The completed thrust duct with fan guard mounting tabs bonded in place. Thickened epoxy has been added to fill the weave of the glass cloth, and a flat surface has been sanded on the bottom of the duct to mount to the hull (see details in drawing).
Part of the bottom rear inner duct liner is cut away where it intersects the lift air box. The duct is carefully aligned, leveled, and glued down to the hull with an epoxy/microsphere mixture.
Detail of the joint between the thrust duct and hull. It is important that epoxy squeeze out from all sides of this joint.
Side view with duct attached.
1/8″ plywood lift air box wall. A triangular wood strip (available at hobby shops is CA glued to the rear edge to provide a good bond to the rear wall of the box.
The sides of the lift air box are now all in place. Since there are strips of wood along the inside corners, the outside corners can be rounded to provide better corners for fiberglass taping.
A single layer of 9 oz cloth is used to laminate the EPS on the topside of the craft. A second layer is used on the sides of the craft where the pilot will likely enter. All plywood surfaces are sealed with epoxy. Epoxy with filler is used to fill the weave of the fiberglass and smooth out any bumps on the topside. If sunken dowels are used to provide anchors for handles, it is important that their locations be marked with sharpie between every step so that they can be found later.
Lift air guides CNC cut from EPS foam in three pieces.
The lift air guides are epoxied to the underside of the 1/8″ plywood lift air splitter plate. In addition to eliminating corners and smoothing airflow inside the lift air box, they make the splitter plate rigid without requiring thicker wood or aluminum braces.
Landing skids on the underside of the craft. The 1/8″ aluminum skids are mounted to 1×2 boards, and then glued to 1/4″ plywood strips which help to spread the load out along the underside of the craft (see drawings for details, dimensions, and exact placement).
A closeup of one of the completed landing skids. The 1/4″ plywood skid base is epoxied to the glass cloth on the underside of the craft, and the edges of the 1/4″ plywood are filleted to the underside with an epoxy/microsphere mixture.