Light aeroplanes and trainers
The light aeroplane movement started in the twenties with the D.H. Moth, of which the cheapness and simplicity, coupled with delightful flying qualities, gave the ordinary man his first chance to fly, either with a club or as a private owner. Flying ceased to be a pioneering achievement and became a pastime, still rather expensive but no longer exclusively reserved for the military, the commercial and the wealthy. Until the midthirties the Moth type of tandem open-cockpit biplane held the field, after which it steadily lost ground in the face of competition from both the low- and the high-wing monoplane.
Klemm and Messerschmitt in Germany made some very light low-wing monoplanes that were easy to fly—the former actually built his first so that his small boy could fly solo. At first, these aeroplanes were too low-powered, like the Lympne machines, but when strengthened and fitted with more powerful engines they proved highly practical. The design was based on a rather large area, thick-section tapered wing with a wooden D-spar and fabric rear portion. The fuselage, a light plywood box, was rather deep, since the pilot sat over the spar, but the whole aeroplane was somewhat cleaner than the wire-braced, strutted biplanes. These monoplanes had a weight advantage at first because their wings did not fold, but the costs of hangarage, which goes by the area occupied, gradually forced a change in outlook. The first step was to make the wing detachable as a whole, so that it could be stowed in a shed alongside the fuselage. This crude expedient was not popular in this country, but it lasted for some time on the Continent, where various competitions put a premium on low tare weight and large payload. These early low-wing monoplanes were undoubtedly the ancestors of the pre-War Miles and Percival monoplanes and most of the personal aeroplanes of today.
As flying became increasingly popular the lack of social intercourse when occupying separate cockpits and conversing by telephone became more and more obvious. There was, too, a natural desire to take the whole family and not just one passenger. These desires were first met by the high-wing monoplane, of which one of the earliest was the D.H. Puss Moth. Making a cabin instead of cockpits made the fuselage cleaner and allowed it to be widened so that two passengers could be placed on staggered seats behind the pilot. The structure was of welded steel tube, which made the fitting of windows easy. The high wing was a traditional wooden "ladder" covered with fabric and was braced at mid-span by steel tube V-struts running up from the fuselage. The rear spars of the wings were hinged to the top longerons of the fuselage for folding. One of the first clean fight aeroplanes, the Puss Moth, proved to have an embarrassingly flat glide and in order to steepen this, the fairings of the undercarriage legs could be turned athwart the air stream.
Almost all present-day high-wing light aeroplanes, such as the Auster, have descended indirectly from the Puss Moth. Fuselages have, in most cases, been widened to take side-byside seats, and details vary considerably, but the principles are the same. In one important particular there has even been a retrograde step: the wings of today do not fold, since there is ( ample hangarage left from the War.
The low-wing monoplane, too, developed into a side-by-' side cabin machine with two, three, or four seats. It became the practice to improve performance by enclosing the wheels in "trousers" or "spats", that is streamlined fairings, and eventually to retract them—so paralleling the fashions of commercial and military aeroplanes. Likewise, such refinements as; landing flaps became standard equipment. As a result of an annual circuit of Europe competition, the Rundflug, in which marks were gained for good take-off, some outstanding high-lift devices were evolved.
Many of these light aeroplanes proved to be such practical vehicles that they were used commercially as taxis and were a boon to the bush operators in the less explored territories of the world. Time after time record flights were made to Australia , to South Africa, and across the Atlantic by light aeroplanes until such feats became almost commonplace. The light aeroplane had become a vehicle and today a flight to the Cape by Auster is far more an everyday occurrence than is a similar journey by car.
After the War, with a potential domestic market of over , 50,000, the U.S. manufacturers embarked on ambitious allmetal light aeroplanes embodying all the latest ideas. Opti- mistic France kept pace, by going into production with the Nord Norecrin. These aeroplanes were metalized models of the pre-War wooden four-seater monoplanes, which had proved to be the ideal family tourer. Two untoward features restricted
this market. Tooling for metal manufacture put up the price, and the greater weight of the metal structure made it necessary to use higher-powered engines, so increasing running costs. Indeed, some American types, such as the Navion, have gone up to 260 h.p.—which may give a high performance, but scarcely justifies the designation "light". This trend has, as in other classes of aeroplane, been constantly recurring. As soon as a light aeroplane was a success someone wanted a little more speed, or a little more load— and up went the power. Then, when the ceiling had been reached someone started at the bottom again with "the really light aeroplane" of forty, fifty, or sixty horsepower.
