Construction/F-4 Phantom II

This high-performance, sport-scale jet is a great performer

This high-performance, sport-scale jet is a great performer

The F-4 Phantom II needs no introduction; it is one of those airplanes with a long and storied career. My desire to build an F-4 came from watching my brother Daren fly his scratch-built electric-ducted-fan-powered F-4. It was a simple design (a box with wings that looked like a Phantom), but it flew like a sport model!

GETTING STARTED

The basic construction of my Phantom retains the simplicity of Daren’s F-4 with just a bit more refinement of the fuselage’s box structure. When the fuselage skeleton is complete, the rest of the construction, including the inlets, is done off the building board.

I chose to use a single fan with a single tailpipe hidden inside the dummy twin-engine nozzles. Designed for a 90mm fan, the model is also equipped with mini retractable landing gear. The cockpit/battery compartment hatch, fan hatch, and tail-cone hatch use magnetic latches. The tail feathers are simple sheet balsa. The horizontal tail uses an inverted Clark-Y airfoil and the rudder linkage is hidden under the elevator hatch. The nose cone and engine nozzles are molded fiberglass.

I like to build the tail feathers and wings before constructing the fuselage, and I recommend building yours in this order. You’ll need the

wings while adding the bulkheads to the fuselage, and you’ll need the tail feathers when building the tail boom. Cut all the pieces out at one time to make a “kit” before beginning construction. Use spray glue to stick the templates to the wood for cutting. The templates on the plans are organized by the type and thickness of wood.

TAIL SURFACES

The rudder is actuated via a torque rod made from a Du-Bro 4-40 strip aileron set. The vertical fin slips into a pocket in the top of the fuselage. The torque rod extends down through

a hole in the horizontal stab center section and into the elevator-hatch area. If you do decide to streamline the fin, wait to do so until after the fuselage is built so that you can trace the top of the tail boom on the fin. Because of the pronounced anhedral, the horizontal stab is built in three pieces: a center section with right

and left stabs glued to it. The plans include stabilizer jig parts used to sand the bevel in the center section and when gluing the two stabs to the center section. These glue joints must be reinforced with fiberglass cloth and resin.

WING CONSTRUCTION

The wings are built using D-tube construction, and the washout between the root and tip rib of the inner panel is built in during construction. The outer panels have no twist.

Two birch-ply stub spars interlock into two birch-ply rib doublers. These interlock with the landing gear and aileron-servo mounts, so the landing loads are transferred directly to the spars. This makes the wings extremely sturdy without adding excess weight. Once the wings are pulled from the board, the tabs are removed and the remainder of the wing construction is done in the jigs. The inner and outer wing panels’ glue joints are reinforced with fiberglass cloth and laminating resin. The ailerons are cut from the wings after they’re built.

FUSELAGE CONSTRUCTION

If you can build a sport model, you’ll be comfortable building the fuselage. Because you have access through all four sides of the fuselage, building the inlet ducts are a piece of cake. There are two sets of bulkhead pieces used to mount the fan unit. Each set has a one-letter suffix: A and B. The A parts are intended for 90mm fan units, and the B parts are meant for 3 1/2-inch fan units. Before beginning construction, check the fit of these parts of your fan unit and then use them when you build your model. Although an F-4 is a pretty boxy design, it does have some curves. The top and bottom corners of the bulkheads are already beveled to accept balsa triangle stock. Balsa sheets are glued to these, then the corners are rounded. Other curvy areas, such as the top of the nose section, the fuselage spine, and tail boom, all use sheeted construction.

The magnetically latched hatches are simple to build and are secure in flight. The cockpit hatch gives you access to the radio equipment, retract hardware, and flight batteries. The fan hatch gives you easy access to the fan as well

as the elevator and rudder servos. The elevator hatch is underneath the horizontal stabs.

The tailhook/splitter plate is attached to the elevator hatch and is also held on with magnets. If you are going to use a receiver battery pack, I suggest mounting it above the fan on the front of the elevator and rudder-servo mount. With my prototype, I placed the receiver pack in the nose section and it was nose-heavy. I needed lead under the elevator hatch to balance it.

