What shall I build?Just to show you we're really going to begin at the beginning, let's start by talking about what a flying model is. Don't make the mistake of thinking a model plane is just a toy "real" one; it's a small flying machine in its own right, based on aerodynamic laws as real as those that govern the functioning of a giant jet transport.
A flying model is a miniature structure capable of supporting itself in stable flight by the action of its surfaces against the air. This can include everything from a folded paper dart to a complex multi-engined R/C scale job. Some models are gliders—throw 'em and they ride smoothly around in the air until they touch the ground. Others have power-driven propellers which rotate, pulling the model forward. The resulting flow of air over the wing lifts the ship from the ground, and the balance of weight, drag, lift, and thrust and the pressure of air against the flying surfaces maintain it in stable climbing flight. When power cuts, there is a readjustment of forces, a new stable balance is struck - and the model glides down. Jet-powered jobs are pushed forward by a stream of high-speed gases ejected toward the rear, but in any case, the power is incidental; the plane flies on its wing, stabilized by its tail surfaces.
Free-flight models fly without control other than inherent stability and trim. A control-line model lifts itself and flies, too, but tethering lines are substituted for inherent stability—with the gain of vertical maneuverability enabling the flyer to enjoy the thrills of high-speed and aerial stunts at close range.
Almost every kind of model can be built either as a high-performance contest model, or as a simpler, tamer sport model. The former are generally more difficult to build, trickier to adjust for flight, more fragile, and except for C/L, likelier to get lost. These ships are for the scientific-minded, the competition fans. The average builder usually has more fun with ships that are content to take off, fly well but not fantastically, and glide in to a good landing; rugged ships with neat lines and dependable performance. Even the contest-bound modeler will feel more secure if he learns about flying with sport jobs before turning loose a timed, dethermalized, superpowered VTO free-flight with a rocket climb and a floating glide. As in most activities, it's a good idea to work your way up gradually to the advanced stages; so before plunging ahead into a project, let's look over the field and see what's available.
fig.2 - Pipsqueak HL glider.
Considering first those models which fly without power (gliders and sailplanes), the simplest are the small hand-launched jobs, usually built from sheet balsa and devoid of non-essentials. These ships can be made as small as three to four inches in span or as large as two feet, and are perfectly capable of gliding right out of sight in a thermal, just as big contest models sometimes do. A good size to begin with is a 7-inch wing span, with wing and tail surfaces cut from 1/32" sheet balsa, and fuselage from 1/8". If you're tired of reading already, you can stop now and build Pipsqueak from the full-size plans shown in Fig. 2. (In fact, it wouldn't hurt to build two, in case one lands on the roof.) You can learn a lot about flying and adjusting a model from a small glider like this, either in a spirit of scientific inquiry or just for the heck of it.
With the possible exception of R/C models, all flying models are essentially gliders; an engine is merely one method of hauling the model into the air. Contest models which achieve flights of many minutes are generally limited to a motor run of no more than ten or twenty seconds.
For gliders between 18-inch and 30-inch span, the addition of ribs to the wing and sometimes the elaboration of the fuselage into a box structure is advisable, for greater strength and improved performance. The ribs supply camber to the wing and increase its rigidity, while the box fuselage gives increased support to the wing and tail. This kind of glider can be sanded and doped to a slick finish without fear of warping, thus increasing the efficiency of the model by reducing friction with the air.
Larger gliders, such as the Nordic type (usually of sailplane configuration, with very high aspect-ratio-the ratio of wing span to chord-as shown in-Fig. 3), are nearly always built up and tissue-covered, for lightness. A well-designed covered frame is very strong for its weight, but of course it can't equal the rugged-ness of the all-balsa jobs, and must be launched with more care; an all-out heave-ho might leave the wings behind. For this reason, a towline is the usual mode of launching these ships. A hook is installed on the lower side of the model just in front of the center of balance, placed so that the line will drop free when the pull is relaxed. The towline is made of heavy linen thread, light fishline, or string swiped from the kitchen drawer, of a length equal to the height you hope the model will reach before releasing (not over about 50 feet at first) and with a bit of rag tied to the end to help you find it after use. By trotting into a slight breeze, you gently tow the model to a good height, and then relax and watch it float around upstairs.
