Become a fan of h2g2
As long as there have been flying machines, there have been those that have made models of them. Indeed, many of the pioneers of aviation, including Samuel Langley and the Wright brothers, tested out their theories with models before committing themselves to the air. Building model aircraft in its various disciplines, was always a popular hobby and reached the height of its popularity during the mid part of the 20th century. To build a model aeroplane was something of a right of passage back then, as most pre-pubescent boys tried to build at least one, learning as they went to use sharp knives, pick glue off their fingers and apply plasters single-handed to slashed fingers, Some even persevered and began to get some sort of result.
Flying was not then the everyday occurrence that it is now. Two world wars in which aviation had played a significant role were still within recent memory and perhaps made people more 'air-minded'. Modelling was popularised with the introduction of a the rather grandiosely named governing body The Society of Model Aeronautical Engineers (SMAE) and the Aeromodeller, a monthly magazine covering all aspects of the hobby. The SMAE also published their own magazine the Model Aeroplane, which was eventually absorbed by Aeromodeller. Such was the interest during the late 1940's to early 50's that the annual Northern Heights Gala Day, the largest model aeroplane meet of its kind, regularly attracted crowds of over 15,000 entrants and spectators at Langley Aerodrome near Slough. In 1948, it was attended by Her Majesty, Queen Elizabeth1, who presented a gold cup to the winner of the duration flying event, Phil Smith.
One of the disciplines of modelling is free-flight scale, the creation of flying replicas of the real thing. Another indication of aeromodelling's popularity was that during the 1970‘s and 80‘s an event sponsored by the Aeromodeller magazine, at the Old Warden Aerodrome near Biggleswade, Bedfordshire, regularly attracted several hundred scale modellers. The Aeromodeller All-Scale Day, held in June, was for many the highlight of the scale modellers year. The attraction of simply, flying free-flight scale models from early morning through to dusk against the backdrop of the Shuttleworth collection of veteran and vintage aircraft was unmissable. Although not now so well attended, that event still exists to this day along with the addition of a second day for radio-control models.
But, with the advent of plastic scale model aircraft, radio controlled flying models, and later, home computers and other distractions, it is undeniable that the enthusiasm for sticking bits of balsa wood together has waned. However, many of those adolescents who attempted it never totally shrugged off their inner boy and carried on building even when old enough to know better. Unfortunately the hobby is not now anything like as popular as it was, but it does still have a significant following.
What's this scale thing anyway?
A scale model aircraft is a reproduction of a full sized aeroplane, proportionately reduced in size to an overall scale that tries to accurately reproduce the appearance of the original. The amount of the reduction is usually expressed as a fraction of the original subject's size. For practical and safety reasons, the size of a free-flight scale model is usually limited to a wing span of approximately 20 to 25 inches (51 to 63 centimeters)for a rubber powered model, and up to around 55 inches (140 centimeters) for those powered by an engine. A handy rule of thumb is to use 1 inch to 1 foot, which gives an easily convertible scale of 1/12th. So, for every foot of span of the real aeroplane, our model would have one inch, and a forty-foot span aircraft scales down to forty inches. This would be a suitable scale for a Diesel powered model. Similarly, reducing the scale still further to say a half inch to one foot gives us 1/24th scale and a 20 inch (51 cm) span model of the full sized. This smaller model would now be more suitable for rubber power.
In the case of a free-flight scale model, it also tries to reproduce the flying characteristics of the original, and if you cross your fingers and squint a little, you may just produce a flight that simulates the real thing. That’s not easy when you consider that the real thing has a living, breathing pilot with hands and feet on the controls, whereas the model has nothing but the inherent stability that is built into it by the modeller. As far as the flying is concerned we are trying to achieve a steady, level or slightly climbing flight from either a hand launch or, if a suitable smooth surface exists at your favourite flying field, a take off from the ground, The flight under power should be with a gently banked left hand turn and a smooth transition from the powered phase of the flight to a glide, so that the model noses gently over as the rubber runs down. Lastly, a flat, descending glide and approach to a landing. In other words no violent manoeuvres should be evident throughout the flight pattern.
Why would you want do it?
