Flight, February 1930

VERY REMARKABLE AEROPLANE
The New De Havilland "Moth III" has an Excellent Performance

   “CENTRE-SECTIONITIS" is a word coined by Mr. Walker, of the De Havilland Aircraft Co., to denote the harmful effects which a disturbance of the airflow over the middle portion of a wing may have on the lift and drag of an aeroplane wing. In the "Moth III," a new monoplane produced by the de Havilland Company, "centre-sectionitis" appears to have been reduced to a very remarkable extent. So far only the experimental machine has been produced and flown, but work on the production type has now commenced, and the first production machine will probably be out in about a month's time. This will differ in certain relatively minor respects from the experimental model, although the changes will not be obvious except upon fairly close inspection.
   The "Moth III" is a high-wing, strut-braced monoplane, with conduite interieure and fitted with an inverted "Gipsy" engine. The engine power is the same as that of the standard Gipsy-Moth, and the gross weight of the "Moth III" is not greatly different from that of the standard machine. In spite of this fact, however, the "Moth III" is something like 20 m.p.h. faster than the "Gipsy-Moth," a fact which indicates that the minimum drag of the new monoplane is very much lower than that of the older machine. This cannot be accounted for entirely by the change from biplane to monoplane. In fact, by the usual method of taking drag coefficients for the various parts of the machine and adding them together to get the total drag, there would be no reason for expecting such a remarkable increase in performance. The reduction in drag must be largely an "interference effect," and its results are of outstanding interest. Reference has already been made to the fact that the top speed is something like 20 m.p.h. greater than that of the "Gipsy-Moth." This means, of course, that the cruising speed is approximately the same as the top speed of the "Gipsy-Moth," so that the new type will probably be able to cruise at something over 100 m.p.h. at a fuel consumption of rather more than 20 miles per gallon. To anyone who does a good deal of touring this figure is of very great importance and should help to make touring by air a good deal cheaper than it already is.
   It is not intended here to give a detailed description of the new "Moth III." This we hope to give when the production machines are beginning to come along. In the meantime, however, it is worth recording that the whole of the lay-out of the general arrangement of this machine was done by Capt. de Havilland himself, and not until small details came to be considered did he hand some of the work over to others. Thus the success which the "Moth III" is bound to achieve will be entirely due to "D.H.," who designed the machine solely to please himself and as his own idea of what the private owner's machine ought to be like. The fact that he has come closer than almost anyone else to Prof. Melvill Jones's "Ideal streamline aeroplane" will be a source of satisfaction to all admirers of this pioneer designer's work. A detailed illustrated description will be published in a few weeks.

Flight, April 1930

AIRCRAFT FOR THE PRIVATE OWNER

MOTHS III & VI

   AFTER having produced Moth biplanes for a number of years, and made a great success of the type, the De Havilland Aircraft Co., Ltd., Stag Lane Aerodrome, Edgware, Middlesex, has turned its attention to the monoplane type, and is marketing this spring two distinct models, the "Moth Three" and the "Moth Six," the former being a 2-3 seater and the latter a 4-6 seater.
   The "Moth Three" is designed for normal use as a two-seater, but provision is made for fitting a third seat, should an owner desire to take two passengers occasionally. The machine has a welded steel tube fuselage but wooden wings. It is a monoplane of the type which the Germans call "shoulder-decker" and is characterised by the fact that the wing does not run across the top of the fuselage which is provided with roof windows, thus improving both the view and the lightness of the cabin. The cabin itself is liberally provided with windows, and the view in all directions is excellent.
   The power plant is a "Gipsy III" which is an inverted "Gipsy II." Apart from the exceptionally fine view forward and downward which this engine gives, the inversion of the engine has resulted in a remarkable reduction in engine noise. It is, in fact, perfectly easy to carry on a conversation in the cabin.
   A novel feature of the "Moth Three" is that the machine is fitted with air brakes. The telescopic struts of the undercarriage are so supported at their ends that they can be rotated through an angle of 90 deg. The extra drag which the struts cause is sufficient to alter the gliding angle from about 1 in 11 to about 1 in 7, and thus it is made much easier for the pilot to bring the machine into a small aerodrome. The effect is very like the application of brakes on a car. One can distinctly feel the machine slow up as the air brakes are applied. The "Moth Three" will be supplied both as a landplane and as a seaplane.
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Flight, April 1930

