- The Cardsharp plan was first published in 2000 and can be purchased via the RCM&E plans service.
Radio controlled model aircraft built from corrugated cardboard are by no means new; In fact, there have been quite a few over the years. My own introduction to this form of construction came with a model called ‘The Craftsman’, a kit manufactured back in the seventies by a firm called ‘Stanley’, as I remember. The model itself spanned 60”, and was a low-wing sports tail dragger; mine was powered by an old favourite Merco 61 and flew superbly, with great aerobatic characteristics (they also did a high wing trainer version, incidentally). I only ever saw a couple of these kits built – I suspect many dedicated ‘balsa-bashers’ were not convinced enough to have a go.
Anyway, these kits went out of production quite quickly, which was a shame because they really did fly well, and were surprisingly robust.
Suitably impressed, I became hooked, and I’ve been collecting nice, large unbent pieces of corrugated cardboard ever since! However, it wasn’t until I read an article by Chuck Felton in the June 1997 edition of the American magazine ‘Flying Models’ that I knew I had to have another go myself. Chuck’s article was a plan feature for his superb control line ‘Macchi C.202 Folgore’ built using – yes, you’ve guessed it – corrugated cardboard. As a result of this, I sat down and drew up some plans for a little (mainly) cardboard delta model, which could be folded and built similar to the paper one’s we used to make as kids (but without the tail). This turned out to be another great flying model, who’s life was cut short all too soon following a mid-air.
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WORKING WITH CARDBOARD
So, are you interested? You are? Great! Let me give you a few tips and suggestions regarding the use of corrugated cardboard. First, I must remind you that cardboard varies in size and weight – we are interested in the 1/8” variety. I managed to get mine from a local box manufacturer; it has brown paper on one side and smooth, white paper on the other. This latter side is ideal for obtaining a decent finish. Supermarkets have got to be an excellent source of supply, i.e. discarded boxes – so go on, do your bit for re-cycling!
White PVA is best for the majority of construction, although Copydex has its uses for smaller items (elevators, ailerons etc.).
For scoring fold-lines I used a pizza cutter, which is basically a handle with a sharp-ish wheel attached. Try to get one that’s about 2.1/2” diameter because you’ll get more control. Practice on some scraps of cardboard before committing yourself to anything serious – oh, and don’t forget you need a metal straight-edge to run along.
If you are going to use Solarfilm or the like for covering, you’ll find that a good bond can be attained on the bare cardboard. For a paint finish, apply two coats of thinned clear dope, and then rub it down; this will give you a receptive surface. Alternatively, you could follow Chuck Felton’s advice and give the cardboard a coat of clear polyurethane mixed with 75% thinners, before cutting or folding; this will, after 48 hours, help to waterproof / fuelproof the cardboard, and tends to make it cut a lot crisper.
- Masking tape
On seams, joints, and exposed edges of the model, I used masking tape (you can use gummed paper strip, but I found this doesn’t stick quite so easily).
For best results, cardboard should be kept at room temperature. Since this material has a habit of absorbing moisture, try to keep it away from damp storage; otherwise, you may find that on a hot day those nice straight wings have a touch of anhederal!
Finally, here’s a neat little trick you can perform on the trailing edges and tips (fin, elevator, ailerons etc.). If you prefer a rounded, sharper look, iron them down with wifey’s domestic clothes iron – simple. Once again, have a practice on some scrap bits before committing yourself to anything serious.
The model presented here is quite simple to build, and with a small parts count, can be put together in a very short time. However, I must emphasise that when it comes to flying, this is not a beginners model – having said that, anyone with a bit of stick time will find it a smooth and responsive flyer.
Okay, cut out all cardboard and wooden parts, making sure that your corrugations are running in the right direction. Score and fold the parts at those positions shown on the plan.
TAILPLANE AND FIN
Simply fold these items, and stick the two halves together with either white glue or Copydex. I normally use this like a contact adhesive and let the glue dry first, before putting the two halves together. While you’re about it, you can give the elevator and ailerons the same treatment. When these parts are dry, iron down the edges as suggested earlier or, simply leave square. To finish off, cover the trailing edges and tips with masking tape or similar, using approx. 3/4” wide strips.
Cut your spars from hard 3/16” sheet, and glue to the wing panels at those positions marked; now, add the 1/8” sheet balsa riblets. Where the two spars join at the wing centre, you can reinforce using a couple of corrugated cardboard pieces. Make these the same height as your spars, and cut with the corrugations running vertical. When all this is dry, glue the tops of your ribs, spars and trailing edges; carefully fold down the top halves of your wing, and pin in place until dry. Add the 1/4” sheet balsa wing tips, and apply your tape to the trailing edge.