So why would you want to make such a thing? Why spend all that time creating a minor work of art then cast it into the air to be at the mercy of every gust of wind that comes along and expect it to survive a reunion with a hard surface? On the practical side it teaches dexterity and it exercises patience. It brings understanding of those fundamental forces of flight that act on an aeroplane, and of aeroplane design and control. It also leads into the history of aviation and the stories of those magnificent men in their flying machines. Rubbing vicarious shoulders with names like Sopwith, Fokker, Ball, Richthofen, Hawker, Bader, Camm and Twiss... Or, it could be just for the pure enjoyment of creating something and the satisfaction of making it fly. On a warm, calm summer evening, watching your creation climb away from your hand, and gently circle around recreates a bygone era and has a charm all of its own. And of course it's fun.
So, Where to Start?
Free-Flight scale models come in various forms and some are easier to get to grips with than others. Currently the main options of flying scale models are either powered by a loop of rubber or a small Diesel engine. The easier of those modes to construct and trim is the rubber powered variant which are generally smaller, lighter and have less built-in detail to conserve on weight, as a rubber band can only produce a very limited amount of power compared to a diesel powered model. On the other hand, the Diesel engine, although not unlimited in power, can certainly provide a much greater scope for the modeller where weight and size is not so severely limited. But the increased loadings imposed by the greater power and weight require a more robust airframe.
Most modellers make models of the aeroplanes that take their fancy, but some aeroplanes make better flying subjects when scaled down than others. What the free-flight model requires more than anything else is inherent stability. So although you just can't wait to build a flying model of the Supermarine Spitfire, the most beautiful aeroplane ever designed, with a combat record second to none, it doesn't necessarily mean it's going to work as a model. In fact, with its compound curves and wing shape it's a difficult aeroplane to model well. As far as free-flight is concerned it's low wing makes it unstable and short nose means a very limited rubber motor run.
This is because the lift generated by the low mounted wing is below the Centre of Gravity of the Aeroplane. It's rather like trying to balance a pencil on your fingertip and push it upwards. As the Centre of Lift acts upwards and the weight of the aeroplane acts downwards the two try to rotate about one-another and turn the aeroplane upside-down. So it can be seen that the Spitfire, like all low wing monoplanes, is inherently unstable. Which is fine for the full sized aeroplane having its pilot to correct the top heavy imbalance, but not for an uncontrolled model. On the other hand, a high wing monoplane or a biplane will both have their C of L above the C of G where the weight of the aircraft effectively hangs off the C of L acting more like a pendulum and giving a stabilising moment.
We could then conclude that WW2 fighters are probably best left to Radio Control modellers, but it’s those aeroplanes that have all the charisma, and of course we really want to make models of them. All is not lost though as there are ways around the problem, but there has to be compromises. We could model the aeroplane with the undercarriage hanging down, as that‘s a sizeable piece of weight that acts like a pendulum and lowers the C of G. We could increase the dihedral of the wings. That’s the upward slope of the wings from their roots to their tips, that will bring the C of L higher. With luck, that will be enough to have the two forces change place and bring a measure of stability, but it is going to be marginal. The compromise being that most low wing fighters had retractable undercarriages and didn’t as a rule fly about with them hanging down. Neither did they have substantial amounts of dihedral, because the stability that dihedral brings is required less than manoeuvrability.
The biplane is a slightly different kettle of fish. What make it a good prospect for the free-flight modeller is that the C of L is effective through the mean height of the two wings, which places it approximately half way between the two. Biplanes with an upper wing of larger area eg a WW1 Nieuport 17 Scout or a Royal Aircraft Factory RE 8, will have the height of the C of L increased because the greater area of the upper wing produces more lift. Biplanes have their own problems though. Many of them were powered by Rotary or Radial engines, which were heavy and short in length, consequently what detracts from their suitability for our purposes is the very short nose. The Sopwith Camel for instance, has a nose that only just protrudes in front of the upper wing’s leading edge. Biplanes were also rigged with flying wires that supported the wings. These induce a high degree of drag which does little for the flying performance of either the model, or for that matter, the real thing. Once again these types can be made to fly with rubber power, but not as easily as a high wing monoplane. Unless the aeroplane in question has a significant length in front of the wing it’s more suitable as a Diesel engine powered model.