For the advanced model glider pilot, the addition of a radio-control unit adds the final touch. A radio-controlled glider is capable of staying aloft for a long time by riding air currents, and in areas where conditions are favorable for soaring, R/C gliders are very popular.
An alternate method of launching either type of glider is the use of a rubber cord, stretched out and released. The length of the cord and the extent to which it is stretched determine the violence of the launch. For small models, try this: Attach a 4-foot length of 1/8" flat rubber to a post one foot high; tie an 8-foot length of string to the rubber, and attach a small wire loop to the end of the string. This is engaged in a hook under the model, the rubber is stretched out as far as you dare - and let 'er go! By varying the angle of launch, the length of the rubber and string, the vigor of the send-off and the trim of the model (nose-heavy for a long fast curve, regular balance for loops and snap-rolls), you can do almost any acrobatic in the book, even with - especially with - a tiny 6-inch glider.
Keith Laumer Photo (model shown is 'V-Girl').
The time comes in the life of every glider pilot when he wants to try a powered model. The transition is easy, particularly if you start with rubber power, employing construction similar to non-powered ships. It is a mistake to think of rubber power as a feeble makeshift, as anyone knows who has ever ducked as a big Open event job—carrying several dozen strands of tough rubber wound to a thousand or so turns-whizzed past. But it is a versatile form of power, applicable to very small and simple models as well as to highly sophisticated endurance ships; and best of all, anyone can operate it with very little practice.
All-balsa ROG (rise-off-ground) models like the one in Fig. 4, of 12-18-inch span, are excellent first projects. They can be bought ready-built or put together in an hour or two, cost very little, are extremely rugged - and a good model of this type can easily climb 200 feet in the air and stay up several minutes, flight after flight. Experience gained in operating a simple ROG is good training for flying more complicated types.
The performance of your ROG can be improved by using tissue-covered built-up flying surfaces. The resultant model is more fragile than an all-wood job, but is correspondingly lighter and has a better glide.
The ultimate development of the basic ROG idea is the wholly built-up endurance model (Fig. 5), having the rubber completely enclosed within a fuselage, and with a precise airfoil formed by closely spaced ribs and multiple stringers. A model of this kind, with its graceful lines, its tight-doped tissue covering, its feather-light weight, and its hand-carved propeller, is a thing of real functional beauty and has been known to inspire small boys and tired businessmen alike to go home and try a hand at modeling.
Construction of these ships is simple and straightforward. Fuselages are usually of box type, and wings and tail generally have constant chord and thus identical ribs, simplifying cutting-out. Machine-cut props are available and work well, for those who don't like to whittle. Conventionally, many of these designs include a "pilot's" compartment with windows; these are called "cabin" models. Those without cabins are "stick" models.
For the modeler with a taste for more realism, the semi-scale sport model is the logical compromise between looks and performance, with the added bonus of simplicity and ruggedness. A semi-scale model has proportions similar to those of man-carrying airplanes, and carries a full complement of cabin windows or open cockpits, wheel pants, fancy paint jobs, etc., all of which add to the joy of watching the little ship flying around overhead. Since these accessories slightly reduce aerodynamic efficiency and add weight, semi-scale models are usually not capable of getting lost out of sight as easily as the pure endurance model, a deficiency which many modelers are willing to forgive.
The fanciest version of rubber power is the scale model, a true replica of a full-sized airplane, on which the perfectionist can lavish the ultimate degree of detail, down to instrument faces, wire rigging, and doors that open and shut, preferably not in flight. The more practical builder usually controls the passion for scale in the interest of practicality, and modifies things sufficiently so that the model will fly well and survive landings. A little added dihedral, a slight increase in rudder area, a modest relocation of the landing gear detract little from the looks of the plane, and help a great deal in action. It is sometimes possible to select a prototype which is perfectly adapted to pilotless flight, but in most cases some modification is called for to achieve inherent stability. In every case it will be necessary to use a special large-size propeller, and if take-off from the ground is to be achieved, this usually means lengthening the landing gear to provide prop clearance.