Glue the upper and lower 3/16” square fuselage longerons in place as per the plan, making sure that your lower one is raised about 1/8” above the fold line – this will allow your fuselage sides to be raised square to the bottom. Put a couple of rubber bands around the fuselage to hold everything square, then glue in the nose doubler; this should butt-up against both upper and lower fuselage longerons. Add the 3/16” crosspieces between your longerons at the rear and centre of the fuselage; when dry, remove the rubber bands, and glue in two pieces of 1/8” ply each side of the nose doubler to form your engine bulkhead. At this stage, you can cover the rear top of your fuselage, from the hatch position, using corrugated cardboard (corrugations should run crosswise).
Drill some holes and fit the engine mount to your front bulkhead (I mounted mine at 45°, to make sure the silencer will not hit the ground on landing; it also keeps the model cleaner). Also, drill a hole for the tank feed and filler tubes.
Next, cut two pieces of 1/8” liteply to form the front and rear hatches. These have 1mm ply locating tongues glued to one end, which slip under your liteply crosspieces at the front bulkhead, and under the cardboard top sheeting to the rear.
The hatches are then secured using small self tapping screws, which fit into a crosspiece located near the cabin centre.
Cut a slot in the rear (top) cardboard sheeting to accept your fin, and glue the latter in place (note: the fin is also glued to the bottom of your fuselage). Glue your tailplane to the fuselage bottom, and cut two pieces of 1/4” triangular strip to use as fairings between the fuselage sides and top of the tailplane.
The wing can now be attached to your fuselage. To do this, lay the fuselage over your wing centre position (which is marked on the plan); press the fuselage down onto the spar, and it should leave a slight mark. This will give you a guide for cutting out the fuselage bottom to accept the spar. Cut a notch so as to allow your fuselage to sit on the lower wing sheeting, between your root ribs. When you are satisfied, glue the whole lot together, and add the 1/4” triangular strip fairings either side.
The next step is to fit your ailerons and elevator. Use whatever method of hinging you prefer; I have used sewn hinges, figure of eight style, with good results. I’m experimenting at the moment with the old cloth type, like the ones we used on control-line models way back.
Test fit your engine to the mount, and drill a hole in the bulkhead for a throttle cable. This needs to be kept fairly close to the fuselage side, because space for the fuel tank is tight. Drill the engine mount, and use self tapping screws to secure.
The throttle servo is mounted on the right-hand side of the tank bay, just in front of the wing spar. For this, I used a micro servo attached to the fuselage side with servo tape; this constitutes the simplest fixing method, and is perfectly adequate for the job. Before fitting, give the tank bay two coats of clear dope, and one of fuelproofer. On the right-hand side of the tank bay, opposite the throttle servo, there should be plenty of room for the switch.
The battery, which in my case is a 250 mAh flat pack, can be attached to the bottom of the fuselage with Velcro, just behind the wing spar. Mount your receiver on top of the battery, again using Velcro, plus some protective foam packing.
This just leaves the elevator and aileron servos. Mount these on 1/8” liteply rails, across the fuselage; the aileron pushrods are threaded 16 gauge wire, and exit through the fuselage sides, before terminating at their horns. Elevator hook-up is by means of a normal balsa pushrod, exiting at the fuselage rear. At this stage, you’ll notice that there is room to fit a couple of mini servos for elevator and rudder – should you desire them.
As I mentioned earlier, Solarfilm adheres well to corrugated cardboard so that may well be your preferred option. The camouflage scheme on my model is just one coat of Humbrol matt enamel (pale blue underneath), with a further coat of Flair Spectrum fuelproofer to finish: in hindsight brighter, easier to see colours, might have been a better idea.
Check that your C of G is as per the plan. You may, in fact, need a little extra weight at the left wing tip in order to counterbalance the offset engine and silencer. Control movements were set as follows: elevator 1/2” each way; ailerons 1/4” each way. These settings give the model quite a lively response, but there’s obviously a lot of room for experiment.
Flying wise, Cardsharp is super-smooth. mine went away on its first flight without requiring any trim changes whatsoever – and that doesn’t happen very often. With my ancient Max 15 glow motor on full song, the model pulled some very nice large jet-style loops, which always look impressive. Rolls were fast enough for me, but with more aileron movement, could be twinkle. Slow speed handling is very impressive, and low fly-by’s are great. When it’s time to land, drag her in nose high, and she’ll touch down gentle as you like.
She’s been such fun, and so good to fly, that I’m seriously thinking about building a larger version (‘C Sharp Major’!). I hope after reading and studying the plans you too will be suitably inspired – go on, have a go at some corrugated modelling!
I would be pleased to answer any queries regarding the model, or corrugated cardboard construction in general. Feel free to write via the magazine’s usual Swanley address.
Aircraft type: Sport
Designed by: Maurice Ashby
Construction: Corrugated cardboard, balsa, ply.
Wing area: 225 sq. in.
Wing loading: 18.5oz / sq. ft.
All-up weight: 29 oz.
Fuselage length: 31"
Engine used: O.S. Max 15
Prop used: 8.5 x 6" (Bolly)
Rec'd no of channels: 3 / 4 (see below)
Control functions: Aileron, elevator, throttle and (optional) rudder
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