Airborne Magazine

Extra 300 Plan: AU$52.80 (2 sheets) plus AU$3.00 Postage & Handling.
Moulded Canopy: AU$27.50 plus P&H (AH$6.00 within Australia).
Accessories pack: Includes Moulded plastic canopy Fibreglass engine cowl Fibreglass wheel pants Pre-shaped aluminium undercarriage legs AU$81.50 plus AU$9.00 p&h

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For unlimited aerobatics the Extra 300s is a real winner.

by Roy Smith


The Extra 300S is a single seat aerobatic aeroplane which is not only attractive but a real high performance machine.

The Extra is stressed to handle high loads and with large control surfaces responses are very rapid.

It will perform any aerobatic manoeuvre with ease, the roll rate is extremely quick, and climb is impressive.

For unlimited aerobatics the Extra 300S is a real winner.



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The fully symmetrical wing is built up in the traditional method but has fully sheeted balsa skin.

Start by cutting out all the ribs, wing brace, leading edge, trailing edge and spars to length Wing ribs W3 and W4 will require a cut out to fit through the wing brace. It is essential to epoxy the wing locating tongue into the wing brace before assembly begins. Build up one side of the wing at a time.

Pin the lower main spar over the plan on a flat building board. Interlock and glue the wing locating tongue with wing brace onto W1 and W2, then glue the unit onto the spar. The overhanging ends of ribs will need to be propped up during assembly. A faint keyline is indicated on the plan to show height of ribs at trailing edge to maintain symmetry.

Continue with gluing of ribs W3 - W10, then glue the aileron spar, false leading edge and top main spar. Check for square before glue dries off. Leave to set before lifting the basic assembled wing off the board.

The opposite wing panel is built up similarly but the two halves can be joined during assembly. Prop up the already built up panel 36mm at the wing tip.

The ailerons and trailing edge of centre section are built separately as triangular units, then fitted to wing.

The aileron torsion rods must be fitted in place before adding the rear centre section. Note that the area where the wing bolts pass through is filled with solid balsa wedged between the ribs and sheeting. Also fill area around W3a with balsa block, and aileron section between W4a and W5.

Skin the wings with 1.5mm balsa sheet. It is best to prepare the sheets joined up to cover the areas first before gluing them to the wing structure.

Add the leading edge, wing tips and plywood lining W3a and aileron ends. Sand entire wing to shape. Bevel the aileron leading edge and fit onto wing with hinges.

Cut out a well for the aileron servo through the top side of the wing. Fit servo and connecting rods to suit. Reinforce the underside of trailing edge around the wing bolt holes. The wing is now complete ready for covering.

Note: an alternative foam core wing can be built for the Extra 300S. Templates of profiles are shown on the plan.


Extra picture The tailplane/elevator and fin/rudder are flat frames, with triangular cross section control surfaces. The frames are built up over the plan, then fully sheeted top and bottom with 1.5mm balsa.

Round off the leading edges of the tailplane and fin, bevel the leading edges of elevator and rudder. Fit control surfaces on with hinges and fix on the control horns to suit.


Cut out all the formers F1 - F8 and engine mounting blocks, M1 - M4. Prepare the fuselage sides by cutting out the balsa sides as indicated on the plan, then strengthening them with gluing of the ply doublers and spruce longeron. Mark the position of formers on the inside faces of the fuselage sides.

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Build up the engine mounting box section or firewall unit ready for insertion into F1 and F2. Use high strength epoxy for these components. With the firewall unit in place start building the lower half of the fuselage over the plan or in a jig. Glue the fuselage sides to formers F1 - F8. Leave to dry.

Install the tailplane seating blocks between F7 and F8, sand to shape. Fit top stringers from F1 - F3a and F5 - F7. Sheet the top fuselage and turtle deck with 3mm balsa sheet. For the tighter curves lightly spray the sheet with a mixture of water and ammonia to help bending. Alternatively the upper fuselage section could be planked. When complete, sheet the cockpit floor with balsa.

The tailplane and fin can now be glued onto the fuselage with balsa block fill above the junction. Sand the block to blend with the form of the fuselage.

Fit the control rods for the rudder and elevator through the fuselage and fix them to formers as required to prevent flexing. Install servos for rudder, elevator and check control movements.

At this stage the undercarriage legs can be made up and fitted onto the fuselage mounting plate M4. Use 3mm bolts and blind nuts or lock nuts epoxied to plate to hold on the UC legs. Add a small balsa block in front of the UC legs, sand to round shape.

Install the engine with mount onto firewall. Temporarily fit the tank, fuel lines and throttle cable. I used a Millennium .61 engine with Pitts type muffler. Fit throttle servo and check movement of cable.

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The fibreglass cowl should now be fitted and held on with small screws into hardwood blocks glued against F1. Cut away cowl sections for prop shaft, muffler, cooling ducts and drill hole for needle valve.

