RAZOR:- this word brings many different ideas to mind, e.g. sharp, cutting, dangerous, etc. Is this plane called Razor because of a play on words so that it sounds like Laser, or because it is designed to be a super sharp performer?

A look at the plan shows this plane to have a deep fuselage, a stubby wing with constant chord, no dihedral and wing span just 7cm longer that the fuselage. Also the stabiliser (tailplane), wing and engine are all on the thrust line, set at 0 degree incidence. Obviously this model is designed for some radical aerobatic flying.

This is a plane that could be your first scratch build project because it uses straight forward building procedures although it does require some experience in flying because of the design.

Now that your interest is aroused read about the construction and flight performance.

LET'S GET BUILDING!
(no cheating by by-passing the construction section)

As has been said in many articles it is a good idea to "kit" the plane as far as possible before starting construction. This helps with the flow of building and it also gives an indication of whether more materials are required for the completion of the project.

WING

This is a simple to build wing that has constant chord, symmetrical section, having nineteen 2.5mm balsa ribs so I chose to use the sandwich method of shaping the ribs. I actually made twenty ribs and put two in the centre just because I wanted to. If you make your ribs this way do not forget that there are seven W1's needed (eight if you do the same as I did) these have the same profile as W2 but have a section cut out to allow for the wing brace (B1) plus the centre one needs to be cut for the servo tray and servo bay.

Now to assembling the wing. A building board at least 130cm in length is required because this wing has no dihedral and is built in one piece.

First lay the plan over the building board and cover with your favourite covering (mine is clear plastic cling wrap). A straight piece of 12.5mm balsa is laid parallel and 93mm back from the spars is pinned to the board. This is to ensure that all the ribs sit at the right height thus ensuring a straight wing. Then the bottom spar is pinned in place and the W2 ribs are secured in place being certain that they are 90 degree to the building board. After the rear section of the W1's are secured in place it is necessary to fit the wing brace (B1), checking the height for fitting of the top spar before gluing.

Glue the front section of the W1's in place followed by the top spar then add the 12.5mm balsa leading edge oversize enough for shaping and to allow for the leading edge sheeting top and bottom. Now attach the 6.5mm balsa trailing edge followed by the 1.5mm balsa trailing edge sheeting.

DO NOT forget to put the ply servo tray between the ribs shown on the plan and then you will be able to put the centre sheeting straight over the servo tray. (Remember to mark the top of the wing so that you can put the hole for the servo in the correct side). After the shear webbing and dowel brace (B2) are glued in place the leading edge top sheeting, centre sheeting and the cap strips are attached. Allow to dry. The wing now may be removed from the building board. Add the sheeting and cap stripping to the under side of the wing. The ailerons are full length strips and are shaped from 12.5mm balsa. The only break in the ailerons is for the fuselage and this centre section houses the aileron torsion rods. The plywood reinforcement plate (R) is glued on top of this centre section for the wing bolts to pull down on.

The wing tips are now added and the whole wing is shaped, final sanding done and the dowels fitted. After this is done the hinge slots may be cut. But do not fit the hinges yet. Also do not forget to cut out the hole for the servo in the top of the wing.

The wing is now ready for covering, but do not cover it before building the fuselage so it can be test fitted.

THE TAIL FEATHERS

These are built up by joining pieces of solid balsa sheet cut to shape. Then the whole setup needs to be sanded and rounded ready for fitment to the fuselage. The only work left is to bend the joiner for the elevators from 2.5mm piano wire and to put the hinge slots in ready for assembly after covering.

FUSELAGE

Having kitted the plane this means that you are ready to start putting the fuselage together. Start by laminating the ply and balsa doublers to the 3mm balsa fuselage sides being sure to make one left and one right side.

From the wing seat forward there is need to also join a top section of the balsa to the fuselage sides to match the shape on the plan. This is necessary because the depth of the fuselage here is greater than the width of a 100 mm wide piece of balsa. Also the 6.5mm square balsa longerons need to be installed where indicated, along the bottom edge of the fuselage. Once this has dried it is time to start putting the formers in place. It is a good idea to mark the fuselage sides for the location of the formers. F1 is marked with centre line and thrust line and also corrected engine mount centre line (vertical) to allow for offset for right thrust.

Then the engine mount is fitted and holes drilled for throttle control and the fuel lines. Here it is necessary to decide whether to put the engine upright, inverted or at some other angle. I chose to have it inverted because I like the cleaner lines it gives to the top of the fuselage. You need to remember that this makes a difference to the tank position in its compartment for correct alignment with the needle valve. Adjust accordingly. Now glue F2, F3 and F4 to one side of the fuselage, checking that F2 is at 90 degree and F3 and F4 are at the correct angle when looking at the plan view of the fuselage.

You may like to make a template from a piece of scrap balsa so that these angles are right. The 6.5mm ply plate (P) will help here to get the correct angle for F4. I used epoxy for the gluing of "P" in place because this is the wing bolt hold-down plate and it needs to be secure. Once this is done it is time to put the other side in place and clamp them until the glue is dry. If you have a fuselage jig then this will help. See the article on building a fuselage assembly jig in Airborne issue No.149. Once this section of the building is done the rear section needs to be pulled together ensuring that it is kept true. I had some problems here because F5, F6 and F7 are made from 3 mm balsa with the grain running vertical and this makes them a little weaker and they tend to bend as the rear of the fuselage is pulled together. So I laminated a piece of 3 mm X 6 mm balsa across the bottom of these formers.