An excellent example of this is the Belgian Tipsy Belfair, which carries two side-by-side at 110 m.p.h. on 60 h.p. Actually designed before the War by E. O. Tips this delightful little aeroplane was modernized and put on the market after peace was declared, but could not be made in quantity because the only suitable engine, the Walter Mikron, came from beyond the Iron Curtain. A similar fate befell the Fairey Junior, another Tips design. This little single-seater makes an excellent comparison with the Belfair. With the same engine, the performance is actually rather lower than that of the two-seater. The reasons for this lie partly in the drag of the open cockpit, but mainly in that of the "plank" wing as opposed to the tapered semi-elliptical one. The Junior was designed for cheap, simple manufacture and the untapered wing was chosen so that only a single rib jig was required. However, if speed is poor and climb only fair after the first thousand feet, the handling qualities are a delight. Also, for purely sporting flying the open cockpit is exhilarating and the pilot simply feels he is part of the Junior and waggling his own tail when he uses the rudder.
Even more drastic efforts to make cheap aeroplanes are tried from time to time. Since the greatest single item in the price of a light aeroplane is its engine, it is not surprising that there have been many attempts to use adaptations of existing motor-cycle and motor-car engines. There were the Lympne light aeroplanes of the early twenties and again in the thirties there was a revival of the ultra-light single-seater. In Britain a gliding enthusiast, C. H. Lowe-Wylde, fitted a motor-cycle engine to an intermediate glider of his own design and called it the B.A.C. Drone. In this little aeroplane the engine was mounted as a pusher, so that the pilot had a wonderful view from his seat in the nose. The wings of the Drone were easily
removable for stowage. With a bare twenty horsepower, the Drone was slow, but was airborne at about 25 m.p.h. because of its large wing area, although the climb was flat due to the low power.
Another, and quite unique, ultra-light was the curious design of a French amateur, Henri Mignet. This was the Pou-du-Ciel, or "Sky Louse", known as the Flying Flea in Britain. Being an amateur in every sense Mignet broke with traditional aerodynamics and engineering when he set out to make himself a foolproof aeroplane that could be built at home. Instead of wing and tail plane he used two wings of nearly equal size one above and ahead of the other. Dihedral and low-slung fuselage gave exceptional lateral stability and made ailerons superfluous. Fore-and-aft control was obtained by altering the incidence of the front wing, which was pivoted at its centre of pressure. A large rudder gave directional stability and control. There was no rudder bar, only a stick; which was pushed back and forth for climb and dive, and rocked left and right to move the rudder for turning.
In the past twenty years Mignet has built several Poux and is at present flying the advanced model illustrated. Before the War there were some nasty accidents with home-made Poux; these were eventually traced to a modification to the wing-incidence controls of Mignet's original design which allowed the aeroplane to develop a stable dive. However, by the time the answer had been found, the type was in disrepute and the War finally killed it. Today, regulations surrounding aviation are so restrictive that a similar ultra-light aeroplane movement is almost impossible, although in France there are a few small aeroplanes flying with converted Volkswagen engines.
Quite in the other direction are the luxury post-War American private types with their automobile-like cabins— complete even to the cigar lighter. In some of these, designers" have got to the point of simplifying the controls. The Ercoupe is an example where rudder and ailerons are interconnected and elevator movement is restricted so that a stall is impossible . With these controls the rudder pedals are eliminated and only a wheel is used for turning, with a push-pull movement for climb and descent. Externally, there is nothing to f reveal the eccentricity of the Ercoupe, apart from the rather unusual twin rudders that are necessary to give stability in yaw.
Another unusual American light aeroplane is the Beech
Bonanza, which has a butterfly tail. Here the controls are conventional , but fin and tail plane, rudder and elevator have been combined. The designer's idea is that by using two surfaces instead of three, weight can be saved. Special gearing separates the action of the yaw/pitch surfaces when rudder bar or wheel are moved. As rudders the surfaces move left or right together (one up, one down) and as elevators they both move up or down.
From the time of the Moth until today it has been usual to fit dual controls in light aeroplanes, and most private flying instruction is done in these general-duty aeroplanes. Military instruction is another matter and trainers specially designed for the work are used.
As a result of experience with the Moth in the R.A.F. a special trainer adaptation was brought into use in 1933. The plywood fuselage was replaced by one of welded steel tubes with fabric covering—save for the top deck where plywood was used to resist the damage caused by rough school handling —because of the greater resistance to heavy landings. The wing centre section was moved forward to give the occupant a parachute exit and the wings, which were thus quite heavily staggered, were slightly swept back to keep the centre of pressure in correct relationship to the c.g. The undercarriage was strengthened to cater for pupils' landings and a 130 h.p. Gipsy Major was fitted to give more urge for rapid "circuits and bumps".
The D.H. 82A, Tiger Moth—not to be confused with the racing monoplane—has been built by the thousand and had an active life in the R.A.F. of nearly twenty years, before being superseded by the Chipmunk. And even after twenty years, not a few are still in service with the R.A.F. as well as in many flying clubs. The reasons for this popularity He not in the external shape, but in the harmonization of the controls, which make the Tiger easy to fly, yet show up any mistakes. General sturdiness, easy maintenance and simplicity are contributory virtues.
