Flight, March 1925

THE DE HAVILLAND "MOTH”
60 H.P. "Cirrus" Engine

   FROM whichever point of view one regards it, the de Havilland "Moth" must be considered a very fine little aeroplane. It may be argued that it is not a light plane, in the sense of the term that has come to be commonly accepted, but it is a low-power aeroplane with a good performance, and it is hoped to be. although naturally this still has to be proved, one of the most reliable little machines of modern times. In fact, the first aim of the designers of machine as well as engine has been this particular feature. The engine, the Aircraft Disposal Company's "Cirrus," described and illustrated in FLIGHT last week, is of fairly large capacity (4,500 c.c), and is capable of flying the machine quite strongly without being run at its maximum permissible "revs." This, naturally, means that there is a good power reserve to enable the machine to take off from a reasonably small field, so that the "Moth," as the new machine is called, will, both on this account and also because of the fairly high top speed which enables headway to be made against a head wind, be well suited to cross-country flying or touring. In fact, the "Moth" is distinctly more than an "aerodrome machine" (i.e., an aeroplane mainly used for short flights in the vicinity of an aerodrome), and should, provided the reliability proves as good as expected, be extremely useful for a variety of purposes. The designers naturally hope that it will be adopted for use by the light 'plane clubs, as it is particularly suitable for school work and "joy-riding," but one can foresee a number of other uses to which the "Moth" can be put. As a fairly low-priced machine for the owner-pilot the type should have much to recommend it, especially as its construction is of the simplest and most straightforward, while the "Cirrus" engine is so much of the motor-car type that anyone with motor-car experience should easily be able to look after it. Moreover, the engine has been designed to give very long service without overhaul, so that the maintenance should be well within the capabilities of the average motorist. Then there is the question of the employment of low-power aeroplanes in the Dominions. Here, also, the "Moth" should be extremely useful, as its performance enables it to fight adverse weather conditions, while its landing speed is low enough to enable the machine to be put down in a small field. Altogether, therefore, if orders are forthcoming in sufficient numbers to allow of placing it on a production basis, one can foresee a very bright future for the de Havilland "Moth." There is still the question of the Air Ministry airworthiness certificate, but we understand that the second machine, now nearing completion, is being built under A.I.D. supervision, and that, therefore, the type may confidently be expected to be "approved."
   On Monday of this week the De Havilland Aircraft Co., Ltd., had invited a number of press representatives to visit the Stag Lane works in order to inspect the "Moth" and to watch it flying. The aerodrome was in a deplorable condition after the incessant rains, and the "Moth" sank in up to its axle in the mud, but for all that it got off with a relatively short run, and, once in the air, the climb was extremely good. A large number of passengers were carried, and incidentally the visitors were, probably quite unconsciously, paying a tribute to the "Cirrus" engine by waiting their turn for a "flip," the thought never occurring to them that the engine might refuse work.