Wind up the rubber band and throw. That's the sort of thing most people would have in mind if asked to describe a model ‘plane. The performance of a rubber powered model depends to a large extent on its weight, so lightness has to be built in. To keep weight down rubber powered models are almost entirely constructed from balsa wood, with perhaps a little wire and thin plywood. One benefit of that is that there is very little required other than a few simple hand tools and glue to produce the finished article.
The finished rubber powered model is driven by a strip of rubber driving a propeller, usually positioned at its front end. Winding the propeller in the reverse direction to its normal operation puts enough turns on the rubber to provide propulsion. The length of the rubber loop limits the number of turns and through that, the duration of the powered part of the model's flight. **The type of rubber used has its origins with continental wine producers. Good quality, strip rubber was originally produced in hanks by the Italian Pirelli company, for viticulturists to tie up their vines. Resourceful modellers found it to be just the right size to provide a source of motive power for their purposes. Unfortunately, it is now only produced in very limited batches and true Pirelli rubber is much prized and sought after. There are other manufactures and rubber of various thicknesses are readily available through specialist outlets.**
The trick with rubber power is to get as long a loop of rubber as possible into the model and to know how many turns can be safely put on without a breakage. Experiencing a breakage where the rubber bunches into a solid mass and destroys the rear end of your pride and joy, is heartbreaking. To know when to stop winding can call for a bit of experimentation and is advisable. Taking the advice of the old adage to wind until it breaks, then back off one turn is not recommended. **Applying those turns is another matter. A suitable loop can take anything up to a thousand turns and winding on those sort of numbers can result in more wear and tear on the already damaged fingers. One way around this is with the use of a cheap hand-drill which are usually geared at around 4 : 1 so that for every turn that you apply to the drill it applies four turns on the rubber. To do this, a hook in drill's chuck engages with a small loop in the model's propeller and provides a helpful labour and finger saving device.**
The other trick with rubber power is to recognise that the configuration of the full-sized aeroplane that is being modelled, largely determines how much rubber can be stuffed into it, usually the maximum length of the loop is about one third longer than the distance between the propeller and the rear fixing. An aeroplane with a long nose has a big advantage in that it allows the use of a longer loop of rubber. Not only because of the length of the nose itself, but because any rubber aft of the models centre of gravity has to be balanced by weight at the front. It follows then, that it is better to be balanced by rubber at the front than add on dead weight that does nothing.
The earliest flying models were concoctions of spruce, bamboo, linen and paper. They were large and ungainly, but nevertheless were flying machines. It wasn't until the advent of Balsa wood in commercial quantities in the 1920‘s that modelling really took off. By the 1930‘s flying scale kits were being marketed by companies such as Keelbuild, Frog and Skybirds. Harking back to the immediate post WW2 years, two major manufacturers, Keil-Kraft and Veron each produced a large range of cheap, balsa-wood kits that were powered by the ubiquitous rubber band. The aforementioned Queens Cup winner Phil Smith designed the majority of the Veron range and Albert E Hatfull, who always signed his plans off with his name forming the shape of a wing's aerofoil designed the greater part of the Keil-Kraft range.
They were reasonable facsimiles of the full size aircraft but due to mass production limitations the quality of the supplied wood was variable, ranging from 'pap' to 'hearts of oak'. The propellers were practically useless and the motor was little better than a large rubber band. The kits provided a plan and building instructions. Parts were printed on sheet wood along with pre-cut strip wood for fuselage and wings, together with tissue paper for covering the framework and if you were very lucky, balsa cement to glue the parts together. In fact, many of these kits could be made to fly quite well, but invariably needed some modification to get any real performance.
Neither of these manufacturers have managed to carry on trading to the present day, but copies of their plans can be found from dedicated collectors and suppliers through the internet. There are also a number of modern suppliers who produce kits of popular subjects that are of excellent quality and incorporate modern design to make them into viable flying models. Many of these new kits also supply transfers of the aeroplanes markings and so remove one of the more difficult aspects of the paint job when finishing the model. These kits are probably the best entry into the scale modelling world, as it is possible with a little care to produce a good facsimile of the real thing.