THE "MOTH THREE"
Latest De Havilland Machine has High Performance

   SUPERFICIALLY there is nothing to indicate that the "Moth Three" monoplane with inverted "Gipsy" engine compares in aerodynamic efficiency with the little "Tiger Moth" produced by the De Havilland Company some years ago. The "Tiger Moth" was an out-and-out racer, with the pilot's head streamlined into the fuselage with extreme care, with the monoplane wing braced entirely by streamline wires, and with an undercarriage reduced to its most compact form, with the springing buried inside the wheels. The "Moth Three," on the other hand, is a cabin monoplane, with the steeply-sloping windscreen usually associated with machines of the conduite interieure type, with strut-bracing of the wing, and with a more or less orthodox undercarriage in which the strut lengths have certainly not been markedly reduced, rather lengthened. At any rate, the compression legs are quite long, being anchored to the top longerons of the fuselage. And yet, in spite of all this, the machine comes within measurable distance of the little "Tiger Moth" in the matter of minimum drag coefficient. Put in another way, the "Moth Three" is a very good approach towards Professor Melvill Jones' ideal streamline aeroplane.
   Mr. C. C. Walker, of the De Havilland Aircraft Company, has coined the expression "centre-sectionitis" for the evil effects which the presence of a fuselage in the centre of a wing may have on the aerodynamic efficiency of the latter. It would appear that in the "Moth Three" this affliction has been very greatly reduced, and yet there is no very obvious reason why this should be so. The two wing-halves stop short at the top longerons, the inner ends of the wings being slightly sloped down towards the fuselage top, which at this point consists of a transparent panel or skylight. Exactly why this arrangement should be better, aerodynamically, than one in which the wing is continued across the top of the fuselage is not at all clear. That it is better seems to be a fact. What may possibly also contribute towards the efficiency of the "Moth Three" is the fact that the wing span is relatively large in proportion to the cross-sectional area of the fuselage, without, however, being as large in proportion as was the span of the Fairey long-distance monoplane. The latter, it may be recollected, was stated by Mr. Fairey to have a maximum L/D of 15. What is the value of this ratio in the “Moth Three" we have no means of knowing. Our opinion that the machine is a very efficient one is based not upon a knowledge of the maximum L/D but upon the minimum drag coefficient, estimated from Professor Everling's "High-speed Figure." This is not the place to explain the derivation of this figure, and for such explanation readers are referred to the original article by Professor Everling, published in THE AIRCRAFT ENGINEER (Monthly technical supplement to FLIGHT) of November 25, 1926, and to the comments thereon by Mr. Mettam of Westland's Technical Staff in THE AIRCRAFT ENGINEER of February 24, 1927.
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   We have gone into this subject at some length because the fact that the drag of the "Moth Three" is unusually low might otherwise easily be overlooked. It is very natural to jump to the conclusion that, as the "Moth Three" has a good deal more maximum power than the ordinary "Gipsy Moth,” the increase in speed is mainly due to this fact. It is partly due to the extra power, of course, but by no means entirely. That this is so might also be deduced from the fact that the increase in power is about 20 per cent., and the increase in speed about 25 per cent.