   We were among the passengers carried during the day, and perhaps a few impressions may be of interest. The machine got away very well, and once off, Mr. Broad, the well-known de Havilland test pilot, climbed her at 1,800 r.p.m. and an air speed of 50-55 m.p.h., at which speed she rapidly gained height. The day was somewhat bumpy, but the "Moth” appeared to rise and fall on an even keel, and no tendency to pitching was observed. In a series of steep curves it was observed that the amount of aileron movement was very small, an indication that, although only the lower plane is fitted with ailerons, lateral control is ample. In normal straightforward flying the ailerons were used surprisingly little, the large dihedral evidently being sufficient to give good stability, yet not so large as to make the machine "wallow." As there was no control stick fitted in the forward cockpit we were not able to ascertain how much elevator control is required, but observation from the ground did not reveal any large movement in ordinary manoeuvres. The rudder bar in the forward cockpit moved very little indeed, so that presumably the large rudder is very effective, and should help very materially to give control at or near the stalling angle.
   The front cockpit proved most comfortable, and by keeping one's face fairly close to the wind screen no appreciable draught was felt, and it was found unnecessary to wear goggles. As soon as one attempted to look over the side, however, the wind was felt, and probably a slightly wider wind screen might be an improvement. The "Cirrus" engine had a most reassuring note, and at no time did one have the slightest idea that it was likely to stop or to give any trouble at all. There was a very marked absence of vibration, and altogether the "Cirrus" sounded and ran more like a "six” than a “four." The noise was very slight, certainly not sufficient to produce that "deafness" which sometimes accompanies sitting behind a larger engine, but it seems likely that still more can and will be done to make the engine even more silent. When throttled down to land it was wholly delightful to float into the aerodrome at about 30 ni.p.h. ground speed. One had the feeling that there was plenty of time to think things over and to decide exactly where to land, and we fancy that when used as a school machine, this feature will be found a most valuable one. ns it can scarcely fail to inspire pupils with confidence.
   At the moment it has not been possible, owing to the unsettled weather, to carry out proper performance tests with the "Moth." but preliminary Tests seem to indicate that the top speed will probably be roughly 90 m.p.h. (144 kms./h.) and the stalling speed about 38 m.p.h. (61 kms./h.). The manoeuvrability appears excellent, and on Monday Mr. Broad repeatedly looped the machine, as well as doing Immelmann turns and spins.
   With these general remarks on the "Moth," we may turn to a more detailed description of the machine. Simplicity and robustness are the main features of the de Havilland "Moth." or D.H.60, to give the machine its official type designation. The number of fittings used, for example, has been reduced to an absolute minimum, and such few as are employed are of very simple form, cheap to manufacture and not likely to require much attention during use. The fuselage, for instance, is a box composed of four longerons, straight plain vertical and horizontal struts, and the whole covered with sheet ply-wood. This type of construction has now been employed for many years by Capt, de Havilland, and has stood the test of time. In actual use it stands up well to fairly rough handling and at the same time it is a form of construction comparatively cheap both in small numbers and in large quantities. The sides and bottom are flat, but the top is deeply cambered. The struts in sides and bottom are not directly attached to the longerons, but are held in place by the three-ply covering, whereas the top (which is, of course, open under the fairing) has its struts secured by angle brackets and bolts to the top longerons, as shown in a sketch.