**When all else fails... read the instructions is good advice. It's even better to read through the instructions first. Most model kits include quite detailed instructions how to build the model and the sequence of assembly. Plans when bought by themselves did not usually include them though. But most models follow a straightforward method and once one has been done the rest are similar. Modelers have their own preferences how they go about it, but it is usual to build the fuselage first, the wings next and the tail surfaces last.**
**There are two main methods of fuselage construction. The first is a box-section which is used for aircraft with a square section body, while the second method is a half-former assembly for aircraft with a rounded section. The box-section fuselage is made by constructing two, profile sides out of strip wood pinned directly on the plan. When removed the sides are seperated by formers and spacers between them giving the basic shape of the fuselage. The detail of cockpit and engine cowlings is then added to complete the assembly. On the other hand the half-former method starts with a central 'profile' of the fuselage pinned out on the plan. Half-formers are then added at right-angles to the profile and finally stringers which run the length of the fuselage in locating notches cut into the half-formers, are added to form a half-shell of a fuselage. This is then removed from the plan and the half-formers and stringers for the other side are added to make a complete fuselage.**
**Formers and half-formers will normally be printed directly onto sheet wood supplied in the kit. It is a good idea to cut out all the half-formers together prior to commencing assembly. Wing ribs will also be printed on the sheet wood and all should be cut out ready for the wing assembly in the same way. The wings and tail surfaces are effectively built in the same manner over the profiles on the plan. It is also good practice to cover the plan with clingfilm when pinning it to the building board. This prevents the assembly you are constructing, becoming attached by the excess glue in the joints to the plan, which otherwise would make its removal from the plan, without damage, nearly impossible. Another method of keeping the plan from becoming part of the model, is to slide a small square of greaseproof baking paper between plan and parts as it is assembled.**
You are going to need some tools:
Models have been made with little more than a single sided razor blade, sandpaper and a pair of pliers. But modellers like their tools, and realistically the minimum requirement is:
- Knife.The mainstay of your toolkit. Modelling knives usually have a replaceable blade as it becomes blunt. A selection of replacement blades are usually available for various cutting functions.
- Pins. Modelling pins are available, which are usually heavier duty than steel or plastic headed dressmaking pins, and are consequently thicker. The thinner pin is less likely to split the wood
- Building board. Which has to be flat. Usually a piece of thick plywood faced with quarter inch thick balsa. If necessary the underside can be battened to keep it flat. But without the battens the underside doubles as a cutting board. The size depends on the size of the models you are likely to build.
- Pliers. Flat and /or pin-nosed. Mostly for bending wire undercarriages and struts.
- Steel Rule. Or similar metal straight edge. Used as a guide to keep the straight edge of the balsa shape you are cutting, straight.
- Junior Hacksaw or Razor Saw. For cutting thicker sections of block balsa.
- Sanding block and Sandpaper. A flat balsa, or other wood block, to wrap with sandpaper for sanding down model profiles. The sandpaper needs only to be medium, fine or flour grades. Course grade is too rough for balsa wood.
- Paintbrushes. For the final finish. and detail work. Preferably a selection should include one artist's brush with a broad, semi-stiff head that can be used for thinned cellulose dope as an adhesive.
- Soldering iron. With electrical resin-cored solder. For all those bits of wire that need to be joined.
- Clingfilm. Or greasproof paper, used to cover the model plan during construction to prevent the glued joints adhering to the plan. This will save the plan for use another time.
- Old Shoebox. To keep it all together.
You will also need something to stick it together with.
**Traditionally the only glue require to build a scale model has been Balsa Cement a cellulose based glue which is fast drying, smells a lot as it dries, but is perfectly adequate for small models. Indeed the majority of joints on scale models of this size are still made in the same way. It also provides an element of great satisfaction peeling the build up of residue from one's fingers and a source of considerable pain if applied into a cut finger. However, modern glues of various sorts are more suitable for some applications, especially when the model's weight size and weight are increasing and with it the likelihood of failure of the joints with a 'hard' arrival on terra-firma. The most useful of those glues are: **
- Balsa cement. Nitro-Cellulose, the traditional basic glue for aeromodellers. Has a joint filling capacity and dries fairly quickly but has slight shrinkage when dried.