Constructional Features

   Structurally the "Moth Three” resembles the well-known “Gipsy Moth" with metal fuselage in that it has a welded-steel tube fuselage and wooden wings, although the fact that the machine is a monoplane has naturally resulted in the wing construction being slightly different. The De Havilland version of welded steel-tube construction is rather different from what one has become accustomed to.
   Generally speaking, square-section tube is used for longerons and struts in the forward portion, and circular-section tube in the rear. The structure is built up as a girder, without the use of wire bracing, the bracing struts running diagonally from corner to corner in the rectangular panels.
   Although the struts, horizontal as well as vertical, are welded to the tubular longerons, the welded joints are not relied upon for taking tensile stresses. Where one or more struts meet a longeron, a thin mild-steel plate digitally shaped to follow the lines of longeron and struts is pinned and welded both to the longeron and to the struts. Thus, each fuselage joint is strengthened against tensile stresses. The fuselage covering is fabric, and in order to prevent it from touching the struts, light fore-and-aft stringers are attached to the struts.
   The fuselage is built in two halves, a bolted joint occurring in each of the four longerons just aft of the cabin. Each side is perfectly flat so that it can be assembled on a flat jig, the top and bottom bracing struts being welded in afterwards when the complete fuselage is being erected. This arrangement results in a sudden change of direction of the fuselage side aft of the cabin, but the longitudinal, fabric-carrying stringers turn this sudden change into a gradual one as far as the centre-line of each side is concerned.
   At the forward end the lower longerons project some distance ahead of the cabin, while the top longerons are dropped nearly 2 ft. so as to provide the forward view from the cabin. The top longerons themselves act as engine bearers, and carry trunnion supports for the feet of the engine.
   The monoplane wing is, as already mentioned, mainly of wood construction. The two main spars have top and bottom flanges of spruce and walls of three-ply. The leading edge is covered with plywood up to the rear edges of the front spar, the resulting D-section wooden "tube" being very strong in torsion.
   Internal drag bracing is in three bays, of which the inner two are braced by duplicate cables and the outer by piano wire. In the bay at the root of the wing the drag bracing is dropped towards the bottom of the wing section so as to accommodate the petrol tanks, which are carried in the wing. The drag bracing struts are round-section steel tubes, and those in way of lift-strut attachments are in duplicate, the two forming a vee with its single point on the rear spar. On the front spar one tube runs straight across, while the second slopes forward and downward to support at its forward end the lift-strut fitting. This, of course, in order to take care of the compressive load which arises from the fact that the rear lift struts are in the plane of the rear spars for folding purposes, while the forward lift struts slope back at a considerable angle from front spar to lower longeron, thereby producing a rearward component. The arrangement is illustrated by a sketch. The wing ribs are of spruce, and of normal construction. The ailerons, of large span and small chord, are hinged to false spars placed a short distance aft of the rear spar. They are provided with the usual De Havilland type of differential control.
   Streamline steel struts forming a vee brace the wings to the lower longerons. A light jury strut is carried on each side, and when the wings are folded this jury strut supports the forward corner of the inner end of the wing, the petrol tanks being carried inside the wing near this point.
   A "split" type of undercarriage is fitted to the "Moth Three," consisting on each side of a telescopic member running to the top longeron, a bent axle to the lower longeron, and a radius rod to the forward bottom corner, near the engine mounting. Rubber blocks of streamline shape provide the shock-absorbtion, and the telescopic legs are further made to act as air brakes by being swivel-mounted at their ends in such a manner that they can be turned through an angle of 90°. Operation of the air brakes is by short cranks connected to a lever by the side of the pilot's seat.
   The tail skid is sprung by a coil spring, and is steerably mounted to facilitate taxying on the ground. The rudder operates the tail skid via a peg in the bottom of the rudder and a fork on the tail-skid spindle. The object of the fork is to permit the rudder a certain amount of movement before the tail skid comes into operation. In this manner shocks transmitted to the rudder by the tail skid-are reduced. On the lower end of the tail-skid spindle is a crank the two arms of which provide stops for the skid and limit its angular movement. Rubber pads are carried on the ends of the crank arms to avoid transmitting hard knocks to the sternpost of the fuselage. The whole tail-skid arrangement is well illustrated by one of our sketches.
   One of the most interesting features of the "Moth Three" is the power plant installation, which consists of a "Gipsy III" inverted engine. This engine is practically identical with the "Gipsy II," except for certain modifications necessitated by the inversion. Owing to the fact that the cylinders are below the crankcase, the forward view from the cabin is remarkable, and is, in fact, very nearly as good as the view one used to obtain from the nacelle of our old "pushers." The four feet which connect the crankcase to the engine bearers rest in trunnions on the latter, and rubber pads are interposed between the feet and the trunnions in order to reduce the amount of vibration transmitted to the aircraft structure. A fireproof bulkhead separates the engine from the cabin. The engine is almost entirely cowled-in by a five-piece cowl, the parts of which are held on by long "skewers." At the back there is a slight gap between the side cowls and the side of the fuselage, so as to provide an escape for the air which enters through a small opening in the forward end of the cowling. Partly let into the port side of the fuselage covering, just aft of the fireproof bulkhead, is an oil tank which also serves as a cooler, this being made necessary because the "Gipsy III" engine is of the dry sump type.
   Mention has already been made of the fact that the petrol tanks are mounted in the wing, one on each side. The tanks are slung on steel straps fastened to light brackets on the main spars, and the removal of a tank is a simple matter. Each tank is provided at its lowest point with a combined petrol gauge and sump, in the form of a plunger working in a tube, the glass of which projects below the wing covering. Thus not only can the pilot see at a glance how much petrol is left in the tanks, but any impurities, etc., drain into the sump and glass, where they are at once seen and can easily be removed. Three sizes of tanks have been standardised, giving ranges of 440 miles, 570 miles, and 700 miles, respectively, the useful load being, of course, correspondingly decreased.