Keith Laumer Photo (model shown is 'Buttons).
Up to now, things have been comparatively quiet, with only the soft whirring of large blades beating the air, impelled by the silent resilience of twisted rubber. When we turn to internal combustion, things are different. These are two types of miniature "gas" engine made especially for model aircraft, both equally loud. This detracts little from the enthusiasm of model builders, many of whom like to start up engines on the bench and run them wide open just to enjoy the scream. We won't be so profligate of power, and will start out looking over the field with a view to getting aloft.
All the rubber-powered types we considered were of the free-flight persuasion; the happy owner does all he can in advance to predetermine a flight pattern, and lets her go; from then on it's up to the built-in settings and the air currents. But with engine power, you have a choice between two basic varieties of model: free-flight or control-line. The latter models are tethered, and are controlled in flight through the tethering line or lines. This control is limited to the up-and-down dimension, since of course the flight path is circular, but a complete pattern of stunts is possible.
But before getting further into control line, let's first take a look at free flight. Within this category are a number of model types which are quite different from anything we have seen in rubber power. The most elementary job, using a small 1/2 A power plant, is the profile fuselage, solid-wing model. Since engines pack considerably more wallop than rubber, a comparatively massive solid fuselage is practical, and of course no provision need be made for housing a long rubber motor. A simple F/F trainer built along these lines is almost indestructible, and can be flown with long motor runs without fear of a flyaway; when the engine cuts, the model will make a fast glide-in without lingering aloft to look for thermals. The profile approach enables the designer to incorporate interesting lines in the model without difficulty, and especially in very small models, to achieve a very neat appearance.
Less attractive perhaps, but a better flyer, is the pylon configuration (Fig. 6a). Here a slender balsa box is adorned up front with a vertical fin rising from the upper surface, providing a mounting platform for the wing above the turbulent slip-stream from the propeller, as well as other aerodynamic advantages.
The pod-and-boom model is another very practical type employing a solid unit as a mounting for engine, L.G., and wing, and with a slender boom extending rearward for the tail (Fig. 6b). These ships can be very light, and if carefully built, can turn in contest performance in spite of all-wood construction.
However, the most practical strength-weight ratio is obtained with a fabric-covered frame. Pylon models sometimes use tissue-covered wings, as do pod-and-boom jobs; but the technique lends itself best to fully built-up frameworks, similar to the box and cabin models of the rubber categories, and more elaborate types. The engine-powered versions differ chiefly in having shorter noses, due to the concentrated weight of the engine. Also, the greater weight-carrying capability of an engine enables the modeler to build more solid, sturdier airframes, and incidentally to indulge in a bit more fanciful design. A little planking, some soft balsa fillets, color dope, all add to the looks of a free-flight sport job, without sacrificing satisfactory performance.
Many sport models are semi-scale, having the approximate lines of a piloted craft, with a cowled ogine, clear plastic canopy or windows, rubber-tired aluminum wheels, decal trim and numerals, etc. This kind of ship provides more year-round fun for the average modeler than either an ungainly looking contest-type ship with a penchant for disappearing behind a distant cloud or a fully scale ship with its flight limitations and its habit of dropping pitot tubes and dummy exhaust sticks in a routine rough landing. Although kit manufacturers tend to ignore this type, the model builders' magazines supply a steady stream of excellent sport designs along with the latest contest winners.
Keith Laumer Photo (model unknown. Looks like a Kinner Sportster).
This is not to discourage the scale enthusiast; for the builder who wants realism, nothing can compare with true scale, complete in every detail; and unlike the case of rubber-powered models, few concessions to flight requirements are needed if the plane is wisely selected. Low-winged ships are dubious free-flight projects and multi-engined jobs are, for all practical purposes, out (except for three-engined ships like the Ford Trimotor, where only the center engine runs, the other two being dummies). But there are plenty of light planes, home-builts, WW I jobs, etc., which can be built and flown with complete success, and undeniably these are the most eye-catching of all models.