- PVA White Glue. Poly Vinyl Acetate, a general purpose wood adhesive with a slower drying time than Balsa-Cement, but does not shrink. The water-proof type, Aliphatic resin, otherwise known as Carpenters glue, has a yellow tint. Unlike ordinary PVA glue it can be sanded without leaving a feathered joint line.
- Epoxy Resin. Two part glue that requires a catalyst to be mixed to the glue so that it sets within a few minutes. Usually used to bond different materials, eg wood to metal. Fills large gaps.
- Cyanoacrolate. Instant glue. Bonds most things together, including fingers. Has no filling capability so the joint faces must be an almost perfect match.
Covering the model is achieved by using a non-soluble tissue paper supplied with the kit. Known as Modelspan it provides a surface to the model. There are other lighter tissues, generally referred to as 'Jap' tissue available through specialist outlets, which although expensive affords a significant weight saving. It's applied using tissue paste (heavy) or a 50/50 diluted cellulose dope/thinners solution (light). After application, the tissue is water shrunk by wetting it down, then allowed to dry to produce a reasonably taut surface. This also helps to remove wrinkles in the tissue. The final treatment is to paint all over with the above thinned dope to seal the tissue surface and render it airtight.
In some cases, especially smaller models where weight saving is of the essence, the model doesn’t have to be painted at all. But it can receive a colour scheme by the use of coloured tissue. This is usually best applied when the model is overall, one colour. Stripes and markings of a different hue can be cut out of a different colour tissue and applied over the base colour to produce a very light model with a very attractive translucent appearance. Otherwise, markings can be painted on. The other, heavier option in the case of more complex colour schemes, usually involving camouflage, is to paint the model in the manner of a large plastic model using enamel or water based acrylic paints. There is almost any colour that could be wished for available in the Humbrol enamel, or Tamiya acrylic ranges.
Detailing (The fun part)
This is the fun part where ingenuity is stretched and brings an air of reality to the model, hopefully without adding too much weight. For a lightly-loaded, rubber model, hinged panels and cover plates can be cut out of paper and stuck in place. Panels likewise, or if simulating an unpainted metal panel, it can be repainted in a slightly lighter or darker silver/gray to contrast with the surrounding panels, giving a much more realistic effect. Panels which are camouflaged and subjected to heavy wear and tear, can be pre-painted in a silver undercoat and after the camouflage paint layer has dried, the point of a modelling knife can be used to tease away and scratch the paint surface to reveal the silver underneath, giving a worn appearance.
**Similarly, a technique favoured by plastic scale modellers called Dry-brushing can be used to simulate wear and tear marks. This is to load a stiff bristled brush with grey or darkened silver and use up the majority ofvthe paint on a piece of paper. When almost 'dry' the brush is applied to the required area and the resulting minimal streaks appear as scratches. This is also quite effective using a matt black paint to represent engine exhaust staining and gun blow-back.**
Flying control surfaces can be drawn on using waterproof ink. Where applicable, rigging wires can be added in the form of monofilament fishing line anchored at the ends with individual paper staples and a drop of super-glue. The list is limited only by the modellers imagination and good reference photographs. Trying to bring about a ‘used’ appearance, particularly on service aircraft in the heat of battle, requires a light touch as it can be overdone, but any scale model always looks better for some detail.
Trimming. (Getting the Thing to Fly)
Getting the model to fly in a wide, flat circle around you, which is the desirable pattern, can be achieved by judicious adjustments to various aspects of the model. First of all there is a balance point, it’s Centre of Gravity. It exists somewhere in the centre of the model and is the point about which everything revolves and the point at which all other forces act. Usually it will be marked on the plan where the designer intends it to be. The actual position on the model needs to be found by balancing the model on an edge. As a rough guide, the model should be level when balanced correctly about one third of the way back from the leading edge of the wing on a monoplane, or about halfway back on the upper wing of a biplane.
If the modeller has been a bit heavy handed with the glue it will almost certainly be aft of where it ought to be, but that can be rectified by the addition of a small piece of lead weight at the front of the model. This should of course be done in a fully flying configuration. That‘s to say with its propeller, rubber motor and everything else it’s going to take to the air with. Don’t forget the pilot and it‘s off to the flying field...
