Cat 25 (oz12149)

About this Plan

Cat 25. Radio control sport aerobatic model.

Quote: "Cat 25 is the fourth design of the series to be presented by Radio Modeller, the most recent being Cat 500 in the February '94 issue. Although most of the airframes designed under the CAT (Coventry Air Tech) marque bear a family style, they are not directly scaled up or down versions of each other, but art each designed to suit a specific function or task.

The Cat 25 is aimed at the general club flyer who wants a machine to improve, or even learn or practice, aerobatics using a cooking 25. Alternatively it is an ideal model for the hodogger freestyle flyer who likes to do everything vertically or at umpteen miles an hour. For this style of flying, fit one of the many ballraced ABS 25s or if you are experienced - ie you have fewer controlled crashes than your fellow flyers - fit a compact 32!

When designing models for the smaller size motors I usually tend to work around a radio package - for 20/25 motors, two standard (148 size) and two midi servos (Hitec 101 or Acoms A10s), but the Cat 25 is packaged around standard servos, hence my nickname for it is 'Fat Cat'. The basic design will be familiar to those of you who have built or studied my prior published designs and features access to the fuel and guidance equipment through the top of the fuselage via the dummy cockpit cover..Enough chit chat, let's get down to building.

Fuselage: This is conventional construction, being a basic box of 1/8 (3mm) balsa sides (prototype used liteply) with 1/32 ply doublers at the nose and hardwood or balsa longerons together with balsa sheet strip pieces. Start by cutting out and assembling the basic side assemblies -weight down while drying. Cut out and laminate, as required, all formers, including drilling holes for engine mounting and wing dowel. Next step is to assemble the basic 'box' upside down - use epoxy for this stage. Make sure everything is square and take great care to ensure the plan form is true and symmetrical about the plan centre line.

The top of the fuselage side is also the datum line to enable accurate positioning of the engine bulkhead. wing angle and installation and nose configuration enables various engine types to be used without a mismatch of the spinner.

Back to the balsa butchering: remove engine and razor plane and sand the fuselage to shape.

Hatch/cockpit cover: This is assembled and finished away from the fuselage and follows normal 'Cat' construction being built up on a 1/16 base, with 1/8 sides and top - note that the front part of the top is a cross-grained lamination, and don't forget the 3/16 doublers.

When dry, sand to shape and cut into two parts between F5 and F5A - the rear part is glued to the rear deck after covering and the front is glued to front 1/4 detachable decking - again after covering. Jumping ahead a little, the bottom of the front deck/cocknit cover is cut. out to clear the nicad pack and receiver, the top being packed with foam to locate and protect the radio gear, I normally fit the locating dowel and local fixing reinforcements, etc after covering. OK, that's about all on the fuselage, except for the wing blocks (or use commercial plastic ones).

The wings: As usual on my prototypes I used a foam core on which the leading edge, trailing edge sheeting, etc is fixed with thinned Copydex, using a thin bead of white glue along all edges. The plan shows either a foam based wing, or conventional built-up structure.

All parts for either wing are the same, with the addition of a balsa/ply main spar and, of course, ribs (note the ply facing on inner ribs). Assemble the built-up wing by pinning down the trailing edge and packing up the main spar (I use trailing edge stock for packing): add leading edge sheeting cappings. and 1/din (6mm) 1,E and let dry thoroughly. Remove from board, turn over, pin down, re-pack under main spar and again add LE, TE and cappings.

When you have two panels - one left and one right, I hope - join together using undercarriage/joiner block - see sketch on plan - and pack up one tip to give total dihedral. After joining and checking for any warp/misallimment, etc., add the hardwood filler blocks and complete centre section sheeting. Finish by sanding to section, add 1/8 tips and reinforce centre section with 4 in cotton (medical) bandage - use white glue well rubbed in.

Cut away centre section to fit fuselage (with foam wings add balsa facing to end faces) and fit liteply facing to front face. Locate dowel hole through F2, drill and fit; finally, tit ply plate for wing bolt reinforcement. Lastly, the centre of the rear 'FE is cut back to accept. a commercial horn set.

Tail feathers: These are made from 3/16 sheet for the vertical surfaces, and 1/4 in for the horizontal bits. Please note the section - no flat plates, thank you! if you are using a cooking motor either use lighter wood or the built up tail as shown on plan. In other words keep the tail end, that's anything behind the wing, light and well sanded. The prototypes have just about balanced right with an ASP/OS SF type motor fitted..."

Cat25: Another size in Harry Gilkes' line of Cat aerobats, to go with the Alley Cat and Mini Cat already on OZ. From the May '94 Radio Modeller, Harry states in the article that it is the fourth Cat model to be presented through RM. As I recall the fourth was the largest model in the series, for 4-stroke power. Named "Street Cat" I think it was a featured plan rather than a free plan and so sadly not in my collection (I had to compact my magazines some 20 years ago and chose to keep only the free plans/articles - I could kick myself now that we have such easy scanning/enlarging technology - there were quite a number of featured plans from the early 90's RM's that I wanted to see again and thankfully they are now cropping up from time to time on OZ!).

Direct submission to Outerzone.

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