The advent of the control-line model opened up a whole new realm of flying model types. These models employ movable elevator surfaces, controllable by the flyer who holds a handle to which lines are attached which in turn operate the flippers, giving up-and-down control (Fig. 7).
With C/L, it became possible for the first time to perform stunts, attain terrific speeds (over 160 mph), engage in aerial combat, all in a small flying area. And in the scale department, multi-engined and unstable low-wing airplanes which had previously been the exclusive domain of the solid-model whittler now impressively took to the air, engines roaring, landing gears folding, lights flashing, in an amazing simulation of the flight of manned craft. Die-hard free-flight men, of course, denounce this development as the end of science in aeromodeling, little better than the twirling of a weight at the end of a string. Anything, they argue, would fly on lines.
This is a prejudiced viewpoint. Every C/L designer has had the deflating experience of trying out a new ship and discovering that, as in the full-scale airplane industry, some ideas which look good on paper just won't fly. The thing which arouses the disdain of the no-strings faction is the elimination of lateral stability as a factor in the performance of a C/L model, due to the confining lines which permit the ship to fly only in a circle (actually, a hemisphere) around the man holding the control handle. However, the skill needed to maintain the model in level flight (no problem with free flight) more than makes up for this, and success depends as much on the flyer as on the model. While anyone can quickly learn to fly a stable C/L model in gentle circles, it is a skill which must be acquired, and the C/L flyer can advance into steadily more complex models, capable of more and more spectacular flight - and correspondingly more demanding of piloting skill.
The inexperienced modeler should start in control line with a specially designed trainer. These models are solidly built of hardwood and solid balsa, have limited control movement and built-in stability, and are underpowered. They can be (and are) repeatedly dived into the ground, clobbered on take-off, brought in to fatal landings - and go right on flying. (The use of concrete runways during this phase of the learning process is not recommended.) By the time the rugged trainer has been battered into a state which precludes any further hope of repair, it is time to step up to a higher-performance ship, having more looks, capable of fancier tricks, and requiring a bit more in the way of trained reflexes on the part of the flyer.
Sport models can be tamed for early flights by setting controls for shorter travel (and less chance for spectacular pilot error) or by using a smaller engine than the ship is designed for; putting the propeller on backwards reduces its efficiency, and helps to slow the model down. After the feel of the new plane has been absorbed, set everything for peak performance and start in on loops, wing-overs, figure eights, and other stunts. With an engine howling and a responsive ship pulling on the lines, there is some real excitement as you feel your way into that first up-and-over!
The C/L model is probably at its best in the stunt category. A high-performance stunt job features a large wing, usually of symmetrical airfoil (it spends as much time flying inverted as right side up), a short fuselage, immense elevators with wide travel, a big power plant, and sometimes flaps linked to the controls for even faster response.
A special type of stunt job, usually lacking landing gear and other external refinements, is the combat model, specially built to seek sudden death in the air. Streamers of tissue paper are attached to the rear of the combat ship, and two flyers take the field together, flying in the same circle. The stated object is merely to cut the other ship's streamer, but in the natural course of events, mid-air collisions, vicious attack dives that don't pull out in time, and other catastrophes make combat a short, fast life for a model. But to a combat man, the spectacle of a darting shark-nosed ship coming over and down, engine screaming, to rake an opponent end-to-end in a lightning pass, then whip up in a cloud of balsa chips to race defiantly around the cleared circle, flaunting an untouched streamer as the other flyer fights to bring his shattered plane in to a dead-stick crash landing—this is living!
A more peaceful version of two-to-a-circle flying is the team race, for which special models are flown. These ships are generally semi-scale types, with landing gears, cowled engines, cockpits and colorful paint jobs. Pilots and ground crews work in close co-operation to keep the model in the air with the engine turning up at maximum rpm, with pit stops for re-fueling or trouble-shooting handled as snappily as at any race track.