Modellers flying fields are mystical places. They are wide open spaces as far as the eye can see. They do not have trees, park benches or any other form of obstruction and the air is always calm. They do have grass at least nine inches deep and there is a short piece of hard surface that looks like a runway at the up-wind end. Most modellers will settle for any one of those attributes, if you have two then pinch yourself because you‘re dreaming.
To begin trimming, face into whatever wind there might be and launch the model at about head height in a descending attitude. Initially a long flat glide with rear control surfaces set neutral should be the result if the C of G is in the right place. If it’s too far forward it will nose-dive in. If, as is more likely, it’s too far aft it will pitch nose up, loose speed then nose dive in. This is the first thing to be corrected and the addition of weight should bring about an extended glide. It is always better to trim slightly nose heavy. Any tendency to turn can be corrected by applying slight opposite rudder. Once this has been achieved we can apply a bit of power. So, winding on a few dozen turns of the propeller should extend the glide until on subsequent tests, with more turns on the rubber the model begins to climb.
The big advantage for rubber power over Diesel is that the power gradually tails off to a point where the propeller is free-wheeling and the transition from power to glide is relatively smooth. The major part of the power delivery from rubber comes as a burst at the beginning of the power run when the motor is fully wound and the model first released. That surge can pull the nose of the model up to an angle of climb that it can’t sustain and the model loses flying speed and drops into a stall. The answer for this is to adjust the thrust angle of the propeller downwards with a little packing behind the propshaft boss so that the thrust of the propeller pulls the nose downwards as well as forward. Couple this with a gentle launch technique, so that the model flies out of the hand on a slightly downwards path, rather than being thrown, should result in a smooth, gently climbing take-off.
What about Jets? I hear you say.
Although it has been done, a propeller does not look very ‘scale’ on a model of a jet aircraft. The aforementioned early model kits also included in their model range, the then, state of the art jet aircraft... Hawker Hunter, Supermarine Swift, MiG, SabreJet. These kits used as a means of propulsion a small rocket engine produced under the trade name Jetex. These motors burned pellets of solid fuel, which produced a jet of gas, of sufficient thrust, to fly small models of up to about 20 inch span. These motors became extremely hot in use and added the exciting prospect of burnt fingers to the slashed ones. Like many other things in this article Jetex ceased to be manufactured in 1972.
However, as a private venture, Dr Jan Zigmund in Czechoslovakia produced a one-use-only and discard, motor as a replacement for the Jetex. Unfortunately after a few years his product was reclassified as a 'firework' and the resulting changes in handling and transporting the goods that became necessary to comply with legislation, made production unviable for a one man operation. Currently electric motors driving an internal ducted fan is the likely successor for simulating model jet propulsion. But that’s another story...
Try Your Hand at Competition?
If you would like to pit your own building and flying skills against other modellers there are regular competitions held for various classes of rubber-powered models. Competitions are held under the rules of the British Model Flying Association (BMFA), the successor to the SMAE. The rules sets differ from class to class. Some classes put emphasis on accuracy and realism in flight, while others require a lesser standard in accuracy and a minimum duration of flight. Model accuracy is judged against documentation supplied by the entrant. The general classes and rules can be found in the BMFA handbook. To enter these competitions the entrant must be a member of the BMFA to comply with insurance requirements. Classes include:
- Scale Outdoor F/F (Rubber) Any model no more than 60cm wing span and 2kg. Accuracy of model and quality of flight is judged which must be over 20 seconds duration.
- Scale Indoor F/F (Kit) Any model built from a kit or kit plan. Must not exceed an overall weight of 150grams. Can be powered by rubber, CO2 or electric. No modifications to the kit assembly permitted.
- Scale Rubber Duration. Stand -off assessment of accuracy. Judged on flight duration.
- Peanut. Models with a wing span no more than 13 inches or 9 inches length.
- Pistachio Models with a wing span no more than eight inches span or six inches length.
Try it... You never know when you might need a bit of aero design theory, especially if the airliner you are travelling in has to make a forced landing in the desert, and like Hardy Kruger you need to cobble together another aeroplane out of the bits to rescue yourself. Neil Armstrong made model aircraft as a boy, and look where it got him.