   The two cockpits are arranged in the usual fashion, that at the rear being normally intended for the pilot, although when dual controls are fitted the machine can, of course, be flown from either cockpit provided the machine is trimmed by carrying a passenger, or equivalent load, in the rear cockpit. From the side elevation and photographs it will be seen that the view from the rear cockpit is very good, and we can personally testify to the excellence of the view from the front cockpit. The seat is comfortable and the cockpit exceptionally roomy for such a small machine. It is intended to fit a speaking tube in the cockpit, so as to facilitate communication between pilot and passenger or pupil. On the first machine this had not yet been fitted, but we understand that it will probably have been installed by now. Access to the front cockpit is facilitated by a small door in the coaming, which allows of stepping from the lower plane into the cockpit without any great difficulty. When closed the door is kept in place by a simple spring-loaded bolt, which can easily be withdrawn by the passenger himself.
   The undercarriage is ot the plain V-type, with the rear "legs" in the form of telescopic tubes sprung by rubber blocks working in compression. The rubber is enclosed in a cylindrical metal casing, so that the light is kept away from it, and it should thus last almost indefinitely. The travel on the legs is not long, some 4 ins. or so, but appears to be ample, and the machine displayed not the slightest tendency to bounce. Of course, pupils cannot be expected to make landings like those made by Mr Broad, but it seems likely that even in the hands of a novice the "Moth" should not be difficult to land.
   The "Cirrus" engine has its four "feet" resting on the top longerons, which are specially strengthened for the purpose, and a very neat cowling surrounds all but the top of the cylinders, in the first machine the exhaust pipe is crossed over the top of the fuselage, to run along the starboard side, but in subsequent machines it will run straight down along the port side, and the door to the front cockpit will be to starboard. The two long breather pipes of the crank-case are hidden inside the engine cowling, and help materially to keep the machine clean. The oil-filler cap, incorporated with the breather pipes, projects through the cowling, and thus allows of replenishing the sump without disturbing anything. The carburettor is placed on the side, above the cowling, where, in case of a backfire setting any small quantity of petrol on fire, it is removed from any inflammable part of the machine, and is, moreover, exposed to the rush of air. A small metal shield serves to prevent the carburettor from getting too cold. The petrol supply (15 gallons normally) is carried in the gravity tank on the top centre section, and there are thus no petrol pumps to get out of order. The oil is carried in the sump of the engine. The petrol carried in the standard tank is sufficient for about 5 hours at cruising speed, or something like 325-350 miles. It is, however, of interest to note that if the machine does not carry a passenger, and a petrol tank is built into the fuselage, the petrol capacity can be increased to suffice for about 12 hours' flying. A hand-starter, operated by a lever in the pilot's cockpit, enables the engine to be started without outside assistance, as was repeatedly demonstrated on Monday last by Mr. Broad.
   The wing construction is extremely simple, with I-section spars, spindled out from the solid, and with very simple ribs. The wing bracing is in the form of streamline wires, and there is but one pair of inter-plane struts on each side. The wings have been designed to fold, an operation occupying but a few minutes, and in the folded state the machine only occupies a width corresponding to the span of the tail plane, or approximately 9 ft. Ailerons are fitted to the bottom plane only, in order to make them more accessible, but the lateral control appears to be sufficient. The ailerons are hinged at the top of the spar, instead of on the centre line, and thus it has been possible to cover the gap between wing and aileron with a fabric strip.
   A detailed weight specification is not available, but we learn that the weight of the machine empty is 764 lbs. Allowing 160 lbs. each for pilot and passenger, about 60 lbs. for luggage and 100 lbs. for petrol, the total loaded weight should thus be in the neighbourhood of 1,250 lbs.