Scale and semi-scale models are excellent C/L projects, since with a flyer at the controls, practically any ship can be flown, regardless of inherent stability problems. Weight is less critical than in free-flight, since relatively immense engines can be used to pull the ship into the air by brute force. Fully operating, retracting landing gears, flaps, and lights can be installed, as well as bomb-drops, rocket-launchers, crop-dusters, etc. In this category of model, the designer and builder have a free hand to add gadgets and try out ideas.
While single-engined ships are simpler to build and fly, the lure of the multi-engined job is one that no modeler should ignore. The sound of two engines running in synchronization at 20,000 rpm is alone worth the trouble, and it's a thrilling sight when a twin-engined scale model moves off down the runway and lifts into smooth fast flight.
Dick Stouffer Photo - Flying a C/L model at night.
C/L scale ships are longer-lived than their F/F brethren, not being so subject to the vagaries of air currents, and it is practical to lavish even more time
on their construction and detailing, with reasonable hope of a long life. Since sheet balsa planking can be used wherever needed without fear of weight problems, beautiful and realistic finishes are more readily gotten, and best of all - your C/L job won't ungratefully fly away.
During the last few years, radio-control equipment for modelers has developed rapidly. Today there are numerous dependable outfits available at reasonable cost, which can be installed and operated successfully by any modeler.
Transmitters and receivers are smaller and less delicate, and installation and wiring have been simplified so that some sets need merely to be placed in the model and plugged in. The builder must, of course, construct the movable control surfaces and link them to an escapement, but this is hardly more complicated than installing controls on a C/L model.
The basic R/C ship employs rudder-only control; this is enough for the flyer to have to think about, the first time in the air. The ship is trimmed for a climbing turn, and the radio impulse is used to turn the rudder strongly in the direction opposite to the built-in turn. By holding the rudder over briefly, the ship can be turned in the desired direction. Holding the rudder hard over brings it around in a tight downward spiral; by snapping the ship out of such a dive, a neat loop can be executed.
After you've become proficient with rudder-only, you can step up to elevator also, and add engine speed control, ailerons, etc. For more than three or four different controls, depending on the escapement used, a multi-channel or other more complex radio installation is necessary. Of course, with increasing complexity comes increasing trouble shooting, and since a skilled flyer can perform every maneuver in the book with rudder-only, it is advisable to stay with simple equipment for a long apprenticeship.
R/C ships are actually a specialized form of free-flight model, generally being of extra-solid construction with massive balsa-block nose sections to reduce engine vibration, heavy-duty landing gears to help cushion the receiver against landing shock, and low-slung stabilizers to simplify installation of rudder controls and increase ease of assembly. R/C ships are underpowered as models go, and have rather sluggish flight characteristics, owing to high weight and low power. Controls are of fail-safe type, and in the event the flyer loses control, the ship merely free-flights until fuel is exhausted. For this reason it is a good idea not to take on more than five or ten minutes' fuel at most. The range of the average receiver is about a mile, though much longer range can be reached under favorable conditions, but it is wise to keep the model close, and not too high - just in case.
Scale R/C models are very popular, and with the low-power, high-weight formula, they can be built with plenty of scale detail and perform well.
In the pursuit of more and different power plants for models, and in keeping with the jet age, the manufacturers have not only raised the internal-combustion engine to a high level of perfection, but have also made available to the modeler a whole range of jet engines which make possible true-scale powered models of the latest fighter planes. Chemical jets are small and not particularly powerful, but are quite practical, easy to operate, and perfectly safe. In addition to being used in scale models, they have proved to be satisfactory glider launchers for those who don't like throwing things and who like to hear a soft hissing noise while their model whizzes around the yard.
An alternate solution to the scale-jet problem is the ducted fan. An engine fitted with a short multi-blade prop is mounted inside the fuselage of the model, and expels air out the rear through a carefully proportioned duct. Engine cooling is a problem here, as well as access to the engine for starting; but the fan does work.
