Introduction: 1/20th Scale Radio Control Optica
Second Prize in the
Make It Fly! Contest 2017
I have been collecting information on this unusual aircraft for over 4 years. I first saw it in a movie called “slipstream”. The Optica was first flown in the public at the 1979 Paris airshow. It was four years later at the 1983 Paris airshow before the company was able to take orders. The plane is ideally suited to slow observation flying, filling the void between helicopters and light aircraft. By 1987, four aircraft had been sold. The fourth plane was placed in trials by the Hampshire police department. Unfortunately, the plane crashed killing all aboard. Investigation cleared the plane from fault, but the delay cost the company. Updated versions were built and the company was bought by Brooklands.
A fire destroyed many of the built and partially built planes. Today there are a handful of planes flying keeping the legend of the Optica alive. Rumors abound about it’s revival. Until then, I will build models.
My first testbed using a S400 motor was called the Frankenfoamy. The plan was published in Model Aviation June 2000. Frankenfoamy video
I continued to work on 1/10 scale plans when GWS came out with a small ducted fan.
The size was perfect for a 1/20 scale version. Foamboard construction would make for a short build time. It flew surprising well…..for a couple of minutes. The batteries available at that time could not handle the 3 amp draw of the fan. Now the new 340 mAh Lipoly cells are a perfect match.
Step 1: Construction of Canopy and Shroud
The fan shroud and canopy are carved from 1 ½ pound styrofoam block. A solid block would be best but laminating two or more works well also. Do not use white glue to laminate foam where you plan to sand. White glue does not sand well. Epoxy is the best bet here. The Canopy is best carved from two blocks held together with contact cement. This allows the blocks to separate to fit on each side of the crutch. Carving may seem daunting but it is easier than it looks. Trace the outline of the part on the sides and the top and bottom. Slice away foam that does not fit inside the outlines with a sharp hobby blade. You will see the shape take form soon.
Step 2: Shaping Canopy and Shroud
Complete the parts to their final shape using course sand paper. Use fine sandpaper to smooth the foam. Light weight spackle can be used to make it smoother. To harden the foam, I used white glue spread over the surface. Once dry, there is very little weight added.
Step 3: Interior Shroud
A long hobby blade is used to carve out the center of the shroud. A rough file helps remove foam from the inside followed by fine sandpaper wrapped around a dowel. Be sure to form a “trumpet” on the leading edge of the shroud. This helps smooth air get to the fan. Fit the fan into the rear of the shroud with the rear flush.
Step 4: Canopy Crutch
The outline of the crutch is traced on Depron. I used the foam box top from a restaurant take home food box. ( free is a very good thing)
Step 5: Strengthen Crutch
A slot is cut into the foam to install the bamboo rod. ( bamboo skewer) This rod strengthens the crutch transferring the nose wheel load to the wing spars.
Laminate a piece of depron over the nose gear wire. Magnets are placed on the canopy halves to mate to the crutch.
Step 6: Wing
The wing is very simple to build. Cut out the shape from the foamboard and then soak in water for about an hour. The paper peels off easily at this point. Clamp one edge of the foam to a table. Raise one side up with a few paint sticks. Now gently use your heatgun to relax the foam. Let the foam cool before unclamping. This adds an airfoil shape that improves the aerodynamics as well as strengthens the wing. Sand the trailing edge to a taper. Cut out the ailerons, beveling the leading edge of the aileron. Hinge with thin packing tape. The aileron control horn is cut from 1/64” ply. Glue in a slot cut into the foam. Cut a notch into the leading edge of the wing for the front spar.
Step 7: Tail Booms
The tail booms are built from three laminations of foam. The center section also includes the vertical stabilizer and a slot for the bamboo rod. Glue the 1/16” landing gear wire onto the center section. One tailboom will also contain the control cable for the elevator.
Step 8: Assemble Booms
Apply epoxy to both sides of the center section, assemble the sides to the boom and then place a weight on the stack until cured. Next sand the boom to shape. You will need to slice ( and glue ) the vertical stabilizer near the boom to get the proper inward cant. The tail boom supports the shape of the airfoil. Part of the wing is cut so that it does not go past ½ the thickness of the boom.
Step 9: Install the Crutch
Install the crutch into the shroud, gluing in place. Insert the fore and aft wing spars in place piercing the crutch. The wing lays onto the aft spar and mates with the front spar which forms the leading edge. Wrap packing tape around the front spar to the wing. Glue the spars in place.
Step 10: Horizontal Stabilizer
Glue the horizontal stabilizer in place after cutting the elevator and hinging with packing tape. Sand the edges. I used the 3/16” foamboard for the tail surfaces. Depron can be used with less scale effect.
Step 11: Controls
The servos are glued to the crutch in a staggered manner. This allows the servos not to interfere with each other.
A screw driver passes through a small hole in the shroud to make adjustments.
Step 12: Aileron Control
The aileron control cable housing is glued to the underside of the wing and pierced through the shroud. ( there is a pass through hole in the crutch ) Each side is passed through a common micro connector on the servo horn. The elevator cable housing is set up in a similar fashion. 1/64” music wire is used instead of the supplied cable to reduce friction.
Step 13: Wheels
There are commercial small wheels available. But building them is fun.
Use the spools in a cassette tape as a hub. Using a compass trace a circle on black foamboard and cut out. Place a wire through the hub and the foam circle. Tracing the hub onto the foam. Cut out the inner circle and insert the hub. Run the wheel on a drill while lightly holding it against a sanding board to true the wheel.
Step 14: Flying
The CG is 1 ¼” behind the leading edge. The battery placement will adjust the CG. Tape the battery in place. Adjust the elevator and aileron throws to ¼” both directions. The small wheels will require a smooth surface to take off. Roll out is about 50 feet to get up to speed. It handles the wind surprisingly well. It will loop and roll but inverted flight is not what the Optica is meant to do. The real plane is a stable observation platform. The model carries on the stability. The Optica model is not twitchy as you might expect from a small 4.3 ounce model.
Step 15: Parts
3/16 foamboard (sturdyboard)
1 ½ pound styrofoam block
sullivan cable housing
1/64” music wire
Bamboo skewer (carbon rod can be used)
1/16” music wire (landing gear)
Thin packing tape
two submicro servos
one dubro micro connector
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