Prior to the War, with monoplanes entering the R.A.F., it was natural to order a monoplane trainer, the Magister, an adaptation of the popular Miles Hawk light aeroplane. The 1 Magister's plywood construction proved much less suitable for training work and it was largely passed over to units as the station "hack".
A monoplane advanced trainer was needed to convert
pilots to service-types and one was bought from the U.S.A., the North American Harvard. A simple rule-of-thumb two-seater the Harvard was, and is, an excellent intermediate trainer, since it has to be handled with respect and the pilot also has a foretaste of the power he will meet in service types. A feature of the Harvard is that all wing taper is on the leading edge, so producing slight sweepback. In pilots unfamiliar with the sharper stalling characteristics of the tapered monoplane this led to many accidents, and, before the War, the Harvard was looked upon as dangerous until "pillar-box" slots were cut in the wing tips, so maintaining aileron control down to the stall.
Post-War British thought on trainers has concentrated on side-by-side seating, so that the instructor can more easily correct the pupil and gain his confidence. Such an arrangement means more power and the new standard trainer the Percival Provost has an Alvis Leonides engine of 550 h.p. Attempts to evolve a design with 250 h.p. resulted in a poor performance by the time it had been loaded with all the military equipment desired by Training Command. In France and in the U.S.A. the R.A.F.'s lead in adopting side-by-side training has been' followed with several designs.
The Provost is a neat low-wing monoplane in light-alloy construction. To give the pupil the right idea from the start flaps and constant-speed airscrew are fitted, but to save time on circuits—as well as to ease maintenance—the undercarriage is fixed. The raised canopy gives a good view in all directions, , but is sufficiently low-set to leave a good airflow over the tail. Several side-by-side trainers with raised hoods have had: peculiar, if not actually dangerous spinning characteristics— and it is not much use teaching a pupil on a machine with non-representative behaviour. The whole design of the Provost's tail is intended to make it come out of a spin correctly, flat fuselage sides give effective side area, the fin and rudder are well ahead of the area blanketed by the tail plane during the spin, and the elevator is large and powerful.
For the R.A.F. Reserve a tandem trainer, the dainty' Chipmunk, first design of D.H. Canada, was adopted—and has since been used also by the R.A.F. It is simply the modern form of the Tiger Moth and is about as simple as a light-alloy low-wing monoplane can be—neither do its good looks belie its crisp flying qualities.;
These may well be the last piston-engined trainers for Service use, since there is not a great deal of sense in teaching a man on piston engines and then having to spend weeks converting him to jet technique. The future is shown by such trainers as the little S.I.P.A. 200 and the Caproni-Trento F.5, both designed as light aeroplanes. There is considerable doubt about the turbine engine for civil use, since fuel consumption is of necessity high at low altitude and neither oxygen nor a pressure cabin are acceptable complications. Furthermore, the very limited endurance as yet possible demands dead accurate navigation, while the slow build-up of thrust means that a misjudged approach is fraught with danger. For racing, or for demonstration, such aeroplanes as the Fouga Midjet can be excellent—in the hands of semi-professional pilots.
To return to the question of trainers. The side-by-side S.I.P.A. 200 is a minute aeroplane that could only be made for jet propulsion. The all-metal nacelle carries the three wheels of the undercarriage and the engine as well as the crew. The high mid-wing is of metal construction and is fitted with double slotted extension flaps. The tail booms are cocked up more to keep the fins clear of the ground than to raise the tail plane above the jet eflux. Deep fillets under the wing duct air into the 330 lb. static thrust Turbomeca Palas centrifugal engine. The S.I.P.A. 200 is a remarkable little aeroplane and it is a worthy successor to Yves Gardan's earlier designs, the delightful S.I.P.A. 901 and the Minicab, tiny side-by-side twoseaters with the handling qualities of a Spitfire.
The F.5, designed by a young Italian free-lance Stelio Frati, is of plywood construction, actually a neat adaptation of conventional glider technique. The essentially clean lowwing monoplane airframe has a long nose because both pilots are seated ahead of the wing inside a glazed canopy. The tail is high, so that the jet can pass underneath. The engine, a Palas, is tucked into a readily detachable fireproof "bath" behind the wing trailing edge. A scoop on each side of the fuselage ducts air into the engine.
In general, the few service jet trainers follow standard jet fighter layouts—plus the extra seat. Those in service in 1953 are all adaptations of fighters—Meteor, Vampire and Shooting Star—but new specially designed types are on the way, such as the Fokker S-14. It is an expensive task to design a special aeroplane where an adaptation will do and it is likely that most advanced instruction in jet flying will continue to be done on adaptations of current or obsolescent fighter and light bomber types.