Flight, January 1927

THE 1927 MODEL "MOTH"
More Powerful Engine and Many Refinements Incorporated

   FOR the first time in the history of aviation, at any rate in the history of British aviation, it has become possible to speak of a new "model" of an aeroplane, in the sense in which the word is used in connection with motor cars, and not as we generally use it in connection with aviation. The de Havilland "Moth" has now reached a stage when it is not a question of a machine that will do its job with an engine of such and such a power, but of what sort of little comforts, what minor refinements, what colour schemes, etc. would the purchaser like. That in itself marks, we think, a definite step in the evolution of the private owner's aeroplane. The de Havilland "Moth" started life with the advantage of lines pleasing to the eye, and in that respect it has remained unchanged. In many details, important to the machine as an aeroplane, and others of value more from the user's point of view, the process of evolution has been at work, with the net result that the 1927 "Moth" marks a very considerable advance on earlier models. Yet this general improvement has not been accompanied by an increase in cost. In fact, exactly the reverse has happened, and the machine is being marketed this year at a price of ?730.
   Taking improvements first, perhaps the greatest change in the 1927 "Moth" is the fitting as standard of the new "Cirrus" Mark II engine in place of the Mark I fitted on the old model. The new engine (which was described and illustrated in FLIGHT of November 11, 1926) is slightly lighter in weight than the Mark I, but its power output is considerably greater, and there is no reason to doubt that the enviable reputation for reliability established by the older model will be worthily maintained by the new. The extra power is naturally reflected in the performance of the 1927 "Moth," which is considerably better than that of the Mark I engine type. Thus the following performance figures are guaranteed: Top speed, 98 m.p.h. (158 km./h.); cruising speed, 75-80 m.p.h. (120-130 km. h.); rate of climb at ground level, 625 ft. per min. (3-18 m. per sec.); ceiling, 15,000 ft. (4,570 m.). These performances relate to a total loaded weight of 1,265 lb. (575 kg.). At the same time the machine is very economical in fuel and oil, the average mileage being 20 miles per gallon (2-8 litres per kilometre). The oil consumption is only 1 pint (about 0-5 litre) per hour. Mention should also be made of the fact that the "Cirrus" engine runs perfectly on ordinary petrol as obtainable at any garage, so that the private owner need never worry about his fuel supplies. This has been well demonstrated during the flight of Stack and Leete to Karachi, which was carried out on any petrol available along the route.
   Statistics compiled from data relating to the flying of "Moths" over something like three-quarters of a million miles show that the cost of upkeep of the machine is, on an average, but a fraction of a penny per mile, this being a result of the special form of construction employed, which is of simple form and very robust.
   Of minor improvements mention should be made of the greater comfort of the cockpits, a more artistic lay-out, with instrument board finished in dull cellulose finish, a small pocket above the dashboard for the stowage of gloves, pipes, maps, and even - yes, why not ? - powder puffs. The luggage compartment behind the aft cockpit now opens into the cockpit itself, and does not have a "hatch" in the deck, as it was found that users sometimes forgot to fasten this, with the result that it flew open when the machine was in the air, although there is no record of week-end cases having been deposited on unsuspecting victims below. A new type of windscreen is being fitted, although those shown in our photographs are, it should be pointed out, of the old pattern. Altogether the 1927 "Moth" is a thoroughly "eyeable" machine, apart from its robustness and reliability, and the factor which it is so important to cultivate in the case of automobiles: pride of ownership, can very justly be applied to the first British standardised private aeroplane.
   As regards the question of cost, the price reduction has been made possible by putting the "Moth" on a quantity production basis. Not, of course, on the scale that automobiles are produced in quantities, but by making a close study of details and setting a shop aside entirely for the production of "Moths." Somewhat elaborate jigs have been made which facilitate the construction of the fuselage, the sides, top and bottom being erected on one of these jigs, the complete fuselage shell leaving the jig absolutely accurate and ready to have the controls, seats, engine mounting, etc., installed. The de Havilland works even boast a chute for the rapid transport of parts from stores to erecting shop. Doubtless the endless belt conveyor will come in time!

Flight, July 1928

THE DE HAVILLAND D.H. 60 X "MOTH”
A.D.C. "Cirrus" Engine

   THE X type "Moth" designed by The de Havilland Aircraft Co., Ltd., is one of the most well-known two-seater light aeroplanes. It can be fitted with land undercarriage, skis or floats, and in these three forms is suitable for undertaking a great variety of duties.
   Fuselage. - This is of three-ply construction with spruce longerons and web members. The passenger is situated between the planes with the pilot at his immediate rear. Full dual control is fitted, the forward "joy-stick" being detachable and the remaining gear being covered up by a robust hinged cowling.
   Wings. - Arranged in the form of a single-bay equal-span biplane, the structure, with the exception of tubular drag struts and wires, is of spruce, and is of orthodox design. The wings fold easily against the fuselage by the swinging into position of two jury struts and the withdrawal of four spring-loaded bolts.
   Engine Installation. - The A.D.C. "Cirrus" engine is bolted direct to the fuselage sides. A streamline petrol tank in the top centre section feeds the carburettor by gravity. Two gallons of oil are carried in the sump, no tank being required. Special attention has been paid to the accessibility of all engine accessories - filters, magnetos, carburettor, etc. Starting up by swinging the propeller is made an easy operation by the installation of an impulse starter on one magneto.
   Undercarriage. - The chassis is of conventional design, having the usual axle, radius rods, bracing cables and shock-absorber legs. The latter are fitted with rubber compression blocks housed in a circular tubular casing, 600 x 100 mm. wheels and tyres are fitted as standard.