The big brothers of the chemical jets are the large liquid-fuel (paraffin) jet engines which operate exactly like the full-size ones, giving off preliminary belches of black smoke and balls of flame, then bursting into an earth-shaking roar. Jet C/L models can turn in speeds approaching 200 mph, and their builders explain that the red heat of the engine while running is not due to friction with the air, but is normal to this type of power. The heat problem places some severe limitations on design for jets, since the engine must either be mounted clear of the model or well insulated to avoid setting the whole project afire. A tankful of fuel is good for several seconds of flight of a violence which must be seen to be appreciated. This type of engine is recommended to those who like: (a) trying to start engines, (b) loud noises, (c) short flights with bad landings, and (d) to be different.
Of course the urge to be different has led modelers to explore many avenues of flight other than the normal configurations and power arrangements. The ornithopter, or wing-flapping model, has its devotees, and while it may never replace the bird, it is an interesting novelty. The canard, or tail-first model, is one of the oldest (the twin pusher of the prehistoric era of modeling was a canard), and is still going strong in some quarters. The main advantage of a canard is that the propeller is in the rear and thus less likely to suffer in a crash; this is a less valuable feature today than in the era when crashes were more frequent and propellers more expensive.
The Delanne configuration, employing two widely staggered wings in place of the usual wing and stabilizer, has been very successfully used on full-scale aircraft, and works well on models. But, except for experimentation, there's not much point in going to all that extra work. Besides, the flight adjustments of a Deland are unfamiliar to modelers, which makes it difficult to test such a ship without destroying it in the process.
The same is true of the helicopter, but in view of the many outstanding advantages of this approach to flight, modelers keep trying. It took the professional aeronautical engineers many decades to solve the problems of stable flight with a manned helicopter, but modelers have persevered in their attempts to build inherently stable choppers - and have succeeded. The sensation caused among the bystanders when the model goes churning its way straight up into the blue is said to be one of the chief rewards of the experimenter.
There are plenty more types: flying wings, amphibians, sea-planes. The ROW (rise-off-water) is a regular contest category, and you can fit floats like those shown in Fig. 8 to most land-plane models for water operation. Models with pusher engines mounted above the cabin, or with outlandish configuration, sometimes fly beautifully. Try 'em all and see.
You can buy construction kits for all the kinds of models mentioned above, and then some. A kit usually contains a clearly printed full-size plan with printed instructions, and all the necessary balsa wood, plywood, tissue, wire, and special fittings to build the model. Kits do not contain dope, cement, engines, or accessories, fuel tanks or tubing; usually kit wheels are of poor quality, and you'll have to buy a set separately. Nowadays (darn it) kit components are increasingly prefabricated, with all parts die-cut or pre-shaped. Since die-cutting produces ragged, splintered edges, and the preshaping of balsa blocks is often inaccurate, with the result that parts don't always fit properly, pre-fab kits in general have brought about lower-quality workmanship. On the other hand, lazy hobbyists who wouldn't go to the trouble to build a model from scratch are enabled to go on flying.
The fact that many kit manufacturers and builders alike seem to overlook is that it's fun to build a model-why have a factory do it for you? You can still get kits that require building rather than mere assembly, of course, and enjoy the pleasures of craftsmanship. You'll learn and pave the way for designing your own.
In considering what to build, don't overlook the model-plane magazines. UK modelers are fortunate in having three first-class monthly publications devoted to the sport, each edited by an experienced, active model-builder.*
These publications are filled with modeling news, scale details, pictures, and articles on every phase of modeling. Even the ads are interesting, containing frequent announcements of new products. There are three or four new model designs in each issue, complete with plans and instructions. If you run out of ideas, just check the mags. In selecting a model be sure to pick something suited to your experience and facilities. A large free-flight model adorning the bedroom ceiling for want of a flying field can be a source of great frustration. Bogging down in scale detail when what you want to do is fly can be equally discouraging. Start off on something that fits your situation, and don't forget that after you gain a little experience, the only limit on the types you can build is the breadth of your own imagination.
* 1. Aeromodeller; PO Box 35, Bridge Street, Hemel Herapstead, Herts HP1 1EE. 2. Radio Control Models & Electronics (at same address as Aeromodeller). 3. Radio Modeller, 64 Wellington Road, Hampton Hill, Middlesex, TW12 1JT.