INLET DUCTS

The inlets are built up using sheet balsa for the inner walls and smooth Bristol paper for the outer walls. Bristol paper doublers and triplers are added after the initial inlet construction is done. The aft inlet duct is built first, then the front. The first step in building the inlets is to assemble the aft inner inlet walls. The back of these are beveled so that the air flows smoothly into the fan. Glue these together over the plans. If you don’t do this, the glue joint or the inlet walls may crack when they’re inserted into the fuselage. Finish the outside faces of the inner inlet walls before gluing them into the fuselage. The top and bottoms of the inner walls should be left unfinished so that the outer inlet walls can be glued to them.

Now, the bottom of the fuselage is sheeted with the grain running across the fuselage, and the rest of the fuselage is sheeted with the grain running lengthwise. Route the wires and air lines before sheeting the top of the fuselage and the engine nacelles. After the fuselage is sheeted, round off the corners on the bottom of the fuselage and the tops and bottoms of the engine nacelles. The inlet lips are then built and shaped on the model. Use masking tape to protect the sides of the nose section while you shape the inlet lips.

FINAL ASSEMBLY

The incidence and dihedral of the wings are pretty much set when the stub spars are inserted into the spar pockets. Make sure the wings’ leading edges are the same when joining the wing and fuselage. I used 30-minute epoxy to glue the wings and tail feathers to the fuselage. Once the stab is mounted, shape the hatch sides to match the stab center section. Make a Y pushrod for the elevator and a straight pushrod for the rudder. Notch the sides of the hatch for the elevator pushrods. Make sure the notches are large enough that the push rods do

not touch the hatch.

I used clear plastic sheet to make the tailpipe. The tailpipe should fit snugly over the back of the fan and inside the oval opening of the engine nozzle. Make sure the tailpipe is parallel to the centerline of the fuselage. Sighting from the front and rear, verify that the nose cone is aligned with the fuselage centerline. Since the entire model is fully sheeted, it can be covered with iron-on film, or fiberglassed and painted after everything is sanded smooth.

IN THE AIR

For your initial test flights, set the control throws to low rates. The model will require a takeoff run of about 150 to 200 feet on level asphalt. Don’t horse it off the runway. Instead, as the model accelerates, apply gentle elevator backpressure and the nose should come up. As it continues to accelerate in this attitude, it will fly off the runway on its own.

The F-4 is stable and responsive at all speeds and is capable of very slow flight. As you descend for landing, hold the model into a level flight attitude with the elevator, and control the rate of descent with throttle. At about 3 feet off the runway, reduce power to idle. Raise the nose to flare and touch down on the mains. Take your time to get to know the model’s handling characteristics. It is a blast to fly and should present you with no surprises. Congratulations! You’re now a Phantom driver.

Though formed parts are not available for the Phantom II, laser-cut wood parts are available from Bob Holman (bhplans. com). For more information, contact Bob at bhplans@aol.com.

The Phantom II is a compact size with excellent slow- and high-speed performance. Here the author shows off the relative size of his EDF jet.

The rib tabs have been removed and the wings have been tack-glued in the wing jigs over the plans. The 1/8-inch balsa wing spars and 1/l16-inch shear webs have been glued to the upper and lower balsa spars. The wings are ready for top sheeting.

The square corners of the fuselage have been rounded. The cockpit hatch base plate is sanded to match the contour of the fuselage. All hatches use magnetic latches.

The fan unit is being fitted to the fuselage and the fan mounting rails have been drilled. 2-56 blind nuts retain the fan. The doubler glued to the front of the fan bulkhead forms a shallow pocket to seal the fan to the inlet ducting.

The main gear mount is placed deep enough in the wing to allow enough clearance for gear doors. At this point, all construction is complete and the model is ready for finishing, then my favorite part—flying!

The hidden aileron linkage has been built from 2-56 hardware. The aileron servo is removable.

Above left: After the tailhook and elevator hatch is built, the stab is mounted and the elevator hatch is sanded to fit the stab. The inside of the elevators are sanded to match the tail-boom contour. Above right: Note the simple, direct linkages to the elevators and rudder. Even though this photo shows that the horizontal stab is bolted to the mount, it is glued on the final version of the model. I wasn’t sure how well the inverted Clark-Y airfoil would work, so I wanted to be able to remove the stab without hacking up the fuselage.