by Mark Sills
Plan No. 664
The Beaufighter has been re-badged by Airborne's R & D department as the "Bo-Fighter" in a profile, fun fly "stand way off, semi scale" version. The plans for this scratch build aircraft are designed for two .15 to .25 engines but at a scrape some rev-head could fit a brace of 32Ős. There's always someone who just has to go to that next level isn't there? The radio needs to be a 4 channel, 5 servo job.
Fuselage and tailplane
Survey the plan and become familiar with all component and balsa sizes needed and make a shopping list as you go. The fuselage is usually where I like to start and on the Bo-Fighter this is the easiest. The profile fuselage is constructed of 12.5mm solid nose and a built up tail area, all sandwiched between 1.5mm balsa sheets.
My method was to begin by photo-copying sections of the plan, nose, rudder and fin section along with the horizontal stabilizer. Place the photocopy of the nose face down onto some 12.5mm balsa sheets which have been joined together, now run a hot iron over the back of the sheet. When you remove the paper a reversed image is transferred onto the balsa sheeting. Use a sharp knife and cut out the nose section. The same technique is used for the horizontal and vertical stabs. Place the nose and fin pieces over the plan, which is covered with plastic wrap to protect the plan from glue. Using the 12.5-mm off cuts and a balsa stripper, cut 19mm strips to size and fit them over the plan until the fuselage begins to take shape. Make sure all the joins fit snugly then pin the pieces over the plan until the fuselage is laid out. Using cyano. adhesive, glue each join carefully and when dry remove the fuselage from the plan. Bend some piano wire for the tail wheel support and install it before sheeting the fuselage with 1.5mm sheets. Using PVA glue, smear it to both sides of the fuselage then fit the sheeting ensuring the grain runs horizontally along the fuselage. Place the fuselage on a flat surface with some weights on top and allow it to dry.
The tail-plane is constructed in two halves as it has a considerable amount of dihedral in it. The halves form an open frame construction and I fixed them together with Mega bond. Shape the tail feathers as per the plan and sand them smooth before you fit the hinges to the elevator.
When the fuselage is dry, sand and shape as per the plan. Mark the location of the 1.5mm ply reinforcing plates in the wing saddle and remove the balsa from under them. Now glue the ply plates into location ensuring they remain flush. Next cut out the slot for the tailplane as per the location on the plan. Slide the tailplane into the fuselage and make sure it is aligned and square before you glue it into position. Hinge and fit the rudder to the fin then place the fuselage aside.
The wing is constructed in three sections, the center panel, which houses all the radio equipment and the two engine nacelles, along with two outer wing panels, which incorporate the ailerons and their servo's.
The two outer wing panels, which include the ailerons, are simple in construction and are built directly over the plan using familiar build up techniques. Remember to include the servo mounting rails and drill a hole in each rib for the servo lead. Joining the wing is easy, lay the centre section on a flat surface over the plan and ensure it won't move. Next, dry fit the outer panel to the centre one with a 25mm packer under the wing tip. Sand whichever edge is necessary to ensure a perfect join, which conforms to the plan layout. I used Gatorbond Ca. and an activator to secure the two sections together, this ensured an instant, very strong, quick gap-filling join. Repeat the process for the other wing panel, this then allows you to final sand the leading and trailing edges.
Saturn Hobbies Oz Tuff was purchased for the covering job. This translucent, iron on film is applied using normal methods with the distinct advantage of being extremely heat tolerant. Sealing down the edges and blasting it with a heat gun, this shrinkable film quickly tighten up to form a tough, smooth surface ready for painting. Flow Gloss paints are available from Saturn Hobbies in a variety of primary colors but unfortunately Beaufighter's aren't, so some creative mixing was needed for the colors. After a lot of experimenting, I ended up with pale grey for the underside and a two-tone green camouflage scheme for the top. Vinyl cut roundelles were added to follow the RAAF's No 31 squadron scheme while some silver and black paint was used to create the cockpit window.
Install the two motors onto the hardwood engine bearers on the side of the nacelles and connect the throttle linkages. Now fit the fuel tanks with the aid of some brass straps, followed by the main undercarriage. Once you have done all the plumbing, its time to individually run in the motors. Adjust the carburetor arm until they both open and close approximately the same amount. With a tachometer check the revs at idle and high speed then compare them, you may need to adjust the throttle clevises until they are running in synchronization and giving off that great harmonic sound we all love from twins. Finally fit the cowls, these are cut from the middle section of a 2 litre drink bottle. Using sharp scissors cut out access holes for our motor and muffler. Paint them up to match the color scheme before screwing them to the nacelles. The effect is rather good for a profile style model. The aircraft should be balanced so that the centre of gravity is 120mm to 130mm back from the wing root leading edge.
Aerobatics I hear you ask, not a problem. Spins, loops and of course snap rolls proved to be no challenge, knife edge flight and even loops are a breeze thanks to that flat fuselage. After a few minutes of fun the slow speed stall was tested to give us an idea what a landing would be like. This was quickly converted into a smooth and predictable landing as one of the motors began to surge. As the Bo-Fighter taxied back, the reasons for the surge was obvious, the tanks were nearly empty! Oops.
As flights progressed my confidence increased enabling low level inverted flight and aerobatics a lot closer to the ground. The response on the Bo-Fighter is great, enabling an abundance of manoeuvres, but I wouldn't call it a competition grade fun-fly.
The next time out the Bo-Fighter was modified with 6-oz tanks and a relocated tail wheel now connected to the rudder. Ground handling was greatly improved, as was hopefully the flight time. The plan has the tail-wheel in the approximate scale position but you may want to change it if you want a little better ground handling. Not a real problem but your choice. With both motors running well, they soon had the Bo-fighter back in the air. This time experimenting with the asymmetric characteristics (what happens if one engine cuts out in flight) was the aim. With one tank filled a third less than the other, it was a cautious wait as the Bo-Fighter circled high in the sky up wind. Five minutes went by before surge, cough, then the death of the port (left) engine. Immediately the plane began to yaw to the left so I feed in right rudder. Surprisingly the Bo-Fighter flew well on one engine as slow graceful circuits were still achievable at full power. Now for the landing, as the throttle is reduced and the plane slows down, less rudder is required. Apart from a little yawing, even with one engine the landing was still slow and simple.
The Bo-Fighter is an excellent introductory aircraft for those wishing they had a twin but canŐt afford one. Now you can! With friendly flight characteristics this profile model wonŐt be too daunting for those never game enough to venture past single engine aircraft and the profile desing doesnŐt cost the earth to build and construction time is way less than a conventional fuselage design. Fly it scale and slow or wring it out, this really is a twin with attitude.
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