Next the 3 mm balsa turtle deck sides and former F4a are glued in place and the sides are sanded flush with the tops of the formers before the 9.5mm balsa top is added. F1 is now epoxied in place being sure to set it for 2 degree right thrust and the sides of the fuselage need to be clamped together and left overnight to allow to dry. Also the undercarriage plate (U) can be epoxied into position at the same time.

After this is done the 6.5mm balsa corner sections can be added to the top edges of the fuel tank compartment and roughly shaped along with the fuel compartment hatch made from 9.5mm balsa. On the plan the cowl is shown permanently attached to the fuselage but I chose to make it removable to give better access to the engine for tuning and setting up. When deciding which way you want to put the engine remember that there has to be sufficient air flow for cooling. With the engine inverted there needed to be air exit ducts put in the sides and bottom of the cowl. Also on the firewall I put ducting to direct the air to these air exit points so that the air would flow more freely.

The tail feathers can now be fitted making sure that the stabiliser is set at the correct incidence and is square to the centre line of the plane. Also the fin needs to be set at right angles to the stabiliser and checked that it is also straight down the middle of the fuselage. On each side of the fin there are fillets made from scrap balsa and these may now be shaped and attached.

Before installing servo mounting points as per plan, I found that the model was slightly nose heavy in this configuration so you may like to place the three servos side by side behind former F3. There is enough room even with standard servos if you are careful. I used nylon snakes (nyrod style) for the rudder and elevator controls, so these need to be installed before the bottom sheeting is put on.

The 6.5mm balsa sheeting is fitted to the bottom of the fuel tank compartment and shaped to give the required contour and to mate with the undercarriage plate. The undercarriage plate is made from 3mm aluminium that is cut, drilled and bent to shape as shown on the plan. This fits flush with the bottom sheeting of the fuselage.

After this stage I test fitted the wing and checked that the incidence was correct before building the canopy/hatch section that fits over the wing. This part needs a little patience to get the shape right and to get it to fit neatly. I built the hatch section first.

This is made by gluing the two 12.5mm sides (C) to the formers F2a, F3a and F4c and once these sides have been planed flat on top and mated to the wing on the bottom I fitted the front lower section of C that goes down to the leading edge. Next the 6.5mm balsa canopy floor is added and shaped so that the 9.5mm balsa top sheeting can be added to the front part of this section. This is then shaped to the desired profile and the canopy can then be made out of balsa "block". (I used left over pieces of 12.5mm balsa).

The plan shows that the hatches are secured by four screws, but I thought that was too many for the finish I wanted. So I designed a latch setup for the rear of the canopy section and tongue under a plate for the front of the fuel tank hatch. Thus reducing the number of screws to one between the wing hatch and the fuel tank compartment hatch.

The whole fuselage now needs to be planed and sanded to shape ready for final smoothing.

FINISHING

The fuselage was given two coats of dope, sanding between coats with about 320 grit paper and then coated with a coat of dope and talc mix. When dry this was sanded with 600 grit dry wet and dry paper. Inside the cowl, the firewall and the tank compartment were given a coat of epoxy resin to seal against fuel penetration.

I then masked the tail feather section ready for painting. The entire fuselage was then given two coats of white enamel (including inside the cowl and tank compartment) and allowed three days to dry before masking and spraying two coats of red to give the desired design.

Next the wing, ailerons and tail feathers were covered with heat shrink and the control surfaces fitted being sure to glue and pin the hinges. I used red Solatrim to give the sunburst design and rudder stripes.

After this was finished I refitted the engine and the radio gear and checked that the C.G. was set at 25% which is 73mm back from the leading edge. The control throws and directions were checked. I set the elevators at 12.5mm, the rudder at 35mm and the ailerons at 12mm. On checking the total weight it was found that the model came in at just over 5lbs or 2.3 kg.

TO THE FIELD

Once at the field (Rebel Flying Club) and the plane is assembled the usual checks for control movement direction and radio range check is done we are ready for the first flight.

The plane tracks well on the ground as most tail-draggers do but is not too happy in a cross wind, although it is quite manageable. In the air this little plane goes where you point it and needs controlling all the time because with no dihedral it does not correct itself in any way. This plane will do just about anything you want it to and probably more than I can do with it. It performs axial and barrel rolls, fast snaps, good inverted performance as is knife edge flight. The Razor spins well and will recover easily in half a turn by letting the sticks go.

An engine cut out and this gave me an opportunity to test the glide rate. The Razor was able to glide down and land into the wind as normal. This plane lands easily but enjoys rolling along because of the large main wheels and generous size tail wheel (It needs a very slow engine idle if you have short grass or else it just keeps wanting to move).

All in all Razor is a sharp performer that is fun and enjoyable to fly.

SPECIFICATIONS Razor