The Cabin

   The "Moth Three" will be marketed as an occasional three-seater. That is to say, the cabin lay-out is such that, normally, the machine will be equipped with two seats, arranged in tandem, with ample leg and elbow room. The seats, upholstery, interior decorations will be very attractive, and from personal experience it can be said that the machine is one of the most delightful to fly in that we have tried. Owing to the enclosed cabin, the inverted engine, and the enclosure of the valve rockers, etc., in steel casings, the noise which reaches the occupants is reduced to a point where it is not in the least objectionable. The profusion of windows, skylight, and windscreen admit plenty of light, so that, although the cabin is not large in actual dimensions, one has not that sense of being "cooped up," which is apt to spoil for some the enjoyment of flying in a small cabin machine.
   The rear seat is arranged to slide along grooves running diagonally across the cabin floor. When the machine is to be used as a three-seater, the rear seat can be slid forward and across the cabin towards the starboard side, and the third seat added behind it, but on the port side. Leg room for the two passengers is then just a little bit cramped, but not seriously so.
   The pilot's seat is the forward one, and the view from it is remarkable. Not only does the inverted engine arrangement make an almost incredible difference to the view, but the windows in front and in the sides, as well as the large skylight, in conjunction with the tapering down of the wing spars towards the roots, afford views in nearly all directions above and below the wing.
   The pilot's controls are the usual, but are very neatly arranged so as to give the impression of the driver's seat of a car rather than the cockpit of an aeroplane. On the port side is the tail trimming gear, and on the starboard the lever which operates the air brakes. In front of the pilot is a very neatly arranged dash with instruments (Smith's), and below that a map table, running right across the width of the cabin, and with wire spring clips for holding maps, etc., down on the map board. The instrument board is pivoted so as to facilitate access to the back of the various instruments.
   Dual controls are provided, so that, if desired, the machine can be used for instructional work. When not in use, the rear control stick is unshipped and placed in clips on the side.
   The "Moth Three" cannot fail to appeal strongly to private owners of aircraft. The price (?1,000) is somewhat high, but not unduly so, in view of the fact that the machine can be used occasionally as a three-seater, and that it has a high performance, coupled with excellent fuel economy at a cruising speed of more than 100 m.p.h.
   The machine is also supplied as a twin-float seaplane. The price is then ?1,250.