A polished aluminium spinner would look fabulous on the Extra 300S but I used a plastic one on mine.

Glue the wing mount plate into the fuselage. Trial fit the wing to the fuselage and check for correct alignment. Drill holes for wing bolts slightly undersized at first to allow for drill and tapping wing mount plate to suit 6.5mm nylon bolts.

With wing bolted in position build up the underside of the fuselage with sheeted panels. Cutting access holes for wing bolts will be necessary to remove wing.

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Make up the tail wheel unit and fix onto the rear end of the model. Join the wheel spats and then fit them onto the main undercarriage legs along with the wheels.

Trim canopy to fit. Paint and decorate cockpit before gluing canopy to fuselage.

Give the entire model a light sanding and prepare for covering.


The model being fully sheeted presents two options for covering. Firstly any variety of iron on films may be used. Secondly the model can be covered with tissue and dope then painted. The choice depends on your preference.

I chose to cover the areas of balsa using Super Monocote; overall white with red bands and stripes plus white for stars. Acrylic lacquer was used for the wheel spats, undercarriage legs and engine cowl.

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Being a popular aerobatic aeroplane there shouldn't be too much difficulty in choosing a scale colour scheme from a full size Extra 300S. Install the engine, fuel tank, fuel lines, all radio gear and linkages. Balance the model to C of G shown on plan. The radio gear used in my Extra was a Futaba FF7 with Futaba 148 servos.

Test flights were conducted by Bob Godfrey while my nerves settled down.

FLIGHT PERFORMANCE The first test took place with all the wrong things going for it. First of all, the wind was blowing strong enough to ground everyone else and the pilot was predominately a mode 2 pilot with the aeroplane set up in mode 1. This coupled with and aircraft that “could” be very sensitive to all pitches made for some very exciting forethought.

After running up the motor, a few high-speed runs up and down the runway were next to see if we could predict any bad situations getting off the ground. None were found.

TAKE OFF The aircraft tracked straight as an arrow down the runway and rotated gently to a comfortable climb out. Very little trim adjustment was necessary.

A couple of circuits were planned for the pilot to get into mode 1 frame of mind when the motor started playing up. It revved from near idle to full power in cycles and the aeroplane just kept going where it was put. It apparently didn't care what the motor was doing as long as it gave enough power to maintain airspeed.

LANDING Set up on a nice gentle glide slope, the aircraft tracked straight into the runway with a slight yaw due to the strong cross wind. A dream to land. You should be able to make almost every landing a greaser.

Aircraft and radio changed to mode 2 and the motor sorted out we were ready to wring it out well and good. The take off was as before.


As with any aircraft, make sure you build strong and light as lighter planes float better. This aircraft was slightly heavy for it's size yet performed predictably at slow speed, doing figure 8's and straight and level at just above idle. Stall is predictable if you're used to this sort of aircraft with the left wing dropping rather quickly, but is easily caught to fly off without much height loss. The aircraft rolls well at slow speed also, owing to it's barn door ailerons.


As expected, the aircraft tracked like it was on rails and went where you pointed it. There were no bad vices noted at full speed, even when banked at 90 degrees and hard elevator applied.


Well, this little aircraft lived up to it's reputation, being able to perform all the manoeuvres in the book and a few that aren't. Rolls are clean and on the point with no down elevator required in the inverted position. Loops are done straight and with ease. Stall turns/hammerheads are a delight and inverted is as easy as right side up. Knife edge no problems and Lomcevacks exciting. I'd have no worries putting this Extra up against an Ultimate Bipe any day of the week.


This is not a beginners aircraft. As with all unlimited aerobatic aircraft, you need to know what you're doing or the responsiveness will just get you to the accident faster! All in all, a pleasing aircraft to fly for an experienced average pilot and precise enough for the seasoned pro to really put on a show.

The Extra 300S is available with accessories through Airborne Plans Service at a cost of $75 + $7.00 for postage and handling and includes: Fibreglass cowl, fibreglass wheel pants, aluminium undercarriage, canopy. Add an extra $40 for plan. Total $122.00


Type: Aerobatic Sport Scale Model Wingspan: 1.4 metre Engine: .60 - .70 Airofoil: Symmetrical 4 channel radio control required
EXTRA 300S plans are available from:
Airborne Plans Service
Extra 300 Plan: AU$52.80 (2 sheets) plus AU$3.00 Postage & Handling.
Moulded Canopy: AU$27.50 plus P&H (AH$6.00 within Australia).
Accessories pack: Includes Moulded plastic canopy Fibreglass engine cowl Fibreglass wheel pants Pre-shaped aluminium undercarriage legs AU$81.50 plus AU$9.00 p&h

Plan No. 615

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This page was last modified on the 19-May-02