A full kit is Available from Gary Law for £3 to members
Please email webmaster@oxfordmfc.bmfa.uk for more details
The Original A4 1/2 size Plan is available to download her
A4 Fullsize Wing template can be downloaded here
A4 fullsize tail and wing sanding high point template can be downloaded here
Oxcat construction and flying instructions – Andy Crisp
Wing – Try to find a nice, softish piece of 1/8″ (3 mm) sheet for this. If you’re keen, glue a very hard piece of 1/16″ x 1/8″ along the leading edge (LE) to prevent dents etc. It should sand into the aerofoil section easily enough.
Cut the blank to shape and mark the high point of the section with a soft pencil. NB: Do all your work on a folded-out newspaper to avoid dents from the blobs of glue on the typical workbench.
Start sanding with a fairly coarse sandpaper from the high point to the trailing edge (TE). Use progressively finer sandpaper (or wet and dry paper) until a reasonable finish develops. Don’t sand the TE too fine. Now sand in the front curved portion from high point to LE. Sand all over with fine wet and dry to get a very smooth finish.
Tail and fins You can hardly expect to get much of a section on 1/16″ sheet, so sand well and round off the leading and trailing edges.
Finish – Shake some fine talcum powder (fragrance optional) on your finger tips and rub into the grain of the wood. Give a coat of thin dope (50% dope + 50% thinners) and leave to dry for half a day. Rub down with the finest wet and dry. Repeat a couple more times on the wing. One coat should be OK for the tail surfaces.Polish up the whole with really worn wet and dry and then the finish should be like a baby’s bottom!
Putting in the dihedral – This is the one difficult bit in the construction.Again,using a soft pencil,mark the position of the joints and cut through the wood using a fine modelling saw or very sharp balsa knife. Place a block under the tip at the correct dihedral height (2″). Arrange the joint line to be on the edge of your building board and carefully sand up and down with medium paper on a sanding block (see diagram on plan). Keep on until you make a nice joint with the centre section. Now do the other tip.
Gluing – With a fine bradawl or similar, poke holes down the grain of the panels to be joined. This will create tiny glue dihedral braces and strengthen the joints no end. Place thin polythene on the bench then weight down the centre section and offer up the tips at the correct angle. I use 5-minute epoxy here. Use sparingly, working into the wood grain. When dry, blend in another thin coat top and bottom with a damp finger. You should now have a wing which does not come apart! If necessary, tidy up the joints with fine wet and dry paper.
Fuselage – It must be said that the original model had a carbon fibre boom (from an old fishing rod tip),but a wooden body would be just as good.A really hard piece of balsa would be OK, but a combination of hard and soft material works better. You could cut a profile of the fuselage from 1 mm ply, then glue, using PVA, 1/16″ sheet balsa either side. Press overnight then sand at your leisure. Or, you could laminate 1/8″ square spruce (or equivalent)with balsa. Both methods are shown on the plan.
Assembly – Glue the components to the body using 5-minute epoxy. If you are right handed, make sure that the left side of the tailplane is slightly tilted up (say 1/8″ ) to give left glide turn-reason explained later! Make sure that the catapult hook, bent up from a paper clip, is well secured by insertion, gluing and cotton binding, likewise the underfin which takes the strain on the launch. Add glue fillets to the wing/fuselage joint, smoothing with a damp finger.
Flying – Add weight to the nose in the form of lead,Plasticine or Blu-Tack so that the model balances 1 1/2″ from the LE of the wing (55% of the root chord). This is important and a good starting point.
Catapult – You might as well use the official BMFA size, ie.2 g rubber attached to a 6″ stick. This works out at a loop of 1/4″ flat approximately 6″ long. A large band, conveniently dropped by the postman, would do at a pinch(or stretch!). If you are right handed, hold the stick in your left hand and pull back the hooked up model with your right hand. Ideally, if you are right handed, your model should fly to the right on power, i.e. under the action of the catapult, and to the left on the glide. If you try both the same way you end up with big holes in the ground.
So, try a few hand test glides for starters. Tweak the back of the top fin to give a touch of left rudder and go from there. Throw firmly into the wind with the nose slightly down. Do this several times to get the ‘feel’ of the model. If it seems ‘nose heavy’ tweak up slightly the TE of the tail. If it stalls, give more rudder and add nose weight.
Now to the catapult launch. The legendary soft grass or Meadow mud, is a good requisite if anything goes wrong! Hook up the model to the rubber. Stretch back and aim into the wind making sure that there is nobody in the way. The ship should shoot up and surprise you with its speed and the height it gains.
If it goes straight up and straight down try banking the model to the right to encourage a spiral climb. Don’t be afraid to really stretch the rubber-as far apart as your arms will go! The wing can take it. A good model could make 40-50 metres in altitude. Alterations to perfect the glide can be made by adding or subtracting small amounts of nose weight
I must admit that all this adjustment is not easy but,when you DO get it right, it’s awonderful feeling when the model rolls off the top into its glide. If you find it in the long grass on the meadow that’s a good feeling as well