Flight, November 1932

British Aircraft

The De Havilland Aircraft Co., Ltd.
Stag Lane, Aerodrome, Edgware, Middlesex

   CAPT. GEOFFREY DE HAVILLAND is one of the oldest (aeronautically speaking) British aircraft designers, having designed his first aircraft somewhere around 1908, and having been actively engaged on aircraft design and construction ever since. The present company has been in existence since shortly after the war, and has branches in many of the Dominions overseas.
   It was the "Moth" which started the de Havilland Company on its post-war career as specialists in civil aircraft, and more particularly in aircraft suitable for the private owner, and more "Moths" have been built and flown over the world than any other type of aeroplane.
   The standard "Moth" with Gipsy II engine is already a familiar sight in almost any country, and needs no description here. A fairly recent version of it is the Gipsy III "Moth," which is offered as an alternative to, and not as a substitute for, the older model. The Gipsy III "Moth" is fitted with the inverted Gipsy III engine, and the view forward is thereby greatly improved. The very clean nose also improves the performance somewhat.

"Puss Moth"

   The "Puss Moth" (Gipsy III) is by now familiar to everyone, and is a 2/3-seater designed for the private owner. It has steel tube fuselage and wooden wings which fold, and is of the cabin type, with large windows giving view, light and air. Its main data are:
   Length o.a 25 ft. (7,6 m.)
   Wing span 36 ft. 9 in. (11,2 m.)
   Wing area 222 sq. ft. (20,6 m».)
   Tare weight 1,265 1b. (575 kg.)
   Disposable load 785 lb. (357 kg.)
   Gross weight 2,050 lb. (932 kg.)
   Maximum speed 128 m.p.h. (206 km./h.)
   Cruising speed 108 m.p.h. (174 km./h.)
   Range (20 gal. = 91 litres) 380 miles (612 km.)
   Range (35 gals. = 159 litres) 665 miles (1 070 km.)

Flight, August 1934

A BRITISH "RUNDFLUG" ENTRY
A "Puss Moth" with Slots and Flaps

   SPECIALLY prepared with slots and flaps, the "Puss Moth" belonging to Mr. W. D. Macpherson has been entered for the 1934 "Rundflug" or International Touring Competition which is being held from Warsaw between August 28 and September 16.
   This ''Puss Moth'' is calculated to have a minimum flying speed of some 35 m.p.h. It has not been altered structurally except for certain modifications necessitated by incorporating slots and flaps. The work was done at Heston, in the Airwork shops, under the general supervision of Mr. Parkes, and to the designs of a "committee" composed of Herr Hoeffner (who is designing a helicopter at Heston), Dr. Lachmann (of Handley Page, Ltd.), and Mr. Martin (of the Baker-Martin Aircraft Company, who are producing a machine which is rumoured to be something rather special), with, of course, general help from the staff of the De Havilland Aircraft Co., Ltd.
   The slots extend the whole length of the wing and are controllable. They are the built-up type and inset so that they form the leading edge of the wing. The ailerons have been modified so as to droop an equal number of degrees without altering the amount of control, and thus assist as flaps. This drooping can only be carried out on the ground, and will therefore only be utilised for the tests in which they are needed. The large flap which forms the inner end of the trailing edge of each wing of a "Puss Moth'' has been altered to hinge downwards and act as a controllable flap. The use of both slots and flaps has naturally altered the distribution of the torsional stresses in the wing, and has necessitated a certain amount of additional internal bracing.
   Other alterations to the machine are :- bulging the sides of the fuselage so that the effective width of the cabin is greater than standard; the addition of extra windows in the rear portion of the cabin; fitting a drift sight in the floor of the cabin; the use of Dowty compression legs in the undercarriage so that full advantage may be taken of the slots and flaps when landing; alterations to allow the cabin doors to be released quickly (as parachutes are carried); fitting a special control to the cabin ventilating system; and fairing of the axle and radius rods of the undercarriage into one clean unit.
   The engine fitted is one of the high compression "Gipsy Major" type with an adjustable pitch Fairey metal airscrew, which should give the machine a higher speed than the standard "Puss Moth," while the slots and flaps will decrease its landing speed. These, coupled with the other modifications, will undoubtedly make Mr. Macpherson's entry a formidable opponent for the foreign machines, many of which are built specially for the competition and which have to be strengthened up before they can be put into production, as in their competition state they would not stand the wear and tear of ordinary usage. That is one of the drawbacks of building machines down to a weight for a competition like this. With its modifications this "Puss Moth" is only just within the specified weight, and will, therefore, be handicapped in comparison with other entries.